Abstract

Following suggestions in the literature that the enkephalins may reduce the release of mediator from adrenergic or painful fibres, in this research we attempt to discover whether these substances have a similar effect at the level of cholinergic fibres of the somatic section. We studied the influence of D-ALA2Leu5-enkephalin (DALE) on single twitch or on the tetanic responses evoked by stimulation of motor nerve-endings in the isolated frog sciatic nerve-gastrocnemius muscle preparation comparing these responses with the ones evoked by direct stimulation of the same muscle. It was found that the DALE invariabily reduced the amplitude of the single twitch or tetanic response or the ability of the preparation to maintain indirect tetanus, while it increased the amplitude of the muscle response evoked by direct stimulation. DALE also, invariably, increased Wedensky d-tubocurarine inhibition. On the basis of suggestions in the literature and of the present findings, it is concluded that DALE reduces acetylcholine impulse release through a presynaptic inhibition mechanism involving specific receptors for the endogenous opiates. Verf.-Referat