Deep nephron and collecting duct function after unilateral reduction in renal mass.

Papillary micropuncture was used to study juxtamedullary nephron and terminal collecting duct function in the remnant kidney when the contralateral kidney was present. Urine osmolality from the remnant kidney was significantly lower than that measured for the control kidney. Surface nephron function appeared unaffected by remnant formation. Delivery of water to the bend of the loop of Henle of deep nephrons was increased. It is proposed that part of this increase in delivery is a consequence of a decrease in water extraction along the descending limb of the loop of Henle. Surprisingly, there was a decrease in fractional sodium delivery to the bend of the loop of Henle. This suggests enhanced fluid reabsorption in the proximal segments of deep nephrons. Water and sodium reabsorption along the terminal segment of the collecting duct was not affected by remnant formation. However, fluid osmolality measured along this segment was lower than that obtained in controls. Values obtained along the descending limb of the loop of Henle of deep nephrons did not differ from collecting duct fluid. This suggests no significant alteration in collecting duct permeability. Rather, the findings of the present study suggest that the lower osmolality of the final urine may be due, in part, to a reduction in the deposition of sodium in the papillary interstitium.