Monoamines in the pancreatic islets of the mouse. Subcellular localization of 5-hydroxytryptamine by electron microscopic autoradiography.

Abstract

By application of autoradiographic technique the cellular and subcellular distribution of radio-activity in mouse pancreatic islets was investigated following intravenous administration of3H-5-hydroxytryptophan. Autoradiographic silver grains, most of which probably represent 5-hydroxytryptamine formed from the labelled precursor, appeared over A2 and B cells, whereas very few grains were recorded over A1 cells at any time investigated (20 min–16 hours) and also when monoamine oxidase was inhibited. Quantitative analysis of autoradiographic sections revealed that the concentration of silver grains over the specific granules of A2 and B cells was 5–10 times higher than over the remaining parts of these cells. In A2 cells the highest grain count was recorded at 20 minutes, in B cells at 1 hour after the injection of label. After 8 hours very few, and after 16 hours no silver grains appeared over islet cells. Inhibition of monoamine oxidase caused an increased retention of label over islet cells, most pronounced over A2 cells. Pretreatment with reserpine abolished the autoradiographic reaction.