STUDIES ON RENAL TUBULAR TRANSPORT

Development of sugar-induced blood pressure elevation after uninephrectomy in a resistant rat strain

Certain rat strains acutely increase blood pressure (BP) when given diets high in NaCl. Prior results showed that "salt-sensitive" rat strains, at least the ones studied, also increase BP in response to sugar loading. To examine this relationship further and learn more about the pathogenesis of sucrose-induced BP elevations, we examined the effects of unilateral nephrectomy (uninephrectomy) on sucrose-induced BP changes. The rationale is based upon the findings that renal mass removal sensitizes BP response to salt loading. Over 15 weeks, augmented sugar (sucrose) consumption by Long-Evans (LE) rats did not increase BP markedly compared to rats consuming a diet relatively low in sugar unless uninephrectomy was performed. The differences in BP caused by the high sugar diet in a uninephrectomized rat could not be explained adequately by alterations in catecholamine excretion, plasma renin activity, excesses in blood volume, or the other parameters examined. However, salt-induced hypertension has been attributed to the presence of circulating substances affecting ion transport. Among the dietary groups, there was a significant correlation between the ability of plasma to depress PAH and TEA renal slice uptake and the difference in BP. This is consistent with the presence of a circulating factor affecting cell transport that has its greatest activity in the high sugar-uninephrectomy group of LE rats. We conclude that reducing renal mass potentiates sugar-induced BP elevation similar to salt-induced BP elevation in a normally resistant rat strain, and the rise of BP may be caused by a circulating factor.

Effect of renal fuels on p-aminohippurate transport in rat renal cortical fragments

The effects of the major renal fuels were studied, i.e., lactate, citrate, palmitate, glutamine, and glucose, at concentrations near those found circulating on the in vitro accumulation of p-aminohippurate (PAH) by rat renal cortical fragments. Only lactate and citrate were found to increase PAH uptake significantly. Noting that 10% v/v normal rat sera enhance PAH accumulation, we studied the renal fuels at 10% circulating concentrations and found that all fuels combined had stimulation comparable to 10% v/v sera. Lactate and the stimulator in normal sera are located in the same Sephadex G-25 fraction of sera. Both lactate, the major renal fuel, and normal sera stimulate the influx and inhibit the efflux of PAH. We conclude that the stimulators to PAH transport in normal sera are, at least in part, renal fuel organic anions.

Evaluation of the renal toxicity of heme proteins and their derivatives: a role in the genesis of acute tubule necrosis

This investigation studies the toxicity of heme proteins and/or their break-down products on renal function. Heme proteinemia precedes acute tubule necrosis at a frequency great enough to suggest a causal relationship between the two events. Physiological and metabolic functions of kidney slices are investigated in several models of acute tubule necrosis. Organic acid and organic base transport is depressed earliest. These alterations in tubule function cannot be explained by ischemia or obstruction alone. Heme proteinemia in rats or incubation of renal slices in medium containing heme proteins yields several interesting observations. Neither in vivo or in vitro do hemoglobin and methemoglobin alone produce a depressive effect on the transport systems studied. However, parallel to many clinical situations, when such secondary insults as hypoxia and elevated ammonia concentrations are included in the experimental design, transport functions are depressed. Ferrihemate, a molecule smaller than hemoglobin or methemoglobin, depresses transport function without secondary insults. From these studies it is concluded that heme proteins play a role in tubule dysfunction seen in acute tubule necrosis. A model is presented that collates these data with other factors known to play a part in the pathogenesis of this renal syndrome.