GENERAL AND COMPARATIVE ENDOCRINOLOGY 60, 138- 143 (1985) Effect of Mammalian Luteinizing Hormone-Releasing Hormone on Plasma Testosterone in Male Alligators, with Observations on the Nature of Alligator Hypothalamic Gonadotropin-Releasing Hormone VALENTINE A. LANCE, KENT A. VLIET,” AND JANICE L. BOLAFFI~ Depurtment of Medicine. Tulane iJni\tersity School of Medicine, NeMs Orleans, Louisiuru 70112; *Department of Zoology, Unirsersity of Florida. Gainesville, Florida 3261 I; and tMetaboiic Reseurch Unit. University qf California, San Francisco, Colijk~rnin 94143 Received December 4. 1984 Mature and subadult male alligators (30-50 kg body wt) were injected with a single dose (500 kg) of synthetic LH-RH. A blood sample was taken immediately before the hormone was injected and additional samples taken either at 24-hr or at 2-hr intervals up to 8 hr followed by a 24-hr sample. Testosterone concentrations in the blood were then determined by radioimmunoassay. LH-RH caused an increase in plasma testosterone in all animals by 2 hr. Plasma testosterone was still significantly higher in the LH-RH-injected animals than in the saline-injected group at 24 hr. Alligators, therefore. differ from other reptiles in that they respond to the mammalian hormone. Hypothalamic tissue from immature alligators was extracted and tested for the presence of immunoreactive LH-RH-like material using two different antisera. One of the antisera (IJ-29) did not cross-react with the tissue extract. whereas a good parallel displacement curve was obtained when the extract was tested against the other antiserum (R-42). Based on the known specificities of the antisera we conclude that alligator hypothalamic tissue contains an LH-RH-like peptide that differs from the mammalian hormone in at least the 8 position. and that alligator LH-RH may be similar to chicken LH-RH. ZI 1985 Academic Pres\. IW. Gonadotropin-releasing hormone (LH- RH) is a decapeptide first isolated from pig hypothalamus (Matsuo et (if., 1971) that stimulates the release of LH and FSH from the anterior pituitary. The mammalian pep- tide is biologically active in teleosts (Breton and Weil, 1973; Crim and Evans, 1980), am- phibians (Thornton and Geschwind. 1974; McCreery and Licht, 1983), and birds (Furr et al., 1973). Attempts to demonstrate bi- ological activity of mammalian LH-RH in reptiles, however, have been either unsuc- cessful or at best ambiguous. Callard and Lance (1977), for example, reported that a single intravenous injection of 4 kg of LH- RH in female freshwater turtles, Chrysemys picta, caused a rise in plasma LH and pro- gesterone. The magnitude and duration of the response among individual turtles were extremely variable. Male Chrysemys picta, on the other hand, showed no increase in gonadotropin or testosterone after acute or chronic injections of physiological or phar- macological doses of the same peptide (Lance, unpublished). As with freshwater turtles, experiments with sea turtles have also given ambiguous results. Licht (1980) reported that in one experiment female Cheionia mydas showed a moderate in- crease in plasma LH in response to an in- travenous injection of 1 mg of LH-RH. In other experiments, however, the mamma- lian peptide or superactive analogues of LH-RH failed to stimulate increases in go- nadotropin or testosterone in Chelonia mydas or Lepidochelys olivacea (Licht, 1982; Licht et al., 1982). Isolated pituitaries from both Chrysemys picta and Pseudemys scripta will, however, secrete LH in re- sponse to physiological doses of LH-RH in a perifusion system (Licht and Porter, 1985). Snakes appear to be unresponsive to 138 0016-6480/85 $1 SO Copyright 0 1985 by Academic Press. Inc. All rights of reproduction in any form reserved.