Effects of centrally administered prostaglandin E(3) and thromboxane A(3) on plasma noradrenaline and adrenaline in rats: comparison with prostaglandin E(2) and thromboxane A(2).

Previously, we reported the involvement of brain omega-6 prostanoids, especially prostaglandin E(2) and thromboxane A(2), in the activation of central sympatho-adrenomedullary outflow in rats. omega-3 Prostanoids, including prostaglandin E(3) and thromboxane A(3), are believed to be less bioactive than omega-6 prostanoids, although studies on the functions of omega-3 prostanoids in the central nervous system have not been reported. In the present study, therefore, we compared the effects of centrally administered omega-3 prostanoids, prostaglandin E(3) and thromboxane A(3), with those of omega-6 prostanoids, prostaglandin E(2) and thromboxane A(2), on the plasma catecholamines in anesthetized rats. Intracerebroventricularly (i.c.v.) administered prostaglandin E(2) (0.15, 0.3 and 1.5 nmol/animal) and prostaglandin E(3) (0.3 and 3 nmol/animal) predominantly elevated plasma noradrenaline but not adrenaline, but the latter was less efficient than the former. On the other hand, U-46619 (an analog of thromboxane A(2)) (30, 100 and 300 nmol/animal, i.c.v.) and Delta(17)-U-46619 (an analog of thromboxane A(3)) (100 and 300 nmol/animal, i.c.v.) both elevated plasma catecholamines (adrenaline>>noradrenaline) to the same degree. These results suggest that centrally administered prostaglandin E(3) is less effective than prostaglandin E(2) to elevate plasma noradrenaline, and that thromboxane A(3) is almost as equipotent as thromboxane A(2) to elevate plasma catecholamines in rats.

An animal model of intrauterine growth retardation induced by synthetic thromboxane a(2).

OBJECTIVE: Intrauterine growth retardation (IUGR) is an important cause of prenatal and neonatal morbidity, and neurologic abnormalities. Although several animal models of IUGR have been developed for scientific investigation, few models approximate the pathophysiology in human fetal growth failure resulting from pregnancy-induced hypertension and preeclampsia. We developed an animal model of IUGR in which fetal growth restriction was induced by administering a synthetic thromboxane A(2) analogue (STA(2)) to the mother. METHODS: Timed pregnant Sprague-Dawley rats were used in this study. STA(2) was delivered into the peritoneal cavity of the pregnant female at a rate of 20 ng/h from day 13 of pregnancy. The effectiveness of this model was evaluated by monitoring the overall growth of the fetuses and neonates and measuring the weight and biochemical composition of individual organs. RESULTS: Fetuses and neonates from the STA(2) group showed a highly significant weight reduction throughout the observation period from day 19 of gestation to postnatal day 7. Weight reduction near and at term exceeded 10% and became more pronounced during the first week after birth. Fetuses on the 20th gestational day exhibited a pattern of growth retardation characteristic of asymmetrical IUGR in which the weight reduction was prominent in the liver with relative sparing of the brain. However, the decrease in brain weight was more than 10%. The protein, DNA, and RNA contents of the liver were lower in the STA(2) group. The protein content of the forebrain and brainstem also decreased significantly in the STA(2) group compared with the control; however, the DNA content of the forebrain was higher in the STA(2) group. CONCLUSIONS: This animal model may mimic human IUGR more closely than previous models because the growth restriction is induced in a truly chronic manner.

Thromboxane A2-induced arrhythmias in the anesthetized rabbit.

Experiments were conducted in the anesthetized rabbit to investigate mechanisms for arrhythmias that occur after left atrial injection of the thromboxane A(2) (TxA(2)) mimetic U-46619. Arrhythmias were primarily of ventricular origin, dose dependent in frequency, and TxA(2) receptor mediated. The response was receptor specific since arrhythmias were absent after pretreatment with a specific TxA(2) receptor antagonist (SQ-29548) and did not occur in response to another prostaglandin, PGF(2alpha). Alterations in coronary blood flow were unlikely the cause of these arrhythmias because coronary blood flow (as measured with fluorescent microspheres) was unchanged after U-46619, and there were no observable changes in the ECG-ST segment. In addition, arrhythmias did not occur after administration of another vasoconstrictor (phenylephrine). The potential involvement of autonomic cardiac efferent nerves in these arrhythmias was also investigated because TxA(2) has been shown to stimulate peripheral nerves. Pretreatment of animals with the beta-adrenergic receptor antagonist propranolol did not reduce the frequency of these arrhythmias. Pretreatment with atropine or bilateral vagotomy resulted in an increased frequency of arrhythmias, suggesting that parasympathetic nerves may actually inhibit the arrhythmogenic activity of TxA(2). These experiments demonstrate that left atrial injection of U-46619 elicits arrhythmias via a mechanism independent of a significant reduction in coronary blood flow or activation of the autonomic nervous system. It is possible that TxA(2) may have a direct effect on the electrical activity of the heart in vivo, which provides significant implications for cardiac events where TxA(2) is increased, e.g., after myocardial ischemia or administration of cyclooxygenase-2 inhibitors.

