Long-term passive wastewater surveillance of SARS-CoV-2 for seven university dormitories in comparison to municipal surveillance

Wastewater-based surveillance (WBS) has been an effective tool for monitoring and understanding potential SARS-CoV-2 transmission across small and large-scale communities. In this study at the University of Saskatchewan, the assessment of SARS-CoV-2 was done over eight months during the 2021-2022 academic year. Wastewater samples were collected using passive samplers that were deployed in domestic sewer lines near adjacent campus residences and extracted for viral RNA, followed by Reverse Transcription quantitative Polymerase Chain Reaction (RT-qPCR). The results showed similar trends for SARS-CoV-2 detection frequencies and viral loads across university residences, the whole campus, and from related WBS at Saskatoon Wastewater Treatment Plant. The maximum daily detection frequency for seven dormitories considered was about 75 %, while maximum daily case numbers for the residences and campus-wide were about 11 and 75 people, respectively. In addition, self-reported rates of infection on campus peaked during similar time frames as increases in viral load were detected at the Saskatoon wastewater treatment plant. These similarities indicate the usefulness and cost-effectiveness of monitoring the spread of COVID-19 in small-scale communities using WBS.

Hypoxia inducible factor (HIF1A) is associated with increased right ventricular fibrosis by T1 mapping cardiac magnetic resonance in patients with repaired tetralogy of Fallot

Background

Right ventricular fibrotic remodeling has been identified pre- and postoperatively in patients with tetralogy of Fallot (ToF) and linked to adverse outcomes. Polymorphisms of hypoxia inducible factor-1-alpha (HIF1α) have been associated with fibrotic burden by cardiac magnetic resonance (CMR) late gadolinium enhancement imaging. Their association with diffuse fibrotic myocardial remodeling is unknown.

Purpose

We sought to determine whether polymorphisms in hypoxia inducible factor (HIF1α) are related to CMR markers of diffuse myocardial fibrosis in pediatric patients with repaired ToF.

Methods

Patients with repaired ToF who had undergone CMR with T1 mapping as well as whole genome sequencing were included. Myocardial native T1 was quantified using a modified Look-Locker inversion recovery sequence and measured in the left ventricular free wall, the interventricular septum, and the right ventricular free wall. Patients who had at least one functioning allele of HIF1α were compared to those who did not using Mann Whitney U test for continuous variables and chi-square or Fischer test for discrete variables. Data are displayed in Table 1 as median (IQR) for continuous variables and frequency (percentage) for discrete variables.

Results

46 patients had both CMR and whole genome sequencing. Only one HIF1α variant was identified in the cohort and present in 13 patients. There were no significant differences in demographics, surgical variables, right or left ventricular volumes or function between the groups (Table 1). Despite a trend towards a lower age at the time of CMR (11.3 vs 13.7 years; p=0.07), patients with HIF1α had higher native T1 values (1094 vs. 1050; p=0.027; Table 1) in the right ventricular outflow tract myocardium, reflecting increased diffuse interstitial ventricular fibrosis in patients with the HIF1α variant.

Conclusion

Hypoxia-inducible factor is associated with imaging markers of increased diffuse right ventricular fibrosis late after repair of tetralogy of Fallot.

Funding Acknowledgement

Type of funding sources: None. Table 1

Twenty-year experience with heart transplantation for infants and children with restrictive cardiomyopathy: 1986-2006

