Uptake of DL-2-hydroxy-4-methylthio-butanoic acid (DL-HMB) in the broiler liver in vivo

The methionine source DL-2-hydroxy-4-methylthio-butanoic acid (DL-HMB; Alim et(TM) feed supplement) is widely used in the poultry industry. The purpose of this study was to determine the capacity of the broiler liver to remove DL-HMB from the circulation. Cannulae were implanted in the carotid artery and hepatic and hepatic portal veins in anesthetized male broilers (3.33 /-0.13 kg BW). In Experiment 1, birds (n=5) were infused with DL-HMB soluti ons (diluted in saline, pH 7.2 to 7.4) into the hepatic portal vein at rate s ranging from 4.4 to 22 mg/min per kg BW, whereas in Experiment 2, birds ( n=6) were infused with DL-HMB at rates ranging from 2.2 to 4.4 mg/min per k g BW. Plasma samples from each vessel were obtained before and after each 1 0-min DL-HMB infusion period with a 10-min clearance period allowed between each DL-HMB infusion. Regression analysis revealed a highly significant co rrelation in the amount Of DL-HMB entering the liver via afferent vessels ( afferent DL-HMB) and DL-HMB removed by the liver (y=0.86(x) - 173, r(2) = 0 .98). The slope of this regression indicates that 86% Of DL-HMB entering in afferent blood (i.e. from both the hepatic artery and hepatic portal vein) was removed or that the liver apparently metabolized 86% of the DL-HMB tha t entered the liver. The results indicate that the broiler liver has the ca pacity to remove DL-HMB from the circulation far in excess of that needed t o metabolize DL-HMB that would enter the liver following gastrointestinal a bsorption in birds fed a conventional poultry diet. In addition, present re sults implicate. the liver as a major site of removal from circulation and further metabolism Of DL-HMB in chickens.