Efectos antitrombóticos y antiinflamatorios de los ácidos grasos omega-3 / Antithrombotic and antiinflammatory effects of omega-3 fatty acids

Los ácidos grasos poliinsaturados de la dieta pueden clasificarse en dos tipos: ácidos grasos omega-3 (n-3) y ácidos grasos omega-6 (n-6). Los ácidos grasos n-3 se metabolizan en el organismo dando lugar a diferentes ácidos grasos n-3, y los de un mayor interés desde el punto de vista cardiovascular son los de cadena larga (PUFA n-3). Tres mecanismos principales parecen estar involucrados en el efecto protector cardiovascular de los ácidos grasos n-3: su efecto antiinflamatorio, su efecto antitrombótico y su acción antiarrítmica. En cuanto a su efecto antitrombótico, hay datos experimentales que indican que la ingesta de ácidos grasos omega-3 tiene un efecto antitrombótico principalmente mediado por una reducción en la formación de tromboxano. Se disponde de datos sobre su efecto antiinflamatorio que demuestran la reducción en la expresión de proteínas de adhesión. Sin embargo, en los estudios de intervención dietética en humanos estos 2 efectos no se repiten de forma consistente en todos los estudios publicados. En esta revisión se analizan los diferentes mecanismos de acción antitrombótica y antiinflamatoria de los ácidos grasos omega-3 (AU)

Dietary polyunsaturated fatty acids can be classified into two main subtypes: omega-3 (n-3) fatty acids and omega-6 (n-6) fatty acids. Omega-3 fatty acids are metabolized in the body into a variety of other omega-3 fatty acids. From the point of view of cardiovascular disease, the most relevant are long-chain omega-3 polyunsaturated fatty acids (omega-3 PUFAs). The cardioprotective effects of omega-3 fatty acids appear to result from three main mechanisms: anti-inflammatory, antithrombotic and anti-arrhythmic mechanisms. With regard to the compounds’ antithrombotic effects, experimental findings indicate that intake of omega-3 fatty acids reduces thromboxane A2 synthesis. The antiinflammatory properties of omega-3 PUFAs seem to be related to their ability to downregulate expression of adhesion proteins. However, these antithrombotic and anti-inflammatory effects have not been consistently observed in dietary modification studies in humans. In this review, we discuss the different mechanisms of action by which omega-3 fatty acids could exert their antithrombotic and anti-inflammatory effects (AU)

Effects of platelet-activating factor and thromboxane A2 on isolated perfused guinea pig liver.

Lipid mediators, thromboxane A2 (TxA2) and platelet-activating factor (PAF), are potent vasoconstrictors, and have been implicated as mediators of liver diseases, such as ischemic-reperfusion injury. We determined the effects of a TxA2 analogue (U-46619) and PAF on the vascular resistance distribution and liver weight (wt) in isolated guinea pig livers perfused with blood via the portal vein. The sinusoidal pressure was measured by the double occlusion pressure (P(do)), and was used to determine the pre- (R(pre)) and post-sinusoidal (R(post)) resistances. U-46619 and PAF concentration-dependently increased the hepatic total vascular resistance (R(t)). The minimum concentration at which significant vasoconstriction occurs was 0.001 microM for PAF and 0.1 microM for U-46619. Moreover, the concentration of U-46619 required to increase R(t) to the same magnitude is 100 times higher than PAF. Thus, the responsiveness to PAF was greater than that to U-46619. Both agents increased predominantly R(pre) over R(post). U-46619 caused a sustained liver weight loss. In contrast, PAF also caused liver weight loss at lower concentrations, but it produced liver weight gain at higher concentrations (2.5 +/- 0.3 per 10g liver weight at 1 microM PAF), which was caused by substantial post-sinusoidal constriction and increased P(do). In conclusion, both TxA2 and PAF contract predominantly the pre-sinusoidal veins. TxA2 causes liver weight loss, while PAF at high concentrations increases liver weight due to substantial post-sinusoidal constriction in isolated guinea pig livers.

