Ionoregulatory responses of the hypophysectomized turtle Chrysemys picta to osmotic stresses

Abstract

The effects of dehydration and hydration on sodium and potassium levels of plasma and urine were studied in sham-operated and hypophysectomized winter turtles. Hydration resulted in a decrease in plasma sodium whereas dehydration produced an increase in both sodium and potassium. Plasma electrolyte concentrations of hypophysectomized turtles were similar to sham-operated controls under all environmental conditions studied. In urine, concentrations of sodium and potassium were temporarily elevated by dehydration but unaffected by hydration. Hypophysectomy had no effect on urine electrolytes except during dehydration, where hypophysectomized turtles produced urine with low sodium and high potassium. We conclude that the pituitary has little influence on osmoregulation in Chrysemys picta belli during the winter.