Effect of streptozotocin-induced diabetes mellitus on release of vasoactive intestinal polypeptide from rodent small intestine

Effect of Streptozotocin-Inducted Diabetes on the Pathophysiology of Enteric Neurons in the Small Intestine Based on the Porcine Diabetes Model

Hyperglycemia is one of the main causes of diabetes complications. Gastrointestinal (GI) disturbances are one of the most frequent complications during diabetes. The porcine digestive tract possesses physiological and pathological similarities to the human digestive tract. This also applies to the innervation of the gastrointestinal tract. In this study, the influence of experimentally-inducted hyperglycemia was examined on the expression of vesicular acetylcholine transporter (VAChT), cocaine- and amphetamine-regulated transcript (CART), galanin (GAL), vasoactive intestinal polypeptide (VIP), and calcitonin gene-related peptide (CGRP) in the enteric nervous system (ENS) neurons in the small intestine of the pig. During the current study, an increased number of neurons containing CART, VIP, GAL, and CGRP under streptozotocin injection were observed. The augmentation of expression included all enteric plexuses present in the small intestine. The same results were obtained in the case of VAChT; namely, chronic hyperglycemia led to an increase in the number of neurons utilizing VAChT in all investigated plexuses. The obtained results suggested that the function of neuropeptides studied in this experiment depended on their localization in the ENS structures, as well as part of the GI tract. Diabetes led to alterations in the neurochemical phenotype of small intestine enteric neurons.

Immunohistochemical study of vasoactive intestinal peptide (VIP) enteric neurons in diabetic rats supplemented with L-glutamine

The purpose of this work was to study the area of the varicosities of nerve fibers of myenteric neurons immunoreactive to vasoactive intestinal peptide (VIP-IR) and of the cell bodies of VIP-IR submucosal neurons of the jejunum of diabetic rats supplemented with 2% L-glutamine. Twenty male rats were divided into the following groups: normoglycemic (N), normoglycemic supplemented with L-glutamine (NG), diabetic (D) and diabetic supplemented with L-glutamine (DG). Whole-mounts of the muscle tunica and the submucosal layer were subjected to the immunohistochemical technique for neurotransmitter VIP identification. Morphometric analyses were carried out in 500 VIP-IR cell bodies of submucosal neurons and 2000 VIP-IR varicosities from each group. L-Glutamine supplementation to the normoglycemic animals caused an increase in the areas of the cell bodies (8.49%) and varicosities (21.3%) relative to the controls (P < 0.05). On the other hand, there was a decrease in the areas of the cell bodies (4.55%) and varicosities (28.9%) of group DG compared to those of group D (P < 0.05). It is concluded that L-glutamine supplementation was positive both to normoglycemic and diabetic animals.

The role of humoral autoimmunity in gastrointestinal neuromuscular diseases

Dysfunction of the gastrointestinal neuromuscular apparatus (including interstitial cells of Cajal) is presumed to underlie a heterogeneous group of disorders collectively termed gastrointestinal neuromuscular diseases (GINMDs). There is increasing experimental and clinical evidence that some GINMDs are immune-mediated, with cell-mediated dysfunction relatively well studied. Humoral (antibody)-mediated autoimmunity is associated with several well-established acquired neuromuscular diseases and is now implicated in an increasing number of less well-characterised disorders, particularly of the central nervous system. The role of autoimmunity in GINMDs has been less studied. Whilst most work has focused on the presence of antibodies directed to nuclear antigens, particularly in the context of secondary disorders such as paraneoplastic intestinal pseudo-obstruction, the possibility that 'functional' anti-neuronal antibodies directed to membrane-bound ion channels may cause disease (channelopathy) is now also being realised. The evidence for humoral autoimmunity as an etiologic factor in primary (idiopathic) and secondary GINMDs is systematically presented using the original paradigms previously applied to established autoimmune neuromuscular disorders. The presence of anti-enteric neuronal antibodies, although repeatedly demonstrated, still requires the identification of specific neuronal autoantigens and validated evidence of pathogenicity.

