Insulin assays and light microscopical studies of digestive organs in protostomian and deuterostomian species and in coelenterates

Abstract

Acid alcohol extracts of the digestive tract of the deuterostomian chordate Ciona intestinalis (a tunicate) and that of the protostomian invertebrates Buccinum undatum, Pecten maximus, and Eledone cirrosa (three molluscs), as well as of the hepatopancreas of Carcinus maenas (a crustacean arthropod) showed insulin activity when tested by the mouse hemidiaphragm insulin assay. The activity in the extracts from Ciona, Buccinum, and Eledone was neutralized by antisera to ox and chicken insulins, but not by antiserum to cod insulin, proving that insulin is present in these three species. The cellular site of this insulin production could not be demonstrated with certainty by conventional histological and histochemical procedures for light microscopical analysis of vertebrate islet parenchyma. Ordinary goblet cells and adjacent coarsely granulated cells seemed to be the only kinds of cells in the mucosa of the digestive canal that showed β-cell staining reactions with aldehyde-fuchsin, chromehematoxylin, and pseudoisocyanin, and that occurred in quantities roughly proportional to the insulin yields. In the intestinal submucosa of Pectan maximus and in the hepatopancreas of the two crustacean arthropods Homarus gammarus and Carcinus maenas, however, scattered dark epithelial cells showed β-cell staining characteristics without any obvious association to cells with typical goblet cell features. Possibly except for an acinar gland in the stomach wall of the whelk and crab, no α 1- or α 2-cells were found in the mucosa of the alimentary tract and in the parenchyma of associated glands in any of the species studied, and the sulfide-silver procedure for detecting heavy metals in these structures gave consistently negative results. Tissues from two cnidarian species, Aurelia aurita and Metridium senile, were devoid of cells that resembled mammalian α- or β-cells, and acid alcohol extracts of these tissues did not contain detectable insulin activity.