CENTRAL EFFECT OF RETE TESTIS FLUID, INHIBIN 32K, AND FOLLICULAR-FLUID ON PLASMA GONADOTROPIN CONCENTRATIONS IN SHEEP - INHIBIN IS NOT THE RETE TESTIS FLUID PROTEIN ABLE TO SUPPRESS LUTEINIZING-HORMONE PULSES

We have previously shown that peripheral administration of rete testis fluid (RTF) proteins was able to suppress LH pulses through the suppr ession of LHRH pulses. This activity was named ''LHRH Statin.'' The ai ms of the present work were to analyze LH inhibition after an intracer ebroventricular injection of RTF and to determine whether inhibin is t he factor responsible for this inhibition. Castrated rams (experiment 1) or ewes (experiment 2) received an intracerebroventricular injectio n of RTF, purified bovine inhibin 32K bovine follicular fluid, or huma n serum albumin as control. Animals were bled every 15 min for 5 h bef ore injection and for 7 h after injection LH mean levels were signific antly lowered (p < 0.01) only in the RFT-treated groups. FSH levels we re not affected irrespective of group, source, or dose of inhibin. The se experiments shaw first, that protein(s) present in ovine RTF can su ppress LH secretion in sheep; second, that bovine follicular fluid or purified bovine inhibin 32K have no effect on LH secretion Furthermore the results suggest that centrally administered inhibin has no effect on FSH secretion under our experimental conditions. Together, these e xperiments clearly demonstrate that inhibin 32K does not exert any ''L HRH statin'' activity.