Idiopathic restrictive cardiomyopathy (RCM) is a rare cardiomyopathy in children notable for severe diastolic dysfunction and progressive elevation of pulmonary vascular resistance (PVR). Traditionally, those with pulmonary vascular resistance indices (PVRI) >6 W.U. x m(2) have been precluded from heart transplantation (HTX). The clinical course of all patients transplanted for RCM between 1986 and 2006 were reviewed. Preoperative, intraoperative and postoperative variables were evaluated. A total of 23 patients underwent HTX for RCM, with a mean age of 8.8 +/- 5.6 years and a mean time from listing to HTX of 43 +/- 60 days. Preoperative and postoperative (114 +/- 40 days) PVRI were 5.9 +/- 4.4 and 2.9 +/- 1.5 W.U. x m(2), respectively. At time of most recent follow-up (mean = 5.7 +/- 4.6 years), the mean PVRI was 2.0 +/- 1.0 W.U. x m(2). Increasing preoperative mean pulmonary artery pressure (PA) pressure (p = 0.04) and PVRI > 6 W.U. x m(2) (chi(2)= 7.4, p < 0.01) were associated with the requirement of ECMO postoperatively. Neither PVRI nor mean PA pressure was associated with posttransplant mortality; 30-day and 1-year actuarial survivals were 96% and 86%, respectively. Five of the seven patients with preoperative PVRI > 6 W.U. x m(2) survived the first postoperative year. We report excellent survival for patients undergoing HTX for RCM despite the high proportion of high-risk patients.

Hypertrophy signaling during peripartum cardiac remodeling

Molecular signaling pathways that regulate peripartum cardiac remodeling are not well understood. Our objectives were to study the role of mitogen-activated protein kinases (MAPKs), protein kinase B (Akt), and endothelial nitric oxide synthase (eNOS) in mediating pregnancy and postpartum (PP) cardiac remodeling. Methods: Adult female Sprague-Dawley rats were divided into nonpregnant ( n = 5), 18 days pregnant ( n = 5), 0 days PP ( n = 7), and 14 days PP ( n = 8). Rats underwent echocardiography under sedation to measure left ventricle (LV) size and function, and Western blots were performed to measure myocardial protein expression of MAPKs (p38, JNK, ERK), Akt, and eNOS. Results: 1) During pregnancy, there was an increase in LV mass (0.62 ± 0.03 to 1.1 ± 0.04 g, P < 0.001), mass/volume ratio (0.7 ± 0.02 to 1.28 ± 0.02 g/ml, P < 0.0001), and ejection fraction (EF) (64 ± 3 to 74 ± 2%). Whereas LV mass and mass/volume ratio returned to prepregnancy values in the PP period, EF remained below normal range (53 ± 3%, P < 0.05). 2) The expression of anti-hypertrophic factors (p38, JNK, Akt) decreased during pregnancy and normalized PP, except JNK, which increased to higher than normal levels. eNOS also increased to higher than baseline levels PP. 3) Activation of p38 and JNK was directly correlated with lower LV mass/volume ratio ( r = −0.81 and −0.71, respectively; P < 0.05). Conclusion: Pregnancy is associated with physiological cardiac hypertrophy. There is rapid reversal of hypertrophy in the PP period while recovery of cardiac function is delayed, possibly related to PP upregulation of JNK. A dysregulation of MAPK signaling may be an important determinant of PP cardiac dysfunction.

Right ventricle in congenital heart disease: is it just a "weaker" left ventricle?

The RV is the dominant ventricle during fetal life. Postnatally, the RV rapidly loses its ability to sustain systemic load. In several forms of congenital heart disease, the RV is the dominant or systemic ventricle. Patients with these lesions often develop progressive RV dysfunction over time. This may be related to differences in morphology, genetic profile and hemodynamic exposure between the LV and RV. This review explores the evolutionary and developmental differences between the LV and RV, the molecular basis of these differences and the potential impact of these differences on long term RV adaptation and function in heart disease.

Simvastatin upregulates coronary vascular endothelial nitric oxide production in conscious dogs

