Increased responsiveness of human pulmonary arteries in patients with positive bronchodilator response.

1. The effects of noradrenaline, endothelin-1, acetylcholine and sodium nitroprusside were studied in isolated pulmonary arteries obtained from 14 patients undergoing lobectomy for lung carcinoma. Seven patients had shown increased response to a bronchodilator test prior to operation. In the remaining patients (control) the bronchodilator test was negative. 2. Artery rings from patients with a positive bronchodilator response showed greater contraction to noradrenaline (pD2 = 6.44 +/- 0.1; Emax = 93 +/- 9% of response to 100 mM KCl) and endothelin-1 (pD2 = 8.92 +/- 0.1; Emax = 130 +/- 16%) than the rings from control patients (pD2 = 6.04 +/- 0.08; Emax = 56 +/- 8% for noradrenaline; pD2 = 8.29 +/- 0.1; Emax = 78 +/- 10% for endothelin-1). There was no significant difference in the contractile responses to 100 mM KCl between arteries from either group of patients. 3. Arterial rings from patients with a positive bronchodilator test achieved 96 +/- 3% of maximal relaxation in response to acetylcholine, whereas rings from control patients achieved a maximal relaxation of 72 +/- 5%. Rings from both the controls and the patients with a positive bronchodilator test achieved complete relaxation in response to sodium nitroprusside but pD2 values were significantly higher in patients with a positive bronchodilator test. 4. Removal of endothelium or treatment with NG-nitro-L-arginine methyl ester of artery rings from both the control and the patients with a positive bronchodilator test reduced the relaxation to acetylcholine (P < 0.05) but did not modify relaxation to sodium nitroprusside. 5. It is concluded that responsiveness of pulmonary arterial smooth muscle to dilator and constrictor agents is increased in patients showing reversibility of airway constriction. Thus hyperresponsiveness of airway smooth muscle may be associated with a similar phenomenon in the surrounding vascular smooth muscle.     

Selectivity of phenytoin and dihydropyridine calcium channel blockers for relaxation of the basilar artery

We addressed the questions of whether or not phenytoin is a direct vasodilator and if it is selective for brain blood vessels, by studying the relaxant effects of phenytoin on isolated segments of canine basilar, femoral, and brachial arteries. Two dihydropyridine calcium channel blockers, nifedipine and PY 108-068, were also studied for comparison with phenytoin and to test for cerebral selectivity. Blood vessels were contracted with K+, prostaglandin F2 alpha, or serotonin. Phenytoin relaxed the basilar artery with low potency (pD2, 4.71 +/- 0.14) and moderate selectivity. Phenytoin also antagonized Bay K 8644 contractions of basilar artery in a noncompetitive manner. Basilar arteries contracted with 60 mM K+ were the most sensitive to nifedipine (pD2, 8.72 +/- 0.18), followed by the mesenteric (pD2, 8.24 +/- 0.07), femoral (pD2, 8.04 +/- 0.18), and brachial (pD2, 7.66 +/- 0.23) arteries. A similar pattern was observed in potassium-depolarized arteries relaxed by PY 108-068. The calcium dependence of contraction was studied using intact muscles depolarized in 60 mM K+ as well as chemically skinned basilar artery. Mean pD2 values for Ca2+-induced contractions of intact, depolarized arteries were not different (basilar, 4.15 +/- 0.13; mesenteric, 4.04 +/- 0.07; femoral, 4.24 +/- 0.11). The mean Ca2+ EC50 of chemically skinned basilar arteries was 8.7 X 10(-7) M, which is similar to the Ca2+ sensitivity of other skinned smooth muscles. The beneficial effect of phenytoin in treating cerebral ischemia may be due in part to relaxation of vascular smooth muscle. The dihydropyridines were potent smooth muscle relaxants with selectivity for the basilar artery.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vasoactive intestinal peptide as a neurotransmitter in the cerebral circulation

Cat cerebral arteries exhibit a non-cholinergic neurogenic vasodilation which is absent in rabbit cerebral arteries. Levels of vasoactive intestinal peptide (VIP) measured by radioimmunoassay are correlated with the presence of a non-cholinergic vasodilation: 270 +/- 66 pmol/g in the cat anterior cerebral artery compared to 10 +/- 2.3 pmol/g in rabbit cerebral arteries. In the absence of endothelial cells, cat cerebral arteries do not relax to acetylcholine, but continue to relax to nerve stimulation. Relaxation responses to VIP also persist. These findings are consistent with the possibility that VIP mediates non-cholinergic vasodilator responses in the cerebral circulation.     

