Absorption and metabolism of benzoic acid in growing pigs

Dietary benzoic acid (BA) supplementation causes a pronounced reduction in urinary pH but only small changes in blood pH. The present study aimed to investigate the portal absorption profile, hepatic metabolism of BA, and renal excretion of hippuric acid (HA) underlying the relatively small impact of BA on systemic acid-base status. Eight growing pigs (BW = 63 +/- 1 kg at sampling) fitted with permanent indwelling catheters in the abdominal aorta, hepatic portal vein, hepatic vein, and mesenteric vein were allocated to 4 sampling blocks and randomly assigned to control (CON; nonsupplemented diet) or BA supplementation (B; control diet + 1% BA top-dressed). Feed intake was restricted to 3.6% of BW and the ration divided into 3 equally sized meals offered at 8-h intervals. Blood pH (7.465 and 7.486 +/- 0.004) and urinary pH (4.99 and 7.01 +/- 0.09) were less (P = 0.03 and P < 0.01) in B compared with CON. The arterial concentration, net portal flux, and net hepatic uptake of BA increased (P < 0.01) in B compared with CON. The net portal flux of BA increased (P < 0.01) after feeding with B, but remained positive (P < 0.01) at all sampling times (n = 8). Recovery of dietary BA as increased net portal flux and hepatic uptake of BA was 87 +/- 5% and 89 +/- 15%, respectively. The recovery of dietary BA as urinary excretion of BA and HA was 0.08 +/- 0.02% and 85 +/- 7%, respectively. It is concluded that the small impact of BA supplementation on systemic acid-base status was caused by a protracted BA absorption and efficient hepatic extraction and glycine conjugation in combination with efficient renal clearance of HA. Together, these physiological mechanisms prevented major BA and HA accumulation in body fluids.