PULMONARY VASODILATOR ACTION OF TOLAZOLINE

The pulmonary vasodilator action of tolazoline in newborn lambs was shown to be mediated via histamine receptors. Maximal changes in pulmonary vascular resistance, ∆PVR, were calculated as percents of the base line value, %∆PVR. The mean %∆PVR after tolazoline, 1 mg/kg, was —25 ± 4% for eight lambs. Four lambs then received the histamine Hi receptor antagonist, diphenhydramine, and the mean %∆PVR due to tolazoline was — 12 ± 4%. Four lambs received the H2 receptor antagonist, metiamide, and the mean %APVR due to tolazoline was —18 ± 5%. After both Hi and H2 antagonists, the mean %∆PVR due to tolazoline was +6 ± 8%. Therefore, both histamine H1 and H2 receptors were involved in the vasodilator response to tolazoline. © 1979 International Pediatric Research Foundation, Inc.