ERYTHROCYTE VELOCITY IN VASA RECTA - EFFECT OF ANTI-DIURETIC HORMONE AND SALINE LOADING

Erythrocyte velocities were determined in vasa recta capillaries of the exposed renal papilla in 35 Munich-Wistar rats anesthetized with Inactin. The ability of the video velocity-tracking system of Intaglietta et al. to detect induced changes in erythrocyte velocity as well as the reproducibility of the measurements by an independent investigator were established. Erythrocyte velocity was determined in hydropenic rats before and after saline diuresis and in water-diuretic rats before and after antidiuretic hormone-induced antidiuresis to study the effects of contrasting diuretic states. Mean erythrocyte velocity increased following saline diuresis from 0.30 .+-. 0.02 to 0.39 .+-. 0.04 mm/s (SE) (P < 0.05) in male rats, but did not change significantly in females (from 0.35 .+-. 0.03 to 0.36 .+-. 0.05 mm/s). The disparity in results between male and female rats was not abolished by ovariectomy. Urinary osmolality rose from 121 .+-. 21 to 558 .+-. 40 mosmol/kg H2O (P < 0.001) following antidiuretic hormone administration and fell to 180 .+-. 41 (P 0.001) with return to water diuresis. Erythrocyte velocity remained unchanged throughout the 3 periods. Saline diuresis was associated with a significant increase but antidiuretic hormone-induced antidiuresis had no effect on erythrocyte velocity in vasa recta.