Lest we forget: Early Canadian contributions to the care of children with congenital heart malformations.

In a century of remarkable progress in medicine, one of the outstanding stories is the development of successful treatment of congenital heart malformations. This achievement is the outcome of the ideas and research of many people. Many of the early 'transforming' advances originated in Canada. Maude Abbott catalogued and classified heart malformations in a clinically meaningful manner. Arthur Charles and David Scott in Toronto, Ontario, produced a clinically useful heparin preparation, and the studies of Bill Bigelow led to the application of hypothermia in cardiac surgery. John Keith and Bill Mustard at Toronto's Hospital for Sick Children, and Arnold Johnson and Tony Dobell at the Montreal Children's Hospital, Montreal, Quebec, established the first Canadian programs devoted to the correction of congenital heart defects in childhood. Mustard devised the first widely successful operation for transposition of the great arteries. Flavio Coceani and Peter Olley discovered the role of prostaglandin E in the ductus arteriosus, and applied that knowledge clinically. The turn of the century is an appropriate time to celebrate these Canadian successes.

Voltage-gated potassium channels in human ductus arteriosus.

We studied tone in the human ductus arteriosus and show that the constriction to oxygen is due to inhibition of voltage-gated potassium channels and, in the acute phase, is independent of endothelin-1.

Persistent pulmonary hypertension of the newborn presenting as the primary manifestation of intracranial arteriovenous malformation of the Vein of Galen.

Arteriovenous malformations of the Vein of Galen continue to present diagnostic and therapeutic challenges in the neonatal period. Approximately 40-50% of all malformations of the Vein of Galen present in the neonatal period, usually with congestive heart failure. These neonates represent the most severe cases and are also the most difficult to manage. We report a case of a neonate with a Vein of Galen Malformation who presented with cyanosis, a cardiac murmur, and severe persistent pulmonary hypertension of the newborn. Cardiac failure developed later in the patient's course. The degree of pulmonary hypertension on echocardiography was used to time endovascular embolization of the Vein of Galen Malformation. Following embolization, his pulmonary hypertension subsided dramatically. We speculate that pulmonary hypertension associated with Vein of Galen Malformations has been underestimated in the morbidity and demise of these neonates, and should be more aggressively monitored and treated.

Response of fetal rabbit ductus arteriosus to bradykinin: role of nitric oxide, prostaglandins, and bradykinin receptors.

Nitric oxide plays a major role in vascular tone control. Increased blood levels of bradykinin (BK), which stimulates nitric oxide biosynthesis, occur at birth. BK effects on ductus arteriosus (DA) tone were investigated in fetal rabbit under fetal (2.5% O2 "low PO2") and neonatal (30% O2 "high PO2") conditions using in vitro isometric tension studies. Intact and endothelium-denuded DA, contracted with norepinephrine (ED75-90), showed a biphasic response to BK, with relaxation at 10(-9) to 10(-7) M BK and contraction at 10(-6) to 10(-5) M BK. BK (10(-6) to 10(-5) M) contracted intact DA from baseline tension, with greater contraction under high PO2. The B2-receptor antagonist D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe-140, 10(-7) M) abolished relaxation, but not contraction, to BK in intact and denuded DA. The B1-receptor antagonist des-Arg9-[Leu5]-BK (10(-7) M) reduced BK-induced contraction but not relaxation in intact DA only. Nitric oxide synthase inhibitors, N(omega)-nitro-L-arginine methyl ester (10(-4) M) and N(omega)-monomethyl-L-arginine (10(-4) M) partially inhibited relaxation to BK in intact DA, with L-arginine (3 x 10(-4) M) reversing N(omega)-monomethyl-L-arginine inhibition. N(omega)-nitro-L-arginine methyl ester (10(-4) M) caused a small but significant inhibition of relaxation to BK in denuded DA. Indomethacin (2.8 x 10(-6) M), a cyclooxygenase inhibitor, abolished relaxation but not contraction to BK in intact and denuded DA. BK-induced relaxation of the DA acts through B2-receptors, releasing both nitric oxide and prostaglandins, whereas endothelial B1-receptors may mediate contraction. BK action on isolated DA changes from relaxation to contraction as its concentration increases, with greater contraction at neonatal PO2. Thus increased BK levels at birth may aid functional closure of the DA.

