Insulin receptors in cystic fibrosis: increased receptor number and altered affinity

Patients with cystic fibrosis are known to have pancreatic disorganization with associated pancreatic exocrine insufficiency. Endocrine hormonal secretion is also affected but diminution in insulin secretion is rarely accompanied by overt diabetes. We studied seven patients with cystic fibrosis to determine their carbohydrate tolerance and the status of peripheral monocyte insulin receptors. Oral glucose tolerance tests showed the presence of mild hyperglycemia and diminished insulin secretion. Mean insulin receptor sites per cell were markedly increased above controls, 25,000 vs 13,100 sites per cell while receptor affinity was diminished. The increase in receptor number could be a consequence of the insulinopenia and/or the decreased body weight of the patients and serve as a compensatory mechanism maintaining a degree of relative insulin sensitivity. Ultimate carbohydrate tolerance may be a function of the patient's ability to maintain increased receptor numbers in the face of hypoinsulinemia and impaired receptor affinity.