Role of angiotensin and adrenoceptors in hemodynamic response to aortic cross-clamping.
An earlier study has shown that angiotensin and catecholamines were responsible for the vasoconstriction observed in the isolated hindlimb preparation during aortic cross-clamping. That study also demonstrated that when vasoconstriction was blocked with an alpha-adrenergic antagonist, phenoxybenzamine, vasodilation was elicited by aortic cross-clamping. The present study tested the hypothesis that this vasodilation was mediated via beta-adrenergic receptors. Eighteen dogs had their hindlimb denervated, vascularly isolated, and pump perfused with blood drained from the inferior vena cava, after passing through a gas-exchanging membrane where oxygen and carbon dioxide tensions were normalized. Left and right thoracotomies were performed, and the aorta and inferior vena cava were cross-clamped. The cross-clamping was associated with 29-37% increase in limb vascular resistance in control dogs (n = 6), in animals pretreated with propranolol (2 mg/kg, n = 6), and in dogs pretreated with a combination of phenoxybenzamine (3 mg/kg) and propranolol (2 mg/kg, n = 6). In animals pretreated with a combination of phenoxybenzamine, propranolol, and enalaprilat (2 mg/kg, n = 6), an angiotensin-converting enzyme inhibitor, limb vascular resistance did not change. This study has confirmed that aortic cross-clamping is associated with vasoconstriction induced by angiotensin and activation of alpha-adrenoceptors and has further demonstrated that vasodilation is attributable to beta-adrenoceptor activation.
Department of Anesthesiology, University of Alabama, Birmingham 35294.
S
S
Gelman
S E
SE
Curtis
W E
WE
Bradley
C T
CT
Henderson
D A
DA
Parks
S M
SM
Cain
D000804:Angiotensin II / Q000502:physiology*; D000818:Animals; D001011:Aorta / Q000502:physiology*; D002395:Catecholamines / Q000097:blood; D003250:Constriction; D004285:Dogs; D015773:Enalaprilat / Q000494:pharmacology; D006439:Hemodynamics / Q000187:drug effects; D006614:Hindlimb / Q000098:blood supply; D009994:Osmolar Concentration; D011941:Receptors, Adrenergic / Q000502:physiology*; D013565:Sympatholytics / Q000494:pharmacology; D014655:Vascular Resistance / Q000187:drug effects
D002395:Catecholamines; D011941:Receptors, Adrenergic; D013565:Sympatholytics; D000804:Angiotensin II; D015773:Enalaprilat