SUMMARY1. Changes in water and solute outputs of hydropaenic, normal and hydrated conscious rats were determined during intravenous infusion (0.2 ml./min) of isotonic (0.9 %) saline for 4 hr; renal tissue composition was determined before, and after 1 or 2 hr, infusion.2. In normal and hydrated rats increased excretion of water and sodium was such that urinary output matched intravenous input from about 2 hr. In hydropaenic rats, the diuretic and natriuretic response was much reduced; a retention of infused saline, equivalent to 15% body weight, occurred over 4 hr.3. A considerable increase in urea output and clearance, and a smaller increase in potassium and ammonium outputs, occurred in all groups.4. The corticomedullary osmolal gradients characteristic of non-diuretic rats were largely dissipated during saline infusion: by 1 hr in normal and hydrated rats, and by 2 hr in the hydropaenic group.5. These changes were ascribable mainly to an increase in tissue water content in all segments, particularly in the hydropaenic group; and to a profound decrease in urea content in all groups.6. Changes in tissue sodium content were smaller, and differed between segments and between the differently hydrated groups. A decrease in papillary content occurred in hydropaenic and normal groups and an increase in cortical and outer medullary content occurred in all groups. 7. After 2 hr saline infusion, incomplete papillary-urinary osmotic equilibration was evident in all groups.8. These changes in medullary osmolality and in papillary-urinary osmotic equilibration preceded the maximal diuresis, and must contribute to the diuresis induced by saline infusion, as in water and osmotic diureses.
SUMMARY1. A comparison was made of various transport properties and electronmicroscopical characteristics of isolated urinary bladders from toads (Bufo bufo) maintained in either tap water or 0 7 % saline (0.7 g NaCl in 100 ml. H20) for 10 days to 2 months.2. In the absence of Pitressin, isolated bladders from saline-adapted toads showed:(a) markedly, and significantly, lower osmotic water flow; (b) moderately, but not significantly, lower urea permeability; (c) no significant change in net sodium transport (measured as shortcircuit current, ISc); and (d) significantly smaller intercellular space/mucosal cell ratios in electron-micrographs.3. Differences in the transport and electron-microscopical characteristics between bladders from water-exposed and saline-adapted toads became more evident in the presence of exogenous Pitressin (10 m-u./ml. serosal solution):(a) the stimulating influence of Pitressin on osmotic water flow, shortcircuit current and urea permeability was considerably smaller in bladders from saline-adapted toads than in those from water-exposed toads; (b) the influence of Pitressin on short-circuit current was reduced more profoundly than that on either water flow or urea permeability; (c) the Pitressin-induced increment in intercellular space/mucosal cell ratio was significantly smaller in electron-micrographs of bladders from saline-adapted toads than in those from water exposed toads.4. The effects of saline adaptation are discussed in relation to decreased permeability of mucosal membrane barriers. 74 P. ACKRILL, J. S. DIXON, R. GREEN AND S. THOMAS
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