Effect of mammalian luteinizing hormone-releasing hormone on plasma testosterone in male alligators, with observations on the nature of alligator hypothalamic gonadotropin-releasing hormone.

Mature and subadult male alligators (30-50 kg body wt) were injected with a single dose (500 micrograms) 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.