Abstract
The release of tritium by Latrodectus antheratus spider venom gland extract, high K + and tyramine, were studied in two noradrenergically innervated tissues of the rat (the isolated hypothalamus and the perfused tail artery) preloaded with 3H-noradrenaline. An increase in 3H release by venom gland extract and by K + was observed in the presence of phenoxybenzamine, an alpha-adrenoceptor blocker. In contrast, the release of 3H by tyramine, an indirect sympathomimetic amine whose action does not depend on the presence of calcium ions, was not modified. Methoxamine, an alpha-adrenoceptor agonist, decreased the 3H release by the venom gland extract and high K +. The results suggest that the venom gland extract releases noradrenaline by a process similar to that evoked by stimulation with high K +, i.e. via a depolarizing mechanism regulated by a negative feedback pathway involving alpha-adrenoceptors.
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