Modification by yohimbine and prazosin of the mechanical response of isolated dog mesenteric, renal and coronary arteries to transmural stimulation and norepinephrine.

Some functions of pre- and postsynaptic alpha-receptors were compared in isolated dog arteries. In mesenteric and renal arteries, contractile responses to transmural electrical stimulation were potentiated by yohimbine, a selective alpha 2-antagonist; the potentiation was greater in mesenteric arteries. Concentration-response curves for norepinephrine were shifted to the right by high concentrations of yohimbine. Prazosin, a selective alpha 1-antagonist, in low concentrations preferentially attenuated the contractile response to transmural stimulation, when compared with the response to equiactive concentrations of norepinephrine. Relaxant responses of coronary arteries to transmural stimulation were also potentiated by yohimbine. Relaxations induced by norepinephrine were not influenced by yohimbine but were potentiated by prazosin. Contractile responses of coronary arteries treated with propranolol to transmural stimulation were abolished by prazosin. It is concluded that the involvement of presynaptic alpha 2-receptors in the negative feedback mechanism in transmitter release differs in a variety of dog arteries and that the adrenoceptors subserving contraction are of both subtypes (alpha 1 and alpha 2) in the mesenteric and renal arteries, but only of the alpha 1 subtype in coronary artery.