Effect of Tolbutamide on “Free” and “Complexed” Serum Insulin

Serum insulin levels have been determined in non-diabetics and non-insulin requiring diabetics during the oral tolbutamide test. Using diluted sera, with the addition of heparin to measure “free” and “complexed” insulin by the rat diaphragm insulin bioassay, there was little evidence that tolbutamide has any appreciable effect on the dissociation of “complexed” insulin by this method. Several patients appeared to have no “complexed” insulin in their sera at any time. Obese subjects had higher serum insulin levels than those of normal weight.