Effects of anoxia and graded acidosis on the levels of circulating catecholamines in turtles

Abstract

We measured circulating levels of catecholamines in painted turtles subjected to anoxia with different degrees of concomitant acidosis at 20°C and in turtles subjected to long-term submergence at 3 and 10°C. Blood levels of both epinephrine (E) and norepinephrine (NE) increased during N 2-breathing, N 2/CO 2 breathing and submergence, with NE generally being present in higher concentrations than E. During submergence at 20°C, anoxic turtles experienced an extreme acidosis and NE levels exceeded 18 000 pg/ml. The greater the degree of acidosis in anoxic turtles the higher were the levels of plasma NE ( log[ NE; pg/ml] = −1.640 × pH a + 15.776, r = −0.826 ). Elevation of plasma E under anoxic conditions was more modest and the correlation between plasma E and pH a was less pronounced log [ E; pg/ml] = −0.329 × pH a + 6.069, r = −0.285 ). Submergence at lower temperatures also resulted in increases in plasma levels of NE, but while plasma E generally increased during anoxia, this elevation was less dramatic than that observed for NE. Exposure of turtles to either mild (6.5% CO 2) or severe (14.5% CO 2) normoxic hypercapnia resulted in no increase in E and only modest increases in NE. Upon resumption of air-breathing in all of the 20°C protocols, turtles rapidly restored E and NE to control levels. The function of elevated plasma catecholamines during anoxia and acidemia in turtles is unknown but may be important in stimulating respiratory and cardiovascular recovery once air-breathing is resumed. Catecholamines may also play a role in mediating the rise in blood glucose we observed in this study, which may be an important factor in maintaining tissue viability during anoxic stress.