Effects of U46619 on contractions to 5-HT, sumatriptan and methysergide in canine coronary artery and saphenous vein in vitro

Glucosamine increases vascular contraction through activation of RhoA/Rho kinase pathway in isolated rat aorta

Diabetes is a well-known independent risk factor for vascular disease. However, its underlying mechanism remains unclear. It has been reported that increased influx of the hexosamine biosynthesis pathway (HBP) induces O-GlcNAcylation of proteins, leading to insulin resistance. In this study, we determined whether or not O-GlcNAc modification of proteins could increase vessel contraction. Using an endothelium-denuded aortic ring, we observed that glucosamine induced OGlcNAcylation of proteins and augmented vessel contraction stimulated by U46619, a thromboxane A(2) agonist, via augmentation of the phosphorylation of MLC(20), MYPT1(Thr855), and CPI17, but not phenylephrine. Pretreatment with OGT inhibitor significantly ameliorated glucosamine-induced vessel constriction. Glucosamine treatment also increased RhoA activity, which was also attenuated by OGT inhibitor. In conclusion, glucosamine, a product of glucose influx via the HBP in a diabetic state, increases vascular contraction, at least in part, through activation of the RhoA/Rho kinase pathway, which may be due to O-GlcNAcylation.

Amplification of sumatriptan-induced contraction in rabbit saphenous vein but not in basilar artery

The modulation of serotonin (5-HT(1B/1D)) receptor-induced vascular contractility by histamine and U-46619 was compared in the rabbit basilar artery and saphenous vein. In the saphenous vein, histamine (5 x 10(-7) M) significantly increased the potency (from pEC(50) of 6.0 to 6.8) and efficacy (from 52.3% to 88.2%) of sumatriptan. Likewise, U-46619 (5 x 10(-9) M) also increased the potency (from pEC(50) of 5.9 to 6.6) and efficacy (from 51.8% to 92.1%) of sumatriptan in the saphenous vein. In contrast, equieffective concentrations of histamine (10(-7) M) and U-46619 (3 x 10(-9) M) failed to amplify contraction to sumatriptan in the basilar artery. Contraction to sumatriptan was inhibited by nitrendipine (10(-7) M) in the basilar artery but not in the saphenous vein, suggesting that different contractile signaling mechanisms are operating in these tissues. Furthermore, U-46619- and thrombin-induced contractility in the basilar artery were also not amplified by histamine, suggesting that lack of amplification of contraction in the basilar artery was not restricted to sumatriptan but was rather a characteristic of this cerebral vessel. These data suggest that in the in vivo plasma milieu sumatriptan will more markedly contract the peripheral saphenous vein than the basilar artery, a cerebral blood vessel.

A thromboxane A(2) system in the Atlantic stingray, Dasyatis sabina

Thromboxane B(2)(TXB(2)) is the stable metabolite of thromboxane A(2)(TXA(2)) and thromboxane B(2)-like immunoreactivity (iTXB(2)) has been identified in the plasma of the Atlantic stingray, Dasyatis sabina (0.57+/-0.03 ng/ml). Plasma levels of iTXB(2) increase if the blood is allowed to clot (3.0+/-0.27 ng/ml). When clotting occurs in the presence of indomethacin, this increase is partially inhibited (1.5+/-0.17 ng/ml), indicating the presence of a cyclooxygenase activity. Radioligand binding analysis using the TXA(2) analog [125I]BOP in isolated kidney membranes revealed a receptor of K(d)=2.88+/-0.51 nM and B(max)=25.6+/-5.9 fmol/mg protein. [125I]BOP binding was displaced by the TXA(2) receptor (TP receptor) agonists U46619 (IC(50)=106.4+/-15.7 nM) and U44069 (IC(50)=88.7+/-13.0 nM), and the antagonist SQ29548 (IC(50)=51.0+/-12.9 nM). Binding was also displaced stereoselectively by the antagonists (-)L657925 (IC(50)=18.9+/-3.8 nM) and (+)L657926 (IC(50)=2025+/-280 nM). Tissue bath studies revealed that U46619, a stable TXA(2) mimetic, elicited concentration-dependent contractions in the ventral aorta which were inhibited in a concentration-dependent manner by the TP receptor antagonist SQ29548. Using a human TP receptor riboprobe, Northern blotting of mRNA isolated from the stingray kidney identified transcripts of 2.8 and 6kb. The 2.8kb transcript is similar to a 2.8kb transcript found in human cells or tissues, but the 6kb transcript may be unique. These data indicate the presence of a TXB(2)-like substance in the blood, a TP receptor in the kidney, TXA(2) biological activity in the ventral aorta, and expression of a TP receptor-like gene.

