Abstract
Seltzer et al. first proposed the insulinogenic index (I. I.), the ratio of Δinsulin to Δglucose after glucose loading, as an index of insulin secretory capacity in terms of a rise in blood glucose. They reported that I. I. tended to decrease shortly after glucose loading in mild diabetics, as compared with normal subjects, and that this decrease in I. I. was more remarkable in moderate diabetics.
The present study was carried out to investigate the I. I. in patients with impaired carbohydrate metabolism caused by endocrine disorders or liver diseases, which is considered to be so-called “secondary diabetes”. The I. I. was calculated on the basis of increments in blood glucose and plasma IRI 30 min after the oral administration of 50 g of glucose. In normal subjects, the I. I. was 1.42, whereas it was 0.44 or 0.09 in mild or moderare to severe diabetics, respectively. In hyperthyroidism, those who showed a glucose tolerance curve of “oxyhyperglycemia” type had an I. I. of 1.11, while those with a diabetic glucose tolerance curve had an I.I. of 0.70. I.I.'s were 0.44 and 0.14 in acromegalics with mild glucose intolerance and with severe glucose intolerance, respectively. In patients with Cushing's syndrome, steroid diabetes and pheochromocytoma, they were 0.98, 1.07 and 0.16, respectively. Patients with acute hepatitis, chronic hepatitis and liver cirrhosis gave I. I'.s of 0.93, 1.35 and 0.59, respectively.
These results suggest that the I.I. is higher in secondary diabetes than in primary diabetes, except for some acromegalic patients with severe glucose intolerance and patients with pheochromocytoma in whom the inhibition of insulin secretion by catecholamines is considered to be the major cause of abnormal glucose metabolism. It appears, therefore, that the I. I. is an useful tool for the differential diagnosis of primary and secondary diabetes.