Cyclooxygenase-2 participates in the late phase of airway hyperresponsiveness after ozone exposure in guinea pigs.

We examined the role of cyclooxygenase in airway hyperresponsiveness and inflammation after ozone exposure in guinea pigs using a non-selective (indomethacin) and a selective (JTE-522) cyclooxygenase-2 inhibitor. Spontaneously breathing guinea pigs were exposed to ozone (3 ppm) for 2 h after treatment with vehicle, indomethacin (10 mg/kg) or JTE-522 (10 mg/kg). Airway responsiveness to inhaled histamine (PC(200)) and bronchoalveolar lavage were assessed before, immediately and 5 h after ozone exposure. Ozone caused a significant airway hyperresponsiveness immediately after exposure, which persisted after 5 h. Neither JTE-522 nor indomethacin affected airway hyperresponsiveness immediately after ozone exposure, but significantly attenuated airway hyperresponsiveness 5 h after exposure, suggesting that cyclooxygenase-2 may participate in the late phase of airway hyperresponsiveness but not in the early phase. Ozone caused a significant increase in the concentration of prostaglandin E(2) and thromboxane B(2) in bronchoalveolar lavage fluid immediately after exposure, which decreased to the basal level 5 h after exposure. This increase in prostaglandin E(2) and thromboxane B(2) was significantly inhibited by JTE-522. An expression of cyclooxygenase-2 was detected not only after ozone exposure but also before, and there was no difference in the number of cyclooxygenase-2-positive cells at any time point. An exogenously applied thromboxane A(2) mimetic, U-46619 (10(-5) M), induced airway hyperresponsiveness 5 h after inhalation, but not immediately or 3 h after inhalation. These data suggest that cyclooxygenase-2 may be constitutively expressed before ozone exposure in guinea pig airway and may synthesize prostaglandin E(2) and thromboxane A(2) transiently under ozone stimulation and that thromboxane A(2) may, in turn, induce the late phase of airway hyperresponsiveness.

Linear type azo-containing polyurethane as drug-coating material for colon-specific delivery: its properties, degradation behavior, and utilization for drug formulation.

A segmented polyurethane containing azo aromatic groups in the main chain was synthesized by reaction of isophorone diisocyanate with a mixture of m,m'-di(hydroxymethyl)azobenzene, poly(ethylene glycol) (Mn = 2000), and 1,2-propanediol. This polyurethane was soluble in various solvents and showed a good coating and film-forming property. A solution-cast film of this polyurethane was found to be degraded in a culture of intestinal flora with the azo group reduction to hydrazo groups, not to amino groups. The film degradation, therefore, was attributed to the decreased cohesive energy in the hydrazo polymer compared with that in the original azo polymer. Then, the drug pellets containing water-soluble drugs (ONO-3708 and OKY-046) were undercoated with (carboxymethyl)(ethyl)-cellulose and overcoated with the azo polymer in order to examine the drug-releasing profiles in the culture of intestinal flora. The releasing rate of drugs from these double-coating pellets was found to depend on the molecular weight and the composition of the polyurethane used as the overcoat as well as the hydrophilicity of the incorporated drugs. Since the polyurethane was glassy and its segment motion or conformational change is frozen, the structure change should be retarded even after partial reduction of the azo groups, resulting in the effective prevention of the drug leakage. These data suggested that the present azo-containing polyurethanes are applicable as coating material of drug pellets in a colon-targeting delivery system.

Thromboxane mimics the pulmonary but not systemic vascular responses to bolus HCl injections in broiler chickens.

