THE COLLECTION AND ANALYSIS OF FLUID FROM SINGLE NEPHRONS OF THE MAMMALIAN KIDNEY

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Abstract
3The methods described in the preceding paper were used to collect fluid from single glomeruli, proximal and distal convoluted tubules in anesthetized guinea pigs, rats and opossums. The amts. of fluid thus collected, though small (0.03 to 0.70 cu.mm.), were sufficient for quantitative analysis. In 59 expts., the composition of this fluid was compared with that of blood plasma in respect to protein, reducing substances (before and after adm. of phlorhizin), exogenous creatinine, osmotic pressure, chloride and sodium. Glomerular fluid was found nearly or entirely free of protein and contained glucose and creatinine in the same concs. as those in plasma water. As this filtrate descended the proximal tubule all of its glucose and about 80% of its fluid content was reabsorbed. Reabsorption of fluid in the proximal convolution was an isosmotic process for there was no increase in the osmotic pressure of the fluid remaining within the tubule lumen; it was not, however, a purely passive reabsorption of unchanged glomerular fluid for the chloride conc. of tubule fluid increased to 1.4 times that of blood plasma. The existence of this increased chloride conc. apparently required that bicarbonate be preferentially re-absorbed by the proximal tubule, but the point was not directly examined. Some evidence was obtained which suggested that the site of water (as opposed to fluid) reabsorption was in the distal convolution rather than in the loop of Henle.

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