Evidence for a central muscarinic action by 1-(2-methyl-3-hydroxy-5-hydroxymethyl-4-pyridyl)-6,7-dihydroxy-1,2, 3,4-tetrahydroisoquinoline in regulating blood pressure in the anesthetized dog.

Anesthetized dogs injected with 1-(2-methyl-3-hydroxy-5-hydroxymethyl-4-pyridyl)-6,7-dihydroxy-1,2, 3,4-tetrahydroisoquinoline (PTIQ) into the common carotid artery, showed an immediate fall in blood pressure, whereas injection into the femoral vein produced a fall in blood pressure after a lapse of approximately 8 sec. Anesthetized dogs pretreated with atropine showed a decrease in mean blood pressure of 22% of control (PTIQ alone) after PTIQ was injected. In contrast, dogs pretreated with methylatropine showed a decrease of 41% of control after PTIQ was injected. Our data suggest that PTIQ may act centrally and peripherally by activation of muscarinic receptors.