Bolus i.v. injections of 1.2 N HCl elicit a rapid but transient pulmonary vasoconstriction in broiler chickens. In mammals, the pulmonary vasoconstrictive response to bolus acid injection depends on increased synthesis of thromboxane A2; however, the vascular responsiveness of domestic fowl to thromboxane previously had not been evaluated. In the present study, we tested the hypothesis that, if HCl triggers pulmonary vasoconstriction by stimulating thromboxane A2 synthesis in broilers, then bolus i.v. injections of the potent thromboxane A2 mimetic U44069 (9,11-dideoxy-9alpha,11alpha-epoxy-methanoprostaglandin++ + F2alpha; 1 micromol/mL; 0.5 mL injected volume) should trigger hemodynamic responses similar to those elicited by HCl (1.2 N; 1.5 mL injected volume). Both HCl and the thromboxane mimetic elicited twofold or greater increases in pulmonary vascular resistance, which in turn increased pulmonary arterial pressure by 50% despite concurrent reductions in cardiac output. The reductions in cardiac output were associated with reductions in stroke volume but not heart rate. The thromboxane mimetic also increased the total peripheral resistance, which minimized the reduction in mean systemic arterial pressure associated with the decrease in cardiac output. In contrast, HCl injections did not increase total peripheral resistance; consequently, the reduction in cardiac output caused the mean systemic arterial pressure to decrease by 30 mm Hg. Mannitol (2.5%; 1.5 mL) was injected i.v. as a volume control, and had no influence on any of the variables. This study provides the first direct evidence that thromboxane is a potent pulmonary vasoconstrictor in broilers, and provides support for the hypothesis that thromboxane mediates the pulmonary vasoconstrictive response to bolus i.v. injections of HCl. The differential response of the systemic vasculature to the thromboxane mimetic and HCl may indicate that cardiopulmonary responses to HCl injections are not mediated solely via thromboxane production. Alternatively, a direct dilatory effect of elevated hydrogen ion concentrations on the systemic vasculature may have counteracted any tendency for simultaneously evolved endogenous thromboxane to elicit systemic vasoconstriction.

Thromboxane A2 acts on the brain to mediate hemodynamic, adrenocorticotropin, and cortisol responses.

Conditions that increase the formation of thromboxane A2 (TxA2) also result in activation of hemodynamic and adrenocortical responses. The purpose of this study was to test the hypothesis that TxA2 acts directly on the brain to mediate these responses. Adult sheep were chronically instrumented with vascular and intracerebroventricular catheters. The TxA2 analog U-46619 (0, 100, or 1,000 ng.kg-1.min-1) and artificial cerebrospinal fluid (CSF) were infused intracerebroventricularly for 30 min. Heart rate increased in response to 100 ng.kg-1.min-1 U-46619 infusions. Heart rate did not change over preinfusion values in response to the highest infusion rate, but values were elevated compared with the postinfusion period. Mean arterial pressure, ACTH, cortisol, hematocrit, and arterial pH (pHa) increased, and arterial partial CO2 pressure (PaCO2) fell in response to 1,000 ng.kg-1.min-1 infusions of U-46619. Plasma vasopressin concentrations and arterial partial O2 pressure did not change. In a second study, U-46619 or artificial CSF was infused intracerebroventricularly during prostaglandin synthase blockade. Blockade reduced but did not prevent blood pressure responses to U-46619 infusion, suggesting that the U-46619 infusions increased prostaglandin synthase metabolism to contribute de novo TxA2 or a second metabolite to augment the blood pressure response. Heart rate, pHa, PaCO2, ACTH, and cortisol responses to U-46619 were not different with blockade. We conclude that TxA2 acts on the brain to mediate blood pressure, heart rate, pHa, PaCO2, hematocrit, ACTH, and cortisol responses. These findings support the hypothesis that TxA2 acts directly on the brain to promote cardiovascular and hormonal responses that may serve a protective function during conditions when TxA2 formation is increased.

The effects of a novel sulphidopeptide leukotriene antagonist, BAY x7195, against elicited bronchoconstriction in the anaesthetized guinea-pig.

