Endocrine cells in oxyntic mucosa of a dog 5 years after pancreatectomy

Glucagon secretion and signaling in the development of diabetes

Normal release of glucagon from pancreatic islet α-cells promotes glucose mobilization, which counteracts the hypoglycemic actions of insulin, thereby ensuring glucose homeostasis. In treatment of diabetes aimed at rigorously reducing hyperglycemia to avoid chronic complications, the resulting hypoglycemia triggering glucagon release from α-cells is frequently impaired, with ensuing hypoglycemic complications. This review integrates the physiology of glucagon secretion regulating glucose homeostasis in vivo to single α-cell signaling, and how both become perturbed in diabetes. α-cells within the social milieu of the islet micro-organ are regulated not only by intrinsic signaling events but also by paracrine regulation, particularly by adjacent insulin-secreting β-cells and somatostatin-secreting δ-cells. We discuss the intrinsic α-cell signaling events, including glucose sensing and ion channel regulation leading to glucagon secretion. We then discuss the complex crosstalk between the islet cells and the breakdown of this crosstalk in diabetes contributing to the dysregulated glucagon secretion. Whereas, there are many secretory products released by β- and δ-cells that become deficient or excess in diabetes, we discuss the major ones, including the better known insulin and lesser known somatostatin, which act as putative paracrine on/off switches that very finely regulate α-cell secretory responses in health and diabetes. Of note in several type 1 diabetes (T1D) rodent models, blockade of excess somatostatin actions on α-cell could normalize glucagon secretion sufficient to attain normoglycemia in response to hypoglycemic assaults. There has been slow progress in fully elucidating the pathophysiology of the α-cell in diabetes because of the small number of α-cells within an islet and the islet mass becomes severely reduced and inflamed in diabetes. These limitations are just now being surmounted by new approaches.

Glucagonocentric restructuring of diabetes: a pathophysiologic and therapeutic makeover

The hormone glucagon has long been dismissed as a minor contributor to metabolic disease. Here we propose that glucagon excess, rather than insulin deficiency, is the sine qua non of diabetes. We base this on the following evidence: (a) glucagon increases hepatic glucose and ketone production, catabolic features present in insulin deficiency; (b) hyperglucagonemia is present in every form of poorly controlled diabetes; (c) the glucagon suppressors leptin and somatostatin suppress all catabolic manifestations of diabetes during total insulin deficiency; (d) total β cell destruction in glucagon receptor-null mice does not cause diabetes; and (e) perfusion of normal pancreas with anti-insulin serum causes marked hyperglucagonemia. From this and other evidence, we conclude that glucose-responsive β cells normally regulate juxtaposed α cells and that without intraislet insulin, unregulated α cells hypersecrete glucagon, which directly causes the symptoms of diabetes. This indicates that glucagon suppression or inactivation may provide therapeutic advantages over insulin monotherapy.

Odyssey between Scylla and Charybdis through storms of carbohydrate metabolism and diabetes: a career retrospective

This research perspective allows me to summarize some of my work completed over 50 years, and it is organized in seven sections. 1) The treatment of diabetes concentrates on the liver and/or the periphery. We quantified hormonal and metabolic interactions involved in physiology and the pathogenesis of diabetes by developing tracer methods to separate the effects of diabetes on both. We collaborated in the first tracer clinical studies on insulin resistance, hypertriglyceridemia, and the Cori cycle. 2) Diabetes reflects insulin deficiency and glucagon abundance. Extrapancreatic glucagon changed the prevailing dogma and permitted precise exploration of the roles of insulin and glucagon in physiology and diabetes. 3) We established the critical role of glucagon-insulin interaction and the control of glucose metabolism during moderate exercise and of catecholamines during strenuous exercise. Deficiencies of the release and effects of these hormones were quantified in diabetes. We also revealed how acute and chronic hyperglycemia affects the expression of GLUT2 gene and protein in diabetes. 4) We outlined molecular and physiological mechanisms whereby exercise training and repetitive neurogenic stress can prevent diabetes in ZDF rats. 5) We and others established that the indirect effect of insulin plays an important role in the regulation of glucose production in dogs. We confirmed this effect in humans and demonstrated that in type 2 diabetes it is mainly the indirect effect. 6) We indicated that the muscle and the liver protected against glucose changes. 7) We described molecular mechanisms responsible for increased HPA axis in diabetes and for the diminished responses of HPA axis, catecholamines, and glucagon to hypoglycemia. We proposed a new approach to decrease the threat of hypoglycemia.

