The Pancreatic Islets of Bony Fishes

Abstract

The biology of the fish endocrine pancreas is discussed from viewpoints of cytology, peripheral physiology, and control of islet secretion. The clear cell often described in Brockmann bodies is probably not a real entity, but the islets of many fish species probably contain a fourth granular cell type in addition to the usual population of A-, B-, and D-cells. Numerous studies employing islet cytotoxins and exogenous hormone treatments have been reported, but a unified concept of islet function in any fish species still does not exist. Recent data indicate that metabolic parameters other than blood sugar must be measured in order to obtain a more accurate assessment of islet function. The direct relationship of the nervous system to islet endocrine cells also raises questions regarding the control of islet secretion and necessitates consideration of laboratory conditions and seasonal or diurnal variation as probable influencing factors of islet activity.