Computerized morphometry of the pulmonary vasculature over a range of intravascular pressures.

Recent availability of computerized image analysis has fostered hope that barium injection and landmarking of pulmonary arteries would be unnecessary for morphometric assessment when using this technique. We reasoned that if barium injection altered morphometric variables, it would do so in a linear fashion correlating with incremental increases in injection pressure of the barium. The two goals of the present study were to determine whether barium injection into arteries affected morphometric measurements and to determine whether incremental increases in injection pressure correlated with alterations in morphometric measurements in a linear fashion. Computerized image analysis was used to measure the internal elastic lamina (IEL) and external elastic lamina (EEL). Medial area (MA), luminal area (LA), percentage of medial thickness, IEL square root of MA, and idealized LA were calculated. Barium injection did not alter morphometric variables in a linear fashion correlating with incremental increases in injection pressure of the barium except the percentage of arteries that filled with barium. Maximum recruitment for pre-acinar arteries occurred at 40 mmHg pressure and 60 mmHg distending pressure for intra-acinar arteries. Incremental increases in injection pressure did not affect IEL, EEL, or calculated morphometric variables. However, IEL, medial thickness, and MA were all smaller in injected vessels than in uninjected vessels. IEL square root of MA and the ratio of measured vs. idealized LA were both increased in injected lungs. We suspect that vascular injection selects for evaluation, a population of smaller, thin-walled vessels, which in the uninjected lungs are collapsed and hence excluded from analysis.

Chronic platelet-activating factor induces a decrease in pulmonary vascular compliance, hydroxyproline, and loss of vascular matrix.

We have previously demonstrated that chronic intravenous platelet-activating factor (PAF) induces morphologic remodeling of pulmonary arteries characterized by a decrease in internal and external elastic lamina circumference, pulmonary arterial contracture, and internal elastic lamina duplication. The mechanism of PAF-induced arterial contracture is unknown. In this study we determined whether PAF caused arterial contracture through cell loss by calculating the number of cell nuclei/total cross-sectional area of arteries. The nuclear ratio was increased in intra- and preacinar pulmonary arteries of PAF-treated rabbits. Hydroxyproline content of lungs stratified by anatomic region was significantly reduced in intra-acinar tissue of PAF-treated rabbits, indicating that PAF-induced vascular contracture was associated with loss of interstitial collagen. We next tested whether these morphologic alterations were associated with decreased pulmonary vascular compliance and increased resistance. Compliance and resistance were determined in isolated, perfused lungs from rabbits chronically treated with PAF. Compliance was calculated: (1) from the slope of the venous occlusion trace (CVO), (2) by increasing left atrial pressure (CLA), (3) by increasing flow (CHF), and (4) by the classic static technique (CAV) of adding volume (2 ml) to a passively drained lung. Vascular compliance was significantly reduced in PAF-treated lungs when measured by all four methods; however, pulmonary vascular resistance was unchanged. We conclude that structural changes that result from chronic intravenous PAF infusion affect the elastic modulus to a greater extent than factors that influence pulmonary vascular resistance.

Platelet-activating factor induces selective pulmonary arterial hyperreactivity in isolated perfused rabbit lungs.

The role of vasoreactivity in PAF-induced pulmonary hypertension (PHT) was assessed in isolated, perfused rabbit lungs. We evaluated the steady-state pulmonary vascular response to five vasoconstrictors: PGF2 alpha, norepinephrine, angiotensin II, PAF, and KCl. Pulmonary arterial pressure and pulmonary vascular resistance (PVR) were significantly greater in lungs of rabbits treated with PAF for 28 days than in control rabbits in response to PGF2 alpha and norepinephrine. When resistance was partitioned by the vascular occlusion method, at baseline the vascular resistance was equally distributed between arterial and venous segments in both experimental groups. Arterial resistance accounted for approximately 76% of PVR during norepinephrine injection and 60% of PVR during PGF2 alpha injection in PAF-treated lungs. Whereas arterial resistance accounted for approximately 63% of PVR during norepinephrine injection and 52% of PVR during PGF2 alpha injection in control lungs, there was no significant difference in the response to angiotensin II, acute PAF, and KCl in lungs from chronic PAF-treated rabbits compared with responses in control rabbit lungs, though the pressor response to acute PAF tended to be blunted in PAF-treated lungs. Chronic PAF treatment results in enhanced pulmonary arterial reactivity to selected autacoids in isolated perfused lungs.

