Interleukin-1 receptor antagonist treatment reduces pulmonary hypertension generated in rats by monocrotaline

Chronic pulmonary hypertension is associated with significant vascular remodeling. We demonstrated recently in the monocrotaline (MCT) and chronic hypoxia rat models of pulmonary hypertension that treatment with platelet-activating factor (PAF) antagonists inhibited the development of chronic pulmonary hypertension. PAF and other lipid mediators interact with interleukin-1. We postulated that chronic treatment with a recombinant human interleukin-1 receptor antagonist (IL-1ra) would inhibit development of chronic pulmonary hypertension in animal models. Rats were either injected with (60 mg/kg) MCT or exposed to a stimulated high altitude of 16,000 feet; half of the animals were treated with twice-daily injections (2 mg/kg) of IL-1ra. At 3 wk after MCT injection or 3 wk of hypoxic exposure, pulmonary artery pressure and right heart ventricle weight/(left ventricle and septum weight), RV/(LV + S), were measured. IL-1ra treatment reduced pulmonary hypertension and right heart hypertrophy in the MCT model, but not in the chronic hypoxia model. Measurement of lung homogenate IL-1 alpha by radioimmunoassay showed elevated levels in the MCT-treated rats throughout the 3-wk observation period. IL-1ra treatment reduced the levels of IL-1 alpha in lung tissue in most of the MCT-treated rats. MCT treatment was also associated with an increase in lung mRNA for IL-1 alpha, IL-1 beta, and IL-1ra. Immunohistology, using an antibody against rat IL-1 alpha, revealed staining of alveolar structures and of vascular and bronchial smooth muscle. In situ hybridization using a human IL-1 alpha cDNA probe demonstrated increased expression of the IL-1 alpha gene in the lung cells after endotoxin or MCT treatment. Northern blot analysis demonstrated low-level expression of IL-1 alpha mRNA in extracts of normal rat lung and increased expression after endotoxin or MCT treatment. We conclude that chronic treatment with human IL-1ra inhibited the development of pulmonary hypertension in the inflammatory (MCT) model, but not in the chronically hypoxic rats. This result indicates that IL-1 participates in the pathogenesis of some forms of pulmonary hypertension.