Vascular resistance changes produced by hyperosmotic solutions

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Abstract
Isolated dog kidneys were perfused with cold solutions containing electrolytes and colloid. These solutions, when made hyperosmotic by adding mannitol or glucose, produced an increase in perfusate flow. The addition of urea or thiourea to the perfusate had little effect. Epinephrine produced no changes in flow resistance when injected into the renal artery at temperatures below 10°C. The vascular resistance changes produced by mannitol were unaffected by ureteral occlusion and distension of the nephrons. Hyperosmotic mannitol solutions also produced large changes in urine flow and glomerular filtration rate which were opposite to vascular flow changes, suggesting that a large resistance change occurred on the efferent side of the glomerulus. It is suggested that hyperosmotic mannitol and glucose solutions produce a fluid shift across some barrier. This shifting fluid alters flow resistance by lumen restriction. This barrier does not have the characteristics usually ascribed to the glomerular membrane nor is it likely that these changes are due to changes in nephron volume.

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