Carbohydrate Metabolism in Pregnancy. XV. Plasma C-Peptide during Intravenous Glucose Tolerance in Neonates from Normal and Insulin-treated Diabetic Mothers*

Abstract

Basal values for C-peptide and the responses to intravenous glucose have been examined 2—4 h after birth in nine infants from normal and nine infants from diabetic mothers (IDM) (including eight who were being treated with insulin antepartum). Potentially cross-reacting antibody-bound proinsulin was removed prior to C-peptide estimations. Values for basal plasma glucose and fractional rates of glucose disposition (K_t) were inversely correlated in normal and IDM. Mean basal plasma glucose levels were significantly lower in the IDM. Although basal Cpeptide values did not differ significantly in the two groups,C-peptide/glucose ratios were significantly higher in IDM. After glucose administration, C-peptide and immunoreactive insulin increased in parallel in the normal infants, with peak values for both peptides being observed in the late plasma specimens. In contrast, in five IDM, maximal increments in C-peptide occurred in the earliest plasma specimen secured after glucose administration,i.e., at +2 or +10 min. Values for K_t in these five IDM exceeded the highest rates found in the other IDM and in the normal infants. For the IDM, but not the normal infants, basal C-peptide correlated with the net increments in plasma C-peptide during the first 10 min after glucose administration, and the 10-min Cpeptide increments correlated with K_t. These relationships suggest that the augmented basal β cell function in the offspring of some insulin-treated mothers may contribute, at least in part, to their heightened acute secretory capacity for insulin and that the greater acute islet responsiveness may, in turn, be linked to their increased capacity for glucose disposition.