Guinea-pig Artery Research Articles

Synthesis and pharmacological evaluation of pyrroloazepine derivatives as potent antihypertensive agents with antiplatelet aggregation activity.

A series of 1-aminoalkyl-pyrrolo[2,3-c]azepin-8-one derivatives was synthesized and evaluated as alpha 1 adrenergic and serotonin 2 (5-HT2) receptor antagonists, with the aim of finding a novel antihypertensive agent potently exhibiting both activities. Some compounds with a 4-[4-(4-fluorobenzoyl)piperidino]butyl group at the 1-position exhibited both activities, and varied significantly in terms of the substituents at the 4-position of the pyrroloazepine ring. Among the compounds obtained in this study, (E)-1-[4-[4-(4-fluorobenzoyl)piperidino]-butyl]-4-hydroxyimino-7- methyl-1,4,5,6,7,8-hexahydropyrrolo[2,3-c]azepin-8-one (15a, SUN9221) displayed potent alpha 1-adrenergic antagonistic activity (pA2 = 8.89 +/- 0.21) and 5-HT2 antagonistic activity (pA2 = 8.74 +/- 0.22) in isolated guinea pig arteries. This compound exhibited antihypertensive activity and a duration of action equivalent to orally administered prazosin or doxazosin, 3 mg/kg, in conscious spontaneously hypertensive rats, as well as potent antiplatelet aggregation activity.

Endothelium-dependent hyperpolarization in resting and depolarized mammary and coronary arteries of guinea-pigs.

1. The membrane potential responses in guinea-pig coronary and mammary arteries attributable to endothelium-derived nitric oxide (NO), prostaglandin (PG) and hyperpolarizing factor (EDHF), and to exogenous NO and the prostacyclin analogue, iloprost, were compared at rest and when depolarized with the thromboxane analogue, U46619. 2. In the coronary artery, stimulation of the endothelium with acetylcholine (ACh) evoked hyperpolarization attributable to NO and a PG with similar pD2s at rest and in the presence of U46619. However, in depolarized tissues, the pD2 of the response attributed to EDHF required a 10 fold lower concentration of ACh compared with at rest. 3. In the mammary artery, lower concentrations of ACh were required to evoke NO- and EDHF-dependent hyperpolarizations in depolarized mammary artery compared with at rest, while PG-dependent hyperpolarization did not occur until the concentration of ACh was increased some 10 fold both at rest and in U46619. 4. The smooth muscle of the coronary artery of guinea-pigs was some 4 fold more sensitive to exogenous NO and iloprost than was the mammary artery. 5. In conclusion, the membrane potential response in arteries at rest, that is, in the absence of constrictor, may be extrapolated to events in the presence of constrictor when NO and PG are under study. However, the sensitivity to ACh and the magnitude of the hyperpolarization attributed to EDHF obtained in tissues at rest may underestimate these parameters in depolarized tissues.

A New Thromboxane Receptor Antagonist, Z-335, Ameliorates Experimental Thrombosis without Prolonging the Rat Tail Bleeding Time

We investigated the antithrombotic activity of Z-335, a new thromboxane A 2 receptor antagonist, using experimental thrombosis models, and also tested its effect on the rat tail bleeding time. Z-335 (0.1, 0.3, and 1 mg/kg, p.o.) dose-dependently prevented the occurrence of arachidonic acid-induced pulmonary thromboembolism in mice. During photochemically induced thrombosis in the femoral artery of guinea pigs, Z-335 (0.3, 1, and 3 mg/kg, i.v.) dose-dependently prolonged the time required to form thrombi. Moreover, Z-335 (10 mg/kg/day, p.o.) strongly suppressed lauric acid-induced hind limb injury in rats. Z-335 (0.3, 3, 30, and 300 mg/kg, p.o.) did not prolong the tail bleeding time in rats. These results strongly suggest that Z-335 ameliorates experimental thrombosis without prolonging the rat tail bleeding time, and may therefore be a useful antithrombotic drug.