Congenital heart disease: six decades of progress.

Congenital heart malformations occur in approximately 1 in 100 live births. Since Robert Gross successfully ligated a persistent ductus arteriosus 60 years ago, there has been enormous progress in the surgical management of even the most complex lesions. More recently, the interventional cardiologist armed with balloons, stents, coils, umbrellas, and laser beams is providing an alternative to surgery for many lesions. Echocardiography combined with Doppler studies is now the most informative diagnostic modality, and its usefulness is being expanded by transesophageal studies. Magnetic resonance imaging is helpful for some lesions not well visualized on echo. Some complex lesions continue to challenge caregivers, especially the hypoplastic left heart syndrome and several variants of pulmonary atresia. Neurological complications in patients with congenital heart disease are not uncommon and are the main theme of this issue.

Expression of cyclooxygenases in ductus arteriosus of fetal and newborn pigs.

OBJECTIVE: We studied the ontogeny of the expression of cyclooxygenase-1 and cyclooxygenase-2 in the ductus arteriosus and evaluated their functional significance. STUDY DESIGN: The expression of cyclooxygenase-1 and cyclooxygenase-2 was studied in ductus arteriosus of fetal (at approximately 75% gestation) and term newborn pig. Effects of selective inhibitors of cyclooxygenase-1 and cyclooxygenase-2 on ductal patency were evaluated by Doppler ultrasonography. RESULTS: Ductus arteriosus of the fetus expressed virtually only cyclooxygenase-1 immunoreactive protein and activity. In contrast, the ductus of the term newborn pig (<45 minutes old) contained proteins of both cyclooxygenase-1 and cyclooxygenase-2, but the latter contributed to >90% of prostaglandin E2 formation. The selective cyclooxygenase-2 inhibitor DuP697 reduced prostaglandin E2 levels in the ductus arteriosus, albeit not in plasma, but did not affect ductal patency in the newborn pig (<1(1/2) hours old); in contrast, the cyclooxygenase-1 inhibitor valeryl salicylate, like indomethacin, markedly reduced levels of prostaglandin E2 in the plasma and ductus arteriosus and caused significant constriction of the ductus arteriosus. CONCLUSION: The ductus arteriosus of the term newborn pig, in contrast to that of the fetus, expresses cyclooxygenase-2, but circulating prostaglandins, arising mostly from cyclooxygenase-1, seem to exert the major control on ductal patency in vivo. Our data suggest that cyclooxygenase-2 inhibitors might be better alternatives for the fetus than nonselective cyclooxygenase blockers if indicated for maternal conditions such as inflammation or for tocolysis.

Evaluation of the Heart and Stroke Foundation of Canada Research Scholarship Program: research productivity and impact.

OBJECTIVE: To compare the research productivity, and its impact, of individuals awarded research scholarships from the Heart and Stroke Foundation of Canada (HSFC) with that of a parallel group of unsuccessful applicants during the funding years 1980/81 to 1989/90 inclusive. Research productivity was defined as the number of peer reviewed publications, and impact was evaluated from the number of publications cited; the number of citations per publication; the number of citations per individual; and the impact score. STUDY SELECTION: Data were collected on 192 individuals. Cohorts were defined as successful and unsuccessful individuals entering the system in the same year. The study comprised 10 separate cohorts. Data were collected on yearly publications and citation counts for each individual. These data, along with journal impact factors, were obtained from the Institute for Scientific Information. CONCLUSIONS: During the 10 years of the study, individuals funded by the HSFC published more papers, more of their papers were cited, and they received more citations per individual than the unfunded comparison group. This consistency in multiple indicators provides strong evidence that funded individuals are more productive and that their work has a greater impact on the body of knowledge in this area. Although this study cannot unequivocally show a direct causal relation between funding and research success, the trend as shown by the indicators studied suggests a beneficial effect.

Basic research: a continuing imperative for clinical practice.

