Life SciQ~es Vol . 13, pp. 1771-1778, 1973 .
Pergamon PressPrinted in Great Britain
HYPOTHERMIC ACTION OF A9-TETRAHYDROCANNABINOL, 11-HYDROXY-A9-TETRAHYDROCANNABINOL AND 11-HYDROXY-AB-TETRAHYDROCANNABINOL IN MICE
Coryce 0 . Haavik and Harold F . Hardman
Department of Pharmacology, The Medical College of WisconsinMilwaukee, Wisconsin 53233
(Received 17 September 1973 ; in final form 2 November 1973)Summary
The hypothermic activity of 09-tetrahydrocannabinol (D9-THC), ametabolite, 11-hydroxy-A 9 -tetrahydrocannabinol (11-OH-D 9 -THC) and 11-hydroxy-De-tetrahydrocannabinol (11-OH-AB-THC) has been determined inmale mice maintained at an ambient temperature of 20 loC . The meanbody temperature of mice that received 2, 4, 16 or 32 mg/kg, i .v., ofa tetrahydrocannabinol was significantly lower than that of vehicletreated mice (p
Tetrahydroca.nnabinol-Induced Hypothermia .
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The ability to lower body temperature is one of many actions of tetrahydro-
cannabinols . These agents are among the most potent hypothermic agents known
Quantitation of the hypothermic action of :: 9 -THC in mice has been re
ported recently by this laboratory (9) .
Since the hypothermic response can be
measured with precision, this assay nw has been used to compare the onset of
action and the intrinsic activity of 11-OH-A 9 -THC and 11-hydroxy-AB-tetrahydro-
cannabinol (11-OH-Ae-THC) with that of A9-THC .
Male Cox mice (19-22 g boy weight) were transferred from animal quarters
to an environmentally controlled room 21 hours prior to drug administration .
In the environmental room ambient temperature was maintained at 20 1C and
humidity controlled at 45-55$ .
Deep rectal temperature was monitored by means
of a thermistor probe and telethermometer (Yellow Springs Instrument Co .) im-
mediately before and for 2 hours after intravenous drug administration . During
this time the animals were restrained by the tail but otherwise were free to
move . The tetrahydrocannabinols (A9-THC, 11-OH-, 9 -THC and 11-OH-AB-THC)~` were
prepared as suspensions in alcohol, Tween 80 and saline (20 mg drug in 0 .1 ml
95$ ethanol, 0 .1 ml Tween 80 and 0 .43 ml 0 .9$ NaCl) . This stock solution was
diluted with vehicle as required so that the desired drug dose was contained
in 0 .1 ml for a 25 g mouse . Vehicle consisted of ethanol, Tween 80 and saline
in the same proportions as in the stock drug solution .
The mean difference in body temperat~se t S .E . from the individual control
values was calculated for each time at which temperature was measured . Sig-
nificance was determined by Student's t-test and set at p c0.05 .
The .dose related nature of the hypothermic response to A9-THC is shown in
Fig . 1 . Administration of 11-OH-D 9-THC and 11-OH-De-THC also resulted in a
dose related hypothermia .
The mean maximal hypothermia produced by these three
~A9 -THC, 11-OH-G 9-THC and 11-OH-GB-THC were supplied by Dr . M . C . Braude,National Institute of Mental Health .
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Mean body temperature decrease after i .v . administration of vehicle~ (~) orof A9-THC at doses of 2 ( d-~ ), 4 ( ~-~ ), 16 ( ~~ ) and 32 (f") mg/kgto mice . Each point represents the mean difference in body temperature t S .E .from the individual control values for at least 14 mice .
agents over the dosage range of 2 to 32 mg/kg is shown in Table 1 .
It can be
seen (table 1) that the hypothermic response to A9-THC increases continuously
over the dose range studied, while the maximum hypothermia following adminis-
tration of either 11-0H-A9-THC or 11-OH-AB-THC has been attained.
The onset of the hypothermic response to A9-THC occurs rapidly (Fig . 1) .
The decrease in mean body temperature during the first 5 minutes after adminis-
tration of vehicle or of a 2 mg/kg dose of A9-THC or 11-OH-A9-THC is shown is
Fig . 2 .
