In a rat model of pulmonary arterial hypertension (PAH), which was established by a single injection of monocrotaline, capsaicin pre-treatment reversed PAH, decreased the levels of macrophage/monocytes, and expression of inflammatory cytokines such as IL-1β, IL-6, and TNF-α in lungs. The gene discussed is IL1B; the disease is pulmonary arterial hypertension.