ACE and pulmonary arterial hypertension: In the monocrotaline (MCT)-induced pulmonary hypertension rat model, C-21 treatment reversed both interstitial and perivascular fibrosis. Furthermore, a decrease in ACE2 messenger RNA (mRNA) levels was observed in MCT-induced pulmonary hypertension animals, which was reversed by C-21 therapy with a two-fold increase in ACE2 levels and a concomitant decrease in ACE expression [23].