To establish a mechanism for the effect of diet therapy on glucose tolerance in maturity-onset diabetes, insulin binding to peripheral mononuclear cells was compared with the results of 100 g-O-GTT and insulin sensitivity tests. A half ng per ml of ¹²⁵I-insulin specific binding to 10⁷ cells was tested in 16 normal subjects, and 18 with maturity-onset diatetes. In the latter, the tests were repeated after a month of diet theray.
In the 18 with untreated diabetes, the insulin sensitivity index (ISI), insulin binding, and its binding sites were decreased significantly compared to those of the normals (p<0.05). Successful diet therapy as proven by body weight loss and by reduced ΣBS, was accompanied by increased ISI, insulin binding, and its binding sites. A significant correlation was observed between ISI and insulin binding after the therapy. However, no statistical correlation was found between insulin binding and the level of fasting serum insulin or ΣIRI during O-GTT.
In conclusion, it can be said that:
1) Decrease of insulin receptor may play a significant role in the progression of glucose intolerance in maturity-onset diabetes.
2) Increases in cellular insulin binding and in insulin sensitivity are important in the improvement of glucose intolerance seen after diet therapy.