Nicotine and cotinine inhibit steroidogenesis in mouse leydig cells

Abstract

Cigarette smoking alters plasma testosterone concentrations in men. The objectives of this study were to determine if nicotine and cotinine, two alkaloid products of cigarettes, affect luteinizing hormone (LH)-stimulated steroidogenesis in isolated adult mouse Leydig cells. Leydig cells from adult Swiss-Webster mice were isolated by linear density gradient and incubated (95% 02, 5% CO2) in minimum essential medium at 37 C for 3 hours with LH (10ng) and with or without nicotine or cotinine (10 −5–10 −7M). Both nicotine and cotinine produced dose response inhibition ( P < 0.05) of LH-stimulated testosterone production (50–70%). The addition of 8-bromo-3′, 5′-cyclic monophosphate (cAMP, 500uM) stimulated steroidogenesis comparable to LH in the absence of the alkaloids, but both nicotine and continine significantly ( P < 0.05) reduced testosterone production in response to cAMP, suggesting that the alkaloids inhibit testosterone production in response to LH distal to the formation of cAMP. In MEM without calcium, LH-stimulated testosterone synthesis was decreased, and neither nicotine nor cotinine significantly affected steroidogenesis. The addition of a calcium ionophore in MEM with normal calcium content enhanced (ifP < 0.05) the inihibitory effects of nicotine and continine on LH-responsive steroidogenesis. A calcium channel blocking agent, verapamil, at 10uM significantly ( P < 0.05) reversed the inhibition of LH-stimulated testosterone production produced by both alkaloids when incubated in the medium with a normal calcium concentration. These results suggest that nicotine and cotinine either affect intracellular calcium content or block the effects of calcium on steroidogenesis in mouse Leydig cells.