Statin drugs can upregulate endothelial nitric oxide (NO) synthase (eNOS) in isolated endothelial cells independent of lipid-lowering effects. We investigated the effect of short-term simvastatin administration on coronary vascular eNOS and NO production in conscious dogs and canine tissues. Mongrel dogs were instrumented under general anesthesia to measure coronary blood flow (CBF). Simvastatin (20 mg. kg(-1). day(-1)) was administered orally for 2 wk; afterward, resting CBF was found to be higher compared with control (P < 0.05) and veratrine- (activator of reflex cholinergic NO-dependent coronary vasodilation) and ACh-mediated coronary vasodilation were enhanced (P < 0.05). Response to endothelium-independent vasodilators, adenosine and nitroglycerin, was not potentiated. After simvastatin administration, plasma nitrate and nitrite (NO(x)) levels increased from 5.22 +/- 1.2 to 7. 79 +/- 1.3 microM (P < 0.05); baseline and agonist-stimulated NO production in isolated coronary microvessels were augmented (P < 0.05); resting in vivo myocardial oxygen consumption (MVO(2)) decreased from 6.8 +/- 0.6 to 5.9 +/- 0.4 ml/min (P < 0.05); NO-dependent regulation of MVO(2) in response to NO agonists was augmented in isolated myocardial segments (P < 0.05); and eNOS protein increased 29% and eNOS mRNA decreased 50% in aortas and coronary vascular endothelium. Short-term administration of simvastatin in dogs increases coronary endothelial NO production to enhance NO-dependent coronary vasodilation and NO-mediated regulation of MVO(2).

Impaired nitric oxide modulation of myocardial oxygen consumption in genetically cardiomyopathic hamsters

We investigated the role of kinin and nitric oxide (NO) in the modulation of cardiac O(2)consumption in Syrian hamsters with overt heart failure (HF) and age-matched normal hamsters. Using echocardiography, the hamsters with heart failure had reduced ejection fraction [31(+/-8) v 76(+/-5)%] and LV dilation [4.9(+/-0. 2) v 5.7(+/-0.3) mm, both P<0.05 from normal]. O(2)consumption in the left ventricular free wall was measured using a Clark-type O(2)electrode in an air-tight chamber, containing Krebs solution buffered with Hepes (37 degrees C, pH 7.4). Concentration response curves to bradykinin (BK), ramiprilat (RAM), amlodipine (AMLO) and the NO donor, S -nitroso- N -acetyl-penicillamine (SNAP) were performed. Basal myocardial O(2)consumption was lower in the HF group compared to normal [316(+/-21) v 404(+/-36) nmol O(2)/min/g, respectively, P<0.05]. In the hearts from normal hamsters BK (10(-4)mol/l), RAM (10(-4)mol/l), and AMLO (10(-5)mol/l) all significantly reduced myocardial O(2)consumption by 42(+/-6)%, 29(+/-7)% and 27(+/-5)% respectively. This reduction was attenuated in the presence of N -nitro- l -arginine methyl ester (l -NAME) [BK: 3.3(+/-1.5)%, RAM: 3.3(+/-1.2)%, AMLO: 2.3(+/-1.2)%, P<0.05]. Interestingly in the hearts from HF group, BK, RAM and AMLO caused a significantly smaller reduction in myocardial O(2)consumption [10(+/-2)%, 2.5(+/-1.3)%, 6.3(+/-2.3)%, P<0.05]. In contrast, the NO donor SNAP reduced myocardial O(2)consumption in both groups and all those responses were not affected by l -NAME. These data indicate that endogenous NO production through the kinin-dependent mechanism is impaired at end-stage heart failure. The loss of kinin and NO control of mitochondrial respiration may contribute to the pathogenesis of heart failure.

Left ventricular assist device implantation augments nitric oxide dependent control of mitochondrial respiration in failing human hearts

OBJECTIVES

The objective of the study was to evaluate nitric oxide (NO) mediated regulation of mitochondrial respiration after implantation of a mechanical assist device in end-stage heart failure.

BACKGROUND

Ventricular unloading using a left ventricular assist device (LVAD) can improve mitochondrial function in end-stage heart failure. Nitric oxide modulates the activity of the mitochondrial electron transport chain to regulate myocardial oxygen consumption (MVO2).

METHODS

Myocardial oxygen consumption was measured polarographically using a Clark-type oxygen electrode in isolated left ventricular myocardium from 26 explanted failing human hearts obtained at the time of heart transplantation.

