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Departments of
1 Surgery and
2 Pharmacology,
A novel cardiac
catheterization technique was devised to investigate the pulmonary
arterial pressure-blood flow relationship in intact spontaneously
breathing rats (ISBR) under physiological conditions with constant left
atrial pressure and controlled blood flow within the normal range.
Observations using this new technique in vivo were contrasted with data
derived with isolated perfused rat lungs in vitro. Unlike results in in
vitro isolated perfused rat lungs, the pressure-flow curves in vivo
were curvilinear, with pulmonary artery pressure increasing more
rapidly at low pulmonary blood flows of 4-8 ml/min and less
rapidly at higher flow rates. Pressure-flow curves were reproducible
and were not altered by 1-1.5 h of arrested perfusion,
cyclooxygenase blockade, or perfusion with aortic or mixed venous
blood. In contrast to results in in vitro isolated perfused rat lungs,
NG-nitro-L-arginine
methyl ester (L-NAME) increased pulmonary arterial pressure
at all but the lowest flow rates with a slight effect on the
curvilinear pressure-flow relationship. L-NAME reversed pulmonary vasodilator responses to acetylcholine and bradykinin and
enhanced the pulmonary vasodilator response to nitroglycerin. The
present data suggest that actively induced pulmonary hypertension is
under greater control by endothelium-derived relaxing factor (EDRF).
Unlike previous results in in vitro perfused rat lungs, results in ISBR
demonstrate that the pulmonary vasodilator response to
adrenomedullin-(13
52) is not mediated by calcitonin gene-related peptide receptors, which are not coupled to the release of EDRF. These
results indicate that this novel technique may provide a useful model
for the study of the pulmonary circulation in the intact chest rat.
pulmonary vascular bed; endothelium-derived relaxing factor-dependent vasodilation; nitric oxide; pressure-flow relationship; adrenomedullin
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