Decrease in intestinal endocrine cells in Balb/c mice with CT-26 carcinoma cells

The density of intestinal endocrine cells, in Balb/c mice with colon 26 (CT-26) carcinoma cells, were examined immunohistochemically at 28 days after implantation. After CT-26 cell administration there was a significant decrease in most of the intestinal endocrine cells (p < 0.01) compared with the control group. The significant quantitative changes in the intestinal endocrine cell density might contribute to the development of the gastrointestinal symptoms commonly encountered in cancer patients.

Changes of the intestinal endocrine cells in the C57BL/6 mouse after implantation of murine lung carcinoma (3LL): An immunohistochemical quantitative study

AIM: To study the distributions and frequencies of intestinal endocrine cells in the C57BL/6 mouse with immunohistochemical method using seven types of specific antisera against chromogranin A (CGA), serotonin, somatostatin, glucagons, gastrin, cholecystokinin (CCK)-8 and human pancreatic polypeptide (hPP) after abdominal subcutaneous implantation of murine lung carcinoma (3LL).

METHODS: The experimental animals were divided into two groups, one is non-implanted Sham and the other is 3LL-implanted group. Samples were collected from six regions of intestinal tract at 28^th d after implantation of 3LL cells (1×105 cell/mouse).

RESULTS: In this study, five types of immunoreactive (IR) cells were identified except for gastrin and hPP. The regional distributions of the intestinal endocrine cells in the 3LL-implanted group were similar to those of the non-implanted Sham. However, significant decreases of IR cells were detected in 3LL-implanted group compared to those of non-implanted Sham. CGA- and serotonin-IR cells significantly decreased in 3LL-implanted groups compared to that of non-implanted Sham. Somatostatin-IR cells in the jejunum and ileum and CCK-8-IR cells in the jejunum of 3LL-implanted groups significantly decreased compared to that of non-implanted Sham. In addition, glucagon-IR cells were restricted to the ileum and colon of non-implanted Sham.

CONCLUSION: Implantation of tumor cell mass (3LL) induced severe quantifiable changes of intestinal endocrine cell density and the abnormality in density of intestinal endocrine cells may contribute to the development of gastrointestinal symptoms such as anorexia and indigestion, frequently encountered in patients with cancer.

Changes of the gastric endocrine cells in the C57BL/6 mouse after implantation of murine lung carcinoma: An immunohistochemical quantitative study

AIM: The regional distributions and relative frequencies of some gastric endocrine cells of C57BL/6 mice were studied by immunohistochemical method using seven types of specific antisera against chromogranin A (CGA), serotonin, somatostatin, gastrin, cholecystokinin (CCK)-8, glucagon and human pancreatic polypeptide (HPP) after subcutaneous implantation of murine lung carcinoma (3LL) cells.

METHODS: The experimental animals were divided into two groups, one is non-implanted sham and the other is 3LL-implanted group. Samples were collected from the two regions of stomach (fundus and pylorus) at 28 d after implantation of 3LL cells (1×10⁵ cell/mouse).

RESULTS: In this study, all the seven types of immunoreactive (IR) cells were identified except for HPP. Most of these IR cells in the gastric portion were generally spherical or spindle in shape (open-type cell) while cells showing round in shape (closed-type cell) were found occasionally. The regional distributions of gastric endocrine cells in the 3LL-implanted group were similar to those of non-implanted sham. However, significant decreases of some types of IR cells were detected in 3LL-implanted group compared to those of non-implanted sham. In addition, the IR cells showing degranulation were numerously detected in 3LL-implanted group. CGA-, serotonin- and somatostatin-IR cells in the fundus and pylorus regions, and gastrin-IR cells in the pylorus regions of 3LL-implanted groups significantly decreased compared to those of non-implanted sham. However, no changes on frequencies of CCK-8- and glucagon-IR cells were demonstrated between 3LL-implanted and non-implanted groups.

CONCLUSION: Endocrine cells are the anatomical units responsible for the production of gut hormones, and the change in their density would reflect a change in the capacity of producing these hormones. Implantation of tumor cell mass (3LL) induced severe quantitative changes of gastric endocrine cell density, and the abnormality in density of gastric endocrine cells may contribute to the development of gastrointestinal symptoms such as anorexia and indigestion, frequently encountered in patients with cancer.