Salt-Load Effects on Osmotic Water Flow, Tritiated Water Diffusion, and the Cardiovascular System inRana pipiensandRana catesbeiana

Abstract

Osmotic water flow (Jv, cm³ · cm⁻² · s⁻¹ X 10⁻⁷) and tritiated water (THO) diffusion (cm · s⁻¹ X 10⁻⁵) were measured in Rana pipiens and Rana catesbeiana. A salt load (0.04 mL 1 M NaCl/g) caused Jv to increase from 10.6 ± 0.80 (n = 16) to 16.9 ± 1.39 (n = 16) and THO diffusion to increase from 3.53 ± 0.16 (n = 16) to 4.06 ± 0.19 (n = 16) in R. pipiens. In R. catesbeiana (0.02 mL 4 M NaCl/g) Jv increased from 8.61 ± 1.39 (n = 6) to 54.4 ± 9.72 (n = 6), and THO diffusion increased from 5.00 ± 0.39 (n = 7) to 7.36 ± 0.91 (n = 7). This is different from the response elicited by antidiuretic hormone (ADH). Antidiuretic hormone (100 mU/g) injection increased Jv from 11.9 ± 1.67 (n = 8) to 47.5 ± 7.22 (n = 8) in R. pipiens and from 14.4 ± 1.11 (n = 4) to 25.0 ± 4.70 (n = 4) in R. catesbeiana but had no effect on THO diffusion, which went from 4.11 ± 0.16 (n = 8) to 4.08 ± 0.22 (n = 8) in R. pipiens and from 3.78 ± 0.14 to 3.44 ± 0.08 (n = 4) in R. catesbeiana. Changes in skin circulation are known to increase both Jv and THO diffusion. Direct evidence for a circulatory involvement was obtained by measuring the sciatic and systemic arterial blood flow in R. catesbeiana with an electromagnetic flowmeter. In response to a salt load these measurements showed 88% and 69% increases in the sciatic and systemic blood flow, respectively. The data suggest that an increase in skin circulation could explain the increase in the Jv and THO diffusion induced by a salt load in frogs.