Thromboxane and prostacyclin production in the perfused rabbit lung

PmttaglmtdinsLeukototrienes and Essential Fatty Acids (1991) 43,239-246 0 Lmgmatt Group UK Ltd 1991

Thromboxane and Prostacyclin Production in the Perfused Rabbit Lung F. A. M. Peeters, R. Van Den Bossche, H. Bult and A. G. Herman University of Antwerp (UIA), Faculty of Medicine, - Wilrijk, Belgium (Reprint requests to HB)

Division of Pharmacology,

B-2610, Antwerpen

ABSTRACT.

We investigated whether prostacyclin formation by the isolated rabbit lung can serve as a measure of pulmonary distress. The basal TXAz and PGIz formation was very low, and depended on the preperfusion history of the lung (low or hiih flow, use of dextran or artilkial perfusate). The basal prostauoid production remained unchanged over a time period of 2 h. Neither was it inftuenced by the serotonin uptake inhibii chlorimipramine and by small changes in temperature (33°C vs 39°C). The PGIz formation was almost independent of hemodynamic alterations such as embolism or vasoconstriction. An enhan& production was only seen after a dramatic increase in flow (from 1.7-S m&kc), and a transient 3-fold increase was observed after administration of 1 mM H& A substantial (up to 40-fold) but transient increase in TXA2 production was measured after 1 mM of H&l*, and the TXA2 production was positively correlated to the increase in pulmonary arterial pressure. However, thromboxane production was also dramatically augmented by hemodynamic alterations such as embolism, increased flow and -. to a lesser extent : vasocoitstriction. We conclude that the determination of the prostanoid production (and particularly the TXAz formation) by the rabbit lung cannot be used as a direct measure of endothelial distress. To this end it is excessively biased by hemodynamic alterations such as recruitment and shear stress.

INTRODUCTION

production can only be useful as a measure of endothelial injury if they respond to (patho)physiological changes in a predictable manner.

PG12 is normally undetectable in aortic blood (l-4) but it appears in the circulation of patients suffering from sepsis associated with shock (5, 6). PG12 formation is also increased during hemodialysis or after cardiopulmonary bypass (7, 8), where the patients suffer from a temporary pulmonary distress. In a previous study we have found PGI2 to be a marker of endothelial distress after complement activation in the dog lung (9). Prostanoid formation by the lung is also enhanced by noxious substances such as H202

MATERIALS The artificial perfusate consisted of a balanced salt solution containing 118.3 mM NaCl, 4.7 mM KCl, 25 mM NaHCOs, 2.5 mM CaC12.2H20, 1.2 mM KH2P04, 3% bovine serum albumin, and 11.1 mM glucose. 6[5,8,9,11,12,14,15-3H(N)]-oxo-prostaglandin Fi, (120-180 Ci/mmol), and [5,6,8,9,11,12,14,153H( N)]-thromboxane B2 (100-160 Ci/mmol) were obtained from New England Nuclear (Dreieich, FRG), bovine serum albumin, bovine gamma globulin, L-norepinephrine bitartrate and trizma base from Sigma (Pasture, Brussels, Belgium), heparin from Leo (Copenhagen, Denmark), pentobarbital from Abbot (Brussels, Belgium), xylocaine from Astra-Nobelpharina (Brussels, Belgium), Rheomacrodex (dextran 40 Ooo 10%) and sterile pyrogen-free NaCl 0.9% solution from Travenol (Lessines, Belgium), Opti-Fluor from Packard Instruments (Downers Grove, IL, USA).

(10).

In the present study we investigated whether thromboxane or prostacyclin can be used as a measure of endothelial distress in the rabbit lung. To this end we have measured the TXA2 and PG12 production by the lung in a variety of experimental situations, i.e. after vasoconstriction, changes in temperature and flow, chlorimipramine administration, experimental embolism and H202 administration. The changes in TXA2 and PG12

Date received 7 December 1990 Date accepted 19 March 1991 239

240

Prostaglandins Leukotrienes and Essential Fatty Acids

Indomethacin was a gift of Merck Sharp and Dohme (Brussels, Belgium), chlorimipramine hydrochloride was a gift of Ciba-Geigy (Groot-Bijgaarden, Belgium), and the RIA data reduction system was a gift of Dr. M. L. Jaffe (M. L. Jaffe & Assoc., Silver Spring, MD, USA). All other chemicals were of analytical grade and obtained from Merck (Darmstadt, FRG) or U.C.B. (Brussels, Belgium).

