Abstract

Mercurials (sulfhydryl inhibitors) and haloalkylamine alpha adrenergic blocking agents (Dibenamine and phenoxybenzamine) exhibit identical action on melanophores of the lizard Anolis carolinensis. Both types of compounds block MSH-induced darkening (melanosome dispersion) of skins but enhance catecholamine-induced darkening. This latter effect is an example of a "catecholamine reversal", characteristic of alpha adrenergic blocking agents, which results from alpha adrenergic inhibition and consequent beta adrenergic stimulation. This suggests that haloalkylamine alpha blocking agents exert their activity through sulfhydryl blockade, which in turn suggests a role for sulfhydryls in alpha adrenergic activity. The inhibition and reversal of MSH-induced darkening by haloalkylamine alpha antagonists and mercurials also suggests a role for sulfhydryls in MSH activity. These actions of Dibenamine and phenoxybenzamine also indicate a possible common sulfhydryl requirement for MSH and the alpha adrenergic receptor. Such a requirement is quite specific and must precede the formation or increase in cyclic adenosine monophosphate since neither Dibenamine nor mersalyl inhibits melanosome dispersion in response to beta adrenergic stimulation, dibutyryl cyclic adenosine monophosphate or theophylline.