SUBSTRATE UPTAKE AND UTILIZATION BY THE KIDNEY OF FED AND STARVED RATS IN-VIVO

In order to obtain information (1) on the quantitative contribution of various circulating substrates to renal metabolism and (2) on the rel ative importance of net luminal and basolateral transport for substrat e uptake, we have precisely quantified the renal blood flow, the urina ry flow, and the rates of substrate handling by the kidney of anesthet ized fed and 72-hour-starved rats. For this, the concentration of twel ve metabolites were simultaneously measured in arterial and venous who le blood and plasma as well as in urine of each rat thanks to the use of microassays based on enzymatic cycling. In fed rats, the main poten tial energy sources were glucose and lactate followed by fatty acids, ketone bodies, citrate and glycerol. and a large inhibition of lactate utilization. The net peritubular uptake of acetoacetate, citrate, gly cerol and free fatty acids demonstrated on both nutritional states was increased by starvation only for glycerol and free fatty acids; net p eritubular efflux of both beta-hydroxybutyrate and ammonium ions was s timulated whereas that of glutamine was converted into net peritubular uptake by starvation.