Diabetes and the enteric nervous system

Diabetes is associated with several changes in gastrointestinal (GI) motility and associated symptoms such as nausea, bloating, abdominal pain, diarrhoea and constipation. The pathogenesis of altered GI functions in diabetes is multifactorial and the role of the enteric nervous system (ENS) in this respect has gained significant importance. In this review, we summarize the research carried out on diabetes-related changes in the ENS. Changes in the inhibitory and excitatory enteric neurons are described highlighting the role of loss of inhibitory neurons in early diabetic enteric neuropathy. The functional consequences of these neuronal changes result in altered gastric emptying, diarrhoea or constipation. Diabetes can also affect GI motility through changes in intestinal smooth muscle or alterations in extrinsic neuronal control. Hyperglycaemia and oxidative stress play an important role in the pathophysiology of these ENS changes. Antioxidants to prevent or treat diabetic GI motility problems have therapeutic potential. Recent research on the nerve-immune interactions demonstrates inflammation-associated neurodegeneration which can lead to motility related problems in diabetes.

Effect of vitamin E on diabetes-induced changes in small intestine and plasma antioxidant capacity in rat

The present study was designed to evaluate the effect of Vitamin E (Vit. E) on diabetes-induced changes in small intestine, lipid peroxidation and plasma antioxidant capacity in rats. Twenty-four rats were divided into three groups (n=8), namely control, non-treated diabetic (NTD) and Vit. E-treated diabetic (VETD) groups. The VETD group received 300 mg of Vit. E daily in drinking water. After 6 weeks, the length and weight of small intestine, villus height, crypt depth and muscular layer thickness showed a significant increase in the NTD group compared to the control group. In the VETD group, these parameters did not show any significant difference compared to the control group. The level of malondialdehyde (MDA) in the red blood cells showed a significant increase in the NTD group, but not in the VETD group, compared to the control group. The plasma antioxidant capacity showed a significant increase in VETD compared to the NTD group. These findings indicate that Vit. E significantly improved small intestinal changes in diabetic rats and that these effects could be mediated at least in part by enhanced plasma antioxidant capacity and reduced lipid peroxidation.

Changes of the different neuropeptide-containing nerve fibers and immunocells in the diabetic rat's alimentary tract

Peripheral neuropathy is a common complication of diabetes mellitus, where neuropeptides and immunocells might play important roles in the pathogenesis of the disease. In this article we have quantified the different neuropeptide-containing nerve fibers and immunocells in the streptozotocin-induced diabetic rat's alimentary tract (tongue, duodenum, colon) using immunohistochemical and immunocytochemical methods. The immunoreactive (IR) nerve fibers were found in all layers of the alimentary tract and their distribution pattern was similar in both control and diabetic groups. Mast cell-nerve fiber contacts were rarely found in the controls. However, after 4 weeks duration of diabetes the number of IR nerve fibers and the immunocompetent cells increased significantly (P < 0.05), and the number of mast cell-nerve fiber contacts was even more significantly increased (P < 0.001). The distance between nerve fibers and immunocells was about 1 mum or even less. Some of the mast cells were degranulated in the vicinity of nerve fibers. No immunocompetent cells were IR for any antisera in the control. However, after the streptozotocin treatment, a large number of the immunocompetent cells showed immunoreactivity for SP and NPY. Counting all immunocompetent cells in whole sections showed that 12.3% of them were IR for SP and 25.4% were IR for NPY. Increased number of SP-containing nerve fibers and immunocells in diabetes mellitus might be the reason for painful neuropathy and might amplify the inflammatory reaction in an axon reflex manner; the released histamine and leukotrienes, cytokines, and chemokines might cause inflammations and lesions of the mucosa.

Down-regulation of vasoactive intestinal peptide and altered expression of its receptors in rat diabetic cardiomyopathy

