Fluid secretion in the nephron: Relation to renal failure

Abstract

It had been generally accepted that glomerular filtration and tubular reabsorption were the basic modes of fluid transport in mammalian nephrons. Recently, evidence was obtained to indicate that net fluid secretion may occur in mammalian nephrons as well. In the pars recta portion of proximal tubules of rabbit kidney net fluid secretion was observed in vitro in response to PAH and other aryl acids in the peritubular bathing medium. Net fluid secretion appeared to be coupled to the transcellular transport of aryl acid from bath to lumen. Serum from uremic subjects stimulated net fluid secretion in the pars recta in a manner similar to PAH. The accumulation of high levels of endogenous aryl acids may contribute to the general organ dysfunction that is a part of the uremic syndrome of advanced renal insufficiency. Futhermore, there is evidence to suggest that the fluid-secretion phenomenon in association with aryl acids may significantly affect renal excretion and morphology in slow-flow states, in patients with cystic kidney disease, and in obstructive nephropathy.