Steroid treatment fails to induce an afternoon luteinizing hormone or prolactin surge in rats exposed to short-term constant light at the time of ovariectomy.
The present study investigated the effects of short-term exposure to constant light, initiated at the time of ovariectomy, on the ability of estradiol (E2) treatment alone or in conjunction with progesterone (P) to induce afternoon surges of LH and prolactin (PRL). Adult Fischer 344 rats, which had been ovariectomized (OVX) and placed into constant light (LL) on day 0, were implanted with Silastic capsules containing E2 on day 7 and an atrial cannula on day 8. On the following day (day 9), hourly blood samples were collected between 12.00 and 20.00 h from LL-exposed animals which had received E2 treatment alone or from LL E2-treated animals which had also received P at 12.20 h. Blood samples from control animals which were OVX and treated with E2, but maintained under a 12-hour light:12-hour dark photoperiod, were also collected. Exposure to 9 days of LL abolished the ability of E2 treatment to induce an afternoon surge of LH or PRL. The addition of P treatment to LL E2-treated animals failed to reinstate an LH or PRL surge. While P treatment in LL E2-treated animals induced a rise in PRL levels, it is unlikely, given the timing, duration, and magnitude of PRL release, that this enhancement was initiated by the same mechanisms which normally generate the afternoon surge. The results from the present study demonstrate that short-term exposure to LL, initiated at the time of OVX, abolishes the E2-induced afternoon surges of LH and PRL.
Lilly Research Laboratories, Division of Eli Lilly and Company, Greenfield, Ind 46140-0708, USA.
M R
MR
Sterner
I R
IR
Cohen
D000818:Animals; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood*; D010052:Ovariectomy; D011374:Progesterone / Q000494:pharmacology; D011388:Prolactin / Q000097:blood*; D051381:Rats; D011916:Rats, Inbred F344; D013256:Steroids / Q000494:pharmacology*; D013997:Time Factors
D013256:Steroids; D011374:Progesterone; D004958:Estradiol; D011388:Prolactin; D007986:Luteinizing Hormone