Altered artery mechanics and structure in monocrotaline pulmonary hypertension

Pulmonary hypertension in rats, induced by an injection of monocrotaline, is associated with changes in the wall structure of the pulmonary arterial bed. We have studied the effects of this remodeling on mechanical properties of cylindrical pulmonary artery segments from rats 21 days after monocrotaline (MCT) injection. Resting and active (KCl induced) circumference-tension relationships were established for segments of extrapulmonary and intrapulmonary arteries isolated from the hilum and the fifth lateral branch from the axial pathway (all preacinar). The thicknesses of the vessel wall, the media, and adventitia were measured at several positions around the circumference of the artery by computerized analysis of histological cross sections of the segments fixed at a standard circumference. Resting and active stress were also calculated. The study shows that active circumferential tension and active stress are reduced in vessels from MCT-treated rats. Based on our findings, it is unlikely that altered contractile function of preacinar arteries contributes significantly to the increased vascular resistance seen in this model.