Histamine-induced vasodilatation in the perfused mesenteric arterial bed of diabetic rats

Monoaminergic Receptors as Modulators of the Perivascular Sympathetic and Sensory CGRPergic Outflows

Blood pressure is a highly controlled cardiovascular parameter that normally guarantees an adequate blood supply to all body tissues. This parameter is mainly regulated by peripheral vascular resistance and is maintained by local mediators (i.e., autacoids), and by the nervous and endocrine systems. Regarding the nervous system, blood pressure can be modulated at the central level by regulating the autonomic output. However, at peripheral level, there exists a modulation by activation of prejunctional monoaminergic receptors in autonomic- or sensory-perivascular fibers. These modulatory mechanisms on resistance blood vessels exert an effect on the release of neuroactive substances from the autonomic or sensory fibers that modify blood pressure. Certainly, resistance blood vessels are innervated by perivascular: (i) autonomic sympathetic fibers (producing vasoconstriction mainly by noradrenaline release); and (ii) peptidergic sensory fibers [producing vasodilatation mainly by calcitonin gene-related peptide (CGRP) release]. In the last years, by using pithed rats, several monoaminergic mechanisms for controlling both the sympathetic and sensory perivascular outflows have been elucidated. Additionally, several studies have shown the functions of many monoaminergic auto-receptors and hetero-receptors expressed on perivascular fibers that modulate neurotransmitter release. On this basis, the present review: (i) summarizes the modulation of the peripheral vascular tone by adrenergic, serotoninergic, dopaminergic, and histaminergic receptors on perivascular autonomic (sympathetic) and sensory fibers, and (ii) highlights that these monoaminergic receptors are potential therapeutic targets for the development of novel medications to treat cardiovascular diseases (with some of them explored in clinical trials or already in clinical use).

Gallic acid improves endothelium-dependent vasodilatory response to histamine in the mesenteric vascular bed of diabetic rats

BACKGROUND

Endothelial dysfunction is one of the many complications caused by diabetes mellitus. The aim of the present study was to evaluate the effects of gallic acid (GA) on the mesenteric vascular bed (MVB) response to histamine in diabetic rats.

METHODS

Forty male Wistar rats were randomly assigned to a control group, an untreated alloxan-induced diabetic group and three diabetic groups treated with different doses of GA. Six weeks after induction of diabetes and GA treatment, total antioxidant capacity (TAC), malondialdehyde (MDA) concentrations, and the vasodilatory response to histamine of the MVB (measured as changes in perfusion pressure) were determined.

RESULTS

The vasodilatory response to histamine and TAC decreased, whereas MDA increased in the plasma from diabetic rats (P < 0.01). However, in the presence of 3 × 10^-5  mol/L N ^G -nitro-l-arginine methyl ester (a nitric oxide synthase inhibitor) and 1 × 10^-5  mol/L indomethacin (an inhibitor of prostaglandin production), the vasodilatory response of the MVB to histamine was reduced in all groups (P < 0.001). Treatment of diabetic rats with 20 and 40 mg/kg per day GA, but not 10 mg/kg per day GA, increased TAC and decreased MDA concentrations (P < 0.01 and P < 0.001 vs untreated diabetic rats, respectively) and significantly improved the vasodilatory response to histamine (P < 0.05 and P < 0.001, respectively).

CONCLUSION

The results show that, in diabetic rats, the endothelium-dependent vasodilatory response of the MVB to histamine is significantly decreased and depends on both nitric oxide- and prostaglandin-producing pathways and may be mediated by oxidative stress. Treatment with the antioxidant GA restored the vasodilatory response of the MVB to histamine.

Co-administration of Grape Seed Extract and Exercise Training Improves Endothelial Dysfunction of Coronary Vascular Bed of STZ-Induced Diabetic Rats

Background

One of the known complications of diabetes mellitus is vascular dysfunction. Inability of the coronary vascular response to cardiac hyperactivity might cause a higher incidence of ischemic heart disease in diabetic subjects. It has been indicated that regular exercise training and antioxidants could prevent diabetic cardiovascular problems enhanced by vascular damage.

