Serial measurements of the concentration of blood glucose from individual ammocoetes show that it is possible to reduce the hyperglycemia produced by handling the animals by gradually reducing the temperature of the environment before anesthetizing them. Using these precautions the blood glucose was found to be 49.5 mg/100 ml of blood (SE ± 1.76). Diabetic symptoms can be produced in ammocoetes by injecting glucose, glycine, or alloxan. Alloxan has been shown to exert its maximum effect at a dose of 50 mg/kg body wt. Low doses of all these substances produce a rise in blood sugar that is accompanied by glycosauria and by secretory activity in the glandular cells of the follicles of Langerhans. Ammocoetes exercise only a limited control over their blood glucose level under these conditions and lose glycogen from both the liver and muscles. It is possible to alleviate the diabetic effects of glycine or of combined injections of glycine and glucose by injecting mammalian insulin. This rapidly lowers the blood glucose, presumably by promoting glycogenesis since liver and muscle glycogen increase during the experiments. There is no increase in the secretory activity of the follicles of Langerhans under these conditions. Injections of glucagon or cobaltous chloride have no specific effect on blood glucose regulation or on the activity of the glandular cells of the follicles. These observations, together with those of previous workers, suggest that the cyclostomes can only produce insulin from glandular cells that are equivalent to the β cells of other vertebrates and in view of the primitive nature of the group and the simple organization of the islet tissue, it seems probable that a similar situation existed in the early vertebrates. © 1969.
