Circadian variations in plasma immunoreactive insulin (IRI) and C-peptide concentrations in adult onset (type II) diabetes mellitus

Abstract

Plasma immunoreactive insulin (IRI), C-peptide and serum glucose concentrations were determined in 19 adult onset non-insulin dependent (type II) diabetics, in one adult onset diabetic on insulin and in 20 non-diabetic subjects matched for sex, age, weight and height. The subjects lived on a schedule of diurnal activity and nocturnal rest (21:00 to 06:00) at Berceni Clinical Hospital, Bucharest, Romania and ate three meals at 08:30, 13:00 and 18:30 and a snack at 10:00 (carbohydrate content: 50 gm, 65 gm, 60 gm and 25 gm respectively). Nine of the diabetic patients were on oral hypoglycemic agents (tolbutamide or meguan), the others were controlled by diet only. Blood was sampled beginning at 08:00 at 4 hourly intervals over a 24-hour span. The circadian variations of IRI, C-peptide and serum glucose were analysed by population mean cosinor. The non-insulin dependent diabetic subjects as a group and the matched non-diabetic subjects showed under the conditions of this study circadian variations in serum glucose, plasma IRI and C-peptide which were identical in timing (acrophase) and amplitude and with the exception of the much higher serum glucose concentrations in the diabetics, not significantly different in the circadian mean concentration (or mesor). The diabetics on oral hypoglycemic agents if investigated separately showed in spite of identical serum glucose concentration a statistically significantly lower circadian mean IRI and C-peptide concentration than either non-diabetic subjects or the diabetics treated by diet only. Acrophase and relative amplitude remained unchanged. Adult onset non-insulin dependent (type II) diabetics maintained on diet only show the same circadian variations in plasma IRI and C-peptide as non-diabetic matched for sex, age, height and weight. The adult onset diabetic on insulin showed an extremely high serum glucose concentration which varied in its timing over the 24-hr span similar to the other subjects. His plasma IRI concentration was about ten times that of the non-diabetic or other diabetic subjects in this study. There was no statistically recognizable circadian variation of IRI. In contrast C-peptide was found at the same concentration as found in the other two groups and showed in all rhythm parameters an identical circadian variation. The circadian acrophase of plasma IRI and C-peptide concentrations in adult onset diabetics and the non-diabetics is the same.(ABSTRACT TRUNCATED AT 400 WORDS)