RESULTS

The rate of decrease in oxygen concentration was expressed as a percentage of baseline. Results of the highest dose of drug are shown. Decrease in MVO2 was greater in LVAD hearts (n = 8) compared with heart failure controls (n = 18) in response to the following drugs: bradykinin (-34+/-3% vs. -24+/-5%), enalaprilat (-37+/-5% vs. -23+/-5%) and amlodipine (-43+/-13% vs. -16+/-5%; p<0.05 from controls). The decrease in MVO2 in LVAD hearts was not significantly different from controls in response to diltiazem (-22+/-5% in both groups) and exogenous NO donor, nitroglycerin (-33+/-7% vs. -30+/-3%). N(w)-nitro-L-arginine methyl ester, inhibitor of NO synthase, attenuated the response to bradykinin, enalaprilat and amlodipine. Reductions in MVO2 in response to diltiazem and nitroglycerin were not altered by inhibiting NO.

CONCLUSIONS

Chronic LVAD support potentiates endogenous NO-mediated regulation of mitochondrial respiration. Use of medical or surgical interventions that augment NO bioavailability may promote myocardial recovery in end-stage heart failure.

Adenosine and ATP cause nitric oxide-dependent pulmonary vasodilation in fetal lambs

We investigated the hypothesis that the purine nucleotide ATP and its nucleoside adenosine cause pulmonary vasodilation in fetal lambs by the release of nitric oxide (NO). We also investigated the potential role of K(+)(ATP) channels in mediating the effects of ATP and adenosine on NO. We surgically prepared 28 fetal lambs to measure pulmonary and systemic pressures and pulmonary flow. We investigated the effects of glibenclamide and pinacidil (inhibitor and agonist, respectively, for K(+)(ATP) channels), N-nitro-L-arginine (N-LA) and its methyl ester, N-nitro-L-arginine methyl ester (L-NAME) (inhibitors of endothelium-derived NO synthesis), and U46619 (a thromboxane mimetic) on pulmonary vasodilation caused by adenosine and ATP. Adenosine decreased the pulmonary artery pressure and pulmonary vascular resistance (PVR) at doses of 0.08-2.5 microM/kg/min and increased the left pulmonary flow at doses of 0.3-2.5 microM/kg/min in control experiments. N-LA, L-NAME and glibenclamide attenuated the effects of adenosine at doses of < 2.5 microM/ kg/min and pinacidil potentiated its effects. ATP decreased the pulmonary artery pressure and PVR and increased the pulmonary flow at doses of 0.15-2.5 microM/kg/min in control experiments. N-LA and L-NAME attenuated the effects of ATP at doses of < 2.5 microM/kg/min, whereas glibenclamide and pinacidil had no effect on the response to ATP. U46619 increased the basal pulmonary vascular tone, but did not significantly alter the vasodilative responses to ATP and adenosine. In conclusion, adenosine and ATP cause NO-dependent pulmonary vasodilation in fetal lambs. The activation of K(+)(ATP) channels plays a role in adenosine-induced pulmonary vasodilation. The mechanism by which ATP causes NO release and pulmonary vasodilation requires further investigation.

Simvastatin acts synergistically with ACE inhibitors or amlodipine to decrease oxygen consumption in rat hearts

Statin drugs, which are cholesterol-lowering agents, can upregulate endothelial nitric oxide synthase (eNOS) in isolated endothelial cells independent of lipid lowering. We investigated the effect of short-term simvastatin administration on NO-mediated regulation of myocardial oxygen consumption (MV(O2)) in tissue from rat hearts. Male Wistar rats were divided into (a) control group (n = 14), and (b) simvastatin group (n = 10, 20 mg/kg/day by oral gavage). After 2 weeks, left ventricular myocardium was isolated to measure MV(O2) using a Clark-type oxygen electrode, and aortic plasma nitrates and nitrites (NOx) were measured. Baseline plasma NOx levels (19+/-2.6 in control vs. 20+/-2.5 microM/L in simvastatin) and baseline MV(O2) (288+/-23 in control vs. 252+/-11 nmol/g/min; p = 0.09) were not significantly different between the two groups. NO-dependent regulation of MV(O2) in response to bradykinin, ramipril, or amlodipine was augmented in simvastatin rats compared with controls (p < 0.05). Decrease of MV(O2) from baseline in response to highest doses in control versus simvastatin groups was as follows-bradykinin, -28+/-5% vs. -44+/-6%; ramipril, -35+/-5% vs. -50+/-8%; and amlodipine, -32+/-9% vs. -42+/-3%. Response to highest dose of NO donor S-nitroso N-acetyl penicillamine (SNAP) was not significantly different in the two groups (-55+/-5% vs. -52+/-7%). Treatment with Nw-nitro-L-arginine methyl ester, inhibitor of NO synthesis, attenuated the effect of bradykinin, ramipril, and amlodipine on MV(O2) (p < 0.05). In conclusion, short-term administration of simvastatin in rats potentiates the ability of angiotensin-converting enzyme (ACE) inhibitors and amlodipine to cause NO-mediated regulation of MV(O2).

