Effects of peroxisome proliferator-activated receptor gamma ligands on monocrotaline-induced pulmonary hypertension in rats

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear hormone receptor superfamily, which regulates transcription of target genes in a ligand-dependent manner. Ligands for PPARgamma have been shown to attenuate proliferation of vascular smooth muscle cells, and to induce apoptosis in several cell lines in vitro. Since monocrotaline (MCT)-induced pulmonary hypertension in rats is characterized by proliferation of pulmonary vascular smooth muscle cells, we hypothesized that PPARgamma ligands may reduce MCT-induced pulmonary hypertension. To test this hypothesis, we treated MCT-injected rats with pioglitazone and troglitazone, synthetic ligands for PPARgamma, for three weeks and measured pulmonary artery pressure and pulmonary vessel wall thickness. TdT-mediated dUTP-biotin nick end labeling (TUNEL) and immunostaining for proliferating cell nuclear antigen (PCNA) were utilized to assess apoptosis and cell proliferation in the pulmonary arterial walls of pioglitazone-treated rats. MCT with pioglitazone or troglitazone treatment significantly reduced pulmonary hypertension and wall thickening of the pulmonary arteries. TUNEL-positive apoptotic cells were not seen in the pulmonary arterial walls of either MCT-injected or control rats with or without pioglitazone. PCNA-positive cells were only seen in the thickened pulmonary arterial walls of MCT rats, but not in the pulmonary arterial walls of controls and of pioglitazone-treated MCT rats. We conclude that PPARgamma ligands reduce MCT-induced pulmonary hypertension and pulmonary vascular wall thickening in rats. Inhibition of MCT-induced cell proliferation in the pulmonary arterial walls may account for this effect