Embed Size (px)
Citation preview
Accepted Manuscript
Title: Effect of the phosphodiesterase type 5 inhibitor tadalafil on pulmonary
hemodynamics in a canine model of pulmonary hypertension
Author: Yasutomo Hori, Chigusa Kondo, Maho Matsui, Maki Yamagishi,
Shozo Okano, Seishiro Chikazawa, Kazutaka Kanai, Fumio Hoshi, Naoyuki
Itoh
PII: S1090-0233(14)00330-X
DOI: http://dx.doi.org/doi:10.1016/j.tvjl.2014.08.009
Reference: YTVJL 4242
To appear in: The Veterinary Journal
Received date: 9-4-2014
Revised date: 8-8-2014
Accepted date: 9-8-2014
Please cite this article as: Yasutomo Hori, Chigusa Kondo, Maho Matsui, Maki Yamagishi,
Shozo Okano, Seishiro Chikazawa, Kazutaka Kanai, Fumio Hoshi, Naoyuki Itoh, Effect of the
phosphodiesterase type 5 inhibitor tadalafil on pulmonary hemodynamics in a canine model of
pulmonary hypertension, The Veterinary Journal (2014),
http://dx.doi.org/doi:10.1016/j.tvjl.2014.08.009.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service
to our customers we are providing this early version of the manuscript. The manuscript will
undergo copyediting, typesetting, and review of the resulting proof before it is published in its
final form. Please note that during the production process errors may be discovered which could
affect the content, and all legal disclaimers that apply to the journal pertain.
1
Effect of the phosphodiesterase type 5 inhibitor tadalafil on pulmonary 1
hemodynamics in a canine model of pulmonary hypertension 2
3
4
Yasutomo Hori a,*
, Chigusa Kondo a, Maho Matsui
a, Maki Yamagishi
a, Shozo Okano
b, 5
Seishiro Chikazawa a, Kazutaka Kanai
a, Fumio Hoshi
a, Naoyuki Itoh
a 6
7 a Laboratory of Small Animal Internal Medicine, School of Veterinary Medicine, 8
Kitasato University, 23-35-1 Higashi, Towada, Aomori 034-8628 Japan 9 b Laboratory of Small Animal Surgery 2, School of Veterinary Medicine, Kitasato 10
University, 23-35-1 Higashi, Towada, Aomori 034-8628 Japan 11
12
13
14
15
* Corresponding author. Tel.: +81 176 249301. 16
E-mail address: [email protected] (Y. Hori). 17
Page 1 of 24
2
Highlights 18
A dog model of pulmonary arterial hypertension was used to evaluate the 19
pharmacology of tadalafil in dogs 20
Intravenous infusion of tadalafil decreased U46619-elevated pulmonary arterial 21
pressure (PAP) and pulmonary vascular resistance (PVR) in dogs without 22
changes in systemic arterial pressure (SAP) and systemic vascular resistance 23
( SVR). 24
Oral administration of tadalafil alone did not change PAP, but decreased 25
U46619-elevated PAP. The effect occurred 1 h after oral administration and was 26
maintained for 6 h. 27
These results suggest that tadalafil improved U46619-induced pulmonary 28
arterial constriction, leading to pulmonary arterial relaxation. 29
30
31
Abstract 32
Phosphodiesterase type 5 (PDE5) inhibitors are used for treating pulmonary 33
arterial hypertension (PAH) in dogs. The long-acting PDE5 inhibitor tadalafil was 34
recently approved for treatment of PAH in humans. Basic information related to the 35
pharmacological and hemodynamic effects of tadalafil in dogs is scarce. In this study, 36
the haemodynamic effects of tadalafil after intravenous (IV) and oral administration 37
were investigated in a healthy vasoconstrictive PAH Beagle dog model induced by 38
U46619, a thromboxane A2 mimetic. Six healthy Beagle dogs were anesthetized with 39
propofol and maintained with isoflurane. Fluid-filled catheters were placed into the 40
descending aorta to measure systemic arterial pressure and in the pulmonary artery to 41
Page 2 of 24
3
measure pulmonary arterial pressure (PAP). U46619 was infused via the cephalic vein 42
to induce PAH. 43
44
IV infusion of U46619 significantly elevated PAP from baseline in a 45
dose-dependent manner. U46619-elevated PAP and pulmonary vascular resistance was 46
significantly attenuated by the simultaneous infusion of tadalafil at 100 and 200 µg/kg/h. 47
Likewise, oral administration of tadalafil at 1.0, 2.0, and 4.0 mg/kg significantly 48
attenuated U46619-elevated PAP in a dose-dependent manner. U46619-elevated 49
systolic and mean PAP decreased significantly 1 h after oral tadalafil administration at 50
4.0 mg/kg, and this effect was maintained for 6 h. In conclusion, tadalafil had a 51
pharmacological effect in dogs and IV infusion of tadalafil induced pulmonary arterial 52
relaxation, while oral administration of tadalafil decreased PAP. These results suggest 53
that tadalafil may offer a new therapeutic option for treating dogs with PAH. 54
55
Keywords: Dog; Phosphodiesterase type 5 (PDE5) inhibitor; Pulmonary arterial 56
hypertension; Tadalafil; Hemodynamic.57
Page 3 of 24
4
Introduction 58
Pulmonary arterial hypertension (PAH) is a progressive disease characterized by 59
chronic elevation in pulmonary arterial pressure (PAP). In veterinary medicine, PAH in 60
