Hypertension alters the endothelial-dependent biphasic response of bradykinin in isolated Microminipig basilar artery

Restoration of Mitochondrial Function Is Essential in the Endothelium-Dependent Vasodilation Induced by Acacetin in Hypertensive Rats

Mitochondrial dysfunction in the endothelium contributes to the progression of hypertension and plays an obligatory role in modulating vascular tone. Acacetin is a natural flavonoid compound that has been shown to possess multiple beneficial effects, including vasodilatation. However, whether acacetin could improve endothelial function in hypertension by protecting against mitochondria-dependent apoptosis remains to be determined. The mean arterial pressure (MAP) in Wistar Kyoto (WKY) rats, spontaneously hypertensive rats (SHR) administered with acacetin intraperitoneally for 2 h or intragastrically for six weeks were examined. The endothelial injury was evaluated by immunofluorescent staining and a transmission electron microscope (TEM). Vascular tension measurement was performed to assess the protective effect of acacetin on mesenteric arteries. Endothelial injury in the pathogenesis of SHR was modeled in HUVECs treated with Angiotensin II (Ang II). Mitochondria-dependent apoptosis, the opening of Mitochondrial Permeability Transition Pore (mPTP) and mitochondrial dynamics proteins were determined by fluorescence activated cell sorting (FACS), immunofluorescence staining and western blot. Acacetin administered intraperitoneally greatly reduced MAP in SHR by mediating a more pronounced endothelium-dependent dilatation in mesenteric arteries, and the vascular dilatation was reduced remarkably by NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthesis. While acacetin administered intragastrically for six weeks had no apparent effect on MAP, it improved the endothelium-dependent dilatation in SHR by activating the AKT/eNOS pathway and protecting against the abnormalities of endothelium and mitochondria. Furthermore, acacetin remarkably inhibited Ang II induced apoptosis by inhibiting the increased expression of Cyclophilin D (CypD), promoted the opening of mPTP, ROS generation, ATP loss and disturbance of dynamin-related protein 1 (DRP1)/optic atrophy1 (OPA1) dynamics in HUVECs. This study suggests that acacetin protected against endothelial dysfunction in hypertension by activating the AKT/eNOS pathway and modulating mitochondrial function by targeting mPTP and DRP1/OPA1-dependent dynamics.

Prostaglandin F2α evokes vasoconstrictor and vasodepressor activities that are both independent of the F prostanoid receptor

The F prostanoid receptor (FP), which accounts for the therapeutic effect of PGF_2α in uterine atony that leads to postpartum hemorrhage and maternal morbidity, could possibly mediate vasoconstrictor effect in small or resistance arteries to elevate blood pressure that limits the clinical use of the agent in patients with cardiovascular disorders. This study aimed to test the above hypothesis with genetically altered mice. Ex vivo and in vivo experiments were performed on control wild-type (WT) mice and mice with deficiencies in FP (FP^-/- ) or thromboxane (Tx)-prostanoid receptor (the original receptor of TxA₂ ; TP^-/- ), and/or those with an additional deficiency in E prostanoid receptor-3 (one of the vasoconstrictor receptors of PGE₂ ; EP3^-/- ). Here, we show that PGF_2α indeed evoked vasoconstrictor responses in the above-mentioned tissues of WT mice, which were however unaltered by FP^-/- . Interestingly, such contractile responses were reversed into dilations by TP^-/- /EP3^-/- . A similar pattern of results was observed with the pressor effect of PGF_2α under in vivo conditions. However, TP^-/- alone (which could largely remove the contractile responses) did not result in relaxation to PGF_2α . Also, either the ex vivo vasodilator effect or the in vivo depressor response of PGF_2α obtained after the removal of TP and EP3-mediated actions was unaltered by FP^-/- . Therefore, both the ex vivo vasoconstrictor action in small or resistance arteries and the systemic pressor effect of PGF_2α can reflect vasoconstrictor activities derived from the non-FP receptors TP and EP3 outweighing a concurrently activated dilator effect, which is again independent of FP.