Endothelium-derived relaxing factor (EDRF) and resistance vessels in an intact vascular bed: a microangiographic study of the rabbit isolated ear.

1. Microradiographic techniques have been used to show that endothelium-derived relaxing factor (EDRF), which is believed to be nitric oxide, influences vasomotor responses in small arteries and arterioles down to 25 micron in diameter in an isolated, intact, buffer-perfused ear preparation of the rabbit. Arteries down to 75 micron in diameter, i.e. the central ear artery (G0) and its first three generations of branch vessels (G1, G2 and G3) were studied quantitatively. 2. Relative constrictor responses to 1 micron 5-hydroxytryptamine (5-HT) and the combination of 1 microM 5-HT and 1 microM histamine diminished progressively from G0 to G3. Constrictor responses to 5-HT were doubled in all generations by 1 microM haemoglobin which abolishes EDRF activity. 3. Relative dilator responses to acetylcholine or to substance P in preconstricted arteries were, in contrast, equal in the different generations. Mean -log (IC50) values calculated from diameter measurements were 7.63 +/- 0.10 M and 9.80 +/- 0.11 M, respectively. These dilator responses were abolished by 1 microM haemoglobin, implying that they were EDRF-mediated. Spatial homogeneity of relative dilator responses was found also with glyceryl trinitrate (10 or 50 microM) whose activity is thought to depend on biotransformation to nitric oxide, in both the presence and the absence of haemoglobin. 4. This finding of spatial homogeneity of the diameter response to changes in EDRF activity (or to glyceryl trinitrate) implies that EDRF influences hydrodynamic resistance more in vessels where constrictor tone is high.     

Effect of the vascular endothelium on noradrenaline-induced contractions in non-pregnant and pregnant guinea-pig uterine arteries.

1. The effect of pregnancy on noradrenaline-mediated contraction of guinea-pig uterine artery rings with both intact and denuded endothelium was investigated. 2. Noradrenaline (25 nM-100 microM) induced concentration-dependent contraction of non-pregnant and pregnant guinea-pig uterine arterial rings with intact endothelium with similar pD2 and maximal response values (non-pregnant: pD2 = 5.85 +/- 0.02, maximal response = 121 +/- 8.2%; pregnant: pD2 = 5.81 +/- 0.04, maximal response = 122 +/- 9.1%). Removal of endothelium did not affect noradrenaline-induced contractions in non-pregnant guinea-pig uterine artery (pD2 = 5.97 +/- 0.02, maximal response = 119 +/- 8.6%). In contrast, in arteries from pregnant guinea-pigs, removal of endothelium shifted concentration-response curve for noradrenaline to the left, without affecting maximal response value (pD2 = 6.36 +/- 0.03, maximal response = 120 +/- 9.0%). 3. The pKA values for noradrenaline were: 5.76 +/- 0.09 and 5.82 +/- 0.10 for non-pregnant guinea-pig uterine artery with intact and denuded endothelium, respectively and 5.74 +/- 0.09 and 5.72 +/- 0.07 for pregnant guinea-pig uterine artery with intact and denuded endothelium, respectively. 4. The receptor occupancy-response relationship for noradrenaline was linear for all types of vessels, except for pregnant guinea-pig uterine artery with denuded endothelium, since half-maximal response to noradrenaline was obtained with 44.8 +/- 6.9% (non-pregnant guinea-pig uterine artery with intact endothelium), 43.3 +/- 6.1% (non-pregnant guinea-pig uterine artery with denuded endothelium) and 44.3 +/- 6.3% (pregnant guinea-pig uterine artery with intact endothelium) receptor occupancy. In pregnant guinea-pig uterine artery with denuded endothelium, occupancy-response relationship for noradrenaline was non-linear since half-maximal response to noradrenaline was obtained with 19.7 +/- 3.3% receptor occupancy. 5. NG-monomethyl-L-arginine (100 microM) and indomethacin (10 microM) did not affect concentration-response curve for noradrenaline in guinea-pig uterine arteries, regardless of pregnancy status or endothelial condition. 6. In quiescent preparations, the alpha-adrenoceptor antagonists, prazosin (5-50 nM) and yohimbine (1-10 microM) produced parallel rightward shifts of the curves for noradrenaline and the slopes of the Schild plots were not significantly different from unity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Influence of the endothelium on histamine-induced relaxation of rat middle cerebral arteries in vitro.