dogs is defined by a systolic/mean PAP of >30/20 mmHg at rest (Johnson, 1999a; 61
Johnson et al., 1999b). PAH can occur secondary to multiple abnormalities of the 62
pulmonary or cardiovascular systems, such as left-sided heart failure, left-to-right 63
cardiac shunting, heartworm disease, and pulmonary disease (Johnson, 1999a; Glaus et 64
al., 2004; Nakamura et al., 2011; Seibert et al., 2010; Uchide and Saida, 2005; Zabka et 65
al., 2006; Bach et al., 2006; Kellum and Stepien, 2007). In severe cases, PAH can lead 66
to right-sided heart failure and death (Johnson, 1999a; Johnson et al., 1999b; Zabka et 67
al., 2006). 68
69
The pathogenesis of PAH involves an imbalance between pulmonary 70
vasoconstriction and vasodilation, which leads to increases in PAP (Humbert et al., 71
2004; Pietra et al., 2004). Thromboxane (TX)A2 is a potent autacoid that induces 72
platelet aggregation and vasoconstriction, and plasma levels are increased in animals 73
and humans with PAH (Adatia et al., 1993; Christman et al., 1992). In dogs, an 74
intravenous (IV) infusion of U46619, a TXA2-mimetic agent, induces pulmonary 75
arterial constriction (Tamura et al., 2001; Yamada et al., 1998; Gong et al., 2000). 76
77
Three classes of pulmonary artery-specific vasodilators have been approved for 78
the treatment of PAH in humans, namely, prostaglandin I2 (prostacyclin), endothelin 79
receptor antagonists, and phosphodiesterase type 5 (PDE5) inhibitors. Of these, PDE5 80
inhibitors, including sildenafil, vardenafil, and tadalafil, are currently available in 81
Page 4 of 24
5
human medicine (Anderson and Nawarskas, 2010; Galiè et al., 2009). Sildenafil has a 82
short half-life of 4 - 5 h and thus requires dosing three times daily (Falk et al., 2010; 83
Supuran et al., 2006). In veterinary medicine, sildenafil is the most frequently used 84
PDE5 inhibitor for treatment of PAH. It reportedly improves symptoms and clinical 85
outcomes in dogs with PAH (Nakamura et al., 2011; Bach et al., 2006; Brown et al., 86
2010; Kellum and Stepien, 2007). 87
88
In contrast, tadalafil has a longer half-life of 17.5 h. and allows for once-daily 89
dosing (Supuran et al., 2006; Arif and Poon, 2011); it is currently approved for the 90
treatment of PAH and erectile dysfunction in humans (Porst et al., 2003; Skoumal et al., 91
2004). Tadalafil may present a new therapeutic option for PAH in dogs because of its 92
less frequent dosing and more sustained benefits. However, only one case report has 93
described the use of tadalafil for the treatment of PAH in dogs (Serres et al., 2006). 94
Basic information on the pharmacological and hemodynamic effects of tadalafil as a 95
treatment for PAH in dogs remains scarce. In the present study, to clarify its pulmonary 96
hemodynamic action, we investigated the effects of tadalafil on PAP and vascular 97
resistance in healthy dogs with U46619-induced acute vasoconstrictive PAH. 98
99
Materials and methods 100
Animals 101
This study was approved by the Institutional Animal Care and Use Committee for 102
Kitasato University (approval number 13-123, 5 December 2013). 103
104
Six Beagle dogs were used in this study (3 males, 3 females; aged 4–5 years; 105
Page 5 of 24
6
weight 10–13 kg). All dogs were determined to be healthy according to the results of 106
complete physical and echocardiography examinations. The dogs were housed 107
individually in cages and fed commercial dry food with free access to water. 108
109
110
Drugs 111
U46619 (9,11-dideoxy-11a,9a-epoxymethanoprostaglandin F2α; U46619, 112
Cayman) was dissolved in ethanol according to the manufacturer’s instructions. 113
Tadalafil (Tadalafil, Acanthus Research) was dissolved in dimethyl sulfoxide (DMSO) 114
for IV infusion or purchased for oral administration (Adcirca 20 mg). Immediately 115
before examination, each drug was diluted in sterile saline to a final concentration of 50 116
µg/mL (for U46619) and 0.2 mg/mL (for Tadalafil), respectively. 117
118
Anesthesia 119
The dogs were sedated with butorphanol (0.2 mg/kg IV), diazepam (0.5 mg/kg 120
SC) and atropine (0.025 mg/kg SC); anesthetized with propofol (6.0 mg/kg IV); and 121
intubated. Anesthesia was maintained using a mixture of 2.0–3.0% isoflurane and 122
oxygen. The end-tidal partial pressure of carbon dioxide in arterial blood (PaCO2) and 123
hemoglobin saturation level of oxygen (SPO2) were monitored and maintained between 124
35–45 mmHg and 95–100%, respectively. Heart rate was monitored using 125
electrocardiography (COLIN BP-608, Nihon Kohden). Respiratory rate was maintained 126
between 10 and 20 breaths/min. Fluid loss was replaced by IV infusion of Ringer’s 127
solution, and the total fluid volume was adjusted to 60 mL/kg/day. Following the 128
examinations, the dogs were allowed to recover from anesthesia. 129
Page 6 of 24
7
130
Hemodynamic measurements 131
