Effects of Hypertonic Mannitol on Renal Vascular Resistance.

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Abstract
Summary and conclusions The renal hemodynamic effects of mannitol were studied in dogs by infusing one kidney in situ with a controlled sinusoidal flow pump, observing changes in pressure, and calculating changes in renal vascular resistance. Intravenous infusions of hypertonic mannitol consistently resulted in diminished renal vascular resistance, both before and after blockade of renal nerves and autonomic ganglia. Decreased renal vascular resistance was also addition of mannitol, dextran, and after addition of mannitol, dextran, or saline into the renal perfusion circuit. When hind limb vascular resistance was measured, it too was decreased by intravenous mannitol. These decreases in vascular resistance correlated with diminished hematocrits of the perfusion fluids. In cross circulation experiments in which whole blood from a donor dog which had received mannitol or dextran intravenously was used as the renal perfusion fluid in the recipient dog, decreased renal vascular resistance was observed. However, when whole blood was infused intravenously to intact preparations, renal resistance was not lowered. These results are considered consistent with the hypothesis that the decrease in renal vascular resistance produced by hypertonic mannitol is not mediated via the autonomic nervous system and is probably due to a combination of decreased blood viscosity and renal vasodilation. The former results from decreased hematocrit, and the latter may be due to decreased transmural vascular pressure associated with diuresis or the presence of a circulating renal vasodilating substance.

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