nicotinic cholinergic agonists inhibit androgen biosynthesis by cultured rat testicular cells the actions of cholinomimetics on androgen biosynthesis were investigated using a primary culture of testicular cells derived from adult hypophysectomized rats testicular cells were maintained in serumfree medium and treated with hcg andor drugs on day 8 of culture media were collected 2 days later for measurement of steroids and camp treatment with hcg increased testosterone production 50fold over control values whereas treatment with cholinomimetics alone failed to increase androgen production concomitant treatment of testicular cells with nicotinic cholinergic agonists lobeline nicotine and dimethylphenylpiperazinium iodide inhibited hcgstimulated androgen biosynthesis in a dosedependent fashion with ic50 values of 3 x 105 17 x 104 and greater than 103 m respectively in contrast two muscarinic cholinergic agonists muscarine and bethanechol failed to inhibit androgen production at concentrations up to 103 m a ganglionic nicotinic antagonist hexamethonium but not a skeletal muscle nicotinic antagonist decamethonium partially blocked the actions of lobeline lobeline 104 m decreased hcgstimulated testosterone production 5075 throughout the 2day culture period however this inhibition was reversible upon removal of the drug lobeline also inhibited hcgstimulated camp accumulation as well as testosterone production induced by cholera toxin 65 inhibition forskolin 50 inhibition or bu2camp 70 inhibition lobeline inhibition of hcgstimulated testosterone production was accompanied by decreases in medium accumulation of 17 alphahydroxypregnenolone 75 17 alphahydroxyprogesterone 85 dehydroepiandrosterone 50 and androstenedione 61 however the medium content of pregnenolone and progesterone were unchanged additional experiments demonstrated that lobeline suppressed the conversion of exogenous progesterone to testosterone but did not affect the conversion of exogenous 17 alphahydroxyprogesterone to testosterone these results indicate that nicotinic but not muscarinic cholinergic agonists inhibit androgen biosynthesis through selective inhibition of 17 alphahydroxylase activity thus endogenous acetylcholine may be involved in the negative regulation of testicular steroidogenesis