Significant early-morning hyperglycemia was observed in insulin-dependent diabetic individuals who were otherwise well controlled while receiving a continuous subcutaneous insulin infusion (CSII) at standard doses. We measured the levels of the five key counterregulatory hormones (CRH) throughout the night for a total of 10 patient-nights in four such patients. No abnormalities in the patterns of glucagon, cortisol, growth hormone, epinephrine, or norepinephrine secretion were observed. Stepping up the daytime basal infusionrate in six affected patients before bedtime by 37.0 ± 7.5% and maintaining the increased infusion until breakfast significantly blunted this early-morning hyperglycemia without causing significant early nighttime hypoglycemia. Plasma glucose concentrations before breakfast averaged 106.8 ± 13.0 mg/dl after increase of the overnight basal infusion rate as compared with 269.8 ± 39.1 mg/dl while receiving a single basal rate over 24 h (P < 0.02). Thus, the “dawn phenomenon” may occur in patients receiving CSII by an unmodified algorithm and may be obviated by a carefully determined step-up in nocturnal basal infusion rate. The mechanism responsible for this phenomenon of increased early-morning insulin need remains to be elucidated.

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