Effect of somatostatin on rabbit isolated coronary arteries

Somatostatin analogues are capable of inhibiting vascular smooth muscle and endothelial cell proliferation. However, little is known about the effect of somatostatin on vascular responses in endothelium-denuded coronary arteries in vitro. The aim of this work was to determine whether or not somatostatin prevented the contractile response induced by 5-hydroxytryptamine and acetylcholine in endothelium-denuded rabbit coronary arteries. Somatostatin attenuated the contraction produced by 5-hydroxytryptamine in both proximal (PC) and distal coronary (DC) arteries (contraction induced by 10(-4) M 5-hydroxytryptamine was inhibited by 10(-6) M somatostatin by 90.8 +/- 11.0% (P < 0.001, n = 9) and by 46.2 +/- 14.0% (P < 0.05, n = 9) in DC and PC, respectively), but concentration-dependently decreased the contraction induced by U46619 (11alpha-epoxy-methanoprostaglandin F2alpha) only in PC arteries, suggesting that the response of PC and DC arteries to somatostatin were qualitatively different. Furthermore, we suggest that somatostatin may enhance acetylcholine-induced relaxation by combination of increasing endothelium-dependent relaxation (by a NO-dependent mechanism) and blocking contraction at the muscle level.

In vivo analysis of adrenergic and serotoninergic constrictions of the rabbit saphenous vein

We aimed to develop a model to study in vivo the rabbit saphenous vein pharmacology and to investigate constrictions mediated by adrenoceptor and 5-HT receptor subtypes. We used the technique of high precision ultrasonic echo-tracking for direct measurement of saphenous vein diameters in pentobarbital anesthetized rabbits. Saphenous vein constrictions induced in rabbits by the alpha(1)-adrenoceptor agonist L-phenylephrine and the 5-HT(1B) receptor agonist sumatriptan were comparable with those induced in dogs but those induced by the 5-HT(1B) and 5-HT(7) receptor agonist 5-carboxamidotryptamine failed to appear in dogs. Dose-related constrictions of rabbit veins were obtained with L-phenylephrine and the alpha(2)-adrenoceptor agonist dexmedetomidine. Frequency-related constrictions of rabbit veins induced by nerve stimulation were partially inhibited by an alpha(1)-adrenoceptor or a postsynaptic alpha(2)-adrenoceptor antagonist (prazosin and SKF 104,078) but not affected by the pre- and post-synaptic alpha(2)-adrenoceptor antagonists BRL 44408 or rauwolscine. Constrictions of rabbit veins to sumatriptan and 5-CT were inhibited by GR 127935 and those induced by quipazine, a 5-HT(2) receptor agonist were prevented by ritanserin. The initial constrictions induced by 5-CT were followed by dilatations which were inhibited by the 5-HT(7) receptor antagonist mesulergine. These data indicate that rabbit saphenous veins, in vivo and at rest, respond to activation of 5-HT(1B) and 5-HT(2) receptors, alpha(1)- and alpha(2)-adrenoceptors and nerve stimulation; the dilator effect mediated by 5-HT(7) receptor activation was also detected. The data validate a new animal model to study superficial vein reactivity and its pharmacological sensitivity.

Effects of the novel antimigraine agent, frovatriptan, on coronary and cardiac function in dogs

