Control Of Vascular Reactivity Research Articles

Blood brain barrier precludes the cerebral arteries to intravenously-injected antisense oligonucleotide

Alternative splicing of the ryanodine receptor subtype 3 (RyR3) produces a short isoform (RyR3S) able to negatively regulate the ryanodine receptor subtype 2 (RyR2), as shown in cultured smooth muscle cells from mice. The RyR2 subtype has a crucial role in the control of vascular reactivity via the fine tuning of Ca2+ signaling to regulate cerebral vascular tone. In this study, we have shown that the inhibition of RyR3S expression by a specific antisense oligonucleotide (asRyR3S) was able to increase the Ca2+ signals implicating RyR2 in cerebral arteries ex vivo. Moreover, we tried to inhibit the expression of RyR3S in vivo. The asRyR3S was complexed with JetPEI and injected intravenously coupled with several methods known to induce a blood brain barrier disruption. We tested solutions to induce osmotic choc (mannitol), inflammation (bacteria lipopolysaccharide and pertussis toxin), vasoconstriction or dilatation (sumatriptan, phenylephrine, histamine), CD73 activation (NECA) and lipid instability (Tween80). All tested technics failed to target asRyR3 in the cerebral arteries wall, whereas the molecule was included in hepatocytes or cardiomyocytes. Our results showed that the RyR3 alternative splicing could have a function in cerebral arteries ex vivo; however, the disruption of the blood brain barrier could not induce the internalization of antisense oligonucleotides in the cerebral arteries, in order to prove the function of RYR3 short isoform in vivo.

Protease activated receptor 2 and the cardiovascular system.

Protease activated receptors (PARs) represent a novel class of seven transmembrane domain G-protein coupled receptors activated by proteolytic cleavage. Up to now, four members of this class of receptors have been identified, PAR1 to PAR4 (Hollenberg, 1999). The mechanism for activation of PARs involves a proteolytic unmasking of an N-terminal sequence that acts as a tethered ligand. In the absence of proteolysis, PAR1, PAR2 and PAR4, but not PAR3, can be activated by synthetic peptides (PAR-activated peptides, PAR-APs) ranging between five and 14 aminoacids, whose sequence mimics the tethered ligand (Dery et al., 1998). The thrombin receptor PAR1 was the first PAR to be discovered and cloned (Vu et al., 1991). Successively, a second member of PAR family was identified by Nystedt (1994) who cloned a mouse genomic DNA sequence encoding a proteolitically activated receptor, related to but with a different sequence from the thrombin receptor PAR1. The receptor was termed PAR2 and it was found to be activated by trypsin that cleaves the receptor within the sequence N34SKGR/SLIGRLETQP48 of its extracellular -NH2 terminus, exposing a tethered ligand, SLIGRLETQP, that binds the cleaved receptor (Figure 1). Synthetic peptides mimicking the tethered ligand sequence, SLIGRLETQ . , can activate the receptor even in the absence of proteolysis. The site for the receptor proteolytic cleavage contains the sequence SLIGRL and SLIGKV, murine and human respectively (Nystedt et al., 1994). Figure 1 Schematic representation of PAR2 activation by trypsin. PAR2 is activated upon trypsin cleavage within the sequence N34SKGR/SLIGRLETQP48 of its extracellular -NH2 terminus. This event unmasks a tethered ligand, SLIGRLETQP, that binds the cleaved receptor ... The physiological ligand of PAR2 has not as yet been identified. However, it has been shown that besides trypsin, the receptor may be activated by tryptase (Molino et al., 1997) and factor Xa (Fox et al., 1997), but it is resistant to activation by thrombin, even at concentrations as high as 100 nM. PAR2 mRNA has been found in several human and animal tissues, including kidney, stomach, pancreas, liver, colon and small intestine (Nystedt et al., 1994). Furthermore, by using immunohistochemical techniques, PAR2 has been localized in almost all human organs; in particular, a strong immunoreactivity has been detected in endothelial and epithelial cells, and in smooth muscle of both vascular and non vascular origin (D'andrea et al., 1998). To date, the physiological and/or pathological role of PAR2 is unknown. The presence of PAR2 on highly vascularized organs strongly suggests a role for the receptor in the control of vascular reactivity (D'andrea et al., 1998). This hypothesis is supported by a large amount of work that has been produced, since its discovery and cloning, giving evidence for the ability of PAR2 in regulating vascular function. On the basis of the present knowledge, the aim of this review is to recapitulate the cardiovascular functions of PAR2.

