METABOLISM OF VASOMOTOR AGENTS BY THE ISOLATED PERFUSED LUNG

Hemodynamic advantage of left atrial epinephrine administration after cardiac operations

Cardiac surgical patients frequently require catecholamines, typically administered via the central venous circulation. Potential disadvantages of this route of administration include catecholamine metabolism by the pulmonary vascular bed before gaining access to the heart and pulmonary vasoconstriction producing increased pulmonary vascular resistance. We therefore prospectively compared administration of epinephrine via the left atrium versus central venous administration of epinephrine with particular interest in cardiac output, mean pulmonary artery pressure, and pulmonary vascular resistance. Fifteen consecutive aortocoronary bypass patients were studied after cardiopulmonary bypass. Epinephrine (mean dose, 0.07 +/- 0.02 micrograms.kg-1.min-1) was administered via the central venous route, then via the left atrium, then via the central venous route again. Hemodynamic data were collected 10 minutes after changing the route of administration. Left atrial administration of epinephrine produced a 35% greater cardiac output, 25% lower pulmonary artery pressure, and 32% lower pulmonary vascular resistance when compared with central venous administration (all significant; p < 0.05). Left atrial epinephrine administration may offer hemodynamic advantage in cardiac surgical patients in whom central venous administration does not produce an adequate cardiac output or in patients with pulmonary hypertension to avoid any further increase in pulmonary vascular resistance.

Pulmonary inactivation of vasopressors following cardiac operations

Vasoactive drugs were infused through catheters in the right atrium and then the left atrium of 34 patients who required either vasopressor or vasodilator support following cardiac operation to determine if the route of infusion affected the aortic blood concentration of these agents. Drugs were given through the right atrium for one hour and then the left atrium for an hour. Both central aortic and pulmonary arterial blood were assayed for drug concentrations, and hemodynamic measurements were made. Sixteen patients receiving dopamine hydrochloride through the left atrium had a 36 +/- 12% (+/- standard error of the mean) increase in aortic concentration of the drug (p less than 0.005) and a 37 +/- 14% increase in cardiac index (p less than 0.005) compared with administration through the right atrium. Seven patients receiving epinephrine showed a 59 +/- 21% increase in aortic concentration (p less than 0.05) and a 21 +/- 10% increase in cardiac index (p greater than 0.05, not significant). Eleven patients receiving sodium nitroprusside achieved a 99 +/- 25% increase in aortic concentration (p less than 0.005) and a 20 +/- 7% increase in cardiac index (p less than 0.05). In all instances, significantly higher central aortic blood concentrations were achieved during left atrial (LA) versus right atrial (RA) infusions. Changes in blood concentration of the drug between the pulmonary artery and the aorta during RA infusion suggest removal or inactivation of these drugs in the pulmonary vasculature.(ABSTRACT TRUNCATED AT 250 WORDS)

Steady-state determination of the contribution of lung metabolism to the total body clearance of drugs: application to carbamazepine

A steady-state approach is proposed to examine the contribution that the lung makes to the total body elimination of medium- to high-clearance drugs. Carbamazepine, a potential candidate of pulmonary metabolism, was investigated by infusion into the femoral vein in seven unrestrained Sprague-Dawley rats (250-300 g). Blood samples (0.45 ml), taken simultaneously from the jugular vein and carotid artery in each rat during the infusion (2-5 days), were assayed in duplicate for carbamazepine by GLC/CI/MS. Venous blood concentrations were used to calculate the total body clearance of carbamazepine, 440 +/- 38 ml/hr (mean +/- SEM), and the difference between simultaneous venous and arterial blood concentrations were used to calculate the extraction ratio of carbamazepine by the lung. The mean extraction ratio of 0.0058 (n = 28) suggests that the lung only contributes approximately 5% to the total body clearance of carbamazepine. It is proposed that this technique could be useful in examining the importance of the lung in the total body clearance of other drugs, and that it has several advantages over some currently used techniques.

