The vasodilatory mechanism of nitric oxide and hydrogen sulfide in the human mesenteric artery in patients with colorectal cancer

Recent studies have focused on the role of gasotransmitters in cancer progression and prevention. Therefore, the current study was designed to explore the vasodilator activity of NO and H₂S in the human mesenteric arteries of patients with colorectal cancer (CRC) via the activation of K⁺ channels. A total of two sets of experiments were established for the current investigation. Blood samples from patients with CRC were obtained to detect serum levels of endocan and malondialdehyde (MDA). The role of K⁺ channels in mediating the vasodilation of the human mesenteric artery in response to sodium nitroprusside (SNP) and sodium disulfide (Na₂S) was assessed. The level of serum endocan was indicated to be decreased in patients with CRC compared with healthy individuals, while the level of serum MDA remained unaltered between groups. The arterial rings pre-contracted with norepinephrine were first relaxed by the cumulative addition of increasing concentrations of either SNP (30 nM-30 µM) or (1-6 mM). Maximal relaxation rates were then calculated at 15 min intervals for 60 min. Pre-incubation of arterial rings for 20 min with individual K⁺ channel blockers was indicated to significantly reduce SNP- and Na₂S-induced relaxation at different time points. Pre-treatment of L-nitro-arginine methyl ester did not alter vasodilation that was induced by Na₂S. Furthermore, vasodilation of the CRC mesenteric artery was not altered by the synergistic application of SNP and Na₂S, while pre-incubation of arterial rings with D,L-propargylglycine significantly enhanced vasodilation induced by SNP. These results indicated that endothelial dysfunction and oxidative stress do not serve roles in the pathogenesis of CRC. The dilatory mechanisms of NO and H₂S in mesenteric arteries of patients with CRC were K⁺ channel- and time-dependent, and the activity of cystathionine γ-lyase enzyme inhibited the ability of exogenous NO in vasodilation processes.

Endothelin-1 and angiotensin-II modulate urotensin-II vasoconstriction in rat aorta exposed to mercury

OBJECTIVES

The aim of this study was to evaluate the possible roles of endothelin-1 and angiotensin-II in urotensin-II vasoconstriction and in endothelial dysfunction induced by mercury.

BACKGROUND

Urotensin-II, the most potent vasoactive peptide, is entwined with the cardiovascular diseases and has been labelled as a new pathophysiological biomarker.

METHODS

Rat aortic rings were pre-incubated with sb-710411, bq-123, and captopril. Doses of human urotensin-II with increased concentrations were applied in all groups in the presence or absence of mercury chloride. In another set of the experiment, aortic rings were treated with a single dose of mercury chloride in the presence of each of the above blockers.

RESULTS

Angiotensin-II and endothelin-1 mediated the vascular responses to the peptide urotensin-II under conditions of both intact endothelium and endothelial impairments induced by mercury. Urotensin-II, angiotensin-II and endothelin-1 significantly participated in vascular responses to mercury chloride.

CONCLUSION

The novel finding was that urotensin-II is potentiated under the condition of endothelial dysfunction. Endothelin-1 and angiotensin-II pathways could be heavily exploited in modulating endothelial dysfunction impacts and peptide vascular actions (Tab. 1, Fig. 4, Ref. 30).

Melatonin attenuates responses to angiotensin II in isolated aortic rings of STZ-induced type 1-like DM rats

BACKGROUND

In patients with diabetes mellitus (DM), vascular endothelial dysfunction (VED) is the main reason for impaired life expectancy. Melatonin (MEL) demonstrates wide-ranging effects across various organs and exhibits pleiotropic characteristics. The current study aims to investigate the modulatory roles of MEL vascular response to angiotensin II (Ang II) and its receptors including angiotensin type 1 receptor (AT-1 R) and angiotensin type 2 receptor (AT-2 R) in isolated thoracic aorta of non-diabetes (non-DM) and diabetes (DM) rats.

METHODS

The thoracic aortae were isolated in order to investigate the influence of MEL on AT-1 R, using valsartan (VAL) and MT-2Rusing luzindole (LUZ) via dose-response curve (DRC) measurement of Ang II reactivity. In addition, AT-1 R was involved in this study, under PD123319 with ADInstrument organ bath (Panlab apparatus, Harvard University, USA).

RESULTS

The maximum response of Ang II was increased significantly in DM condition. In addition, AT-1 R was completely blocked under VAL, while AT-2 R was upregulated in the DM group. The combination of VAL and PD123319 led to abolishing the Ang II effect dramatically as well. Melatonin alone reduced Ang II in the DM group dramatically. This effect was also observed with MEL, PD1213319, and VAL combination, as well as, with MEL, LUZ, and PD1213319 combination.

