Studies of pituitary-adrenal-testis interaction in sheep. I. The effects of repeated injections of adrenocorticotrophic hormone during the breeding season

The administration of 0.5 mg of long-acting adrenocorticotrophic hormone (ACTH, Synacthen-Depot) twice daily for 5.5 d to four adult rams during the breeding season had no consistent effect on plasma follicle stimulating hormone (FSH) concentrations. In contrast, it suppressed both plasma luteinizing hormone (LH) and testosterone concentrations. The responses to injections of 5 ug of gonadotrophin releasing hormone (GnRH), as measured by maximum concentrations reached and areas under the response curves, were also suppressed. These findings suggest that ACTH exerts its suppressive efects on LH at the pituitary level.