Effects of eicosanoids and nitric oxide on the noradrenaline-induced contractions in the rat mesenteric bed

Ultra-low dose beta-irradiation induces constriction of rabbit carotid arteries via the endothelium

PURPOSE

To investigate the action of ultra-low dose beta-radiation (ULDBR) on isolated segments of blood vessels.

MATERIALS AND METHODS

We used the pharmacological model of isolated rabbit carotid arteries with intact or mechanically removed endothelium. Specific vascular responses to beta-irradiation were registered after addition of (90)Sr in the concentration range between 12 and 96 microCi l(-1) to the organ bath containing physiological salt solution (PSS).

RESULTS

Intact vascular rings, preconstricted with 20 mM K(+)-PSS, developed an additional constriction upon the addition of (90)Sr depending on the absorbed radiation dose (21.5, 42.9, 85.8, and 171.6 microGy) and the dose rate (51.5, 103.0, 206.0 and 412.0 microGy h(-1)). The vasoconstriction due to (90)Sr was absent in the endothelium-denuded vascular segments indicating the endothelium dependent action of ULDBR. Irradiation did not alter the endothelium dependent relaxation of rabbit carotid arteries induced by acetylcholine. The endothelium dependent responses to ULDBR were abolished after increasing the extra-cellular K(+) to 40 mM.

CONCLUSIONS

ULDBR acts on rabbit carotid arteries as a pharmacological signalling agent because ULDBR effects were completely reversible. ULDBR-mediated contractile responses of the vessels are endothelium dependent. The resistance of acetylcholine endothelium-dependent relaxation of rabbit carotid arteries to ULDBR indicates that the polyphosphoinositide-nitric oxide (NO) signalling cascade is not impaired by ULDBR in endothelial cells.

Ethanol consumption increases blood pressure and alters the responsiveness of the mesenteric vasculature in rats

Chronic ethanol consumption and hypertension are related. In the current study we investigated whether changes in reactivity of the mesenteric arterial bed could account for the increased blood pressure associated with chronic ethanol intake. Changes in reactivity to phenylephrine and acetylcholine were investigated in the perfused mesenteric bed from rats treated with ethanol for 2 or 6 weeks and their age-matched controls. Mild hypertension was observed in chronically ethanol-treated rats. Treatment of rats for 6 weeks induced an increase in the contractile response of endothelium-intact mesenteric bed to phenylephrine, but not denuded rat mesenteric bed. The phenylephrine-induced increase in perfusion pressure was not altered after 2 weeks' treatment with ethanol. Moreover, acetylcholine-induced endothelium-dependent relaxation was reduced by ethanol treatment for 6 weeks, but not 2 weeks. Pre-treatment with indometacin, a cyclooxygenase inhibitor, reduced the maximum effect induced by phenylephrine (Emax) in endothelium-intact mesenteric bed from both control and ethanol-treated rats. No differences in the Emax values for phenylephrine were observed between groups in the presence of indometacin. L-NNA, a nitric oxide (NO) synthase (NOS) inhibitor, increased the Emax for phenylephrine in endothelium-intact mesenteric bed from control rats but not from ethanol-treated rats. Levels of endothelial NOS (eNOS) mRNA were not altered by chronic ethanol consumption. However, chronic ethanol intake strongly reduced eNOS protein levels in the mesenteric bed. This study shows that chronic ethanol consumption increases blood pressure and alters the reactivity of the mesenteric bed. Moreover, the increased vascular response to phenylephrine observed in the mesenteric bed is maintained by two mechanisms: an increased release of endothelial-derived vasoconstrictor prostanoids and a reduced modulatory action of endothelial NO, which seems to be associated with reduced post-transcriptional expression of eNOS.

Noradrenaline and angiotensin II modify vascular prostanoid release in fructose-fed hypertensive rats

1 A fructose-enriched diet induces hypertension, metabolic alterations and insulin resistance in rats, resembling human metabolic syndrome. Previously, we found that prostanoid production was altered in fructose-fed rats. 2 This study analysed the effects of incubation with noradrenaline (NA) and angiotensin II (Ang II) on prostanoid release in mesenteric vascular beds from control and fructose-fed rats. Animals which received fructose solution (10% w/v) for 22 weeks showed higher systolic blood pressure and triglyceridaemia. 3 In controls, NA increased 6-keto-prostaglandin (PG) F(1)alpha (prostacyclin metabolite) and thromboxane (TX) production. Ang II increased only TX release. In fructose-fed animals, NA increased 6-keto-PG F(1)alpha and TX. PGF(2)alpha (vasoconstrictor) was also elevated. Ang II also increased PGF(2)alpha and PGE(2) levels. 4 In conclusion, in fructose rats Ang II in vitro stimulates a vasoconstrictor prostanoid not stimulated in controls. This could be related to the observed in vivo blood pressure increase. In fructose-fed animals, NA and Ang II also augment vasodilator prostanoids, suggesting a compensatory mechanism because of long-term hypertension.

