Using blood pressure telemetry to assess acute changes in arterial stiffness in rats after nitric oxide synthase inhibition or environmental tobacco smoke exposure

Although environmental tobacco smoke (ETS) exposure has been reported to acutely increase arterial stiffness in humans, understanding of the underlying mechanisms is unclear and few studies have measured these effects in experimental animals. One potential mechanism for the increased arterial stiffness is reduced nitric oxide (NO) bioactivity as a result of oxidative stress. Thus, the objective of this study was to determine whether acute changes in arterial stiffness could be detected using arterial pulse wave dP/dt in blood pressure telemetry implanted rats and to investigate the role of NO in regulating dP/dt. Intravenous injection of acetylcholine (0.91 ng/kg) decreased and norepinephrine (0.02 mg/kg) increased dP/dt compared to saline vehicle (0.5 mL/kg). Injection of the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME; 30 mg/kg) decreased plasma nitrate/nitrite (NOx), but transiently increased dP/dt. ETS at low and high doses had no effect on dP/dt, but increased plasma NOx levels at high ETS exposure and increased plasma nitrotyrosine levels in both ETS groups. In conclusion, acute changes in NO production via acetylcholine or L-NAME alter the arterial pulse wave dP/dt consistently with the predicted changes in arterial stiffness. Although acute ETS appears to biologically inactivate NO, a concomitant increase in NO production at high ETS exposure may explain why dP/dt was not acutely altered by ETS in the current study.     

Vasoactive mediators and pulmonary hypertension after cigarette smoke exposure in the guinea pig.

The pathogenesis of pulmonary hypertension in patients with chronic obstructive pulmonary disease is not understood. We have previously shown increased levels of mediators that control vasoconstriction (endothelin-1), vascular cell proliferation (endothelin-1 and vascular endothelial growth factor), and vasodilation (endothelial nitric oxide synthase) in the intrapulmonary arteries of animals exposed to cigarette smoke. To determine whether these mediators could be implicated in the structural remodeling of the arterial vasculature and increased pulmonary arterial pressure caused by chronic cigarette smoke exposure, guinea pigs were exposed to daily cigarette smoke for 6 mo. Pulmonary arterial pressures were measured. Intrapulmonary artery structure was analyzed by morphometry, artery mediator protein expression by immunohistochemistry, and artery mediator gene expression by laser capture microdissection and real-time RT-PCR. We found that the smoke-exposed animals developed increases in pulmonary arterial pressure and increased muscularization of the small pulmonary arteries. Gene expression and protein levels of all three mediators were increased, and pulmonary arterial pressure correlated both with the levels of mediator production and with the degree of arterial muscularization. We conclude that chronic smoke exposure produces increased vasoactive mediator expression in the small intrapulmonary arteries and that these mediators are associated with vascular remodeling as well as increased pulmonary arterial pressure. These findings support the idea that hypertension in chronic obstructive pulmonary disease is a result of direct cigarette smoke-mediated effects on the vasculature and suggest that interference with endothelin and VEGF production and activity or augmentation of nitric oxide levels may be beneficial.     

Determination of the nicotine metabolites cotinine and trans-3'-hydroxycotinine in biologic fluids of smokers and non-smokers using liquid chromatography-tandem mass spectrometry: biomarkers for tobacco smoke exposure and for phenotyping cytochrome P450 2A6 activity

The nicotine metabolite cotinine is widely used to assess the extent of tobacco use in smokers, and secondhand smoke exposure in non-smokers. The ratio of another nicotine metabolite, trans-3'-hydroxycotinine, to cotinine in biofluids is highly correlated with the rate of nicotine metabolism, which is catalyzed mainly by cytochrome P450 2A6 (CYP2A6). Consequently, this nicotine metabolite ratio is being used to phenotype individuals for CYP2A6 activity and to individualize pharmacotherapies for tobacco addiction. In this paper we describe a highly sensitive liquid chromatography-tandem mass spectrometry method for determination of the nicotine metabolites cotinine and trans-3'-hydroxycotinine in human plasma, urine, and saliva. Lower limits of quantitation range from 0.02 to 0.1ng/mL. The extraction procedure is straightforward and suitable for large-scale studies. The method has been applied to several thousand biofluid samples for pharmacogenetic studies and for studies of exposure to low levels of secondhand smoke. Concentrations of both metabolites in urine of non-smokers with different levels of secondhand smoke exposure are presented.     

