Concerning the Hormonal Regulation of Androgen Binding Protein in Rat Testis1

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Abstract
Androgen binding protein (ABP) was measured in testis following an acute injection of FSH [follicle-stimulating hormone] to ascertain whether this protein could serve as an endpoint marker to FSH action in the Sertoli cell. A single i.v. injection of oFSH (ovine FSH) (200 .mu.g NIH [National Institutes of Health]-S-10) rapidly stimulated ABP activity in testis of either 10 or 14 day 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, hyopohysectomy of these animals returned sensitivity within 3 days. The acute stimulation of ABP by FSH was dependent upon both the route hormone administration and the dose of FSH. The rapid decrease in ABP activity following FSH could be prevented by injection of a 2nd dose of hormone. ABP activity was increased by intratesticular injection of an analog of cyclic[c]AMP, 8-bromo cAMP. This response was also dose-dependent, and the 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 then examined. Two hundred micrograms of a variety of crude pituitary hormone preparations (LH, GH, PRL [luteinizing hormone, growth hormone and prolactin, respectively] and ACTH) were stimulatory. When highly purified hormones were utilized, hFSH (human FSH) (LER-1577) did not increase testicular ABP, whereas 1 .mu.g of oLH (Papkoff) was maximally stimulatory. All compounds (including peptide hormones and nucleotides) which acutely elevated ABP activity also increased intratesticular concentrations of testosterone. A single i.p. injection of testosterone produced a steroid specific stimulation of ABP which reached maximal levels within 1 h. 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.