The anesthetized dogs were positioned in left lateral recumbency. A 3-Fr 132
fluid-filled catheter was placed via the left femoral artery into the descending aorta to 133
measure systolic, mean, and diastolic systemic arterial pressure (SAP). A 4-Fr 134
fluid-filled catheter or a Swan-Ganz catheter (5 Fr thermodilution catheter, TC-504, 135
Nihon Kohden) was inserted through the jugular vein and advanced into the pulmonary 136
artery to measure the systolic, mean, and diastolic PAP. Similarly, mean right 137
ventricular pressure (RVP) and mean central venous pressure (CVP) were also 138
measured. 139
140
Mean pulmonary capillary wedge pressure (PCWP) and cardiac output (CO) were 141
measured using a Swan-Ganz catheter. CO was calculated as the average of the three 142
measurements obtained by thermodilution (CCOM monitor, CO-203, Terumo) with an 143
injection of 5 mL of normal saline kept at 4 °C (Tamura et al., 2001; Gong et al., 2000). 144
145
Pulmonary vascular resistance (PVR), systemic vascular resistance (SVR), and 146
PVR to SVR ratio (Rp/Rs ratio) were calculated using the following formulae (Tamura 147
et al., 2001): 148
149
PVR = (mean PAP – mean PCWP)/CO 150
SVR = (mean SAP – mean CVP)/CO 151
Rp/Rs ratio = PVR/SVR 152
153
Page 7 of 24
8
All pressures were measured using fluid-filled transducers (TruWave Disposable 154
Pressure Transducer, Nihon Kohden) and recorded by polygraphy (Omniace RT 3200, 155
NEC). After completing the procedures, a 20- to 30-min equilibration period was 156
allowed to stabilize hemodynamics. Heart rate, SPO2 and blood pressures were recorded 157
initially as a baseline. 158
159
Study protocols 160
Study 1 161
The infusion rates of U46619 were established based on previous reports 162
(Tamura et al., 2001; Yamada et al., 1998). U46619 was infused at rates of 0.1, 0.3, 0.6 163
and 0.9 µg/kg/min for 10–20 min via the cephalic vein. SAP and PAP were measured 164
under anesthesia. 165
166
Study 2 167
After pretreatment with IV U46619 (0.9 µg/kg/min) for 10 min, tadalafil was 168
infused simultaneously at rates of 50, 100, and 200 µg/kg/h for 10 min. The infusion 169
rate of U46619 was maintained until the end of tadalafil infusion. This study was 170
conducted with a crossover design. The order of tadalafil administration (50, 100, and 171
200 µg/kg/h) was randomly assigned to each dog. After completing the first procedure, 172
a stabilization period of at least 30 min was provided to re-establish a stable baseline 173
condition. The dogs were then randomly assigned to receive one of the remaining 174
treatments, and each dog received each of the three doses. SAP was measured using a 175
fluid-filled catheter and PAP, mean RVP, mean CVP, mean PCWP and CO were 176
measured with a Swan-Ganz catheter under anesthesia. SVR, PVR, and the Rp/Rs ratio 177
Page 8 of 24
9
were calculated. 178
179
Study 3 180
The dose-dependent effects of oral tadalafil were determined. The dogs were 181
divided into placebo, U46619, and tadalafil groups. A single dose of placebo (for the 182
placebo and U46619 groups) was administered orally. Tadalafil were administered 183
orally at 1.0, 2.0, and 4.0 mg/kg in the tadalafil group. PAP was measured under 184
anesthesia 3 h after administration. 185
186
Study 4 187
The time-dependent effects of oral tadalafil were determined 1, 2, 3, and 6 h after 188
oral administration. The dogs were divided into three groups, namely, placebo, U46619 189
and tadalafil. A single dose of placebo (for the placebo and U46619 groups) was 190
administered orally. Similarly, tadalafil at 4.0 mg/kg was administered orally to the 191
tadalafil group. PAP was measured under anesthesia. 192
193
In Studies 3 and 4, U46619 (0.9 µg/kg/min) was simultaneously infused for 10 194
min at each time point in the U46619 and tadalafil groups. Sterile saline was 195
administered for 10 min in the control group. Both studies were conducted with a 196
crossover design. Each drug was given randomly, and the interval between treatments 197
was at least 3 days. After each washout period, the dogs were then randomly assigned to 198
receive one of the remaining treatments. This continued until each dog had received all 199
treatments. 200
201
Page 9 of 24
10
Statistical analyses 202
Normality of data was assessed with the Kolmogorov–Smirnov test. Data are 203
presented as means ± standard deviation (SD). One-way analysis of variance (ANOVA) 204
was used to compare the results among the groups in Studies 1, 2, and 3. In Study 4, 205
one-factor repeated measures ANOVA was used to compare the time-dependent 206
changes in heart rate and PAP with the baseline values. Two-way ANOVA was used to 207
compare the time-dependent changes in PAP among the groups. The significance of the 208
differences between the mean values of the each condition was tested with Tukey’s 209
multiple-comparison test. P <0.05 was considered statistically significant. 210