Pregnancy-Induced Decrease in Evoked Excitatory Junction Potentials in Guinea Pig Uterine Artery

The effects of stimulating the intramural nerves on the membrane potential and tension in the uterine artery of virgin guinea pigs were compared with the responses during pregnancy. In all tissues the amplitude of the excitatory junction potential (EJP) increased as the stimulus voltage was increased. The rate of increase in EJP amplitude in tissues from virgin animals greatly exceeded that recorded in late pregnant tissues. EJPs were abolished by tetrodotoxin but were resistant to blockade by α-adrenoceptor antagonists. Stimulation of the nerves also evoked a slow depolarization and contraction which were abolished by both tetrodotoxin and α-adrenoceptor antagonists. The amplitudes of the depolarizations and contractions were not correlated. The role of EJPs and α-adrenoceptor activation in the control of vascular function is discussed. Fluorescence histochemistry revealed a decrease in the density of the catecholamine innervation that was correlated with a decrease in catecholamine content as pregnancy progressed. In addition, there appeared to be a difference in the arrangement of the fluorescent varicosities, with a shift from varicosities that were close to the outer layer of smooth muscle in virgin tissues to those that were more distantly dispersed in the adventitia during late pregnancy. The changes would be expected to reduce the effectiveness of vasoconstrictor drive to the uterine artery as pregnancy progresses.

Inhibitory action of insulin-sensitizing agents on calcium channels in smooth muscle cells from resistance arteries of guinea-pig.

1. The actions of troglitazone, pioglitazone, metformin and bezafibrate, agents that improve insulin-resistance, on voltage-dependent Ca2+ channels in arterial smooth muscle cells were examined by use of the conventional and nystatin-perforated whole-cell clamp methods. Single cells were freshly isolated from resistance mesenteric arteries of guinea-pigs. The actions of these agents on 77 mM K+-induced contraction of the isolated arteries were also examined with the use of isometric tension recording. 2. The thiazolidinedione derivatives, troglitazone and pioglitazone, inhibited whole-cell Ca2+ currents in a dose-dependent manner with dissociation constants of 3.0 microM and 44.9 microM and Hill coefficients of 0.61 and 0.68, respectively. These two agents inhibited the 77 mM K+-induced contraction with similar potencies as those inhibiting the Ca2+ currents. Metformin and bezafibrate had no apparent effects on the Ca2+ current or high K+-induced contraction. 3. The inhibitory action of troglitazone on Ca2+ currents was not affected by the command potential, the holding potential, or the stimulation frequency, suggesting that its mode of the action differs from that of known organic Ca2+ channel antagonists. 4. The inhibitory action of troglitazone on Ca2+ currents was not affected by the addition of insulin to, or the removal of glucose from, the solutions. 5. In conclusion, the thiazolidinedione derivatives directly inhibited the voltage-dependent Ca2+ channels in a different manner from that of organic Ca2+ channel antagonists. This inhibitory action on Ca2+ channels was not a common feature of insulin-sensitizing agents.

Nitric oxide is a sensory nerve neurotransmitter in the mesenteric artery of guinea pig

Previous studies have shown that the guinea pig inferior mesenteric artery receives spinal sensory vasodilatory innervation, which can be activated by colon distention and electrical nerve stimulation. In the present study, we investigated the hypotheses that nitric oxide synthase (NOS) is present in guinea pig primary sensory neurons in the dorsal root ganglion (DRG) and in nerve fibers surrounding the mesenteric arteries, and that nitric oxide (NO) is a sensory neurotransmitter in the inferior mesenteric artery in vitro. Double-labeling immunohistochemistry showed that neuronal NOS-IR was found in 12% of cells of guinea pig thoracic and lumbar DRGs; in 95.1% of these cells it was colocalized with substance P (SP), and SP immunoreactivity (SP-IR) was present in 23% of cells of the same DRGs. Neuronal NOS-like immunoreactivity was localized in nerve fibers surrounding guinea pig mesenteric artery and 25% of them were double stained with SP-IR. Endothelium-denuded inferior mesenteric artery preparations in vitro were incubated with guanethidine (30 μM, 30 min) and pre-contracted with methoxamine (30 μM). The NO donors, sodium nitroprusside (1 μM) and l-nitrosocysteine (300 μM), produced 91.0±5.5 and 90.4±9.6% vasodilatation of total vasodilatation in the vessel segments, respectively, which was capsaicin- or tetrodotoxin-insensitive. Repetitive electrical field stimulation of the preparations produced a frequency-dependent vasodilatation which was reduced by pretreatment with capsaicin or by tetrodotoxin (10 μM). The NOS inhibitor N ω -nitro- l-arginine ( l-NNA) (100 μM, 30 min) diminished the nerve-evoked vasodilatation from 41.8±8.4 to 21.4±9.7% at 2 Hz and from 50.8±5.6 to 19.0±7.3% at 15 Hz ( P<0.05), whereas N G-nitro- l-arginine methyl ester ( l-NAME, 100 μM−1 mM) did not significantly inhibit the relaxation. The stereo isomer nitro- d-arginine ( d-NNA, 100 μM, 30 min) was ineffective. These findings suggest that NO is a neurotransmitter released from primary sensory nerves which mediates vasodilatation in vitro.

