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Recent reports have indicated that genetically obese hyperinsulinemic mice (ob/ob) and Zucker rats (fa/fa) compared with their lean controls have elevated levels of pituitary and plasma B-endorphins, opiates that can stimulate insulin secretion. In this study we have measured opiate levels by a radio-receptor assay in gastro-intestinal tissues and pancreas in ob/ob and fa/fa animals and their controls. Ob/ob mice showed significantly higher levels than control mice (+/+) in most gastro-intestinal tissues and pancreas. Levels in fa/fa rats did not differ from their controls. Radioimmunoassay of pancreas for B-endorphins, revealed higher levels in ob/ob vs +/+ mice, while there was no difference in the obese and lean rats. Fasting tended to decrease gastro-intestinal opioids in mice, while B-endorphin levels rose. It is concluded that opiates may play a significant role in the obesity of the ob/ob mouse and that this genetic obesity differs from that in Zucker rats.

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