211
Results 212
As baseline values before the induction of anesthesia, mean heart rate was 115 ± 213
29 beats/min, respiratory rate 41 ± 33 breaths/min and body temperature 38.7 ± 0.2 °C. 214
215
The dose-dependent hemodynamic effects of IV U46619 in Study 1 are shown in 216
Fig. 1. SPO2 remained unchanged during the study (baseline; 97.5 ± 1.5%, 0.1 217
μg/kg/min; 97.5 ± 1.5%, 0.3 μg/kg/min; 98.2 ± 0.8%, 0.6 μg/kg/min; 98.3 ± 0.8%, 0.9 218
μg/kg/min; 98.3 ± 1.4%). Compared with baseline, the heart rate and SAP did not 219
change with IV infusion of U46619. In contrast, IV infusion of U46619 changed the 220
PAP in a dose-dependent manner from baseline. Systolic PAP was significantly higher 221
than baseline at U46619 infusion rates of 0.6 and 0.9 µg/kg/min. The mean and diastolic 222
PAP were also significantly higher than baseline at infusion rates of 0.3, 0.6 and 0.9 223
µg/kg/min. 224
225
Page 10 of 24
11
The hemodynamic effects of simultaneous infusion of tadalafil and U46619 were 226
investigated in Study 2. U46619-elevated systolic, mean and diastolic PAP were slightly 227
lower with simultaneous infusion of tadalafil at 50 µg/kg/h. In contrast, 228
U46619-elevated systolic, mean and diastolic PAP were significantly lower with 229
simultaneous infusion of tadalafil at 100 and 200 µg/kg/h (Fig. 2). Changes in the other 230
hemodynamic measurements are shown in Table 1. The heart rate did not change with 231
U46619 and/or any dose of tadalafil. The SAP increased with U46619, but the change 232
was not statistically significant. SAP did not change with simultaneous infusion of any 233
dose of tadalafil. U46619 significantly increased the RVP, CVP and PCWP from 234
baseline, but these parameters were not changed by simultaneous infusion of tadalafil. 235
The CO decreased with U46619, but the change was not statistically significant; CO did 236
not change with simultaneous infusion of any dose of tadalafil. As a result, although 237
U46619 significantly increased PVR and SVR from baseline, simultaneous infusion of 238
tadalafil at 50, 100 and 200 µg/kg/h resulted in a significantly lower PVR than that seen 239
with U46619 (Fig. 3). Similarly, the Rp/Rs ratio was significantly higher than baseline 240
with U46619 and significantly lower with simultaneous infusion of tadalafil than that 241
seen with U46619 (Fig. 3). 242
243
The dose-dependent effects on PAP 3 h after a single oral administration of 244
tadalafil were investigated in Study 3 (Fig. 4, Table 2). Oral administration of tadalafil 245
alone did not change the systolic, mean or diastolic PAP or heart rate compared with 246
placebo. U46619-elevated systolic, mean, and diastolic PAP did not change by oral 247
administration of tadalafil at 1.0 mg/kg. In contrast, the U46619-elevated systolic, mean, 248
and diastolic PAP were significantly lower with prior oral administration of tadalafil at 249
Page 11 of 24
12
2.0 and 4.0 mg/kg. 250
251
Based on the results of study 3, the time-dependent effects on PAP after a single 252
oral administration of tadalafil were investigated in Study 4 (Fig. 5, Table 3). Neither 253
U46619 infusion nor oral tadalafil changed the heart rate from baseline. U46619 254
significantly elevated the systolic, mean and diastolic PAP for 6 h compared to baseline. 255
Despite prior administration of tadalafil at 4.0 mg/kg, the U46619 infusion significantly 256
elevated the systolic, mean and diastolic PAP from 1 to 6 h. However, oral tadalafil 257
administration significantly decreased U46619-elevated systolic and diastolic PAP at 3 258
and 6 h compared to the U46619 group. Similarly, oral tadalafil significantly decreased 259
U46619-elevated mean PAP at 1 h and until 6 h. 260
261
Discussion 262
The pathogenesis of PAH is poorly understood, but an imbalance between 263
vasoconstriction and vasodilation contributes to the development of PVR (Humbert et 264
al., 2004; Kellihan and Stepien, 2012; Pietra et al., 2004). For example, TXA2 is a 265
potent autacoid that induces platelet aggregation and vasoconstriction, and there is 266
experimental and clinical evidence that its plasma levels are increased in animals and 267
humans with PAH (Adatia et al., 1993; Christman et al., 1992). 268
269
U46619, a TXA2-mimetic agent, increased PVR in isolated canine lungs 270
(Stephenson et al., 1998), indicating that U46619 directly stimulates vasoconstriction of 271
the pulmonary artery. In the present study, an IV infusion of U46619 significantly 272
elevated PAP in a dose-dependent manner. In addition, U46619 at a rate of 0.9 273
Page 12 of 24
13
µg/kg/min significantly elevated PVR and particularly the Rp/Rs ratio from baseline 274
suggesting that U46619 stimulates pulmonary arterial constriction in dogs and that the 275
pulmonary artery is a main target of TXA2 (Tamura et al., 2001; Yamada et al., 1998; 276
