Hypoglycemia-Dependent β2-Adrenoceptor Downregulation: A Contributing Factor to Hypoglycemia Unawareness in Patients with Type-1 Diabetes?Schwab K.O. · Menche U. · Schmeisl G. · Lohse M.J.
aDepartment of Pharmacology and Toxicology, University of Würzburg, bDepartment of Pediatrics, University of Freiburg, and cDiabetes-Reha-Klinik Fürstenhof, Bad Kissingen, Germany
To evaluate the influence of the incidence and unawareness of hypoglycemia on lymphocyte β2-adrenoceptor densities, we measured β2-adrenoceptor density using [125I]-iodocyanopindolol and CGP 12177 before and after 1 week of treatment optimization in 33 adults with type-1 diabetes mellitus. Diabetes treatment of all patients was modified to improve their glycemic control. During this week, all patients had to complete a protocol with 7 daily glucose measurements, one of which was at night. The subjective symptoms were evaluated in case of hypoglycemia. A significant correlation between a hypoglycemia incidence below (but not above) the threshold of 2.75 mmol/l (50 mg/dl) and β2-adrenoceptor densities on lymphocytes was found after the study week (r = –0.72, p < 0.00001). Nine patients suffering from hypoglycemia unawareness had a significantly higher incidence of hypoglycemia (p < 0.002) and lower β2-adrenoceptor densities on lymphocytes compared to 24 patients who recognized all of their hypoglycemic episodes (p < 0.004). We conclude that downregulation of β2-adrenoceptor densities on lymphocytes occurs as a result of recurrent hypoglycemia defined as glucose levels of <2.75 mmol/l. β2-Adrenoceptor densities are decreased in patients with subjective hypoglycemia unawareness and might contribute to the reduced β-adrenergic sensitivity in this subgroup of patients.
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