Effect of cortisol on the response to gonadotrophin releasing hormone in the boar.

The effect of intracarotid perfusion of 40 mg cortisol for 1 h on the hormonal response to three different doses of an intramuscular injection of synthetic gonadotrophin releasing hormone (GnRH) was compared to that of GnRH injected during intracarotid perfusion with 0.9% (w/v) NaCl solution in five boars. The increase in production of LH, above basal values, in response to injection of 0.25 microgram GnRH midway through perfusion was only slightly greater (P greater than 0.05) in boars receiving cortisol compared to that when the same boars received saline. When 0.5 microgram GnRH was injected midway through perfusion, a significantly greater (P less than 0.05) increase in production of LH above basal levels occurred during cortisol administration than occurred when saline was given. Injection of 1.0 microgram GnRH in boars during cortisol perfusion resulted in significantly greater (P less than 0.01) production of LH, above basal levels, compared to the increase above basal levels that resulted when this dose of GnRH was given during intracarotid saline treatment. Increases in plasma values of testosterone reflected the increases in levels of LH. The results suggest that acute elevations in plasma cortisol may, under some circumstances, enhance the increased production of LH in the boar by increasing the responsiveness of the anterior pituitary gland to GnRH.