Inflammatory Response and Apoptosis in Newborn Lungs after Meconium Aspiration

An important feature of meconium-instilled newborn lungs is an inflammatory response and apoptotic cell death. It was recently demonstrated by our group and supported by several other investigators in a relatively short period of time. Apoptosis exists also in healthy lungs, but in meconium-instilled lungs its level is usually dramatically higher. Apoptosis is characterized by loss of cell function, decrease in cell size, and its morphology. Apoptosis plays an important role in normal cell life, but increased levels of apoptosis induce great damage for any tissues. Apoptosis in the lungs has been greatly overlooked for the past decade, and meconium-induced apoptosis is a relatively new event and not effectively studied at the present time. This Review summarized current knowledge regarding meconium-induced inflammation and apoptosis in newborn lungs.

Effect of pulsatile flow on microvascular resistance in adult rabbit lungs

We have determined the effect of pulsatile flow on segmental vascular resistance in lungs from 29 adult rabbits. In group I (n = 4), II (n = 8), and III (n = 8) lungs were isolated. In group IV (n = 9) rabbits were anesthetized, their chests were opened, and lungs were studied in vivo. Group I and II lungs had steady-flow perfusion: group I with intact vasotonus and group II with papaverine treatment. Group III lungs (papaverine treated) were perfused for two consecutive 45-min periods with steady and pulsatile flow. In all isolated lungs and in lungs of five anesthetized rabbits, we measured pressures in subpleural 20- to 50-microns-diam arterioles and venules by use of the micropipette servo-nulling method. Measurement of distribution of blood flow in lungs of four anesthetized rabbits by use of radiolabeled microspheres revealed no abnormality of blood flow to the micropunctured lobe. We found that total and segmental vascular resistances were similar in group I and II lungs, with microvessels representing 55% of total resistance. In group III lungs, total resistance was 30% lower during pulsatile flow than during steady flow because of a lower microvascular resistance. Lungs in vivo (group IV) had a significantly lower total vascular resistance than isolated lungs and had a low fractional resistance in microvessels (approximately 28%). We conclude that, in isolated perfused adult rabbit lungs, vascular resistance is very high, particularly in the microvascular segment, and that pulsatile flow decreases microvascular resistance.

Effect of pentoxifylline in rabbit pulmonary circulation: influence of age and vasomotor tone

We determined the influence of vasomotor tone and age on pentoxifylline (PTX) effects in rabbit lungs. Lungs of adult, juvenile, and neonatal rabbits were isolated and perfused with blood at constant flow in zone 3. In adult lungs only, pressures were measured in 20- to 50-microns-diameter subpleural arterioles and venules (by micropuncture) to partition the circulation into arteries, microvessels, and veins during baseline, after PTX infusion (20 mg/kg), and terminally, after treatment with papaverine. In some adult and juvenile lungs, vasomotor tone was elevated with KCl, and some adult lungs were pretreated with indomethacin to inhibit cyclooxygenase. We found that PTX's vasodilator effect was influenced by age; it was approximately 52, approximately 65, and approximately 82% as effective as papaverine in untreated neonatal, juvenile, and adult lungs, respectively, and approximately 49 and approximately 93% as effective as papaverine in KCl-constricted adult and juvenile lungs, respectively. The site(s) of PTX action depended on basal vasomotor tone; in lungs with moderate tone, PTX dilated arteries only, and in lungs with high tone, PTX dilated both arteries and veins. Cyclooxygenase inhibition did not attenuate PTX effects. We conclude that, in rabbit lungs, PTX dilates arteries and veins and that the magnitude of PTX effect is dependent on age and basal vasomotor tone.

Segmental vascular resistance during pulsatile and steady perfusion in 3- to 5-wk-old rabbit lungs

To determine the mechanisms by which pulsatile perfusion reduces vascular resistance in isolated lungs, we compared the effects of pulsatile versus steady perfusion on total and segmental vascular resistance in isolated lungs of 3- to 5-wk-old rabbits. Lungs were perfused alternately with steady and pulsatile flow for 45-min periods at a constant total arteriovenous pressure drop. Blood flow was adjusted to keep mean pulmonary arterial pressure at 20 cmH2O, when left atrial and airway pressures were 8 and 6 cmH2O, respectively. We partitioned the pulmonary circulation into three longitudinal vascular segments, i.e., arteries, microvessels, and veins, by measuring pressures in 20- to 50-microns-diameter subpleural arterioles and venules by the micropipette servo-nulling method. We found that in the isolated, perfused 3- to 5-wk-old rabbit lung, in which arteries and veins are the main sites of resistance, pulsatile flow results in a 20-36% reduction in total vascular resistance, mainly due to a reduction in arterial and venous resistances. The decrease in total vascular resistance was similar in lungs that were untreated or treated with papaverine, indicating that the effect of pulsatile flow was not due to active vasomotion. The reduction in arterial resistance was greater than that in veins (31-55 vs. 19-22%), especially when pulse amplitude was high (5-10 vs. 20-30 cmH2O). Total vascular resistance was also lower after 45 min of pulsatile perfusion with a pulse rate of 200 pulses/min than 80 pulses/min (0.126 +/- 0.04 vs. 0.154 +/- 0.059 cmH2O.min.ml-1.kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoconstrictor response to prostacyclin in rabbit pulmonary circulation