METHODS General methodology 55 New Zealand white rabbits of either sex (2.96 f 0.07 kg) were anaesthetized with pentobarbital sodium (30 m&g i.v.) or with chlorpromazine hydrochloride (25 mg/kg i.m.) followed by pentobarbital sodium (15-20 mg/kg i.v.). Heparin (200 IU/kg) was injected i.v., xylocaine (10 mg) was injected intradermally over the larynx and ex-/ trathoracic trachea. Rabbits were exsanguinated via a catheter placed in the left carotid artery. The thorax was opened, the trachea was clamped, cannulas were placed in the pulmonary artery, via the right ventricle, and in the left atrium. The lung was removed from the chest and mounted vertically in a perspex perfusion chamber. The lungs were ventilated with a mixture of 20% 02-75% N2-5% CO2 (Palmer ventilator, 25 ml/stroke, 30 strokes/min). After several inflations to a pressure of approximately 8 torr to reverse atelectasis, the end inspiratory pressure was adjusted to 4 torr, and the end expiratory pressure to 1 torr. Initially the lungs were perfused at 1.0 ml/s with 200 ml of dextran (mol wt 40 000, 200-400 ml, used in the time study #l, vasoconstriction and flow experiment) or artificial perfused (all other experiments) to remove most of the residual blood. Then the perfusion with fresh artificial perfusate solution and recirculation of the perfusate (1.5-5 ml/s) was started. The venous pressure was kept constant at about 0.5 torr above the end expiratory pressure by adjusting the height of the reservoir into which the perfusate drained from the left atrium. The temperature of the perfusate and the perfusion chamber were maintained constant by means of a heating circuit. The pulmonary arterial, (Ppa), venous and ventilatory inlet and outlet pressures were constantly recorded. The lungs were initially perfused for 15-30 min to allow for stabilization. Starting at time 0 and at 15 min intervals, 5 ml venous outflow samples were collected in a tube containing indomethacin (5 pg/ml) for the measurement of PG12 and TXA;! production. In the H202 experiment, a sample for PG12 and TXA2 measurement was also taken 5 min after HzOz administration. In the present

performed

experiment

we have

additionally

a set of injections of serotonin

to esti-

mate the facilitated uptake of this amine by the lung as a measure of endothelial distress (1 I). The methodology and results are subject of a separate manuscript (12 and Peeters et al, submitted), Parameters that are derived from the serotonin injections and that are ustd in the present study include the flow rate (Q, ml/set, gravimcttic determination of venous samples collefted in a fixed time period) and the organ volume (QT, ml, determined from the flow rate and the residence time of a bolus of serotonin in the lung). All data are expressed as value + S.E.M. and the significance between two data sets was calculated with a paired Student’s t-test. Time studies In a first study (Time study #l), five control lungs were perfused for 45 min. Samples for TXA2 and PGI2 taken between the serotonin injections (i.e. at 0 and 15, and at 30 and 45 min) were pooled. In a second experiment (Time study #2) six lungs were perfused for 105 min. The serotonin-free intervals included O-30,45-60 and 75-105 min. Vasoconstriction experiment In six lungs, samples for TXA2 and PG12 were taken during the baseline period (at 0 and 15 min), and during experimental vasoconstriction (30 and 45 min). Vasoconstriction of the pulmonary circulation was obtained by infusion of 15-148 PM of norepinephrine (NE). The infusion rate (0.71.7 ml/min) was adjusted to maintain a constant increase of the pulmonary arterial pressure of about 10 torr. Temperature experiment Six lungs were perfused for 15 min to allow stabilization. In four lungs the initial perfusion temperature was 39°C. After taking the samples for TXAz and PGIz (at 0 and 15 min), the temperature was switched to 33°C. Samples were taken at this temperature (at 30 and 45 min) and the temperature was switched back to 39°C (samples at 45 and 60 min). In the two remaining lungs the tempcrature sequence was inverted (starting at 33”C, then 39°C and back 33°C). For each lung, the samples taken at the same temperature were pooled, so that 6 low and 6 high temperature data were ohtaincd. Flow experiment

