Effect of Castration and Steroid Treatment on the Release of Gonadotropins by the Rat Pituitary-Hypothalamus Complex In Vitro

Summary

Comparative in vitro studies on the release of LH and FSH by pituitary-hypothalamus complex (PHC) with intact portal plexus and whole pituitary (PI) from adult male rats showed that PHC released LH at a greater rate and in larger amounts than PI. PHC and PI released FSH in comparable amounts and rates. Attempts were made to correlate serum gonadotropin levels to that released by PHC and PI at 1, 3, 7, 14, 21 and 46 days of post-castration (PC). Sham operated animals served as controls. Castration increased serum LH and FSH levels but in different profiles. CPHC and CPI (PHC and PI from castrated rats) released less LH than NPHC and NPI (PHC and PI from sham operated controls) till day 14 PC after which CPHC and CPI released more LH than NPHC and NPI respectively. Castration abolished the intrinsic capacity of PHC to secrete more LH than PI. CPHC and CPI secreted significantly less FSH than NPHC and NPI at 1, 3 and 7 days PC. At days 14 and 21 of post-castration PCNCP or CPI and NPHC or NPI released similar amounts of FSH. Administration of 5 α-dihydrotestosterone (DHT, 1 mg/rat/day) or estradiol valerate (EV, 1 μg/rat/day) immediately following castration prevented the rise in serum LH and FSH but increased the amounts of LH and FSH released by CPHC and CPI. The treatment caused a marked stimulation of FSH released by CPI. DHT or EV administered from day 41 to day 46 PC reduced the circulating levels of LH and FSH but markedly stimulated the release of gonadotropins by CPHC and CPI. It is suggested that discretely separate mechanisms control the release of LH and FSH by the pituitary.

Key-Words:

Castration - Pituitary - Hypothalamus - In Vitro - LH - FSH