Comparative effects of epinephrine, norepinephrine, and a gentle handling stress on plasma lactate, glucose, and hematocrit levels in the American bullfrog ( Rana catesbeiana)

Abstract

The effects of a single infusion of epinephrine or norepinephrine and of a 2-min handling stress on plasma lactate, glucose, and hematocrit levels were compared in the American bullfrog ( Rana catesbeiana). The catecholamines were administered, and serial blood samples were collected, via a cannula placed in the truncus arteriosus. Plasma lactate was estimated by the lactate dehydrogenase method and glucose by the glucose oxidase method. Dose-dependent increases occurred in plasma lactate, glucose, and hematocrit levels after the infusion of 50 and 500 μg/kg body weight of epinephrine. Norepinephrine infusion resulted in dose-dependent increases in hematocrit levels, but plasma lactate and glucose levels were not increased significantly by 50 μg/kg body weight of norepinephrine. The infusion of 500 μg/kg body weight of norepinephrine caused a lactacidemia that was similar to that which occurred with the same dose of epinephrine, but the hyperglycemia was less. The plasma lactate increases after handling were similar to those that occurred after treatment with 500 μg/kg body weight of the catecholamines; however, the hematocrit elevations were less and the glucose levels were not increased significantly. In addition, the plasma lactate and hematocrit responses to handling were more rapid than those that occurred after the catecholamines. The results suggest that immediate physiological adjustments to a sudden threat are mediated in the bullfrog by direct nervous stimulation of the relevant organs. Catecholamines and corticoids secreted by the adrenal glands probably function synergistically and sequentially when a stress is more severe and/or more prolonged than the brief, gentle handling employed in this study.