Effects of hydrin 2 on cutaneous electrical properties of Rana pipiens.

Electrical properties were measured in isolated skin patches from leopard frogs (Rana pipiens) to explore the possibility that hydrin 2 (vasotocinyl-gly) may regulate cutaneous ion transport. Hydrin 2 is a neurohypophysial peptide commonly implicated in rehydration of anurans. Experimental frogs were given either one or two intraperitoneal (i.p.) injections of hydrin 2 in saline solution, each calculated to achieve a final blood concentration of 81 ng/ml. After a 2-h equilibration period, the frogs were euthanized and abdominal skin removed for study in a Ussing chamber. Results of this study confirm that exposure of R. pipiens to hydrin 2 promotes a highly significant increase in transepithelial potential (TEP) and short-circuit current (Isc), with both treatment and treatment x time interactions in doubly injected frogs (repeated measures ANOVA). The apparent decrease in cutaneous R of experimental animals was not significant. Supplemental additions of hydrin 2 to the serosal bath provoked changes in TEPs, Iscs, and Rs which are difficult to interpret. In a dose-response study, 10-fold increases in serosal hydrin 2 concentration triggered significant changes in TEP and Isc, with maximal responses observed at 10 ng/ml. Because hydrin 2 is known to facilitate "cutaneous drinking" in anurans, this study suggests a correlation between ion and water transport across the skin.