Basic biomedical research is essential to progress in prevention and treatment of disease and often results in massive economic benefits to society. Despite this, the financial and institutional bases that support basic scientists is under threat in our rapidly changing society. Polio vaccination is cited as an outstanding example of both an unexpected outcome of basic research and an enormous economic return to society on the original research investment. Interventional catheterization and the potential of successful gene therapy for cystic fibrosis are further examples of great potential economics benefits flowing from fundamental research. One great impediment to adequate investment in basic research is the lack of understanding of its nature. Canadian scientists need to be much more active in bridging the cultural gap between science and society and especially in educating national policy makers about the major economic benefits resulting from previous investments in basic biomedical research.

Pharmacokinetic-pharmacodynamic modelling for captopril in healthy anaesthetized piglets.

The use of the angiotensin converting enzyme inhibitor, captopril, specially in children, has been empirical. This is because the relationship between the pharmacokinetics and pharmacodynamics of captopril has not been clearly defined. It is not usually feasible to obtain the serial kinetic-dynamic data necessary to study this relationship in infants. The piglet was therefore investigated as an animal model in which to study the relationship between the kinetics and dynamics of captopril. The standard pharmacokinetic parameters for captopril in healthy anaesthetized piglets were found to be within the range reported for humans. ClTB was estimated to be 1.42 +/- 0.33 L h-1 kg(-1); t1/2 was 0.44 +/- 0.08 h; Vdss was calculated to be 0.64 +/- 0.13 L kg(-1); t1/2 and AUC0-infinity was estimated to be 145 +/- 27 ng h mL(-1). The observed haemodynamic response was qualitatively similar to that in humans. Aortic pressure was reduced by 42 +/- 18%; heart rate was reduced by 21 +/- 11%. A parametric pharmacokinetic (two-compartment)-pharmacodynamic (linear) model has been established to describe plasma captopril concentration and aortic pressure relationship. Based on the observed results, the piglet was considered to be a viable model for our purpose.

Synergism between prostaglandin E2 and isoproterenol in stimulating glucose oxidation in the heart.

The increase in cardiac contractile function following adrenergic stimulation is accompanied by increased glucose metabolism. Since prostaglandin E2 (PGE2) can internalize beta-receptors, we determined what effects PGE2 and isoproterenol have on glycolysis and glucose oxidation in the isolated working rat heart. All hearts were perfused with Krebs-Henseleit buffer containing 11 mM [5-3H, 14C(U)]glucose, 100 microU/mL insulin, and 3% albumin. In the presence of 0.4 mM palmitate and 1.25 mM free Ca2+, isoproterenol (3 x 10(-8) M) increased the heart rate x peak systolic pressure product from 27 +/- 1 to 43 +/- 1 mmHg.beats.min-1.10(3) (1 mmHg = 133.3 Pa). This was accompanied by an increase in glycolytic rates from 3564 +/- 231 to 7775 +/- 475 nmol.g-1 dry weight min-1 and an increase in glucose oxidation from 930 +/- 72 to 2591 +/- 239 nmol.g-1 dry weight.min-1. Addition of PGE2 (10(-9) M) did not affect the isoproterenol stimulation of glycolysis, but caused a further increase in glucose oxidation (to 3863 +/- 495 nmol.g-1 dry weight.min-1). In the absence of isoproterenol, 10(-9) M PGE2 had no effect on either glycolysis or glucose oxidation. When perfusate [Ca2+] was raised to 2.5 mM, a significant increase in glycolysis was seen in control hearts (from 3564 +/- 231 to 5679 +/- 374 nmol.g-1 dry weight.min-1). The effects of isoproterenol and PGE2 on glucose metabolism remained, although the synergistic effects of PGE2 on glucose oxidation were less dramatic. When 1.2 mM palmitate was present in hearts perfused with 2.5 mM Ca2+, a decrease was seen in both glycolysis (from 5679 +/- 374 to 3027 +/- 346 nmol.g-1 dry weight.min-1) and glucose oxidation (from 1056 +/- 170 to 221 +/- 29 nmol.g-1 dry weight.min-1). Even at this high concentration of fatty acid, isoproterenol stimulated glucose oxidation (from 221 +/- 29 to 859 +/- 69 nmol.g-1 dry weight min-1), and addition of PGE2 resulted in a significant further increase (1021 +/- 139 nmol.g-1 dry weight.min-1). These data demonstrate that concentrations of PGE2 that bind to the high affinity cardiac PGE2 receptor have no effect on glucose metabolism in the absence of beta-agonists. In the presence of isoproterenol, which dramatically stimulates both glycolysis and glucose oxidation, PGE2 has a synergistic effect on glucose oxidation at lower fatty acid concentrations. These findings suggest that PGE2 receptors in the heart function to potentiate rather than decrease beta-adrenergic stimulation of glucose metabolism.

