This study was designed to assess the interorgan relationships of glutamine and alanine in the conscious, overnight fasted dog, and to determine changes which occur with progressive fasting. Dogs were fasted for 18 hr (n = 6), 48 hr (n = 6), and 96 hr (n = 6) prior to the study. Catheters had been previously implanted in the femoral artery, renal vein, portal vein, and hepatic vein, and were used for blood sampling at 30-min intervals during the 3-hr experimental period. Hepatic and renal blood flows were determined by indocyanine green and para-aminohippuric acid (PAH) extraction methods, respectively. Balance data (micromoles/kilogram/minute) were estimated by multiplying the appropriate arteriovenous concentration differences by blood flows. Hepatic uptake of glutamine decreased 50% after a 48-hr fast, and by 96 hr, the liver became a net producer of glutamine. Gut utilization remained constant throughout fasting. The kidney's utilization gradually increased with fasting. The hepatic extraction of alanine fell with fasting, declining to 40% of its original uptake at 96 hr. The gut's production of alanine fell during the first 48 hr of fasting, but remained stable thereafter. The kidney's production of alanine increased throughout the period of starvation. The arterial concentration of glutamine rose with fasting, while that of alanine fell even with a 48 hr fast. The liver, by becoming a net producer of glutamine, and the kidney, by increasing its production of alanine, decrease demands for peripheral release of these two amino acids, and thus may have protein-sparing actions during fasting.
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