Splanchnic metabolism of amino acids in healthy subjects: Effect of 60 hours of fasting

Abstract

Brief starvation is accompanied by decreased circulating levels of most amino acids, which has been attributed to an increased splanchnic uptake of amino acids, primarily alanine, for gluconeogenesis. However, quantitative data on splanchnic exchange of amino acids and gluconeogenic precursors is lacking. Consequently, arterial concentrations and splanchnic exchange of whole blood amino acids, ketone bodies, glucose, and gluconeogenic precursors were measured in 16 prolonged fasted (60 to 64 hours) and 15 overnight fasted (12 to 14 hours) healthy, nonobese subjects. After the 60-hour fast net splanchnic glucose production decreased by 41% to 0.31 ± 0.02 μmol/L ( P < .001), whereas the splanchnic uptake of gluconeogenic precursors increased and could account for the total glucose output. Net splanchnic uptake of taurine, threonine, serine, glycine, lysine, histidine, and arginine rose significantly in response to fasting ( P < .05 to .01) due to increased splanchnic fractional extraction. Although the splanchnic fractional extraction of alanine was augmented by 40% ( P < .001), net splanchnic uptake was not influenced by fasting. Total net splanchnic uptake of amino acids increased by 68%, from 231 ± 44 μmol/min in the postabsorptive state to 388 ± 63 μmol/min (mean ± SEM) ( P < .05) in the 60-hour fasted state. However, only one half of this rise was accounted for by gluconeogenic amino acids.