1. After operation, changes in nitrogen metabolism occur. Although increased flux of amino acids from peripheral to splanchnic organs after operation has been described, substrate utilization by the individual organs in the splanchnic area is less well characterized. We were specifically interested in substrate flux across the spleen as it is an organ with important immunological functions.

2. Therefore, hindquarter, gut, spleen and liver fluxes of amino acids, ammonia, glucose, lactate and blood gases were measured for 4 days after a standard operation in pigs. In a separate control group, fluxes were measured 2–3 weeks after this operation and these values were assumed to represent the normal situation.

3. One day after operation, the hindquarter effluxes of glutamine, alanine and several essential amino acids were increased (P<0.001), but these normalized at the end of the observation period. In the same period, liver glutamine uptake increased (P<0.01), concomitantly with increased HCO-3, glucose and urea production, which also normalized. Portal drained viscera ammonia production decreased, concomitant with decreased glutamine uptake (P<0.001). After operation, the splenic release of ammonia increased sevenfold (P<0.05) and that of lactate increased from −158 ± 544 to 3294 ± 642 nmol min−1 kg−1 body weight (P<0.001). Glucose uptake increased from −964 ± 632 to −3933 ± 1524 nmol min−1 kg−1 body weight and glutamine efflux (391 ± 143) reversed to uptake (−752 ± 169 nmol min−1 kg−1 body weight) (P<0.001).

4. The experiments show that after operation in the pig, amino acid flow is from peripheral tissue to liver, probably for gluconeogenesis. The increased postoperative splenic metabolism possibly represents an indication of increased substrate utilization by the immune system.

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