Effects of prolactin on water balance and kidney function in bullfrog tadpoles

Abstract

In four experiments of similar design, stage III–XII bullfrog tadpoles were treated for 5–13 days with either 10 μg/day ovine prolactin (PRL) or 10 μl/day saline (0.7% NaCl). In all cases, saline-treated tadpoles lost ca. 10% of their body weight, whereas PRL-treated animals either maintained their weight or gained slightly. Compared with controls, PRL-treated tadpoles showed a significantly higher water content and a 10–20% increase in inulin space (= extracellular volume). PRL treatment also significantly decreased plasma [Na +] (but not total extracellular [Na +]), and the rates of renal inulin clearance (= glomerular filtration rate) and urine production. PRL-treated tadpoles showed significant retention of the water taken up in response to a salt load. These data suggest that the PRL-induced weight gain observed in bullfrog tadpoles is accompanied by major changes in renal function and the size, water content, and sodium concentration of the extracellular fluid compartment.