Activity of boldine on rat ileum

Boldine shows a concentration-dependent relaxation effect on the rat ileum preparation with a pD2 of 3.77 +/- 0.12. The alkaloid also produces a concentration-dependent parallel shift of the curve-response to acetylcholine, therefore it directly interferes with the cholinergic mechanism associated with the contraction, behaving as a competitive antagonist with a pA2 of 4.78 +/- 0.19. On the other hand, boldine produces a nonparallel shift of the contraction response induced by barium, revealing the occurrence of a non-competitive antagonism. This effect could be the result of interference with intracellular events associated with the barium-induced changes in calcium pools.