Fluorescence histochemical observations on the uptake and metabolism of tryptophan in the endocrine cells of the hypophysis.

The present work was undertaken to study the significance of the uptake of precursors of biogenic amines, L-dopa and 5-hydroxytryptophan, in the cells of the pars distalis of the mammalian hypophysis. The results of our own earlier studies suggested that L-dopa and 5-hydroxytryptophan may be taken up by the cells of the pars distalis which possess in their cell membranes the system for active transport of amino acids. In the present study, an effort is made to demonstrate the uptake of the amino acid, tryptophan, which is generally used for the protein synthesis. It was observed that after the administration of tryptophan the small cells of the pars distalis exhibited specific formaldehyde-induced fluorescence characterizing tryptophan and its metabolites. It was also noted that after the administration of tryptophan blue fluorescence was observed in some cells of the pars distalis prior to formaldehyde vapour treatment. The blue fluorescence may be due to the presence of quinoline metabolites of tryptophan formed in the cells. This new observation offers good possibilities to study the metabolism of tryptophan at the cellular level. The results of the present work support the suggestion that L-dopa or 5-hydroxytryptophan is taken up by cells of the pars distalis which possess the mechanism for general active transport of amino acids in the cell membrane.