Do Testicuiar Opiates Regulate Leydig Cell Function?

Abstract

beta-Endorphin is believed to be synthesized in testicular Leydig cells. To gain more information about the role of this and other endogenous opioid peptides in the testis, opiate antagonists (naloxone and nalmefene, 100 micrograms/testis) were administered intratesticularly to hemicastrated adult rats. Leydig cell function was evaluated by measurement of serum testosterone and testosterone production in vitro. Estimation of androgen binding protein (rABP) was used as an index of Sertoli cell function. Serum testosterone was reduced significantly by intratesticular administration of naloxone and nalmefene in treated animals. Systemic administration of these antagonists had no effect at the doses used. Testes from treated animals incubated in vitro with or without hCG produced significantly less testosterone than vehicle-treated control testes. Hemicastration reduced rABP synthesis and secretion; however, treatment with opiate antagonists did not alter the amount of this protein in the serum or epididymides of these rats. These observations suggest that endogenous testicular opiates modulate testosterone secretion by Leydig cells.

Regulation of Male Fertility by the Opioid System

“…Consequently, β-endorphin is involved in the control of the precise levels of testosterone that are required for proper spermatogenesis. Furthermore, β-endorphins have been reported to inhibit the proliferation and differentiation of Sertoli cells stimulated by FSH in the testes (60) and to alter the proliferative dynamics of Sertoli cells and enhance the levels of ABP after treatment of the testes of newborn rats with the opioid antagonist nalmefene (58). Taken together, these findings suggest that EOPs inhibit the development of Sertoli cells and thus may contribute to maintaining the quiescent sexual state of the testes before puberty (61).…”

“…However, intratesticular administration to rats of the opioid antagonist naloxone and nalmefene was found to decrease basal secretion of testosterone and reduce levels of serum testosterone (58). Binding studies have not detected opioid receptors in Leydig cells (45), which suggests that EOPs indirectly regulate the secretion of testosterone.…”

“…On the other hand, β-endorphins synthesized by Leydig cells produce an inhibitory paracrine effect on Sertoli cell function (58,59). Specifically, β-endorphins inhibit the production of ABP stimulated by FSH in Sertoli cells, and this inhibition is reversed in the presence of naloxone (36).…”

Propranolol inhibits the compensatory increase in androgen secretion after unilateral orchidectomy in rats

“…As both Leydig cells (Poyet & Labrie, 1983;Anakwe et al, 1985a) and Sertoli cells (Heindel et ai, 1980) contain ß-receptors it is unclear whether the effect is a direct one on Leydig cells or an indirect one mediated by Sertoli cells. There is also a report (Gerendai, Shaha, Thau & Bardin, 1984) …”

Role of salsolinol in the regulation of pituitary prolactin and peripheral dopamine release

“…Given a possible future use of such compounds, it is clear that better understanding of the integrated role of DA and SAL is a critical aspect in respect of the whole organism. The in-vitro effect of SAL and DOM alone and in combination on the levels of testosterone released into the medium from either the right or the left testis incubated in vitro [69]. n = 7, mean ± SEM; *P \ 0.05, compared with NaCl-treated control values…”