Canine coronary microvessel NO production regulates oxygen consumption in ecNOS knockout mouse heart

We have previously shown that NO production by tissues following stimulation with bradykinin or other agonists can regulate oxygen consumption in skeletal muscle, heart and kidney. From those studies and from those using agonists, which classically release NO from blood vessels and which are unable to regulate tissue oxygen consumption in heart from ecNOS knockout mice, we concluded that vascular NO production is capable of regulating tissue oxygen consumption. The goal of these studies was to directly address the concept that NO production by blood vessels can regulate tissue oxygen consumption using a classical transfer paradigm. Microvessels, capable of producing NO, were prepared from canine hearts using a sieving technique, cardiac tissue was taken from mice lacking the ability to produce NO from ecNOS (ecNOS -/- mice) and tissue oxygen consumption measured in vitro using a Clark type electrode in a sealed chamber. Bradykinin (10(-7)to 10(-4)M) had no effect on tissue oxygen consumption when administered to heart from ecNOS -/mice as expected and no effect on oxygen consumption by isolated canine coronary microvessels (0+/-5% at 10(-5)M). However when coronary microvessels were co-incubated with heart from ecNOS -/- mice, bradykinin caused a dose dependent reduction in tissue oxygen consumption reaching a maximum of 44+/-10% at 10(-4)M. The effects of bradykinin were entirely abolished by L -NAME. The calculated concentration range for NO in these studies was 2.9 to 293 n M, within estimated physiologic range for the activity of NO on cytochrome oxidase. These data indicate that coronary microvessels can regulate cardiac oxygen consumption through a NO dependent mechanism.

Vascular potassium channels mediate oxygen-induced pulmonary vasodilation in fetal lambs

The pulmonary vascular resistance decreases at birth secondary to release of endothelium-derived nitric oxide (EDNO). EDNO release is a calcium-dependent process, and endothelial potassium (K+) channels regulate intracellular calcium flux. We investigated the hypothesis that potassium channels mediate oxygen-induced pulmonary vasodilation and EDNO release in fetal lambs. We instrumented 18 near-term fetal lambs at 122-126 days of gestation to measure pulmonary pressures, flow, and resistance. We studied hemodynamic effects of (1) 100% oxygen; (2) pinacidil, an ATP-sensitive K+ (KATP) channel agonist, and (3) S-nitroso-N-acetylpenicillamine (SNAP), a NO donor. We studied the effects of glybenclamide, a K(ATP) channel antagonist, tetraethylammonium chloride (TEA), a preferential KCa channel antagonist, and nitro-L-arginine (NLA), an NO synthase inhibitor, on the response to some of the above agents. Oxygen-induced pulmonary vasodilation was inhibited by both glybenclamide and TEA, indicating that K(ATP) and K(Ca) channels mediate pulmonary vasodilator response to oxygen. Blocking NO synthesis with NLA inhibited pinacidil-mediated pulmonary vasodilation, indicating that K(ATP) channel activation stimulates NO release. SNAP-mediated pulmonary vasodilation was inhibited by TEA, but not glybenclamide, indicating that K(Ca) channels, but not K(ATP) channels, mediate effects of NO on vascular smooth muscle relaxation. In conclusion, K+ channels mediate oxygen-induced pulmonary vasodilation in fetal lambs. K(ATP) channels appear to mediate EDNO release, while K(Ca) channels probably mediate NO effects on vascular smooth muscle.

