Breeding condition, temperature, and the regulation of salt and water by pituitary hormones in the red-spotted newt, Notophthalmus viridescens

In vivo integumental transepithelial potential (TEP) in the Eastern red-spotted newt ( Notophthalmus viridescens) increases linearly with external [Na +] from 0.1 to 10 m M and is anion independent. Both integumental TEP and osmotic permeability are higher in laboratory-conditioned (LC, terrestrial) than in breeding-condition (BC, aquatic) newts at temperatures of 5–25°. Prolactin (PRL) treatment of LC newts decreased both TEP and rate of water uptake. Arginine vasotocin (AVT) treatment resulted in a substantial increase in water uptake in LC newts, while little or no AVT response was seen in PRL-treated or BC newts. Hypophysectomy (HX) or ergocryptine treatment increased TEP in BC newts, whereas HX + PRL maintained TEP at control levels. Although ergocryptine and HX were without effect on water uptake in BC newts kept at 5° for 9 days, HX + ACTH increased water uptake. HX produced a substantial fall in serum [Na +] in BC newts, while either PRL or ACTH replacement elevated serum [Na +]. Combined ACTH and PRL treatment returned serum [Na +] to control levels. These data suggest that high endogenous prolactin plays a significant role in maintaining serum [Na +] and integumental permeability and transport characteristics in breeding-condition N. viridescens. Although PRL and ACTH are both sodium retaining in the aquatic breeding stage, these two hormones promote opposite effects on the integument; PRL decreases both water uptake and integumental TEP, whereas ACTH (presumably acting through the adrenals) increases water uptake and possibly TEP.