Histamine relaxed PGF2 alpha-precontracted rat isolated middle cerebral arteries (ID approximately 230 microns) concentration dependently with a pD2 of 5.31 (EC50: 5 x 10(-6) M). Cimetidine induced a concentration-dependent rightward shift of the histamine concentration-response curve of endothelium-intact arteries. The slope of the Schild plot was indistinguishable from unity, and the estimated pA2 for cimetidine was 6.14. The selective H2-receptor agonist dimaprit induced a concentration dependent relaxation of the cerebral arteries similar to that induced by histamine. This indicates that the histamine receptor mediating the relaxation in rat middle cerebral arteries belongs to the H2-receptor subtype. 2-Pyridylethylamine, a selective H1-receptor agonist, induced a small concentration-dependent contraction of the arteries with a pD2 of 4.16. Mepyramine, a selective H1-receptor antagonist had no potentiating effect on the relaxation induced by histamine, suggesting either that the contractile effect of 2-pyridylethylamine is nonselective or that H1 receptors mediating contraction are of minor importance for the overall histamine response. The selective H3-receptor agonist, (R)-alpha-methylhistamine, was without effect in a specific concentration range (10(-7)-10(-5) M) excluding participation of H3 receptors in the histamine-induced relaxation of these vessels. Indomethacin did not affect the vessel response to histamine, but removal of the endothelium and treatment of endothelium-intact arteries with 3 x 10(-6) M methylene blue induced a similar 0.5 log rightward shift of the histamine concentration-response curve.(ABSTRACT TRUNCATED AT 250 WORDS)     

Urocortin relaxes rat tail arteries by a PKA-mediated reduction of the sensitivity of the contractile apparatus for calcium.

1. Urocortin is an endogenous vasodilator although the mechanism of vasorelaxation is not completely understood. The hypothesis that an alteration of smooth muscle calcium concentration is involved was tested using isometric tension recording and calcium fluorimetry. The relationship between contraction and intracellular calcium was also estimated. 2. Urocortin produced a concentration dependent relaxation (pD(2) 8.59+/-0.06, n=6) of vessels pre-contracted with a physiological salt solution containing 42 mM KCl (42 mM K-PSS). 3. Removal of the endothelium did not alter the effect of urocortin, pD(2) was 8.49+/-0.11, n=5. 4. Corticotropin-releasing factor relaxed 42 mM K-PSS pre-contracted vessels with less potency compared to urocortin (pD(2) 6.99+/-0.28, n=5). 5. Urocortin at 100 nM relaxed vessels pre-contracted with 42 mM K-PSS by 59.6+/-4.6% (n=8) and vessels pre-contracted with 500 nM noradrenaline by 25.2+/-6.8% (n=6). Both effects were not accompanied by a change in the intracellular calcium concentration. 6. Urocortin at 100 nM produced a significant rightward shift of 0.33+/-0.07 units of normalized intracellular calcium (n=5) of the relationship between tension and intracellular calcium. 7. The urocortin-induced relaxation was considerably reduced in the presence of 0.3 mM Rp-8-CPT-cAMPS, a cyclic AMP-dependent protein kinase (PKA) inhibitor. 8. The PKA-activator Sp-5,6-DCl-cBIMPS relaxed 42 mM K-PSS pre-contracted vessels (pD(2) 4.98+/-0.07, n=6). Sp-5,6-DCl-cBIMPS at 0.1 mM relaxed vessels by 85.3+/-2.5% (n=5), but did not change the intracellular calcium concentration. 9. In conclusion, the data show that urocortin is a potent, endothelium-independent dilator of rat tail arteries and suggest that this effect is mediated by PKA causing a reduction of the sensitivity of the contractile apparatus for calcium.     

Inhibitory effect of 4-aminopyridine on responses of the basilar artery to nitric oxide

