Patterns of LH secretion in castrated bulls (steers) during intravenous infusion of androgenic and estrogenic steroids: pituitary response to exogenous luteinizing hormone-releasing hormone.
Five steers were used in a 5 x 5 Latin square design to investigate negative feedback on luteinizing hormone (LH) secretion by androgenic and estrogenic steroids. Vehicle (200 microliter 30% ethanol/min), testosterone (20 micrograms/min), 5 alpha-dihydrotestosterone (20 micrograms/min), estrone (2 micrograms/min) and estradiol-17 beta (2 micrograms/min) were administered by continuous 12 h infusion at weekly intervals. At the end of each infusion period animals were given an intravenous injection of luteinizing hormone-releasing hormone (LHRH, 1000 ng). LH secretion in steers was characterized by pulses which occurred at intervals of 40 to 60 min. Estradiol-17 beta abolished pulsatile LH release and suppressed mean LH levels. The LH response to LHRH was greater however, in steers infused with estradiol-17 beta than in steers infused with vehicle only. The latter finding indicates a positive feedback action of estradiol-17 beta on the pituitary. In contrast to the results obtained with estradiol-17 beta, infusion with estrone had no effect on either the pattern of LH secretion or the pituitary response to LHRH. Testosterone and 5 alpha-dihydrotestosterone infusion also failed to influence LH secretory patterns in steers. Similar results for testosterone were obtained in a second experiment where this steroid was infused at a rate of 80 micrograms/min. The results of this study suggest that in the male bovine, estradiol-17 beta exerts negative feedback at the level of the hypothalamus to block pulsatile LHRH release. The results also support the contention that chronic castrates are insensitive to acute androgen feedback.
D000728:Androgens / Q000494:pharmacology*; D000818:Animals; D002369:Castration; D013196:Dihydrotestosterone / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology*; D004970:Estrone / Q000494:pharmacology; D005246:Feedback; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D013739:Testosterone / Q000494:pharmacology
D000728:Androgens; D004967:Estrogens; D013196:Dihydrotestosterone; D004970:Estrone; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D004958:Estradiol; D007986:Luteinizing Hormone