Transport of amino acids in whole blood and plasma of sheep

Comparisons of amino acid transport in both whole blood and plasma were made across the portal-drained viscera, liver, kidneys, and hindquarters in sheep. Lyophilized samples could be stored at -20 degrees C for up to 17 wk with little or no changes observed on reanalysis. Only glutamine, taurine, and serine showed any loss (18, 23, and 16%) over a 3.5-yr period. However, there was no concomitant rise in glutamate over the same period, suggesting that glutamate does not simply deamidate. There were no differences in arterial concentrations of alanine, citrulline, isoleucine, and valine between whole blood and plasma. However, glutamate, asparagine, glycine, serine, threonine, taurine, ornithine, leucine, lysine, phenylalanine, and tyrosine were higher in whole blood compared to plasma, and glutamine and arginine were lower. Whole blood and plasma fluxes for all amino acids were positively correlated, and there were no differences in their regression lines among tissues. Plasma, however, underestimated amino acid transport glutamine, glutamate, and taurine at greater rates than plasma. It is concluded that blood cellular transport, per unit volume, was always concomitant to and usually at the same rate as plasma transport over all tissues measured. Plasma therefore reflects amino acid transport but underestimates total transport to about the extent of the packed cell volume and in cases of glutamine, glutamate, and taurine, perhaps even more.