Expression of cytochrome CYP2B1/2 in nonpregnant, pregnant and fetal rats exposed to tobacco smoke

Four-month-old female Wistar rats were exposed for 20 days to tobacco smoke obtained from non-filter cigarettes. During the exposure, concentration of tobacco smoke was monitored indirectly by measuring the CO level (1500 mg/m3 air). The efficacy of exposure was assessed by measuring urine nicotine and cotinine levels. Cigarette smoke did not change total cytochrome P450 and b5 protein levels in any of the organs studied, and most of these organs did not show any changes in the activity of reductases associated with these cytochromes. Following exposure to tobacco smoke, fetal rat liver expressed CYP2B1/2 protein; in newborns (day 1) both liver and lung showed CYP2B1/2 protein expression and very low pentoxyresorufin O-dealkylase activity. Western blot analysis of adult liver, lung, heart, but not of brain microsomes, showed that tobacco smoke induced CYP2B1/2 in both nonpregnant and pregnant rats, though its expression was lower in the livers and hearts of pregnant females. In the rat and human placenta, neither rat CYP2B1/2 nor human CYP2B6 showed basal or tobacco smoke-induced expression at the protein level. This study shows clearly that the expression of CYP2B1/2, which metabolizes nicotine and some drugs and activates carcinogens, is controlled in rats by age-, pregnancy-, and tissue-specific regulatory mechanisms.     

Effect of cigarette smoking on nitric oxide, structural, and mechanical properties of mouse arteries

Cigarette smoking (CS) is a major risk factor for vascular disease. The aim of this study was to quantitatively assess the influence of CS on mouse arteries. We studied the effect of short-term (6 wk) and long-term (16 wk) CS exposure on structural and mechanical properties of coronary arteries compared with that of control mice. We also examined the reversibility of the deleterious effects of CS on structural [e.g., wall thickness (WT)], mechanical (e.g., stiffness), and biochemical [e.g., nitric oxide (NO) by-products] properties with the cessation of CS. The left and right coronary arteries were cannulated in situ and mechanically distended. The stress, strain, elastic modulus, and WT of coronary arteries were determined. Western blot analysis was used to analyze endothelial NO synthase (eNOS) in the femoral and carotid arteries of the same mice, and NO by-products were determined by measuring the levels of nitrite. Our results show that the mean arterial pressure was increased by CS. Furthermore, CS significantly increased the elastic modulus, decreased stress and strain, and increased the WT and WT-to-radius ratio compared with those of control mice. The reduction of eNOS protein expression was found only after long-term CS exposure. Moreover, the NO metabolite was markedly decreased in CS mice after short- and long-term exposure of CS. These findings suggest that 16 wk of CS exposure can cause an irreversible deterioration of structural and elastic properties of mouse coronary arteries. The decrease in endothelium-derived NO in CS mice was seen to significantly correlate with the remodeling of arterial wall.     

Early effects of tobacco smoke exposure on vascular dynamics in the microcirculation.

The purpose of these studies is to examine the early effects of chronic tobacco smoke exposure on vascular dynamics in the mesenteric microcirculation. Female rats were exposed daily to tobacco smoke from five reference cigarettes for a period of 2 mo. At the end of this period the smoke-treated rats had gained 12 g less than sham-treated controls, and arterial blood pressure in the smoke-treated animals was slightly less than pressure in the sham-treated animals. These are characteristic effects of tobacco smoke exposure on rats. Following the treatment period, red blood cell (RBC) velocity in single mesenteric capillaries and microvascular pressures in arterioles and venules were measured in accordance to established methods. There was no significant difference in pressure distribution on the arterial side of the mesenteric vascular network, but pressure in the venules of the smoke-treated animals was significantly higher than that of the sham-treated group. In association with the higher venular pressure in the smoke-treated animals, capillary RBC velocity (an index of capillary flow) was significantly lower. The reduction in velocity was in proportion to the decrease in pressure drop (arteriole-venule) across the capillary network.     

