Canine Cerebral Arteries Research Articles

Effects of isoflurane on K+ and Ca2+ conductance in isolated smooth muscle cells of canine cerebral arteries.

Although isoflurane is a known cerebral vasodilator, the mechanism of isoflurane-induced vasodilation is not clear. The purpose of this study was to investigate the effects of 2.6% isoflurane (1.2 mM) on macroscopic calcium and potassium channel currents in voltage-clamped canine middle cerebral artery cells. Cells were dialyzed with K(+)-glutamate solution and superfused with Tyrode's solution for measurement of potassium current (n = 20). Stepwise depolarization from a holding potential of -60 mV to beyond -30 mV elicited an outward, slowly inactivating potassium current that was reduced 50% +/- 2% and 81% +/- 3% (mean +/- SEM) in the presence of 1 mM 4-aminopyridine and 30 mM tetraethylammonium, respectively. Calcium ionophore (A23187, 10 microM) increased the potassium current by 76% +/- 3%, suggesting calcium dependency. Isoflurane reduced the amplitude of the potassium current by 35% +/- 4%. Calcium current was measured in cells dialyzed with solution containing 130 mM Cs(+)-glutamate and superfused with solution containing 10 mM BaCl2 and 135 mM tetraethylammonium to pharmacologically isolate the calcium current (n = 13). Under these conditions, progressive depolarizing steps from -60 mV elicited an inward current that was maximally activated at +20 mV and essentially eliminated by 1 microM nifedipine. This current, resembling a long-lasting (L-type) Ca2+ channel current, was reduced 40% +/- 4% by isoflurane. The results of this study suggest that isoflurane acts directly at the vascular muscle membrane to suppress transmembrane calcium and potassium currents. The decrease in calcium current would cause vasodilation; however, the concomitant decrease in potassium current may partially antagonize the depressant effect of isoflurane mediated through calcium current reduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of guanylate cyclase-cGMP systems in halothane-induced vasodilation in canine cerebral arteries.

The cellular mechanisms through which halothane dilates blood vessels remain largely unknown. The present studies were designed to determine the effects of 0.59 and 0.9 mM halothane (equivalent to 2.0% and 3.0%, respectively) on tissue cyclic guanosine 3,5-monophosphate (cGMP) level and guanylate cyclase enzyme activity in canine middle cerebral arteries. Rings of cerebral arteries preconstricted with 5-hydroxytryptamine (0.2 microM) were exposed for 15 min to low or high concentrations of halothane or for 5 min to sodium nitroprusside (50 microM). The vessels were instantaneously frozen by immersing them in liquid N2; they then were homogenized, and the tissue cGMP levels were determined using radioimmunoassay. Halothane produced 2.23 +/- 0.44- and 4.47 +/- 0.87-fold increases in tissue cGMP levels over control at 0.59 and 0.9 mM, respectively. Sodium nitroprusside, a nitrovasodilator, also increased the tissue cGMP level 7.80 +/- 1.36-fold over the control value. To understand better the mechanisms of halothane-induced increase of tissue cGMP level, the effects of this anesthetic agent on guanylate cyclase enzyme activity were examined. Halothane, unlike sodium nitroprusside, did not modulate the activity of the soluble guanylate cyclase enzyme. However, halothane (1.0 mM), like atrial natriuretic factor (5 microM), stimulated the particulate guanylate cyclase enzyme activity. LY-83583 (6-anilino-5,8-quinolinedione, 10 microM), an agent that inhibits soluble guanylate cyclase activity, significantly reduced the response of the vessels to calcium ionophore (A23187, 0.4 microM), an endothelium-dependent vasodilator, without producing a significant effect on halothane-induced vasodilation. These results suggest that halothane-induced vasodilation of cerebral blood vessels is partly mediated by an increase in tissue cGMP levels.(ABSTRACT TRUNCATED AT 250 WORDS)

DIRECT VASOCONSTRICTOR AND VASODILATOR EFFECTS OF PROPOFOL IN ISOLATED DOG ARTERIES

We have measured the direct effects of propofol 10(-7)-10(-4) mol litre-1 on isolated canine cerebral, coronary, mesenteric, femoral and renal arteries. In arterial strips precontracted submaximally with potassium chloride or prostaglandin F2 alpha (PGF2 alpha), propofol induced further contractions at low concentrations (10(-6)-10(-5) mol litre-1) and relaxation at high concentrations (10(-4) mol litre-1). Intrafat, which contains soya bean oil, egg phosphatide and glycerol in similar concentration to the emulsion formulation of propofol, had a small relaxant effect at a concentration corresponding to propofol 10(-4) mol litre-1. In humans, clinically relevant plasma concentrations of propofol have been reported to be 1-5 x 10(-5) mol litre-1, 97-99% of which is bound to plasma proteins. Therefore, the results obtained in this study demonstrated that clinically relevant concentrations of propofol did not have direct vasodilator effects.

