Experimental hypertension produces diverse changes in the regional vascular responses to endothelin-1 in the rabbit and the rat.
OBJECTIVE
To examine the effects of hypertension on systemic and regional haemodynamic responses to endothelin-1.


METHODS
Comparison of responses between age-matched control and hypertensive rabbits (two-kidney, two wrapped), and between spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats.


METHODS
Arterial pressure, heart rate and blood flow responses to 0.2 nmol/kg intravenous endothelin-1 were measured in conscious animals. Blood flow was measured by pulsed ultrasound Doppler in the ascending aorta, distal abdominal aorta, left renal artery and superior mesenteric artery.


RESULTS
Endothelin-1 produced qualitatively similar effects in the hypertensive and control animals. In the systemic circulation, brief initial vasodilation preceded sustained vasoconstriction. In the hindlimb, marked vasodilation preceded relatively minor vasoconstriction, and profound vasoconstriction occurred in the renal and mesenteric vascular beds. In the rats but not the rabbits, fleeting vasodilation preceded the renal and mesenteric vasoconstriction. Significant differences between hypertensive and control animals were: accentuation of the pressor effect and heart rate responses in hypertensive animals of both species, and accentuation of hindlimb vasodilation in hypertensive rabbits but not SHR; and attenuation of the depressor effect in SHR but not hypertensive rabbits, attenuation of the mesenteric vasoconstriction in both hypertensive rabbits and rats, and attenuation of renal vasoconstriction in SHR.


CONCLUSIONS
The increased responses to endothelin-1 of some variables in the hypertensive animals may involve structural changes in the resistance vessels. However, the reduced responses in the mesenteric vasculature of both species and the renal vasculature of the SHR are due to some mechanism other than structural change.
Roberts-Thomson
P
P
Department of Medicine, Flinders Medical Centre, Bedford Park, South Australia.
McRitchie
R J
RJ
Chalmers
J P
JP
D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects; D016232:Endothelins / Q000097:blood / Q000494:pharmacology*; D006439:Hemodynamics / Q000187:drug effects*; D006614:Hindlimb / Q000098:blood supply; D006973:Hypertension / Q000000981:diagnostic imaging / Q000503:physiopathology*; D007668:Kidney / Q000098:blood supply / Q000000981:diagnostic imaging; D008297:Male; D008638:Mesenteric Arteries / Q000000981:diagnostic imaging / Q000187:drug effects; D011817:Rabbits; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D018617:Ultrasonography, Doppler, Pulsed; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects*
D016232:Endothelins