Vasoactive intestinal peptide (VIP) is a vasorelaxant peptide that addresses two receptor subtypes, VPAC1 and VPAC2. It stimulates insulin secretion and mediates anti-inflammatory effects and has been proposed for treatment of type 2 and autoimmune diabetes. In the heart, VIP is produced and released primarily by intrinsic neurons and improves cardiac perfusion and function. Here, we investigated the involvement of this system in the events underlying development of experimentally induced diabetic cardiomyopathy. Rats received a single streptozotocin injection, and cardiac VIP content [radioimmune assay (RIA)], expression of the VIP precursors VPAC1 and VPAC2 [real-time reverse transcription-polymerase chain reaction (RT-PCR)], and VPAC1 and VPAC2 tissue distribution (immunohistochemistry) were assessed 4, 8, and 16 weeks thereafter and compared with corresponding vehicle-treated controls. Cardiac neuropathy manifests progressively during the first 4 months of diabetes at the preproVIP mRNA and VIP peptide level and is accompanied by initial down-regulation of VPAC2 at one prime target of VIP-containing axons, i.e., smooth muscle cells of coronary arterioles. VPAC1 is expressed by macrophages. After initial changes that are specific for atria and ventricles, respectively, VPAC1 and VPAC2 expression return to control levels at 16 weeks despite ongoing loss of VIP. Given the cardioprotective role of the VIP signaling system, the persistence of receptors has therapeutic implications since it is the prerequisite for trials with VPAC2 agonists.

Changes in serotonin levels and 5-HT receptor activity in duodenum of streptozotocin-diabetic rats

Few previous studies have discussed the changes in serotonin receptor activity in the small intestine of diabetic animals. Therefore, we examined serotonin content in duodenal tissue and dose-dependent effects of serotonin agonists and antagonists on the motor activity of ex vivo vascularly perfused duodenum of streptozotocin (STZ)-diabetic rats. Serotonin content was significantly increased in enterochromaffin cells but not altered in serotonin-containing neurons in STZ-diabetic rats. Motor activity assessed by frequency, amplitude, and percent motility index per 10 min of pressure waves was reduced in the duodenum of diabetic rats, and this reduction was reversed by insulin treatment. Serotonin dose dependently increased the motor activity in control rat duodenum but only a higher concentration of serotonin increased the motor activity in diabetic rats. The 5-hydroxytryptamine (5-HT) receptor subtype 4 (5-HT(4)) antagonist SB-204070 dose dependently reduced motor activity in both control and diabetic rats, whereas the 5-HT(3) receptor antagonist azasetron, even at a higher concentration, failed to affect motor activity in diabetic rat duodenum but dose dependently reduced motor activity in control rat duodenum. These results suggest that 5-HT(3) receptor activity was impaired but 5-HT(4) receptor activity was intact in STZ-diabetic rat duodenum. Such an impairment of 5-HT(3) receptor activity may induce the motility disturbance in the small intestine of diabetes mellitus.

The role of tumor necrosis factor-alpha in the pathogenesis of anorexia and bulimia nervosa, cancer cachexia and obesity

In this paper a new immunological model of anorexia and bulimia nervosa will be presented in which the inflammatory cytokines are conceived as the fundamental regulators of body metabolism. This conception differs from the conventional view in which the inflammatory cytokines are perceived primarily as peptide molecules utilized by the immune system to control infection, inflammation and tissue or neuronal damage. Given that the inflammatory cytokines are also fundamental regulators of body metabolism, when they become dysregulated they create physiological chaos which results in the development of a number of autoimmune, metabolic and psychiatric disorders. In this proposed immunological model of anorexia and bulimia nervosa, elevated tumor necrosis factor-alpha features as the primary cause of these conditions. Pathophysiological parallels are drawn between anorexia nervosa and cancer cachexia in terms of the causal role the cytokines, neuropeptides and neurotransmitters play in the manifestation of shared symptoms. These shared symptoms include elevated tumour necrosis factor-alpha, down-regulated interleukin-2 and interleukin-4 and depletion of lean body mass. Furthermore, the following neuropeptides are dysregulated in both anorexia nervosa and cancer cachexia: vasoactive intestinal peptide, cholecystokinin, corticotropin-releasing factor, neuropeptide Y, peptide YY and beta-endorphin. In addition, in anorexia and bulimia nervosa, secretion of the neurotransmitter serotonin is inhibited while norepinephrine is enhanced. It will be argued that the causal interplay between the cytokines, neuropeptides and neurotransmitters initiates a cascade of biochemical events which may result in either anorexia or bulimia nervosa, or cancer cachexia. The extent to which these inflammatory cytokines, neuropeptides and neurotransmitters are causally efficacious in the pathogenesis of other autoimmune disorders, such as diabetes mellitus and rheumatoid arthritis, will also be addressed.