Endothelium-dependent vasodilator effect of Euterpe oleracea Mart. (Açaí) extracts in mesenteric vascular bed of the rat

Açai (Euterpe oleracea Mart.) a fruit from the Amazon region, largely consumed in Brazil is rich in polyphenols. Experiments were undertaken to determine whether hydro-alcoholic extract obtained from stone of açaí induces a vasodilator effect in the rat mesenteric vascular bed precontracted with norepinephrine (NE) and, if so, to elucidate the underlying mechanism. Açai stone extract (ASE, 0.3-100 microg) induced a long-lasting endothelium-dependent vasodilation that was significantly reduced by N(G)-nitro-l-arginine methyl ester (l-NAME) and (1)H-[1,2,3] oxadiazolo [4,4-a] quinoxalin-l-one (ODQ) and abolished by KCl (45 mM) plus l-NAME. In vessels precontrated with NE and KCl (45 mM) or treated with K(Ca)(+2) channel blockers (charybdotoxin plus apamin), the effect of ASE was significantly reduced. However this effect is not affect by indomethacin, glybenclamide and 4-aminopiridine. Atropine, pyrilamine, yohimbine and HOE 140 significantly reduced the vasodilator effect of acetylcholine, histamine, clonidine and bradykinin, respectively, but did not change the vasodilator effect of ASE. In cultured endothelial cells ASE (100 microg/mL) induced the formation of NO that was reduced by N(G)-nitro-l-arginine (l-NA, 100 microM). The present study demonstrates that the vasodilator effect of ASE is dependent on activation of NO-cGMP pathway and may also involve endothelium-derived hyperpolarizing factor (EDHF) release. The vasodilator effect suggest a possibility to use ASE as a medicinal plant, in the treatment of cardiovascular diseases.

Augmented Endothelium-Derived Hyperpolarizing Factor-Mediated Relaxations Attenuate Endothelial Dysfunction in Femoral and Mesenteric, but Not in Carotid Arteries from Type I Diabetic Rats

Individual vascular beds exhibit differences in vascular reactivity. The present study investigates the effects of streptozotocin-induced type I diabetes on endothelium-dependent responses of rat carotid, femoral, and mesenteric arteries. Rings with and without endothelium, suspended in organ chambers for isometric tension recording, were contracted with phenylephrine and exposed to increasing concentrations of acetylcholine. In carotid and femoral arteries, acetylcholine produced concentration- and endothelium-dependent relaxations that were abolished by Nomega-nitro-L-arginine methyl ester (L-NAME; specific nitric-oxide synthase inhibitor) and were impaired slightly in preparations from streptozotocin-treated rats (STZ-rats). This impairment could be prevented by L-arginine. In femoral arteries incubated with L-NAME, acetylcholine caused endothelium-dependent contractions that were abolished by 3-[(6-amino-(4-chlorobenzensulfonyl)-2-methyl-5,6,7,8-tetrahydronapht]-1-yl) propionic acid (S18886) (antagonist of thromboxane A2/prostaglandins H2-receptors) and reversed to relaxation by indomethacin (inhibitor of cyclooxygenase). The latter relaxation was inhibited by charybdotoxin plus apamin, suggesting a role of endothelium-dependent hyperpolarizing factor (EDHF). This EDHF-mediated component was augmented slightly in arteries from STZ-rats. In mesenteric arteries, relaxations to acetylcholine were only partially inhibited by L-NAME, and the L-NAME-resistant component was abolished by charybdotoxin plus apamin. In the mesenteric arteries from STZ-rats, L-NAME-sensitive relaxations to acetylcholine were reduced and the EDHF-component was augmented. These findings demonstrate a marked heterogeneity in endothelium-dependent responses in rat arteries and their differential adaptation in the course of type I diabetes. In particular, the EDHF-mediated component not only compensates for the reduced bioavailability of nitric oxide in the femoral and mesenteric artery but also counteracts the augmented endothelium-dependent contractions in the former.

