Inhibin biosynthesis by human prostatic tissue was investigated in vitro. Serum levels of inhibin as well as tissue concentrations in different cells and zones of the normal and benign hyperplastic prostates were determined. Immunocytochemical localization of inhibin identified the involvement of epithelial but not stromal cells in the synthesis and release of prostatic inhibin into the circulation. The endocrine and paracrine functions of prostatic inhibin remain to be elucidated.

Using specific radioimmunoassays, serum prolactin, TSH, LH, FSH, and inhibin levels were estimated in normal subjects and in patients with benign prostatic hyperplasia (BPH) before and after tumor resection. In the case of BPH, there was a significant rise in inhibin levels as compared to age-matched control groups, whereas LH and FSH levels were decreased significantly. The levels of inhibin and prolactin were significantly reduced after surgery, but no consistent changes in LH, FSH, or TSH levels were noted. The changes observed in hormonal levels in the BPH patients were not related to patient's age or size of the tumor.

Homogeneous preparation of human seminal plasma inhibin (molecular weight 13,500) was iodinated with 125I to a specific activity of about 40-45 microCi/micrograms and tested for binding to a rat prostate crude membrane preparation. The binding of inhibin was a saturable process as well as time and temperature dependent. This binding was displaceable in a dose-dependent manner by unlabelled inhibin. Other hormones such as LH, FSH, Prl, and TSH from rat or human origin did not influence the binding of labelled inhibin to rat prostate membrane. Of various age groups of rats studied, the maximum binding was observed in 75-day-old rats. The radiolabelled inhibin also showed specific binding to rat pituitary. The preliminary studies regarding involvement of steroids in the control of inhibin receptors in prostate and pituitary indicated that testosterone activates the inhibin receptors at the prostatic level whereas estradiol did not have any effect. However, estradiol increases the pituitary receptors for inhibin as compared to testosterone.

Summary:  The hormonal regulation of inhibin biosynthesis by human benign hyperplastic prostate tissue was studied by determining the incorporation of 3H‐leucine. 3H‐inhibin, synthesized de novo, was immunoprecipitated from the culture media using specific antibodies to human prostatic inhibin. Testosterone and estradiol had no effect on inhibin biosynthesis whereas hFSH and PMSG had stimulatory effect. A decrease in inhibin biosynthesis was noticed on the addition of LHRH, TRH, hCG, hLH and human prolactin. Zusammenfassung:  Mittels des Einbaues von 3H‐Leucin wurde die hormonelle Regulation der Inhibin‐Biosynthese durch menschliches Gewebe von benigner hyperplastischer Prostata untersucht. 3H‐Inhibin wurde immunpraecipitiert von den Kulturmedien unter Verwendung von spezifischen Antikörpern gegen menschliches Prostata‐Inhibin. Testosteron und Oestradiol hatten keinen Einfluß auf die Inhibin‐Biosynthese, während humanes FSH und PMSG einen stimulierenden Effekt besaßen. Ein Rückgang der Inhibin‐Biosynthese konnte beobachtet werden nach Zusatz von LH‐RH, hCG, hLH und menschlichem Prolaktin.