APLNR and pulmonary arterial hypertension: However, the study reported that apelin mRNA and protein expressions were markedly depressed in spontaneously hypertensive rats (SHR) [10] The new study confirmed that Elabela/Toddler expression, as an endogenous agonist of the APJ receptor, was reduced in cardiopulmonary tissues from pulmonary arterial hypertension (PAH) patients and PAH rat models [25].