Lack of Rapid Enhancement of Insulin Action After Oral Glucose Challenge in Myotonic Dystrophy Free

Oral glucose administration to normal humans stimulates insulin release and simultaneously enhances the action of insulin by producing a rapid increase in tissue insulin sensitivity by a mechanism separate from the amount of hormone released. We determined whether insulin-resistant patients with myotonic dystrophy lose the ability to produce the normal rapid increase in tissue insulin action after oral glucose. Nine ambulatory, nonobese men with myotonic dystrophy were studied with 120-min euglycemic insulin infusions (20 mU · M⁻² · min⁻¹) given before and after glucose ingestion (4 and 5 patients received 15- and 25-g loads, respectively). Identical studies were performed in nonobese normal volunteers (16 and 13 patients received 15- and 25-g oral glucose loads, respectively). Glucose infusion rates at 20-120 min (GIR_20-120) during euglycemic insulin infusions without prior glucose were 2.87 ± 0.6 mg · kg⁻¹ · min⁻¹ in patients with myotonic dystrophy compared to 4.70 ± 0.3 mg · kg⁻¹ · min⁻¹ in normal subjects. Euglycemic insulin infusions after glucose ingestion were begun after arterialized blood glucose values had returned to baseline. After glucose ingestion by normal subjects, GIR_20-120 increased by 44.4 ± 7.1% (P < .0001) and by 46.8 ± 8.6% (P < .0002) with 15- and 25-g glucose loads, respectively. GIR_20-120 in the nine patients with myotonic dystrophy showed no significant increase after glucose ingestion. These results confirmed the existence of a decrease in whole-body insulin sensitivity in myotonic dystrophy and indicated that the patients lack the normal mechanism that enhances insulin action after oral glucose. This deficiency in insulin action may diminish the normal anabolic effect of insulin and may be a contributory factor for the muscle wasting seen in these patients.