1. The novel leukotriene antagonist Bay x7195, has been evaluated against bronchoconstriction induced by leukotriene D4 (LTD4), the thromboxane A2 (TXA2) mimetic U46619, histamine and antigen, in the guinea-pig in vivo by use of a modified Konzett-Rössler preparation. 2. LTD4, given intravenously (i.v.) at 1 or 3 microg kg(-1) in the presence of indomethacin and sotalol, caused a 50-70% maximal bronchoconstriction in most animals. 3. BAY x7195, given i.v., orally (p.o.), by aerosol or dry powder insufflation, in lactose, reduced LTD4-induced bronchoconstriction dose-dependently. The approximate ID50 values were 83 microg kg(-1), 3 mg kg(-1), 0.0003% w/v for 20 breaths and 20 microg respectively. 4. The action of BAY x7195 (10 mg kg(-1), p.o.) was long lasting, causing significant inhibition of the LTD4-induced response (88% reduction) 8 h after dosing. 5. When given intravenously, in the presence of selected antagonists, BAY x7195 caused a dose-related reduction in the antigen-induced response, with an approximate ID50 of 2 mg kg(-1). 6. At 3 mg kg(-1), i.v., a dose which abolished the response to LTD4, BAY x7195 had no effect on U46619- or histamine-induced bronchoconstriction. 7. BAY x7195 is a potent, selective and long acting antagonist of LTD4-induced bronchoconstriction, in an anaesthetized, ventilated guinea-pig model. It is therefore worthy of clinical evaluation in diseases believed to involve the sulphidopeptide leukotrienes, such as asthma.

A guinea-pig model of ultrasonically nebulized distilled water-induced bronchoconstriction.

Ultrasonically nebulized distilled water-induced bronchoconstriction (UNDW-IB) is specific to asthma. The mechanisms underlying UNDW-IB are not fully understood, and no reproducible animal model has been reported. The purpose of this study was to develop a guinea-pig model of UNDW-IB. Ultrasonically nebulized distilled water (UNDW) was inhaled 20 min after an aerosolized antigen challenge in passively sensitized and artificially ventilated guinea-pigs. UNDW was also inhaled 5 and 20 min after 0.1 mg x mL(-1) methacholine inhalation in nonsensitized animals. In addition, 0.1 mg x kg(-1) S-1452, a thromboxane A2 antagonist, or saline was given intravenously 5 min before UNDW inhalation in sensitized animals. The inhalation of UNDW caused bronchoconstriction, when inhaled 20 min after an antigen challenge in sensitized guinea-pigs. UNDW inhalation did not produce bronchoconstriction after saline inhalation in nonsensitized or sensitized guinea-pigs, or after antigen inhalation in nonsensitized animals. Methacholine-induced bronchoconstriction did not evoke UNDW-IB. Neither did S-1452 reduce the UNDW-IB. In conclusion, the guinea-pig model of ultrasonically nebulized distilled water-induced bronchoconstriction developed in this study suggests that allergic reaction, but not bronchoconstriction, can induce bronchial hyperresponsiveness to ultrasonically nebulized distilled water, and that thromboxane A2 is not involved in ultrasonically nebulized distilled water-induced bronchoconstriction.

Postinjury thromboxane receptor blockade ameliorates acute lung injury.

BACKGROUND: Acute lung injury is associated with pulmonary hypertension, intrapulmonary shunting, and increased microvascular permeability, leading to altered oxygenation capacity. Thromboxane A2 has been found to be a central mediator in the development of septic and oleic acid (OA)-induced acute lung injury. Our previous study demonstrated a beneficial effect of preinjury thromboxane A2 receptor blockade. The current study examines the efficacy of postinjury receptor blockade on oxygenation capacity and pulmonary hemodynamics in an isolated lung model of OA-induced acute lung injury. METHODS: Four groups of rabbit heart-lung preparations were studied for 60 minutes in an ex vivo perfusion-ventilation system. Saline control lungs received saline solution during the first 20 minutes of study. Injury control lungs received an OA-ethanol solution during the first 20 minutes. Two treatment groups were used: T10, in which the thromboxane receptor antagonist, SQ30741, was infused 10 minutes after the initiation of OA infusion; and T30, in which the thromboxane receptor antagonist was infused 30 minutes after OA infusion. RESULTS: Significant differences were found in oxygenation (oxygen tension in T10 = 62.6 +/- 11.7 mm Hg, T30 = 68.2 +/- 21.2 mm Hg; injury control = 40.2 +/- 9.0 mm Hg, saline control = 123.5 +/- 16.01 mm Hg; p < 0.001) and percentile change in pulmonary artery pressure (T10 = 1.1% +/- 19.4% increase, T30 = 11.2% +/- 7.3% increase; injury control = 47.6% +/- 20.5%, saline control = 4.2% +/- 6.81%; p < 0.001). CONCLUSIONS: This study demonstrates that blockade of the thromboxane A2 receptor, even after the initiation of acute lung injury, eliminates pulmonary hypertension and improves oxygenation.