Gong et al., 2000). 277
278
In addition to its effect on the pulmonary artery, U46619 insignificantly elevated 279
SAP, significantly elevated PCWP and SVR and insignificantly decreased CO. Similar 280
to our results, a previous study demonstrated that the SAPs, SVR and PCWP increased 281
following infusion of U46619 as CO decreases (Gong et al., 2000). U46619 produced 282
concentration-dependent contractions in canine isolated coronary, mesenteric and 283
femoral arteries, which were inhibited by a TXA2 antagonist (Matsuzaki et al., 1992). 284
These results indicate that U46619 stimulates systemic arterial constriction in addition 285
to its effect on the pulmonary artery. U46619-elevated systemic arterial constriction and 286
decreased CO might lead to an increase in PCWP. 287
288
Tadalafil, a specific PDE5 inhibitor, has greater affinity for PDE5 compared to 289
other PDE5 inhibitors (Francis and Corbin, 2003; Corbin and Francis, 2002) and 290
induces a significant reduction in PAP and PVR in patients with PAH (Ghofrani et al., 291
2004; Mukhopadhyay et al., 2006). PDE5 is located primarily in the corpora cavernosa 292
of the penis and pulmonary arterial smooth muscle (Senzaki et al., 2001). Its main role 293
is to degrade cyclic guanosine monophosphate (cGMP) in these tissues. PDE5 294
inhibition increases cGMP bioavailability, which causes smooth muscle relaxation and 295
decreased vasomotor tone (Francis and Corbin, 1999; Lincoln et al., 2001). In the 296
present study, IV infusion of tadalafil significantly decreased the U46619-elevated PAP 297
Page 13 of 24
14
in a dose-dependent manner. In addition, the U46619-elevated PVR and Rp/Rs ratio 298
were significantly lower with simultaneous infusion of tadalafil without significant 299
changes in SAP and SVR. The results indicate that tadalafil has a pharmacological 300
effect in dogs and that it induces pulmonary arterial but not systemic arterial relaxation. 301
302
Tadalafil is widely used to treat humans with PAH and erectile dysfunction (Porst 303
et al., 2003; Skoumal et al., 2004). Previous clinical studies in humans reported that 304
tadalafil improved 6-min walk test results and quality of life (Galiè et al., 2009; 305
Pepke-Zaba et al., 2009). In veterinary medicine, sildenafil is generally used for dogs 306
with PAH. This agent reportedly improves clinical signs and outcomes in dogs with 307
PAH (Nakamura et al., 2011; Bach et al., 2006; Brown et al., 2010; Kellum and Stepien, 308
2007). In contrast, tadalafil has infrequently been used in dogs with PAH. One case 309
report of a 7-day treatment with oral tadalafil (1 mg/kg) in a dog showed improvement 310
in clinical signs such as cyanosis, syncope, and tachypnea, and decreased systolic PAP 311
from 122 to 96 mmHg as estimated by continuous-wave Doppler echocardiography of 312
the tricuspid jet (Serres et al., 2006). However, no detailed information regarding the 313
hemodynamic efficacy of oral tadalafil in dogs is available. In the present study, we 314
have demonstrated that oral tadalafil at 2 and 4 mg/kg decreases U46619-elevated PAP 315
in dogs without significant changes in heart rate, whereas tadalafil alone did not affect 316
PAP. Our results suggest that oral administration of tadalafil induces a reduction in PAP 317
in dogs. 318
319
Pharmacokinetic studies of tadalafil in humans report an 81% bioavailability, a 320
maximum drug concentration time (Tmax) of 2 h, and a 17.5 h half-life (Francis and 321
Page 14 of 24
15
Corbin, 2003). Indeed, tadalafil is absorbed within 20 min after oral administration and 322
shows a peak effect 70 to 90 min after oral administration in humans (Forgue et al., 323
2006; Ghofrani et al., 2004; Mukhopadhyay et al., 2006). In contrast, pharmacokinetic 324
data for tadalafil in dogs remain scarce. The current study demonstrated that oral 325
tadalafil at a dosage of 4 mg/kg showed a maximum effect. Thus, we deliberately chose 326
a high dose to induce a marked hemodynamic effect and determine the time-dependent 327
effects of tadalafil. Oral tadalafil significantly decreased U46619-elavated mean PAP at 328
1 h, and this effect was maintained for 6 h. These results indicate that oral 329
administration of tadalafil in dogs was efficacious within 1 h and that the effect is 330
maintained for at least 6 h. However, further studies are required to clarify the 331
pharmacokinetics of tadalafil in dogs. 332
333
Our study has several limitations. We could not exclude the possibility that 334
general anesthesia may have modulated the hemodynamic effects of tadalafil. Although 335
oral tadalafil at 2 and 4 mg/kg lowered the U46619-induced increase in PAP, the 336
optimum clinical dosage remains unknown. Reportedly, common side effects in humans, 337
including headache, facial flushing, nasal congestion, dyspepsia, and transient visual 338
