AGE-DEPENDENT CHANGES IN THE SYNTHESIS AND RELEASE OF PITUITARY GONADOTROPINS IN THE MALE RAT FOLLOWING LH-RH AND CRYPTORCHIDISM

摘要

Even with more understanding regarding the ‘shift’ in the hypothalamic sensitivity threshold occurring with the onset of puberty the synthesis and release of the pituitary gonadotropins in the intact male rat still remains in the dark. We have studied the pituitary content and circulating levels of LH and FSH in the intact animal and under the modulatory effects of LH-RH and bilateral cryptorchidism during sexual maturation. Both gonadotropins registered increment in content with maturation until day 35 of life and then declined. The peripheral levels however were not parallel with maturation, and while LH level rose to a new postmaturation height, the FSH concentration showed characteristic decline with maturity. With LH-RH the maximal depletion in the pituitary reserve of LH occurred at day 35 within 10–30 min post-LH-RH, during which period the peripheral circulation registered maximal concentration. Most prominent depletion of the pituitary reserve of FSH was also noted in the 35-day-old animals 30 min post-LH-RH with a concomitant rise in the peripheral concentration. Bilateral cryptorchidism caused marked depletion of the pituitary reserve of LH during this critical 30–35 day of life and raised the peripheral concentration to a high level. FSH, however, registered a simultaneous higher pituitary content and circulating level at comparable ages. The data revealed that the age 30–35 day in the life of the male rat is associated with the most dynamic changes in this regulatory mechanism.