1. Voltage-dependent K+ channels are present in cerebral arteries and may modulate vascular tone. We used 200 microM 4-aminopyridine (4-AP), thought to be a relatively selective inhibitor of voltage-dependent K+ channels at this concentration, to test whether activation of these channels may influence baseline diameter of the basilar artery and dilator responses to nitric oxide (NO) and cyclic GMP in vivo. 2. Using a cranial window in anaesthetized rats, topical application of 4-AP to the basilar artery (baseline diameter = 240+/-5 microm, mean +/- s.e.mean) produced 10+/-1% constriction. Sodium nitroprusside (a NO donor), acetylcholine (which stimulates endothelial release of NO), 8-bromo cyclic GMP (a cyclic GMP analogue), cromakalim (an activator of ATP-sensitive K+ channels) and papaverine (a non-NO, non-K+ channel-related vasodilator) produced concentration-dependent vasodilator responses that were reproducible. 3. Responses to 10 and 100 nM nitroprusside were inhibited by 4-AP (20+/-4 vs 8+/-2% and 51+/-5 vs 33+/-5%, respectively, n=10; P<0.05). Responses to acetylcholine and 8-bromo cyclic GMP were also partially inhibited by 4-AP. In contrast, 4-AP had no effect on vasodilator responses to cromakalim or papaverine. These findings suggest that NO/cyclic GMP-induced dilator responses of the basilar artery are selectively inhibited by 4-aminopyridine. 4. Responses to nitroprusside were also markedly inhibited by 10 microM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (an inhibitor of soluble guanylate cyclase; 16+/-4 vs 1+/-1% and 44+/-7 vs 7+/-1%; n=10; P<0.05). 5. Thus, dilator responses of the rat basilar artery to NO appear to be mediated by activation of soluble guanylate cyclase and partially by activation of a 4-aminopyridine-sensitive mechanism. The most likely mechanism would appear to be activation of voltage-dependent K+ channels by NO/cyclic GMP.     

Relaxation of sheep cerebral arteries by vasoactive intestinal polypeptide and neurogenic stimulation: inhibition by L-NG-monomethyl arginine in endothelium-denuded vessels.

1. Perivascular nerves of the sheep middle cerebral artery show immunoreactivity for both vasoactive intestinal polypeptide (VIP) and calcitonin gene-related peptide (CGRP). 2. Rings of endothelium-denuded sheep middle cerebral artery precontracted with 5-hydroxytryptamine were relaxed by CGRP (maximum relaxation = 87.8 +/- 8.1%, pD2 = 7.81 +/- 0.12, n = 12) and by VIP (maximum relaxation = 55.1 +/- 4.1%, pD2 = 7.65 +/- 0.04, n = 18). Rings of endothelium-denuded cat middle cerebral artery precontracted with U46619 were also relaxed by vasoactive intestinal polypeptide (maximum relaxation = 53.1 +/- 6.1%, pD2 = 7.82 +/- 0.11, n = 6). 3. Haemolysate (1 microliters ml-1) inhibited VIP-induced relaxation in endothelium-denuded sheep and cat middle cerebral artery (n = 6) but had no effect on the CGRP-induced relaxation of the sheep middle cerebral artery (n = 6). 4. The relaxant response to VIP in endothelium-denuded sheep middle cerebral artery was inhibited by methylene blue (10 microM) and augmented by either M&B 22948 (10 microM) or superoxide dismutase (150 units ml-1). Indomethacin (1 microM) had no effect. 5. The addition of L-NG-monomethyl arginine (100 microM) inhibited both neurogenic and VIP-induced relaxation of endothelium-denuded sheep MCA by 56 +/- 6% and 60 +/- 6% (n = 5) respectively. The CGRP-induced relaxation was unaffected. 6. It is concluded that neurally mediated vasodilatation in the sheep middle cerebral artery is mediated largely by VIP through a direct action on smooth muscle through a cyclic-GMP-mediated mechanism that appears to involve synthesis of nitric oxide from L-arginine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Arg8]-vasopressin-induced responses on coronary and mesenteric arteries of rats with myocardial infarction: the effects of V1a- and V2-receptor antagonists

After myocardial infarction, plasma levels of [Arg8]-vasopressin rise to recover hemodynamics. The vascular responses to [Arg8]-vasopressin were studied in vitro in isolated hearts and mesenteric artery segments of rats with 1-day and 3-week-old infarcts, in absence and presence of the V1a-receptor antagonist SR-49059 and the V2-receptor antagonist OPC-31260. Vascular responses of coronary arteries were similar in sham and infarcted hearts. On average, coronary flow was maximally decreased by 70 +/- 3% from baseline values of 11.1 +/- 0.3 ml/min, with pD2 values of 10.52 +/- 0.05. In mesenteric artery segments of sham and infarcted rats, maximal contractile forces, expressed as percentage of contraction to 125 mM KCl, were similar (232 +/- 23% and 239 +/- 8%, respectively). However, pD2 values from infarcted rats (9.22 +/- 0.07) were significantly lower compared with sham (9.55 +/- 0.07) rats. In coronary as well as mesenteric vessels, the vasoconstrictor responses, being more susceptible to SR-49059 (apparent pA2, between 9.12 and 9.82) than to OPC-31260 (apparent pA2, between 6.21 and 6.92), seemed mediated by the V1a receptor. These data indicate that in mesenteric but not in coronary vessels, an altered responsiveness to vasopressin could be observed. Responses are mediated mainly by the V1a receptor.     