impairment, have been associated with tadalafil administration (Supuran et al., 2006). 339
The current study did not evaluate the potential chronic effects and side effects of 340
tadalafil in dogs. 341
342
Conclusions 343
IV infusion of tadalafil decreased U46619-elevated PAP and PVR in dogs 344
without changes in SAP and SVR. Oral administration of tadalafil alone did not change 345
Page 15 of 24
16
PAP, but decreased U46619-elevated PAP 1 h after oral administration and the effect 346
was maintained for 6 h. The results suggest that tadalafil improved U46619-induced 347
pulmonary arterial constriction, leading to pulmonary arterial relaxation. 348
349
Conflict of interest statement 350
None of the authors of this paper has a financial or personal relationship with 351
other people or organizations that could inappropriately influence or bias the content of 352
the paper. 353
354
References 355
Adatia, I., Barrow, S.E., Stratton, P.D., Miall-Allen, V.M., Ritter, J.M., Haworth, S.G., 356
1993. Thromboxane A2 and prostacyclin biosynthesis in children and 357
adolescents with pulmonary vascular disease. Circulation 88, 2117-2122. 358
359
Anderson, J.R., Nawarskas, J.J., 2010. Pharmacotherapeutic management of pulmonary 360
arterial hypertension. Cardiology in Review 18, 148-162. 361
362
Arif, S.A., Poon, H., 2011. Tadalafil: a long-acting phosphodiesterase-5 inhibitor for the 363
treatment of pulmonary arterial hypertension. Clinical Therapeutics 33, 364
993-1004. 365
366
Bach, J.F., Rozanski, E.A., MacGregor, J., Betkowski, J.M., Rush, J.E., 2006. 367
Retrospective evaluation of sildenafil citrate as a therapy for pulmonary 368
hypertension in dogs. Journal of Veterinary Internal Medicine 20, 1132-1135. 369
370
Brown, A.J., Davison, E., Sleeper, M.M., 2010. Clinical efficacy of sildenafil in 371
treatment of pulmonary arterial hypertension in dogs. Journal of Veterinary 372
Internal Medicine 24, 850-854. 373
374
Christman, B.W., McPherson, C.D., Newman, J.H., King, G.A., Bernard, G.R., Groves, 375
B.M., Loyd, J.E., 1992. An imbalance between the excretion of thromboxane 376
and prostacyclin metabolites in pulmonary hypertension. The New England 377
Journal of Medicine 327, 70-75. 378
379
Corbin, J.D., Francis, S.H., 2002. Pharmacology of phosphodiesterase-5 inhibitors. 380
International Journal of Clinical Practice 56, 453-459. 381
382
Page 16 of 24
17
Falk, J.A., Philip, K.J., Schwarz, E.R., 2010. The emergence of oral tadalafil as a 383
once-daily treatment for pulmonary arterial hypertension. Vascular Health and 384
Risk Management 6, 273-280. 385
386
Forgue, S.T., Patterson, B.E., Bedding, A.W., Payne, C.D., Phillips, D.L., Wrishko, R.E., 387
Mitchell, M.I., 2006. Tadalafil pharmacokinetics in healthy subjects. British 388
Journal of Clinical Pharmacology 61, 280-288. 389
390
Francis, S.H., Corbin, J.D., 1999. Cyclic nucleotide-dependent protein kinases: 391
intracellular receptors for cAMP and cGMP action. Critical Reviews in 392
Clinical Laboratory Sciences 36, 275-328. 393
394
Francis, S.H., Corbin, J.D., 2003. Molecular mechanisms and pharmacokinetics of 395
phosphodiesterase-5 antagonists. Current Urology Reports 4, 457-465. 396
397
Galiè, N., Brundage, B.H., Ghofrani, H.A., Oudiz, R.J., Simonneau, G., Safdar, Z., 398
Shapiro, S., White, R.J., Chan, M., Beardsworth, A., et al., 2009. Tadalafil 399
therapy for pulmonary arterial hypertension. Circulation 119, 2894-903. 400
401
Ghofrani, H.A., Voswinckel, R., Reichenberger, F., Olschewski, H., Haredza, P., 402
Karadas, B., Schermuly, R.T., Weissmann, N., Seeger, W., Grimminger, F., 403
2004. Differences in hemodynamic and oxygenation responses to three 404
different phosphodiesterase-5 inhibitors in patients with pulmonary arterial 405
hypertension: a randomized prospective study. Journal of the American 406
College of Cardiology 44, 1488-1496. 407
408
Glaus, T.M., Soldati, G., Maurer, R., Ehrensperger, F., 2004. Clinical and pathological 409
characterisation of primary pulmonary hypertension in a dog. The Veterinary 410
Record 154, 786-789. 411
412
Gong, F., Shiraishi, H., Kikuchi, Y., Hoshina, M., Ichihashi, K., Sato, Y., Momoi, M.Y., 413
2000. Inhalation of nebulized nitroglycerin in dogs with experimental 414
pulmonary hypertension induced by U46619. Pediatrics International 42, 415
255-258. 416
417
Humbert, M., Morrell, N.W., Archer, S.L., Stenmark, K.R., MacLean, M.R., Lang, I.M., 418
Christman, B.W., Weir, E.K., Eickelberg, O, Voelkel, N.F., et al., 2004. Cellular 419
and molecular pathobiology of pulmonary arterial hypertension. Journal of the 420
American College of Cardiology 43, S13-S24. 421
422
Johnson, L., 1999a. Diagnosis of pulmonary hypertension. Clinical Techniques in Small 423
Animal Practice 14, 231-236. 424
425
Johnson, L., Boon, J., Orton, E.C., 1999b. Clinical characteristics of 53 dogs with 426
