Flow dependence of vasopressin-stimulated hydraulic conductivity in rabbit collecting tubule.

Flow rate dependence of both electrolyte and nonelectrolyte transport in various nephron segments has been described. Prior studies have used relatively leaky epithelia in which the flow rate-dependent transport phenomena can be explained in terms of alterations in axial and radial concentration profiles. In this study, the flow rate dependence of either vasopressin or cyclic adenosine monophosphate-stimulated water flux (Jv), hydraulic conductivity (Lp), and osmotic permeability (Pf) were measured in isolated perfused rabbit cortical collecting tubules. Increasing perfusion rate from 6.0 +/- 0.4 to 20.7 +/- 1.2 nl/min results in highly significant increases in Jv (131%) and in Lp and Pf (120%). In this relatively tight epithelium, osmotic equilibrium did not occur. Although the mechanism of this effect remains to be elucidated, the present results mandate maintenance of constant flow rates when examining the perfused cortical collecting tubular response to vasopressin.