Relaxation induced by histamine is not endothelium dependent in tail arteries of L-NAME-treated rats

The present study was carried out to evaluate the relaxation induced by histamine in tail arteries of rats after chronic inhibition of nitric oxide (NO) synthesis with the inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) compared to tail arteries of control rats. The maximum relaxation induced by histamine was greater in control (88.09% +/-5.50, n=6) than in L-NAME arteries (47.33% +/-6.40, n=6), although pD(2) values were not different between the two groups (control: 4.89+/-0.08; L-NAME: 4.81+/-0.10). After incubation with 100 microM L-NAME in vitro, the maximum relaxation induced by histamine was only reduced in the control arteries (44.93% +/-2.35, n=6), whereas it had no effect on aortas of rats pretreated with this inhibitor. The incubation with 100 microM L-NAME had the same effect as endothelium removal in both arterial groups. Furthermore, the relaxation induced by histamine was unaffected by indomethacin. The combination of L-NAME and the histamine antagonist cimetidine completely abolished the relaxation induced by histamine in both arterial groups. These results show that when NO synthesis is impaired, the relaxation induced by histamine is endothelium independent, and when NO-synthase is active, the relaxation involves both NO released from endothelial cells and an endothelium-independent mechanism that is sensitive to cimetidine.     

Alterations of cyclo-oxygenase products and NO in responses to angiotensin II of resistance arteries from the spontaneously hypertensive rat.

1. The involvement of cyclo-oxygenase (COX) products and nitric oxide (NO) in contractile responses of resistance arteries to angiotensin II (AII) were investigated in small mesenteric arteries from spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats. 2. In endothelium intact vessels, AII induced concentration-dependent responses without any significant difference between the two strains. However, removal of functional endothelium resulted in enhanced sensitivity to AII, the pD2 value increasing from 8.4 +/- 0.2 to 8.9 +/- 0.2 (P < 0.05) in WKY and from 8.2 +/- 0.1 to 8.6 +/- 0.1 (P < 0.05) in SHR (not significantly different between strains, n = 9 - 12). In addition, endothelium removal enhanced maximal contractions elicited by AII in SHR (1.4 +/- 0.1 to 2.1 +/- 0.2 mN mm-1, n = 5; P < 0.05) but not in WKY (1.0 +/- 0.1 to 1.2 +/- 0.1 mN mm-1, n = 5) vessels. 3. In the absence of functional endothelium, the COX inhibitor indomethacin (10(-5) M) reduced contractile responses elicited by AII in SHR arteries, resulting in 33 +/- 5% (n = 5) decrease in maximal contraction. However, it produced minimal if any, effect on responses of WKY vessels. In both strains, the TP receptor antagonist GR32191 B (3 x 10(-6) M) did not modify contractions elicited by AII in these conditions. 4. In the presence of functional endothelium, indomethacin (10(-5) M) almost abolished the responses to AII in both strains. GR32191 B (3 x 10(-6) M) reduced the sensitivity of WKY arteries to AII (pD2 = 8.1 +/- 0.1, P < 0.01) without any effect on maximal contraction. In SHR arteries, it markedly reduced maximal contraction (47 +/- 3.5%). 5. In both strains, the NO synthase inhibitor NG-nitro-L-arginine methy lester (L-NAME; 10(-4) M) had no effect in the absence of functional endothelium but it markedly reduced the inhibitory influence of endothelium on contractile responses to AII. Furthermore, in arteries with endothelium, it reduced the effect of both indomethacin and GR32191 B to the same level as observed in vessels without functional endothelium. 6. The results suggest that enhanced contraction caused by COX products was counteracted by enhanced relaxation caused by endothelium-derived NO in resistance mesenteric arteries of the SHR exposed to AII, compared to WKY arteries. The COX products involved in alterations of SHR responses comprised an endothelium-derived prostaglandin activating TP receptors and another nonendothelial unidentified vasoconstrictor compound which did not activate these receptors.     

The interaction between indomethacin and contractile agents on human isolated airway muscle.