Characterization of purine receptors in fetal lamb pulmonary circulation

Activation of P1 purinergic receptors by adenosine and P2 receptors by ATP plays an important role in pulmonary vasodilation that occurs at birth in fetal lambs. Purine receptors occur in several subtypes, and the effects of their stimulation vary with the specific type involved. We characterized the subtypes of P1 receptors in fetal lamb pulmonary circulation at 128-132 d gestation by investigating the effects of the following adenosine analogs: N6-cyclopentyl adenosine (A1 selective), 2-phenylaminoadenosine (A2 selective), 2-p-(2-carboxyethyl)phenethyl-amino-5'-N-ethylcarboxamidoadenosine (A2A selective), N6-benzyl-5'-N-ethylcarboxamidoadenosine (A3 selective), and adenosine and 5'-N-ethylcarboxamidoadenosine (nonselective). We repeated the studies after treatment of animals with A1 antagonist 1,3-dipropyl-8-cyclopentylxanthine or A2 antagonist 1,3-dipropyl-7-methylxanthine. Identification of P2 receptors was done by investigation of the effects of P2x agonist beta,gamma-methylene-L-ATP and P2x and P2y agonist ATP. The studies were repeated after the treatment of animals with P2x antagonist suramin and the P2y antagonist cibacron blue. N6-cyclopentyl adenosine caused a significant decrease in heart rate and did not change pulmonary blood flow or pulmonary vascular resistance (PVR). The effect of N6-cyclopentyl adenosine on heart rate was abolished by 1,3-dipropyl-8-cyclopentylxanthine but not by 1,3-dipropyl-7-methylxanthine. 2-Phenylaminoadenosine, 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine, 5'-N-ethylcarboxamidoadenosine, and adenosine caused significant increases in pulmonary flow and decreases in PVR, and their vasodilator effects were attenuated by the A2 antagonist 1,3-dipropyl-7-methylxanthine and not by 1,3-dipropyl-8-cyclopentylxanthine. N6-benzyl-5'-N-ethylcarboxamidoadenosine did not alter pulmonary flow or PVR. The P2x agonist beta,gamma-methylene-L-ATP caused a decrease in heart rate and had no effect on pulmonary flow and PVR. ATP caused a significant increase in pulmonary flow and decrease in PVR without affecting heart rate. The vasodilator effects of ATP were attenuated by cibacron blue and not by suramin. These data demonstrate that adenosine and ATP cause pulmonary vasodilation by activation of A2A and P2y receptors, respectively, in fetal lambs.

Nitric oxide modulates mitochondrial respiration in failing human heart

Background-Our objective for this study was to investigate whether nitric oxide (NO) modulates tissue respiration in the failing human myocardium. Methods and Results-Left ventricular free wall and right ventricular tissue samples were taken from 14 failing explanted human hearts at the time of transplantation. Tissue oxygen consumption was measured with a Clark-type oxygen electrode in an airtight stirred bath containing Krebs solution buffered with HEPES at 37 degrees C (pH 7.4). Rate of decrease in oxygen concentration was expressed as a percentage of the baseline, and results of the highest dose are indicated. Bradykinin (10(-4) mol/L, -21+/-5%), amlodipine (10(-5) mol/L, -14+/-5%), the ACE inhibitor ramiprilat (10(-4) mol/L, -21+/-2%), and the neutral endopeptidase inhibitor thiorphan (10(-4) mol/L, -16+/-5%) all caused concentration-dependent decreases in tissue oxygen consumption. Responses to bradykinin (-2+/-6%), amlodipine (-2+/-4%), ramiprilat (-5+/-6%), and thiorphan (-4+/-7%) were significantly attenuated after NO synthase blockade with N-nitro-L-arginine methyl ester (10(-4) mol/L; all P<0.05). NO-releasing compounds S-nitroso-N-acetyl-penicillamine (10(-4) mol/L, -34+/-5%) and nitroglycerin (10(-4) mol/L, -21+/-5%), also decreased tissue oxygen consumption in a concentration-dependent manner. However, the reduction in tissue oxygen consumption in response to S-nitroso-N-acetyl-penicillamine (-35+/-7%) or nitroglycerin (-16+/-5%) was not significantly affected by N-nitro-L-arginine methyl ester. Conclusions-These results indicate that the modulation of oxygen consumption by both endogenous and exogenous NO is preserved in the failing human myocardium and that the inhibition of kinin degradation plays an important role in the regulation of mitochondrial respiration.