P-281 - Endothelium-dependent contraction induced by somatostatin in canine cerebral arteries

P-281 - Endothelium-dependent contraction induced by somatostatin in canine cerebral arteries

Ischemia-Reperfusion Does Not Affect Reactivity of Isolated Canine Basilar Artery

The effect of ischemia-reperfusion on endothelium-dependent relaxations and reactivity of vascular smooth-muscle cells was studied in rings of basilar arteries obtained from six dogs exposed to 12 min of complete global cerebral ischemia followed by 100 min of reperfusion. Three sham-operated control dogs served as controls. Ischemia was induced either by an increase in intracranial pressure or by aortic occlusion. The rings were suspended for isometric tension recording in physiological salt solution. Ischemia-reperfusion did not affect endothelium-dependent relaxations to vasopressin and bradykinin. In rings without endothelium relaxations to sodium nitroprusside, molsidomine (SIN-1), and papaverine as well as contractions to 5-hydroxytryptamine and KCl were preserved. These results demonstrate that in large canine cerebral arteries, ischemia-reperfusion of these durations does not affect relaxations mediated by activation of endothelium or direct relaxations and contractions of vascular smooth-muscle cells.

Prostaglandin F2 alpha-induced endothelium-dependent relaxation in isolated monkey cerebral arteries

Effects of prostaglandin F2 alpha (PGF2 alpha) on isolated monkey and dog cerebral arteries were investigated to reevaluate PGF2 alpha's possible action on the endothelium. Low concentrations of PGF2 alpha ranging from 10(-11) to 10(-8) M produced a dose-dependent relaxation in the monkey arteries. PGF2 alpha (10(-7) M) produced a transient contraction followed by a small relaxation, whereas higher concentrations (greater than 10(-6) M) of PGF2 alpha induced only contractions. The PGF2 alpha-induced relaxation was not observed in the canine cerebral arteries. The PGF2 alpha-induced relaxation of the monkey cerebral arteries was not affected by treatment with 10(-7) M propranolol, 10(-7) M atropine, or 10(-6) M cimetidine. In monkey cerebral arteries without endothelium, PGF2 alpha in concentrations ranging from 10(-11) to 10(-6) M caused no relaxation. Treatment with 5 X 10(-5) M aspirin, 3 X 10(-5) M NG-monomethyl-L-arginine, and 10(-5) M oxyhemoglobin significantly suppressed the PGF2 alpha-induced relaxation. These results suggest that low concentrations of PGF2 alpha may produce an endothelium-dependent relaxation in monkey cerebral arteries and that the relaxation may be mediated by release of both endogenous vasodilative prostaglandins and endothelium-derived relaxing factor from endothelial cells.

Endothelins: vasoconstrictor effects and localization in canine cerebral arteries

1. The vascular effects of endothelin and localization of endothelin-like immunoreactivity were characterized in isolated cerebral arteries of dogs. 2. Endothelin-like immunoreactivity was detected in a few populations of endothelial cells of dog basilar artery. 3. Endothelin-1, endothelin-2 and endothelin-3 contracted isolated ring preparations of cerebral arteries in a dose-dependent manner independently of the presence of endothelium. The ED50 values (and 95% confidence intervals) for the contraction were 411 pM (242-697 pM) and 478 pM (295-776 pM) for endothelin-1 and endothelin-2, respectively. Endothelin-3 induced vascular contraction at a higher concentration (ED50 = 26.5 nM, 95% confidence interval = 15.7-45.7 nM). 4. The increases in tone induced by endothelin-1 and endothelin-2 did not return to the resting level after repeated washings, while a rinse with Krebs solution reversed the vasoconstrictor response to endothelin-3. The endothelins did not cause any vasodilator response in arteries precontracted with uridine 5'-triphosphate even in the presence of intact endothelial cells. 5. NiCl2 (1 mM) attenuated the contractions induced by endothelin-3 (10-300 nM) and those to relatively low doses (1 nM) but not higher doses (10-100 nM) of endothelin-1 and endothelin-2. The contractions in response to endothelin-1, endothelin-2 and endothelin-3 were greatly attenuated in Ca(2+)-free solutions although high concentrations of endothelin-1 and endothelin-2 still evoked contractions. 6. These results suggest that the vasoconstriction induced by endothelin-3 and lower doses of endothelin-1 and endothelin-2, largely depends on the influx of Ca2+ ions. The apparent insensitivity to Ni2+ shows that additional distinct mechanisms also operate in the vasconstrictor responses to high concentrations of endothelin-1 and endothelin-2. 7. The presence of endothelin-like immunoreactivity in endothelial cells suggests that endothelin is a potential endogenous spasmogen.

