Tissue uptake of catechol and indole amino acids histochemical studies on the rat iris

Rat irises exposed to DOPA in vitro and subsequently treated with the histochemical technique of Falck and Hillarp for catecholamines show accumulation of a fluorescent formaldehyde condensation product within the capillary endothelial cells. A similar accumulation was observed when rat irises were exposed to 5-OH-Tryptophan and α-methyl-dopa but not after exposure to the corresponding amines. Fluorescent products were also observed in the same cells when control irises were treated with the trihydroxyindole histochemical reaction. It is concluded that certain catechol and indole amino acids accumulate within the endothelial cells of the rat iris capillaries in a manner similar to that observed in brain capillaries. Furthermore, small amounts of DOPA are probably present within these cells normally.