IN-VITRO BIOACTIVITY OF GONADOTROPIN SURGE ATTENUATING FACTOR IS NOT AFFECTED BY AN ANTIBODY TO HUMAN INHIBIN

The effect of anti-inhibin antibodies on gonadotrophin surge attenuati ng/inhibiting factor (GnSAF/GnSIF) and its effect on gonadotrophin sec retion in a pituitary cell bioassay were determined by culturing rat p ituitary cells in a serum-free medium to which inhibin and a partially purified preparation of gonadotrophin surge inhibiting factor (GnSIF) were added. The samples were treated with an anti-inhibin antiserum a nd basal and GnRH-stimulated FSH and LH secretion were measured by rad ioimmunoassay of the culture supernatant. Inhibin had a dose-dependent inhibitory effect on both basal and GnRH-stimulated FSH secretion and also on GnRH-stimulated LH secretion. Anti-inhibin antibody blocked t he inhibition of FSH secretion, except at the highest two doses of hum an inhibin (1.25 ng ml(-1), P=0.04; 2.5 ng ml(-1), P=0.0004). The GnSI F preparation inhibited basal and GnRH-stimulated FSH and GnRH-stimula ted LH secretion and was not affected by the anti-inhibin antibody. Th e novel hormone, GnSIF, is different from inhibin.