Inhibitory role of prolactin in the downregulation of testicular follicle-stimulating hormone receptors in mice

Previous studies have shown that follicle-stimulating hormone (FSH) reduced its own receptors (downregulation) in the testis of adult mice. In the present study, we further examined the effect of prolactin (PRL) on the downregulation of testicular FSH receptors using hypophysectomized adult mice. FSH binding per testis increased after hypophysectomy, reaching a peak 5-10 days after the operation, and decreased thereafter. Hypophysectomized mice were given s.c. injections of 100 μg ovine PRL (NIADDK-oPRL) and/or 2 μg ovine FSH (NIADDK-oFSH) twice daily for 5 or 10 days beginning from 5 or 10 days after hypophysectomy. The 5-day treatment with a combination of oPRL and oFSH maintained the level of testicular FSH binding that was decreased by the treatment with oFSH alone, while the 5-day treatment with oPRL alone did not influence the testicular FSH binding. The change in the FSH binding per Sertoli cell was comparable to that in the binding per testis. A similar result was obtained by the 10-day treatment. Therefore, PRL was suggested to have an inhibitory role in the downregulation of testicular FSH receptors by FSH in adult mice.