[Contrast medium enhanced magnetic resonance angiography. Theory, technique and practical implementation]. / Kontrastmittelverstärkte Magnetresonanzangiographie. Theorie, Technik und praktische Durchführung.

Contrast enhanced (CE) magnetic resonance angiography affords angiographic depiction of extended vascular territories with high quality and diagnostic value. A prerequisite is the fast acquisition of a three-dimensional gradient-echo data set during the injection of a bolus of a T1-shortening contrast agent. We describe the dependence of the quality of CE-MRA on technical parameters of different MR-scanners and consider some fundamental facts and practical guidelines concerning the contrast agent injection.

The effect of steroidal and nonsteroidal anti-inflammatory agents on granulocyte migration into bovine pulmonary artery intimal explants.

To determine whether steroidal or non-steroidal anti-inflammatory agents inhibit granulocyte migration, we measured granulocyte adherence to and migration across the intact endothelial layer of bovine pulmonary artery intimal explants. Explants were placed endothelium uppermost in chemotaxis chamber with either fetal calf serum (FCS) or zymosan activated plasma (ZAP) in medium 199 in the lower well and 5 X 10(6) separated 51Cr labelled granulocytes/ml in medium 199 + FCS in the upper well. Methylprednisolone (0.3 and 3.0 mg/ml), indomethacin (5 and 50 microM) and ibuprofen (10 and 100 microM) were also added to the upper well of some chambers. After 30, 60, 120 or 180 minutes of incubation the chambers were dismantled. Granulocyte adherence was assessed by rinsing the explant in 0.1% trypsin; the number of radioactive counts in the trypsin wash represented the number of adherent cells. Those remaining in the explant represented the number of granulocytes that migrated into the explant. At each time studied, chemotaxin-induced granulocyte migration was 2-3 times that of unstimulated or random migration (180 min incubation with FCS = 30.5% +/- S.E. 2.1; with ZAP in lower well = 61.6 +/- 3.4). Both unstimulated and chemotaxin-induced migration was significantly decreased from 30 minutes by 3.0 mg/ml of methylprednisolone (180 min incubation with ZAP in lower well = 22.3 +/- 5.8), but not by 0.3 mg/ml. However, one hour pretreatment of either the granulocytes or the explant with 3.0 mg/ml methylprednisolone had no significant effect on granulocyte migration. In contrast, granulocyte migration was unaltered by treatment with either indomethacin or ibuprofen. Methylprednisolone, indomethacin and ibuprofen had little effect on granulocyte adherence. We conclude that granulocyte migration across an intact endothelial layer is inhibited by high dose corticosteroids but not by cyclooxygenase inhibitors. This suggests a plausible rationale for use of high doses of corticosteroids in clinical states where granulocytes may mediate tissue injury.

Pulmonary hypertension and increased vasoreactivity caused by repeated indomethacin in sheep.

Six chronically catheterized awake sheep were given the cyclooxygenase inhibitor indomethacin (5 mg/kg) twice a day over a 3-wk period. Three sheep receiving vehicle alone served as controls. Pulmonary arterial, left atrial, and systemic arterial pressures, cardiac output, blood gases, and pH were measured biweekly. Pulmonary vasoreactivity to 12% O2 and an analogue of prostaglandin H2 (PGH2-A) was also assessed. As a percent of base line, indomethacin caused a doubling in pulmonary vascular resistance (3 wk = 190 +/- 26%, mean +/- SE) and a 50% increase in pulmonary arterial pressure (3 wk = 151 +/- 9%). Vasoreactivity to 12% O2 increased approximately fourfold during the 1st wk of treatment and then declined. Vasoreactivity to PGH2-A increased steadily, nearly doubling by 3 wk. Light-microscopic counts of peripheral lung biopsy tissue revealed marked sequestration of granulocytes. Morphometric techniques applied to lungs removed at autopsy and fixed with the pulmonary arteries distended with barium gelatin mixture showed a significant reduction in number of barium-filled peripheral arteries and reduction in their external diameter. We conclude that repeated administration of indomethacin alters pulmonary vasoreactivity and causes sustained pulmonary hypertension. Structural studies reveal peripheral lung inflammation and changes in the arterial circulation that are perhaps more consistent with maintained vasoconstriction than chronic pulmonary hypertension.

