High doses of prolactin inhibit testosterone secretion in rat leydig cells
The effect of prolactin on dispersed rat Leydig cells was investigated. Leydig cells from adult rat testes of proven fertility were isolated via collagenase digestion and dispersion. About 100,000 Leydig cells/ml were incubated with graded concentrations of prolactin in the presence or absence of luteinizing hormone (LH) and theophylline for 3hr. at 37oC. Leydig cell viability was assessed by trypan blue dye exclusion method. The reaction was terminated by the addition of cold (4oC) Dulbeccos's modified Eagle's medium (DME) and testosterone in suitable aliquots was estimated by a validated radioimmunoassay technique. Prolactin inhibited in vitro Leydig cell steroidogenesis at doses of 1.25-10.00 i.u/L but only potentiatated the effect of LH at doses ranging between 0.31 and 0.62 i.u/L. LH had no effect on prolactin (2.5 - 10.0 I.U/L) inhibited testosterone secretion. Theophylline (10mM/L) did not produce any stimulatory effect on prolactin - inhibited testosterone seretion by Leydig cells in vitro. At lower doses of prolactin, theophylline was significantly lower (P<0.01) than that produced by LH at lower doses of prolactin. The results showed that high doses of prolactin inhibited testosterone secretion in rat Leydig cells and the mechanism of action of prolactin on Leydig cell steroidogenesis could be via cAMP second messenger system.
Keywords: Prolactin, Testosterone, Leydig Cells.