Muscarinic effects on the hydroxy- and methoxyindole pathway in the rat pineal gland

Abstract

ABSTRACT [3H]Quinuclidinyl benzylate ([3H]QNB)-binding sites, showing similar properties to cholinergic muscarinic receptors in other tissues, were disclosed in the rat pineal gland. Functionality of these receptors was demonstrated, as in-vitro muscarinic activation by pilocarpine increased the pineal metabolic production of the hydroxyindole derivatives 5-hydroxytryptophan and serotonin, with a slight effect on melatonin biosynthesis. Electric-field stimulation of pineal slices caused similar metabolic effects. These effects were inhibited by muscarinic blockade with atropine and enhanced by neostigmine inactivation of acetylcholinesterase. These results suggest that acetyl-choline is the neurotransmitter involved. Cholinergic activity may, therefore, regulate indole metabolism in the pineal gland. Journal of Endocrinology (1989) 123, 205–211