Leukotriene Inhibition Prevents and Reverses Hypoxic Pulmonary Vasoconstriction in Newborn Lambs

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Leukotriene Inhibition Prevents and Reverses Hypoxic Pulmonary Vasoconstriction in Newborn Lambs LEUKOTRIENE INHIBITION AND HPV 437 003 1-3998/85/1905-0437$02.00/0 PEDIATRIC RESEARCH Vol. 19, No. 5, 1985 Copyright O 1985 International Pediatric Research Foundation, Inc. Printed in U.S.A. Leukotriene Inhibition Prevents and Reverses Hypoxic Pulmonary Vasoconstriction in Newborn Lambs MICHAEL D. SCHREIBER, MICHAEL A. HEYMANN, AND SCOTT J. SOIFER The Cardiovascular Research Institute and the Departments of Pediatrics, Physiology, and Obstetrics, Gynecology, and Reproductive Sciences, University of California, Sun Francisco, California 94143 ABSTRACT. The effects of the leukotriene antagonist have been isolated from the lung lavage fluid of newborn infants FPL 57231 on the circulation were studied in sponta- with persistent pulmonary hypertension syndrome but not from neously breathing normoxic and hypoxic newborn lambs in newborn infants with other lung diseases (14). These findings order to evaluate the role of leukotrienes in the perinatal suggest that leukotrienes may play a role in maintaining the control of hypoxic pulmonary vasoconstriction. Hypoxia elevated pulmonary vascular tone in the normal fetus in utero produced a 58% increase in pulmonary arterial pressure and also in the mediation of hypoxic pulmonary vasoconstriction (p < 0.05) and a 37% increase in pulmonary vascular after birth. The effects of the leukotriene antagonist FPL 5723 1 resistance (p < 0.05). Hypoxic pulmonary vasoconstriction on the circulation were therefore studied in normoxic and hy- was abolished by the prior infusion of FPL 57231. Pul- poxic spontaneously breathing newborn lambs. monary arterial pressure increased by only 8% and pul- monary vascular resistance decreased by 10% from nor- METHODS moxia. The infusion of FPL 57231 during hypoxia-induced pulmonary vasoconstriction reversed the increase in pul- Surgical procedure and drug preparation. Six mixed-breed monary arterial pressure (p e 0.05) and pulmonary vas- newborn lambs from 3-7 days old were operated on under local cular resistance (p < 0.05). The hypoxia-induced increase anesthesia with 1% lidocaine hydrochloride. Polyvinyl catheters in cardiac output was maintained during the infusion of were placed in both hind limb arteries and veins and advanced FPL 57231. Leukotrienes may play a significant role in to the descending aorta and inferior vena cava, respectively. A the mediation of hypoxic pulmonary vasoconstriction. Leu- no. 5 French flow-directed thermodilution catheter, with the kotriene inhibition with FPL 57231 may be useful in the proximal injection port 15 cm from the tip, was introduced into management of infants with persistent pulmonary hyper- the jugular vein and advanced into the pulmonary artery for tension syndrome. (Pediatr Res 19: 437-441,1985) measuring pulmonary arterial and pulmonary arterial wedge pressures. Right atrial pressure was measured through the prox- imal port. Cardiac output was determined by the thermodilution Abbreviations technique and calculated by computer (Electro-Catheter model PPHN, persistent pulmonary hypertension of the newborn 5000, Electro-Catheter Corp., Rahway, NJ). Three milliliters of PG, prostaglandin iced-saline was injected into the proximal port for each measure- PG12, prostacyclin ment. Each cardiac output value was taken as the average of three determinations. Following surgery, the lambs were placed in a sling under a radiant warmer to maintain body temperature. An intravenous infusion of dextrose in water was started. Two horns were allowed for recovery. The exact mechanisms by which hypoxia produces pulmonary FPL 5723 1 was prepared immediately before each experiment vasoconstriction remain unknown. The production and release as a 1% solution in sterile water. of the noncyclooxygenase products of arachidonic acid from the Experimental Protocol. FPL 57231 infusion prior to the onset lung may play an important role. Leukotrienes, the 5'-lipoxygen- of hypoxia. Following the recovery period, baseline vascular ase metabolites of arachidonic acid, are produced by mast cells pressures, cardiac output, and arterial blood gas measurements (1, 2), alveolar macrophages (3), and pulmonary vascular tissue were made in room air (NORMOXIA). Normocarbic hypoxia (4-6). Leukotrienes induce smooth muscle contraction in a was then induced by placing a loosely fitting bag over the lamb's variety of tissues (7-10). Leukotriene D4 infused into the pul- head and adding nitrogen with 5% C02to the gas mixture. The monary artery of young lambs produces pulmonary arterial F102 was varied to produce a Pao2 of 30-40 mm Hg in each hypertension (1 1). Leukotriene inhibition with FPL 57231 (Fi- animal. Measurements were made after 10 rnin of