Insulin Secretion by the Transplanted Neonatal Pancreas during Food Intake in Fasted and Fed Rats

In order to investigate the physiological role of the autonomic nervous system on insulin secretion, neonatal pancreases were implanted under the kidney capsule of alloxan diabetic rats, resulting in recovery from diabetes, with denervated insulin secreting tissue. Rats were also provided with permanent double cardiac catheters allowing simultaneous infusion and rapid blood sampling with free movement. Intracardiac glucose infusion caused, coincident with the rapid rise of blood glucose, an increase of plasma insulin in the first minute in both controls and transplanted rats. After ingestion of food plasma insulin in normal control rats increased in the first minute, and prior to the first rise of glucose, from 23 ± 2 mU/l to 66 ± 4 mU/l in the fed state, and from 9 ± 3 mU/l to 34 ± 3 mU/l after 24 h of fasting. In contrast, this response was absent in the transplanted animals. In the fed state maximum insulin responses were attained at 20 minutes and were 63 ± 10 mU/l for controls, 104 ± 15 mU/l for transplants and 20 ± 3 mU/l for rats which recovered from diabetes one week after alloxan. The concomittant glucose responses were 22 ± 2, 34 ± 3 and 45 ± 4mg/100 ml respecitively. Ingestion of a meal after fasting showed a similar decreased insulin response and insulinogenic index at t = 20 in both the transplanted and control group. Histology and electronmicroscopy of the transplanted pancreas showed vascularized groups of well granulated B-cells. The data of these experiments suggest that 1) The early insulin response after food intake is under direct control of the autonomic nervous system, 2) Glucose homeostasis is disturbed after transplantation, 3) Mainly humoral factors are responsible for the decreased insulin response after fasting.