Abstract
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 cyproheptadine) and dopamine (DA) blockers (haloperidol and sulpiride) produced no apparent changes in fluorescence pictures after injection of L-5HTP. α-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-5HTP. Sulpiride had no effect. Haloperidol decreased the 5-HT content. MAO inhibitor resulted in a vast accumulation of 5-HT. Some differences were noted between the L-5HTP metabolism and that of L-dopa: e.g. (I) 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 increased 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.