Administration of chronic intravenous platelet-activating factor induces pulmonary arterial atrophy and hypertension in rabbits.

Platelet-activating factor (PAF), a lipid mediator of inflammation, was given by continuous intravenous infusion to rabbits for 2, 4, and 8 weeks, and morphologic and hemodynamic findings were correlated. Pulmonary arterial pressure (PAP), cardiac output, and right atrial pressure were measured, and total pulmonary resistance was calculated. In cross-sections of intraparenchymal pulmonary arteries, internal elastic lamina circumference and intimal and medial areas were measured. The ratio of the weight of the right ventricle to the weight of the left ventricle plus septum, and alveolar/artery ratios were also obtained. In bronchoalveolar lavage fluid, total and differential cell counts were determined. After 2 weeks of PAF treatment, PAP rose by 4 mm Hg. The increase in PAP became significant by 4 weeks and remained so at 8 weeks of treatment. Total pulmonary resistance nearly doubled by 2 weeks and continued to be elevated throughout 8 weeks of PAF treatment. Cardiac output fell significantly to 0.26 liters/minute at 2 weeks of PAF treatment and remained low at 4 weeks. By 8 weeks of treatment, it normalized. The significant rise in total pulmonary resistance at 2 and 4 weeks correlated with the rise in PAP and the fall in cardiac output. The alveolar/artery ratio was increased at 2 weeks of treatment and progressively increased at 4 and 8 weeks, reaching statistical significance at 8 weeks. In intra-acinar arteries, after 2 weeks of treatment, there was a reduction in total cross-sectional area (within the external elastic lamina), medial area, and internal elastic lamina circumference measured by computerized image analysis of 5-microns thick Verhoeff Van Gieson-stained sections. Changes in total area, medial area, and internal elastic lamina circumference persisted after 4 and 8 weeks of treatment. In preacinar arteries, similar changes occurred that were significant only after 8 weeks of treatment. Other findings apparent at 2 weeks of treatment included right ventricular hypertrophy and a marked decline in the number of macrophages and lymphocytes recovered from bronchoalveolar lavage fluid. We conclude that chronic intravenous infusion of PAF in rabbits induces remodeling of pulmonary arteries, specifically reduction of the internal elastic lamina, with consequent narrowing of arterial lumens producing increased pulmonary vascular resistance and pulmonary hypertension. We attribute the increase in alveolar/artery without evident vessel obliteration, to a shortening of arterial length, which is of insufficient magnitude to overcome the effect of vessel narrowing on vascular resistance.

A rabbit model of pulmonary hypertension induced by the synthetic platelet-activating factor acetylglyceryl ether phosphorylcholine.

Development of effective treatment for human pulmonary hypertension (PHT) has been hampered by an incomplete understanding of its pathogenesis. We present a rabbit model of PHT based on platelet-activating factor (PAF), a potent phospholipid autacoid synthesized by a variety of mammalian cells. PAF was intravenously infused into rabbits for 4 wk. After the infusion, rabbits underwent pulmonary arterial catheterization for hemodynamic evaluation, and lung tissue was morphometrically analyzed for changes in cross-sectional areas of intima and media, and alteration in number of small pulmonary arteries. The heart was evaluated by the method of Fulton for right ventricular hypertrophy. Mean pulmonary arterial pressure was 20 +/- 2 mm Hg in PAF-treated rabbits compared with 12 +/- 1 mm Hg in vehicle-treated control rabbits. PAF induced a trend toward loss of small muscular pulmonary arteries, measuring 50 to 200 microns in diameter, and right ventricular hypertrophy. There was a decrease in circumference of the internal elastic lamina in vessels accompanying alveolar ducts and in alveolar walls, and a relative increase in the intimal cross-sectional area of these vessels. These lesions were associated with a trend toward medial hypertrophy. No increase in lung water was found. Pressure changes occurred in the absence of alterations in hematocrit and arterial partial pressure of oxygen. We conclude that chronic intravenous infusion of PAF, a naturally synthesized substance, into rabbits provides a potentially useful model for the study of vascular changes associated with PHT.