Distribution and morphometric quantitation of pancreatic endocrine cell types in the frog, Rana pipiens.

Cells reactive to anti-anglerfish insulin, anti-porcine glucagon, anti-synthetic somatostatin, and anti-bovine pancreatic polypeptide were identified in adult Rana pipiens male pancreases using peroxidase anti-peroxidase immunohistochemistry. Insulin positive cells are columnar shaped and arranged in cords. Glucagon positive and somatostatin positive cells are located around the core of insulin positive cells. Isolated cells and clusters of cells of only one cell type are also found. Adjacent sections stained with anti-glucagon and anti-bovine pancreatic polypeptide showed that glucagon positivity and pancreatic polypeptide positivity are found in the same cells. Comparison of double stained adjacent sections confirmed the presence of these two antigens in the same cells, and further showed the occasional presence of cells which are positive to only glucagon or pancreatic polypeptide. Staining of rat pancreas with these two antisera showed that glucagon and pancreatic polypeptide are present in two distinct cell populations. Morphometric quantitation of immunohistochemically stained sections of Rana pipiens pancreases showed that about 2% of the pancreas is endocrine tissue. Of this, 43% is comprised of insulin positive cells, and 43% is occupied by glucagon-pancreatic polypeptide positive cells. Somatostatin positive cell occupy about 14% of the total islet volume. The presence of glucagon and pancreatic polypeptide in the same cell population in the frog, but in different cell populations in mammals, may reflect special functional adaptation in this species, or a close relation of these two hormones and their cells of production during evolution.