EFFECTS OF ALPHA-INHIBIN-92 FRAGMENTS AND ALPHA-INHIBIN-92 ANTISERUM ON THE CONTROL OF FOLLICLE-STIMULATING-HORMONE RELEASE IN MALE-RATS

Alpha-inhibin-92 (alpha-IB-92) has been characterized from human semin al plasma and found to be active in suppressing FSH release in vitro a nd in vivo. In order to determine if smaller fragments of this 92 amin o acid peptide would still be active to suppress FSH release, we have evaluated 5 of these fragments for their effects on FSH and LH release in the present study. Five alpha-IB-92 fragments (1-34, 1-46, 35-65, 35-92 and 66-92) were synthesized and injected intravenously (iv) into castrated adult rats (2 days post operation). Only fragments alpha-IB -92-(35-65) and alpha-IB-92-(66-92) significantly lowered plasma FSH, but not LH, at doses of 10 mu g. These fragments exerted a preferentia l FSH-suppressing effect, but their activities were less than that of alpha-IB-92. In view of the rapid action of these peptides and the pre ferential FSH suppressing effect, they could be useful clinically to s uppress FSH release. To determine the possible physiologic significanc e of alpha-IB-92, we injected antiserum raised against alpha-IB-92 int o immature male rats and evaluated its effects on FSH and LH release. Normal rabbit serum (NRS) or anti-alpha-IB-92 serum was injected iv th rough indwelling jugular catheters into conscious, unrestrained 18 day -old male rats. Blood samples (0.2 ml) were collected at various inter vals. Intravenous injection of alpha-IB-92 antiserum (0.1 ml/rat) sele ctively elevated plasma levels of FSH but not LH from 2-8 h post-injec tion in 18 day-old male rats (P<0.01). Since immunoneutralization of a lpha-IB-92 significantly elevated FSH release in immature rats, alpha- IB-92 has a physiological inhibiting role in control of FSH but not LH release at this stage of development.