In vitro transfer of L-alanine, L-histidine and carnosine across the rumen epithelium of sheep

The objectives of this, experiment were to study the transfer of free amino acids (alanine, histidine) and dipeptide (carnosine) of different concentrations from the mucosal to the serosal side of the rumen epithelium after 60 min of incubation in vitro. Experiments were carried out on the rumen epithelium taken from twenty four young sheep. The transfer of alanine and carnosine was not significantly different between concentrations of 0.5 and 1 mmol.l(-1). Only the transfer of histidine increased in both cases from 0.036 +/- 0.007 to 0.074 +/- 0.002 mmol.l(-1). The transfer of histidine rose with increasing concentration from 1 mmol.l(-1) to 5 or 10 mmol.l(-1) (from 0.074 0.002 to 0.191 +/- 0.012 or 0.449 +/- 0.013 mmol.l(-1)). Alanine increased from I to 5 mmol.l(-1) (from 0.037 +/- 0.005 to 0.163 +/- 0.007) but the 10 mmol.l(-1) concentration did not affect transfer of alanine (0.184 +/- 0.054 mmol.l(-1)). The opposite result was found in carnosine. The 5 mmol.l(-1) concentration did not affect the transfer of carnosine compared with 1 mmol.l(-1) (0.048 +/- 0.004 v.s. 0.036 +/- 0.005 mmol.l(-1)) but the transfer of carnosine was six times higher in the 10 mmol.l(-1) versus 5 mmol.l(-1) (0.273 +/- 0.055 v.s. 0.048 +/- 0.004 mmol.l(-1)). The results of this study indicate that amino acids can transfer more easily through the rumen wall in lower initial concentrations than the dipeptide carnosine can.