Antihypertensive and endothelium-dependent vasodilator effects of Alpinia zerumbet, a medicinal plant

Alpinia zerumbet (K. Schum), a medicinal plant originated from West Asia, is used in the northeast and southeast of Brazil as infusions or decoctions as a diuretic, antihypertensive, and antiulcerogenic. Experiments were undertaken to determine whether a hydroalcoholic extract obtained from leaves of Alpinia zerumbet (AZE) induces vasodilation in the mesenteric vascular bed (MVB), and an antihypertensive effect was also assessed in rats with DOCA-salt hypertension. In MVB precontracted with norepinephrine, AZE induces a long-lasting endothelium-dependent vasodilation that is not reduced by indomethacin. Inhibition of NO synthase by NG-nitro-L-arginine methyl ester (L-NAME) and guanylyl cyclase by 1H-[1,2,3]oxadiazolo [4,4-a]quinoxalin-1-one (ODQ) reduces the vasodilator effect of AZE. In vessels precontracted with norepinephrine, the vasodilator effect of AZE was not changed by 4-aminopyridine, glibenclamide, or by charybdotoxin plus apamin. Concentrations of atropine, pyrilamine, and yohimbine that significantly reduced the vasodilator effect of acetylcholine, histamine, and clonidine, respectively, did not change the vasodilator effect of AZE. HOE 140, which significantly reduced the vasodilator effect of bradykinin, induced a slight but significant reduction on the vasodilator effect of AZE. Chronic oral administration of AZE induced a significant reduction in systolic, mean, and diastolic arterial pressure in rats with DOCA-salt hypertension. Probably the vasodilator effect of AZE is dependent on the activation of the NO-cGMP pathway and independent of activation of ATP-dependent, voltage-dependent, and calcium-dependent K+ channels. Bradykinin receptors may also participate in the vasodilator effect of AZE. Finally, the vasodilator and antihypertensive effects of AZE demonstrated in the present study provide experimental support for the indication of Alpinia zerumbet as an antihypertensive medicinal plant.

Involvement of endothelial cyclo-oxygenase metabolites in noradrenaline-induced contraction of rat coronary artery

1. Noradrenaline (NA; 0.3 micromol/L) caused a contraction of the rat coronary artery that markedly increased in the presence of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME; 100 micromol/L) and arachidonic acid (1 micromol/L; P < 0.05). 2. The present experiments attempted to elucidate the endothelium dependency of the contraction and to pharmacologically characterize the factors involved in the contraction induced by NA (0.3 micromol/L) in the presence of L-NAME and arachidonic acid in ring preparations of the rat coronary artery. 3. The NA (0.3 micromol/L)-induced contraction was attenuated by a chemical remover of the endothelium (saponin at concentrations of 0.1 and 0.4 mg/mL) in a concentration-dependent manner (P < 0.05). 4. The cyclo-oxygenase (COX)-1 inhibitor flurbiprofen (0.01-1 micromol/L) and the COX-2 inhibitor nimesulide (0.01-1 micromol/L) attenuated the NA-induced contraction in a concentration-dependent manner and the inhibitory effect of flurbiprofen was significantly more potent than that of nimesulide (P < 0.05). The 5-lipoxigenase inhibitor ZM-230487 (1 micromol/L) did not affect the NA-induced contraction. 5. The thromboxane A2 (TXA2) synthetase inhibitor OKY-046 (30 micromol/L) and the TXA2 antagonist S-1452 (0.1-10 micromol/L) did not attenuate the NA-induced contraction. 6. These results indicate that the contraction induced by NA in the rat coronary artery in the presence of L-NAME and arachidonic acid is endothelium dependent and is due to endothelial COX metabolites of arachidonic acid.