Objectives

The aim of this study was to determine the effects of grape seed extract (as antioxidant), with and without exercise training on coronary vascular function in streptozotocin induced diabetic rats.

Materials and Methods

Fifty male Wistar rats weighing 200 – 232 grams were randomly divided into five groups of 10 rats each: sedentary control, sedentary diabetic, trained diabetic, grape seed extract (200 mg/kg) treated sedentary diabetic and, grape seed extract treated trained diabetic. Diabetes was induced by one intraperitoneal injection of streptozotocin. After eight weeks, coronary vascular responses to vasoactive agents were determined.

Results

The endothelium dependent vasorelaxation to acetylcholine was reduced significantly in diabetic animals; exercise training or grape seed extract administration partially improves this response. However, exercise training in combination with grape seed extract restores endothelial function completely. The endothelium independent vasorelaxation to sodium nitroprusside was improved by combination of exercise training and grape seed extract. On the other hand, the basal perfusion pressure and vasoconstrictive response to phenylephrine did not change significantly.

Conclusions

The data indicated that co-administration of grape seed extract and exercise training had more significant effects than exercise training or grape seed extract alone; this may constitute a convenient and inexpensive therapeutic approach to diabetic vascular complications.

Stimulation of histamine H2 receptors activates TRPC3 channels through both phospholipase C and phospholipase D

Histamine plays an important role in many physiological functions; and a change in cytosolic Ca(2+) ([Ca(2+)](i)) may be an early signal in these processes. In the present study, we investigated the activation mechanism of TRPC3, the Canonical Transient Receptors Potential 3 Channels, by histamine via a non-capacitative Ca(2+) entry pathway. TRPC3 was transfected into HEK293 cells and the cells were treated with thapsigargin to deplete the intracellular Ca(2+) stores; re-addition of Ca(2+) initiated a capacitative Ca(2+) entry (CCE). A subsequent application of histamine evoked another Ca(2+) influx on top of the CCE signal only in the TRPC3-transfected HEK293 cells, indicating that histamine can activate TRPC3 via a non-capacitative Ca(2+) entry pathway (non-CCE). This histamine-induced non-CCE was abolished by cimitidine, a histamine H(2) receptors antagonist, but not by histamine H(1) receptor antagonists pyrilamine and diphenhydramine. KT5720, a protein kinase A (PKA) inhibitor, had no effect on the histamine-induced non-CCE. This histamine-induced non-CCE was partially reduced by U73122, a phospholipase C (PLC) inhibitor, and by butan-1-ol, a phospholipase D (PLD) inhibitor. When both PLC and PLD inhibitors were simultaneously applied, the non-CCE signal was completely abolished. Taken together, our results showed, for the first time, that histamine could activate TRPC3 via histamine H(2) receptors, and both PLC and PLD participated in this process.

Inhibition of acetylcholine-induced EDHF response by elevated glucose in rat mesenteric artery

The effects of high glucose on endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxations of isolated rat mesenteric artery and the possible involvement of reactive oxygen species in these responses were investigated. After precontraction with phenylephrine (3 x 10(-8)-10(-7) M), acetylcholine (10(-8)-3 x 10(-6) M) and A 23187 (10(-8)-3 x 10(-6) M), a calcium ionophore, induced concentration-dependent relaxations in the presence of N(W)-nitro-l-arginine methyl ester (L-NAME) (10(-4) M) and indomethacin (10(-5) M). These relaxations were abolished in the presence of charybdotoxin (2 x 10(-7) M) plus apamin (10(-7) M) and were assumed to be mediated by EDHF. Effects of elevated glucose were examined by incubating the arterial rings for 6 h in Krebs-Henseleit solution containing 22.2 mM glucose. Under these conditions relaxation to acetylcholine was significantly attenuated but was unchanged when the tissues were incubated for 6 h in solution containing 11.1 mM mannitol used as hyperosmotic control. Addition of superoxide dismutase (SOD) (75 U/ml) and combination of SOD with catalase (200 U/ml) during incubation with high glucose significantly preserved the impairment of EDHF-mediated relaxations to acetylcholine. A 23187-induced endothelium-dependent relaxation was not affected by high glucose. Similarly, relaxations to pinacidil (10(-10)-10(-5) M) and to sodium nitroprusside (SNP) (10(-10)-3 x 10(-7) M) were also unchanged in the rings exposed to high glucose. These results suggest that in rat mesenteric arteries exposed to elevated glucose receptor-dependent EDHF-mediated relaxations (acetylcholine-induced) are impaired whereas receptor-independent ones (A 23187-induced) and responses to smooth muscle relaxants that exert their effects through mechanisms independent of endothelium are unaffected. Our findings lead us to propose that reactive oxygen species like superoxide ((.)O(2)(-)) and hydrogen peroxide (H(2)O(2)) do seem to play a role in the impairment of EDHF-mediated relaxations in the presence of elevated glucose.

