Effect of meralluride on solute and water excretion in hydrated man: comments on site of action

Effect of sodium balance on arterial blood pressure and renal responses to prostaglandin A1 in man

The effect of sodium balance on systemic arterial blood pressure and the renal response to intravenous infusion of prostaglandin A 1 (PGA 1 ) was studied in hypertensive subjects. PGA 1 (0.4 µg/kg min -1 ) was infused for 1 hour in ten hypertensive subjects who were receiving a constant diet containing 40 mEq of sodium and 80 mEq of potassium. During PGA 1 infusion a significant fall in both systolic and diastolic arterial blood pressure occurred. There was a significant rise in urine flow rate, renal plasma flow, and urine sodium excretion; plasma renin activity (PRA) rose slightly but not significantly. Eight of the ten subjects and one additional subject were then placed on furosemide (80 mg/day) for 1 week. In all subjects, a significant weight loss and a rise in midday PRA occurred with the administration of the diuretic. Systolic blood pressure fell, but diastolic pressure was unchanged. Following salt depletion with furosemide, PGA 1 infusion studies were repeated. PGA 1 then produced no significant change in systolic or diastolic blood pressure. Urine flow, renal plasma flow, and urine sodium excretion rose, but the degree of increase was markedly less than that observed prior to furosemide administration. In the salt-depleted subjects, a significant rise in PRA occurred during PGA 1 infusion. The results indicate that volume depletion diminishes the systemic and renal hemodynamic response to infused PGA 1 but enhances the PRA response. The increased PRA response during PGA 1 infusion observed in saltdepleted subjects might in part account for the blunted hemodynamic changes. Alternatively, recent evidence indicates that the enhanced production of endogenous vasodilating prostaglandins which occurs in the salt-depleted state might account for the diminished hemodynamic responses to exogenous PGA 1 .

The postobstructive kidney. Observations on nephron function after the relief of 24 hr of ureteral ligation in the dog

After the relief of 24 hr of complete unilateral ureteral obstruction in the dog, the experimental kidney is characterized by a decrease in filtration rate and an increase in fractional and often absolute excretion of sodium before and after the administration of mannitol. In the hydrated state, the failure to conserve sodium is associated with increases in fractional free water clearance and fractional sodium supply to water-freeing sites signifying that the augmented sodium excretion is derived from a proximal source. In the hydropenic state there is decreased fractional free water reabsorption, and sometimes free water excretion, in the postobstructive kidney. An early plateau in free water reabsorption is associated with an increased fractional excretion of sodium. These findings are attributed to the early development of distal nephron impermeability to water as a result of enhanced distal tubular supply and transport of sodium. There is a decrease in maximal tubular reabsorptive capacity (Tm) of glucose in the post-obstructive kidney which is, however, less marked than the decrease in filtration rate. The fall in filtration rate is to some extent likely due to a dropping out of nephrons from the circulation while the remaining nephrons are hypoperfused. The magnitude of the sodium reabsorptive defect is markedly exaggerated as the concentration of nonreabsorbable solute (mannitol) in the glomerular perfusate is increased. It is concluded that the postobstructive increase in sodium excretion during mannitol administration is in part due to a limit in the capacity to reabsorb sodium against a concentration gradient in the proximal tubule.

Effects of hypotonic saline loading in hydrated dog: evidence for a saline-induced limit on distal tubular sodium transport

We performed studies on dogs under hydrated conditions, utilizing the rate of free water formation (C(H2O)) as an index of the rate of distal tubular sodium transport. Since C(H2O) could be progressively increased with no evidence of a maximal rate during loading with hypotonic (2.5%) mannitol, it was concluded that there is no limit on distal tubular sodium transport during mannitol loading. In contrast, during hypotonic (0.45%) saline loading C(H2O) rose initially, but as urine flow (V) exceeded 25% of the filtered load C(H2O) attained maximal levels (up to 20% of the filtered load) and remained stable as V increased to 50% of the filtered load. It was concluded that saline loading progressively inhibits proximal sodium reabsorption. Initially, the distal tubule absorbes a large fraction of the proximal rejectate and sodium excretion rises slightly. Eventually, an alteration in distal sodium transport appears which culminates in a maximal rate or transport limit. This distal transport limit provoked by saline loading could not be characterized by a classical Tm as seen with glucose and does not seem to be consequent to high rates of flow through the distal tubule. Regardless of the precise nature of this limit, the major increment in sodium excretion develops during saline loading only after saline alters the capacity of the distal tubule to transport sodium.