Effects of Adrenocorticotropin and Corticosterone on the Negative Feedback Action of Testosterone in the Adult Male Rat

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Abstract
Injections of ACTH (Synacthen depot) to intact male rats resulted in high serum levels of corticosterone and progesterone, and decreased levels of luteinizing [LH], FSH and testosterone. In gonadectomized rats with low serum testosterone levels (.apprx. 1 ng/ml) induced by a small testosterone-filled silicone elastomer capsule, ACTH inhibited the postcastration rise in LH and FSH, and reduced the weights of the prostate and seminal vesicles. After adrenalectomy the inhibitory effects of ACTH on serum gonadotropins and organ weights were almost totally absent. Administration of corticosterone acetate (10 mg/day) to gonadectomized and adrenalectomized male rats resulted in high serum levels of corticosterone (.apprx. 400 ng/ml) which were .apprx. 3 times higher than those measured in intact control animals. Nevertheless, in these rats the serum levels of LH and FSH were as high as those measured in gonadectomized and adrenalectomized oil-treated rats. When in addition to the injections of corticosterone acetate, a small testosterone-filled capsule was implanted, the postcastration rise in FSH was fully inhibited, whereas the serum levels of LH were below the level of detection. Significant inhibition of the postcastration rise in LH and FSH also occurred when smaller quantities of corticosterone acetate were given. Since in gonadectomized and adenalectomized male rats similar testosterone-filled capsules did not prevent the postcastration rise in LH and FSH, a high serum level of corticosterone increases the sensitivity to the negative feedback effects of testosterone.

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