Doppler-derived evidence of pulmonary hypertension: 1992-1996. Journal of 427
Veterinary Internal Medicine 13, 440-447. 428
429
Page 17 of 24
18
Kellihan, H.B., Stepien, R.L., 2012. Pulmonary hypertension in canine degenerative 430
mitral valve disease. Journal of Veterinary Cardiology 14, 149-164. 431
432
Kellum, H.B., Stepien, R.L., 2007. Sildenafil citrate therapy in 22 dogs with pulmonary 433
hypertension. Journal of Veterinary Internal Medicine 21, 1258-1264. 434
435
Lincoln, T.M., Dey, N., Sellak, H., 2001. Invited review: cGMP-dependent protein 436
kinase signaling mechanisms in smooth muscle: from the regulation of tone to 437
gene expression. Journal of Applied Physiology 91, 1421-1430. 438
439
Matsuzaki, T., Noguchi, K., Nakasone, J., Uezu, K., Higuchi, M., Sakanashi, M., 1992. 440
Effects of the new thromboxane A2 antagonist vapiprost on isolated canine 441
blood vessels. Arzneimittel-Forschung 42, 1318-1322. 442
443
Mukhopadhyay, S., Sharma, M., Ramakrishnan, S., Yusuf, J., Gupta, M.D., Bhamri, N., 444
Trehan, V., Tyagi, S., 2006. Phosphodiesterase-5 inhibitor in Eisenmenger 445
syndrome: a preliminary observational study. Circulation 114, 1807-1810. 446
447
Nakamura, K., Yamasaki, M., Ohta, H., Sasaki, N., Murakami, M., Bandula Kumara, 448
W.R., Takiguchi, M., 2011. Effects of sildenafil citrate on five dogs with 449
Eisenmenger's syndrome. Journal of Small Animal Practice 52, 595-598. 450
451
Pepke-Zaba, J., Beardsworth, A., Chan, M., Angalakuditi, M., 2009. Tadalafil therapy 452
and health-related quality of life in pulmonary arterial hypertension. Current 453
Medical Research and Opinion 25, 2479-2485. 454
455
Pietra, G.G., Capron, F., Stewart, S., Leone, O., Humbert, M., Robbins, I.M., Reid, 456
L.M., Tuder, R.M., 2004. Pathologic assessment of vasculopathies in 457
pulmonary hypertension. Journal of the American College of Cardiology 43, 458
S25-S32. 459
460
Porst, H., Padma-Nathan, H., Giuliano, F., Anglin, G., Varanese, L., Rosen, R., 2003. 461
Efficacy of tadalafil for the treatment of erectile dysfunction at 24 and 36 hours 462
after dosing: a randomized controlled trial. Urology 62, 121-125. 463
464
Seibert, R.L., Maisenbacher, H.W. 3rd, Prosek, R., Adin, D.B., Arsenault, W.G., 465
Estrada, A.H., 2010. Successful closure of left-to-right patent ductus arteriosus 466
in three dogs with concurrent pulmonary hypertension. Journal of Veterinary 467
Cardiology 12, 67-73. 468
469
Senzaki, H., Smith, C.J., Juang, G.J., Isoda, T., Mayer, S.P., Ohler, A., Paolocci, N., 470
Tomaselli, G.F., Hare, J.M., Kass, D.A., 2001. Cardiac phosphodiesterase 5 471
(cGMP-specific) modulates beta-adrenergic signaling in vivo and is 472
down-regulated in heart failure. Federation of American Societies for 473
Experimental Biology Journal 15, 1718-1726. 474
475
Serres, F., Nicolle, A.P., Tissier, R., Gouni, V., Pouchelon, J.L., Chetboul, V., 2006. 476
Page 18 of 24
19
Efficacy of oral tadalafil, a new long-acting phosphodiesterase-5 inhibitor, for 477
the short-term treatment of pulmonary arterial hypertension in a dog. Journal 478
of Veterinary Medicine. A, Physiology, Pathology, Clinical Medicine 53, 479
129-133. 480
481
Skoumal, R., Chen, J., Kula, K., Breza, J., Calomfirescu, N., Basson, B.R., Kopernicky, 482
V., 2004. Efficacy and treatment satisfaction with on-demand tadalafil (Cialis) 483
in men with erectile dysfunction. European Urology 46, 362–369. 484
485
Stephenson, A.H., Sprague, R.S., Lonigro, A.J., 1998. 5,6-Epoxyeicosatrienoic acid 486
reduces increases in pulmonary vascular resistance in the dog. The American 487
journal of physiology 275, H100-109. 488
489
Supuran, C.T., Mastrolorenzo, A., Barbaro, G., Scozzafava, A., 2006. 490
Phosphodiesterase 5 inhibitors--drug design and differentiation based on 491
selectivity, pharmacokinetic and efficacy profiles. Current Pharmaceutical 492
Design 12, 3459-3465. 493
494
Tamura, M., Kurumatani, H., Matsushita, T., 2001. Comparative effects of beraprost, a 495
stable analogue of prostacyclin, with PGE(1), nitroglycerin and nifedipine on 496
canine model of vasoconstrictive pulmonary hypertension. Prostaglandins, 497
Leukotrienes, and Essential Fatty Acids 64, 197-202. 498
499
Uchide, T., Saida, K., 2005. Elevated endothelin-1 expression in dogs with heartworm 500
disease. The Journal of Veterinary Medical Science 67, 1155-1161. 501
502
Yamada, T., Yukioka, H., Hayashi, M., Asada, A., Inoue, M., 1998. Effects of inhaled 503
nitric oxide on platelet-activating factor-induced pulmonary hypertension in 504
dogs. Acta Anaesthesiologica Scandinavica 42, 358-368. 505
506
Zabka, T.S., Campbell, F.E., Wilson, D.W., 2006. Pulmonary arteriopathy and 507
idiopathic pulmonary arterial hypertension in six dogs. Veterinary Pathology 508
43, 510-522. 509
510
Figure Legends 511
Fig. 1. Dose-dependent hemodynamic effects of U46619 with intravenous 512