Mechanism of the Enhanced Vasoconstrictor Responses to Endothelin-1 in Canine Cerebral Arteries

Vasoconstrictor effects of endothelin-1 (ET) were investigated in endothelium-denuded strips of cerebral (basilar and posterior cerebral) and mesenteric arteries of the dog. ET produced a concentration-dependent contraction in these arteries. Contractile responses to lower concentrations (below 3 x 10(-10) M) of ET were significantly greater in the cerebral arteries than in the mesenteric artery. Inhibition by nifedipine of the contractile responses to ET was greater in the basilar artery than in the mesenteric artery. After the inhibition by 10(-7) M in the mesenteric artery. After the inhibition by 10(-7) M nifedipine, the remaining responses to ET were similar in the two arteries. Cerebral arteries, but not the mesenteric artery, relaxed significantly from the resting level when placed in a Ca2(+)-free solution containing 0.1 mM EGTA (0-Ca solution). Readdition of Ca2+ to the cerebral arteries placed in the 0-Ca solution caused a biphasic contraction that was sensitive to nifedipine. When 10(-9) M ET was introduced before the Ca2(+)-induced contraction, this peptide produced only a very small contraction, but enhanced the Ca2(+)-induced contraction. The extent of the enhancement induced by ET was much greater in the cerebral arteries than in the mesenteric artery. These results indicate that the enhanced responses to ET in the cerebral arteries were dependent to a large extent on Ca2+ influx through voltage-dependent Ca2+ channels (VDCs). It is likely that the VDCs in these arteries are more activated in the resting state than those in the mesenteric artery.

Vasoinhibitory effect of NP-252, a new dihydropyridine derivative, in canine cerebral artery

The vasoinhibitory effect of NP-252, a 1,4-dihydropyridine derivative Ca ++ antagonist, was examined in canine cerebral artery, and this effect was compared with that of nifedipine. NP-252 (10 −7 M) and nifedipine (10 −6 M) nearly abolished the contraction induced by addition of Ca ++ to Ca ++-free medium containing KCl. NP-252 (10 −6 M) and nifedipine (10 −6 M) attenuated the contraction produced by thromboxane A 2 agonist (STA 2) in normal medium, and the resultant contractions were 22% (n = 6) and 35% (n = 6) of the control contraction, respectively. The vasoinhibitory effects of NP-252 were significantly stronger than those of nifedipine in canine cerebral artery. NP-252 (10 −7 and 10 −6 M) dose-dependently attenuated nifedipine-resistant Ca ++-contraction in the presence of STA 2 in both canine cerebral and coronary arteries. The inhibitory effect of combined treatment with NP-252 (10 −6 M) and nitroglycerin (10 −6 M) on nifedipine-resistant Ca ++-contraction in the cerebral artery was additive. These results indicate that NP-252 possesses a stronger vasoinhibitory effect than that of nifedipine in canine cerebral artery.

O-005 - The effects of Arg-vasopressin on the canine cerebral arteries.

O-005 - The effects of Arg-vasopressin on the canine cerebral arteries.

