J Thorac Cardiovasc Surg 2001;122:180-1

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.

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.

Denopamine is an orally active beta 1 agonist whose cardiovascular action in the newborn is unknown. We evaluated its circulatory effects during normoxia in newborn piglets less than 7 days of age. The piglets were acutely instrumented under general anesthesia with an electromagnetic flow probe around the main pulmonary artery and catheters in the main pulmonary artery, aorta, left ventricle, and the right and left atria. A Millar high-fidelity catheter was used to measure left ventricular dp/dt. The ductus arteriosus was ligated. Denopamine was administered in the right atrium as a continuous infusion of 2, 4, and 8 micrograms/kg per min for 10 min each. Although cardiac index, heart rate and left ventricular dp/dt increased dose-dependently by 46.0 +/- 18.2%, 87.1 +/- 34.9% and 159.9 +/- 42.4%, respectively, stroke index was not significantly altered. Unlike pulmonary artery pressure (which increased dose-dependently), aortic pressure increased with 2 and 4 micrograms/kg per min denopamine, respectively, it fell with 8 micrograms/kg per min denopamine. Similarly, the systemic vascular resistance decreased with the high dose (8 micrograms/kg per min). There was no significant change in pulmonary vascular resistance. Denopamine is potently inotropic in the adult. However, its circulatory effect in the neonate is dependent on its chronotropic action. Furthermore, denopamine is a systemic vasodilator at high doses in the neonatal circulation.

Three modified procedures for the separation of cardiac myosin light chains are carefully compared. Ion-exchange chromatography gives a purified cardiac myosin light chain 1, whereas light chain 2 is always contaminated by light chain 1. Reversed-phase high-performance liquid chromatography gives the best resolution of these light chains and needs only 20 min for each run. However, it requires pure preparation of myosin light chains before separation. Isoelectric precipitation is the simplest procedure and suitable for large quantities of material. Although it gives the highest yield the separation is not adequate. A modified and rapid procedure for the isolation of cardiac and skeletal total myosin light chains is also presented.

We have recently shown that a cytochrome P-450-based mechanism is important for the generation of contractile tension by the ductus arteriosus and have now examined whether the same mechanism operates in the ductus venosus. Carbon monoxide (CO/O2 ratio, 0.27) and cytochrome P-450 inhibitors [metyrapone; 4-phenylimidazole; 14-isocyano, 15-(methoxymethyleneoxy)-5Z,8Z,11Z- eicosatrienoic acid; alpha-naphthoflavone] were tested in vitro on the ductus venosus sphincter from mature fetal lambs. Each preparation was precontracted with indomethacin (2.8 x 10(-6) M). Carbon monoxide completely relaxed the ductus, and its action was reversed by illumination with monochromatic light. Peak photocontraction occurred at 450 nm. With the exception of alpha-naphthoflavone, all cytochrome P-450 inhibitors were also relaxant agents. Alpha-naphthoflavone (the sole type I inhibitor tested) produced instead a modest contraction that was often transient. Relaxation brought about by both carbon monoxide and drugs was fully reversed by the thromboxane A2 analog 9,11-epithio-11,12-methano-thromboxane A2 and by excess potassium (55 mM). Carbon monoxide was equally effective in the intact ductus and the ductus denuded of endothelium, whereas cytochrome P-450 inhibitors were marginally less effective in the latter preparation. These findings indicate that the ductus venosus sphincter, like the ductus arteriosus, relies on an intramural cytochrome P-450 mechanism to develop its contractile tone. The actual constrictor remains to be characterized in both vessels.

In a conscious newborn piglet model, exogenous leukotriene D4 was found to be a potent pulmonary and systemic vasoconstrictor with significant left ventricular depressant effect. The pulmonary pressor effect was seen only in the arterioles and not the veins. In hypoxia the pulmonary response was less. The findings were similar to that in lambs. The role of leukotrienes in hypoxic pulmonary vasoconstriction and the foetal pulmonary circulation needs further elucidation.

Angiotensin II, a vasoconstrictor, has been previously demonstrated to produce a secondary vasodilatation due to release of prostaglandins. Because of this effect, we investigated whether infusion of exogenous angiotensin II via miniosmopumps in rats during a 1-wk exposure to chronic hypobaric hypoxia might prevent pulmonary hypertension, right ventricular hypertrophy, and vascular changes. We instrumented the rats with indwelling cardiovascular catheters and compared the hemo-dynamic and structural response in animals given angiotensin II, indomethacin in addition to angiotensin II (to block prostaglandin production), or saline with or without indomethacin. We then determined whether angiotensin II infusion also prevents acute hypoxic pulmonary vasoconstriction. We observed that exogenous angiotensin II infusion abolished the rise in pulmonary artery pressure, the right ventricular hypertrophy, and the vascular changes induced during chronic hypoxia in control saline-infused rats with or without indomethacin. The protective effect of angiotensin II was lost when indomethacin was given to block prostaglandin synthesis. During acute hypoxia, both angiotensin II and prostacyclin infusions similarly prevented the rise in pulmonary artery pressure observed in saline-infused rats and in rats given indomethacin or saralasin in addition to angiotensin II. Thus exogenous angiotensin II infusion prevents chronic hypoxic pulmonary hypertension, associated right ventricular hypertrophy, and vascular changes and blocks acute hypoxic pulmonary hypertension, and this is likely related to its ability to release vasodilator prostaglandins.

