Ultrastructure of B-cells of Langerhans islets in rats after the administration of L-leucine.

The results of studies with electron microscope supported the earlier biochemical findings on the stimulation of insulin secretion with the aid of L-leucine. The changes of the cell organelles of B-cells showed that both the synthesis and the release of insulin were activated, while the secretion by specific granules was unchanged. The stimulation of B-cells was accompanied by numerous membrane-like structures ("myelin-like figures") which were presumably formed from the endoplasmic reticulum.