Gonadotrophin levels in male voles (Microtus agrestis) reared in long and short photoperiods

摘要

Summary. Male voles were reared from birth to the age of 56 days in photoperiods of 16L:8D or 6L:18D. In 16L:8D testes increased 10-fold in size between the age of 14 and 56 days, and there were concomitant increases in diameter of seminiferous tubules and seminal vesicle weight. Spermatozoa were present in tubules by 35 days. In 6L:18D no significant changes with age occurred in testis size, diameter of seminiferous tubules or seminal vesicle weight. LH secretion increased with age in 16L:8D, but not in 6L:18D, and pituitary and plasma levels were higher in the former than in the latter by 35 days. Pituitary levels of FSH were high up to 21 days in 16L:8D, and up to 35 days in 6L:18D. At 35 days the mean pituitary level was significantly higher in the 6L:18D than in 16L:8D. Plasma levels of FSH were significantly higher in 16L:8D at 14 and 21 days, and then gradually declined. In 6L:18D plasma FSH rose to a maximum at 35 days, but did not reach the levels occurring at an earlier age in voles in 16L:8D. The relationship between pituitary and plasma levels of FSH in the two photoperiods is compatible with the idea of a storage and a readily releasable pool of the hormone within the pituitary gland. In 16L:8D changing levels of LH and FSH seem to be due to the onset of testicular activity with consequent feedback effects of testicular hormones upon the anterior pituitary gland.