Confocal imaging analysis of ATP-induced Ca2+ response in individual endothelial cells of the artery in situ.

The mechanisms for mobilization of intracellular free Ca2+ have been studied in various types of isolated and cultured cells, but little is known about Ca2+ mobilization in individual cells in situ. We tried to establish imaging analysis of intracellular free Ca2+ concentration ([Ca2+]i) in individual cells loaded with the acetoxymethyl ester of fluo 3 in situ, using laser scanning confocal microscopy. The method permitted us to distinguish signals from endothelial and smooth muscle cells of guinea pig artery. Addition of ATP to the artery caused a transient increase in endothelial [Ca2+]i. It was concluded that the response was induced via P2Y purinoceptors, because adenosine 5'-O-(2-thiodiphosphate), but not UTP, caused a similar response independent of extracellular Ca2+. The percentage of cells that responded to ATP (1-10 microM) and the peak amplitude of the transient increase in [Ca2+]i were dose dependently increased. Using rapid xy-scanning and line-scanning modes, we confirmed that 10 microM ATP induced Ca2+ waves, at a rate of 10-30 microns/s, after a lag time of approximately 3 s. These results show that [Ca2+]i waves within endothelial cells are physiologically induced by ATP via P2Y purinoceptor, but not P2U purinoceptor, in aortic strips in situ. The method should be of use in the study of vascular physiology and pathophysiology.

Antithrombotic effects of KBT-3022, a novel antiplatelet agent, in an arterial thrombosis model in the guinea-pig

We examined the antithrombotic effect of KBT-3022, a novel antiplatelet agent, on photochemically induced arterial thrombosis in the guinea-pig saphenous artery, and compared its effect with that of aspirin and that of ticlopidine. Pretreatment with KBT-3022 [0.1 mg (0.2 μmole), 0.3 mg (0.7 μmole), 1 mg (2.2 μmole) and 3 mg (6.7 μmole)/kg, p.o.] 3 h prior to thrombosis induction prolonged the time required to achieve the thrombotic occlusion and inhibited the collagen (low concentration, 0.2 μg/ml; high concentration, 1 μg/ml)-induced platelet aggregation in whole blood ex vivo, each effect being concentration-dependent. The effects were tested of ticlopidine [30 mg (99.9 μmole), 100 mg (333.1 μmole) and 300 mg (999.2 μmole)/kg, p.o.] and aspirin [10 mg (55.5 μmole), 30 mg (166.5 μmole) and 100 mg (555.1 μmole)/kg, p.o.]. Both drugs prolonged the time to occlusion (but only at their highest concentration), and also inhibited the collagen (low concentration)- induced platelet aggregation in whole blood ex vivo. Aspirin [100 mg (555.1 μmole)/kg, p.o.], but not ticlopidine (at any concentration), inhibited the collagen (high concentration)-induced platelet aggregation. A good correlation was found between the antithrombotic and antiplatelet-aggregating effects of both KBT-3022 and aspirin, but not of ticlopidine. The antithrombotic potency of KBT-3022 was 300 times that of aspirin and 1000 times that of ticlopidine. These observations suggest that KBT-3022 may be clinically effective against platelet-rich thrombosis. Drug Dev. Res. 40:217–222, 1997. © 1997 Wiley-Liss, Inc.

