Driving forces over the peritubular capillary membrane in the rat kidney during antidiuresis and saline expansion.

Abstract

AbstractKällskog, Ö. and M. Wolgast. Driving forces over the peritubular capillary membrane in the rat kidney during antidiuresis and saline expansion. Acta physiol. scand. 1973. 89. 116–125.The driving forces operative over the renal peritubular capillary membrane has been investigated on a series of male Sprague‐Dawley rats. The hydrostatic capillary pressure was measured by micropuncture technique using a servo‐controlled counter pressure device according to Wiederhielm. The oncotic pressure was estimated from the protein concentration, calculated as the arithmetic mean of the concentration in the proximal end (=plasma concentration/1‐filtration fraction) and that in the distal end of the capillary (= plasma concentration). For estimation of the corresponding interstitial variables a small (50 μm) PCV catheter‐was put into the subcapsular space. The hydrostatic pressure was measured with the same system as for capillaries and the oncotic pressure from the protein concentration in samples withdrawn via the microcatheter. Under control antidiuretic conditions the capillary hydrostatic pressure averaged 11.1 mm Hg and the oncotic 27.7 mm Hg. In the interstitium the corresponding pressures amounted 1.3 mm Hg and 4.0 mm Hg, respectively. In saline expansion the interstitial hydrostatic pressure almost doubled whereas the oncotic pressure decreased towards zero, partly compensating the decrease in net driving force caused by the decreased plasma oncotic pressure following the expansion. Data from lymph flows suggest that the capillary membrane has a small and a large pore system and from these suggestions a model for the regulation nf renal interstitium is presented.