Nine lungs were perfused during a 15 min stabilization period. Five of these lungs were pcrfuscd at the highest flow rate (5.0 ml/set) during the full 15 min stabilization period. At 15 and 30 min

TX and PGI, Production in Perfused Rabbit Lung

samples were taken for TXB2 and PG12 measurement. Then the flow was decreased to 3.6 ml/s (samples at 30 and 45 min) and to 1.7 ml/s (samples at 60 and 75 min). The four other lungs were initially perfused for 12 min at the highest flow (5.0 ml/s) but the flow was lowered to 1.7 ml/s for another 3 min. The preperfusion at the 5.0 ml/s flow was found to be necessary to open all blood vessels and avoid ‘reperfusion’ injury when the flow was increased (with concomitant recruitment). Samples were taken during the low flow (15 and 30 min). Afterwards the flow was increased to 3.6 ml/s (samples taken at 30 and 45 min) and to 5.0 ml/s (samples taken at 60 and 75 min). Chlorimipramine administration Eight lungs were initially perfused for 15 min (sampled at 0 and 15 min). Another set of samples was taken at least 10 min after administration of 1 PM of chlorimipramine (at 45 and 60 min). Experimental embolism Eight lungs were perfused for 15 min (sampled at 0 and 15 min). Partial vascular occlusion was established by injecting 285 mg beads (400-500 pm) into the pulmonary circulation (time 35 min). Samples for TXAz and PG12 determination were taken at 45 and 75 min. The same amount of beads were injected again (time 80 min), followed by sampling at 90 and 105 min. H&

administration

Samples for TXA2 and PG12 determination were taken during the 30 min stabilization period (O30 min). At time 45 min, H202 was added to the perfusate (final concentration 1 mM) and samples for RIA were taken during the first 15 min contact period (45-60 min). A second set of samples was taken during the recovery period (75-105 min). Radioimmunoassay of PGIz and TXAz TXA2 and PG12 were assessed by radioimmunoassay (RIA) of their non-enzymatic metabolites, thromboxane Bz (TXB2) and 6-oxo-prostaglandin F1, (6-oxo-PGF1,). The RIA was carried out according to Granstrom and Kindahl (13). The medium consisted of a Tris buffer (trizma base 12.1 g; EDTA 0.8 g; HCl 3 M until pH 7.4, distilled water until 2 liter). Buffer (200 or 300 ~1)~ standard (100 ~1) or sample (100 or 200 pl), 100 ~1 bovine gammaglobulin 0.5%, 100 ~1 antiserum (prepared in our laboratory (14) and 1/8000 diluted), and 100 ~1 3H-6-oxo-PGF1, or 3H‘I%32 (6600 dpmj .were added (final volume of

241

700 pl), mixed and incubated overnight at 4°C. Then proteins were precipitated with 700 ~1 of propyleneglycol 4000 (25% in distilled water) at 4°C and immediately centrifuged (1 h, 4”C, 1800 g). One ml supernatant was mixed with 1 ml distilled water and 12 ml of Opti-Fluor, and counted for radioactivity. In each RIA a standard curve (42000 pg for 6-oxo-PGFl,, and 2-1000 pg for TXB2) was included. The dose interpolation was calculated on an IBM personal computer according to a 4 parametric model described by Dudley et al (15), using a RIA Data Reduction System (Ver 4.0) which was a gift from Dr M. L. Jaffe (M. L. Jaffe & Assoc., Silver Spring, MD, USA). The cross-reactivities in the assay of 6-0x0PGF,,:l.O%; 15-HETE and 15PGFI, were: HPETE:O.Ol%; PGE2, 15-oxo-PGE2, TXB2 and arachidonic acid < 0.1% . The cross-reactivities the assay of TXB2 were:PGD*:8.9%; ~GF~.:~.o%; PGE,:0.9%; 6-oxo-PGF1, : 0.1% ; 15-oxo-13,lCdihydro-PGI$,, 15-HETE and 15HPETE < 0.01%; arachidonic acid < 0.001% (14, 16). PG12 is rapidly decomposed to its stable metabolite 6-oxo-PGF1, (the latter product is therefore directly correlated to the PGIz formation). Since PG12 and 6-oxo-PGF1, are not cleared by the pulmonary circulation (17, 18), 6-oxo-PGFt, accumulates in the perfusate during the course of the experiment. Based on the levels in the successive samples, the PG12 formation per unit of time (pmol/min) was calculated, taking into account the reduction in total perfusate volume as a consequence of successive sampling, and the increase in volume due to the addition of fresh (6-oxo-PGFt, free) perfusate. Where possible, the values obtained immediately after the serotonin injections and subsequent fraction collection were discarded, since they were perturbed by the changes in perfusion volume. These values might also be influenced by a vasoactive effect of the passing serotonin boius. Results are given as pmol PG12 formed per min. Since the pulmonary endothelium has the capacity to remove TXB2 from the perfusate (9), the formation (pmol/min) was calculated by multiplying the instantaneous outflow concentration (pmol/ml) by the flow rate (ml/min). For each lung, the values at different time points, but belonging to a fixed ‘condition’ (i.e. before vasoconstriction vs after vasoconstriction) are pooled.