モルモット膝神経節の微細構造 虚血モデルにおける形態変化

Bell's palsy is the most common type of peripheral facial nerve palsy and it is often preceded by dysgeusia. The facial palsy is induced by damage throughout peripheral facial nerve fibers. However, reduced gustation in the early stages of Bell's palsy could result from damage of the geniculate ganglion cells as well as the peripheral nerve fibers. In order to clarify the pathogenesis of dysgeusia observed in cases of Bell's palsy, ultrastructural changes in the geniculate ganglion cells were observed in three ischemic facial palsy models. Ischemia was induced in guinea pigs by; 1) permanent interruption of the petrosal branch of the middle meningeal artery, 2) freezing of the upper tympanic part of the facial nerve canal using dimethylether liquid propane gas, without exposure of the facial nerve bundle, 3) temporary ligature of the carotid arteries after permanent interruption of both the vertebral arteries and petrosal branch of the middle meningeal artery of guinea pigs. Severe peripheral facial palsy was seen in all of the three ischemic models by 7 days after surgery. However, ultrastructural changes were observed in several light cells of the geniculate ganglion only in the model using freezing. Cytoplasmic changes included the degeneration of ganglion cell nuclei and the accumulation of myeloid bodies in nerve fibers. The findings suggest that the dysgeusia observed in cases of Bell's palsy could be mainly induced by complete ischemia of local facial nerve canal.

Mechanism of action of nitric oxide donors on voltage-activated calcium channels in vascular smooth muscle cells

The effects of nitric oxide (NO) donors on inward barium current (IBa) in freshly isolated smooth muscle cells (SMC) of the guinea pig mesenteric artery and on inward calcium current (ICa) in SMC of the canine coronary artery were studied using a patch-clamp recording technique in whole-cell configuration. The inward current in SMC of the guinea pig artery was shown to flow through a single type of calcium channels, which have characteristics of high-threshold slowly inactivated channels of L-type. Nitroglycerin (NG) and sodium nitroprusside (NP) reversibly inhibitedIBa in a dose-dependent manner. Effects of NO donors onIBa were related to the changes in voltage-dependent properties of calcium channels. In particular, NG and NP accelerated the current inactivation, and their blocking effects increased with the membrane depolarization. Methylene blue, the guanylate cyclase inhibitor, decreased the inhibitory action of NG onIBa by a factor of 5. 8-Bromo-cGMP, the membrane-permeant cGMP analog, evokedIBa inhibition similar to that caused by NO donors. In the canine coronary artery, NO donors also inhibitedICa flowing through the L-type calcium channels. It has been concluded that NO originating from NG and NP inhibits activity of L-type calcium channels in vascular SMC; it is possible that cGMP-dependent processes are involved.

Chronic hypoxia does not alter the effects of pregnancy on contractile sensitivity to phenylephrine in isolated guinea pig arteries.

Chronic hypoxia does not alter the effects of pregnancy on contractile sensitivity to phenylephrine in isolated guinea pig arteries.

COCHLEAR ISCHEMIA AND CHANGES IN COMPOUND ACTION POTENTIALS IN THE GUINEA PIG

To determine the degree of decrease in cochlear blood flow (CoBF) which causes compound action potentials (CAPs) to disappear, a cochlear ischemic model was created by compressing the internal auditory artery in guinea pig. CoBF was measured with a laser Doppler flowmeter, and CAPs were recorded with an electrode placed on the round window membrane. The amplitude and latency of the N1 wave of CAPs changed as CoBF decreased. When CoBF diminished to as much as 70% below the original level, N1 disappeared. In this study, we also observed the N1 recovery process following CoBF reperfusion after 20 minutes of cochlear ischemia. N1 recovery in the group with an incomplete decrease in CoBF was better than in the group with a complete decrease in CoBF. These findings suggest that both the degree of compromise of CoBF and the duration of ischemia are important factors affecting the recovery of auditory function.

Endothelium-dependent hyperpolarization. Beyond nitric oxide and cyclic GMP.

