Effects of<scp>dl</scp>-2-hydroxy-4-methylthiobutyrate on the first-pass intestinal metabolism of dietary methionine and its extra-intestinal availability

The present study was conducted in a one-factorial arrangement to determine the effects ofdl-2-hydroxy-4-methylthiobutyrate (dl-HMTB) on the first-pass intestinal metabolism of dietary methionine and its extra-intestinal availability. Barrows (n6; aged 35 d; weight 8&#183;6 kg), implanted with arterial, portal, mesenteric and gastric catheters, were fed a diet containingdl-methionine (dl-MET) ordl-HMTB once hourly and infused intramesenterically with 1 %p-aminohippurate and intragastrically with [1-13C]methionine at 7&#183;0 μmol/kg body weight per h. Arterial and portal blood samples were taken at hourly intervals until 6 h of tracer infusion and pigs was then killed for collection of muscle, intestine, liver and kidney samples. The net portal appearance of methionine, expressed as the fraction of ingested directly availablel-methionine, was higher (P dl-HMTB than in thedl-MET diet, and there was no difference (P = 0&#183;26) in the fractional portal balance of [1-13C]methionine between the diets. [1-13C]methionine enrichment (tracer:tracee ratio; mol/100 mol amino acid) in the jejunum, arterial and portal plasma, liver, kidney and muscle was also not different (P&gt;0&#183;05) between the groups. Over the 6 h period after the start of feeding, the average concentration of citrulline both in the arterial and portal plasma was higher (P dl-HMTB than in thedl-MET group, and arterial plasma ornithine and taurine concentration was also higher (P dl-HMTB than in thedl-MET group. However, plasma urea concentration both in the arterial and portal vein was lower (P dl-HMTB than in thedl-MET group. These results suggested that the potential difference in the first-pass use of methionine by the intestine between thedl-HMTB anddl-MET diets might affect intestinal and systemic metabolism of other amino acids, which may provide new important insights into nutritional efficiency of different methionine sources.