Amlodipine promotes kinin-mediated nitric oxide production in coronary microvessels of failing human hearts

Recently, we found that amlodipine can release nitric oxide (NO) from canine coronary microvessels, which raises the question of whether amlodipine can also promote coronary NO production in failing human hearts. The goal of this study was to define the effect of amlodipine on NO production in failing human hearts and to determine the role of kinins in the control of NO production induced by amlodipine. Six explanted human hearts with end-stage heart failure were obtained immediately at transplant surgery. Coronary microvessels were isolated as previously described, and nitrite, the stable metabolite of NO in aqueous solution, was measured using the Griess Reaction. Amlodipine (10(-10) to 10(-5) mol/L) significantly increased nitrite production in coronary microvessels in a dose-dependent manner. The increase in nitrite in response to the highest dose of amlodipine (79%) was similar in magnitude to either that of the angiotensin-converting enzyme inhibitor ramiprilat (74%) or the neutral endopeptidase inhibitors phosphoramidon (61%) and thiorphan (72%). Interestingly, the increase in nitrite production induced by amlodipine was entirely abolished by N(omega)-nitro-L-arginine methyl ester and also HOE-140 (a bradykinin-2 antagonist) and dichloroisocoumarin (a serine protease inhibitor that blocks kallikrein activity). These results indicate that amlodipine can promote coronary NO production in failing human hearts and that this effect is dependent on a kinin-mediated mechanism.

Synergy of amlodipine and angiotensin-converting enzyme inhibitors in regulating myocardial oxygen consumption in normal canine and failing human hearts

The production of endogenous nitric oxide, which regulates myocardial oxygen consumption, is decreased in heart failure. As with angiotensin-converting enzyme (ACE) inhibitors, amlodipine, a calcium antagonist, increases kinin-mediated nitric oxide production in coronary microvessels. We investigated the possibility of synergy between ACE inhibitors and amlodipine in regulating myocardial oxygen consumption. Left ventricular myocardium was isolated from 6 healthy dog hearts and 5 human hearts with end-stage heart failure at the time of orthotopic heart transplantation. Myocardial oxygen consumption was measured before and after administration of bradykinin, S-nitroso N-acetyl penicillamine (SNAP, a nitric oxide donor), ramiprilat (an ACE inhibitor), amlodipine, and the combination of a sub-threshold dose of ramiprilat (10(-8) md/L) + amlodipine. These experiments were repeated with L-nitro-arginine methyl ester (L-NAME, an inhibitor of nitric oxide synthesis), dichloroisocoumarin (an inhibitor of kinin synthesis), and HOE 140 (a B2 kinin-receptor antagonist). Baseline myocardial oxygen consumption in canine hearts was 182 +/- 21 nmol/g/min. Bradykinin and SNAP caused dose-dependent reductions in myocardial oxygen consumption (p <0.05). Ramiprilat and amlodipine caused a 10 +/- 3.2% and 11 +/- 0.8% reduction in myocardial oxygen consumption, respectively, when used alone (p <0.05). In the presence of a subthreshold dose of ramiprilat, amlodipine caused a larger (15 +/- 1.7%) reduction in myocardial oxygen consumption compared with either drug used alone (p <0.05). In human hearts, baseline myocardial oxygen consumption was 248 +/- 57 nmol/g/min. Amlodipine caused a larger reduction in myocardial oxygen consumption when used with ramiprilat (22 +/- 3.2%) as compared with amlodipine alone (15 +/- 2.6%). The effect of both drugs was attenuated by L-NAME, dichloroisocoumarin, and HOE 140 (p <0.05). In conclusion, ACE inhibitors and amlodipine act synergistically to regulate myocardial oxygen consumption by modulating kinin-mediated nitric oxide release, and this combination of drugs may be useful in the treatment of heart failure.