Endothelium: a distributed organ of diverse capabilities

A historical survey of the growth of ideas about the circulation of the blood and about the endothelium is provided as a background to the specialized papers that follow. Over the years, in the course of clarifying its structure and function, the status of the endothelium has gradually evolved from that of an inert semipermeable barrier that determines the exchange of substances between blood vessels and tissue spaces to that of a specialized organ that is unusual in its dispersion throughout the body as the lining of blood vessels. This unique arrangement has enabled it to play different roles in different parts of the vascular tree and in different organs and to manifest distinctive responses to injury according to its structure and location. As a corollary, because its responsiveness is strongly influenced by its ambience and neighboring tissues, it seems inevitable that extrapolations from function in vitro to function in vivo require considerable prudence.

A model of delayed aortic coarctation employing arterial and venous catheters for chronic blood sampling in conscious dogs

We have developed a reproducible model of cardiac hypertrophy in conscious, unrestrained dogs after recovery from surgical trauma. The model has many potential applications due to the availability of non-stressful blood sampling from four arterial and/or venous vascular locations. Samples of blood for biochemical or pharmacological measurements were obtained from the carotid and femoral arteries as well as the pulmonary artery and inferior vena cava. Left ventricular hypertrophy up to 128% of the non-operated control animals was produced at 96 h post-intraluminal aortic coarctation. Inflation of a balloon in the descending aorta increased outflow resistance and resulted in hypertrophy. Hemodynamic parameters of cardiac function were obtained via a Swan-Ganz cardiac output catheter located permanently in the pulmonary artery. Complications observed in the dog model were minimal and mortality did not occur during the experimental period. This animal model employing multiple implanted catheters for blood sampling plus the ability to impose aortic coarctation in the unrestrained animal provides a flexible model system for biochemical and pharmacological research.

The isolated perfused lung--a critical evaluation

Recent refinement and application of the technique of perfusing isolated intact lung preparations from suitable experimental animal has enhanced our knowledge of the non-respiratory functions of the lung. The technique consists of perfusion with whole blood or constituted media via pulmonary artery or artificially ventilated lungs. Such preparations have been known to be especially useful for studies of uptake, metabolism and disposition of exogenous and endogenous substances. Recent advances in unilateral, split-lung perfusion in which left and right lungs are unilaterally perfused simultaneously have enabled investigators to maintain paired controls during perfusion. Such techniques are useful in the study of the interactions of endogenous and exogenous chemicals in the lung tissue. Differences between subcellular or lung slice preparations and intact lung perfusion are to be expected on the basis of distorting natural vascular and extra-vascular barriers in the case of in vitro preparations. Areas in which perfused lungs have not been extensively used include uptake and disposition of gases, solvents and vapors, effects of toxic chemicals on respiratory and non-respiratory functions of the lung and alteration of pulmonary mechanisms and hemodynamics in the presence of interacting chemical or physical stimuli. With suitable modifications, application of isolated perfused lung preparations for these investigations should be technically feasible in the future.

Production of 5-hydroxyindoleacetic acid from serotonin by cultured endothelial cells

Endothelial cells cells from bovine aorta and human umbilical vein and fibroblasts from human foreskin were cultured and subsequently evaluated for ability to metabolize serotonin (5-HT) to 5-hydroxyindoleacetic acid (5-HIAA). Cells were incubated for three hours with 4 X 10(-6) M [14C] 5-HT creatinine sulfate. [14C] 5-HIAA was separated from labeled 5-HT by column chromatography and measured for scintillation counting. Production of 5-HIAA by bovine aorta cells was 39.0+/-7.5 (S.E.M., n=6) nmoles per 10(9) cells per hour. Production of 5-HIAA was markedly inhibited by the presence of 10(-4) M iproniazid (an inhibitor of monoamine oxidase) or 10(-4) M imipramine (an inhibitor of amine transport). 5-HIAA was the only product of 5-HT metabolism detected by thin layer chromatography. Production of 5-HIAA by human umbilical vein endothelial cells was 5.4+/-2.0 nmoles per 10(9) cells per hour (n=5) and by human foreskin fibroblasts was 3.9+/-1.4 nmoles per 10(9) cells per hour (n=5). The results obtained during incubation in the presence and absence of inhibitors indicate that bovine aorta endothelial cells maintained in tissue culture are able to transport serotonin with subsequent production of 5-HIAA. By contrast, human umbilical vein endothelial cells and fibroblasts exhibited relatively low rates of 5-HT uptake and metabolism.