1 Concentration-effect curves to acetylcholine and histamine were produced in fresh human bronchial muscle (2 to 4 h after removal from the patients) and in preparations previously stored at 4 degrees C for 12 h. 2 Sensitivities of fresh human airway muscle preparations to acetylcholine (pD2 value, 5.89 +/- 0.03; n = 4) and histamine (pD2 values, 5.41 +/- 0.03; n = 13) were similar. There was no significant difference in the sensitivities of stored preparations (acetylcholine: pD2 value, 5.70 +/- 0.06; n = 23 and histamine: pD2 value, 5.44 +/- 0.07; n = 16) when compared to the fresh preparations. 3 Indomethacin did not significantly change the basal tone in preparations of either fresh or stored human airway muscle. 4 A low concentration of indomethacin (0.17 muM) significantly reduced responsiveness and sensitivity to histamine in stored bronchi but not in fresh bronchi. The acetylcholine concentration-effect curves were unaltered by exposure to this concentration of indomethacin in either fresh or stored tissues. High concentrations (1.7 muM and 17 muM) depressed the maximal responsiveness of the bronchi to both agonists. 5 These results suggest indirectly that the regulatory role of prostaglandins in human airway muscle may be different from that in other species.     

Comparative in vitro study of a series of organic nitroesters: unique biphasic concentration-effect curves for glyceryl trinitrate in isolated bovine arterial smooth muscle and lack of stereoselectivity for some glyceryl trinitrate analogues.

Four different organic nitroesters, constituting a homologous series based on unbranched polyalcohols, were compared with regard to in vitro relaxation of isolated bovine mesenteric arteries contracted with 2.5 microM phenylephrine. The organic nitroesters included ethylene glycol dinitrate (EGDN), dinitratopropane (DPN), glyceryl trinitrate (GTN), and tetranitratobutane. Glyceryl trinitrate exhibited a biphasic concentration-effect relationship, with pD2 values of 11.5 +/- 0.5 and 7.2 +/- 0.2 for the high-pD2 and low-pD2 component of the relaxation curve, respectively. The high-pD2 and low-pD2 component contributed 28 and 72% of the maximal response, respectively. EGDN, DPN, and tetranitratobutane induced monophasic concentration-effect curves with pD2 values of 7.4 +/- 0.1, 7.8 +/- 0.2, and 6.9 +/- 0.6, respectively. Stereoisomeric forms of DPN and tetranitratobutane showed no difference with regard to relaxing potency in bovine mesenteric artery. GTN has a partly unique mechanism for vascular smooth muscle relaxation that distinguishes this compound from other related organic nitroesters.     

Characterization of changes in mechanical responses to histamine in omental resistance arteries in pre-eclampsia

Changes in the effect of histamine on the smooth muscle of resistance arteries in pre-eclampsia were investigated by measuring isometric contractions in endothelium-denuded strips of omental resistance arteries from pre-eclamptic and normotensive pregnant women (pregnancy-term matched). Histamine (0.03 -1 microM) caused concentration-dependent relaxation of the contraction induced by 9, 11-epithio-11,12-methano-thromboxane A(2) (STA(2)) in strips from both groups. Sensitivity (for pre-eclampsia: pD(2)=6.66+/-0.04, n=5 and for normotensive pregnant women: pD(2)=7.07+/-0.03, n=10, P<0.001) was lower and the maximum response (90.6+/-0.6% vs 95.5+/-1.1%, P<0.05) was smaller in strips from pre-eclamptic women. Although 8-bromoadenosine-3', 5'-cyclic monophosphorothioate (Sp-isomer: Sp-8-Br-cAMPS, 0.1 - 0.3 mM), a phosphodiesterase (PDE)-resistant activator of adenosine-3',5'-cyclic monophosphate (cyclic AMP)-dependent protein kinase, concentration-dependently attenuated the contraction induced by STA(2) in strips from both groups, the sensitivity (for pre-eclampsia: pD(2)=3.68+/-0.04, n=5 and for normotensive pregnant women: 3.94+/-0.09, n=7, P:=0.02) was lower and the maximum response (64.2+/-2.4% vs 74.9+/-4.4%, P:<0.05) was smaller in pre-eclampsia. In beta-escin-skinned strips, the pD(2) value for the contraction-inducing effect of Ca(2+) did not differ significantly between the two groups (for pre-eclampsia, n=6; for normotensive pregnant women, n=6). Thus, omental resistance arteries from human subjects with pre-eclampsia showed (i) a weaker H(2)-receptor-mediated relaxation to histamine and (ii) a weaker cyclic AMP-analogue-induced relaxation, suggesting that the reduced action of histamine may be partly due to a decreased effect of cyclic AMP.     

