CIRCULATING ANTIDIURETIC HORMONE IN RATS: EFFECTS OF DIETARY ELECTROLYTES AND PROTEIN

Plasma antidiuretic activity, believed to be antidiuretic hormone (ADH), has been studied in undisturbed rats: 1) fed diets containing normal amounts of protein but varying concentrations of sodium and potassium salts; 2) fed high-protein diets with and without supplementary urea and NaCl; or 3) dehydrated for periods up to 3 days. Plasma ADH in control rats was generally below the assay sensitivity of 4 µU/ml. With 24 hr dehydration ADH averaged 6.8 µU/ml plasma, and after 48–72 hr dehydration, 18.1 µU/ml. Of animals fed 27% protein diets, only in those whose diet contained very high salt (6% NaCl) was the average ADH level significantly elevated (about 5.5 µU/ml) and considerable variation from animal to animal was observed. Rats fed high-protein diets showed a more consistent rise in circulating ADH (range 4–8 µU/ml); many were above 6 µU/ml, calculated to produce maximal antidiuresis in the rat. High plasma ADH in dehydrated rats, or in rats fed high-salt diets may be explained by changes in plasma osmolality. The mechanisms producing increased ADH with high-protein intake are less clear. The possible effect of chronically elevated endogenous ADH on the renal concentrating mechanism is briefly discussed.

ELECTRON MICROSCOPY OF ABSORPTION OF TRACER MATERIALS BY TOAD URINARY BLADDER EPITHELIUM

The absorption of Thorotrast and saccharated iron oxide by the epithelium of the toad urinary bladder was studied by electron microscopy. Whether the toads were hydrated, dehydrated, or given Pitressin, no significant differences in transport of colloidal particles by epithelial cells were observed. This implies that these physiological factors had little effect on the transport of the tracer particles. Tracer particles were encountered in three types of epithelial cells which line the bladder lumen, but most frequently in the mitochondria-rich cells. Tracer materials were incorporated into the cytoplasm of epithelial cells after being adsorbed to the coating layer covering the luminal surface of the cells. In the intermediate stage (1 to 3 hours after introducing tracer) particles were present in small vesicles, tubules, and multivesicular bodies. In the later stages (up to 65 hours), the particles were more commonly seen to be densely packed within large membrane-bounded bodies which were often found near the Golgi region. These large bodies probably were formed by the fusion of small vesicles. Irrespective of the stages of absorption, no particles were found in the intercellular spaces or in the submucosa. Particles apparently did not penetrate the intercellular spaces of the epithelium beyond the level of the tight junction.