SEX-STEROID AND THYROID-HORMONE CONCENTRATIONS IN JUVENILE ALLIGATORS(ALLIGATOR-MISSISSIPPIENSIS) FROM CONTAMINATED AND REFERENCE LAKES INFLORIDA, USA

Sex-steroid and thyroid hormones are critical regulators of growth and reproduction in all vertebrates, and several recent studies suggest t hat environmental chemicals can alter circulating concentrations of th ese hormones. This study examines plasma concentrations of estradiol-1 7 beta (E-2), testosterone (T), triiodothyronine (T-3), and thyroxine (T-4) in juvenile alligators (60-140 cm total length) from two contami nated lakes and one reference lake in Florida. First, the data were an alyzed by comparing hormone concentrations among males and females fro m the different lakes. Whereas there were no differences in plasma E-2 concentrations among animals of the three lakes, male alligators from the contaminated lakes (Lake Apopka and Lake Okeechobee) had signific antly lower plasma T concentrations compared to males from the referen ce lake (Lake Woodruff). Concentrations of thyroid hormones also diffe red in animals of the three lakes. with T-4 concentrations being eleva ted in Lake Okeechobee males compared to Lake Woodruff males. Second, the relationship between body size and hormone concentration was exami ned using regression analysis. Most notably for steroid hormones, no c lear relationship was detected between E-2 and total length in Apopka females (r(2) = 0.09, p = 0.54) or between T and total length in Apopk a males (r(2) = 0.007, p = 0.75). Females from Apopka (r(2) = 0.318, p = 0.09) and Okeechobee (r(2) = 0.222, p = 0.09) exhibited weak correl ations between T-3 and total length. Males from Apopka (r(2) = 0.015, p = 0.66) and Okeechobee (r(2) = 0.128, p = 0.19) showed no correlatio n between T-4 and total length. These results indicate: some of the pr eviously reported abnormalities in steroid hormones of hatchling allig ators persist, at least, through the juvenile years; steroid and thyro id hormones are related to body size in juvenile alligators from the r eference lake, whereas alligators living in lakes Apopka and Okeechobe e experience alterations in circulating thyroid and steroid hormones i n relationship to body size; and a number of the hormone abnormalities reported previously for Lake Apopka alligators are observed in alliga tors from Lake Okeechobee-a lake associated with numerous contaminant sources but no major chemical spill. The endocrine alterations reporte d in this study are hypothesized to be a response to embryonic exposur e to endocrine-disrupting contaminants.