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Lack of effect of D600 on α<inf>1</inf>-adrenoceptor-mediated contractions of rat isolated anococcygeus muscle

Abstract:

The experiments concerned the contractile responses of rat anococcygeus muscle to the selective α1-adrenoceptor agonists cirazoline, phenylephrine, methoxamine, St 587, Sgd 101/75, amidepphrine and SK&F 89748-A and the effect of the calcium entry blocker D600 on the responses. The effects of noradrenaline, adrenaline, K+, tyramine and electrical field stimulation were studied as well. The potency series of the various agonists on rat anococcygeus muscle differed from the series for rat and guinea-pig aorta, indicating differences in the structure of the α1-adrenoceptors on these tissues. D600 was ineffective in inhibiting contractions of rat anococcygeus muscle to the various agonists, but effectively attenuated the responses to K+ in anococcygeus muscle from rats pretreated with reserpine or in prazosin-induced preparations. These data indicate that α1-adrenoceptor activation in rat anococcygeus muscle triggers contractions which do not primarily require the influx of extracellular calcium. In this respect, the smooth muscle from the rat anococcygeus muscle differs from vascular smooth muscle from this species. © 1984.