Urea production in Rana pipiens: Effects of dehydration and aldosterone administration

Abstract

1. 1. Serum urea and urea production are observed to increase following 10 hr of dehydration in 0.15 M Nacl in frogs, Rana pipiens, treated in the spring-summer (SS) but not the fall-winter (FW) months (Jungreis, 1971). 2. 2. This increase in urea production was thought to result from elevated glucocorticoid activity in SS but now FW frogs, but measurement of serum tilers of corticosterone, the “primary” glucocorticoid in R. pipiens, failed to support this model (Jungreis, 1970). 3. 3. The effects of aldosterone (aldo), the “primary” mineralocorticoid in this species, on the seasonal increase in urea production were therefore studied. Administration of aldo mimicked the effects of dehydration by inducing the seasonal increase in urea production in SS frogs only. 4. 4. The involvement of aldo in vivo in the seasonal increase was supported by an increased rate of inter-renal aldo synthesis following dehydration in the SS and a decreased rate of synthesis following dehydration in the FW months. 5. 5. Administration of aldo to FW frogs failed to cause an increase in urea production, indicating that one difference between FW and SS frogs is in the capacity of aldo to stimulate gluconeogenesis. 6. 6. Despite the ability of aldo to induce the seasonal increase in urea production, measurement of serum aldo titers by radioimmunoassay failed to uncover a positive correlation between serum aldo and urea production. 7. 7. It is therefore proposed that the serum titer of aldo reflects the level of mineralocorticoid activity, while aldo's glucocorticoid activity is expressed through a seasonally influenced differential tissue responsiveness.