Proinsulin is converted to insulin and C-peptide in the pancreatic islet cells; the latter two polypeptides are then secreted in equimolar concentration. Thus, measurement of C-peptide may provide an alternative means of studying B-cell function in pregnant, insulin-treated, diabetic patients and in their newborn infants (IDM). Using this approach, B-cell function was studied in eight normal, ten juvenile onset and five gestational diabetic patients at the time of delivery. Normal maternal and cord CPR (C-peptide immunoreactivity levels, mean ± SEM, were 1.5 ± 0.3 and 0.9 ± 0.1 ng/ml, respectively. In six of ten juvenile onset diabetics, CPR levels were undetectable, while in four CPR was elevated. Five gestational diabetic women had elevated CPR levels. Cord CPR levels were significantly higher in all IDM than in the normal controls. A prompt rise in CPR was seen following intravenous glucose load in four IDM. Gel filtration of selected sera demonstrated both C-peptide and proinsulin, the latter protein being bound to circulating insulin antibodies which have crossed the placenta. Thus, active B-cell secretion composed of proinsulin, C-peptide and presumably insulin is present during insulin therapy in gestational, in some juvenile-onset-diabetic, pregnant women and in their offspring.
Cord blood C-peptide: Glucose ratio ? A good indicator of B cell function in infants of diabetic mothers