Metamorphic Changes in the Blood Sugar and the Pancreatic Islets of the Frog, Rana Clamitans.

The pancreatic islets of several species of amphibians undergo differentiation from a larval to an adult type at the time of metamorphosis (Frye, ’59). Some of the changes include an increase in the amount of cytoplasm, an increase in cytoplasmic basophilia and afFinity for standard pancreatic stains, lengthening of the cells and pronounced polarization toward the capillaries, and an accumulation of histochemically demonstrable insulin. This description pertains to the insulin-secreting beta cell, which is the only, or strongly predominant cell type in the amphibian islet (Miller, ’60). The total picture is suggestive of a functional differentiation of the beta cell during the period of metamorphosis. If this interpretation is correct the greater part of larval life must be spent without insulin, which is an indispensable factor in the blood sugar homeostasis of adult vertebrates. Two other lines of evidence are in accord with the histological and histochemical data: (a ) extirpation of the dorsal pancreatic rudiment of embryos of the salamander, Ambystoma punctatum an operation which results in total absence of islets of Langerhans in the larva has no effect upon larval survival or the rate of growth and differentiation (Frye, ’62); (b) in Rana pipiens larvae subjected to subtotal pancreatectomy no significant elevation of blood glucose values was observed, nor was growth inhibited so long as digestion was not impaired (Frye, unpublished data). The purpose of this report is to describe some experiments which test the hypothesis that the larval pancreatic islets are non-functional or weakly functional and only attain full functional status after metamorphosis.