Effects of prostanoids on phenylephrine-induced contractions in the mesenteric vascular bed of rats with streptozotocin-induced diabetes mellitus

The main aim of this study was to compare the vascular reactivity of the perfused (Krebs, 4 ml/min) mesenteric vascular bed (MVB) isolated from rats with streptozotocin (STZ)-induced diabetes of 8 weeks duration to that of the MVB from non-diabetic (ND) Wistar rats. There were no differences in basal perfusion pressure between the MVB isolated from STZ and ND rats. The addition of indomethacin to the perfusate increased the basal perfusion pressure in both ND (18.8 +/- 0.7 vs 29.4 +/- 3.7 mmHg, p < 0.05) and STZ rats (18.3 +/- 0.9 vs 27.2 +/- 2.6 mmHg, p < 0.05), suggesting the release of a vasodilator prostaglandin. Remotion of the endothelium did not affect this response, indicating that prostaglandin was released from vascular smooth muscle. The response to phenylephrine was reduced in STZ rats compared to ND rats (2.3 [1.6-3.8] vs 8.3 [3.5-19.4], ED50. [IC 95%]) and was not modified by removal of the endothelium or by perfusion of L-nitro-arginine (50 microM). In contrast, indomethacin was able to reduce the response to phenylephrine in ND but not in STZ rats (2.3 [1.6-3.8] vs 4.7 [3.2-6.0], ED50. [IC 95%], p=0.02), suggesting that the blunted response to phenylephrine observed in STZ was due to the abolition of the release of prostaglandin by vascular smooth muscle. In conclusion, experimental diabetes induction in the rat is followed by a reduction of the contractile effect of phenylephrine due to the lack of release of a vasoconstrictor prostaglandin from vascular smooth muscle.

Opposite effects of endogenous nitric oxide and prostaglandin F2alpha in the rat mesenteric bed

1. The relationship between the effects of endogenous nitric oxide (NO) and prostanoids on the noradrenaline (NA)-induced contractions and the mechanisms involved were investigated in the rat perfused mesenteric bed, using NG-nitro-L-arginine methyl ester (l-NAME), a NO synthase inhibitor and sodium nitroprusside (SNP), a NO donor. 2. The constrictor responses to NA were reduced to 50% by the cyclooxygenase inhibitor 10 microm indomethacin as well as by 1 microM SNP. When indomethacin and SNP were perfused simultaneously the contractions were further reduced. 3. The NA-induced contractions were increased by the addition of 400 microM L-NAME and the addition of either indomethacin or SNP abolished such increases. The simultaneous perfusion of both agents further reduced the contractions. 4. Removal of the endothelium increased NA-induced contractions to a similar extent as L-NAME and this increase was abolished by indomethacin as well as by SNP. 5. The perfusion of 10 microM NA augmented the release of prostaglandin (PG) F2 alpha by the mesenteric bed without modifications in any other prostanoid. In the presence of L-NAME, this effect was further increased. However, SNP abolished the NA-induced stimulation of PGF2 alpha release. 6. In de-endothelialized preparations NA also stimulated PGF2 alpha production as observed in intact preparations. This effect was more marked in the presence of L-NAME; in contrast, SNP abolished the stimulation. 7. In conclusion, the present results suggest an opposite action between NO and PGF2 alpha on the NA-induced contractions in the rat mesenteric bed.

Endothelium-dependent and -independent vasodilator effects of eugenol in the rat mesenteric vascular bed

The possible involvement of the endothelium in the vasodilator action of eugenol was investigated in the mesenteric vascular bed (MVB) of the rat. Bolus injections of eugenol (0.2, 2 and 20 micromol) and acetylcholine (ACh; 10, 30 and 100 pmol) induced dose-dependent vasodilator responses in noradrenaline-precontracted beds that were partially inhibited by pretreatment of the MVB with deoxycholate (1 mg mL(-1)) to remove the endothelium (approximately 14% and approximately 30% of the control response remaining at the lowest doses of ACh and eugenol, respectively). The vasodilator effect of glyceryl trinitrate (1 micromol) was unaltered by deoxycholate. In the presence of either N(omega)-nitro-L-arginine methyl ester (300 microM) or tetraethylammonium (1 mM)the response to ACh was partially reduced, whereas eugenol-induced vasodilation was unaffected. Similarly the vasodilator effect of eugenol was not inhibited by indometacin (3 microM). Under calcium-free conditions the vasoconstrictor response elicited by bolus injections of noradrenaline (10 nmol) was dose-dependently and completely inhibited by eugenol (0.1-1 mM). Additionally, the pressor effects of bolus injections of calcium chloride in potassium-depolarized MVBs were greatly reduced in the presence of eugenol (0.1 mM), with a maximal reduction of approximately 71% of the control response. Our data showed that eugenol induced dose-dependent, reversible vasodilator responses in the rat MVB, that were partially dependent on the endothelium, although apparently independent of nitric oxide, endothelium-derived hyperpolarizing factor or prostacyclin. Furthermore, an endothelium-independent intracellular site of action seemed likely to participate in its smooth muscle relaxant properties.