RESULTS Weight and hemodynamic data Table 1 summarizes the flow, organ volume and pulmonary artery pressure for the eight experimental

242

Prostaglandins Leukotrienes

and Essential Fatty Acids

Table 1 Flow rate (b), lung vascular volume (&) and perfusion pressure in the pulmonary artery (Ppa) for the different experimental situations Experiment

Experimental

Time study #l (n=S)

condition

& mi/sec

B, ml

Time 15-30 min Time 30-45 min

1.84 f 0.02 1.85 f 0.20

6.29 f 0.38 6.13 + 0.46

4.2 + 0.8 4.3 f 0.8

Time study #2 (n=6)

Time O-30 min Time 45-60 min Time 75-105 min

2.00 + 0.03 2.01 I? 0.04 2.00 f 0.03

9.30 * 1.07 9.51 + 0.93 8.85 + 0.74

8.7 + 1.0 8.8 + 1.0 9.0 + 1.0 .

Vasoconstriction (n=6)

Before NE During NE

2.12 f 0.15 2.11 + 0.14

7.49 f 0.68 6.12 f 0.57’

6.3 + 1.0 15.3 + 1.2+

Temperature (n=6)

39°C 33°C

1.84 * 0.07 1.83 + 0.10

5.74 + 0.32 6.52 + 0.54

7.1 + 0.9 7.6 If: 0.9+

Flow study (n=9)

1.7 ml/s 3.6 ml/s 5.0 ml/s

1.71 f 0.01 3.55 + 0.03’ 4.96 ?I 0.04”

5.81 !I 0.35 6.78 + 0.24+ 8.38 z!z0.73+’

Chlorimipramine experiment (n=8)

Before chlorimipramine After chlorimipramine

2.02 f 0.04 2.02 + 0.03

7.07 + 0.44 6.14 f 0.43

Embolism experiment (It=@

Before embolism After 1st embolism After 2nd embolism

2.00 + 0.03 1.97 + 0.03 1.98 + 0.04

7.57 + 0.53 5.84 + 0.52+ 4.12 + 0.46+$

5.6 + 0.6 9.1 + 1.7+ 16. 1 + 4 .Ott

H,O, experiment (n=5, 4)

Before H202 (n=5) O-15 min after (n=5) 30-60 min after (n=4)

1.89 + 0.06 1.88 f 0.07 1.92 f 0.06

8.87 f 1.11 8.10 + 1.05+ 9.66 + 1.55

10.4 f 1.3 11.5 + 1.3 10.8 + 1.3

Ppa torr

7.1 f 0.5 11.9 f 0.7+ 14.6 + 0.5+$ 8.0 + 1.0 8.6 + 0.9

’ : significantly different from the value obtained under ‘baseline conditions’ (i.e. the first line in each experimental situation) $p c 0.05). : significantly different from the value immediately above (p < 0.05). For the H,O, experiment, only the lungs that survived addition of H202 were included. NE = norepinephrine.