administration. Data are shown as means ± standard deviation (SD). SAP, systemic 513
arterial pressure; PAP, pulmonary arterial pressure. aP < 0.05 vs. baseline,
bP < 0.01 vs. 514
baseline, cP < 0.001 vs. baseline. 515
516
Fig. 2. Changes in pulmonary arterial pressure (PAP) with simultaneous infusion of 517
tadalafil and U46619. Data are shown as means ± standard deviation (SD). BL, 518
baseline; U46, U46619. aP < 0.01 vs. baseline,
bP < 0.001 vs. baseline,
cP < 0.05 vs. 519
U46619, dP < 0.01 vs. U46619. 520
521
Fig. 3. Changes in pulmonary vascular resistance (PVR) with simultaneous infusion of 522
tadalafil and U46619. Data are shown as means ± standard deviation (SD). BL, 523
Page 19 of 24
20
baseline; U46, U46619; Rp/Rs ratio, pulmonary resistance to systemic arterial 524
resistance ratio. aP < 0.01 vs. baseline,
bP < 0.001 vs. baseline,
cP < 0.05 vs. U46619,
dP 525
< 0.01 vs. U46619. 526
527
Fig. 4. Dose-dependent changes in systolic pulmonary arterial pressure (PAP) after oral 528
administration of tadalafil. Data are shown as means ± standard deviation (SD). U46619 529
was infused at a rate of 0.9 µg/kg/min for 10 min at 3 h after oral administration of each 530
drug. U46, U46619; PL, placebo. aP < 0.001 vs. control,
bP < 0.05 vs. U46619,
cP < 531
0.001 vs. U46619. 532
533
Fig. 5. Time-dependent changes in systolic pulmonary arterial pressure (PAP) after oral 534
administration of tadalafil. Data are shown as means ± standard deviation (SD). BL, 535
baseline. Baseline represents data before drug administration under anesthesia in each 536
group. aP < 0.001 vs. baseline,
bP < 0.01 vs. U46619. 537
538
Page 20 of 24
21
Table 1 Hemodynamic effects of intravenous infusion of tadalafil and U46619. 539
540
Baseline
U46619
0.9 µg/kg/min
U46619 + tadalafil
50 µg/kg/h 100 µg/kg/h 200 µg/kg/h
Heart rate (bpm) 116 ± 21 104 ± 18 102 ± 18 102 ± 19 99 ± 19
SPO2 (%) 97.5 ± 1.5 97.5 ± 1.5 98.2 ± 0.8 98.3 ± 0.8 98.3 ± 1.4
Systolic SAP (mmHg) 96 ± 22 108 ± 22 105 ± 13 105 ± 13 111 ± 17
Mean SAP (mmHg) 68 ± 13 82 ± 13 82 ± 12 82 ± 5 88 ± 13
Diastolic SAP (mmHg) 53 ± 10 74 ± 9 73 ± 11 73 ± 4 83 ± 5
Mean RVP (mmHg) 3.4 ± 3.5 12.4 ± 3.43
8.9 ± 2.81
8.7 ± 2.81
8.4 ± 3.11
Mean CVP (mmHg) -0.1 ± 1.7 3.7 ± 2.12
3.3 ± 2.11
3.7 ± 2.22
3.3 ± 2.21
Mean PCWP (mmHg) 1.8 ± 2.9 8.7 ± 4.32
8.3 ± 4.01
6.3 ± 3.5 6.3 ± 3.4
CO (L/min) 1.7 ± 0.6 1.1 ± 0.4 1.2 ± 0.5 1.1 ± 0.4 1.2 ± 0.4
SVR (dyn/s/cm-5
) 49.4 ± 16.3 71.8 ± 30.61
84.4 ± 39.01
87.0 ± 28.21
88.1 ± 29.11
541
Data are shown as means ± standard deviation (SD). Baseline represents data before 542
drug administration under anesthesia in each group. SAP, systemic arterial pressure; 543
RVP, right ventricular pressure; CVP, central venous pressure; PCWP, pulmonary 544
capillary wedge pressure; CO, cardiac output; SVR, systemic vascular pressure. 545
1P < 0.05 vs. baseline,
2P < 0.01 vs. baseline,
3P < 0.001 vs. baseline. 546
547
548
549
Page 21 of 24
22
Table 2 550
Dose-dependent effects on heart rate and pulmonary arterial pressure (PAP) after oral 551
administration of tadalafil. 552
553
554
Data are shown as means ± standard deviation (SD). 555
1P < 0.01 vs. control,
2P < 0.001 vs. control,
3P < 0.05 vs. U46619,
4P < 0.001 vs. 556
U46619. Bpm, beats/min. 557
558
Control U46619
0.9 µg/kg/min
Tadalafil U46619 + tadalafil
1 mg/kg 2 mg/kg 4 mg/kg 1 mg/kg 2 mg/kg 4 mg/kg
Heart rate (bpm) 116 ± 21 111 ± 23 111 ± 23 111 ± 24 117 ± 21 107 ± 24 109 ± 19 112 ± 13
Systolic PAP (mmHg) 7.0 ± 3.9 29.6 ± 6.42
8.7 ± 3.4 9.6 ± 3.5 9.1 ± 2.7 25.6 ± 5.12
23.8 ± 4.82,3
20.6 ± 4.12,4
Mean PAP (mmHg) 4.4 ± 2.8 21.4 ± 2.52
3.3 ± 1.7 5.1 ± 2.5 4.2 ± 2.3 17.3 ± 1.62
16.6 ± 2.52,3
14.9 ± 2.81,4
Diastolic PAP (mmHg) 1.8 ± 2.3 15.2 ± 2.82
0.7 ± 1.4 1.6 ± 1.3 -0.1 ± 2.2 12.4 ± 0.82
11.5 ± 3.22
9.7 ± 2.72,3
Page 22 of 24
23
Table 3 Time-dependent effects on heart rate and pulmonary arterial pressure (PAP) 559
after oral administration of tadalafil. 560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
Data are shown as means ± standard deviation (SD). Baseline represent data before drug 588
administration under anesthesia in each group. 589 1P < 0.001 vs. baseline,
2P < 0.05 vs. U46619 at the same time point. Bpm, beats/min. 590
591
Heart rate (bpm) Baseline 1 h 3 h 6 h
Control 118 ± 27 116 ± 28 103 ± 34 106 ± 29
U46619 117 ± 25 112 ± 18 110 ± 20 100 ± 25
U46619 + tadalafil 116 ± 20 119 ± 13 108 ± 19 117 ± 24
Mean PAP (mmHg) Baseline 1 h 3 h 6 h
Control 3.9 ± 2.3 3.7 ± 2.7 5.1 ± 2.3 4.1 ± 1.6
U46619 4.4 ± 2.6 19.3 ± 3.01 20.7 ± 3.1
1 20.2 ± 2.1
1
U46619 + tadalafil 3.2 ± 2.1 14.9 ± 3.11,2
14.8 ± 3.01,2
15.4 ± 3.51,2
Diastolic PAP (mmHg) Baseline 1 h 3 h 6 h
Control 0.9 ± 1.2 0.9 ± 1.4 1.3 ± 2.0 0.6 ± 0.9
U46619 1.3 ± 2.0 13.9 ± 3.21 13.8 ± 4.1
1 14.7 ± 2.7
1
U46619 + tadalafil 0.4 ± 1.0 10.4 ± 3.31 8.8 ± 3.2
1,2 10.7 ± 2.9
1,2
Page 23 of 24
24
592
Page 24 of 24