Efficiency of aerosolized nitric oxide donor drugs to achieve sustained pulmonary vasodilation.

Inhalation of nitric oxide (NO) causes selective pulmonary vasodilation, but demands continuous supply of the gaseous agent. We investigated the suitability of aerosolization of NO-donor drugs for achieving sustained reduction of pulmonary vascular tone. In buffer-perfused rabbit lungs, stable pulmonary hypertension was achieved by continuous infusion of the thromboxane-analogue U46619. The NO-donor drugs molsidomine, 3-morpholinosydnone-imine (SIN-1), sodium nitroprusside (SNP) and glyceryl-trinitrate reduced the pulmonary hypertension in a dose-dependent fashion, whether admixed to the perfusate or inhaled as alveolar-accessible aerosol particles (aerosolization time 3-6 min), with an efficiency ranking of SNP > SIN-1 >> molsidomine and glyceryl-trinitrate. Notably, nearly identical dose-response curves were obtained when corresponding molar quantities of the most potent agents, SNP and SIN-1, were applied either via transbronchial or via intravascular routes, with respect to rapidity of onset, extent (pressure reduction to near baseline) and duration (>90 min) of vasorelaxation. Appearance of sydnonimines in the perfusate after aerosolization and reduction of SIN-1 efficacy when nebulized in nonrecirculatingly perfused lungs demonstrated substantial entry of this prodrug into the vascular space after alveolar deposition. In contrast, undiminished vasodilatory efficacy of aerosolized SNP under conditions of non-recirculating perfusion suggested predominant efficacy via local NO release for this agent. We conclude that short aerosolization maneuvers of NO-donor drugs are suitable to achieve dose-dependent, extensive and sustained vasodilation in the pulmonary circulation, thus offering a new therapeutic approach in pulmonary hypertension.

Changes in reactivity towards 5-hydroxytryptamine in the renal vasculature of the diabetic spontaneously hypertensive rat.

BACKGROUND: Diabetes and hypertension are both associated with an increased risk of renal disease. The combination of these diseases produces marked acceleration of the problems. OBJECTIVE: To examine the reactivity in the renal vasculature of diabetic hypertensive rats. METHODS: We investigated the reactivity towards 5-hydroxytryptamine (5-HT) in Krebs solution-perfused kidneys of diabetic normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). In addition, the interaction between the thromboxane A2 mimetic U46619 and 5-HT was examined. RESULTS: Discrete dose-response curves were obtained for the response to 5-HT (0.1-30 micrograms/g kidney) in Krebs solution-perfused kidneys of control and diabetic WKY rats and SHR. The following order of reactivity was determined: control SHR > diabetic SHR > control WKY rats = diabetic WKY rats. The thromboxane A2 mimetic U46619 (10 ng/ml) potentiated responses to 5-HT significantly in kidneys of diabetic WKY rats and control SHR, but not in kidneys from control WKY rats and diabetic SHR. CONCLUSIONS: The differential affected reactivity towards 5-HT kidneys from diabetic and hypertensive rats might be due to previously documented differences in receptor number. The marked effect of U46619 on the reactivity towards 5-HT in kidneys of diabetic and control rats indicates that this interaction might be important given the increased levels of thromboxane A2 reported to occur in these diseases. The reason for the lack of effect of thromboxane/prostaglandin receptor stimulation on responses to 5-HT in the combined model (i.e. diabetic hypertensive rats) needs to be determined.

Thromboxane A2 acts at a site perfused by the carotid vasculature to mediate cardiovascular and adrenocortical responses.

