Comparison of the Effects of Bretylium, Guanethidine and Bethanidine on Smooth Muscle Responses to Different Rates of Sympathetic Nerve Stimulation

Abstract

The relative effects of bretylium, guanethidine and bethanidine on smooth muscle responses to different rates of sympathetic nerve stimulation have been compared. The responses studied were vasoconstriction in the femoral vascular bed and contraction of the spleen in anaesthetized cats, vasoconstriction in perfused ears of rabbits and inhibition of pendular movements in rabbit isolated ileum preparations. Except in the isolated ileum, the action of bretylium on curves relating the frequency of nerve stimulation and the effect on response was different from that of guanethidine.Whereas bretylium caused relatively greater inhibition of responses to high stimulus frequencies and depressed the slopes of the curves, guanethidine preferentially suppressed responses to low stimulus frequencies and caused roughly parallel shifts of the curves. In each situation tested bethanidine was the most potent of the three blocking agents and in general its effect on frequency/response curves was intermediate between those of bretylium and guanethidine.

Effect of Adrenergic Neuron Inhibitors on the Vascular Response to Sympathetic Nerve Stimulation

“…A similar result was reported by Boura and Green (2) for the nictitating membrane in the cat. Our findings on the ability of bretylium to suppress predominantly the transmission of high impulse frequency correlate well with those of Green and Robson (4).…”

The relationship of the renal vascular activity of angiotensin II to the autonomic nervous system.

“…The ability of guanethidine or bretylium to abolish the response to angiotensin II administered intra-arterially was compromised by previous administration of tyramine. The administration of tyramine (100 to 500 ,g per kg) restored the renal vascular activity of angiotensin II after that activity had been blocked by guanethidine ( Figure 6 Figure 7) the sympathetic postganglionic fiber (bretylium ted dog, ex-and guanethidine) (14) or by agents that alter iedjtio, ef sympathetic activity by a central action (hydralainjections do zine) (15 (23). With these qualifications in mind, a tentative construction of the relationship between angiotensin II and the autonomic nervous system will be attempted.…”

Modification by Az-55, Guanethidine and Bretylium of Responses of Atria and Aortic Strips to Transmural Stimulation

“…On the other hand, no qualitative difference between AZ-55, guanethidine and bretylium was detected in the present study on the chronotropic response to transmural stimulation: the inhibitory effect of these drugs at a stimulus frequency of 100/sec was greater than that at the lower frequencies. No difference between guanethidine and bretylium is also observed in studies of the inhibitory response of isolated rabbit ileum to periarterial nerve stimulation (9).…”