Search

The temporal relationship between exposure to prolactin (PRL) and luteinizing hormone (LH) induction of LH receptors was investigated in hypophysectomized adult male rats. Testicular homogenate membrane preparations were incubated with [125I]hCG for analysis of LH/hCG binding. Seven days after hypophysectomy, the rats were injected with 100 micrograms/day of PRL for another 7 days and then given a single 10-micrograms dose of LH at 2, 4, 6, 12, 24, or 36 hours after the last PRL injection. The priming effect of PRL on LH induction of receptors was not observed if LH was administered 2 to 12 hours from the last PRL injection. However, after this inhibitory period, injections of LH to PRL-primed rats resulted in induction of LH receptors and the effect persisted for 36 hours. This study supports previous reports demonstrating a unique dependence upon PRL for LH up-regulation of the LH receptor and characterizes the brief refractory period following exposure to PRL.

The time course for LH induction of luteinizing hormone (LH) receptors as reflected in binding of 125I-labeled hCG was investigated in hypophysectomized adult male rats. A low dose of oLH (10 micrograms) was administered to hypophysectomized adult male rats following pretreatments with prolactin, follicle-stimulating hormone (FSH), growth hormone (GH), or saline. Testicular binding of hCG was determined at different times following the LH injection using Leydig cell membrane preparations from a testicular homogenate. Seven days after hypophysectomy, hCG binding was at a nadir of 19 +/- 7% (mean +/- SD) of control values. Pretreatment with prolactin (100 micrograms/day) for 7 days was associated with a nonsignificantly different hCG binding that was 30 +/- 5% of control values. Prolactin pretreatment plus a single 10 micrograms LH i.p. injection increased 125I hCG binding up to 56 +/- 10% of control values within 30 minutes of the LH injection. Luteinizing hormone-induced hCG binding persisted at a high level (51 +/- 4% of control values) for 2 hours but returned to hypophysectomized control levels 6 hours after the i.p. LH injection. Seven days pretreatment with FSH or GH at 100 micrograms/day plus 10-micrograms LH injections was also tested. Neither FSH nor GH had a statistically significant effect on hCG binding nor could they mimic the ability of prolactin to allow for LH induction of hCG binding in the hypophysectomized adult male rats. These studies suggest that the induction or "up-regulation" of Leydig cell hCG binding by ovine LH is rapid and specifically dependent upon pre-exposure to prolactin.