CONCLUSIONS

Melatonin has been demonstrated to modulate both AT-1 R and AT-2 R and has influenced the reactivity of Ang II in the aortas of diabetic rats through highly complex mechanisms.

Vascular actions of Ang 1-7 and Ang 1-8 through EDRFs and EDHFs in non-diabetes and diabetes mellitus

The renin-angiotensin system (RAS) plays a pivotal role in regulating vascular homeostasis, while angiotensin 1-8 (Ang 1-8) traditionally dominates as a vasoconstrictor factor. However, the discovery of angiotensin 1-7 (Ang 1-7) and Ang 1-8 has revealed counter-regulatory mechanisms mediated through endothelial-derived relaxing factors (EDRFs) and endothelial-derived hyperpolarizing factors (EDHFs). This review delves into the vascular actions of Ang 1-7 and Ang 1-8 in both non-diabetes mellitus (non-DM) and diabetes mellitus (DM) conditions, highlighting their effects on vascular endothelial cell (VECs) function as well. In a non-DM vasculature context, Ang 1-8 demonstrate dual effect including vasoconstriction and vasodilation, respectively. Additionally, Ang 1-7 induces vasodilation upon nitric oxide (NO) production as a prominent EDRFs in distinct mechanisms. Further research elucidating the precise mechanisms underlying the vascular actions of Ang 1-7 and Ang 1-8 in DM will facilitate the development of tailored therapeutic interventions aimed at preserving vascular health and preventing cardiovascular complications.

The roles of melatonin and potassium channels in relaxation response to ang 1-7 in diabetic rat isolated aorta

In a circadian cycle, the pineal gland produces and releases melatonin (MEL) into the bloodstream. By activating distinct melatonin receptors, MEL has been shown to variably change vascular endothelial dysfunction (VED) to various vascular beds. This study investigates the interaction of melatonin (MEL) and potassium ion (K+) on angiotensin 1-7 (Ang 1-7) vasorelaxant in streptozotocin (STZ)-induced diabetes mellitus (DM) and non-diabetes mellitus (non-DM) male albino rat aortic rings. The isometric tension of isolated aortic rings was assessed by generating a dose-response curve (DRC) for Ang 1-7 using a PowerLab data acquisition system. Accordingly, three experimental sets were carried out. In the first set the aortic rings were exposed MEL and MEL agonist ramelteon (RAM) and MEL antagonist luzindole (LUZ). In the second set, the aortic rings were exposed to various non-selective calcium activated potassium channel (KCa) blockers, including tetraethylammonium (TEA), a small and large-conductance calcium-activated K+ [(SKCa) and (BKCa)] channels blocker charybdotoxin (ChTx) and intermediate calcium-activated K+ channel (IKCa) blocker clotrimazole (CLT). In the third set, the aortic rings were exposed to various selective K+ channels blockers, including the selective blocker of KATP channel, glibenclamide (Glib), 4-aminopyridine (4-AP), a selective blocker of Kv channels and BaCl2, delayed inward rectifier K+ channels (Kir) blocker. The results highlight the significant role of MEL in modulating vascular reactivity, particularly in the DM aorta. By enhancing the vasorelaxant effects of Ang 1-7 through mechanisms involving its receptors and antioxidant activities, MEL demonstrates its potential to counteract oxidative stress and VED associated with diabetes. These findings advance the understanding of vascular reactivity in diabetes and suggest MEL as a promising therapeutic agent for improving vascular health in diabetic conditions.

The impact of melatonin and its agonist on blood pressure and serum endothelin-1 in continuous light and pinealectomized rats

The present study investigates the roles of melatonin (MEL) and its agonist ramelteon (RAM) on blood pressure regulation, nitric oxide (NO), and oxidative stress and plasma endothelin-1(ET-1) levels in continuous light exposure and pinealectomized conditions. This study includes two experiments. The first experiment involved control, continuous light emitting diode (LED) exposure, continuous LED + MEL administration, and continuous LED + RAM. The second experiment included control, pinealectomy, pinealectomy + MEL administration, pinealectomy + RAM administration, and pinealectomy + continuous LED exposure. The present results showed significant increase of systolic blood pressure (SBP) of continuous LED exposure group, pinealectomy, and pinealectomy with continuous LED exposure. On the contrary, MEL and RAM both decreased SBP. Additionally, the continuous LED exposure considerably increased malondialdehyde (MDA). However, MEL increased both plasma ET-1 slightly and ET-1 significantly but RAM dramatically increased ET-1. While, both of MEL and RAM decreased MDA. In the second experiment, while MDA dramatically increased after pinealectomy and pinealectomy with LED illumination, ET-1 and NO were only a little reduced. Melatonin elevated plasma ET-1 and NO significantly. While, MDA was greatly reduced by MEL but not by RAM. The results suggested that MEL and RAM could attenuate SBP mostly via increasing NO generation and oxidative stress reduction.

