Influence of glomerular filtration rate on the rate of para-aminohippurate secretion by the rat kidney: micropuncture and clearance studies.

Net secretion rate of para-aminohippurate (PAH) in the proximal convolution of the rat kidney changes concomitantly with single nephron glomerular filtration rate (GFR) and intratubular flow rate. Reabsorption of PAH in the proximal convolution is negligible. The PAH concentration profile along the length of the proximal convolution does not change markedly with variations in GFR. Net PAH secretion by single nephrons, measured at the end of proximal convolutions, is about one-half that measured at the beginning of distal convolutions and in final urine. As in the entire kidney, at constant renal plasma flow and concentration of PAH, renal secretion rate of PAH also changes concomitantly with GFR. It is concluded that PAH secretion along the loop of Henle (i.e., probably along the pars recta) is also related to single nephron GFR, as is PAH secretion in the proximal convolution.