Obesity increases prostanoid-mediated vasoconstriction and vascular thromboxane receptor gene expression

OBJECTIVES

Vasoconstrictor prostanoids have been implicated in abnormal vasomotion in atherosclerosis and hypertension.

METHOD

Using lean and diet-induced obese mice, we investigated whether obesity affects vascular function or expression of genes involved in prostanoid action.

RESULTS

In lean C57BL/6J mice, at high concentrations acetylcholine caused endothelium-dependent contractions in the carotid artery but not in the aorta. Endothelium-dependent contractions to acetylcholine were blocked by the non-selective cyclooxygenase (COX) inhibitors indomethacin and meclofenamate, or a prostaglandin H2/thromboxane A2 receptor antagonist, but not by inhibitors of COX-2, thromboxane synthase or cytochrome P450 monooxygenase. Obesity increased endothelium-dependent contractions to acetylcholine in the carotid artery, and prostanoid-mediated vasoconstriction was now present in the aorta. Similarly, contractions to endothelin-1 were largely blocked by meclofenamate and were increased in the aorta of obese mice. Real-time quantitative polymerase chain reaction analysis of the thromboxane receptor gene in the carotid artery revealed a robust upregulation in obese animals (18-fold, 0.05); in comparison, obesity had a less pronounced effect on thromboxane synthase (2.1-fold increase, 0.05), or preproendothelin-1 gene expression (4.2-fold increase, 0.05).

CONCLUSIONS

These data demonstrate that obesity augments prostanoid-dependent vasoconstriction and markedly increases vascular thromboxane receptor gene expression. These changes are likely to promote the development of vascular disease, hypertension and thrombosis associated with obesity.

Defibrotide modulates prostaglandin production in the rat mesenteric vascular bed

Defibrotide 1 microM, a polydeoxyribonucleotide extracted from mammalian organs, reduced the contractile responses to noradrenaline (NA) in the rat isolated and perfused mesenteric vascular bed, in intact as well as in de-endothelialized preparations. Defibrotide was without effect on the acetylcholine-induced relaxations of U-46619-precontracted mesenteric vascular beds. Moreover, defibrotide increased 6-keto prostaglandin (PG) F(2alpha) (stable metabolite of prostacyclin) release sixfold in the presence, but not in the absence of the endothelium, with no modification on the release of other prostanoids. Defibrotide also inhibited the NA-induced increase in PGF(2alpha) release, in both intact and de-endothelialized mesenteric vascular beds. In conclusion, the present results show that defibrotide modulates PG production in the mesenteric bed and that the observed inhibition of the contractile responses should be due to the impairment of the NA-induced increase in PGF(2alpha) release.

Prostanoid release and constrictor responses to noradrenaline in the rat mesenteric vascular bed in non-insulin-dependent diabetes mellitus

1. The administration of streptozotocin (STZ) to 2-day old rats induced a non-insulin-dependent diabetes mellitus (NIDDM)-like state, with mild hyperglycaemia and no alterations in body weight at the adult age. 2. In the isolated and perfused mesenteric vascular bed of NIDDM animals, the constrictor responses to either noradrenaline (NA) or potassium chloride (KCl) were not modified as compared with age-matched non-diabetic controls. 3. The reduction in NA contractions induced by the cyclooxygenase inhibitor, 10 microM indomethacin in the control group was absent in the NIDDM rats. 4. The increase in the NA-induced contractions caused by endothelium removal was suppressed by indomethacin in the controls but not in the NIDDM group. 5. The prostanoid release from the mesenteric vascular beds of NIDDM rats was markedly reduced as compared with non-diabetic controls. Noradrenaline increased production of the constrictor prostaglandin (PG) F2alpha in control but not in NIDDM rats. 6. In summary, these results show that in STZ-induced NIDDM rats, there is an impairment of the prostanoid production, as well as a suppression of the role of prostanoids in the contractile effects of NA in the mesenteric vascular bed. These alterations are more severe than those previously observed in a model of insulin-dependent diabetes mellitus (IDDM), in which hyperglycaemia and reduction of body weight were more marked. The conclusion is that, in these models of diabetes and in the preparation studied, vascular alterations and modifications of glycaemia and body weight are not closely related.