Transmembrane currents in capillary endothelial cells are modulated by external Mg2+ ions.

The capillary endothelium of the brain is involved essentially in the preservation of the blood-brain barrier and in the regulation of brain microcirculation. As a biological membrane lining the inner wall of blood vessels, the endothelium is exposed to many environmental alterations of the blood composition. In this context, it is known that changes in the concentration of extracellular magnesium ions ([Mg2+]o) play important roles in the control of vascular reactivity, by modulating the myogenic tone and the contractile response of vascular smooth muscle cells to various physiological and pharmacological stimuli (Altura & Altura, 1981). Recent studies on endothelial cells demonstrate that changes in [Mg2+]o can modify the state of the cytosolic free calcium (Zhang et al, 1993). The aim of the present study was, therefore, to investigate whether in fact this modulatory effect of Mg2+ could be ascribed to some effect on the excitability of the cell membrane of endothelial cells. For this purpose, transmembrane currents of rat brain capillary endothelial cells (BCECs) were investigated in whole-cell experiments with the patch-clamp technique (Hamill et al, 1981).KeywordsCapillary Endothelial CellTest PulseCytosolic Free CalciumBrain Capillary Endothelial CellTransmembrane CurrentThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Sumatriptan‐induced saphenous venoconstriction in the anaesthetized dog through 5‐HT1‐like receptor activation

1. The role of vasoconstrictor 5-HT1-like receptors in the control of vascular reactivity in vivo has been relatively little studied, particularly with regards to venous function. Using an anaesthetized dog model, we have investigated the haemodynamic profile of the selective 5-HT1-like agonist, sumatriptan, focussing on the reactivity of the saphenous venous bed. The key feature of our experimental model was the implantation of ultrasonic crystals on the adventitial surface of the lateral saphenous vein to provide direct and continuous measurement of drug-induced changes in vein diameter. Saphenous vein pressure was measured simultaneously via a proximal branch. 2. Sumatriptan 1-30 micrograms kg-1, i.v., produced pronounced dose-related reductions in saphenous vein diameter which reached congruent to 40% at the highest dose tested. Sumatriptan also produced modest increases in mean blood pressure, total peripheral resistance and left ventricular end diastolic pressure but had little or no effect on cardiac output, heart rate, cardiac contractility or saphenous venous pressure. Sumatriptan-induced reductions in saphenous vein diameter were strongly antagonized by the 5-HT1-receptor antagonist, methiothepin (0.3 mg kg-1, i.v.) but were unaffected by the 5-HT2 antagonist, ketanserin (0.3 mg kg-1, i.v.). 3. Hence, 5-HT1-like receptor stimulation in vivo can result in a powerful local venoconstrictor effect.

Platelet activating factor levels in pre-eclampsia and normal pregnancy

SummaryThe objective of the study was to compare platelet activating factor (PAF) concentrations in pre-eclamptic and healthy normotensive pregnant women. Blood samples for measurement of platelet count, urea and creatinine, and of PAF by thin layer chromatography and high performance liquid chromatography were obtained from seven pre-eclamptic and seven healthy primigravidae. The main outcomes were PAF concentrations in the pre-eclampsia and control groups and correlation of PAF concentrations with gestational age. PAF concentration in the pre-eclamptic group was lower than that of the controls (18˙8 versus 36˙0, P = 0˙001). Both groups exhibited a correlation between plasma PAF levels and gestational age (study group, r =-0˙84; control group, r=-0˙79). Decreased circulating PAF levels in the pre-eclamptic group may represent loss of physiological control of vascular reactivity and platelet function by PAF.