Characterization of the Effect of Endothelins in Canine Cerebral Arteries

In a few populations of endothelial cells of dog basilar arteries, endothelin (ET)-like immunoreactivity was detected to be present. ET-1, ET-2, and ET-3 caused vasoconstrictor responses but not vasodilator responses in isolated ring preparations of dog cerebral arteries in vitro. The ED50 values for the contractions were 411 pM, 478 pM, and 26.5 nM for ET-1, ET-2, and ET-3, respectively. NiCl2 (10(-3) M) attenuated the contractions induced by ET-3 (10(-8)-3 x 10(-7) M) and those to relatively low doses (10(-9) M) but not higher doses (10(-8)-10(-7) M) of ET-1 and ET-2. The contractions in response to ET-1, ET-2, and ET-3 were greatly attenuated in Ca(2+)-free solutions, although high concentrations of ET-1 and ET-2 still evoked contractions. These results suggest that the vasoconstriction induced by ET-3 and lower doses of ET-1 and ET-2 largely depends on the influx of Ca2+ ions. Furthermore, additional distinct mechanisms may contribute to the vasoconstrictor effects of high concentrations of ET-1 and ET-2. The presence of endothelin-like immunoreactivity in endothelial cells suggests that endothelin is a potential endogenous spasmogen.

Endothelin: a potential modulator of cerebral vasospasm

1-(5-Isoquinolinesulfonyl)-homopiperazine, HA1077, is a calcium antagonist with anti-vasospastic properties. This compound blocks intracellular actions of calcium in a variety of experiments. In the present study, we examined the effects of HA1077 on the vascular actions of endothelin, an endothelium-derived vasoactive peptide, in dogs in vitro and in vivo. Intracisternal injections of endothelin (0.01 nmol) produced a significant vasospasm, as measured by angiography, similar to that seen in the canine hemorrhage model. Infusion of HA1077 led to a significant dilatation of the spastic basilar artery in endothelin-treated dogs. The rank order of in vitro contractile activity in canine cerebral arteries was a stable thromboxane A 2 analog > endothelin > 5-hydroxytryptamine > prostaglandin F 2α > histamine > noradrenaline. HA1077 effectively antagonized the endothelin-induced contraction of canine basilar arterial strips in both calcium-containing and calcium-free medium. The present results indicate that HA1077 is an effective antagonist for endothelin in vitro and in vivo.

Endothelium-dependent response to histamine in canine and monkey cerebral arteries

Endothelium-dependent response to histamine in canine and monkey cerebral arteries

O-048 - Endothelin: a potential modulator of cerebral vasospasm

1-(5-Isoquinolinesulfonyl)-homopiperazine, HA1077, is a calcium antagonist with anti-vasospastic properties. This compound blocks intracellular actions of calcium in a variety of experiments. In the present study, we examined the effects of HA1077 on the vascular actions of endothelin, an endothelium-derived vasoactive peptide, in dogs in vitro and in vivo. Intracisternal injections of endothelin (0.01 nmol) produced a significant vasospasm, as measured by angiography, similar to that seen in the canine hemorrhage model. Infusion of HA1077 led to a significant dilatation of the spastic basilar artery in endothelin-treated dogs. The rank order of in vitro contractile activity in canine cerebral arteries was a stable thromboxane A2 analog greater than endothelin greater than 5-hydroxytryptamine greater than prostaglandin F2 alpha greater than histamine greater than noradrenaline. HA1077 effectively antagonized the endothelin-induced contraction of canine basilar arterial strips in both calcium-containing and calcium-free medium. The present results indicate that HA1077 is an effective antagonist for endothelin in vitro and in vivo.

P-090 - Inhibitory effect of NKY-722 on endothelium-independent and -dependent contractions in canine cerebral arteries

P-090 - Inhibitory effect of NKY-722 on endothelium-independent and -dependent contractions in canine cerebral arteries

O-121 - Endothelium-dependence of contractile responses to angiotensins in canine cerebral arteries

O-121 - Endothelium-dependence of contractile responses to angiotensins in canine cerebral arteries

Endothelin acts in feline and canine cerebral arteries from the adventitial side.

We investigated the in vivo vasoconstrictor effect of endothelin, a recently characterized vasoconstrictor peptide from vascular endothelium, in the basilar arteries of five cats and five dogs. Basilar artery caliber was angiographically measured under anesthesia before (control) and after either vertebral artery infusion or cisternal injection of the peptide. In cats, 5-500 pmol endothelin induced a dose-dependent basilar artery contraction in vivo when injected intracisternally; within 3 minutes after injection of 500 pmol endothelin, basilar artery caliber was decreased by 73 +/- 4% compared with control diameter before injection. The vasoconstriction was extremely long-lasting; no significant recovery of basilar artery caliber was observed for up to 2 hours after injection. In contrast, infusion of up to 3,000 pmol endothelin into the vertebral artery had no appreciable effect on basilar artery caliber. Similar results were obtained in dogs; vasoconstriction was maintained for as long as 12 hours. Our observations suggest that endothelin acts in cerebral vessels from the adventitial side, not from the luminal side, possibly due to the presence of the blood-arterial wall barrier. The long-lasting nature of endothelin-induced constriction of the cerebral arteries in vivo suggests that the peptide might be involved in the pathogenesis of cerebral vasospasm.

