Micropuncture study of water, electrolytes, and urea movements along the loops of henle in psammomys

Abstract

A B S T R A C T The mechanism by which the osmotic pressure increases in tubular fluid along the descending limb of the loop of Henle was examined in Psammomys undergoing salt diuresis. In two series of experiments, micropuncture samples were collected either from proximal and distal convolutions at the surface of the cortex, or from loops of Henle and collecting ducts at the surface of the extrarenal part of the papilla. Inulin-'H, urea-14C, Na+, and K+ concentrations, as well as osmotic pressure, were determined in all micropuncture samples.Net movements of water along the descending and ascending limbs of the loop could not be deduced by comparing inulin data obtained from convoluted tubules and from loops of Henle, since there appeared to be a large difference in the filtration rate of the superficial glomeruli (9 nl/min) and the deep ones (21.4 nl/min) under the conditions of these experiments.The results indicate that no large net movement of water occurred along the loop since a) only 23% of the filtrate was reabsorbed along the loop of Henle (including pars recta) of superficial nephrons despite the fact that all these loops reached markedly hypertonic regions; b) there was no positive correlation between (F/P) in early distal samples and the simultaneous osmotic pressure of the urine; c) when (F/P)In and (F/P)osm in loop samples were correlated, the increase in inulin concentration accounted only for 15% of the increase in osmotic pressure. Therefore, 85% of the concentrating process taking place along the descending limb must have resulted from net addition of solutes; this was directly supported by Na+ and K+ measurements in the loop samples, which showed that, at the tip of A partial report of this work was presented at the XXIV

Micropuncture study of hypertonic mannitol diuresis in the proximal and distal tubule of the dog kidney

“…It has recently become evident that two major functionally distinct groups of nephrons, cortical and juxtamedullary, exist in the rat (27)(28)(29) The conditions of the present study more closely resemble those used for TC'-o studies. Free water reabsorption, as conventionally measured (Co.m-V), is a valid estimate of the amount of water reabsorbed in the collecting system, and thus considered to be an indirect assessment of sodium transport in the loop, only in so far as two conditions are met: (a) tubule fluid reaching the collecting duct is isosmotic and (b) osmolar reabsorption in the collecting duct is negligible.…”

“…Tubule fluid samples were analyzed for sodium and potassium with a helium-glow photometer' by the method of Vurek and Bowman (15). 28 prepared electrolyte standards, handled as unknowns, gave mean recoveries for sodium of 98.8% (±+5.3% SD) and for potassium of 97.9% (±9.1%o SD). The mean recoveries from 15 standards containing mannitol (2 g/100 ml) were 100.3% (±2.2% SD) for sodium and 100.9% (±13.7% SD) for potassium.…”

Intestinal transport of water and electrolytes during extracellular volume expansion in dogs

“…No model has been found in the literature which would explain the findings of the studies presented here, although bidirectional fluxes have been documented in the intestine (22)(23)(24), kidney (25)(26)(27)(28)(29), frog skin (30), toad bladder (31), and gill (32). The apparent independence of mucosal to serosal and serosal to mucosal flux demonstrated here and in the studies of Visscher et al (22,23), and the unequal unidirectional osmotically driven fluxes of sucrose through the frog skin (33), and of water through the frog intestine (24), both suggest that different pathways are involved, but offer no insight about whether those pathways are transcellular or intercellular.…”

Consequences of potassium recycling in the renal medulla. Effects of ion transport by the medullary thick ascending limb of Henle's loop.

“…The unambiguous evidence of K secretion by the thin descending limb of Henle's loop or the pars recta (1,4,32) has prompted a series of experiments investigating the pathways for this recycling. It is now generally accepted that the K secreted by the distal convoluted tubule and cortical collecting tubule is in part reabsorbed across the outer medullary and/or papillary collecting tubule (1,2,6) and accumulates in the medullary interstitium.…”