Comparative absorption of 2-hydroxy-4-(methylthio)-butanoic acid and L-methionine in the broiler chick

The absorption of [1-14C]2-hydroxy-4-(methylthio)butanoic acid (HMB) and L-methionine (L-Met) was evaluated in the broiler chick. Methods included in vitro intestinal tissue uptake and appearance in the plasma from ligated intestinal segments in situ, and from crop intubations. Intestinal uptake of L-Met was partially inhibited with 2,4-dinitrophenol, while HMB uptake was unaffected. The uptake of L-Met conformed to Michaelis-Menten kinetics except that no plateau was reached. This indicated that L-Met absorption may be accomplished by both concentration and energy-dependent processes. The in vitro uptake of HMB in relation to concentration was linear indicating that its absorption was concentration dependent. Absorption of HMB and L-Met after crop intubation indicated higher plasma concentrations of HMB than of L-Met, particularly at higher doses. Both compounds were absorbed at similar rates at concentrations 50-100 times below physiological concentrations and absorption rates were different at different small intestinal locations. These results indicate that the ability to use HMB as a source of methionine would not be limited by absorption.