Table 2 TxB, formation (pmol/min) for the different experimental Experiment

n

Description

set-ups

TXB, formation pmol/min

Time study #l

Time O-15 min Time 15-30 min

4.5 f 6.9 +

1.7 2.0

Time study t2

Time O-30 min Time 45-60 min Time 75-105 min

1.1 + 2.5 f 2.4 +

2.4 1.4 1.2

Vasoconstriction experiment

Before NE During NE

4.9 f 17.4 +

1.2 8.1

Temperature experiment

39°C 33°C

2.4 f 2.3 f

0.5 0.6

Flow experiment

Low flow Medium flow High flow

Chlorimipramine experiment

Before chlorimipramme After chlorimipramine

Embolism experiment

Before embolism After 1st embolism After 2nd embolism

1.6 + 0.2 3.9 + 0.6’ 16.9 + 4.7+*

Before H2Q O-5 min after H,O* 5-15 min after (n=5) 30-60 min after (n=4)

1.9 80.4 10.9 4.7

H,O, experiment

t<:~;&ificantly

7

different from the measurement

8.4 -I 1.7 25.7 + 3.3+ 50.4 + 7.3+* 1.7 + 3.0 +

0.5 0.7

+ 1.6 f 43.0’ + 4.2 f 2.8

under baseline conditions (p

*: significantly different from the preceding condition (p < 0.05).

TX and PGI, Production in Perfused Rabbit Lung

set-ups. The perfusion temperature was 37°C except in the temperature experiment, where the temperature was switched between 33°C and 39°C. During embolism, vasoconstriction and immediately after administration of HzOz, the organ volume decreases with - in the case of embolism and vasoconstriction - an increase in the pulmonary artery pressure. Lowering the temperature from 39°C to 33°C causes a slight vasoconstriction which does not alter the vascular volume. Increasing the flow dramatically augments both the organ volume (recruitment) and the pulmonary artery pressure.

243

ministration of 1 mM Hz02 caused a dramatic but transient increase in TXAz production. In addition, the TXB2 were positively correlated with the height of the pressure response seen after Hz02 administration (Spearman’s coefficient of rank correlation, r = 0.98, Figure). TXB2 production also enhanced significantly after glass bead embolization, and when the flow rate was increased.

65

Table 2 summarizes the results of the TXBz RIA. The baseline values in the different experiments differed markedly. In 5 sets of experiments, the basal formation was below 3 pmol/min. In the time study #l and vasoconstriction experiment formation was less than 5 pmol/min, and in the flow experiment 8.4 pmol/min. In the two time studies, the TXB;! formation did not change during the experiment. Neither was it altered by chlorimipramine or small changes in perfusion temperature. Vasoconstriction increased TXB2 formation in several lungs, but other lungs hardly responded. Due to the large variation, the overall increase was not statistically significant. Ad-

-0

0

5

10 min

Table 3 6-oxo-PGF,, formation (pmoi/min) for the different experimental set-ups Experiment

n

Description

PGI, formation pmol/min

Time study #I

Time O-15 min Time 15-30 min

3.1 f 0.6 2.5 + 0.9

Time study #2

Time O-30 min Time 45-60 min Time 75-105 min

1.5 + 0.4 2.2 + 0.4 1.4 f 0.2

Vasoconstriction experiment

Before NE During NE

3.8 f 0.6 3.3 + 1.1

Temperature experiment

39°C 33°C .

2.3 f 0.4 3.2 ? 0.3

Flow experiment

Low flow Medium flow High flow

6.5 f 1.2 7.7 f 1.2 10.3 + 1.5+

Chlorimipramine experiment

Before chlorimipramine After chlorimipramine

1.9 f 0.6 2.4 f 1.1

Embolism experiment

Before embolism After 1st embolism After 2nd embolism

2.2 f 0.6 2.6 f 0.5 4.3 f 1.3

Before H2Q O-5 min after H,O, 5-15 min after (n=5) 30-60 min after (n=4)

2.9 9.6 3.1 1.5

’ : significantly different from the baseline measurement

(p < 0.05).

