Renal function in response to reduced osmotic load in larval salamanders.

STIFFLER, DANIEL F., AND RONALD H. ALVARADO. Rena/function in response to reduced osmotic load in larval salamanders. Am. J. Physiol. 226(5) : 1243-l 249. 1974.-Renal function was studied in larval Ambystoma gracile and Dicamptodon ensatus exposed to several osmoh&ties. Clearance methods were employed in free-swimming larvae using inulin as a GFR marker. GFR, as calculated from the rate of appearance of inulin in the bath, declined from 0.113 to 0.023 ml/10 g-h (A. g racile) and from 0.166 to 0.006 nil/10 g-h (D. ensatus) between 2 mosM (tap water) and 300 mosM (sucrose). In experiments involving urine collection (A. gracile), urine flow . decreased from 0.078 in controls to 0.018 ml/10 g-h in the ZOOmosM group while GFR decreased from 0.104 to 0.028 ml/l 0 g-h. The latency for the reduction in GFR is about 2 h; however, the return to normal GFR after return to tap water takes about 6 h. Fractional reabsorption of water increased from 25 to 37a/, in the ZOO-mosM group, while fractional reabsorption of Na+, K+, and Cldecreased slightly. The results indicate that both glomerular and tubular factors (and possibly the bladder or cloaca) are involved in the response to reduction in osmotic load; however, the decrease in GFR predominates. loaded,” which itself causes physiological changes only partially related to volume regulation. The objectives of this report are: I) to evaluate various aspects of renal function in unanesthetized, free-swimming larval salamanders under “normal” conditions (i.e., in dechlorinated tap water); and 2) to study volume regulation, as reflected by renal responses to acute changes in osmotic load induced by adjusting the concentration of an impermeant nonelectrolyte in the external medium. The osmotic load is defined here as being the water taken on osmotically by the animals.