Androgen induced norepinephrine release from postganglionic neurons mediates accessory sex organ smooth muscle proliferation.

PURPOSE: Guinea pig seminal vesicle smooth muscle displays an initial androgen dependent, proliferative response during early puberty, followed by progression to an androgen resistant, amitotic state in adults. We determined the role of norepinephrine in androgen dependent pubertal proliferation and in the subsequent terminal differentiation of adult seminal vesicle smooth muscle.
MATERIALS AND METHODS: Guinea pig seminal vesicle provided a suitable model since its unique anatomy allowed clean harvest of smooth muscle without epithelium. Norepinephrine release from postganglionic adrenergic nerve terminals in seminal vesicle smooth muscle was measured using several techniques. Prazosin sensitive electrical field stimulation of contractile responses qualitatively assessed norepinephrine release. Norepinephrine release was quantified directly in vitro from incubated seminal vesicle smooth muscle minces and indirectly ex vivo from intact tissue using the endogenous seminal vesicle smooth muscle concentration ratio of 3,4-dihydroxyphenylglycol-to-norepinephrine (Sigma Chemical Co., St. Louis, Missouri). Norepinephrine mediated seminal vesicle smooth muscle proliferation was assessed by the time course relationships of androgen induced norepinephrine release, protein kinase C activation-depletion and increases in total DNA, the impact of in vivo reserpine induced norepinephrine depletion on protein kinase C activation-depletion and the mitogenic response, and the alpha1-adrenoceptor mediated mitogenic response in cultured seminal vesicle smooth muscle cells.
RESULTS: In prepubertal smooth muscle androgen induced norepinephrine release from postganglionic neurons. The effect was independent of preganglionic innervation. Increased norepinephrine release was concurrent with the onset of androgen induced protein kinase C activation-depletion and cellular proliferation. In vivo norepinephrine depletion to 1% or less of control values by chronic reserpine treatment selectively antagonized the androgen induced increases in smooth muscle DNA and protein kinase C down-regulation. Norepinephrine depletion by reserpine neither induced apoptosis nor altered cell number. Cell culture experiments demonstrated that alpha1-adrenoceptors mediated the proliferative response to norepinephrine. Together these findings indicate that increased norepinephrine release has an obligatory role in androgen dependent muscle cell proliferation during puberty. Terminally differentiated smooth muscle in adults was characterized by androgen resistance to elevated norepinephrine release and protein kinase C activation.
CONCLUSIONS: Androgen induced norepinephrine release from postganglionic neurons in seminal vesicle smooth muscle mediated the proliferative response that occurs in early pubertal development. Normal uncoupling of elevated norepinephrine release and protein kinase C activation-depletion may represent a key event in the normal terminal differentiation of accessory sex organ smooth muscle in adults.