Acute effect of hCG on testicular and epididymal levels of androgen binding protein (ABP) in the immature rat.

We have studied the acute effect of hOG and testosterone administration to immature rats, on testicular (particulate fraction and cytosol) and epididymal (cytosol) ABP levels. One and four hours after a single dose of 10 IU hCG/rat, ABP concentration decreased slightly in testicular membranes and cytosol, but increased markedly in epididymal cytosol (169 +/- 5 and 182 +/- 5 at 1 and 4 h respectively, compared to 113 +/- 13 fmoles/mg protein in control animals, mean +/- SEM). Since testicular and epididymal concentrations of testosterone increased after hCG, as expected, the effect might have been mediated by gonadotrophin stimulated testosterone production in Leydig cells. To test this hypothesis, the hCG effect was studied in rats that previously had received aminoglutethimide to block steroidogenesis. Under these conditions, hCG failed to increase epididymal ABP. Finally, administration of testosterone propionate was also able to stimulate epididymal ABP, but with delayed response: the increase was observed 4 h after injection (212 +/- 18 compared to 127 +/- 28 fmoles/mg protein in control animals, mean +/- SEM). It is concluded that the hCG-induced increase of intratesticular androgen levels results in rapid passage of ABP from testis to epididymis.