EFFECTS OF LONG-TERM CORTICOSTERONE IMPLANTS ON GROWTH AND IMMUNE FUNCTION IN JUVENILE ALLIGATORS, ALLIGATOR-MISSISSIPPIENSIS

Sixty juvenile alligators were implanted subcutaneously with slow rele ase pellets of corticosterone or placebo. Alligators were divided into five different groups such that each group received a different dose. A blood sample was taken prior to and 4 days after the implants were in place to measure hormone levels, Additional blood samples were coll ected at 1 month and 3 months. At 4 days corticosterone levels ranged from 3,400 ng/ml in the group treated with the high dose to 40 ng/ml i n the group implanted with the low dose, The extremely high dose cause d 40% mortality within 4 weeks. It was evident that the pellets did no t release the hormone for the expected 90 days. Circulating levels of corticosterone were back to baseline levels by 3 months. Hormone level s achieved at 4 days were a reliable predictor of subsequent growth. R ate of growth was negatively correlated with plasma corticosterone at 4 days (r(2) = 0.711) and at 1 month (r(2) = 0.544) posttreatment. Dif ferential white blood cell counts performed after 1 month of treatment showed a clear effect of the implant. Alligators treated with cortico sterone had decreased percentages of lymphocytes, eosinophils, and bas ophils and had a higher heterophil/lymphocyte (H/L) ratio than the pla cebo group. Furthermore, histological examination of the spleen reveal ed a significant depletion of lymphoid cells in alligators treated wit h the highest dose of hormone, The results from this study demonstrate that exogenous carticosterone can mimic the effects of prolonged stre ss in juvenile alligators. (C) 1997 Wiley-Liss, Inc.