The interactions between melatonin and the renin-angiotensin system (RAS) in vascular attenuation in diabetic and non-diabetic conditions

BACKGROUND

The hormone melatonin (MEL), primarily acknowledged for its role in regulating circadian rhythms, has demonstrated itself to be a complicated molecule with significant implications for vascular physiology. Melatonin exerts extensive physiological effects directly via the MEL receptor type 1 (MT1R) and the MEL receptor type 2 (MT2R), as well as indirectly through the improvement of antioxidant vascular tone.

OBJECTIVE

This review aims to analyse the intricate relationships between MEL and the renin-angiotensin system (RAS) in the vascular attenuation of non-diabetic (non-DM) and diabetic (DM) contexts. Alterations in the expression of RAS components and their dysregulation are prevalent in diabetes. Melatonin exhibits vasoprotective advantages in non-diabetic conditions. In the context of DM, vascular problrms such as vascular endothelial dysfunction (VED), hypertension, and atherosclerosis result from the dysregulation of MEL-RAS interactions. Comprehending the actions of MEL on RAS components in diabetes vasculature is essential for formulating tailored pharmaceutical therapy methods.

CONCLUSION

This review consolidates existing knowledge regarding the vascular effects of MEL in relation to RAS activation, emphasising its potential role as a modulating factor for angiotensin 1-8 (Ang 1-8), angiotensin-converting enzyme 2 (ACE2), and angiotensin 1-7 (Ang 1-7) in the management of vascular complications associated with DM.

The vascular influence of melatonin on endothelial response to angiotensin II in diabetic rat aorta

The current study explored melatonin (MEL) and its receptors, including MEL type 1 receptor (MT1) receptor and MEL type 2 receptor (MT2), along with the angiotensin-converting enzyme 2 (ACE2), influence on vascular responses to angiotensin II (Ang II) in rat aortic segments of normal and diabetic rats. The isolated aortic segments were exposed to MEL, the MEL agonist; ramelteon (RAM), the MEL antagonist; luzindole (LUZ), and an ACE2 inhibitor (S, S)-2-(1-Carboxy-2-(3-(3,5-dichlorobenzyl)-3 H-imidazol-4-yl)-ethylamino)-4-methylpentanoic acid,) on Ang II-induced contractions in non-diabetic normal endothelium (non-DM E+), non-diabetic removed endothelium (non-DM E-), and streptozotocin-induced diabetic endothelium-intact (STZ-induced DM E+) rat aortic segments, as well as their combination in STZ-induced DM E + segments, were also included. The current results showed that MEL and RAM shifted Ang II dose-response curve (DRC) to the right side in non-DM E + and non-DM E- aorta but not in STZ-induced DM E + aorta. However, ACE2 inhibition abolished Ang II degradation only in STZ-induced DM E + segments, not in non-DM E + segments. Additionally, the combinations of MEL-LUZ and RAM-ACE2 inhibitor caused a rightward shift in Ang II response in STZ-induced DM E + segments, while the MEL-LUZ combination decreased Ang II DRC. The findings suggest that the effects of MEL and ACE2 inhibitor on Ang II responses depend on the condition of the endothelium and the distribution of the MEL receptors.

The roles of angiotensin-converting enzyme 2 inhibitor, melatonin and its agonist on angiotensin II reactivity in intact and denuded rat aortic rings

BACKGROUND

The pineal product melatonin (MEL) modulates blood vessels through G protein-coupled receptors (GPCRs) called melatonin type 1 receptor (MT1R) and melatonin type 2 receptor (MT2R), in that order. The renin-angiotensin system (RAS), which breaks down angiotensin II (Ang II) to create Ang 1-7, is thought to be mostly controlled by angiotensin-converting enzyme-2 (ACE2).

AIM

The current work examines the involvement of ACE2 inhibitor, MEL, and ramelteon (RAM) in the vascular response to Ang II activities in the endothelial denuded (E-) and intact (E+) rat isolated thoracic aortic rings.

METHOD

The isometric tension was measured to evaluate the vascular Ang II contractility using dose response curve (DRC).

RESULTS

MEL and RAM caused a rightward shift of Ang II in endothelium E + and endothelium E- aorta.

CONCLUSION

According to the current study, the distribution of MEL receptors and the endothelium's condition are related to the vasomodulatory effect of MEL and ACE2 on Ang II attenuation. These physiological interactions can control vascular tone and increase Ang II reactivity denude endothelial layaer.