Temporal changes in the serum levels of gonadotrophins and testosterone in male rats bearing subcutaneous implants of 5 alpha-dihydrotestosterone.

This study has assessed the effect of s.c. implants of 5 alpha-dihydrotestosterone (DHT) on the blood levels of testosterone and gonadotrophins in intact and castrated adult male rats. The rats were bled via cardiac puncture at 1, 3, 7, 14, 21, 28, 35, 42, 49, 56, 63 and 70 days after DHT implantation. On days 28 and 49 post-implantation, rats were injected with LHRH (25 ng) and bled 15 min later. In intact rats bearing DHT implants, the serum levels of LH and testosterone were suppressed significantly with no significant changes in FSH levels. Ventral prostate, seminal vesicles and the pituitary were reduced significantly in weight when compared with controls with empty implants. DHT significantly inhibited LHRH-induced release of FSH in intact rats. In castrated rats, DHT implants inhibited the secretion of both LH and FSH, with a rise in serum DHT levels. DHT stimulated the LHRH-induced release of LH but inhibited FSH. DHT implants increased the weight of the seminal vesicles and ventral prostate but inhibited the weight of the pituitary when compared to castrated rats bearing empty implants. This study demonstrates specific inhibition of serum LH and testosterone by DHT implants in intact adult rats.