Bradykinin in reflex cardiovascular responses to static muscular contraction

We examined the contribution of bradykinin to the reflex hemodynamic response evoked by static contraction of the hindlimb of anesthetized cats. During electrical stimulation of ventral roots L7 and S1, we compared the cardiovascular responses to hindlimb contraction before and after the following interventions: inhibition of converting enzyme (kininase II) with captopril (3-4 mg/kg, n = 6); inhibition of kallikrein activity with aprotinin (Trasylol, 20,000-30,000 KIU/kg, n = 8); and injection of carboxypeptidase B (500-750 U/kg, n = 7). Treatment with captopril augmented the rise in mean arterial blood pressure and maximal time derivative of pressure (dP/dt) caused by static contraction from 21 +/- 3 to 39 +/- 7 mmHg and 1,405 +/- 362 to 2,285 +/- 564 mmHg/s, respectively. Aprotinin attenuated the contraction-induced rise in mean arterial blood pressure (28 +/- 4 to 9 +/- 2 mmHg) and maximal dP/dt (1,284 +/- 261 to 469 +/- 158 mmHg/s). Carboxypeptidase B reduced the cardiovascular response to static contraction. Thus the mean arterial blood pressure response was decreased from 36 +/- 12 to 24 +/- 11 mmHg, maximal dP/dt from 1,618 +/- 652 to 957 +/- 392 mmHg/s, and heart rate from 12 +/- 2 to 7 +/- 1 beats/min. These data suggest that stimulation of muscle afferents by bradykinin contributes to a portion of the reflex cardiovascular response to static contraction.     

Indexes of diastolic RV function: load dependence and changes after chronic RV pressure overload in lambs

Diastolic function is a major determinant of ventricular performance, especially when loading conditions are altered. We evaluated biventricular diastolic function in lambs and studied possible load dependence of diastolic parameters [minimum first derivative of pressure vs. time (dP/dt(min)) and time constant of isovolumic relaxation (tau)] in normal (n = 5) and chronic right ventricular (RV) pressure-overloaded (n = 5) hearts by using an adjustable band on the pulmonary artery (PAB). Pressure-volume relations were measured during preload reduction to obtain the end-diastolic pressure-volume relationship (EDPVR). In normal lambs, absolute dP/dt(min) and tau were lower in the RV than in the left ventricle whereas the chamber stiffness constant (b) was roughly the same. After PAB, RV tau and dP/dt(min) were significantly higher compared with control. The RV EDPVR indicated impaired diastolic function. During acute pressure reduction, both dP/dt(min) and tau showed a relationship with end-systolic pressure. These relationships could explain the increased dP/dt(min) but not the increased tau-value after banding. Therefore, the increased tau after banding reflects intrinsic myocardial changes. We conclude that after chronic RV pressure overload, RV early relaxation is prolonged and diastolic stiffness is increased, both indicative of impaired diastolic function.     

Nitric Oxide and Blood Pressure in Mice Lacking Extracellular-Superoxide Dismutase

Nitric oxide is a major vasorelaxant and regulator of the blood pressure. The blood vessels contain several active sources of the superoxide radical, which reacts avidly with nitric oxide to form noxious peroxynitrite. There are large amounts of extracellular-superoxide dismutase (EC-SOD) in the vascular wall. To evaluate the importance of EC-SOD for the physiology of nitric oxide, here we studied the blood pressure in mice lacking the enzyme. In chronically instrumented non-anaesthetized mice there was no difference in mean arterial blood pressure between wild-type controls and EC-SOD mutants. Extensive inhibition of nitric oxide synthases with N -monomethyl- l -arginine however resulted in a larger increase in blood pressure, and infusion of the nitric oxide donor nitrosoglutathione caused less reduction in blood pressure in the EC-SOD null mice. We interpret the alterations to be caused by a moderately increased consumption of nitric oxide by the superoxide radical in the EC-SOD null mice. One role of EC-SOD may be to preserve nitric oxide, a function that should be particularly important in vascular pathologies, in which large increases in superoxide formation have been documented.     

