Intrarenal heterogeneity for fluid, phosphate, and glucose absorption in the rabbit

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Abstract
Fluid, phosphate and glucose absorption rates were measured in proximal convoluted tubules dissected from the rabbit and perfused in vitro with ultrafiltrate of rabbit serum. Each tubule was identified at dissection as being derived from a superficial (SF) or juxtamedullary (JM) nephron. The secretory rates of para-aminohippurate (JPAH) were measured to characterize the tubules as being early (JPAH < 300 fmol .cntdot. mm-1 .cntdot. min-1) or late (JPAH > 300 fmol .cntdot. mm-1 .cntdot. min-1). Fluid absorption rates were significantly higher (P < 0.01) in 20 JM convoluted tubules (1.16 .+-. 0.10 nl .cntdot. mm-1 .cntdot. min-1) than in 20 SF segments (0.85 .+-. 0.07 nl .cntdot. mm-1 .cntdot. min-1) and were also higher in later than in early portions (1.17 .+-. 0.08 vs. 0.84 .+-. 0.08 nl .cntdot. mm-1 .cntdot. min-1). Phosphate absorption was significantly higher in early tubules (11.05 .+-. 1.15 pmol .cntdot. mm-1 .cntdot. min-1) than in later (3.82 .+-. 0.48 pmol .cntdot. mm-1 .cntdot. min-1) but did not differ between SF and JM nephrons. Glucose absorption was also higher in early convoluted segments than in later portions (93.4 .+-. 3.0 vs. 58.0 .+-. 8.4 pmol .cntdot. mm-1 .cntdot. min-1; P < 0.001). Internephronal heterogeneity exists in the rabbit for proximal fluid absorption rates and axial heterogeneity exists for fluid, phosphate and glucose absorption.