The question of whether to use insulin in the evening or in the morning during combination therapy in patients with non-insulin-dependent diabetes mellitus (NIDDM) is controversial. We compared the acute effects of 12-h nocturnal or daytime insulin infusions on the 24-h glucose profile in 20 patients with NIDDM.
NIDDM patients were 56 ± 2 (mean ± SE) years of age and had a body mass index of 29.6 ±1.1 kg/m2; fasting plasma glucose concentration of 12.2 ± 0.5 mM; and fasting C-peptide concentration of 0.9 ± 0.2 nM. Each patient was studied twice. On one occasion, the patient received a 12-h intravenous infusion of insulin (mean 1.5 ± 0.1 1U/h) during the day, and on the other occasion an identical dose of insulin was infused during the night. Blood glucose, insulin, c-peptide, and free fatty acid concentrations were determined for 24 h.
The mean 24-h free insulin concentrations were similar in both studies (150 ± 12 vs. 162 ± 12 pM, daytime versus nocturnal insulin infusion). The mean 24-h free fatty acid concentration was 18% lower in the nocturnal than in the daytime (309 ± 30 vs. 376 ± 30 μM, P < 0.001) insulin infusion study. The mean 24-h C-peptide concentration was less suppressed if insulin was infused overnight than during the day (1.3 ± 0.2 vs. 1.1 ± 0.2 nM, P < 0.01). The mean 24-h plasma glucose concentrations were identical in both studies (11.1 ±0.6 vs. 11.4 ± 0.7 mM, daytime versus nocturnal insulin infusion). We also searched for factors predicting the decrease in the blood glucose concentration during the nocturnal insulin infusion. The best predictors were a high initial blood glucose concentration at 2200 and a low fasting C-peptide concentration. These factors explained, independent of each other, 50% of the rate of decrease in the plasma glucose concentration.
Despite better suppression of lipolysis and less suppression of endogenous insulin secretion by nocturnal than daytime insulinization, the hypoglycemic effect of these two treatments is similar.