H,O, experiment

7

TXB*

(pmol/min)

Figure The left panel shows the increase in pulmonary arterial pressure (Ppa, torr) after administration of 1 mM H,O, in 7 different lungs. The lungs represented by the 3 upper curves developed severe edema and did not survive the whole time course of the experiment. In the four lower curves the pressure peaks were small and short lasting. In the right panel the relationship is shown between the TXB, concentrations (pmol/min) and the pulmonary arterial pressure peaks (Ppa, torr) after administration of 1 mM H2q. The r and p values were calculated with the Spearman’s coefficient of rank correlation.

+ + f *

0.9 2.7$ 0.8 0.4

244

F’rostaglandins Leukotrienes and Essential Fatty Acids

6-0x0.PGFl, Table 3 summarizes the results of the 6-oxo-PGFr, for all experiments. As with the TXB2 concentrations, there was a marked difference between the basal values for the different experiments. Five sets of experiments had a basal formation smaller than 3 pmol/min. The time study #l and vasconstriction experiment showed a basal formation between 3 and 4 pmol/min, and the flow experiment a value of 6.5 pmol/min. The 6-oxo-PGFi, formation was remarkably insensitive to the different experimental conditions. An increased production was seen when the flow rate was changed from low to high. A substantial but transient PG12 peak was seen after addition of hydrogen peroxide. This peak was not correlated to the observed pressure peak. The 6-oxo-PGFt, formation was not altered in any other experimental situation.

DISCUSSION The present study is a compilation of the TXB2 and 6-oxo-PGFi, measurements in a variety of experimental set-ups examined in our laboratory. In two time study experiments we showed the stability of the TXB2 and 6-oxo-PGFi, values under control conditions. It should be pointed that the present experiments were also used for the determination of the serotonin uptake by the lung (12 and Peeters et al, submitted). Boluses of serotonin generally ranging from 0.02-162 nmol were injected, giving intracapillary concentrations up to 31 FM. The two time studies indicate that these serotonin injections did not influence the basal prostanoid production. This is consistent with the observations of Shepro and Hechtman (19), who found that incubation with lo-‘* to 10m3M 5-HT did not stimulate PGIz or TXA2 production by primary cultures or aortic endothelial cells. Neither administration of chlorimipramine (a blocker of serotonin uptake) nor changes in temperature influenced the prostanoid production, although these two experimental conditions significantly altered the kinetic parameters of 5-HT uptake (12 and Peeters et al, submitted). Since prostanoid production is enzyme-dependent, it could be expected that prostanoid formation would diminish at lower temperatures. We were unable to observe such a decrease, presumably because the formation at 39°C was already near the detection limit of the RIA. The TXA2 production was very sensitive to changes in organ hemodynamics. An increased production and/or decreased clearance was observed

when the flow was increased, during vasoconstriction (although not significant) and after experimental embolism. These three situations have one aspect in common: an increased flow velocity through the pulmonary vessels. It is well documented that PG12 formation increases when the shear stress to the endothelial cells increase, e.g. because of vasoconstriction (20, 21), glass bead embolization (22) or at increased flow rates (20,2325), and the vasodilator action of PGI2 could regulate the flow capacity of the organ. Although TXA2 is known to be released by pulmonary endothelial cells (26, 27), much less is known about the influence of shear stress on the TXA2 production. Townsley et al (22) found an increased TXB2 formation after glass bead embolization in isolated canine lungs, but Van Grondelle et al (20) did not find a correlation between flow rate and TXB2 formation in isolated guinea pig lungs. In the flow experiments we do not believe that recruitment accounted completely for the increased prostanoid formation. Indeed, TXBz formation increased 6-fold while the organ volume increased less than 2-fold. Therefore, the enhanced prostanoid formation seemed to result partially from an increased shear stress at higher flows. Another supporting argument is, that the TXA2 production increased after embolism, even though the organ volume diminished in this experiment. An increased shear stress can also partially explain the substantially higher basal prostanoid production in the flow experiment. In the flow study, the lungs were preperfused with a flow of 5 ml/s, compared to a preperfusion rate of 2 ml/s in all other situations. However, the preperfusion with dextran may also cause the increased basal prostanoid production in the flow study. The preperfusion with dextran is indeed the most obvious explanation for the increased basal prostanoid production in the time study #l and the vasoconstriction experiment. The PG12 formation was far less influenced by hemodynamic changes. An increased production was only observed when the flow was changed from low (1.7 ml/s) to high (5 ml/s), while no significant fluctuations were seen during vasoconstriction or after embolism. Reactive oxygen species such as H202 are potent initiators of lipid peroxidation. Oxidized phospholipid fatty acids (containing arachidonic acid) are readily cleaved by phospholipase A2 as a step in prostaglandin biosynthesis (27-29). In our experiments, both TXB2 and 6-oxo-PGFi, production increased dramatically after addition of 1 mM H202. The increase was however very transient, and no significantly enhanced levels were detected 15 min after H202 administration. The different sensitivity between TXA2 and PGIz production was very clear: PGI:! production increased 3-fold, while