Impact of the Renin-Angiotensin System on the Endothelium in Vascular Dementia: Unresolved Issues and Future Perspectives

The effects of the renin-angiotensin system (RAS) surpass the renal and cardiovascular systems to encompass other body tissues and organs, including the brain. Angiotensin II (Ang II), the most potent mediator of RAS in the brain, contributes to vascular dementia via different mechanisms, including neuronal homeostasis disruption, vascular remodeling, and endothelial dysfunction caused by increased inflammation and oxidative stress. Other RAS components of emerging significance at the level of the blood-brain barrier include angiotensin-converting enzyme 2 (ACE2), Ang(1-7), and the AT2, Mas, and AT4 receptors. The various angiotensin hormones perform complex actions on brain endothelial cells and pericytes through specific receptors that have either detrimental or beneficial actions. Increasing evidence indicates that the ACE2/Ang(1-7)/Mas axis constitutes a protective arm of RAS on the blood-brain barrier. This review provides an update of studies assessing the different effects of angiotensins on cerebral endothelial cells. The involved signaling pathways are presented and help highlight the potential pharmacological targets for the management of cognitive and behavioral dysfunctions associated with vascular dementia.

Bradykinin increases BP in endotoxemic rat: functional and biochemical evidence of angiotensin II AT1 /bradykinin B2 receptor heterodimerization

BACKGROUND AND PURPOSE

Bradykinin may induce vasoconstriction in selected vessels or under specific experimental conditions. We hypothesized that inflammatory stimuli, such as endotoxin challenge, may induce the dimerization of AT₁ /B₂ receptors, altering the vascular effects of bradykinin.

EXPERIMENTAL APPROACH

Wistar rats received LPS (1 mg·kg^-1 , i.p.) and were anaesthetized for assessment of BP. Mesenteric resistance arteries were used in organ baths and subjected to co-immunoprecipitation and Western blot analyses.

KEY RESULTS

At 24 and 48 hr after LPS, bradykinin-induced hypotension was followed by a sustained increase in BP, which was not found in non-endotoxemic animals. The B₂ receptor antagonist Hoe-140 fully blocked the responses to bradykinin. The pressor effect of bradykinin was not prevented by prazosin, an α₁ -adrenoceptor antagonist, but it was inhibited by the AT₁ receptor antagonist losartan or the Rho-kinase inhibitor Y-27632. Endotoxemic rats also displayed enhanced pressor responses to angiotensin II, which were blocked by Hoe-140. Co-immunoprecipitation isolated using anti-B₂ or anti-AT₁ receptor antibodies showed that resistance arteries presented augmented levels of the AT₁ /B₂ receptor complexes at 24 hr after LPS injection. The presence of AT₁ /B₂ receptor heterodimers did correlate with the development of losartan-sensitive contractile responses to bradykinin and potentiation of angiotensin II-induced contraction, which was prevented by Hoe-140.

CONCLUSIONS AND IMPLICATIONS

Endotoxin challenge is a stimulus for AT₁ /B₂ receptor heterodimerization in native vessels and shifts the B₂ receptor-dependent vascular effect of bradykinin to a more complex pathway, which also depends on AT₁ receptors and their intracellular signalling pathways.

TP and/or EP3 receptors mediate the vasoconstrictor and pressor responses of prostaglandin F2α in mice and/or humans

The vasoconstrictor and/or pressor effects of prostaglandin (PG)F_2α participate in the development of vascular pathologies and limit the clinical use of the agent. This study aimed to determine the receptor types responsible for the vasoconstrictor activity of PGF_2α and whether they mediate the pressor response evoked by the prostanoid under in vivo conditions. Experiments were performed on genetically altered mice and/or on vessels from these mice or humans. Here we show that deletion of the thromboxane-prostanoid receptor (TP^-/-) abolished or drastically diminished the contraction to PGF_2α in isolated mouse vessels (some of which were resistance arteries) and reduced the elevation in blood pressure evoked by the prostanoid under in vivo conditions. In accordance, TP antagonism abolished the contraction in small arteries of human omentum. Further deletion of E prostanoid receptor type 3 (EP3^-/-) removed the PGF_2α-evoked contraction that remained in some TP^-/- arteries and added to the effect of TP^-/- on the elevation in blood pressure evoked by the prostanoid under in vivo conditions. In contrast, the uterine contraction to PGF_2α mediated via the F prostanoid receptor (FP) was unaltered in TP^-/-/EP3^-/- mice. These results demonstrate that the non-FP receptors TP and/or EP3 mediate the vasoconstrictor and pressor effects of PGF_2α, which are still of concern under clinical conditions.-Liu, B., Li, J., Yan, H., Tian, D., Li, H., Zhang, Y., Guo, T., Wu, X., Luo, W., Zhou, Y. TP and/or EP3 receptors mediate the vasoconstrictor and pressor responses of prostaglandin F_2α in mice and/or humans.

