DISSOCIATION OF THE REPRODUCTIVE AND PROLACTIN PHOTOPERIODIC RESPONSES IN MALE GOLDEN-HAMSTERS

The response of prolactin (PRL) and that of the pituitary-testicular a xis to inhibitory photoperiods were compared in immature and young adu lt hamsters. In the first experiment, 14-day-old hamsters were transfe rred from 14L:10D to 12L:12D or 8L:16D. At 21, 28, 35, and 49 days of age, body weights, testes weights, and plasma LH were similar in all g roups. In contrast, the levels of PRL were lower in animals on 8L:16D or 12L:12D than in those on 14L:10D at 35 and 49 days of age. In a sec ond experiment, 80-day-old hamsters were transferred from 14L:10D to e ither 12L:12D or 8L:16D. At 5-wk intervals, they were weighed and bled by cardiocentesis and the length of the testes was measured. Photoper iods of 12L:12D and 8L:16D induced testicular regression, which was co mplete by 15 wk Thereafter, augmented levels of FSH preceded spontaneo us recrudescence of the testes in animals on both photoperiods. Serum PRL levels were significantly depressed within 5 wk after transfer to either 8L:16D or 12L:12D. After 15 wk as the testes were increasing in size in both groups, circulating PRL levels increased in animals expo sed to 8L:16D, whereas in animals exposed to 12L:12D, PRL remained at or below the sensitivity of the assay. In a final experiment, on the d ay before parturition, pregnant hamsters were transferred to either 6L :18D, 6L:30D, 6L:42D, or 6L:54D or were held on 14L:10D. There were no differences in testicular weights, plasma LH, or plasma thyroxine (T- 4) of the pups from these dams at 21, 36, or 48 days of age. On the ot her hand, PRL levels at these ages were elevated in the 6L:30D and the 6L:54D groups as compared to the 6L:18D and the GL:42D groups. The re sults suggest that the response of PRL to photoperiod may be experimen tally dissociated from that of the hypothalamo-pituitary-testis axis t o photoperiod. Like the response of the reproductive system in the adu lt, the response of PRL incorporates a circadian oscillator in the sys tem that measures day length.