A fixed dose of glucose, irrespective of body weight, used for i.v. glucose tolerance tests in rats with hypothalamic obesity and in non-obese control rats caused almost identical blood glucose increments in both kinds of rats, and the K values (coefficients of glucose assimilation) were not significantly different. Glucose doses proportional to body weight caused much larger increments of blood glucose in the obese animals but the K value was not significantly different from that for the controls.
On the other hand, the insulin sensitivity of obese rats was found to be less than that of control rats when a fixed dose of the hormone was given. When the insulin dosage was proportional to body weight, the fall of fasting blood glucose produced in the obese animals was not significantly different from that in the control group. In vitro, the diaphragm muscle of the obese animals was insensitive to the action of insulin as compared with controls. There was no evidence of insulin insensitivity of the obese animals' adipose tissue; the very low metabolic activity of the adipose tissue of both the control and obese animals may have been responsible. The interpretation of these findings is discussed in the light of similar work in human obesity.