In the present work, the presence of gastric inhibitory polypeptide (GIP) receptors and their functional role in the adrenal cells of three patients with food-dependent Cushing's syndrome were studied. RT-PCR and in situ hybridization studies demonstrated the presence of GIP receptor in the adrenals of the three patients. The presence of this receptor was also demonstrated in two human fetal adrenals, but not in two normal adult human adrenals or in the adrenals of one patient with nonfood-dependent Cushing's syndrome. Freshly isolated cells from patient adrenals responded in a dose-dependent manner to the steroidogenic action of both ACTH and GIP, whereas cells from normal adrenals responded only to ACTH. Treatment of cultured normal adrenal cells with ACTH, but not with GIP, increased the messenger ribonucleic acid (mRNA) levels of cholesterol side-chain cleavage cytochrome P-450, P450c17, and 3beta-hydroxysteroid dehydrogenase, whereas both hormones enhanced these mRNAs in patients' adrenal cells, although the effects of ACTH were greater than those of GIP. Moreover, pretreatment with ACTH enhanced the steroidogenic responsiveness of both normal and patient adrenal cells, whereas GIP caused homologous desensitization, and this was associated with a marked reduction of GIP receptor mRNA levels, as demonstrated by RT-PCR and in situ hybridization. Finally, both ACTH and GIP inhibited DNA synthesis in one patient's adrenal cells, whereas in normal adrenal cells only ACTH had this effect. In conclusion, the present data demonstrate that ectopic expression of functional GIP receptors is the main cause of food-dependent Cushing's syndrome.

Intravenous insulin therapy is the gold standard therapy for glycaemic control in hyperglycaemic critically ill adult patients. However, hypoglycaemia remains a major concern in critically ill patients, even in some populations who are not receiving infused insulin. Furthermore, the influence of factors such as glycaemic variability and nutritional support may conceal any benefit of strict glycaemic control on morbidity and mortality in these patients. The recently revised guidelines of the American Diabetic Association/American College of Clinical Endocrinologists no longer advocate very tight glycaemic control or normalization of glucose levels in all critically ill patients. In the light of various concerns over the optimal glucose level and means to achieve such control, the use of glucagon-like peptide-1 or its analogues administered intravenously may represent an interesting therapeutic option.

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