Facilitation of granulocyte migration into bovine pulmonary artery intimal explants by intact viable endothelium.

To characterize the role of normal endothelium in granulocyte chemotaxis, the authors measured granulocyte adherence to and migration into bovine pulmonary artery intimal explants. Explants were placed, endothelium uppermost, in chemotaxis chambers with zymosan-activated plasma in the lower well and 5 X 10(6)/ml 51Cr-labeled granulocytes in the upper well. After 15, 30, 60, 120, 180, or 240 minutes incubation at 37 C, granulocyte adherence was measured by removal of adherent granulocytes from the endothelial layer with a 0.1% trypsin wash and counting of radioactivity in the wash. Scanning electron microscopy confirmed that this technique removed the majority of adherent cells from the endothelial surface without disrupting its continuity. Migration was calculated by counting of the remaining radioactivity in the explant. Granulocyte migration with Medium 199 alone in the lower well (random migration) was 36 +/- 3% by 3 hours. Chemotaxis-induced migration at each time studied was 1.5-2 times random migration. Granulocyte adherence was between 4% and 9% in both groups at all times examined. In some experiments, either endothelium was removed from explants or explants were fixed with glutaraldehyde prior to experimentation. Removal of endothelium resulted in a two-fold increase in granulocyte adherence but no significant difference in migration, compared with intact intimal explants. Glutaraldehyde fixation of explants resulted in more tightly adherent granulocytes and significantly less migration. With lactate dehydrogenase as a marker of endothelial cell damage, granulocyte migration in response to zymosan-activated plasma did not injure endothelium. It is concluded that, in blood vessels, chemotaxis is an interactive process between granulocytes and endothelium and that intact, viable endothelium facilitates granulocyte migration.

Effect of N-acetylcysteine on the pulmonary response to endotoxin in the awake sheep and upon in vitro granulocyte function.

Oxygen free radicals released during endotoxemia may contribute to the lung injury of the adult respiratory distress syndrome (ARDS). As this syndrome occurs frequently after gram-negative sepsis in humans, we studied the effect of intravenous N-acetylcysteine (NAC), a free radical scavenger, upon the endotoxin (E)-induced model of ARDS in awake sheep. In vivo studies demonstrated that NAC attenuates the endotoxin-induced rise in pulmonary artery pressure (62 +/- 3 torr with E control vs. 43 +/- 3 torr for E + NAC), and markedly diminishes the rise in lymph flow at 1 h (8.5 +/- 1.2 vs 4.5 +/- 0.6 ml/15 min) and 4 h (5.0 +/- 0.6 vs. 3.3 +/- 0.4 ml/15 min), respectively, for E control vs. E + NAC. NAC also markedly attenuated the alterations in lung mechanics after endotoxemia. Dynamic compliance at 2 h after endotoxemia was 44 +/- 6% of base line for E vs. 76 +/- 10% of base line for E + NAC. Resistance to airflow across the lung at 1 h postendotoxin was 811 +/- 280% of base line for E vs. 391 +/- 233% of base line for E + NAC. NAC substantially reduced the 1 h postendotoxin rise in lymph concentrations of thromboxane B2 (8.29 +/- 3.28 vs. 2.75 +/- 1.93 ng/ml for E vs. E + NAC) and 6-keto-prostaglandin-F1 alpha (0.91 +/- 0.27 vs. 0.23 +/- 0.12 ng/ml for E vs. E + NAC). In addition, in vitro studies were performed which revealed NAC to be a potent free radical scavenger in both biologic and nonbiologic free radical generating systems. NAC decreased phorbol-stimulated granulocyte aggregation in a concentration-dependent manner in vitro. Minimal effects were observed, however, upon leukocyte degranulation at the concentrations of NAC achieved during the in vivo tests. Thus, NAC significantly attenuated all monitored pathophysiologic changes in the endotoxin model of ARDS in sheep, possibly by its ability to scavenge toxic oxygen free radicals. A direct impairment of the ability of inflammatory cells to generate oxygen radicals cannot be ruled out.

Septicemia and lung injury.

The results of investigations undertaken by the authors which deal with the functional and structural changes in the lungs resulting from gram-negative bacterial endotoxemia and the mechanisms of these changes are analyzed. The authors emphasize the major roles played by granulocytes and metabolites of arachidonic acid in mediating endotoxin-induced lung injury.