Amines and the rat exocrine pancreas: (2) Effects of receptor blockers on turnover of L-5HTP.

The metabolism of L-5HTP by the rat exocrine pancreas, and effects of blockers on the metabolism were studied by fluorescent histochemical and chemical methods. Histochemically, 5-hydroxytryptamine (5-HT) blockers (methyserigide and cyprohepatdine) and dopamine (DA) blockers (haloperidol and sulpiride) produced no apparent changes in fluorescence pictures after injection of L-5HTP. alpha-blockers (phenoxybenzamine and phentolamine) and monoamine oxidase (MAO) inhibitor (iproniazide) produced an increased accumulation of 5-HT fluorescence in the apical regions of acinar cells where the zymogen granules are stored. Chemically, the 5-HT blockers decreased the 5-HT content after injection of L-5HPT. Sulpiride had no effect. Haloperidol decreased the 5-HT content. MAO inhibitor resulted in a vast accumulation of L-dopa: e.g. (1) L-5HTP was more slowly eliminated, and (2) 5-HT blockers produced a decreased content of 5-HT after injection of L-5HTP, in contrast to the finding that DA-blockers produced an incresed content of DA after injection of L-dopa. The mechanism responsible for the differences is discussed in relation to the possible pharmacological effects of L-5HTP and L-dopa on the secretion from the exocrine pancreas of rats.