The ductus arteriosus (DA) is kept open during fetal development by the continuous relaxant effects of prostaglandins (PG), primarily E2. Although this PGE2 is probably intramurally produced. a subsidiary role for blood-borne PGE2 and PGI2 is not excluded. PGE2 synthetic activity develops early in the developing ductus and is greater in immature than in mature tissues. Ductus sensitivity to PGE2 is greatly diminished after exposure to oxygen. Arachidonic acid (the precursor of PGE2) may inactivates cytochrome P-450, completely reverses the contractile tension of the DA at both low (4 to 12 torr) and high (511 to 712 torr) oxygen tension and is equally effective in the presence and absence of indomethacin. Carbon monoxide-induced relaxation occurs with a PCO/PO2 ratio of 0.27 and is reversed by white light and by monochromatic light with maximal reversal seen at 450 nm wavelength. Both these findings favor involvement of a cytochrome P-450. Metyrapone and phenylimidazole, chemical inhibitors of cytochrome P-450, also relax the ductus. These findings suggest that ductus tone is controlled through the opposing activities of cyclooxygenase and monooxygenase products of AA. The former predominate in the fetus, and the latter at birth when they induce closure/

In patients with pulmonary hypertension associated with congenital heart defects, ultrastructural abnormalities are observed in endothelial cells, which suggest heightened metabolic function. If endothelial production of the von Willebrand factor (vWF) is increased, this may be associated with abnormal interactions with platelets leading to worsening of the pulmonary hypertension. We therefore evaluated vWF in 30 patients with pulmonary hypertension (25 with congenital heart defects) and in 30 individuals with normal pulmonary arterial pressure (12 with congenital heart defects). We measured the antigenic (vWF: Ag) and biologic (VWF: rist) activity of vWF in plasma and assessed endothelial vWF: Ag directly by an immunoperoxidase stain applied to lung biopsy tissue. Because of considerable variance and small size, the group of five patients with pulmonary hypertension and without congenital heart defects were excluded from statistical analyses. Patients with pulmonary hypertension and congenital heart defects had significant higher vWF: Ag levels than individuals with normal pulmonary arterial pressure without congenital heart defects (p less than .05), whereas values in those with normal pressure and congenital heart defects were intermediate. In lung biopsy tissue available from 29 patients in this study and from 11 others we previously reported, immunostain of pulmonary arterial endothelium for vWF was intense (suggesting increased production) in 29 of 32 with pulmonary hypertension and congenital heart defects and in only one of eight with normal pulmonary arterial pressure and congenital heart defects (p less than .01). Only three patients with congenital heart defects and pulmonary hypertension and increased vWF: Ag, however, had increased vWF: rist. Compatible with this discrepancy was a loss of vWF high-molecular weight forms as determined by both crossed immunoelectrophoresis and multimeric analysis. Our results suggest that increased vWF in most patients with congenital heart defects and pulmonary hypertension is associated with increased production of a biologically deficient molecule lacking high-molecular weight forms.

Persistent fetal circulation may be primary or secondary to other causes. Apart from treating the underlying cause, its management may include ventilatory support and the use of vasodilators, whose value may be limited by marked systemic hypotension. Milrinone is a new cardiotonic agent with smooth muscle-relaxant properties. Unlike its predecessor amrinone, milrinone is less likely to be limited by tachyphylaxis. We evaluated the effect of Milrinone on the neonatal pulmonary circulation in conscious newborn lambs; in particular, on the pulmonary arteriolar constrictor effect of leukotriene D4 (LTD4) during normoxia and hypoxia.

The atrial and ventricular myosin light chains of human, monkey and sheep hearts were compared by dodecylsulfate polyacrylamide gel electrophoresis. The atrial light chain 2 and ventricular light chain 2 are similar among these mammals. However, the atrial light chain 1 of monkey has different electrophoretic mobility from those of human and sheep. The monkey ventricular light chain 1 has same mobility as that of sheep but different from that of human.

The prostaglandin (PG) endoperoxide, PGH2, and the thromboxane (TX) A2 analog, 9,11-epithio-11,12-methano-TXA2, were tested in vitro on the ductus venosus sphincter from fetal (premature and mature) and neonatal (1-day-old) lambs. PGH2 relaxed the indomethacin-contracted fetal ductus in a dose-dependent manner and its action was reduced after treatment with 15-hydroperoxyarachidonic acid. In contrast, reduced glutathione did not affect the PGH2 relaxation in the indomethacin-treated ductus, nor did it modify the response of the untreated ductus to constrictor stimuli. Unlike PGH2, the stable 9 alpha,11 alpha-epoxymethano-PGH2 analog contracted the vessel. Similarly, the TXA2 analog was a contractile agent, its action exceeding that of the PGH2 analog in potency and efficacy. The TXA2 analog was active on preparations from both premature (minimum 117 days gestation) and mature lambs, but a maximal effect was attained during the perinatal period. These results confirm the existence of a PG-mediated relaxing mechanism in the ductus venosus and suggest that the active compound is PGI2. This mechanism is likely responsible for keeping the ductus patent in the fetus. TXA2, formed within the liver parenchyma, is well suited for playing a role in postnatal closure of the vessel.

The myosin light chain composition of sheep interatrial and interventricular septa were analysed by one- and two-dimensional polyacrylamide gel. The interventricular septum has myosin light chain composition indistinguishable from that of ventricular myosin. Myosin from the interatrial septum contains three light chains, two of which co-migrated with the two atrial light chains (ALC1 and ALC2), while the third co-migrated with ventricular light chain 2 (VLC2). ALC1 are more abundant than ALC2 or VLC2 suggesting a mixed myosin population. Myosin with ALC1 and VLC2 light chain composition may be present, and its possible relationship with cardiac "conducting" cells is discussed.