Dexamethasone: Benefit and Prejudice for Patients Undergoing On-Pump Coronary Artery Bypass Grafting

STUDY OBJECTIVES

Cardiac surgery with cardiopulmonary bypass (CPB) results in perioperative organ damage caused by the systemic inflammatory response syndrome (SIRS) and ischemia/reperfusion injury. Administration of corticosteroids before CPB has been demonstrated to inhibit the activation of the systemic inflammatory response. However, the clinical benefits of corticosteroid therapy are controversial. This study was designed to document the effects of dexamethasone on cytokine release and perioperative myocardial, pulmonary, renal, intestinal, and hepatic damage, as assessed by specific and sensitive biomarkers.

DESIGN AND PATIENTS

A prospective, double-blind, placebo-controlled, randomized trial for dexamethasone was conducted in 20 patients receiving either dexamethasone (1 mg/kg before anesthesia induction and 0.5 mg/kg after 8 h; n = 10) or placebo (n = 10). Different markers were used to assess the SIRS: interleukin (IL)-6, IL-8, IL-10, C-reactive protein (CRP), and tryptase; and organ damage: heart (plasma heart-type fatty acid binding protein, cardiac troponin I [cTnI], creatine kinase-MB), kidneys (N-acetyl-glucosaminidase [NAG], microalbuminuria), intestine (intestinal-type fatty acid binding protein [I-FABP]/liver-type fatty acid binding protein [L-FABP]), and liver (alpha-glutathione S-transferase).

RESULTS

Dexamethasone modulated the SIRS with lower proinflammatory (IL-6, IL-8) and higher antiinflammatory (IL-10) IL levels. CRP and tryptase were lower in the dexamethasone group. cTnI values were lower in the dexamethasone group at 6 h in the ICU (p = 0.009). Patients in the dexamethasone group had a longer time to tracheal extubation (18.86 +/- 1.13 h vs 15.01 +/- 0.99 h, p = 0.02 [mean +/- SEM]), with a lower oxygenation index at that time: Pa(O2)/fraction of inspired oxygen ratio, 37.17 +/- 1.8 kPa vs 29.95 +/- 2.1 kPa (p = 0.009). The postoperative glucose level (10.7 +/- 0.6 mmol/L vs 7.4 +/- 0.5 mmol/L, p = 0.005) was higher in the dexamethasone group. Serum glucose was independently associated with intestinal injury (urine I-FABP peak, R2 = 42.5%, beta = 114.4 +/- 31.4, significant at p = 0.002; urine L-FABP peak, R2 = 47.3%, beta = 7,714.1 +/- 1,920.9, significant at p = 0.001) and renal injury (urine NAG, R2 = 32.1%, beta = 0.21 +/- 0.07, significant at p = 0.009). Tryptase peaks correlated negatively with peaks of intestinal and renal injury biomarkers.

CONCLUSION

Even while inhibiting SIRS, dexamethasone treatment offered no protection against transient, subclinical, perioperative abdominal organ damage. Tryptase release could have a preconditioning effect, offering protection against perioperative intestinal and renal damage. Dexamethasone treatment resulted in more pronounced postoperative pulmonary dysfunction, prolonged time to tracheal extubation, and initiated postoperative hyperglycemia in patients undergoing elective on-pump coronary artery bypass graft surgery.