Water balance in the California newt, Taricha torosa.

Both dehydration to 87% of original body weight (Wo) and arginine vasotocin (AVT: 20 mU/g) elicited rapid weight gains (ca. 9% of Wo in the 1st h) when terrestrial-phase T. torosa were given access to water. In each case, net weight gain resulted from increased integumental osmosis and antidiuresis. Mesotocin (0.001 -- 0.1 micrograms/g) elicited modest but significant weight gains (ca. 1%/h) caused solely by increased integumental osmosis. Integumental water uptake from wet moss was 66% that of totally immersed animals. Water movement from ventral to dorsal body surface occurred along channels on the skin. Urinary bladder storage capacities in excess of 50% of Wo were observed. Following AVT administration, bladder water resorption increased significantly, while glomerular filtration rate dropped to 16% of control values. The structural and physiological adaptations for water balance in T. torosa are comparable to those found in some terrestrial anurans.