Summary A specific antiserum has been generated against inhibin-like material (ILM) of prostatic origin. Using the immunoperoxidase technique, localization of ILM has been examined in a total of 114 prostates including normal (4 specimens), malignant (46) and hyperplastic (55) In the present study, we report immunocytochemical localization of inhibin-like material (ILM) in prostatic tissue. Inhibin is involved in the suppression of FSH synthesis and secretion. Of the various forms of inhibin-like materials (ILM) present in human seminal plasma, a peptide having a molecular weight of 10,400 daltons has been isolated in purified form from this laboratory (Thakur et al., 1981) the amino acid sequence of which has been reported (Sheth et al., 1984a; Johnson et al., 1984;Seidah et al., 1984). This peptide-ILM has been shown to be of prostatic origin (Sheth et al., 1984b;Beksac et al., 1984) and chemically similar (Johansson et al., 1984)

The complete sequence of a 94 amino acid human seminal plasma polypeptide exhibiting inhibin-like activity is presented. This molecule, called /I-inhibin, selectively and specifically suppresses the release of pituitary FSH in vivo as well as in vitro. It does not affect the secretion of LH. Such a novel acidic protein contains a very basic C-terminal segment which is easily cleaved by mild tryptic digestion. It is predicted that the FSH inhibiting activity may reside within this region of the molecule. This would imply a post Gln-Arg cleavage to release the basic C-terminal active moiety.

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Administration of hCG to normal healthy men caused 40 fold increase in circulating levels of inhibin at 24 hr. FSH levels decreased between 72-120 hr of hCG injection. Although, testosterone levels were maintained at higher levels during hCG therapy for more than 10 days, inhibin and FSH levels returned back to pretreatment levels, indicating involvement of hCG in the regulation of circulating levels of inhibin.