Fluid uptake in the renal papilla by vasa recta estimated by two methods simultaneously

Abstract

Fluid uptake by vasa recta was determined by two independent methods, videomicroscopy and the micropuncture technique, in the exposed papilla of nine antidiuretic rats to reconcile differences in values previously obtained by the two techniques. Erythrocyte velocity (Vrbc) and diameter (D) in descending vasa recta (DVR) (n = 22) and ascending vasa recta (AVR) (n = 31) near the "base" of the papilla were measured. Using a conversion function determined in vitro, Vrbc was transformed into mean blood velocity (Vblood). From D and Vblood, mean blood flow (Q) in DVR and AVR was calculated. In DVR, mean Vrbc, D, and Q were 1.06 +/- 0.01 mm/s, 16.3 +/- 0.4 micron, and 10.6 +/- 1.4 nl/min, respectively. In AVR, each corresponding value differed significantly, 0.47 +/- 0.06 mm/s (P less than 0.001), 19.8 +/- 0.8 micron (P less than 0.001), and 5.65 +/- 1.3 nl/min (P less than 0.025), respectively. Blood samples from DVR and AVR were obtained by micropuncture from the same location. Plasma protein concentration (g/dl) was 5.1 +/- 0.6 in DVR, 4.0 +/- 0.4 (P less than 0.05) in AVR, and 3.6 +/- 0.3 (P less than 0.025) in the renal vein. Assuming no net transcapillary loss of protein, total plasma outflow exceeded inflow by 29%, the excess representing fluid uptake; and to reconcile the blood flow and plasma protein concentrations found, functioning AVR should outnumber functioning DVR by a ratio of 2.1-2.4 to 1, depending on local hematocrit. Given the total number of AVR + DVR = 2,944 (at the base), capillary fluid uptake was calculated to range between 1.5 and 2.6 microliter/min.

Effect of sodium chloride gradients on water flux in rat descending vasa recta.

“…Water is transported from the lumen of DVR to the papillary interstitium despite the fact that plasma oncotic pressure exceeds hydraulic pressure in the hydropenic Munich-Wistar rat. Sanjana et al recognized that a large negative pressure within the papillary interstitium could not explain this observation because water is transported from the papillary interstitium into ascending vasa recta (3,16,17). Based upon this analysis Experimental model.…”

Effect of arginine vasopressin on renal medullary blood flow. A videomicroscopic study in the rat.

“…The preparation of the FITC gamma globulin has been described previously (7). The papilla was illuminated with fluorescent light (excitation wave length < 490 nm, emission wave length > 530 nm), and the image of the microscopic field was transmitted to a high sensitivity television camera (model 4410 SIT; Cohu Inc., San Diego, CA), displayed on a television monitor, and documented on videotape (7,8). 2-3 different areas near the base of the papilla were recorded, each for 3-5 min.…”

“…VR3c was measured by a dual-slit technique from the videotape recordings as described previously (7,8). Photometric signals from two nearby sites on the same capillary were analyzed and the transit time of erythrocytes was obtained by a time series cross-correlation of the two signals using an automated digital cross-correlation system.…”

“…Inulin was determined with the anthrone method (15 (2) Total papillary blood inflow was calculated as the product of average value of QDVR multiplied by the total number of functioning DVR of 906; and total papillary outflow was calculated from QAVR and number of functioning AVR of 2,038. The number of DVR and AVR were obtained from the total number of VR of 2,944 (7) at the base of the exposed papilla, and the functional ratio of AVR to DVR of 2.25 (8) was obtained at the same location. The volume of fluid reabsorbed in the exposed papilla and removed by VR was taken as the difference between inflow and outflow of blood (7,8).…”

“…We recently adapted videomicroscopy to study blood flow in the renal papilla. This method combined with modern fluorescence techniques (6) allows a continuous and quantitative measurement of blood flow in the exposed renal papilla in the rat (7,8).…”