Segmental heterogeneity in the mechanism of sodium nitroprusside-induced relaxation in ovine pulmonary artery

Segmental heterogeneity in relaxation response to nitric oxide (NO) was examined using NO donor sodium nitroprusside (SNP) in second- (medium) and fourth-generation (small) ovine isolated intralobar pulmonary arteries. In vessels precontracted with serotonin, NO donors SNP and S-nitroso-N-acetylpenicillamine (SNAP) were more potent in relaxing medium, in comparison to the small, arteries. Soluble guanylyl cyclase (sGC) inhibitor [1,2,4]oxadiazolo-[4,3-a]quinoxaline-1-one (ODQ 3 microM) caused a profound inhibition of SNP relaxation in small as compared with medium-sized arteries. However, both basal and SNP (10 microM)-stimulated intracellular cyclic guanosine monophosphate (cGMP) content was identical in these 2 arterial segments. The Na,K-ATPase inhibitor ouabain (1 microM) had a marked inhibitory effect on SNP-mediated relaxation in both segments. There was no segmental difference in SNP (10 microM)-stimulated plasma membrane Na,K-ATPase activity and ouabain-sensitive Rb-uptake. 4-AP (1 mM), a relatively selective inhibitor of Kv channels, decreased the potency of SNP relaxation by about 10-fold in the medium-sized vessels. On the other hand, 4-AP was without effect on the vasodilator potency of SNP in small vessels. Interestingly, in the presence of 4-AP, SNP was equipotent in dilating both medium (pD2 = 5.80 +/- 0.07; Emax = 84 +/- 1.6%, n = 7) and small (pD2 = 5.74 +/- 0.15; Emax = 83 +/- 2.5%, n = 7) pulmonary arteries. In conclusion, the results of the present study suggest that Kv channels determine the segmental heterogeneity of NO-mediated relaxation in ovine pulmonary artery.     

The resistance of some rat cerebral arteries to the vasorelaxant effect of cromakalim and other K+ channel openers.

1. Cromakalim (0.01-30 microM) and sodium nitroprusside (SNP, 0.01-100 microM) were tested for their ability to relax a number of pre-contracted small arteries (approximate diameter 200-700 microM at 100 mmHg) from the rat, rabbit and guinea-pig. 2. In the rat, SNP (0.01-100 microM) caused near maximal relaxation in all vessels studied including the middle cerebral, anterior cerebellar, basilar, mesenteric and renal arteries. Cromakalim (0.01-30 microM) relaxed pre-contracted mesenteric and renal arteries but was only a weak relaxant of all the rat cerebral arteries with the exception of the basilar artery. Similar experiments using mesenteric and cerebral vessels from the rabbit and guinea-pig showed cromakalim could relax pre-contracted vessels in a concentration-dependent manner. 3. Two other K+ channel openers, nicorandil and pinacidil, were also tested for their ability to relax rat cerebral arteries. Nicorandil (0.01-100 microM) was ineffective in the rat anterior cerebellar artery at concentrations up to 100 microM. Pinacidil (0.01-100 microM) caused significant vasorelaxation, although high concentrations were required (greater than 10 microM) and the response was insensitive to the effects of glibenclamide (3 microM). 4. Electrophysiological experiments with the rat anterior cerebellar artery showed that cromakalim (up to 30 microM) failed to influence the resting membrane potential of impaled single smooth muscle cells. 5. The results showed that some rat small cerebral arteries were resistant to the effects of K+ channel openers including cromakalim, pinacidil and nicorandil. This is peculiar to this vascular tree since the same vessels from other species do not exhibit the same behaviour.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impaired cholinergic dilator response of resistance arteries isolated from patients with Raynaud''s disease

