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-mu-M) caused the relaxation of the longitudinal ileal segments. The relaxation induced by 300-mu-M was followed by vigorous contractions. 3. Thalicminine caused only mild relaxation of the trachea. 4. Thalicminine (0.3-300-mu-M) caused concentration-dependent relaxation of epinephrine-precontracted aorta and main pulmonary artery. 5. Propranolol (1-mu-M) failed to reduce the relaxation or to affect the EC50 value of thalicminine on the ileum or the pulmonary artery. 6. Quinacrine (10-mu-M), 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.