A Study of the Effect of B‐EP and Naloxone on the Function of the Hypothalamo‐Pituitary‐Testicular Axis of the Rat

Abstract

To investigate whether endogenous opioid peptides (EOP) play an important role in intragonadal regulation of testicular function and regulation of the hypothalamic‐pituitary‐gonadal axis of the male rat, the authors employed two principal methods: culture of testicular Leydig cells and Sertoli cells, and in vitro perifusion of hypothalamo‐pituitary Leydig cells of the adult rat. The results demonstrated that incubation of Leydig cells with B‐endorphin (B‐EP 10−9 = 10−6 mol/L) or naloxone (NAL 10−5 = 10−8 mol/L) manifested no significant changes of non‐stimulated or hCG‐stimulated testosterone secretion both in 20 and 60 day‐old rats. Similar results were obtained when the cells were treated with B‐EP (10−10 = 10−7 mol/L) for 48 h during culture. Pretreatment of incubated Leydig cells with B‐EP in similar concentrations for 48 h showed no effect on the response to hCG stimulation. In addition, treatment with B‐EP in vitro for 24 or 72 h manifested no effects on estradiol production by aromatization of cultured Sertoli cells. Neither NAL 10−5 given in vitro nor NAL (5 mg/body weight) injected subcutaneously 1 h before decapitation affected LH and testosterone release from the perifused hypothalamo‐pituitary Leydig cells system. These results could not support the hypothesis that B‐EP is a local regulator of testicular function. The physiological significance of EOP in regulating the function of gonadal axis of adult male rat remains to be investigated further.