Blood flow and blood pressure are determined by an integration of reflex, humoral, and local vascular control mechanisms. Knowledge of these mechanisms has mushroomed over the past 15 years, particularly in the area of local endothelium-dependent vasomotor control. This has stemmed from the pioneering report in 1980 by Robert Furchgott1 demonstrating that the endothelium releases a vasodilator substance in response to acetylcholine. This concept has been expanded with knowledge that the endothelium releases a variety of relaxing and contracting factors that regulate the underlying smooth muscle.2 The most widely known endothelium-derived relaxing factor, nitric oxide, is released from endothelial cells in response to shear stress or stimulation of different receptors for a variety of neurohumoral mediators on the endothelial cell surface.3 The increase in endothelial cell calcium initiated by these stimuli increases the activity of a constitutively expressed enzyme, nitric oxide synthase, which converts l-arginine to nitric oxide and citrulline.4 5 6 7 Nitric oxide thus formed diffuses to and inhibits contraction of the underlying vascular smooth muscle.3 The physiological significance of the production of endothelial nitric oxide is suggested by the vasoconstriction observed in most vascular beds8 9 10 11 12 13 and the increase in systemic arterial blood pressure,14 15 16 which occurs on infusion of inhibitors of nitric oxide synthase. This observation further implies that under normal conditions, endothelial cells are locally liberating nitric oxide which effectively inhibits vasoconstriction arising by other mechanisms. Thus, normal vascular homeostasis depends in the periphery on a balance between neurally and humorally mediated vasoconstriction in skeletal muscle, mesentery, and the kidney, and local endothelium-dependent vasodilatation. In the truly vital areas of the heart, brain, and genitalia, vasodilator neural mechanisms reinforce the vasodilator influence of the endothelium.17 All is not known regarding the …

Physiological dilation of uteroplacental arteries in the guinea pig depends on nitric oxide synthase activity of extravillous trophoblast

Physiological dilation of uteroplacental arteries in the guinea pig depends on nitric oxide synthase activity of extravillous trophoblast

β-Adrenoceptor stimulation activates large-conductance Ca2+-activated K+ channels in smooth muscle cells from basilar artery of guinea pig

We studied the effect of isoproterenol on the Ca2+-activated K+ (BK) channel in smooth muscle cells isolated from the basilar artery of the guinea pig. Cells were studied in a whole-cell configuration to allow the clamping of intracellular Ca2+ concentration, [Ca2+]i. Macroscopic BK channel currents were recorded during depolarizing test pulses from a holding potential (VH) of 0 mV, which was used to inactivate the outward rectifier. The outward macroscopic current available from a VH of 0 mV was highly sensitive to block by external tetraethylammonium Cl (TEA) and charybdotoxin, and was greatly augmented by increasing [Ca2+]i from 0.01 to 1.0 microM. With [Ca2+]i between 0.1 and 1.0 microM, 0.4 microM isoproterenol increased this current by 58.6 +/- 17.1%, whereas with [Ca2+]i at 0.01 microM a sixfold smaller increase was observed. With [Ca2+]i > or = 0.1 microM, 100 microM dibutyryl -adenosine 3':5: cyclic monophosphate (cAMP) and 1 microM forskolin increased this current by 58.5 +/- 24.1% and 59.7 +/- 10.3%, respectively. The increase with isoproterenol was blocked by 4.0 microM propranolol extracellularly, and by 10 U/ml protein kinase inhibitor intracellularly. Single-channel openings during depolarizing test pulses from a VH of 0 mV recorded in the whole-cell configuration under the same conditions (outside-out-whole-cell recording) indicated a slope conductance of 260 pS. In conventional outside-out patches, this 260-pS channel was highly sensitive to block by external TEA, and in inside-out patches, its probability of opening was greatly augmented by increasing [Ca2+]i from 0.01 to 1.0 microM. Outside-out-whole-cell recordings with [Ca2+]i > or = 0.1 microM indicated that 100 microM dibutyryl-cAMP increased the probability of opening of the 260-pS channel by 152 +/- 115%. In inside-out patches, the catalytic subunit of protein kinase A increased the probability of opening, and this effect also depended on [Ca2+]i , with a 35-fold larger effect observed with 0.1-0.5 microM Ca2+ compared to 0.01 microM Ca2+. We conclude that the BK channel in cerebrovascular smooth muscle cells can be activated by beta-adrenoceptor stimulation, that the effect depends strongly on [Ca2+]i, and that the effect is mediated by cAMP-dependent protein kinase A with no important contribution from a direct G-protein or phosphorylation-independent mechanism. Our data indicate that the BK channel may participate in beta-adrenoceptor-mediated relaxation of cerebral vessels, although the importance of this pathway in obtaining vasorelaxation remains to be determined.

