A Mitra, SJ Feinmark and PO Alderson
Department of Radiology, College of Physicians and Surgeons, Columbia- Presbyterian Medical Center, New York, New York 10032, USA.

To investigate the mechanisms responsible for the accelerated radioaerosol transalveolar clearance rates caused by acute balloon occlusion of the pulmonary arterial tree in dogs, the effects of vagal tone (n = 5) and prostaglandins (n = 21) including thromboxane were evaluated. In 15 animals, serial pulmonary arterial and aortic blood samples were acquired to evaluate pertinent metabolic products. Balloon occlusion of a localized arterial territory caused significant acceleration of technetium-99m diethylenetriamine pentaacetic acid (Tc- 99m DTPA) clearance in the zone immediately distal to the occlusion (baseline clearance half-time 23.1 +/- 0/7 min versus 19.3 +/- 0.4 min, mean +/- SEM, p < 0.05). Vagotomy had no effect on occlusion- accelerated clearance. However, significant (p < 0.05) normalization did occur in the presence of indomethacin (21.9 +/- 0.4 min) and meclofenamic acid (20.4 +/- 0.5 min). Plasma values of thromboxane rose dramatically (pulmonary blood baseline 119 pg/ml to > 40,000 pg/ml) and transiently immediately after pulmonary vascular occlusion, and this rise was blunted significantly (peak pulmonary thromboxane B2 [TXB2] concentration = 668 pg/ml, p < 0.05) by meclofenamic acid. Significant normalization of local DTPA clearance rates also occurred in the presence of a thromboxane receptor blocker (n = 4), even when blood levels of thromboxane were elevated. Changes in transalveolar DTPA clearance rates after balloon occlusion of pulmonary arteries seem to a significant extent to be thromboxane-mediated.