Hormonal and metabolic responses of juvenile alligators to cold shock

Juvenile alligators became completely immobile 5 min after immersion in ice water and remained in rigor for 40 min when removed from the water, but recovered righting responses within 5 min after immersion in tepid water. A blood sample was taken prior to the treatment, at 1 hr post-treatment and at 24 and 48 hr after recovery. Plasma norepinephrine, epinephrine, and dopamine were measured using high-pressure liquid chromatography (HPLC), and corticosterone by radioimmunoassay (RIA). Plasma ions, phosphate, and lipids were measured on an autoanalyzer and blood smears were taken for differential white cell counts. Norepinephrine and epinephrine were close to 4 ng/ml at the initial bleed: at I hr post-treatment epinephrine increased to 7 ng/ml and norepinephrine rose to over 40 ng/ml. Mean plasma dopamine was less than 0.7 ng/ml at the initial bleed and post-treatment means were as high as 10 ng/ml, but values were too variable to show statistical significance. Plasma corticosterone rose significantly at 1 hr and returned to levels not significantly different from initial at 24 and 48 hr. Despite the massive increase in catecholamines, plasma glucose did not change throughout the experiment. Plasma triglyceride increased significantly at 24 and 48 hr and plasma cholesterol decreased significantly at 24 and 48 hr. All other plasma components with the exception of calcium and sodium showed changes. Both lymphocytes and heterophils increased at 48 hr and other white cell types showed a decrease. Overall, these results suggest that short-term cold exposure is less stressful to alligators than simple restraint. J. Exp. Zool. 283:566-572, (C) 1999. Wiley-Liss, Inc.