The role of nitric oxide in cardiac depression induced by interleukin-1 beta and tumour necrosis factor-alpha.

1. Myocardial dysfunction during septic shock is associated with enhanced production of cytokines such as interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha (TNF-alpha). These cytokines depress cardiac mechanical function by a mechanism which is not well defined. 2. Bacterial endotoxin or cytokines cause the expression of Ca(2+)-independent nitric oxide (NO) synthase in cardiac myocytes, vascular endothelial cells and endocardial endothelial cells, causing enhanced production of NO. As NO has negative inotropic actions on cardiac muscle, we tested the sum effects of IL-1 beta plus TNF-alpha in the intact heart to determine whether enhanced expression of NO synthase activity in the cells that comprise the heart is involved in cardiac depression associated with cytokine stimulation. 3. Rat isolated working hearts perfused with IL-1 beta plus TNF-alpha showed a markedly greater depression in contractile function, measured as cardiac work, after 2 h of perfusion compared with time-matched control hearts. The depressant action of IL-1 beta plus TNF-alpha was first apparent after 1 h of perfusion; no early (15 min) cardiac depressant actions were seen. 4. The competitive inhibitor of Ca(2+)-dependent and Ca(2+)-independent NO synthases, NG-nitro-L-arginine methyl ester (L-NAME, 3 microM) when given concurrently with IL-1 beta plus TNF-alpha prevented the loss in contractile function such that these hearts after 2 h of perfusion had similar function to time-matched controls. L-NAME did not acutely reverse the loss of contractile function in hearts exposed for 2 h to IL-1 beta plus TNF-alpha. The protective action of L-NAME in the presence of cytokines was concentration-dependent and was not seen at a higher concentration (10 micro M) due to the significant reduction in coronary flow observed at this concentration.5. In contrast, when L-NAME (3 micro M) was given in the absence of IL-l beta plus TNF-alpha it depressed contractile function over the 2 h perfusion period by significantly reducing coronary flow.6. Inhibition of protein synthesis with cycloheximide (Cx) abolished the loss in function that occurred over 2h in both control and IL-1 beta plus TNF-a-treated hearts.7. Inducible, Ca2+-independent NO synthase activity was not observed in freshly isolated hearts but was observed in control hearts perfused for 2 h in vitro and was doubled in hearts perfused with IL-1 beta plus TNF-a. Cx prevented the expression of Ca2+-independent NO synthase in both control and cytokine-treated hearts.8. In summary, these results suggest that the depression of myocardial function by IL-l beta plus TNF-alpha is mediated, at least in part, by induction of Ca2+-independent NO synthase activity in the heart.

Plasma fatty acid levels in infants and adults after myocardial ischemia.

High levels of fatty acids are detrimental during reperfusion of ischemic hearts in part because of an inhibition of myocardial glucose use. We therefore measured plasma fatty acids during and after myocardial ischemia in both adult and pediatric patients. In adult patients undergoing thrombolytic therapy after an acute myocardial infarction, plasma fatty acids levels were elevated on admission to hospital (0.96 +/- 0.06 vs 0.40 +/- 0.01 mmol/L in healthy control subjects) and remained elevated throughout the initial 48 hours of hospitalization. In adult patients undergoing cardiac surgery, plasma fatty acids were markedly increased during surgery and at the time of the release of the aortic cross clamp (2.21 +/- 0.54 and 1.61 +/- 0.32 mmol/L, respectively). In children and infants (mean age 4.33 +/- 0.44 years) who had surgery to correct congenital heart defects, fatty acid levels during surgery increased to 3.27 +/- 0.26 mmol/L and remained elevated during immediate reperfusion (1.91 +/- 0.15 mmol/L) and for 24 hours after surgery (1.67 +/- 0.22 mmol/L). Because experimental studies have shown that high levels of fatty acids are detrimental to recovery of adult animal hearts, we determined the effect of high fatty acid levels on reperfusion recovery of isolated working hearts from 1-day-old rabbits perfused with 0.4 mmol/L palmitate (normal fat) or 1.2 mmol/L palmitate (high fat) and subjected to 50 minutes of global ischemia followed by aerobic reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of myocardial plasmalogen and diacyl phospholipids and their arachidonic acid content using high-performance liquid chromatography.

