Hydrogen Peroxide, An Endogenous EDHF, Plays An Important Role In Coronary Autoregulation In Vivo

*Toyotaka Yada, **Hiroaki Shimokawa, *Osamu Hiramatsu,*Tatsuya Kajita, *Fumiyuki Shigeto, *Masami Goto, *Yasuo Ogasawara,#Fumihiko Kajiya

*Dept. of Medical Engineering, Kawasaki Medical School,Kurashiki, Japan**Dept. of Cardiovascular Medicine, Kyushu University Graduate School of Medicine, Fukuoka, Japan#Dept. of Cardiovascular Physiology, Okayama UniversityGraduate School of Medicine and Dentistry, Okayama, Japan

(Circulation, T. Yada et al, 2003)

Background

Catalase inhibits EDHF-mediated Responses to Bradykininin Human Mesenteric Arteries

Indo + L-NNA

Indo + L-NNA + catalase

0

50

100

Rel

axat

ion,

%

678910BK (- log M)

n=4

*

-30

-20

-10

0Bradykinin 10-7 M

Hyp

erpo

lariz

atio

n, ∆

mV

n=3=3*

* P < 0.05(T. Matoba and H. Shimokawa et al. Biochem Biophys. Res. Commun. 2002)

Coronary Autoregulation

Low Perfusion Pressure High Perfusion Pressure

50

100

mmHg150

50

100

mmHg150

AIM

To evaluate the Role of Hydrogen Peroxide as an Endogenous EDHF and the Possible Interaction among Nitric Oxide, EDHF and Adenosine in Coronary Autoregulation of Canine Subepicardial Microvessels In Vivo.

Experimental Setup

Venous Sampling of Coronary Sinus

Blood FlowVelocimeter

AoP & LVP

Arterial Sampling

Infusion PumpWindkessel

RollerPump

CCDMicroscope

Experimental Protocol

(1) Coronary perfusion pressure was changed in a stepwise manner from 100 to 70, 50 and 30 mmHg before and after inhibition of NO synthase (L-NMMA, 200 µM) or of hydrogen peroxide (Catalase, 40,000U/kg iv and 240,000U/kg ic) with L-NMMA.

(2) Vasodilator responses of small arteries (>100 µm) and arterioles (<100 µm) were evaluated by CCD microscope.

(3) Coronary venous samples were drawn, and vascular responses were evaluated after L-NMMA and Catalase plus adenosine receptor blockade (8-sulfophenyltheopkylline, 25 µg/kg ic).

Vascular Responses to Acetylcholine

30

10

0

20

Control

L-NMMA

L-NMMA+Catalase

＊ p<0.05 vs. Control

30

10

0

20

Control

L-NMMA

L-NMMA+Catalase

＊＊

＊ %C

hang

e in

Dia

met

er

%C

hang

e in

Dia

met

er

Arteriole (< 100 µm)Small Artery (> 100 µm)

(Circulation, T. Yada et al, 2003)

Microvascular Responses during

Decreasing Perfusion Pressure

Perfusion Pressure (mm Hg)(Circulation, T. Yada et al, 2003)

-10

-5

0

5

10

15

30 50 70 100

*

* p<0.05, vs. Control

Control

after L-NMMA (L)after L+Catalase

Arteriole (< 100 µm)Small Artery (> 100 µm)%

Cha

nge

in D

iam

eter

05

1015

20

2530

30 50 70 100

*

*

Feed-back Arteriolar Responses during Coronary Autoregulation

(Circulation, T. Yada et al, 2003)

Catalase plus L-NMMA

0

5

10

15

20

L-NMMA plus catalase

** *

**

*** **

* P<0.05** P<0.01

CPP 70mmHgCPP 50mmHgCPP 30mmHg

Coronary Venous Adenosine

*P<0.05, **P<0.01 vs. control; #P<0.05, ##P<0.01 vs. L-NMMA; †P<0.01 vs. L-NMMA plus catalase

Arteriolar Responses afterAdenosine Receptor Blockade

%C

hang

e in

Dia

met

er

Cor

onar

y ve

nous

aden

osin

e (µ

M)

Perfusion Pressure (mm Hg)Control diameter (µm)

Compensatory Effect of Adenosine

050

100150200250

300350400

30 50 70 100

†

#

##*

*

**

-10-505

101520253035

30 40 50 60 70 80 90 100

*

**

*

**

#

#

†

L-NMMA plus catalaseL-NMMAControl

L-NMMA plus catalase plus 8-SPT

(Circulation, T. Yada et al, 2003)

SUMMARY

After NO inhibition, vasodilator responses were attenuated mainly in small arteries (>100 µm), whereas combined infusion of NO inhibition plus catalase abolished the autoregulatory vasodilation in both small arteries and arterioles ( <100 µm).

CONCLUSION

Hydrogen peroxide, an endogenous EDHF, plays an important role of vasodilation in coronary autoregulation of canine subepicardial microvessels in vivo.