Diurnal Variation of Melatonin Concentration in the Cerebrospinal Fluid of Unanesthetized Microminipig

BACKGROUND/AIM

The aim of this study was to develop a method for sequentially collecting cerebrospinal fluid (CSF) from an unanesthetized microminipig, which shares many physiological and anatomical similarities with humans, such as diurnality, and investigate the diurnal variation of melatonin concentration in the CSF.

MATERIALS AND METHODS

A catheter was placed percutaneously into the subarachnoid space of an anesthetized animal, and the tip of the catheter was placed into the cisterna magna under X-ray. We then sequentially collected CSF at light-on and -off times from the unanesthetized animal for several weeks. After catheter placement, a period of one week or more was necessary to relieve the contamination of RBCs in the CSF.

RESULTS

A higher melatonin level in the CSF was noted during lights-off time, and the level was higher than that in the serum.

CONCLUSION

This model of sequential collection of CSF will contribute to research in brain functions.

Hydrogen Sulfide Attenuates Hypertensive Inflammation via Regulating Connexin Expression in Spontaneously Hypertensive Rats

BACKGROUND Hydrogen sulfide (H2S) has anti-inflammatory and anti-hypertensive effects, and connexins (Cxs) are involved in regulation of immune homeostasis. In this study, we explored whether exogenous H2S prevents hypertensive inflammation by regulating Cxs expression of T lymphocytes in spontaneously hypertensive rats (SHR). MATERIAL AND METHODS We treated SHR with sodium hydrosulfide (NaHS) for 9 weeks. Vehicle-treated Wistar-Kyoto rats (WKYs) were used as a control. The arterial pressure was monitored by the tail-cuff method, and vascular function in basilar arteries was examined by pressure myography. Hematoxylin and eosin staining was used to show vascular remodeling and renal injury. The percentage of T cell subtypes in peripheral blood, surface expressions of Cx40/Cx43 on T cell subtypes, and serum cytokines level were determined by flow cytometry or ELISA. Expression of Cx40/Cx43 proteins in peripheral blood lymphocytes was analyzed by Western blot. RESULTS Chronic NaHS treatment significantly attenuated blood pressure elevation, and inhibited inflammation of target organs, vascular remodeling, and renal injury in SHR. Exogenous NaHS also improved vascular function by attenuating KCl-stimulated vasoconstrictor response in basilar arteries of SHR. In addition, chronic NaHS administration significantly suppressed inflammation of peripheral blood in SHR, as evidenced by the decreased serum levels of IL-2, IL-6, and CD4/CD8 ratio and the increased IL-10 level and percentage of regulatory T cells. NaHS treatment decreased hypertension-induced Cx40/Cx43 expressions in T lymphocytes from SHR. CONCLUSIONS Our data demonstrate that H2S reduces hypertensive inflammation, at least partly due to regulation of T cell subsets balance by Cx40/Cx43 expressions inhibition.

Corpus luteum Regression Induced by Prostaglandin F2α in Microminipigs During the Normal Estrous Cycle

Induction of corpus luteum regression and subsequent estrus using prostaglandin F2α (PGF2α) in microminipigs was investigated. Microminipigs with normal estrous cycle were treated with PGF2α as 0.75 mg (0.75 PG group, n=3) or 1.5 mg (1.5 PG group, n=4) dinoprost injected into the vulva at 24-h intervals at 10 days after the onset of estrus (D0), D1 and D2. Three microminipigs were not treated (control group). The estrous interval in the 1.5 PG group was significantly shortened compared to the control and 0.75 PG groups. Plasma progesterone levels started to decline and reached the base line in the 1.5 PG group significantly faster than in the control group. In conclusion, we demonstrate that multiple PGF2α treatments can induce corpus luteum regression and estrous synchronization in female microminipigs.