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J Szyjewicz

Publications and source records attributed to J Szyjewicz.

7 recordsLinked to original sources
PubMed1984

Proximal tubular Na, Cl, and HCO3 reabsorption and renal oxygen consumption.

The majority of the oxygen consumed by the rat kidney appears to occur in the proximal tubule. Therefore changes in metabolically linked ion transport in this segment of the nephron should result in changes in renal oxygen consumption. To study the role of bicarbonate reabsorption in metabolically linked proximal tubular ion transport a series of micropuncture-clearance-extraction experiments were performed comparing the effects of the carbonic anhydrase inhibitor benzolamide and of hypertonic sodium bicarbonate infusion with control conditions in the rat. End-proximal tubular fluid and chloride reabsorption were measured. From these, the rates of sodium and bicarbonate reabsorption were estimated. Simultaneously with the tubular fluids, extraction collections were obtained for determination of renal oxygen consumption. Both benzolamide and hypertonic bicarbonate reduced proximal tubular fluid reabsorption while concomitantly reducing the transepithelial gradient for chloride. The mean rate of renal oxygen consumption did not differ from the control rate in either experimental group and could be dissociated from the calculated net rates of proximal tubular sodium, chloride, and bicarbonate reabsorption. We interpret these data as evidence that proximal tubular hydrogen ion secretion supporting bicarbonate reabsorption requires at most small amounts of oxidative energy, less than detectable by these techniques. The data, in contrast, support the conclusion that the chloride-bicarbonate transepithelial gradient appears to be an important passive driving force in vivo for proximal tubular fluid reabsorption.

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PubMed1982

Evidence for an osmotic effect of glucose in the in vivo rat proximal tubule.

A series of micropuncture experiments were performed to assess whether phlorizin inhibition of proximal tubular glucose reabsorption inhibits proximal tubular fluid reabsorption due to a change in the transepithelial osmotic gradient for glucose. End proximal tubular filtrate reabsorption was measured, control vs experimental, in the same rat. The effects of infusing phlorizin in one group were compared to those of graded small infusions of mannitol in a second group of rats. In the phlorizin series tubular fluid and peripheral plasma were analyzed for glucose. Net renal sodium and renal oxygen consumption were measured in these same rats. In the mannitol series tubular fluid and peripheral plasma mannitol concentrations were determined. The results show that phlorizin inhibits proximal tubular fluid and glucose reabsorption without changing renal oxygen consumption. Mannitol inhibits proximal fluid reabsorption per unit transepithelial concentration difference to the same extent as does glucose during phlorizin infusion. We interpret these data as most consistent with the conclusion that the reduction in proximal tubular fluid reabsorption during phlorizin infusion is primarily due to the resultant change in the effective transepithelial osmotic gradient for glucose. Normally this gradient favors net fluid reabsorption. During phlorizin it favors retention of fluid in the proximal tubular lumen.

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PubMed1978

Superficial nephron tubular-vascular relationships in the rat kidney.

Silicone rubber injections of methyl salicylate-cleared rat kidneys were performed. In 50 of 56 injections of superficial nephrons with their accompanying blood supply, the efferent vessel and early proximal tubule were closely approximated. In 18 of 21 tubular injections filling through the pars recta, the proximal tubule folded upon itself with early and late proximal segments, in close contact, located over their parent glomerulus, and the midproximal segments separate and located over their parent interlobular artery. The distribution of blood was serially through the early-late proximal region above the glomerulus via a long unbranched efferent vessel, via branches over the capsular surface, via capillaries down through the midproximal region, then into the interlobular vein. The observed anatomical pattern of the superficial nephron appears to permit direct functional interactions between the juxtaposed early and late proximal tubule, and in turn may effect midproximal function via the distribution of blood (modified by early proximal) from the efferent vessel to midproximal convolutions. In addition, the relationship between specific segments of the proximal tubule and specific portions of the postglomerular peritubular blood supply may be important in determining the distribution of peritubular physical forces to these nephrons.

Animals↗
PubMed1976

Early postglomerular plasma concentrations of chloride, sodium, and inulin in the rat kidney.

Sodium, chloride, and inulin concentrations were measured in plasma collected from the terminal portions of long efferent vessels at the subcapsular surface of the rat kidney. Sodium concentration equaled and the concentrations of chloride and inulin were less than those in peripheral plasma. During benzolamide infusion, chloride concentration equaled while inulin concentration remained less than in peripheral plasma. In free-flow micropuncture samples collected randomly during control conditions, chloride concentration rose rapidly in the early proximal tubule and then remained elevated and constant throughout the remainder of the proximal tubule accessible to micropuncture. These experiments indicate that normally tubular reabsorbate low in chloride and inulin is added to the blood traversing the early postglomerular vessels before reaching the kidney surface. Bases on the analyses of proximal tubular fluid, this type of reabsorbate appears available only from the early proximal tubular segment. We conclude that a close functional relationship exists between the first segment of the proximal tubule and the early postglomerular blood supply characteristic of the superficial cortical nephron.

Animals↗
PubMed1976

Single-nephron function and renal oxygen consumption during rapid volume expansion.

Isotonic volume expansion reduces net filtrate reabsorption in the proximal tubule while increasing it in Henle's loop. To determine the role oxidative metabolism plays in these processes, experiments were performed on rats initially hydropenic and then rapidly volume expanded with isotonic Ringer solution. Whole-kidney sodium reabsorption, oxygen consumption, and single-nephron function were measured simultaneously. During volume expansion, net renal sodium reabsorption increased concomitantly with a fall in oxygen consumption and a reduction in proximal tubular absolute filtrate reabsorption. The increase in quantity of nonreabsorbed filtrate delivered into the loop of Henle greatly exceeded the amount excreted in the urine. Thus, filtrate reabsorption by the distal nephron segments increased. These data provide evidence that acute volume expansion reduces oxygen-dependent active solute transport in the proximal tubule. The increase noted in distal nephron sodium reabsorption appears nonoxygen dependent, energized by anaerobic glycolysis or occurring passively.

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