Effect of osmolality on glucose metabolism in rabbit kidney cortex and medulla in vitro

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Abstract
Slices of rabbit kidney cortex and medulla were incubated aerobically in media of varying osmotic concentrations. When medium osmolality was reduced below 280–300 mosmoles/kg H2O, by means of decreased sodium chloride and sucrose concentrations, there was an osmotically determined increase in cortical glucose utilization and oxidation, lactate production, and slice weight. Between 280 and 300 mosmoles/kg H2O maximal cortical slice weight loss and inhibition of glucose metabolism occurred, with little further change when medium osmolality was increased to 415 mosmoles/kg H2O. With urea, slice weight and relatively maximal glucose metabolism were maintained at all medium osmotic concentrations between 67 and 548 mosmoles/kg H2O. In contrast, slices of kidney medulla revealed a capacity for extensive glucose oxidation in hyperosmotic media (1,066 mosmoles/kg H2O), while maximal lactate production occurred in hypoosmotic media (67 mosmoles/kg H2O). The findings are interpreted as suggestive of responsiveness of cortical and medullary intermediary metabolism to changes in the "effective" extracellular-to-intracellular osmotic gradient.