We have determined the effect of prostacyclin (PGI2) on segmental vascular resistance in rabbit lungs. Lungs of 26 rabbits were isolated and perfused with blood; 16 adult, greater than 6 months old, five juvenile, 6-8 week old and five neonatal, 2-3-week old. Six of the adult lungs were pretreated with indomethacin to block cyclooxygenase, prior to infusion of PGI2. In all lungs, flow was adjusted initially to keep pulmonary artery pressure approximately 20 cmH2O, left atrial and airway pressures being 8 and 6 cmH2O, respectively (zone 3), and then kept constant. We measured pulmonary artery pressure continuously and in the 10 untreated adult lungs, in which a vasoconstrictor response to PGI2 was obtained, we also measured pressures in 20-50 microns diameter subpleural arterioles and venules by the micropipette-servonulling method. We found that in juvenile and neonatal rabbit lungs, PGI2 did not change total vascular resistance significantly but in untreated adult lungs, it caused a significant increase in total vascular resistance only after a dose of 10 micrograms/kg. This age-related difference in vasoconstrictor response to PGI2 was not related to baseline total vascular resistance in the three groups of lungs. In adult lungs, vasoconstriction occurred mainly in arteries with a small effect in veins. Circulating levels of thromboxane B2, leukotriene C4, and 6-keto-PGF1 alpha increased following PGI2 infusion in adult lungs, whereas in neonatal lungs, only 6-keto-PGF1 alpha increased significantly. Indomethacin pretreatment completely abolished the vasoconstrictor response to PGI2. We conclude that PGI2-induced vasoconstriction is age and dose dependent in isolated rabbit lungs and that a cyclooxygenase product, such as thromboxane A2, may play a role in mediating the vasoconstriction.

Pulmonary vascular pressure profile in adult ferrets: measurements in vivo and in isolated lungs

We have determined the vascular pressure profile in lungs of adult ferrets utilizing an anaesthetized open chested preparation and have compared the pressure profile in vivo with that in isolated, perfused lungs. Ten adult ferrets, mean body weight 980 +/- 108 g, were studied. For in vivo measurements, five ferrets were anaesthetized, mechanically ventilated and the left chest wall resected. Pressures were measured in the pulmonary artery, left atrium and by micropuncture, in 20-50 microns diameter subpleural arterioles and venules. During micropuncture, ventilation was stopped for 1-2 min and the lungs kept distended at an airway pressure of 6 cmH2O. Left atrial pressure was raised to approximately 8 cmH2O with saline infusion so that lungs were in Zone 3. Cardiac output was measured by thermodilution. Lungs of five other ferrets were isolated and perfused with a steady flow roller pump. In these lungs blood flow was adjusted so that pulmonary artery pressure was similar to that in anaesthetized ferrets, with airway and left atrial pressures at 6 and 8 cmH2O respectively (Zone 3). Blood haematocrit (35 +/- 7%) was similar in the two groups. In lungs of anaesthetized ferrets total arteriovenous pressure drop was 12.1 +/- 1.9 cmH2O, with cardiac output being 210 +/- 80 ml kg body weight-1 min-1. Fractional resistance in arteries was 37%, 37% in microvessels and 26% in veins. In isolated ferret lungs, though blood flow was only 48 +/- 10 ml kg body wt-1 min-1 for the same total arteriovenous pressure drop as in vivo, the longitudinal distribution of vascular resistance was similar to that in live ferrets.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary arterial and venous constriction during hypoxia in 3- to 5-wk-old and adult ferrets

