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D. Andrew Crain, Louis J. Guillette, Jr., Andrew A. Rooney, and Daniel B. Pickford

Department of Zoology, University of Florida, Gainesville, FL 32611 USA

Abstract
Many environmental contaminants alter the reproduction of animals by altering the development and function of the endocrine system. The ability of environmental contaminants to alter the endocrine system of alligators was studied both in a descriptive study in which juvenile alligators from a historically contaminated lake were compared to animals from a control lake and in an experimental study in which hatchling control alligators were exposed in ovo to several endocrine-disrupting standards and two modern-use herbicides. Endocrine status was assessed by examining plasma hormone concentrations, gonadal-adrenal mesonephros (GAM) aromatase activity, and gonadal histopathology. In the descriptive study, juvenile alligators from the contaminated lake had significantly lower plasma testosterone concentrations (29.2 pg/ml compared to 51.3 pg/ml) , whereas plasma 17ß-estradiol concentrations did not vary when compared to controls. GAM aromatase activity was significantly decreased in the alligators from the contaminated lake (7.6 pmol/g/hr compared to 11.4 pmol/g/hr) . In the experimental study, the endocrine-disrupting standards had the expected effects. 17ß-Estradiol and tamoxifen caused sex reversal from male to female, with a corresponding increase in aromatase activity. Vinclozolin had no apparent effect on male or female alligators. Among the herbicides tested, atrazine induced GAM aromatase activity in male hatchling alligators that was neither characteristic of males nor females, although testicular differentiation was not altered. Exposure to 2,4-dichlorophenoxyacetic acid had no effect on the endocrine parameters that were measured. Together, these studies show that exposure to some environmental chemicals (such as atrazine) can alter steroidogenesis in alligators, but the endocrine alterations previously noted for Lake Apopka, Florida, alligators can not be fully explained by this mechanism. Key words: alligator, aromatase, atrazine, contaminants, 2, 4-D, endocrine disruption, hormones. Environ Health Perspect 105:528-533 (1997)

Address correspondence to D.A. Crain, Department of Zoology, 223 Bartram Hall, University of Florida, Gainesville, FL 32611 USA. D.B. Pickford's current address is Department of Physiology, Pharmacology, and Toxicology, University of Manchester, Manchester, England.

We thank A. Woodward, Florida Game and Freshwater Fish Commission, and F. Percival, National Biological Service, for assistance in collecting juvenile animals and eggs. J. Joss and M. Smith kindly provided information about aromatase assay techniques, D. Spiteri assisted with the histology, and K. Bjorndal and D. Evans provided helpful editorial comments. G. Masson of the U.S. Fish and Wildlife Service provided intellectual and financial assistance. Funding for this project was provided through an EPA Graduate Student Fellowship (U-914738-01-0) , an EPA Grant (CR821437) , and an NIEHS Grant (PR471470) . All lab work was conducted in full compliance with guidelines of the University of Florida Institutional Animal Care and Use Committee, and field work was conducted under permit from the Florida Game and Freshwater Fish Commission.

Received 23 September 1996 ; accepted 5 February 1997.