Comparative left ventricular function following atrial, septal, and apical single chamber heart pacing in the young

Ventricular pacing, typically initiated from a RV apical electrode, inherently causes abnormal biventricular activation, decrease LV function, and causes histopathological changes. Since pacing initiated in childhood can be expected to have a more protracted course compared with the adult, the consequences of this alteration in LV hemodynamics gain added significance among the young pacemaker recipient. The purpose of this study was to evaluate the potential of improving paced LV function by a septal electrode implant site. Acute alterations in cardiac index, LV pressure, and contraction indices, including dP/dt, Vmax, and Vpm, were compared among 22 patients (median age 10 years) with normal cardiac anatomy during intracardiac electrophysiological studies. LV hemodynamics were measured during intrinsic rhythms and following 15 minutes of atrial, RV apical, and septal pacing at an appropriate exercise rate for age of 150 ppm. Results showed a significant decrease in LV dP/dt, Vmax, and Vpm, and increase in LV end-diastolic pressure only with apical pacing. Septal pacing, in spite of loss of any atrial contribution to ventricular filling, maintained comparable indices with intrinsic and atrial paced rhythms. This study demonstrates that normalized LV function is maintained by septal and deteriorates with apical pacing acutely among young, nonischemic hearts. Continued evaluation of appropriate pacing electrode designs to permit septal implant is needed to ensure optimal chronically paced LV function.

Purine nucleotides contribute to pulmonary vasodilation caused by birth-related stimuli in the ovine fetus

We investigated the hypothesis that the purine nucleotides ATP and adenosine mediate the pulmonary vasodilation that occurs at birth in fetal lambs. We instrumented 44 fetal lambs to measure left pulmonary arterial pressure and flow. In control studies, we investigated the effects of sequential ventilation with 10, 50, and 100% O2 on fetal pulmonary arterial pressure and flow and pulmonary vascular resistance (PVR). We also measured the blood and plasma ATP levels in the pulmonary artery and left atrium in the control studies. In three separate groups of studies, we investigated the effects of 8-phenyltheophylline, an adenosine-receptor antagonist, and cibacron blue, an inhibitor of ATP-sensitive P2y receptors, given alone or in combination, on the response of PVR to sequential ventilation. Fetal arterial PO2 increased during ventilation with 50 and 100% O2 but not with 10% O2. Ventilation with 10% O2 caused a 4-fold increase in pulmonary blood flow and a 10-fold decrease in PVR. Ventilation with 50 and 100% O2 caused a 7-fold increase in pulmonary blood flow and a 20-fold decrease in PVR. Blood and plasma ATP levels in the pulmonary artery and blood ATP levels in the left atrium increased significantly during ventilation with 50 and 100% O2 but not with 10% O2. Pretreatment of animals with 8-phenyltheophylline attenuated the increase in pulmonary flow and decrease in PVR caused by ventilation at all fractions of inspired O2 (FIO2 levels). Pretreatment of animals with cibacron blue attenuated pulmonary vasodilation at 50 and 100% FIO2. Combined treatment with 8-phenyltheophylline and cibacron blue caused complete inhibition of the decrease in PVR in response to ventilation at the three FIO2 levels. Incubation of fetal red blood cells in vitro with 100% O2 caused an increase in ATP production. An increase in arterial PO2 in the fetus causes an increase in blood ATP levels, and an inhibition of ATP receptors attenuates the O2-induced decrease in PVR. Adenosine-receptor inhibition attenuates both ventilation- and O2-induced changes in PVR. Increased synthesis and release of ATP plays a major role in causing pulmonary vasodilation in response to birth-related stimuli in the ovine fetus.