Halothane inhibits endothelium-dependent relaxation elicited by acetylcholine in human isolated pulmonary arteries

Chronic aldosterone administration causes Nox2-mediated increases in reactive oxygen species production and endothelial dysfunction in the cerebral circulation

OBJECTIVES

An elevated plasma aldosterone level is an independent cardiovascular risk factor. Although excess aldosterone promotes cardiovascular disease, no studies have examined the effect of increased plasma aldosterone on the cerebral circulation. A major source of vascular reactive oxygen species (ROS) during cardiovascular disease is the NADPH oxidases. Because Nox2-containing NADPH oxidase (Nox2 oxidase) is highly expressed in the cerebral endothelium, we postulated that it might contribute to ROS generation and vascular dysfunction in response to aldosterone. Here, we examined the effect of aldosterone and Nox2 oxidase on ROS production and endothelial dysfunction in the cerebral circulation, and whether the effects of aldosterone are exacerbated in aged mice.

METHODS AND RESULTS

In adult (average age ∼24-25 weeks) wild-type and Nox2-deficient (Nox2(/y)) mice, neither vehicle nor aldosterone (0.28  mg/kg per day for 14 days) affected blood pressure (measured using tail-cuff). By contrast, aldosterone treatment reduced dilation of the basilar artery (measured using myography) to the endothelium-dependent agonist acetylcholine in wild-type mice (P < 0.05), but had no such effect in Nox2(/y) mice (P > 0.05). Aldosterone increased basal and phorbol dibutyrate-stimulated superoxide production (measured using L-012-enhanced chemiluminesence) in cerebral arteries from wild-type but not from Nox2(/y) mice. In aged wild-type mice (average age ∼70 weeks), aldosterone treatment increased blood pressure, but had a similar effect on cerebral artery superoxide levels as in adult wild-type mice.

CONCLUSION

These data indicate that Nox2 oxidase mediates aldosterone-induced increases in ROS production and endothelial dysfunction in cerebral arteries from adult mice independently of blood pressure changes. Aldosterone-induced hypertension is augmented during aging.

Vasorelaxant and antihypertensive effects of formononetin through endothelium-dependent and -independent mechanisms

AIM

To investigate the mechanisms underlying the vasorelaxant effect of formononetin, an O-methylated isoflavone, in isolated arteries, and its antihypertensive activity in vivo.

METHODS

Arterial rings of superior mesenteric arteries, renal arteries, cerebral basilar arteries, coronary arteries and abdominal aortas were prepared from SD rats. Isometric tension of the arterial rings was recorded using a myograph system. Arterial pressure was measured using tail-cuff method in spontaneously hypertensive rats.

RESULTS

Formononetin (1-300 μmol/L) elicited relaxation in arteries of the five regions that were pre-contracted by KCl (60 mmol/L), U46619 (1 μmol/L) or phenylephrine (10 μmol/L). The formononetin-induced relaxation was reduced by removal of endothelium or by pretreatment with L-NAME (100 μmol/L). Under conditions of endothelium denudation, formononetin (10, 30, and 100 μmol/L) inhibited the contraction induced by KCl and that induced by CaCl(2) in Ca(2+)-free depolarized medium. In the absence of extracellular Ca(2+), formononetin (10, 30, and 100 μmol/L) depressed the constriction caused by phenylephrine (10 μmol/L), but did not inhibit the tonic contraction in response to the addition of CaCl(2) (2 mmol/L). The contraction caused by caffeine (30 mmol/L) was not inhibited by formononetin (100 μmol/L). Formononetin (10 and 100 μmol/L) reduced the change rate of Ca(2+)-fluorescence intensity in response to KCl (50 mmol/L). In spontaneously hypertensive rats, formononetin (5, 10, and 20 mg/kg) slowly lowered the systolic, diastolic and mean arterial pressure.

CONCLUSION

Formononetin causes vasodilatation via two pathways: (1) endothelium-independent pathway, probably due to inhibition of voltage-dependent Ca(2+) channels and intracellular Ca(2+) release; and (2) endothelium-dependent pathway by releasing NO. Both the pathways may contribute to its antihypertensive effect.

