Concerning the hormonal regulation of androgen binding protein in rat testis

Androgen binding protein (ABP) was measured in testis following an acute injection of FSH to ascertain whether this protein could serve as an endpoint marker of FSH action in the Sertoli cell. A single intravenous injection of oFSH (200 μg NIH-S-10) resulted in a rapid stimulation of ABP activity in testis of either 10- or 14-day old rats. Maximal increases were noted by 2 h in both cases (undetectable to 0.9, and 0.3 to 1.5 pmol ABP/mg protein in 10- and 14-day-old rats, respectively) and by 4 h ABP activity had again returned to control values. Although FSH failed to acutely stimulate ABP in 60-day-old rats, hypophysectomy of these animals resulted in a return of sensitivity within 3 days. The acute stimulation of ABP by FSH was also shown to be dependent upon both the route of hormone administration and the dose of FSH. Finally, the rapid decrease in ABP activity following FSH could be prevented by injection of a second dose of hormone. ABP activity was also increased by intratesticular injection of an analog of cyclic AMP, 8-bromo cAMP. This response was also dose-dependent and trie time course of response was indistinguishable from that resulting following FSH. A test of nucleotide specificity revealed that any adenine nucleotide would stimulate ABP, whereas guanine compounds were ineffective. Peptide hormone specificity was next examined. It was determined that 200 μg of a variety of crude pituitary hormone preparations (LH, GH, PRL and ACTH) were stimulatory. However, when highly purified hormones were utilized, hFSH (LER-1577) did not increase testicular ABP whereas 1 μg of oLH (Papkoff) was maximally stimulatory. Further studies revealed that all compounds (including peptide hormones and nucleotides) which resulted in acute elevation of ABP activity also increased the intratesticular concentration of testosterone. Moreover, a single ip injection of testosterone produced a steroid specific stimulation of ABP which reached maximal levels within 1 h. These findings suggest that the acute regulation of ABP activity in the testis may be a result of the intratesticular concentration of testosterone and not due to a direct effect of FSH as had been previously hypothesized.