Contraction Of Rabbit Aorta Research Articles

Potent α-adrenoceptor action of soterenol on vascular and other smooth muscle

Treatment with soterenol (0.3–300 μg/kg, i.v.) increased the mean arterial blood pressure and decreased heart rate in rabbits. Soterenol caused a dose-dependent contraction of rabbit aorta and portal vein, guinea-pig vas deferens and cat nictitating membrane which was inhibited by phentolamine. Other β-agonists such as isoproterenol, salbutamol and terbutaline did not exhibit similar effects. Soterenol had potent stimulant action on the α-receptor of the smooth muscle.

Pharmacologic receptor activity of rabbit aorta. Effect of dithiothreitol and N-ethylmaleimide.

N -ethylmaleimide (NEM), an alkylating agent that covalently binds sulfhydryl groups, and dithiothreitol (DTT, Cleland's reagent), which reduces disulfide bridges to sulfhydryl groups, affected drug-induced contractions of rabbit aorta. NEM depressed aortic responses to potassium chloride (KCl), norepinephrine, serotonin, histamine, and angiotensin II. This action was attributed to an interaction of NEM with sulfhydryl groups vital to either the membrane function or the contractile apparatus. DTT had minimal effects on responses to KCl, norepinephrine, and serotonin; it potentiated aortic contractions produced by histamine and abolished responses to angiotensin II. Enhancement of the histamine response by DTT was not accompanied by an effect on the histamine-metabolizing enzymes or by an alteration in the K B and pA 2 values for pyrilamine. The results suggest that a disulfide bridge plays a prominent role in both histamine and angiotensin receptor activity of rabbit aorta. With regard to the histamine receptor system, two possibilities exist: (1) reduction of a disulfide bridge at some vital point increases receptor activity or (2) the histamine receptor system, normally in a reduced state, is oxidized in the artificial environment of the tissue bath and needs to be reduced to regain full activity.

Differential effects of substrate depletion on drug-induced contractions of rabbit aorta.

Differential effects of substrate depletion on drug-induced contractions of rabbit aorta.

Analysis of the cardiovascular effects of 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride (Catapres)

J. W. CONSTANTINE and W. K. McSHANE, Analysis of the cardiovascular effects of 2-(2,6-dichlorophenylamino) -2'imidazoline hydrochloride (Catapres), European J. Pharmacol. 4 (1968) 109–123. The nature of the blood pressure response (pressor followed by depressor) caused by intravenous administration of Catapres was analyzed in preparations ranging from isolated tissues to intact animal. Contractions of rabbit aorta and dog vein caused by Catapres are inhibited by α-adrenergic blockers. Catapres protects α-adrenergic receptors from blockade by phenoxybenzamine. It is concluded that the hypertensive effect of Catapres is due to sympathomimetic constriction of peripheral vasculature. Blood pressure and heart rate of dogs decreased following administration of Catapres into the vertebral artery at doses ineffective intravenously, indicating that hypotension and bradycardia are centrally mediated. The direct causes of hypotension depend upon the dose of Catapres. At low doses hypotension is des solely to reduction in peripheral resistance. Higher doses decrease peripheral resistance and cardiac output. Excessive doses lower cardiac output; peripheral resistance is not affected or increased. Catapres does not exaggerate postural hypotension in dogs or monkeys.