AIMS: We examined the effect of cooling on the response to the endothelium-dependent and -independent dilators, acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, in human microvessels in vitro, and compared the responses between Raynaud's disease (RD) patients and controls, in order to assess the pathogenic role of the endothelium in RD. METHODS: Subcutaneous resistance arteries were dissected from gluteal fat biopsies taken from patients with RD (n=18) and from age-and sex-matched control subjects (n=17). Vessels were cannulated in a small vessel arteriograph, in which a pressure of 50 mmHg was maintained across the vessel wall. Cumulative concentration-response curves for ACh (10-10-10-4 m ) and SNP (10-10-10-3 m ) were generated in vessels at either 37 degrees C or 24 degrees C, with endothelium intact for ACh and removed for SNP (n=6 per group). RESULTS: Neither dilator showed significant differences in sensitivity when comparing responses between vessels from RD patients and controls, at either temperature, but the maximal relaxation to ACh was depressed in vessels from RD patients compared with controls at 37 degrees C (Emax=45+/-13 in RD vs 89+/-4 in controls; P=0.004). CONCLUSIONS: These results support the hypothesis that impaired endothelium-dependent vasodilatation is involved in the pathophysiology of RD.     

Human urotensin-II is an endothelium-dependent vasodilator in rat small arteries

The possible role of the endothelium in modulating responses to human urotensin-II (U-II) was investigated using isolated segments of rat thoracic aorta, small mesenteric artery, left anterior descending coronary artery and basilar artery. Human U-II was a potent vasoconstrictor of endothelium-intact isolated rat thoracic aorta (EC(50)=3.5+/-1.1 nM, R(max)=103+/-10% of control contraction induced by 60 mM KCl and 1 microM noradrenaline). However the contractile response was not significantly altered by removal of the endothelium or inhibition of nitric oxide synthesis with L-NAME (100 microM). Human U-II did not cause relaxation of noradrenaline-precontracted, endothelium-intact rat aortae. Human U-II contracted endothelium-intact rat isolated left anterior descending coronary arteries (EC(50)=1.3+/-0.8 nM, R(max)=20.1+/-4.9% of control contraction induced by 10 microM 5-HT). The contractile response was significantly enhanced by removal of the endothelium (R(max)=55.4+/-16.1%). Moreover, human U-II caused concentration-dependent relaxation of 5-HT-precontracted arteries, which was abolished by L-NAME or removal of the endothelium. No contractile effects of human U-II were found in rat small mesenteric arteries. However the peptide caused potent, concentration- and endothelium-dependent relaxations of methoxamine-precontracted vessels. The relaxant responses were potentiated by L-NAME (300 microM) but abolished in the additional presence of 25 mM KCl (which inhibits the actions of endothelium-derived hyperpolarizing factor). The present study is the first to show that human U-II is a potent endothelium-dependent vasodilator in some rat resistance vessels, and acts through release of EDHF as well as nitric oxide. Our findings have also highlighted clear anatomical differences in the responses of different vascular beds to human U-II which are likely to be important in determining the overall cardiovascular activity of this peptide.     

Comparison of the pharmacological properties of EDHF-mediated vasorelaxation in guinea-pig cerebral and mesenteric resistance vessels

In the presence of L-NNA (100 microM), indomethacin (10 microM) and ODQ (10 microM), acetylcholine induced a concentration-dependent vasorelaxation of guinea-pig mesenteric and middle cerebral arteries precontracted with cirazoline or histamine, but not with high K(+), indicating the contribution of an endothelium-derived hyperpolarizing factor (EDHF). In cerebral arteries, charybdotoxin (ChTX; 0.1 microM) completely inhibited the indomethacin, L-NNA and ODQ-insensitive relaxation; iberiotoxin (IbTX, 0.1 microM), 4-aminopyridine (4-AP, 1 mM), or barium (30 microM) significantly reduced the response; in the mesenteric artery, ChTX and IbTX also reduced this relaxation. Glibenclamide (10 microM) had no affect in either the mesenteric or cerebral artery. Neither clotrimazole (1 microM) nor 7-ethoxyresorufin (3 microM) affected EDHF-mediated relaxation in the mesenteric artery, but abolished or attenuated EDHF-mediated relaxations in the cerebral artery. AM404 (30 microM), a selective anandamide transport inhibitor, did not affect the vasorelaxation response to acetylcholine in the cerebral artery, but in the mesenteric artery potentiated the vasorelaxation response to acetylcholine in an IbTX, and apamin-sensitive, but SR 141816A-insensitive manner. Ouabain (100 microM) almost abolished EDHF-mediated relaxation in the mesenteric artery, but enhanced the relaxation in the cerebral artery whereas the addition of K(+) (5 - 20 mM) to precontracted guinea-pig cerebral or mesenteric artery induced further vasoconstriction. These data suggest that in the guinea-pig mesenteric and cerebral arteries different EDHFs mediate acetylcholine-induced relaxation, however, EDHF is unlikely to be mediated by K(+).