The effects of frovatriptan (VML 251/SB-209509) on coronary artery function were investigated in isolated coronary arteries from beagle dogs. Low concentrations of frovatriptan produced contraction with -logEC50 7.55 +/- 0.08 (n = 11). The maximal observed contraction attained was 56 +/- 7% of the control 5-hydroxytryptamine (5-HT; 10 microM) response. At high concentrations of frovatriptan (>6 microM), reversal of sumatriptan (10 microM)-induced contractions was noted. In arteries precontracted with the thromboxane mimetic, U46619, frovatriptan produced a bell-shaped concentration-response relation with a maximal response at 600 nM. Concentrations of frovatriptan >2 microM produced marked reversal of tone, with full relaxation of precontracted tissues at 200 microM. In anesthetized, open-chest mongrel dogs, intravenous (n = 5) or intracoronary (n = 5) artery administration of frovatriptan (0.0001-1 mg/kg) had no consistent effect on left ventricular end-diastolic pressure, left end-systolic pressure, cardiac contractility, aortic blood flow, systemic peripheral resistance, coronary blood flow, coronary vascular resistance, mean arterial blood pressure, or heart rate when compared with vehicle (n = 3). Intravenous sumatriptan produced minor effects on blood pressure and heart rate. Intracoronary artery administration of sumatriptan (0.0003 mg/kg) produced an increase in systemic peripheral resistance to 120.5 +/- 8.2% compared with vehicle (97.8 +/- 5.4%; p < 0.05). This dose of sumatriptan also produced a significant increase in coronary blood flow and decrease in coronary vascular resistance. Intravenous administration of sumatriptan produced a dose-related reduction in left ventricular diastolic pressure with a reduction to 58.3 +/- 8.3% and 41.7 +/- 25% of control values observed at 0.3 and 1 mg/kg, respectively; however, administration of sumatriptan by an intracoronary route had no effect. In a model of myocardial infarction, comparable doses of sumatriptan (1.0 mg/kg) or frovatriptan (0.1 mg/kg), in terms of their effect on carotid vascular resistance, had no significant effect on infarct size. Frovatriptan had no effect on coronary blood flow after reperfusion; however, sumatriptan produced a significant reduction in coronary blood flow for < or =3 h. These studies show that frovatriptan has the capability of relaxing coronary arteries in vitro, has no overall effect on cardiac function at rest with no effect on coronary hemodynamics after myocardial infarction, and has a profile superior to that of sumatriptan.

Effects of sumatriptan on coronary flow and left ventricular function in the isolated perfused guinea pig heart

The effects of the 5-HT1B/D receptor agonist, sumatriptan, on coronary flow (CF) and left ventricular function in the isolated perfused guinea pig heart were investigated in the presence and absence of coronary endothelial dysfunction induced by nitric oxide (NO) synthase inhibition with Nomega-nitro-L-arginine methyl ester (L-NAME; 10 microM). Hearts were perfused under constant pressure (80 cm H2O) with oxygenated (95% O2/5% CO2) Krebs bicarbonate buffer (pH 7.4) and were driven at 4 Hz. In the absence of L-NAME (n=37), sumatriptan (0.1-32 microM) failed statistically significantly to affect left ventricular developed pressure (LVDP; maximal change, -8.1+/-1.8%; NS vs. vehicle), left ventricular end-diastolic pressure (LVEDP; +10.4+/-9.8%, NS), or CF (-12.2+/-1.4%; NS compared with vehicle). L-NAME per se significantly reduced coronary flow (CF; -26.3+/-2.9%; p < 0.001), thereby increasing coronary vascular tone, and decreased LVDP (-17.1+/-1.8%; p < 0.01). In hearts perfused with L-NAME (10 microM; n=61), sumatriptan (0.1-32 microM) still failed significantly to affect CF (maximal change, 0.2+/-5.7%, NS) but concentration-dependently increased LVEDP [maximal increase, 89.0+/-30.3%; p < 0.05; geometric mean EC50 3.6 (2.9-5.7) microM], which was not prevented by the 5-HT1B/D receptor antagonist, GR 127935 (0.1 microM; maximal increase, 51.8+/-11.1%; n=48, NS compared with sumatriptan alone). In conclusion, sumatriptan failed significantly to affect CF even in the presence of endothelial dysfunction. LV function similarly remained unaffected in normal hearts, but sumatriptan produced diastolic contracture in the presence of coronary endothelial dysfunction by a mechanism apparently not involving 5-HT1B/D receptors. Collectively the data indicate that 5-HT1B/D receptor expression or effector coupling or both are absent or low in the guinea pig heart, because no detectable functional responses were observed.

Contractile responses evoked by dihydroergotamine, naratriptan and sumatriptan in the canine isolated coronary artery

