Portal-drained visceral metabolism of 3-hydroxybutyrate in sheep

The present experiment was conducted to study the impact of portal-drained visceral (PDV) metabolism of arterial 3-OH-butyrate on estimates of the portal recovery of intraruminally infused butyrate. Three multicatheterized and rumen-fistulated Leicester ewes were subjected to three intraruminal infusion protocols in a Latin square design: control (C; water), butyrate (B; 20 mmol x h(-1)), and butyrate (20 mmol x h(-1)) + propionate (40 mmol x h(-1)) (BP). During the experiments, the sheep were infused with 1,2,3,4-13C4-D-3-OH-butyrate in a mesenteric vein. Portal recoveries of intraruminally infused butyrate and propionate were obtained by comparing Treatments B and BP, respectively, with Treatment C. The portal net appearance of butyrate and the portal net appearance of butyrate + 3-OH-butyrate accounted for 20 +/- 2% and 48 +/- 14% of intraruminally infused butyrate, respectively. Metabolism by the PDV tissues accounted for 32 to 44% of the whole-body irreversible loss rate of 3-OH-butyrate (12.0 to 24.7 +/- 0.5 mmol x h(-1)). The portal net appearance of butyrate plus the unidirectional PDV output of 3-OH-butyrate accounted for 62 +/- 5% of the intraruminally infused butyrate, and this estimate was comparable to the portal recovery of intraruminally infused propionate (62 +/- 7%). The results from the present study show that the extent of epithelial butyrate oxidation is overestimated and the portal recovery of butyrate carbon underestimated if only portal net appearance rates of butyrate and 3-OH-butyrate are considered.