The diabetes-induced functional and distributional changes of the alpha 1-adrenoceptor of the abdominal aorta and distal mesenteric artery from streptozotocin-induced diabetic rats

Key elements determining the intestinal region-specific environment of enteric neurons in type 1 diabetes

Diabetes, as a metabolic disorder, is accompanied with several gastrointestinal (GI) symptoms, like abdominal pain, gastroparesis, diarrhoea or constipation. Serious and complex enteric nervous system damage is confirmed in the background of these diabetic motility complaints. The anatomical length of the GI tract, as well as genetic, developmental, structural and functional differences between its segments contribute to the distinct, intestinal region-specific effects of hyperglycemia. These observations support and highlight the importance of a regional approach in diabetes-related enteric neuropathy. Intestinal large and microvessels are essential for the blood supply of enteric ganglia. Bidirectional morpho-functional linkage exists between enteric neurons and enteroglia, however, there is also a reciprocal communication between enteric neurons and immune cells on which intestinal microbial composition has crucial influence. From this point of view, it is more appropriate to say that enteric neurons partake in multidirectional communication and interact with these key players of the intestinal wall. These interplays may differ from segment to segment, thus, the microenvironment of enteric neurons could be considered strictly regional. The goal of this review is to summarize the main tissue components and molecular factors, such as enteric glia cells, interstitial cells of Cajal, gut vasculature, intestinal epithelium, gut microbiota, immune cells, enteroendocrine cells, pro-oxidants, antioxidant molecules and extracellular matrix, which create and determine a gut region-dependent neuronal environment in diabetes.

Chronic diabetes and hypertension impair the in vivo functional response to phenylephrine independent of α1-adrenoceptor expression

Diabetes and hypertension can coexist and exacerbate each other. In the early stages of diabetes, there is a decreased vascular response of the sympathetic nervous system (SNS), probably due to lower expression of α₁-adrenoceptors; however, it is unclear how diabetes in advanced stages changes the functionality of the SNS, especially the expression of α₁-adrenoceptors. Thus, the aim of this work was to analyse the functional response to phenylephrine, a selective α₁-adrenoceptor agonist, and the expression of α₁-adrenoceptors in chronic diabetes and hypertension. Male SHR and WKY rats aged 10-12 weeks were administered either streptozotocin (60 mg/kg i.p.) or a vehicle (control group). Eight weeks after administration, dose-response curves to phenylephrine were generated and the gene and protein expression of α₁-adrenoceptor subtypes (α_1A-, α_1B- and α_1D-adrenoceptors) in the heart and aorta were measured. The response to phenylephrine was diminished in hypertensive rats and in normotensive diabetic rats. The coexistence of both diabetes and hypertension produced an even smaller response to phenylephrine than that observed for each condition separately. In the heart and aorta of diabetic rats, no changes in α_1A-, α_1B- or α_1D-adrenoceptor mRNA expression were observed; however, protein expression was increased, mainly for the α_1D-adrenoceptor. Hypertension increased mRNA and protein expression of α₁-adrenoceptors in a tissue-dependent manner. The coexistence of both diabetes and hypertension produced differences in the regulation of mRNA and protein expression (increase or decrease) in both the heart and aorta. In conclusion, diabetes, hypertension and the coexistence of both pathologies impairs the in vivo response to phenylephrine. However, the differences in α_1A-, α_1B- and α_1D-adrenoceptor expression cannot explain the reduced response to the agonist. This should be further explored in future experiments.

Increased Contractile Response to Noradrenaline Induced By Factors Associated with the Metabolic Syndrome in Cultured Small Mesenteric Arteries

This study investigated the effect of the metabolic syndrome associated risk factors hyperglycemia (glucose [Glc]), hyperinsulinemia (insulin [Ins]) and low-grade inflammation (tumor necrosis factor α [TNFα]) on the vasomotor responses of resistance arteries. Isolated small mesenteric arteries from 3-month-old Sprague-Dawley rats, were suspended for 21-23 h in tissue cultures containing either elevated Glc (30 mmol/l), Ins (100 nmol/l), TNFα (100 ng/ml) or combinations thereof. After incubation, the vascular response to noradrenaline (NA), phenylephrine, isoprenaline and NA in the presence of propranolol (10 µmol/l) was measured by wire myography.

RESULTS

Arteries exposed only to combinations of the risk factors showed a significant 1.6-fold increase in the contractile NA sensitivity, which suggests that complex combinations of metabolic risk factors might lead to changes in vascular tone.

Gut region-specific diabetic damage to the capillary endothelium adjacent to the myenteric plexus

OBJECTIVE

Damage in the capillaries supplying the MP has been proposed as a critical factor in the development of diabetic enteric neuropathy. We therefore investigated connections between STZ-induced diabetes and the BM morphology, the size of caveolar compartments, the width of TJs, the transport of albumin, and the quantitative features of Cav-1 and eNOS expression in these microvessels.

METHODS

Gut segments from diabetic rats were compared with those from insulin-treated diabetics and those from controls. The effects of diabetes on the BM, the caveolar compartments, and the TJs were evaluated morphometrically. The quantitative features of the albumin transport were investigated by postembedding immunohistochemistry. The diabetes-related changes in Cav-1 and eNOS expression were assessed by postembedding immunohistochemistry and molecular method.

RESULTS

Thickening of the BM, enlargement of the caveolar compartments, opening of the junctions, enhanced transport of albumin, and overexpression of Cav-1 and eNOS were documented in diabetic animals. Insulin replacement in certain gut segments prevented the development of these alterations.

CONCLUSIONS

These data provide morphological, functional, and molecular evidence that the endothelial cells in capillaries adjacent to the MP is a target of diabetic damage in a regional manner.