Observations on the pharmacology of thalicminine, an oxyaporphine alkaloid from Thalictrum isopyroides

1. The effects of the oxyaporphine alkaloid thalicminine on guinea-pig isolated ileum, trachea, aorta and pulmonary artery and on blood pressure and heart rate of anesthetized guinea-pigs were studied. 2. Thalicminine (1-300 microM) caused the relaxation of the longitudinal ileal segments. The relaxation induced by 300 microM was followed by vigorous contractions. 3. Thalicminine caused only mild relaxation of the trachea. 4. Thalicminine (0.3-300 microM) caused concentration-dependent relaxation of epinephrine-precontracted aorta and main pulmonary artery. 5. Propranolol (1 microM) failed to reduce the relaxation or to affect the EC50 value of thalicminine on the ileum or the pulmonary artery. 6. Quinacrine (10 microM), on the Other hand, potentiated thalicminine-induced relaxation and reduced the EC50 on the aorta and the pulmonary artery suggesting the interference of thalicminine with arachidonic acid metabolism. 7. In anesthetized Animals, intravenous injections of 0.37-1.1 mg kg of thalicminine caused transient reduction of systolic and diastolic blood pressure and heart rate. Both parameters returned to their normal values in about 10 min.