Within 2 minutes the mean body temperatures of both groups of drug
treated mice were significantly lower (p
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Mean Maximum Decrease S .E . ( C) in Rectal Temperature afterL V . Administration of A9-THC, 11-OH-D 9-THC or 11-OH-D9-THC to Mice
(Ambient Temperature = 20C)
Dose A9-THC 11-OH-A 9 -THC 11-OH-AB-THCmg/kg
X S .E .
X S .E .
X t S .E .
3 .47 t 0 .40 (16)
4 .28 0 .39 (8)
3 .00 t 0 .24 (8)
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~ VEHICLE~ eTHC
05 LO 1 .5 2A 2S 30 a5 4A 4,5 50
FIG . 2
Mean body temperature decrease after i .v . administration of vehicle, A9-THC or11-OH-A9-THC . Each point represents the mean difference in body temperature tS .E . from the individual control values for at least 8 mice .
eTrlce n-oH eoTHC 2mih~ ."
FIG . 3
Mean body temperature decrease after i .v . administration of vehicle, e9 -THC or11-OH-AB-THC . Each point represents the mean difference in body temperature tS .E . from the individual control values for at least 8 mice .
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Intravenous administration of 11-OH-A 9-THC to man produced
tachycardia and a feeling subjectively evaluated as a marihuana-like "high ."
The onset, magnitude and duration of tachycardia does not differ significantly
from that produced by intravenous administration of a comparable dose of A9-
THC . The psychological assay suggests that D9 -THC has greater efficacy and a
longer duration of action than does 11-OH-A 9 -THC (7) . Although the reports of
these investigators demonstrate that 11-0H-A 9-THC has activity on the cardio-
vascular and central nervous systems, the rapid onset of action of 09 -THC in
these systems suggests that prior conversion to an active metabolite may not
be required .
Gill and Jones (10) have measured the effect of D9-THC on be-
havior of mice pretreated with SKF 525A, an inhibitor of oxidative drug metab
Since this treatment significantly elevated brain 11-OH-D 9 -THC without
producing a comparable increase in behavioral effect, no conclusion could be
drawn regarding the relative pharmacological importance of D9-THC and 11-OH-
A9-THC as mediators of the behavioral response .
Investigations from many laboratories have established that the tetrahy-
drocannabinols are potent hypothermic agents (8) . Since the dose related
nature of the hypothermic response can be demonstrated and quantitated without
difficulty (9), this system is of value for comparing the activity of A9-THC
with that of its metabolite, 11-OH-A 9-THC . In addition, the activities of
11-OH-D 9-THC and another hydroxy tetrahydrocannabinol, 11-OH-Ae-THC have been
A significant hypothermic response has been shown to develop within two
minutes after intravenous administration of 2 mg/kg of A9 -THC, 11-OH-D 9 -THC or
Since these data do not show a lag in the onset of hypothermia
produced by D9-THC as compared to its major metabolite, 11-OH-A 9-THC, it ap-
pears likely that both G9 -THC and 11-OH-A 9-THC have activity per ae in this
This possibility is supported by the fact that no significant differ-
ence has been found in the hypothermia produced by A9-THC and by 11-OH-D 9 -THC
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during the firet 5 minutes after injection .
A comparison of the dose-response relationship of these drugs (Table 1)
shows that 11-OH-A9-THC alone cannot account for the hypothermia seen follow-
ing D9 -THC .
The maximum hypothermic response which A9 -THC can produce at an
ambient temperature of 20C has not been measured in the experiments reported
here, and may not be attainable at doses below the LD50 (48 mg/kg) .
tract, the lack of a significant difference between the hypothermic response
to doses of 4, 16 and 32 mg/kg of 11-OH-09-THC or 11-OH-DB-THC indicates that
the maximum response to these agents has been attained . Since this maximum issignificantly leas than the highest value measured after A9-THC, the intrinsic
activity of 11-OH-A9 -THC is lower than that of the parent compound, D9-THC.
The intrinsic activity of 11-OH-AB-THC also is less than that of A9-THC, and
in addition, appears to be less than that of 11-OH-d9-THC.
The data show that although the three tetrahydrocannabinola tested cannot
be distinguished on the basis of onset of action, they differ significantly in
intrinsic activity. The conclusion appears justified that in this system
pharmacological activity resides in each of the tetrahydrocannabinols studied .
We thank Fred Colline, Canillia Laboy, Jeannine Moore and Timothy Siglock
for their valuable technical assistance .
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