Diabetes mellitus by repeated stress in rats bearing chemical diabetes

Stress-related endocrinological and psychopathological effects of short- and long-term 50Hz electromagnetic field exposure in rats

It is believed that different electromagnetic fields do have beneficial and harmful biological effects. The aim of the present work was to study the long-term consequences of 50 Hz electromagnetic field (ELF-EMF) exposure with special focus on the development of chronic stress and stress-induced psychopathology. Adult male Sprague-Dawley rats were exposed to ELF-EMF (50 Hz, 0.5 mT) for 5 days, 8h daily (short) or for 4-6 weeks, 24h daily (long). Anxiety was studied in elevated plus maze test, whereas depression-like behavior of the long-treated group was examined in the forced swim test. Some days after behavioral examination, the animals were decapitated among resting conditions and organ weights, blood hormone levels as well as proopiomelanocortin mRNA level from the anterior lobe of the pituitary gland were measured. Both treatments were ineffective on somatic parameters, namely none of the changes characteristic to chronic stress (body weight reduction, thymus involution and adrenal gland hypertrophy) were present. An enhanced blood glucose level was found after prolonged ELF-EMF exposure (p=0.013). The hormonal stress reaction was similar in control and short-term exposed rats, but significant proopiomelanocortin elevation (p<0.000) and depressive-like behavior (enhanced floating time; p=0.006) were found following long-term ELF-EMF exposure. Taken together, long and continuous exposure to relatively high intensity electromagnetic field may count as a mild stress situation and could be a factor in the development of depressive state or metabolic disturbances. Although we should stress that the average intensity of the human exposure is normally much smaller than in the present experiment.

The effect of chronic psychological stress on corticosterone, plasma metabolites, and immune responsiveness in European starlings

Although increases in glucocorticoid concentrations during acute stress are believed to help animals survive stressful events, chronic changes in glucocorticoid concentrations can alter metabolism and lead to disease. We studied the effect of chronic psychological stress on corticosterone (CORT), corticosterone binding globulin (CBG), glucose, and triglyceride concentrations as well as immune responsiveness to a T-cell mitogen challenge in European starlings, Sturnus vulgaris. To induce chronic stress we used a chronic stress protocol consisting of five stressors (loud radio, cage tapping, cage rolling, human voice, and bag restraint) administered in random order for 30 min for 4 times/day over 18 days. Total CORT decreased throughout the chronic stress period, which parallels a previous study with starlings. CBG capacity did not significantly change with chronic stress, thus free CORT followed the same pattern of attenuation as total CORT during chronic stress. Despite the change in regulation of CORT release, daytime glucose and triglyceride concentrations did not change with chronic stress. In addition, immune responsiveness in chronically stressed and unstressed birds was similar. Our results, together with a previous study using a similar CSP in European starlings, suggest that starlings physiologically dampen the HPA axis during chronic psychological stress to avoid pathology associated with chronically augmented CORT concentrations such as hyperglycemia and impaired immune function.

Effect of chronic psychological stress on insulin release from rat isolated pancreatic islets

Despite documented studies, the exact role of stress on diabetes is still unclear. The present study investigates the effect of chronic psychological stress on insulin release from isolated rat pancreatic islets. Male Wistar rats were divided into two groups of control and stressed (n=8/group). The animals of the stressed group were exposed to restraint stressors (1 h twice daily) for 15 or 30 consecutive days. At the beginning and end of the experimental periods, the animals were weighed and blood samples taken to determine the fasting plasma levels of glucose, insulin and corticosterone. On the following day the pancreatic islets of 5/group of the above animals were isolated and the static release of insulin in the presence of different glucose concentrations (2.8, 5.6, 8.3, 16.7 mM) was assessed. The results showed that in the stressed group, fasting plasma glucose levels were increased significantly on the 15th day as compared to the control group. However there was no significant increase on the 30th day. Fasting plasma insulin was significantly decreased on the 15th and 30th days of the experiment in the stressed group. Stressed rats showed significantly higher fasting plasma corticosterone levels, only on the 15th day, as compared to the control rats. In response to increasing concentrations of glucose, insulin release from islets of the stressed group was increased significantly on the 30th day of the experiment as compared to the control group. We conclude that chronic psychological stress could increase responsiveness of pancreatic beta cells to glucose, in vitro, and thus, low insulin levels of the stressed animals, in vivo, may be due to reason(s) other than the reduction of insulin releasing capacity of pancreatic beta cells.

Animal models provide insight into psychosomatic factors in diabetes

OBJECTIVE

To review the literature regarding the use of animal models in research addressing psychosomatic aspects of diabetes.

METHOD

We examine the key findings in animal model vs. human research in the area of stress and diabetes. Previous research has suggested that stress is a potential contributor to chronic hyperglycemia in diabetes. Stress affects metabolic activity via the stimulation of a variety of hormones that can result in elevated blood glucose levels. In patients with diabetes, due to a relative or absolute lack of insulin, stress-induced increases in glucose cannot be properly metabolized. Additionally, regulation of these stress hormones may be abnormal in diabetes.

