Pulmonary vascular responses to ma huang extract.

OBJECTIVE To test the hypothesis that ma huang induces a pressor response in the pulmonary vascular bed of the cat by activating alpha(1)-adrenergic receptors DESIGN Prospective vehicle-controlled study. SETTING Research laboratory at Texas Tech University School of Medicine, Lubbock, TX. SUBJECTS Intact chest preparation; adult mongrel cats. INTERVENTIONS The effects of phentolamine, a nonselective alpha receptor blocker, and prazosin, an alpha(1) selective antagonist, were investigated on pulmonary arterial responses to ma huang, phenylepherine, norepinephrine, and U-46619, a thromboxane A(2) mimic. MEASUREMENTS AND MAIN RESULTS Lobar arterial perfusion pressure was continuously monitored, electronically averaged, and recorded with constant flow in the isolated left lower lobe vascular bed of the cat. Phentolamine and prazosin significantly reduced vasoconstrictor pulmonary perfusion pressure increases induced by ma huang. CONCLUSIONS Ma huang has significant vasopressor activity in the pulmonary vascular bed of the cat mediated predominantly by alpha(1)-adrenergic receptor activation.