Nitric oxide and blood pressure in mice lacking extracellular-superoxide dismutase

Nitric oxide is a major vasorelaxant and regulator of the blood pressure. The blood vessels contain several active sources of the superoxide radical, which reacts avidly with nitric oxide to form noxious peroxynitrite. There are large amounts of extracellular-superoxide dismutase (EC-SOD) in the vascular wall. To evaluate the importance of EC-SOD for the physiology of nitric oxide, here we studied the blood pressure in mice lacking the enzyme. In chronically instrumented non-anaesthetized mice there was no difference in mean arterial blood pressure between wild-type controls and EC-SOD mutants. Extensive inhibition of nitric oxide synthases with N -monomethyl- l -arginine however resulted in a larger increase in blood pressure, and infusion of the nitric oxide donor nitrosoglutathione caused less reduction in blood pressure in the EC-SOD null mice. We interpret the alterations to be caused by a moderately increased consumption of nitric oxide by the superoxide radical in the EC-SOD null mice. One role of EC-SOD may be to preserve nitric oxide, a function that should be particularly important in vascular pathologies, in which large increases in superoxide formation have been documented.     

Endothelin-1 response to mental stress in early ischemic lesions of the extremities due to systemic sclerosis

We studied circulating levels of endothelin-1, catecholamines and nitric oxide after a mental arithmetic test in 14 patients with early ischemic lesions of the extremities due to systemic sclerosis and slightly impaired peripheral vascular flow. The test induced an increase (P < 0.01) in blood pressure, heart rate, endothelin-1 and catecholamine levels, whereas it did not change the low basal levels of nitric oxide. In healthy subjects (n = 20) the test significantly (P < 0.01) decreased endothelin-1 without affecting nitric oxide. The low basal levels of nitric oxide and the high plasma concentration of endothelin-1 after psychological stress cannot be explained by an impaired release from the limited ischemic lesions alone. This suggests a diffuse microvascular derangement that aggravates the course of peripheral microvascular ischemic lesions.     

Organ blood flow and cardiac contractility in anaesthetized cats at 5 bar (500 kPa) ambient pressure

Previous in vivo and in vitro experiments have demonstrated increased cardiac contractility and increased total myocardial blood flow (Qmyocardial) when rats were exposed to normoxic 5-bar (500 kPa) ambient pressure. In the present study, regional blood flow was measured using the microsphere method on nine anaesthetized cats at surface and normoxic 5-bar (500 kPa) ambient pressure. Left ventricular pressure (LVP) and cardiac contractility, measured as peak left ventricular +dP/dt and -dP/dt were measured in six of the cats. Arterial pressure, heart rate and cardiac output remained unchanged after compression, but total Qmyocardial increased by 29% (P less than 0.01) and cerebral blood flow increased by 66% (P less than 0.05). At the same time +dP/dt and -dP/dt was increased by 83% and 102%, respectively (P less than 0.01), while LVP was enhanced by 14% (P less than 0.05). Except for a moderate decrease in partial pressure of oxygen, acid base status in arterial blood remained unchanged. The results indicate that the effects of increased ambient pressure on the heart are general physiological phenomena, which are not only limited to the laboratory rat.     