Specific and unspecific removal of circulating noradrenaline in pulmonary and systemic vascular beds in man

In order to study the extent and degree of specificity of the removal of circulating noradrenaline (NA) from the blood stream, during a single passage through the vascular beds of the lungs and of the forearm musculature of unanaesthetized, healthy young men, the following radiometric method was used: A misture of 3H-NA with 14C-inulin and 125I-labelled human serum albumin was injected proximally to the bed under study; six serial blood smaples were drawn distally to it, with about 15 s interval, and the disappearance of 3H-NA relatively to that of 14C-inulin and 125I-albumin was determined. 3H-NA was found to be removed from the blood stream in both these vascular beds. However, in the forearm the removal of 3H-NA was much greater, and apparently to a large extent due to specific trapping in the tissues, since the clearance of 3H-NA over the vascular bed of the forearm markedly exceeded that of 14C-inulin. During passage through the lungs removal of 3H-NA was less marked, and apparently largely unspecific, since it was initially essentially equal to that of 14C-inulin. This suggests that removal of circulating ergones of small molecular size, from the blood stream passing through the lungs, may occur initially by unspecific filtration/diffusion. Their subsequent fate would depend on whether the extraluminal tissues, supplied by the lung circulation, possess specific mechanisms for concentrating and/or inactivating each particular compound.

The removal of noradrenaline in the pulmonary circulation of rat isolated lungs

1. Removal of noradrenaline by isolated lungs of the rat, perfused via the pulmonary artery with Krebs bicarbonate solution has been studied.2. A constant removal (40.2%) was observed over a concentration range of 2-50 ng noradrenaline/ml (12-300 nM). At 100 ng/ml (600 nM), the removal is significantly reduced to 33.5%.3. The removal of noradrenaline was inhibited by cocaine (1 muM), but not by normetanephrine (5 muM), metaraminol (10 muM), phenoxybenzamine (10 muM) and 5-hydroxytryptamine (110 and 560 nM).4. We conclude that the removal of noradrenaline in the lungs does not involve an uptake process comparable with those previously described for this amine. The uptake process for noradrenaline in the lung is similar to that for 5-hydroxytryptamine and may be unique to this tissue.

Pulmonary extraction of 5-hydroxytryptamine and norepinephrine before and after cardiopulmonary bypass in man

Pulmonary extraction of 14 C-5-hydroxytryptamine and 3 H-norepinephrine was estimated in patients undergoing aortocoronary saphenous vein grafting. Identical mixtures of both amines were administered intravenously before Cardiopulmonary bypass and again just after bypass. Immediately after each injection, 6 ml of blood was withdrawn into tubing, at a constant rate, simultaneously from both the pulmonary artery and the left atrium. Each set of tubing was then divided into six segments, and the 3 H and 14 C content of each segment was measured. In this manner, total isotope collected and blood isotope concentration as a function of time at the two sampling sites were compared directly. Before bypass in every patient studied, less 5-hydroxytryptamine and norepinephrine were withdrawn on the left than on the right of the lungs, implying pulmonary extraction of both amines. In nine patients, the mean percent extraction was 65 ± 4% for 5-hydroxytryptamine and 23 ± 5% for norepinephrine ( P < 0.005). After bypass, the percent extraction of both norepinephrine and 5-hydroxytryptamine was increased in all but one patient; values for norepinephrine were increased to a realtively greater extent. These data represent a direct demonstration of 5-hydroxytryptamine and norepinephrine extraction by human lungs and also suggest that total Cardiopulmonary bypass may alter the process.