GHRL and idiopathic pulmonary arterial hypertension: Damico et al. discovered a direct association between high serum endostatin concentrations and poor functional status, decreased exercise tolerance, invasive hemodynamic variables and mortality.56 Furthermore, research by Kumpers et al. demonstrated that high angiopoietin 2 blood concentration correlates with high pulmonary vascular resistance and is consequently an accurate predictor of survival.57 Lastly, Yang et al. detected high ghrelin concentrations in IPAH patients.58 Ghrelin is a hormone produced in the gastrointestinal tract responsible for regulating appetite.