5-HT1-like and 5-HT2A receptors mediate 5-hydroxytryptamine-induced contraction of rabbit isolated mesenteric artery.

The contractions induced by 5-hydroxytryptamine (5-HT) and the 5-HT1-like receptor agonist, sumatriptan, were investigated in the open ring preparations of rabbit mesenteric artery in order to characterize the 5-HT receptors. 5-HT induced concentration-dependent contractions. Sumatriptan did not induce any contraction of unstimulated rings, whereas it elicited concentration-dependent contractions in preparations given a moderate tone by a threshold concentration of prostaglandin F2 alpha (PGF2 alpha). Pargyline, cocaine or normetanephrine were without significant effect on the contractions induced by 5-HT and sumatripan. The 5-HT concentration-effect curve was clearly biphasic. Methiothepin (0.01 microM) shifted the both phases of the concentration-effect curve to the right. Ketanserin (0.1 microM) shifted the second, low affinity, phase and prazosin did not alter concentration-effect curve to 5-HT. The sumatriptan concentration-effect curve was shifted by methiothepin (0.01 microM) to the right (pKB = 9.19) but not by ketanserin (1 microM). Concentration-effect curves to 5-HT and sumatriptan were not affected by the 5-HT3 receptor antagonist tropisetron (1 microM). These results suggest that 5-HT1-like type receptors are responsible for the first phase of 5-HT-induced contraction and 5-HT2A receptor for the second phase, in rabbit mesenteric artery. Sumatriptan-induced contractions appear to be mediated by 5-HT1-like type receptors in this artery. These results also suggest that this kind of amplification may be a common feature of vascular 5-HT1-like type receptor as has been shown in other vascular segments such as rabbit femoral, iliac and renal arteries, and guinea-pig iliac artery.

Role of nitric oxide and neuropeptides in neurogenic vasodilatation of the guinea pig mesenteric artery

Although dense networks of adrenergic nerves are present and noradrenaline causes vasoconstriction, electrical field stimulation failed to elicit any constriction of the isolated ring preparation of the guinea pig mesenteric artery. In the presence of an active tone, a vasodilator response was elicited by electrical field stimulation in endothelium-removed tissues. Nonadrenergic, noncholinergic nerves mediate the electrical field stimulation-induced vasodilator response, since guanethidine and atropine did not affect while tetrodotoxin abolished it. Multiple mediators seem to participate in this vasodilatation. NADPH-diaphorase-positive nerves, calcitonin gene-related peptide (CGRP)- and vasoactive intestinal peptide (VIP)-immunoreactive nerves were present in the mesenteric artery. Nitro- l-arginine but not nitro- d-arginine suppressed the electrical field stimulation-induced vasodilator response with rapid onset and l-arginine restored it. VIP and CGRP relaxed the tissue in a dose-dependent manner. Pretreatment of the animals with capsaicin partly reduced the electrical field stimulation-induced vasodilator response. CGRP-(8-37), a CGRP antagonist, slightly attenuated the vasodilator response induced by both electrical field stimulation and CGRP. Glibenclamide, an inhibitor of ATP-sensitive K + channels, decreased the nitro- l-arginine- and capsaicin-insensitive component of the electrical field stimulation-induced vasodilator response. Zinc protoporphyrin IX, an inhibitor of CO formation, did not affect the electrical field stimulation-induced response. In the presence of nitro- l-arginine without an active tone, electrical field stimulation induced a vasoconstrictor response that was sensitive to bunazosin and guanethidine. The results show that the electrical field stimulation-induced vasodilator response of the mesenteric artery of guinea pigs is mediated by nitric oxide (NO), CGRP and some yet unidentified substance(s). Elimination of the vasodilator response unmasked the adrenergic vasoconstrictor response to electrical field stimulation.

Role of membrane potential in endothelium-dependent relaxation of guinea-pig coronary arterial smooth muscle.