Increases in thromboxane A2 (TxA2) synthesis are associated with hemodynamic responses and activation of the hypothalamus-pituitary-adrenal axis. This study tested the hypothesis that TxA2 acts on a site perfused by the carotid vasculature to mediate these responses. The TxA2 mimetic U46619 was infused for 30 min into the carotid artery or the vena cava of chronically instrumented adult sheep at doses of 0, 0.25, 0.5, and 1.0 microgram.kg-1.min-1. Mean arterial pressure increased in response to carotid or vena cava U46619 infusions of 0.5 and 1.0 microgram.kg-1.min-1. Heart rate was elevated in response to carotid (0.5 and 1.0 microgram.kg-1.min-1) or vena cava (1.0 microgram.kg-1.min-1) infusions of U46619. Paco2 declined and pH2 increased significantly in response to carotid infusions of 0.5 and 1.0 microgram.kg-1.min-1 but did not change in response to vena cava infusions. Adrenocorticotropic hormone (ACTH) increased in response to carotid infusions of 0.5 microgram.kg-1.min-1, while cortisol increased in response to infusions of 0.25, 0.5, and 1.0 microgram.kg-1.min-1. ACTH and cortisol did not change in response to vena cava infusions. Pao2, hematocrit, and arginine vasopressin did not change significantly. Pulmonary artery pressure and total peripheral resistance increased while cardiac output decreased in response to carotid or vena cava U46619 infusions of 1 microgram.kg-1.min-1; carotid and vena cava responses were not different from one another. We conclude that increases in blood pressure are mediated by peripheral PGH2/TxA2 receptor activation and that pituitary adrenal, blood gas, and heart rate responses are mediated by PGH2/TxA2 receptor activation at a site perfused by the carotid vasculature.

The in vitro effects of phosphodiesterase inhibitors on the human internal mammary artery.

The internal mammary artery (IMA) is the preferred conduit for myocardial revascularization, but it changes diameter in response to injury or thromboxane release to decrease myocardial blood supply. Papaverine, a phosphodiesterase (PDE) inhibitor, is injected in the IMA bed during surgery to prevent spasm. We evaluated the ability of papaverine and cyclic adenosine monophosphate PDE Type III (cAMP-PDE) inhibitors (amrinone, enoximone, and milrinone) in vitro to reverse the constriction of human IMA rings, induced by a thromboxane A2 analog, U46619, and evaluated amrinone's ability to modify the constricting effect of norepinephrine (NE). All cAMP-PDE inhibitors produced complete relaxation of U46619-induced contractions. The contractions necessary to produce 50% relaxation (EC50) were within therapeutic ranges. The vasodilatory potency of amrinone was greater after NE than after U46619 (EC50, 1.9 +/- 0.5 vs 4.3 +/- 2.2 x 10(-5)M; mean +/- SD; P < 0.05). Response to constriction after a submaximal dose of NE was attenuated to 38% (P < 0.001) from that observed in the control rings by a pretreatment with amrinone. These results suggest that cAMP-PDE inhibitors have the potential utility to reverse IMA spasm, and represent a potential therapeutic modality for IMA spasm after myocardial revascularization.

K+ channel-opening action contributes to the preventive effects of nicorandil on U46619-induced vasoconstriction of canine large coronary arteries in vivo.

The antispasmogenic effects of nicorandil on epicardial coronary artery vasoconstriction were compared with those of a K+ channel opener, cromakalim, and a nitrovasodilator, nitroglycerin, in open-chest dogs. Intracoronary administration of U46619 (0.5-1.0 micrograms), a stable thromboxane A2 analogue, reduced the external diameter of the left circumflex coronary artery with no marked alternations in systemic hemodynamics. This U46619-induced vasoconstriction of large epicardial coronary arteries was dose-dependently prevented by the intracoronary infusion of nicorandil (1-10 micrograms/kg/min), cromakalim (0.03 micrograms/kg/min) and nitroglycerin (1 micrograms/kg/min). After pretreatment with glibenclamide (3 mg/kg, i.v.), and ATP-sensitive K+ channel blocker, these effects of nicorandil and cromakalim were inhibited significantly, whereas the response to nitroglycerin remained unchanged. Nicorandil (3 micrograms/kg/min), cromakalim (0.03 micrograms/kg/min) and nitroglycerin (1 micrograms/kg/min) increased coronary blood flow. However, the inhibitory effects of each drug on the U46619-induced vasoconstriction were not influenced by the partial occlusion of the left circumflex coronary artery, which kept coronary blood flow constant. This indicates a direct antispasmogenic effect of K+ channel openers, which is independent of that mediated by the response to flow. Furthermore, our results suggest that, by this effect, nicorandil protects large coronary arteries from U46619-induced vasoconstriction.

Airway hyper- or hyporeactivity to inhaled spasmogens 24 h after ovalbumin challenge of sensitized guinea-pigs.

