Abstract

Background:
Pulmonary hypertension (PH) is a progressive disorder characterized by vasoconstriction, in situ thrombosis, and remodeling of small pulmonary arteries, leading to increased pulmonary vascular resistance and right ventricular failure. Despite extensive research using diverse animal models, the pathogenesis of this arteriopathy remains incompletely understood. The pyrrolizidine alkaloid monocrotaline (MCT) is a well-established agent for inducing PH in rats through endothelial injury and subsequent precapillary vascular remodeling.

Aim:
The objective of this study was to investigate the lobar distribution of pulmonary lesions in a wellcharacterized rat model of MCT pulmonary hypertension through hemodynamic, arterial blood gas analysis (ABG), and immunohistochemical assessments, in order to contribute to the pathophysiological characterization of this experimental model in veterinary and comparative medicine.

Methods:
Twenty rats were assigned to two groups: control (n = 10) and PH (n = 10; single subcutaneous dose of MCT, 80 mg/kg). After an eight-week induction period, animals underwent hemodynamic, ABG, and immunohistochemical evaluations.

Results:
Rats with PH exhibited significantly increased mean pulmonary arterial pressure (42.90 ± 9.04 mmHg vs. 21.2 ± 4.51 mmHg; p = 0.0003, Student’s t-test) and decreased blood pH (p < 0.05, Student’s t-test). Immunohistochemistry demonstrated expression of CD31, von Willebrand factor, endothelin-1, and α-smooth muscle actin. Histopathological analysis confirmed vascular remodeling in 80% of PH animals (p < 0.05, χ² test) and revealed a predominance of lesions in the cranial lobe (p < 0.05, χ²).

Conclusion:
These findings demonstrate marked lobar heterogeneity of pulmonary and vascular lesions in monocrotaline-induced PH and support the utility of this model for veterinary research, experimental animal medicine, and comparative pulmonary pathology.

Key words: Histopathology; Lung lobes; Pulmonary artery; Rat; Vascular remodeling.