1. Membrane potential and tension were measured simultaneously in ring segments of main coronary artery of guinea-pigs. The synthetic thromboxane A2 analogue U46619 depolarized the tissues from -58 +/- 2 to -40 +/- 1 mV and increased tension by 12 +/- 1 mN mm-1. Nitric oxide (NO) and Iloprost, the stable analogue of prostacyclin, evoked hyperpolarization and relaxation. 2. The concentration of NO required to evoke half-maximal hyperpolarization (EC50 of 2 x 10(-5) M) was 40-fold higher than that which was required to induce relaxation (EC50 of 5 x 10(-7) M). The EC50 for Iloprost-induced hyperpolarization (3 x 10(-8) M) was similar to that for relaxation (4 x 10(-8) M). 3. Glibenclamide (10(-6) M) abolished the hyperpolarization in response to both NO and Iloprost but was without effect on the amplitudes of the relaxations over the complete concentration-response curves. 4. Acetylcholine evoked concentration-dependent hyperpolarization and relaxation in the presence of N omega-nitro-L-arginine methyl ester (NAME; 10(-5) M) and indomethacin (10(-6) M), and these responses were attributed to endothelium-derived hyperpolarizing factor (EDHF). The hyperpolarization produced by EDHF always preceded relaxation, and relaxation never occurred at concentrations of acetylcholine that were insufficient to evoke hyperpolarization. 5. The concentration-hyperpolarization and concentration-relaxation curves in response to acetylcholine were not affected by glibenclamide or barium (1-3 mM) but were shifted to the right 4- and 5-fold, respectively, by 1 mM tetraethylammonium. The hyperpolarization and relaxation evoked by acetylcholine were also reduced in a parallel manner when the potassium concentration in the superfusate was increased. 6. Hyperpolarizing current steps, applied to spiral strips of coronary artery denuded of endothelium and depolarized and constricted with U46619, caused relaxation. The relationship between hyperpolarization and relaxation evoked electronically was similar to that which was due to EDHF in intact tissues stimulated with acetylcholine. 7. It is concluded that the ability of NO or Iloprost to relax guinea-pig coronary artery does not depend upon hyperpolarization of the smooth muscle. In contrast, hyperpolarization is likely to play a major, if not the only, role in the relaxation in response to EDHF in this tissue.

Adenosine receptors mediate both contractile and relaxant effects of adenosine in main pulmonary artery of guinea pigs

In guinea pig main pulmonary artery precontracted with noradrenaline, adenosine exerted an initial phasic contraction followed by a tonic contraction and a slow relaxation. After selective blockade by 1,3-dipropyl-8-cyclopentylxanthine (DPCPX: 10 nM) of A1 receptors, adenosine only elicited a rapid relaxation. This initial response was characterized by use of adenosine (AR) and its analogues N6-cyclopentyl-adenosine (CPA), R-N6-phenylisopropyladenosine (R-PIA), 2-chloroadenosine (CADO), 5'-N-ethyl-carboxamidoadenosine(NECA), N6-2-(4-aminophenyl) ethyl adenosine (APNEA) and 2-p-((carboxyethyl)-phenethylamino)-5'-carboxamidoadenosine (CGS 21 680). The order of potency of the adenosine analogues for purine-induced phasic contraction was CPA > R-PIA > NECA = APNEA > AR > CGS 21 680 suggesting the involvement of activation of A1 type adenosine receptors in the contraction phase. DPCPX antagonized the CPA-induced contraction with a pA2 = 9.27 +/- 0.26, but the Schild plot slope parameter was significantly lower than unity (0.58 +/- 0.09). In contrast, in electrically driven guinea pig atrial myocardium (a tissue reported to possess A1 receptors), the DPCPX-CPA antagonism was purely competitive (pA2 = 8.95 +/- 0.06; slope = 0.93 +/- 0.06). In the presence of 300 nM DPCPX, the rank order of potency for the purine-induced fast relaxation was NECA > CADO = AR > CGS 21 680 = R-PIA > CPA. The NECA- and adenosine-induced relaxation was influenced neither by 300 nM CP 66713 (an antagonist at A2a receptors), nor by endothelial removal and inhibition of nitric oxide synthase (100 microM NG-nitro-L-arginine: L-NOARG).(ABSTRACT TRUNCATED AT 250 WORDS)

P2-49 - Inhibitory action of betaxolol, β1,-selective adrenoceptor antagonist, on voltage-dependent calcium channels in guinea pig artery and vein

P2-49 - Inhibitory action of betaxolol, β1,-selective adrenoceptor antagonist, on voltage-dependent calcium channels in guinea pig artery and vein