Hyperproinsulinemia is not a characteristic feature in the offspring of patients with different phenotypes of type II diabetes.

OBJECTIVE: The purpose of this work was to study whether there are differences in plasma proinsulin levels and proinsulin-to-specific insulin ratio in the offspring of patients with different phenotypes of type II diabetes.
DESIGN: Eleven glucose-tolerant offspring of type II diabetic patients with deficient insulin secretion phenotype (IS group), nine glucose-tolerant offspring of patients with insulin-resistant phenotype (IR group), and fourteen healthy control subjects without a family history of diabetes were studied.
METHODS: Plasma specific insulin, plasma proinsulin, and plasma C-peptide levels were measured during a 2-h oral glucose tolerance test and during hyperglycemic clamp.
RESULTS: Plasma proinsulin levels during the oral glucose tolerance test and the hyperglycemic clamp did not differ among the study groups. The IR group had a lower fasting plasma proinsulin-to-specific insulin ratio (10.3+/-1.7%) than the control group (15.4+/-1.4%; P<0.05) and the IS group (18.6+/-2.7%; P<0.05). Furthermore, the IR group had lower plasma proinsulin-to-specific insulin ratio at 30, 60 and 90 min after the oral glucose load than the IS group. However, there were no significant differences in proinsulin-to-C-peptide ratio during the oral glucose tolerance test among the study groups. In stepwise multiple regression analysis, hepatic specific insulin extraction in the fasting state (beta =0.65; P<0.001) and fasting blood glucose (beta =0.32; P<0.05) together explained 52% of the variation in fasting plasma proinsulin-to-specific insulin ratio.
CONCLUSIONS: Hyperproinsulinemia is not a characteristic finding in glucose-tolerant offspring of type II diabetic probands with deficient insulin secretion or insulin-resistant phenotype. The differences in proinsulin-to-specific insulin ratios were most likely explained by different hepatic extraction among the study groups.