β 2-Inhibin contains the active core of human seminal plasma β-inhibin: synthesis and bioactivity

The complete synthesis of the C-terminal 28 residues segment 67–94 of human seminal plasma jS-Inhibin, called β 2-Inhibin, is reported. The Inhibin-like activity of the native 94 amino acids β-Inhibin is compared to that of the synthetic replica of β 2-Inhibin. In all assays used both peptides effectively suppress the FSH release induced by LHRH but have little effect on the LH release. In the mouse both peptides are equipotent on a mole basis. In the rat the synthetic β 2-Inhibin is 3–10 times more potent than β-Inhibin. Both peptides are active in rat anterior pituitary primary culture assays where maximum suppression of FSH release induced by LHRH occurs around 300 pmol ml of β 2-Inhibin. In contrast, maximum suppression of FSH release in the mouse pituitary assay occurs at 10–15 pmol ml of either Inhibin.