Effect of neutral alpha- and omega-amino acids and basic alpha-amino acids on uptake of L-histidine by intestinal mucosa, testis, spleen and kidney in vitro: a comparison with effect in brain.

1. The effect of the D- and L-isomer of neutral alpha-amino acids, of omega-amino acids, and of basic L-alpha-amino acids on uptake of L-histidine in vitro has been investigated in intestinal mucosa, testis, spleen and kidney cortex, and compared with the effect in brain.2. Neutral alpha-amino acids produced inhibition that was in general greater the longer the carbon chain of the inhibiting amino acid. There were minor variations with different tissues.3. omega-amino acids produced little or no inhibition, with only slight variation between tissues. There was a tendency towards less inhibition the longer the carbon chain.4. The effect of basic amino acids varied with different tissues. With one exception, all produced significant inhibition with intestinal mucosa and testis. With spleen and kidney, inhibition was slight or absent, and resembled the effect produced by the omega-amino acids. With brain (previously reported elsewhere) the short-chain amino acids produced considerable inhibition, those having longer carbon chains little or none.5. Proline produced significant inhibition in brain and spleen, but none in the other tissues. Tryptophan had no effect with kidney.6. The findings are considered as further evidence for a relation between the extent to which an amino acid can be taken up by a given tissue and the specificity of the transport systems in that tissue. They also support the view that the nature of certain transport systems may vary considerably between different tissues.