Role of proximal convoluted tubule in pressure diuresis in the rat.

The role of different nephron segments in the diuretic response to acute arterial hypertension was studied with tubular microperfusion. Early proximal convolutes were perfused with synthetic glomerular ultrafiltrate; fluid was collected from the last visible loop of the same proximal or from the first loop of the distal tubule. In late proximal collections, an increase of arterial pressure of 24 +/- 2 mmHg reduced reabsorption of tubular fluid 44 +/- 4%. Perfusate chloride concentration fell, but only 2 meq/liter, so that chloride reabsorption was inhibited in proportion to the inhibition of fluid reabsorptions, with a corresponding increase in chloride delivery to the loop of Henle. In early distal collections, there was no significant difference of the early distal flow rate with hypertension, but early distal chloride concentration increased 31 +/- 8% and chloride load increased 45 +/- 12%. Qualitatively similar increases were obtained from paired collections made from free-flowing early distal tubules. Inhibition of proximal fluid reabsorption is a primary response to acute hypertension and may contribute to pressure diuresis. In addition, this inhibition increases the strength of the luminal signal to the macula densa, enhancing the autoregulatory response to hypertension.