Effect of methylene blue on cardiac output response to exercise in dogs

To determine whether the increase in cardiac output during mild to moderate exercise is related to an increase in the tissue redox potential, we compared the responses of cardiac output, total body oxygen consumption, and arterial blood lactate-to-pyruvate ratio (a measure of NADH/NAD) to treadmill exercise between dogs treated with normal saline and those treated with a hydrogen acceptor, new methylene blue. Normal saline was infused into the left atrium in the first group of dogs at a rate of 0.38 ml/min throughout the treadmill exercise (2.5 mph and 5.0 mph on a 6% incline, each for 20 min). In the second group, methylene blue was administered as a loading dose (4 mg/kg) before exercise, followed by a continuous infusion (0.15 mg X kg-1 X min-1) throughout exercise. A similar infusion of methylene blue was given to a third group of dogs without exercise; it reduced the arterial lactate-to-pyruvate ratio from 6.70 +/- 0.35 to 4.12 +/- 0.27 but had no or little effects on cardiac output, heart rate, arterial pressure, and left ventricular dP/dt and (dP/dt)/P. Treadmill exercise doubled cardiac output and increased total body O2 consumption three- to fourfold in the first two groups but increased arterial blood lactate-to-pyruvate ratio only in group 1 (6.0 +/- 0.54 to 9.97 +/- 0.91). The relationship between cardiac output and total body O2 consumption was unaffected by the simultaneous administration of methylene blue during exercise. Groups 1 and 2 also did not differ in their heart rate, left ventricular dP/dt and (dP/dt)/P, and plasma catecholamine responses to exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of naloxone on systemic and regional hemodynamic responses to exercise in dogs

To determine whether endogenous opiates have a role in circulatory regulation during mild to moderate exercise, 11 chronically instrumented dogs were exercised on a treadmill up a 6% incline at 2.5 and 5.0 mph, each for 20 min, after treatment with either the opiate receptor antagonist naloxone (1 mg/kg bolus and 20 micrograms.kg-1.min-1 infusion) or normal saline. Naloxone increased plasma beta-endorphin and adrenocorticotropic hormone at rest but had no effect on resting heart rate, aortic pressure, cardiac output, left ventricular time derivative of pressure (dP/dt) and ratio of dP/dt at a developed pressure of 50 mmHg and the developed pressure (dP/dt/P), or plasma catecholamines. Plasma beta-endorphin and adrenocorticotropic hormone increased during exercise. In addition, graded treadmill exercise produced proportional increases in heart rate, cardiac output, aortic pressure, left ventricular dP/dt and dP/dt/P, and blood flow to exercising muscles, right and left ventricular myocardium, and adrenal glands. However, there were no differences in the circulatory responses to exercise between animals receiving naloxone and normal saline. Thus the endogenous opiate system probably does not play an important role in regulating the systemic hemodynamic and blood flow responses to mild and moderate exercise.     

Aortic and Carotid Arterial Stiffness and Epigenetic Regulator Gene Expression Changes Precede Blood Pressure Rise in Stroke-Prone Dahl Salt-Sensitive Hypertensive Rats

Multiple clinical studies show that arterial stiffness, measured as pulse wave velocity (PWV), precedes hypertension and is an independent predictor of hypertension end organ diseases including stroke, cardiovascular disease and chronic kidney disease. Risk factor studies for arterial stiffness implicate age, hypertension and sodium. However, causal mechanisms linking risk factor to arterial stiffness remain to be elucidated. Here, we studied the causal relationship of arterial stiffness and hypertension in the Na-induced, stroke-prone Dahl salt-sensitive (S) hypertensive rat model, and analyzed putative molecular mechanisms. Stroke-prone and non-stroke-prone male and female rats were studied at 3- and 6-weeks of age for arterial stiffness (PWV, strain), blood pressure, vessel wall histology, and gene expression changes. Studies showed that increased left carotid and aortic arterial stiffness preceded hypertension, pulse pressure widening, and structural wall changes at the 6-week time-point. Instead, differential gene induction was detected implicating molecular-functional changes in extracellular matrix (ECM) structural constituents, modifiers, cell adhesion, and matricellular proteins, as well as in endothelial function, apoptosis balance, and epigenetic regulators. Immunostaining testing histone modifiers Ep300, HDAC3, and PRMT5 levels confirmed carotid artery-upregulation in all three layers: endothelial, smooth muscle and adventitial cells. Our study recapitulates observations in humans that given salt-sensitivity, increased Na-intake induced arterial stiffness before hypertension, increased pulse pressure, and structural vessel wall changes. Differential gene expression changes associated with arterial stiffness suggest a molecular mechanism linking sodium to full-vessel wall response affecting gene-networks involved in vascular ECM structure-function, apoptosis balance, and epigenetic regulation.     

