EFFECTS OF HYPOPHYSECTOMY AND PROLACTIN ON THE WATER-BALANCE RESPONSE OF THE NEWT, TARICHA-TOROSA

Prolactin [PRL] treatment (20 .mu.g/day for 7 days) of intact terrestrial T. torosa lowered the rates of both H2O uptake (from 51.1 .+-. 2.1 to 32.1 .+-. 1.4 .mu.l/g per h) and urine formation (from 52.4 .+-. 2.7 to 31.1 .+-. 1.9 .mu.l/g per h). Compared with shams, hypophysectomized (HX) newts also showed lower rates of H2O uptake and urine formation (from 59.3 .+-. 3.4 to 38.9 .+-. 2.0 .mu.l/g per h and from 54.9 .+-. 3.8 to 34.5 .+-. 2.4 .mu.l/g per h, respectively). PRL treatment of hypophysectomized newts (HX + P) further lowered the rates of H2O uptake (to 28.6 .+-. 2.0 .mu.l/g per h) and urine formation (to 23.2 .+-. 1.7 .mu.l/g per h). S.c. injection of 200 mU arginine vasotocin (AVT) elicited a 20.6 .+-. 1.6% weight gain after 4 h in sham-operated control newts, compared with 15.1 .+-. 1.1% in HX and 7.6 .+-. 1.2% in HX + P animals. Weight gains in sham-HX and HX groups resulted from both an increase in cutaneous osmotic permeability and a reduction in rate of urine formation. Even after AVT stimulation, cutaneous permeability in HX newts did not equal that found in uninjected control (sham) animals. Weight gain in AVT-injected HX + P animals was due almost entirely to decreased urine production, with cutaneous permeability remaining essentially unchanged. Evidently PRL acts to decrease integumental permeability in amphibians, rather than to increase it as was previously thought.