Number and size of islets of Langerhans in pregnant, human growth hormone-expressing transgenic, and pituitary dwarf mice: effect of lactogenic hormones.

To determine the effects of lactogenic hormones on pancreatic islet size and numbers, islets of 3-month-old female mice were intravitally stained by an ip injection of an alkaline-alcohol solution of diphenylthiocarbazone (dithizone; 100 micrograms/g BW). After 15 min, animals were killed, and pancreases were removed, diced, cleared in glycerol, and whole mounted on slides. Major and minor axes of Zn dithizoate-stained islets were measured at x40 magnification. Islet areas and volumes were calculated. Animals and appropriate controls studied included 16-day pregnant, two lines of human GH-expressing transgenic, and two lines of pituitary PRL- and GH-deficient dwarf mice. Islet numbers per pancreas ranged from about 500-1200 in all groups except the transgenic mice, in which two of five animals in one group and one of five in the other showed significant increases in islet numbers (> 3 x SD control mean). In all cases, significant (P 150 microns) islets. Our results with dwarf mice show that maintenance of islet numbers is not dependent upon pituitary PRL or GH; however, results with transgenic mice suggest that prolonged high levels of lactogens may induce islet neogenesis. The islet area and volume results for all of the mice studied support the hypothesis that lactogenic hormones are potent regulators of islet mass.