Autoradiographic Localization of Quinuclidinyl Benzilate Binding to Rat Pituitary Gland

Abstract

The location of muscarinic receptors in the rat pituitary gland was examined with an autoradiographic technique. Slides containing 10 or 20 μm horizontal sections of tissue were incubated in a solution of 1 nM[³H]quinuclidinyl benzilate (QNB) in phosphate-buffered saline to label muscarinic receptors. Autoradiograms were produced by placing the slides into X-ray cassettes with tritium-sensitive film and processing the film 8–10 weeks later. Minimal binding occurred when sections were incubated in 1 nM[³H]QNB plus 1 μMatropine. Highest specific binding of QNB was found in the anterior and intermediate lobes along their border with the pituitary cleft. Patches of high binding were also seen penetrating the intermediate lobe and at the border between the intermediate and neural lobes. The remainder of the intermediate lobe had background density of autoradiographic grains. Moderate density of specific binding was found throughout the anterior lobe. Low specific binding occurred in the neural lobe.

Cholinergic Stimulation of Inositol Phosphate Production in Cultured Anterior Pituitary Cells

“…GH release) may be mediated, at least in part, by receptor-activated polyphosphoinositide hydrolysis. In addition, acetylcholine and carbachol's relation with other intracellular pathways and with hormone release is discussed.There is now extensive physiological and biochemical evidence for the existence of functional muscarinic cholin ergic receptors in the anterior pituitary [1,10,20,26].Regional distributions of these receptors have been con firmed by autoradiographic techniques [18].Recently, data were presented suggesting that acetyl choline interacts with these receptors to exert a direct, mod ulatory effect on pituitary hormone secretion. In rats, syste mic administration of the acetycholine receptor antagonist atropine inhibits growth hormone (GH) release [19], while both pilocarpine and eserine, two cholinergic agonists, in crease the release of the hormone [9].…”