Antifertility effect of an octapeptide, a fragment of FSH binding inhibitor, in the common marmoset (Callithrix jacchus).

The follicle-stimulating hormone (FSH) binding inhibitor (FSHBI) has been identified as one of the factors present in follicular fluid exerting autocrine/paracrine effects on FSH actions in the ovary. Our group has isolated FSHBI from human ovarian follicular fluid and deduced its partial amino acid sequence from the N-terminal region. A synthetic peptide corresponding to this sequence also demonstrated FSH binding inhibitory activity in vitro. The objective of the present study was to elucidate the effect of the octapeptide on ovarian cyclicity and pregnancy in the common marmoset. For the study, three groups of postpartum marmosets were treated with the octapeptide during the follicular phase. Administration of the octapeptide from days 6-10 postpartum (pp) predominantly induced luteal insufficiency in two of seven and two of five marmosets at a dose of 100 microg/day (group 1) and 300 microg/day (group 2), respectively. This was confirmed by the presence of small regressing corpora lutea on day 13 pp. Pregnancy was terminated prematurely in one animal from each of these groups. The treatment impaired fertility by 43% and 60% in the marmosets of groups 1 and 2, respectively. In view of the fact that FSH levels peak on day 2 and day 6 of the follicular phase in marmosets, a third group was administered 200 microg/day octapeptide from days 1-8 pp. The treatment induced luteal insufficiency in one out of four marmosets, while premature termination of pregnancy occurred in two other marmosets of this group, demonstrating a 75% effect on pregnancy. Thus, treatment of marmosets with the octapeptide, a fragment of the FSHBI, predominantly induced luteal insufficiency as well as resorption of the fetus leading to impairment of fertility.