Comparative effects of nicorandil and nitroglycerin on tracheal and vascular smooth muscle in the dog, in vivo and in vitro.

The effects of nicorandil (NCR) on tracheal and vascular smooth muscle in the dog were compared with those of nitroglycerin (NTG) in in vitro and in vivo preparations. In the isolated tracheal strip and coronary artery preparations contracted with KCl (30 mM), the ability of NCR to relax these muscles and arteries by 50% was 1/10-1/15 as potent as NTG. In blood-perfused tracheal preparations, single doses of NCR and NTG injected into the tracheal artery produced dose-related decreases in the intraluminal pressure (ILP) of the trachea (relaxation) and increases in the tracheal blood flow (TBF). When the potency of NCR relative to that of NTG was compared on the basis of doses decreasing the ILP and increasing the TBF by 50%, NCR was 822 times less potent than NTG in producing tracheal relaxation and 572 times less potent in producing tracheal vasodilation. The effects of NCR on the ILP and TBF were not antagonized by propranolol. In non-perfused tracheal preparations, the two drugs administered i.v. elicited the effects in a similar dose-dependent manner; decreases in systemic blood pressure (SBP), left ventricular systolic pressure (LVP), pressure-rate product (PRP), femoral vascular resistance (FVR), and ILP and increases in heart rate (HR) and LVdP/dt max. The results show that NCR has a potent bronchodilating action and that its pharmacological profile is somewhat similar to NTG.