Muscarinic M-1 and M-3 receptors are present and increase intracellular calcium in adult rat anterior pituitary gland

Physiological and biochemical evidence indicates the existence of functiona l muscarinic cholinergic receptors in the anterior pituitary, The selectivi ty of these receptors has been characterised by studying the binding of [H- 3]quinuclidinyl benzilate ([H-3]QNB) and [H-3]diphenyl-acetoxy-N-methyl-pip eridine ([H-3]4-DAMP) in membrane preparation of male rat anterior pituitar y at 25 degrees C, Competition experiments with receptor selective muscarin ic antagonists were used to characterise specific selective muscarinic rece ptor binding. Both [H-3]QNB and [H-3]4-DAMP bound to anterior pituitary mem branes at low concentrations, binding was saturable and was potently displa ced by 4-DAMP (M-1, M-3 subtypes selective antagonist) > atropine (general) > pirenzepine (M-1). Methoctramine (M-2) didn't antagonise the [H-3]QNB bi nding efficiently. Acetylcholine and carbachol increased the intracellular Ca2+ level in 62% and 65% of cultured rat anterior pituitary cells in a dos e-dependent manner, and this effect was prevented by pirenzepine. Based on these results we suggest that both M-1 and M-3 muscarinic receptors are pre sent and active in the majority of cells in the rat anterior pituitary glan d, but their physiological role in the adult rat remains to be examined. (C ) 1999 Elsevier Science Inc.