The time course of changes in renal tissue composition during water diuresis in the rat

Abstract

SUMMARY1. The time course and extent of changes in the composition of renal tissue slices in water diuresis were determined by sacrificing groups of rats before and during the intravenous infusion of dextrose (2.5 g/100 ml.) in amounts sufficient to administer over 2 hr, and subsequently to maintain for up to 74 hr, a positive fluid load of 4 % body weight.2. The corticomedullary osmolal gradient characteristic of the nondiuretic rats was progressively dissipated until, at 74 hr, only papillary tip concentrations were higher than those of other segments.3. The changes in individual constituents followed different time courses: (i) an increase in water content in all segments, particularly the papilla, was almost complete by 1 hr, preceding the maximal increases in urine flow; (ii) a marked decrease in papillary and medullary urea content in the first hour was followed by a slower, progressive decrease leading to an almost complete dissipation of the urea gradient by 74 hr; (iii) small, non-significant decreases in sodium content occurred in all segments in the first hr, followed by a further small, progressive decrease in papillary sodium content; (iv) changes in ammonium and potassium concentrations were mainly related to those in water content, since the contents of these solutes showed only small changes.4. By 2 hr, differences in the rates of decline of osmolal and urea concentrations in urine and papilla led to urinary concentrations significantly lower than papillary values. The steep papilla-urine urea concentration difference became smaller, but remained significant even at 74 hr.5. The findings are discussed in terms of changes in countercurrent mechanisms, particularly as influenced by anti-diuretic hormone.6. The development of papilla/urine urea concentration ratio greater than unity is also considered in terms of passive transport with changes in membrane permeability.

Effects of Ethacrynic Acid on the Isolated Collecting Tubule

“…If during ethacrynic acid diuresis the collecting system becomes less sensitive to ADH, the pattern of solute distribution in the concentrating kidney may be shifted towards that of a kidney undergoing water diuresis. In the latter situation a decrease in medullary osmolality is well known (33).…”

Pathogenesis of nephrogenic diabetes insipidus due to chronic administration of lithium in rats.

“…The mechanism by which this renal depletion of urea develops in Li-rats should be briefly considered. Water diuresis in conscious rats was shown to lower P, and the cortico-papillary gradient of urea (44,45); urea content in the renal cortex is also lower in HHDI rats with chronic water diuresis (37). Based on other reports (19,20) and our survey of Pr, chronic treatment with oral Li apparently does not diminish GFR.…”

Effects of water diuresis and osmotic (mannitol) diuresis on urinary solute excretion by the conscious rat

“…If progressive suppression of endogenous A.D.H. leads to reduced collecting duct permeability to urea, this would be a transient phenomenon in water diuresis, despite the maintenance of medullary solute concentration gradients (Atherton et al 1968b). Any contribution made by medullary solute to an increment in the output of individual solutes would depend on the relative time courses and magnitude of changes in medullary interstitial and tubular concentrations, and in tubular membrane permeability.…”