Cardiac effects of endothelin receptor antagonism in endotoxemic pigs

Myocardial depression in sepsis is frequently encountered clinically and contributes to morbidity and mortality. Increased plasma levels of endothelin-1 (ET-1) have been described in septic shock, and previous reports have shown beneficial effects on cardiovascular performance and survival in septic models using ET receptor antagonists. The aim of the current study was to investigate specific cardiac effects of ET receptor antagonism in endotoxicosis. Sixteen domestic pigs were anesthetized and subjected to endotoxin for 5 h. Eight of these pigs were given tezosentan (dual ET receptor antagonist) after 3 h. Cardiac effects were evaluated using the left ventricular (LV) pressure-volume relationship. Endotoxin was not associated with any effects on parameters of LV contractile function [end-systolic elastance (Ees), preload recruitable stroke work (PRSW), power(max)/end-diastolic volume (PWR(max)/EDV) and dP/dt(max)/end-diastolic volume (dP/dt(max)/EDV)] but with impairments in isovolumic relaxation (time constant for pressure decay, tau) and mechanical efficiency. Tezosentan administration decreased Ees, PWR(max)/EDV, and dP/dt(max)/EDV, while improving tau and LV stiffness. Thus, dual ET receptor antagonism was associated with a decline in contractile function but, in contrast, improved diastolic function. Positive hemodynamic effects from ET receptor antagonism in acute endotoxemia may be due to changes in cardiac load and enhanced diastolic function rather than improved contractile function.     

Bradykinin-induced chemoreflexes from skeletal muscle: implications for the exercise reflex

We examined the cardiovascular response to bradykinin stimulation of skeletal muscle afferents and the effect of prostaglandins on this response. Intra-arterial injection of 1 microgram bradykinin into the gracilis muscle of cats reflexly increased mean arterial pressure by 16 +/- 2 mmHg, left ventricular end-diastolic pressure by 1.6 +/- 0.6 mmHg, maximal dP/dt by 785 +/- 136 mmHg/s, heart rate by 11 +/- 2 beats/min, and mean aortic flow by 22 +/- 3 ml/min. The hemodynamic responses were abolished following denervation of the gracilis muscle. The increases in mean arterial pressure and maximal dP/dt were reduced by 68 and 45%, respectively, following inhibition of prostaglandin synthesis with indomethacin (2-8 mg/kg iv). Treatment with prostaglandin E2 (PGE2, 15-25 micrograms ia) restored the initial increase in mean arterial pressure, but not dP/dt, caused by bradykinin stimulation. Injection of PGE2 (15-30 micrograms ia) into the gracilis, without prior treatment with indomethacin, augmented the bradykinin-induced increases in mean arterial pressure and dP/dt. We conclude that small doses of bradykinin injected into skeletal muscle are capable of reflexly activating the cardiovascular system and that prostaglandins are necessary for the full manifestation of the corresponding hemodynamic response. The pattern of hemodynamic adjustment following bradykinin injection into skeletal muscle is very similar to that induced by static exercise. Therefore, it is possible that intense exercise provides a stimulus for this bradykinin-induced reflex in vivo.     

Altered vascular reactivity in arterioles of chronic intermittent hypoxic rats.