Contractile responses evoked by the 5-HT IB/D receptor agonists, dihydroergotamine, naratriptan and sumatriptan, were compared in canine isolated coronary artery rings before and after endothelial dysfunction as obtained by inhibition of nitric oxide synthase with Nw-nitro-L-arginine methyl ester (L-NAME; 10 microM). The three agonists contracted rings in the potency order of dihydroergotamine (geometric mean pD2 value with 95% confidence limits in parentheses: 6.9 [5.3-7.9] and 7.0 [5.4-7.3] in the absence and presence of nitric oxide synthase (NOS) inhibition [I], respectively) > or = naratriptan (6.8 [5.7-7.3] and 6.4 [5.7-6.6]) > sumatriptan (4.8 [3.6-5.6] and 5.0 [3.6-5.6]) independently of the presence or absence of L-NAME. In absence of L-NAME, efficacy, as assessed by the mean maximal contractile response (Emax), tended to be greater, although not significantly, for sumatriptan and naratriptan compared to dihydroergotamine. L-NAME per se markedly increased developed tension (43.0 +/- 4.6 mN; n = 50) and potentiated maximal responses (0.6 +/- 0.2 and 10.7 +/- 2.4 mN for dihydroergotamine in the absence and presence of L-NAME respectively; 1.7 +/- 0.6 and 18.7 +/- 3.7 mN for naratriptan; 2.5 +/- 0.6 and 21.3 +/- 3.8 mN for sumatriptan; P < 0.01 in each case). Emax values of sumatriptan and naratriptan were greater than those produced by dihydroergotamine in the presence of L-NAME but remained lower than the sub-maximal contractile responses evoked by the thromboxane A2 analogue, U-46619 (ie, 32.4 +/- 5.2 mN in the absence of L-NAME; n = 50), or L-NAME per se. In conclusion, 5-HT IB/D receptor agonist efficacies in contracting coronary arteries are relatively low under basal conditions and are potentiated in the presence of a dysfunctional endothelium, whereas agonist potencies remain unaffected.

The effect of forskolin on 5-HT1-like and angiotensin II-induced vasoconstriction and cyclic AMP content of the rabbit isolated femoral artery

1. A characteristic feature of vasoconstrictor 5-HT1-like receptors in vitro is that responses mediated by these receptors are enhanced by other vasoconstrictor agents. In the present study, we have examined the influence of cellular cyclic AMP on vasoconstrictor responses to activation of 5-HT1-like receptors in isolated ring segments of the rabbit femoral artery (RbFA), and determined whether modulation of this second messenger underlies the ability of angiotensin II, an endogenous vasoconstrictor, to enhance 5-HT1-like responses. 2. In the presence of 0.1 microM ketanserin (to antagonize 5-HT2-receptors) and 0.3 microM prazosin (to antagonize alpha 1-adrenoceptors), 5-HT produced a concentration-related contraction, which was significantly augmented by pre-contraction of the vessel with 0.1-0.45 nM ([A30]) angiotensin II. Responses to 5-HT in the presence of angiotensin II were inhibited by the 5-HT1-like/5-HT2 antagonist, metergoline (1 microM). 3. The directly-acting adenylyl cyclase activator, forskolin (1 microM), abolished responses to angiotensin II and caused a rightward shift and concomitant depression of the 5-HT concentration-effect (E/[A]) curve. Higher concentrations of forskolin (> 10 microM) abolished responses to 5-HT and 1 microM sodium nitroprusside abolished responses to 5-HT and angiotensin II (n = 7). 4. In the presence of angiotensin II (0.1-0.45 nM), however, 1 microM forskolin failed to inhibit 5-HT-induced contractions; the E/A curve for 5-HT (in the presence of forskolin and angiotensin II) was not significantly different from that produced in the presence of angiotensin II alone. Similarly, the presence of angiotensin II (0.1-0.45 nM) was also able to overcome partially the inhibitory effect of 1 microM sodium nitroprusside against 5-HT-induced contractions (n = 7). In marked contrast, 5-HT failed to elicit a contraction in the presence of angiotensin II and 10 microM forskolin (n = 5). 5. 5-HT (1 microM) significantly reduced basal cyclic AMP accumulation by 35%, whereas angiotensin II (0.45 nM) was without effect. The combination of angiotensin II and 5-HT failed to alter significantly the reduction in cyclic AMP produced by 5-HT alone. Forskolin (1 microM) increased cyclic AMP levels 7 fold above basal, but neither 1 microM 5-HT nor a combination of 1 microM 5-HT and 0.45 nM angiotensin II produced a significant decrease in cyclic AMP content. 6. Whilst moderate concentrations of forskolin can inhibit the responses to either agent, simultaneous activation of angiotensin II and 5-HT1-like receptors can overcome the inhibitory effect of elevated levels of cyclic AMP. Since the potentiating effect of angiotensin II, in either the presence or absence of forskolin, occurs without significant alteration of cellular cyclic AMP, it seems likely that a cyclic AMP-independent pathway is implicated in the synergistic interaction between angiotensin II and vasoconstrictor 5-HT1-like receptors.