A high-performance liquid chromatographic method for the assay of diacyl and plasmalogen (alk-1-enyl) phospholipid content and the determination of their fatty acid content from tissue homogenates is described. Myocardial phospholipids are rich in plasmalogens and have a high content of unsaturated fatty acids, including arachidonic acid, esterified in the sn-2 position. Using a three-stage HPLC assay we have analyzed the phospholipid subclass content and the amount of arachidonic acid esterified to these fractions extracted from isolated perfused rat hearts. After HPLC separation of total myocardial phospholipids, the phosphatidylcholine and phosphatidylethanolamine peak fractions are treated with phospholipase C to remove polar head groups and ultraviolet-absorbing benzoate derivatives are made. Separation and quantification of diacyl and plasmalogen content of the total phospholipids with nanomolar sensitivity is then achieved using isocratic elution with a silicic acid HPLC column. The separated plasmalogen and diacyl glycerobenzoates are then subjected to alkaline hydrolysis to remove fatty acids from the sn-2 position. The 2-(2,3-napthalimino)ethyltrifluoromethanesulfonate esters of the free fatty acids are then prepared and analyzed with subnanomolar sensitivity using reverse-phase chromatography with gradient elution. As plasmalogen-specific phospholipase A2 is activated during myocardial ischemia and comprises the majority of total phospholipase A2 activity in the heart, this methodology allows for a sensitive and complete determination of the changes in the mass of these phospholipids and their arachidonic acid content.

Solubilization and purification of the prostaglandin E2 receptor from cardiac sarcolemma.

A prostaglandin E2 (PGE2) receptor was solubilized and isolated from cardiac sarcolemma membranes. Its binding characteristics are almost identical to those of the membrane bound receptor. [3H]PGE2 binding to solubilized and membrane bound receptor was sensitive to elevated temperature and no binding was observed in the absence of NaCl. No significant effects of DTT, ATP, Mg2+, Ca2+ or of changes in buffer pH were observed on [3H]PGE2 binding to either solubilized or membrane-bound receptor. Unlabelled PGE1 displaced over 90% of [3H]PGE2 from the CHAPS-solubilized receptor. PGD2, PGI2, PGF2 alpha and 6-keto-PGF1 alpha were not effective in displacing [3H]PGE2 from the receptor. Scatchard analysis of [3H]PGE2 binding to CHAPS-solubilized receptor revealed the presence of two types of PGE2 binding sites with Kd of 0.33 +/- 0.05 nM and 3.00 +/- 0.27 nM and Bmax of 0.5 +/- 0.04 and 2.0 +/- 0.1 pmol/mg of protein. The functional PGE2 receptor was isolated from CHAPS-solubilized SL membrane using two independent methods: first by a WGA-Sepharose chromatography and second by sucrose gradient density centrifugation. Receptor isolated by these two methods bound [3H]PGE2. Unlabelled PGE1 and PGE2 displaced [3H]PGE2 from the purified receptor. Scatchard analysis of [3H]PGE2 binding to purified receptor revealed the presence of the two binding sites as observed for the membrane bound and CHAPS-solubilized receptor. SDS-polyacrylamide gel electrophoresis of the purified receptor fractions revealed the presence of a protein band of M(r) of approx. 100,000. This 100-kDa was photolabelled with [3H]azido-PGE2, a photoactive derivative of PGE2. We propose that this 100-kDa protein is a cardiac PGE2 receptor.