Seasonal effects of hyper‐osmotic sodium chloride on urea production in the frog, Rana pipiens

Abstract

ABSTRACT1. Spring-summer frogs, Rana pipiens, acclimated at 22.5"C or 27°C were dehydrated in 0.15 M NaCl for up to 24 hours. After 10 or 24 hours of treatment, the concentration of urea in serum increases relative to the concentrations of urea measured in serum of frogs kept in tap water or 0.125 M NaC1.The increase in the concentration of urea in serum of spring-summer frogs was associated with an increase in body urea and an increased rate of urea production.When fall-winter frogs, acclimated at 20°C, were dehydrated in 0.15 M NaCl for 12.5 hours, no increase in the concentration of urea in serum was observed, relative to frogs treated with tap water or 0.125 M NaC1. After 48 hours, the concentration of urea in serum of frogs treated with 0.15 M or 0.125 M NaCl was the same, but both were significantly greater than tap water treated frogs.4. The metabolic basis for the increase in the rate of urea production observed in spring-summer but not fall-winter frogs in response to hyperosmotic sodium chloride is discussed. 2. 3.In the course of a preliminary study designed to explore the relationships between the activities of liver and kidney enzymes associated with urea production and the proportion of waste nitrogen excreted as ammonia or urea, it was observed that, following short term mild dehydration in air, leopard frogs ( R a m pipiens) in the spring and summer but not in the fall and winter had higher concentrations of urea in serum than did tap water treated frogs (Jungreis, '71). While the increased concentrations of urea in serum of spring-summer frogs were suggestive of an increased rate of urea production, the inability to quantitatively collect excreted urine made it impossible to conclude that the increased concentration represents an increase in urea production. Consequently, a different type of dehydration was employed which would permit quantitative determination of both the quantity of urea excreted as well as the quantity of urea retained in the animal's body.When frogs Rana pipiens were dehydrated in 0.15 M NaCl (hyper-osmotic to J. EXP. ZOOL., 178: 403-414 serum colloid osmotic pressure) for under 24 hours, spring-summer but not fallwinter animals were observed to have increased concentrations of urea in serum.When total urea excretion was simultaneously measured, an increase in urea production was found to have accompanied the increased concentration of urea in serum.