Neurokinins induce relaxation of human pulmonary vessels through stimulation of endothelial NK1 receptors

The effects of neurokinins and neurokinin receptor selective agonists have been investigated on human intralobar pulmonary vessels. Substance P (SP) and [Sar(9) Met(O(2)) ]SP(11), a selective NK(1) receptor agonist, induced concentration-dependent relaxation of pulmonary vessels precontracted with phenylephrine. The mean negative log (M) EC (50) values for SP and [Sar (9) Met(O2))]SP(11) were 8.6 and 8.9, respectively, on arterial preparations and 8.9 and 8.6, respectively, on venous preparations. Relaxations to [Sar(9) Met(O(2) ) ]SP were abolished by the NK receptor antagonist SR140333. The relaxations to a second application of [Sar(9) Met(O (2)) ]SP were markedly reduced, suggesting a rapid desensitization of the NK(1) receptor. Such desensitization was not observed with acetylcholine. The selective NK receptor agonist, [Nle(10)]NKA, and the selective NK (3) receptor agonist, [MePhe(7)]NKB, caused neither contractions nor relaxations of pulmonary vessels. The NK(1) receptor-mediated relaxations were abolished by removing the endothelium or by a combination of -nitro-L-arginine and indomethacin, whereas each compound exerted a partial inhibitory effect. Similar results were observed with acetylcholine. Positive immunostaining for NK(1) receptors was only found in the endothelium. Reverse transcription-polymerase chain reaction detected messenger RNA for NK(1) receptors without any detection of messenger RNA for NK(2) or NK(3) receptors. In conclusion, human pulmonary arteries and veins express endothelial NK(1) receptors that mediate relaxation through a combination of cyclooxygenase and nitric oxide activities and are subjected to rapid tachyphylaxis.

Sevoflurane and bradykinin-induced calcium mobilization in pulmonary arterial valvular endothelial cells in situ: sevoflurane stimulates plasmalemmal calcium influx into endothelial cells

Kinins locally synthesized in the cardiovascular tissue are believed to contribute to the regulation of cardiovascular homeostasis by stimulating the endothelial cells to release nitric oxide, prostacyclin, or a hyperpolarizing factor via autocrine-paracrine mechanisms. This study was designed to investigate the action of sevoflurane on bradykinin-induced Ca2+ mobilization in endothelial cells in situ. Utilizing fura-2-loaded rat pulmonary arterial valve leaflets, the effects of sevoflurane were examined on bradykinin-induced increases in intracellular Ca2+ concentration ([Ca2+]i) in endothelial cells in situ. In the presence of extracellular Ca2+ (1.5 mM), bradykinin (3-30 microM) produced an initial phasic and a subsequent tonic increase in [Ca2+]i in a concentration-dependent manner. However, it produced only the phasic increase in [Ca2+]i in the absence of extracellular Ca2+. Sevoflurane (5%, 0.67 mM) inhibited both the phasic and tonic responses to bradykinin. In these experiments, sevoflurane (3-5%) generated sustained increases (approximately 20-40% of the bradykinin-induced maximal increase in [Ca2+]i) in the resting [Ca2+]i level. Sevoflurane still increased [Ca2+]i after depletion of the intracellular Ca stores with ionomycin (0.1 microM ). However, the sevoflurane-induced increase in [Ca2+]i was eliminated by removal of the extracellular Ca and attenuated by NiCl (1-3 mM). In conclusion, in the pulmonary arterial valvular endothelial cells, sevoflurane inhibits both bradykinin-induced Ca2+ release from the intracellular stores and bradykinin-induced plasmalemmal Ca2+ influx. In addition, sevoflurane appears to stimulate the plasmalemmal Ca2+ influx and thereby increase the endothelial [Ca2+]i level. Sevoflurane might influence the pulmonary vascular tone through its direct action on the pulmonary arterial valvular endothelial cells.

How to assess endothelial function in human blood vessels

This brief review discusses the ways, if and when available, to examine endothelium-dependent changes diameter in human blood vessels. It stresses the problems in ensuring proper matching between arteries (and veins) from different human sources. It briefly considers the evidence in vitro supporting the role of endothelium-derived nitric oxide, hyperpolarizing factor and contracting factors (including metabolites of arachidonic acid and endothelin). It emphasizes the difficulty in extrapolating observations obtained in isolated arteries (and veins) to the intact human circulation. The overall conclusion is that the interpretations derived from animal work apply to the human vasculature.