Recurrent episodic hypoxia (EH) is a feature of sleep apnea that may be responsible for some chronic cardiovascular sequelae such as systemic hypertension. Chronic EH (8 h/day for 35 days) causes elevation of diurnal resting (unstimulated) mean arterial blood pressure (MAP) in the rat. We used in vivo video microscopy to examine arteriolar reactivity in the cremaster muscle of male Sprague-Dawley rats subjected to 35 days of EH. Cremaster muscles of EH (n = 6) and control (n = 6) rats were exposed to varying doses of norepinephrine (NE) (10(-10) to 10(-5) M), ACh (10(-9) to 10(-5) M), and endothelin-1 (10(-12) to 10(-8) M). In a separate experiment, EH (n = 5) and control (n = 6) rats were given one dose of a nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 10(-5) M). We also examined endothelial NOS mRNA from the kidneys of EH-stimulated and control (unstimulated) rats. Telemetry-monitored EH rats showed a 16-mmHg increase in MAP over 35 days, whereas control rats showed no change. The response to NE and endothelin-1 were similar for EH and control rats. ACh vasodilatation of arterioles in EH rats was significantly attenuated compared with that of controls. The degree of vasoconstriction in response to blockade of the nitric oxide system by L-NAME was significantly less (83% of baseline diameter with L-NAME) for arterioles of EH rats compared with that for controls (61% of baseline diameter), implying lower basal resting nitric oxide release in the EH rats. Whole kidney mRNA endothelial NOS levels were not different between groups. These data support the hypothesis that chronic elevation of blood pressure associated with EH involves increased peripheral resistance from decreased basal release or production of nitric oxide after 35 days of EH.     

Alteration in myocardial oxygen balance during exercise after beta-adrenergic blockade in dogs

The effects of beta-adrenergic blockade upon myocardial blood flow and oxygen balance during exercise were evaluated in eight conscious dogs, instrumented for chronic measurements of coronary blood flow, left ventricular pressure, aortic blood pressure, heart rate, and sampling of arterial and coronary sinus venous blood. The administration of propranolol (1.5 mg/kg iv) produced a decrease in heart rate, peak left ventricular (LV) dP/dt, LV (dP/dt/P, and an increase in LV end-diastolic pressure during exercise. Mean coronary blood flow and myocardial oxygen consumption were lower after propranolol than at the same exercise intensity in control conditions. The oxygen delivery-to-oxygen consumption ratio and the coronary sinus oxygen content were also significantly lower. It is concluded that the relationship between myocardial oxygen supply and demand is modified during exercise after propranolol, so that a given level of myocardial oxygen consumption is achieved with a proportionally lower myocardial blood flow and a higher oxygen extraction.     

Chronic endothelin A receptor blockade in lambs with increased pulmonary blood flow and pressure

Endothelin receptor blockade is an emerging therapy for pulmonary hypertension. However, hemodynamic and structural effects and potential changes in endogenous nitric oxide (NO)-cGMP and endothelin-1 signaling of chronic endothelin A receptor blockade in pulmonary hypertension secondary to congenital heart disease are unknown. Therefore, the objectives of this study were to determine hemodynamic and structural effects and potential changes in endogenous NO-cGMP and endothelin-1 signaling of chronic endothelin A receptor blockade in a lamb model of increased pulmonary blood flow following in utero placement of an aortopulmonary shunt. Immediately after spontaneous birth, shunt lambs were treated lifelong with either an endothelin A receptor antagonist (PD-156707) or placebo. At 4 wk of age, PD-156707-treated shunt lambs (n = 6) had lower pulmonary vascular resistance and right atrial pressure than placebo-treated shunt lambs (n = 8, P < 0.05). Smooth muscle thickness or arterial number per unit area was not different between the two groups. However, the number of alveolar profiles per unit area was increased in the PD-156707-treated shunt lambs (190.7 +/- 5.6 vs. 132.9 +/- 10.0, P < 0.05). Plasma endothelin-1 and cGMP levels and lung NOS activity, cGMP, eNOS, preproendothelin-1, endothelin-converting enzyme-1, endothelin A, and endothelin B receptor protein levels were similar in both groups. We conclude that chronic endothelin A receptor blockade attenuates the progression of pulmonary hypertension and augments alveolar growth in lambs with increased pulmonary blood flow.