ACUTE REGULATION OF INSULIN RELEASE BY THE PITUITARY GLAND IN RELATION TO HYPERINSULINAEMIA AND OBESITY

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Abstract
The pituitary glands from mice rendered obese by gold thioglucose treatment and by dietary manipulation, and pituitary glands from lean mice after a high food intake or a glucose load, were shown to stimulate insulin secretion from isolated pancreatic islets. The insulin releasing activity of pituitary glands from obese (ob/ob) mice was reduced by fasting for 24 and 48 h. Results obtained with pituitary glands from ob/ob and from lean ob/ + and + /+ mice suggest that the insulin releasing property manifests a gene dosage effect. Pituitary glands from 3-week-old (young) ob/ob mice stimulated insulin secretion to the same extent as pituitary glands from 3-month-old (adult) ob/ob mice. The pancreatic islets of young ob/ob mice were shown to be somewhat more responsive to stimulation by the pituitary factor than were lean ob/ + or + / + islets from this age group. The concept that high insulin level, partly under pituitary control, and high caloric intake may be interlinked and may, in combination, be a major factor in producing obesity is discussed. Furthermore, it is suggested that the pituitary insulin releasing factor may play a role in the early development of obesity in the animal models studied.