Monocrotaline is an 11-membered macrocyclic pyrrolizidine alkaloid derived from the seeds of the Crotalaria spectabilis plant. Monocrotaline is activated to the reactive pyrrole metabolite dehydromonocrotaline in the liver, a reaction that is highly dependent on cytochrome P-450 (CYP3A4). Monocrotaline induces a syndrome characterized, among other manifestations, by pulmonary hypertension, pulmonary mononuclear vasculitis (acute necrotizing pulmonary arteritis in about one-third of the animals), and right ventricular hypertrophy. Monocrotaline is widely used to model pulmonary arterial hypertension in rodents. Monocrotaline aggregates on and activates the extracellular calcium-sensing receptor (CaSR) of pulmonary artery endothelial cells to trigger endothelial damage and, ultimately, induces pulmonary hypertension.

Dimethylphenylpiperazinium (DMPP) is an agonist of nicotinic acetylcholine receptor. DMPP regulates smooth muscle contractility. In addition, it exerts anti-inflammatory properties.