TX and PGI, Production in Perfused Rabbit Lung

TXA2 production increased 40-fold. Further, the rise in TXES2 production (but not the PGIz production) was correlated to the increased pressure peak after Hz02 administration, supporting a role for TXAz as a mediator of H202 induced vasoconstriction. In a previous study in dog lungs (9) we found formation was an indicator of that 6-oxo-PGFi,, lung injury after complement activation. Our present results support this finding for the rabbit lung, but the PG12 production in the rabbit lung is much less sensitive to experimental changes. Indeed, 1 mM H202, which caused severe edema formation in 3 out of 7 lungs only caused a 3-fold increase in PG12 production. Therefore, in the rabbit lung, TXA;! is much more sensitive as a marker of pulmonary distress (40-fold increase after Hz02), perhaps because biosynthesis and clearance are affected simultaneously. However, it seems excessively influenced by hemodynamic alterations and it is also unclear which cell type is responsible for the increased biosynthesis. References 1. Bult H., Beetens J. R., Herman A. G. Blood levels of 6-oxo-prostaglandin F,, during endotoxin-induced hypotension in rabbits. Eur. J. Pharmacol., 63: 47-56, 1980. 2. Bult H.. Herman A. G. Vascular resoonses and their suppression: the role of endothdlium. In: “Handbook of inflammation. Vol 5: The pharmacology of inflammation”. Eds. Bonta I. L., Brav M. A.. Parnham M. J.. Elsevier Science Publishers B. V., p. 83-105’1985. 3. Flynn J. T. The role of arachidonic acid metabolites in endotoxin shock II: involvement of prostanoids and tromboxanes. In: “Handbook of endotoxin. Vol 2: pathophvsiologv of endotoxin”. Eds. Hinshaw L. B., Elsevier Sc&rce Publishers B.V., p. 237-285, 1985. 4. Huttemeier P. C., Watkins W. D., Peterson M. B., Zapol W. M. Acute pulmonary hypertension and lung thromboxane release after endotoxin infusion in normal and leukopenic sheep. Circ. Res., 50: 688-694,1982. 5. Rie M., Peterson M., Kong D., Quinn D., Watkins D. Plasma prostacyclin increases during acute human sepsis. Circ. Shock, 10: 231, 1983. 6. Slotman G. J., Burchard K. W., Williams J. J., D’Arrezzo A., Yellin S. A. Interaction of prostaglandins, activated complement, and granulocytes in clinical sepsis and hypotension. Surgery, 99: 744-751, 1986. 7. Edlund A., Bomfim W., Kaijser L., Olin C.. Patron0 C., Pinca E., Wennmalm A. Pulmonary formation of prostacyclin in man. Prostaglandins, 22: 323-332,198l. 8. Leithner C., Sinzinger H., Stummvoll H. K., Klein K., Silberbauer K.,-Peskar B. A. Enhanced 6-oxo-PGF,, levels in plasma during hemodialysis. Prostaglandhrs Med., 5: 425-427, 1980. 9. Bult H., Heiremans J. J., Herman A. G., Malcorps C. M. A., Peeters F. A. M. Prostacyclin biosynthesis and reduced 5-I-IT uptake after complement-induced endothelial injury in the dog isolated lung. Br. J. Pharmacol., 93: 791-802, 1988. 10. Lamy M., Deby-dupont G., Pincernail J., Braun M., Duchateau J., Deby G., Van Erck J., Bodson

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