RESULTS

Human studies on the role of stress in the onset and course of type II diabetes are few and are limited by the constraints and logistics of examining life stress in humans. However, animal research allows for tight experimental control and the manipulation of factors that may contribute to the development and/or course of diabetes, such as stress, eating behavior, the nutrient content of food, and physical activity. Disease processes can be examined at a mechanistic level in animals which is typically limited in human research.

CONCLUSIONS

There is a large body of animal work to support the notion that stress reliably produces hyperglycemia in type II diabetes. Furthermore, there is evidence that the autonomic nervous system plays a role in the pathophysiology of this condition in both animals and humans. Examination of eating behavior and nutrient content of food in animal models of diabetes has shed light on the role of these factors in the development of diabetes, as well as obesity. Finally, genetic research using animal models of diabetes will provide new directions for research in humans to delineate the genetic contribution to the development of diabetes.

Physiological responses to acute stress in alloxan and streptozotocin diabetic rats

Physiological responses to acute stress were assessed in alloxan diabetic, streptozotocin diabetic and control laboratory rats. Rats were prepared with indwelling tail artery catheters to allow for direct measurement of mean arterial pressure (MAP, mmHg) and heart rate (HR, beats per minute) and remote sampling of blood. Within 24 hours after surgery, basal values of MAP and HR were determined. Two days after surgery, rats were subjected to 5 minutes of intermittent footshock. Blood samples were collected before footshock stress and immediately and 15 minutes after termination of footshock. Plasma levels of norepinephrine (NE) and epinephrine (EPI) increased significantly above basal values in all animals exposed to acute footshock stress. However, in approximately one-half of alloxan and streptozotocin diabetic rats, plasma levels of EPI under basal conditions and following footshock stress were elevated significantly compared to controls and the remaining diabetic animals. We have denoted these subgroups of diabetic animals as reactive responders (plasma EPI greater than controls) and nonreactive responders (plasma EPI similar to controls), respectively. Plasma levels of NE under basal conditions and following footshock stress were similar in reactive responders and nonreactive responders compared to matched controls. Baseline blood glucose levels were elevated in alloxan and streptozotocin diabetic rats compared to controls. Blood glucose levels increased reliably in all animals following footshock stress. Basal MAPs were reduced significantly in both subgroups of alloxan and streptozotocin diabetic rats compared to matched controls. In contrast, resting HRs were similar between diabetic rats and their corresponding controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological aspects of diabetes mellitus: prospects for pharmacological modification

It is now well known that insulin-dependent diabetes is a chronic progressive autoimmune disease. The prolonged prediabetic phase of progressive beta-cell dysfunction is associated with immunological abnormalities. A prediabetic period is suggested by the appearance of islet cell antibodies, anti-insulin antibodies, and anti-insulin receptor antibodies. The existence of activated T lymphocytes and abnormal T cell subsets are also other markers. There is still no concensus about the use of the immunosuppression superimposed upon conventional insulin therapy in early diagnosed IDDM and the follow-up of the relatives of IDDM patients who share the genetic predisposition and serological markers for the risk of future onset of IDDM. Treatment in the prodromal period cannot be justified because a link between the disease and early markers such as ICA has not been established with certainty (Diabetes Research Program NIH, 1983). Many immunopharmacological manipulations were reported to be effective in animal models. However, most of them are not readily applied to human subjects. Moreover, IDDM patients are now believed to be heterogeneous, with a complex genetic background. HLA-DR, and more recently DQ, are closely related to the genetic predisposition to IDDM but those genes are not themselves diabetogenic. The contribution of autoimmunity does not appear to be uniform, and in some cases, the contribution of virus is considered more important. There is a lack of a marker for the future onset of IDDM. ICA and ICSA were found after mumps infection, but the existence of those autoantibodies and even the co-existence of HLA-DR3 do not always indicate the future trend to insulin dependency. More precise markers will be disclosed through the biochemical analysis of the target antigens on pancreatic beta-cell for islet antibodies and effector T cells. Much safer and more effective immunopharmacological treatment will be developed through animal experimentation using rat and mouse models. The recent development and interest in this field will further facilitate the attainment of the goal for the complete prevention of IDDM.

Promotion of diabetes onset by stress in the BB rat

The purpose of the present study was to address the question of whether environmental stress affects the age of onset and incidence of overt insulin-dependent diabetes mellitus in an animal model of human Type 1 (insulin-dependent) diabetes. Thirty-five diabetes prone BB rats of both sexes were divided into two groups: experimental animals were exposed to multiple, concurrent, and unpredictable environmental stressors, while littermate controls were exposed to a standard lab environment. Groups were housed in two separate, sound attenuated, independently ventilated, and restricted rooms. By age 150 days, experimental group animals had developed overt diabetes at a significantly earlier age.