The effect of osmotic stress and hypophysectomy on blood and urine urea levels in frogs

Abstract

1. 1. Elimination of urea in the excreta of frogs ( Rana pipiens) decreases from normal levels of 12 mg N per 100 g body weight per day to about 2 mg when animals are placed in 150 mM NaCl. There is a tendency to return to normal levels on prolonged exposure and complete recovery on return to tap water. 2. 2. NaCl treatment causes a threefold increase in blood urea level from normal values of 10 mg N per 100 ml. The higher level is maintained during at least 5 days in NaCl solution but returns to normal within 2 days in tap water. 3. 3. The pattern of decrease in urea excretion and increase in blood urea in salt solution is not significantly changed after removal of the adenohypophysis. Total N excretion is not altered when hypophysectomized animals are placed in salt solution. 4. 4. The results with R. pipiens are discussed in relation to those with other anuran species. Increased blood urea and decreased urea excretion are characteristic responses of anurans to environmental changes of a potentially dehydrating character. The degree of response varies in different species and the adaptive significance probably varies as well. The control mechanisms are unknown but differ in some respects at least from those controlling changes in active salt transport in response to osmotic stress.