Abstract
Chromaffin cells isolated from guinea-pig adrenal glands secrete catecholamines in response to acetylcholine, nicotine, pilocarpine, veratridine, and high [K+]. Both substance P and somatostatin inhibit acetylcholine-induced catecholamine secretion. The maximal inhibition of acetylcholine-induced catecholamine secretion produced by substance P and by somatostatin is approximately 60%: the concentrations of the peptides required for half-maximal inhibition of secretion are approximately 0.8 and 2 μM. respectively. The maximal inhibition of catecholamine secretion produced by somatostatin and that caused by substance P are not additive. The effects of the peptides on secretion are readily reversible. Somatostatin and substance P also inhibit nicotine-induced catecholamine secretion, but they do not inhibit catecholamine secretion stimulated by pilocarpine, veratridine, or high [K+]. Thus, these peptides specifically inhibit catecholamine secretion linked to stimulation of nicotinic receptors. The inhibition of acetylcholine-induced catecholamine secretion by somatostatin is noncompetitive with respect to acetylcholine, Na+ or Ca2+.Immunoreactive somatostatin and substance P are present in guinea-pig adrenal glands. It is suggested that these peptides may play a role in the regulation of catecholamine secretion from the adrenal medulla.
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