Influence of a cholinergic agent, oxotremorine, on sympathetic reflexes

Administration of cholinergic substances by various routes has been reported to produce marked cardiovascular effects. The present study examined the influence of a muscarinic agonist, oxotremorine, on aspects of sympathetic function. The compound reduced blood pressure and spontaneous sympathetic outflow in anesthetized cats after blockade of peripheral muscarinic receptors with methylatropine. Effects on potentials evoked in the splanchnic nerve by stimulation of an intercostal nerve, i.e., the somatosympathetic reflex, were also evaluated. Oxotremorine did not modify the initial or "spinal" component of the reflex but markedly reduced the amplitude and increased the latency of the secondary or "supraspinal" phase. Atropine antagonized the inhibitory response. Effects of oxotremorine differed importantly from those produced by baroreceptor and coronary chemoreceptor activation and administration of clonidine and methyldopa which also attenuated the amplitude of the supraspinal component but did not alter its latency. Consequently, oxotremorine depresses sympathetic function at loci within the brainstem and cord by mechanisms not identical with those mediating responses to these reflexes and drugs.