Morphometric evaluation of B-cell function during glucose infusion in control and hyperresponsive rats.

According to their general appearance, the ultrastructural morphology of their organelles and their functional status, B cells can be divided into dark, unresponsive B cells with condensed mitochondria and narrow RER-cisternae, and pale activated B cells with orthodox mitochondria and distended RER. In control rats, during a three hour glucose infusion experiment, there is a shift from a majority of dark B cells to a majority of pale B cells, and a decrease in the proportion of dark and mixed islets in favour of the pale islets. No degranulation however (dark and light granules) occurs. In adult youngsters of severely diabetic mothers, known to be hyperresponsive to glucose stimulation, a more important mass of pale activated B cells is present in basal conditions, and is not augmented by stimulation. Dark and mixed islets are scarce in these animals and some degranulation occurs. The data illustrate that in control and in hyperresponsive rats, the B cells manage very well, to meet the increasing demand of insulin without any signs of exhaustion or damage. The data confirm in vivo, and at the morphological level, the concepts of functional heterogeneity and of dose-dependent recruitment of pancreatic B cells. Moreover functional heterogeneity of islets is suggested.