Control of Vascular Reactivity in Pregnancy Induced Hypertension

To evaluate the possibility that vascular reactivity in umbilical artery is different in normal and pre-eclamptic condition, we assessed an “in vitro study” on strips of umbilical arteries removed at the end of normal and pre-eclamptic pregnancy. We studied the reactivity of those arteries to prostaglandin A1 and prostaglandin F2α-The dose-response analysis to prostaglandins on normal umbilical arteries were between 10−7 and 10−4; in contrast, the results obtained on arteries removed at the end of pre-eclamptic pregnancies were not consistent. In this group a tendency to two different distributions seemed to occur and was related to different clinical features of pre-eclampsia, namely the early and the late onset of the disease. Our results suggest that the various clinical pictures of pre-eclampsia correlate with different conditions of vascular reactivity.

Interaction of nonsteroidal anti-inflammatory drugs with antihypertensive and diuretic agents: Control of vascular reactivity by endogenous prostanoids

Indomethacin and some other nonsteroidal anti-inflammatory drugs partially antagonize the blood pressure lowering effect of drugs used to treat hypertension. They can also produce a mild elevation of blood pressure in normotensive individuals. The elevated arterial pressure caused by these agents is associated with Increases in the vascular resistance of mainly the renal and splanchnic beds. This may be due to direct inhibition of the synthesis of vasodilator prostanoids, or it may be due to indirect potentiation of the action of the sympathetic nervous system or of angiotensin II. Nonsteroidal antiinflammatory drugs also cause renal retention of sodium and this probably contributes to their hypertensive effects. In humans, the sodium retention may involve increased reabsorption in the proximal tubule. Although a direct tubular action is possible, these drugs may change proximal sodium reabsorption by their vascular effects. However, the exact mechanism is not understood. These interactions are clinically significant and may complicate the treatment of common diseases.

Influence of Pregnancy, Prostacyclin and Labetalol on the Vascular Response to Angiotensin II in the Rat

The mean arterial blood pressure and the vascular response to angiotensin II were studied in chronically catheterized and unanesthetized rats.Pregnancy significantly decreased the pressor response. This effect could be mimicked by prostacyclin infusions in non pregnant rats, whereas labetalol had an opposite effect.The model seems suitable for investigations into the control of vascular reactivity, and reinforces the hypothesis that the relative vascular refractoriness to angiotensin II during pregnancy could result, at least in part, from the action of vasodilator prostaglandins, in this instance prostacyclin

Oral administration of theophylline to modify pressor responsiveness to angiotensin II in women with pregnancy-induced hypertension

Normally, women become refractory to the pressor effects of infused angiotensin-II (A-II) early in pregnancy. Gravid women destined to develop pregnancy-induced hypertension (PIH) lose this refractoriness to A-II several weeks prior to the detection of hypertension. Normal pregnant women also lose their A-II refractoriness after treatment with prostaglandin synthetase inhibitors and, in this regard, become similar to gravid women who are destined to develop PIH. From this observation, we have concluded that a prostaglandin(s) or a prostaglandin-related substance(s) is likely involved in the mediation of vascular reactivity to A-II during pregnancy. The present study was conducted to ascertain if control of vascular reactivity during pregnancy also involves the cyclic nucleotides. Since theophylline is known to inhibit the action of phosphodiesterase, an action that results in increased cellular levels of cyclic 3′,5′-adenosine monophosphate (cAMP), we evaluated the effective pressor dose of A-II before and after the administration of theophylline to women with mild PIH who were beyond the 28th week of gestation. The effective pressor dose of A-II in these women with PIH before theophylline treatment was 7.3 ± 1.4 ng. × kg.−1 × min.−1 (mean and standard error). Following treatment of these women with the equivalent of 500 mg. of theophylline daily for four days, the effective pressor dose of A-II was 16.7 ± 3.8 ng. × kg.−1 × min.−1 (p < 0.025. These findings are consistent with the view that a prostaglandin(s) synthesized in the arteriole may modulate the vascular refractoriness to A-II by altering the intracellular level of cAMP in vascular tissues.