hypoxia and sons, plc, Loughborough, UK), a leukotriene receptor antagonist stable pulmonary hypertension (HYPOXIA). The lamb was re- (12), significantly increases pulmonary blood flow and decreases turned to room air. pulmonary vascular resistance in fetal lambs (13). Leukotrienes After the lambs resumed baseline values (NORMOXIA), an Received October 9, 1984; accepted December 27, 1984. intravenous infusion of FPL 5723 1 (1 mg. kg-'. min-I) for 20 Requests for reprints should be addressed to Dr. Scott J. Soifer, Cardiovascular rnin was started. Measurements were made after 10 rnin of the Research Institute M-342A, University of California, San Francisco, CA 94143. infusion (NORMOXIA + FPL 57231). Hypoxia was then in- Supported in part by grants from the American Lung Association and U.S. Public Health Service Program Project Grant HL 24056. M.D.S. is recipient of the duced as the drug infusion continued, and measurements were American Heart Association, California affiliate fellowship award. S.J.S. is recipient made after another 10 rnin (HYPOXIA + FPL 57231). The of New Investigator Award HL 29941 from the NHLBI. infusion was stopped as hypoxia continued, and measurements 438 SCHREIBER ET AL. were made after 15 min. The lambs were returned to room air. infusion of FPL 5723 1 (HYPOXIA + FPL 5723 1). Pulmonary Measurements were also made with an equivalent infusion of arterial pressure increased by only 8% and pulmonary vascular sterile water vehicle during normoxia and hypoxia. resistance decreased by 10% compared to NORMOXIA. Pul- FPL 57231 infusion started during hypoxia. Six to 24 hr were monary arterial pressure and pulmonary vascular resistance dur- allowed for recovery from the above experiment. In five lambs ing HYPOXIA + FPL 5723 1 were significantly lower than during baseline measurements were made in room air (NORMOXIA). HYPOXIA (p< 0.05). There were no significant changes in Normocarbic hypoxia was again induced producing hypoxemia systemic arterial pressure and systemic vascular resistance com- (Pao* 30-40 mm Hg) and stable pulmonary hypertension. After pared to HYPOXIA. The 24% increase in cardiac output during 10 min, measurements were repeated (HYPOXIA). Hypoxia was continued and an infusion of FPL 5723 1 (2 mgkg-'. min-') was started. Measurements were made after 10 min (HYPOXIA + FPL 5723 1). The drug infusion was then stopped, and the lambs I * ~<0.05vs NORMOXIA were returned to room air. Measurements and calculations. Pulmonary and systemic ar- terial and right atrial pressures were measured with Statham P23 Db pressure transducers and recorded continuously on a Beck- I- 5 5 E man multichannel direct-writing recorder. Mean pressures were >, E obtained by electrical integration. Heart rate was measured with a a cardiotachometer triggered from the systemic arterial pressure. zauw 20- Cardiac output, pulmonary arterial wedge pressure, and systemic .........:_:.:.:.:.:.:. ....................... arterial blood gases were measured during all normoxia and ............... .............................. hypoxia periods after a steady-state had been reached. The ab- - ............... 2 10 ........................ sence of intracardiac shunting was determined by indicator di- a .............. lution technique. The validity of the thermodilution method has W .............. I ................::. been reported previously ( 15, 16). Pulmonary vascular resistance .............. .............. was calculated as the mean pulmonary arterial pressure minus 0 - mean pulmonary arterial wedge pressure divided by cardiac NORMOXIA HYPOXlA NORMOXIA NORMOXIA HYPOXIA output per kilogram. Systemic vascular resistance was calculated + + as the mean systemic arterial pressure minus mean right atrial pressure divided by cardiac output per kilogram. The mean f SD was computed for the vascular pressures, resistances, cardiac output, heart rate, and arterial blood gases during all normoxic and hypoxic conditions. The differences in these variables were compared by two-way analysis of variance and the Newman-Keuls test for multiple comparisons (I 7). A p c 0.05 was considered statistically significant. RESULTS FPL 57231 inxusion prior to the onset of hypoxia (Table I, Fig. 1). Normocarbic hypoxia (HYPOXIA) produced a 58% increase in pulmonary arterial pressure from 18.1 f 2.7 to 28.6 k 3.2 mm Hg (pc 0.05) and a 37% increase in pulmonary vascular resistance from 44.0 * 6.6 to 60.4 f 6.8 mm Hg.1-I. min-I .kg-' (p< 0.05) compared to normoxia. Systemic arterial pressure was unchanged. Systemic vascular resistance decreased - by 16% during HYPOXIA (pc 0.05), as cardiac output in- NORMOXIA HYPOXIA NORMOXIA NORMOXIA HYPOXIA creased by 1 %. + + 9 FPL5723I FPL57231 Infusing FPL 5723 1 during normoxia (NORMOXIA + FPL 5723 1) produced no significant changes in the hemodynamic Fig. 1. The effects of an infusion of FPL 5723 1 prior to
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