Effect of prolactin on transcutaneous Na transport in the Japanese newt, Cynops pyrrhogaster.

The effect of ovine prolactin (PRL) on the electric parameters related to active Na transport across the skin was investigated in the Japanese newt, Cynops pyrrhogaster. Spring newts living in a pond or stream for breeding and autumn newts migrating from water to land for hibernation were collected and used for the experiments. Autumn newt skin was found to have a higher transepithelial potential difference (TEP) and higher resistances to the active Na current (RNa) and to the shunt pathway (RS) than spring newt skin. Injection of PRL, 20 micrograms/g body wt, into autumn newts every other day for 2 weeks induced an increase in RNa, resulting in decreases in TEP and the short-circuit current (SCC), but barely changed the skin resistance (RM), the electromotive force of the active Na current (ENa), or RS. On the other hand, such injections of PRL into spring newts induced decreases in TEP and SCC, but had no effect on RM, ENa, RNa, or RS. Autumn newts appear to be more sensitive to PRL than spring newts. Insofar as autumn newts are concerned, it is concluded that the effect of PRL is probably due to blockade of the Na channel rather than inhibition of Na pump activity.