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

Abstract

The present study was conducted in a one-factorial arrangement to determine the effects of dl-2-hydroxy-4-methylthiobutyrate (dl-HMTB) on the first-pass intestinal metabolism of dietary methionine and its extra-intestinal availability. Barrows (n 6; aged 35d; weight 86kg), implanted with arterial, portal, mesenteric and gastric catheters, were fed a diet containing dl-methionine (dl-MET) or dl-HMTB once hourly and infused intramesenterically with 1% p-aminohippurate and intragastrically with [1-13C]methionine at 70mol/kg body weight per h. Arterial and portal blood samples were taken at hourly intervals until 6h 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 available l-methionine, was higher (P<005) in the dl-HMTB than in the dl-MET diet, and there was no difference (P=026) in the fractional portal balance of [1-13C]methionine between the diets. [1-13C]methionine enrichment (tracer:tracee ratio; mol/100mol amino acid) in the jejunum, arterial and portal plasma, liver, kidney and muscle was also not different (P>005) between the groups. Over the 6h period after the start of feeding, the average concentration of citrulline both in the arterial and portal plasma was higher (P<005) in the dl-HMTB than in the dl-MET group, and arterial plasma ornithine and taurine concentration was also higher (P<005) in the dl-HMTB than in the dl-MET group. However, plasma urea concentration both in the arterial and portal vein was lower (P<005) in the dl-HMTB than in the dl-MET group. These results suggested that the potential difference in the first-pass use of methionine by the intestine between the dl-HMTB and dl-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. © 2010 The Author.