Effects of calcitonin gene-related peptide on canine cerebral artery strips and the in-vivo vertebral blood flow in dogs

The effects of calcitonin gene-related peptide (CGRP) on canine cerebral arteries and on vertebral blood flow were investigated in-vivo and in-vitro and the findings compared with the effects of vasoactive intestinal peptide (VIP) and substance P. Administration of CGRP into the vertebral artery caused a dose-dependent and long-lasting increase in blood flow. The in-vivo vasodilatory effects of substance P and VIP were short-lasting. CGRP (0.1 to 100 nmol/l) elicited a concentration-dependent relaxation of the isolated middle cerebral and basilar arteries when the tissues were precontracted by exposure to prostaglandin F2 alpha (PGF2 alpha). This effect was not antagonized by propranolol, atropine, tetrodotoxin, (N-Ac-Tyr1, D-Phe2)-growth hormone-releasing factor(1-29)-NH2 or (D-Pro2, D-Trp7,9) substance P. CGRP also reduced concentration-dependently the contraction of cerebral arteries induced by KCl or 9,11-epithio-11,12-metano-thromboxane A2 (STXA2). Mechanical removal of the endothelium did not abolish the vasodilatory response to CGRP. In PGF2 alpha-contracted canine cerebral arteries, VIP (0.1 to 100 nmol/l) was less potent a vasodilator than CGRP. At low concentrations (0.01 to 1 nmol/l) substance P elicited a rapid and short-lasting relaxation, and in the absence of endothelium this relaxation disappeared. These findings are clear evidence that CGRP modulates vascular tone.

Superoxide anion is an endothelium-derived contracting factor

The calcium ionophore A23187 causes endothelium-dependent contractions in canine basilar arteries. Removal of the endothelium, or treatment with indomethacin or superoxide dismutase (SOD), prevented the endothelium-dependent excitatory effect of the calcium ionophore. Catalase and deferoxamine were without effect. Superoxide anion generated by xanthine plus xanthine oxidase in the presence of catalase caused contractions of the vascular smooth muscle, which were abolished by SOD or heat inactivation of xanthine oxidase. The A23187-induced production of prostaglandins F2 alpha and E2 and thromboxane B2 was abolished by the removal of endothelium and by treatment with indomethacin but was not affected by the presence of SOD plus catalase. These observations are consistent with the hypothesis that superoxide anion, rather than prostaglandins generated by hydroperoxidase activity of cyclooxygenase, is an endothelium-derived contracting factor in canine cerebral arteries.

Differential Vasorelaxant Effects of Milrinone and Amrinone on Contractile Responses of Canine Coronary, Cerebral, and Renal Arteries

The vasorelaxant effects of milrinone and amrinone in canine coronary, cerebral, and renal arterial rings or strips contracted by either K+-depolarization, U46619 (a thromboxane mimetic), or prostaglandin F2 alpha (PGF 2 alpha) were quantitated. Milrinone was more potent as a vasorelaxant in coronary arteries relative to cerebral or renal arteries regardless of the mode of contraction; amrinone was coronary selective with K+ contraction only. When comparing potency in arteries contracted by different agonists, milrinone was significantly more potent as a vasorelaxant in all three arteries contracted by either U46619 or PGF2 alpha than in arteries contracted by K+ depolarization, whereas amrinone was only selective for U46619-induced contractions in cerebral arteries. This profile of activity for milrinone was similar to that of sodium nitrite and isoproterenol and dissimilar from the calcium entry blocking agents nimodipine and nifedipine. In conclusion, this study shows that coronary vascular selectivity exists for milrinone and amrinone. Moreover, the relaxant profiles of milrinone and amrinone, with different sources of vascular smooth muscle, are unlike those of calcium entry blocking agents and more similar to the profiles of agents that modulate cyclic nucleotide levels.