1. The aim of this study was to determine whether an inhalation of ovalbumin (OA, 10 or 20 mg ml-1) by conscious OA-sensitized guinea-pigs leads to airway hyperreactivity to spasmogens 24 h later. In contrast to most previous studies, the spasmogens (5-HT, methacholine (MCh), U-46619 and adenosine) were administered by inhalation and airway function was measured in conscious guinea-pigs. 2. Guinea-pigs were sensitized by i.p. injection of 10 micrograms OA and 100 mg aluminium hydroxide in 1 ml normal saline; 14-21 days later they were exposed to an inhalation of 5-HT, MCh, U-46619 or adenosine. Specific airway conductance (sGaw) was measured in conscious animals by whole body plethysmography. The spasmogens caused bronchoconstriction, measured as a reduction in sGaw from the pre-inhalation basal values. Dose-related bronchoconstrictions were observed with 5-HT, MCh and U-46619. 3. The effect of an ovalbumin macroshock challenge upon the responses to each spasmogen were examined by giving an inhalation of aerosolized OA at 24 h (or 7 days in the cause of adenosine) after an initial spasmogen challenge. Eighteen to twenty-four hours after the OA macroshock, the same guinea-pigs were exposed to a repeated inhalation of 5-HT, MCh, U-46619 or adenosine. 4. U-46619 was the only spasmogen to demonstrate hyperresponsiveness, the peak change in sGaw being increased from -12.3 +/- 9.9 to -38.8 +/- 5.0% by 10 mg ml-1 OA challenge. In contrast, the ovalbumin challenge (20 mg ml-1) inhibited the bronchoconstrictions to 5-HT (50 micrograms ml-1) and MCh (100 micrograms ml-1). Adenosine demonstrated bronchoconstriction in sensitized guinea-pigs but no significant change in the response was observed after an OA challenge. 5. All results were compared with a control group of sensitized guinea-pigs receiving a NaCl challenge. The bronchoconstrictor responses to 5-HT, MCh, U-46619 or adenosine did not differ significantly before and after the saline challenge, indicating reproducibility of the responses. 6. In further experiments, guinea-pigs were exposed to inhalation of 5-HT (50 micrograms ml-1) or MCh (300 micrograms ml-1) 24 h before atropine (10 micrograms, 100 micrograms or 1 mg ml-1) and again at 0.5 to 1.5 h afterwards. Atropine, antagonized the 5-HT- and MCh-induced bronchoconstrictions over the same antagonist dose-range. This suggests that the bronchoconstriction induced in the conscious guinea-pig by 5-HT is mediated primarily via muscarinic receptors, possibly by a vagal reflex. The inhibition of the responses to 5-HT and MCh by OA challenge would therefore appear to be related to interference with a common cholinergic pathway for these spasmogens. 7. In summary, airway hyperresponsiveness was evident at 24 h after OA challenge as measured by an enhanced bronchoconstrictor response to inhaled U-46619. When 5-HT or MCh were used as the spasmogens, an opposing decrease in responsiveness was observed. This was presumed to be due to an inhibition of cholinergic pathways by the OA challenge. Adenosine caused a bronchoconstriction in the sensitized animals but this was not enhanced by the OA challenge.

Effects of hypoxia and vascular tone on endothelium-dependent and -independent responses in developing lungs.

Both increases and decreases in endothelium-derived nitric oxide (EDNO) activity have been described in the developing pulmonary vasculature. We hypothesized that differences in baseline vasomotor tone and/or oxygen tension may contribute to this variability. Pulmonary arterial dose responses to endothelium-dependent and -independent vasodilators acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were measured in indomethacin-treated lungs of 1- to 2-day-old (2D) and 1-mo-old (1M) lambs. During 4% O2 ventilation, baseline pulmonary vascular resistance (PVR) and the dilator response to both ACh and SNP were greater in 2D lungs. However, when baseline PVR values were matched at both ages during either hypoxia or infusion of a thromboxane mimetic under normoxic conditions, developmental differences in ACh-induced vasodilation were minimal. Furthermore, hypoxia itself did not alter the responses to ACh in 2D lungs. In contrast, SNP caused greater vasodilation in 2D than in 1M lungs regardless of baseline PVR. These data and studies suggest that whereas high PVR enhances EDNO synthesis, responsiveness to ENDO decreases as synthesis of ENDO increases in developing lungs studied under basal conditions.