Jens Pedersen

Glucagon is secreted from the pancreatic alpha cells upon hypoglycemia and stimulates hepatic glucose production. Type 2 diabetes is associated with dysregulated glucagon secretion, and increased glucagon concentrations contribute to the diabetic hyperglycemia. Antagonists of the glucagon receptor have been considered as glucose-lowering therapy in type 2 diabetes patients, but their clinical applicability has been questioned because of reports of therapy-induced increments in liver fat content and increased plasma concentrations of low-density lipoprotein. Conversely, in animal models, increased glucagon receptor signaling has been linked to improved lipid metabolism. Glucagon acts primarily on the liver and by regulating hepatic lipid metabolism glucagon may reduce hepatic lipid accumulation and decrease hepatic lipid secretion. Regarding whole-body lipid metabolism, it is controversial to what extent glucagon influences lipolysis in adipose tissue, particularly in humans. Glucagon receptor agonists combined with glucagon-like peptide 1 receptor agonists (dual agonists) improve dyslipidemia and reduce hepatic steatosis. Collectively, emerging data support an essential role of glucagon for lipid metabolism.

Glucagon is usually viewed as an important counterregulatory hormone in glucose metabolism, with actions opposing those of insulin. Evidence exists that shows glucagon is important for minute-to-minute regulation of postprandial hepatic glucose production, although conditions of glucagon excess or deficiency do not cause changes compatible with this view. In patients with glucagon-producing tumors (glucagonomas), the most conspicuous signs are skin lesions (necrolytic migratory erythema), while in subjects with inactivating mutations of the glucagon receptor, pancreatic swelling may be the first sign; neither condition is necessarily associated with disturbed glucose metabolism. In glucagonoma patients, amino acid turnover and ureagenesis are greatly accelerated, and low plasma amino acid levels are probably at least partly responsible for the necrolytic migratory erythema, which resolves after amino acid administration. In patients with receptor mutations (and in knockout mice), pancreatic swelling is due to α-cell hyperplasia with gross hypersecretion of glucagon, which according to recent groundbreaking research may result from elevated amino acid levels. Additionally, solid evidence indicates that ureagenesis, and thereby amino acid levels, is critically controlled by glucagon. Together, this constitutes a complete endocrine system; feedback regulation involving amino acids regulates α-cell function and secretion, while glucagon, in turn, regulates amino acid turnover.

Evaluation of the impact of anesthesia on oral glucose tolerance in mice. Anesthesia is often used when performing OGTT in mice to avoid the stress of gavage and blood sampling, although anesthesia may influence gastrointestinal motility, blood glucose, and plasma insulin dynamics. C57Bl/6 mice were anesthetized using the following commonly used regimens: (1) hypnorm/midazolam repetitive or single injection; (2) ketamine/xylazine; (3) isoflurane; (4) pentobarbital; and (5) A saline injected, nonanesthetized group. Oral glucose was administered at time 0 min and blood glucose measured in the time frame -15 to +150 min. Plasma insulin concentration was measured at time 0 and 20 min. All four anesthetic regimens resulted in impaired glucose tolerance compared to saline/no anesthesia. (1) hypnorm/midazolam increased insulin concentrations and caused an altered glucose tolerance; (2) ketamine/xylazine lowered insulin responses and resulted in severe hyperglycemia throughout the experiment; (3) isoflurane did not only alter the insulin secretion but also resulted in severe hyperglycemia; (4) pentobarbital resulted in both increased insulin secretion and impaired glucose tolerance. All four anesthetic regimens altered the oral glucose tolerance, and we conclude that anesthesia should not be used when performing metabolic studies in mice.

Recent case reports suggest that treatment with glucagon-like peptide-1 (GLP-1) agonists results in clinical improvement of psoriasis. The purpose of this study was to determine whether GLP-1 receptors (GLP-1Rs) are found in the skin of healthy volunteers and psoriasis patients and if so, whether GLP-1Rs are located on keratinocytes or immune cells. Three mm-punch skin biopsies were taken for gene expression analysis from six healthy volunteers and from affected and unaffected skin of six psoriasis patients. In addition, a blood sample was obtained from all participants. Cultured human keratinocytes were either untreated or incubated with tumor necrosis factor- α (TNF-α), interferon-γ (IFN-γ) or a combination of TNF-α and IFN-γ for 48 h. Total RNA was extracted from all the samples, reversely transcribed and analysed for the expression of GLP-1R using real-time PCR. Gene expression analysis showed expression of GLP-1Rs in five of six skin biopsies from psoriasis plaques, in one of six biopsies from unaffected psoriatic skin and in one of six biopsies from healthy skin. GLP-1R expression was found in the blood of both healthy volunteers and psoriasis patients. No GLP-1R expression was found in either stimulated or unstimulated cultured human keratinocytes. Our results show increased presence of GLP-1Rs in psoriasis plaques and that this most likely is due to infiltration with immune cells. This offers a possible explanation for the positive effect of treatment with GLP-1R agonists in patients with psoriasis.