Splanchnic galactose extraction is regulated by coingestion of glucose in humans.

When compared with galactose alone, coingestion of glucose with galactose decreases plasma galactose. The objective of this study was to determine if this was due to increased peripheral clearance or increased first pass clearance of galactose. Five adult volunteers were studied on 2 occasions during infusion of [6,6-(2)H(2)]glucose and [1-(13)C]galactose and ingestion of galactose alone at 11, 22, and 33 micromol x kg(-1) x min(-1) or galactose plus glucose at 11, 22, and 33 micromol x kg(-1) x min(-1) of each sugar. At 33 micromol x kg(-1) x min(-1) of galactose alone (1) plasma galactose increased to 2.3 +/- 0.3 mmol/L and galactose rates of appearance (Ra) to 18.3 +/- 1.6 micromol x kg(-1) x min(-1); (2) plasma glucose and glucose Ra were unaffected; (3) splanchnic extraction of galactose plateaued at approximately 15 micromol x kg(-1) x min(-1); and (4) galactose became the primary source of glucose Ra (75% +/- 9%). Coingestion of glucose and galactose at 33 micromol x kg(-1) x min(-1) each resulted in (1) decreased plasma galactose (0.3 +/- 0.1 mmol/L) and galactose Ra (6.4 +/- 1.8 micromol x kg(-1) x min(-1)); (2) increased plasma glucose and insulin; (3) doubling of splanchnic extraction of galactose; and (4) decreased contribution of galactose to glucose Ra (11% +/- 4%). We conclude that coingestion of glucose with galactose increases the splanchnic extraction, but decreases the conversion of galactose to glucose.