Exogenous GnRH overrides the endogenous annual reproductive rhythm in green iguanas, Iguana iguana.
Female green iguanas, Iguana iguana, were caught in Belize, Central America (17 degrees N), in December, at the onset of seasonal gonadal activity. The animals were immediately transferred to San Diego (32 degrees N). Ovarian follicular development continued, with peak plasma hormone levels measured in January and February; 200 pg/ml for progesterone (P) and 800 pg/ml for total estrogens (Et = estradiol [E2] + estrone [E1]). E2 was the predominant estrogen throughout the cycle. Follicular atrophy was indicated in April with circulating progesterone and estrogen levels decreasing to baseline (refractory phase) levels (P = 20 pg/ml; Et = 50 pg/ml). Approximately midway through the refractory phase of their annual reproductive cycle (late May), either the D-Arg6 analog of Chicken II or mammalian GnRH was administered via intraperitoneal osmotic pumps for 14 days to nine females. The analog of chicken II induced a fivefold increase in total circulating estrogens within 3-4 days after implantation. Both continuous and pulsatile delivery of the chicken II analog produced a similar pattern of steroidogenic response. A radical sham control animal showed no increase in steroidogenesis. Mammalian GnRH produced a pattern of similar duration, although the magnitude of the steroidogenic response was only half that produced by the chicken II analog. Estrogen titers approached baseline levels in all treatment groups two days after treatment ceased. Progesterone levels increased in all treatment groups during the delivery of exogenous GnRH, although the increases were not consistent. Untreated male cagemates housed with treated females exhibited increased territoriality, courtship behavior, and mating, which began on day 4 or 5 of the treatment period. The control female was not courted by its male cagemate.
D000818:Animals; D004958:Estradiol / Q000097:blood; D004970:Estrone / Q000097:blood; D005260:Female; D007076:Iguanas / Q000502:physiology*; D008116:Lizards / Q000502:physiology*; D008297:Male; D010507:Periodicity; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology*; D011374:Progesterone / Q000097:blood; D012098:Reproduction / Q000187:drug effects*; D012621:Seasons
D010906:Pituitary Hormone-Releasing Hormones; D004970:Estrone; D011374:Progesterone; D004958:Estradiol