We have determined the sites of hypoxic vasoconstriction in ferret lungs. Lungs of five 3- to 5-wk-old and five adult ferrets were isolated and perfused with blood. Blood flow was adjusted initially to keep pulmonary arterial pressure at 20 cmH2O and left atrial and airway pressures at 6 and 8 cmH2O, respectively (zone 3). Once adjusted, flow was kept constant throughout the experiment. In each lung, pressures were measured in subpleural 20- to 50-microns-diam arterioles and venules with the micropipette servo-nulling method during normoxia (PO2 approximately 100 Torr) and hypoxia (PO2 less than 50 Torr). In normoxic adult ferret lungs, approximately 40% of total vascular resistance was in arteries, approximately 40% was in microvessels, and approximately 20% was in veins. With hypoxia, the total arteriovenous pressure drop increased by 68%. Arterial and venous pressure drops increased by 92 and 132%, respectively, with no change in microvascular pressure drop. In 3- to 5-wk-old ferret lungs, the vascular pressure profile during normoxia and the response to hypoxia were similar to those in adult lungs. We conclude that, in ferret lungs, arterial and venous resistances increase equally during hypoxia, resulting in increased microvascular pressures for fluid filtration.

Pulmonary vascular pressure profile in 2-3-week-old, 5-6-week-old and adult ferrets

We have previously reported age-related differences in the pattern of vascular pressure drop in rabbit lungs (Raj et al., Pediatric Res. 20:1107-1111, 1986). The purpose of this study was to investigate if there were similar age related differences in the ferret lung. To determine the profile of vascular pressures and the longitudinal distribution of vascular resistance in arteries, microvessels and veins, we isolated and blood perfused lungs of 20 ferrets (8 adults greater than 6 months of age; six 5-6-week-old and six 2-3-week-old). All lungs were perfused under similar experimental conditions with blood flow adjusted to keep pulmonary artery pressure constant at approximately 20 cmH2O, when left atrial pressure was 8 cmH2O. Lungs were inflated to 6 cmH2O airway pressure with a gas mixture so that blood Po2 was greater than 100 Torr. Microvascular pressure measurements were obtained in each lung in subpleural 20-50 microns diameter arterioles and 20-50 microns diameter venules using the micropipette servonull method. Blood flow achieved in all three groups of lungs was similar. We found that in adult ferret lungs, 40% of total vascular resistance was in arteries, 40% in microvessels and 20% in veins. In 2-3-week-old and 5-6-week-old ferret lungs, the fractional distribution of resistance in arteries, microvessels and veins was similar to that in adult ferret lungs. We conclude that, unlike in the rabbit, the pulmonary vascular pressure profile does not change with age in the ferret.

Effect of pentoxifylline on hemodynamics, alveolar fluid reabsorption, and pulmonary edema in a model of acute lung injury

We investigated the effect of pentoxifylline (PTX) on the development of pulmonary edema in a model of adult respiratory distress syndrome in rabbits. Lung injury was induced by repeated saline lavages in adult rabbits weighing 2.5 to 3.5 kg. Rabbits pretreated with PTX (20 mg/kg bolus followed by 20 mg/kg/h infusion) developed significantly lower amounts of lung edema 4 h after saline lavage (extravascular lung water to dry weight ratio [W/D], 6.9 +/- 0.6 SD versus 8.9 +/- 0.5 in control animals). PTX produced a 25% increase in cardiac output, but there were no differences between treated and untreated groups in calculated pulmonary vascular resistance or microvascular pressure. To determine whether PTX could have lowered pulmonary venous resistance and thus lowered effective microvascular pressure for fluid filtration, we directly measured pulmonary artery and left atrial pressures, and measured by micropuncture the pressure in 20 to 40 microns subpleural venules in four open-chested rabbits 3 to 4 h after lavage. Venous resistance was low (venous pressure drop 0.9 +/- 0.1 mm Hg) and was unchanged by PTX infusion. To determine if PTX decreased lung water by accelerating active alveolar fluid reabsorption, a single 60-ml aliquot of saline was instilled into the lungs of normal rabbits treated with saline or PTX. Both groups had a similar decrease in lung water content 1 and 4 h later. Our data indicate that PTX reduces edema formation in rabbits after saline lavage, not by lowering microvascular pressures for fluid filtration or by acceleration alveolar fluid reabsorption, but possibly by its anti-inflammatory effect on neutrophil function.

Prostacyclin and thromboxane in diabetic children

Plasma concentrations of a stable metabolite of prostacyclin, 6-keto-prostaglandin Fla (6-keto-PGF1a), and the ability of platelets to generate thromboxane B2 (TxB2), a metabolite of thromboxane A2, during spontaneous clotting of the blood were measured in 40 diabetic children and 16 healthy controls. The diabetics' platelets generated TxB2 to a lesser extent than those of controls, whereas no difference was seen in plasma 6-keto-PGF1a concentration. The balance and duration of diabetes were not related to TxB2 or 6-Keto-PGF1a. The results do not support the theory that an absolute or relative prostacyclin deficiency could trigger the onset of diabetic vascular complications.