General pharmacological properties of cilostazol, a new antithrombotic drug. Part II: Effect on the peripheral organs.

The pharmacological effects of the new antithrombotic drug, cilostazol (6-(4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-qui nolinone, OPC-13013) on the peripheral nervous system and miscellaneous organs were studied. Cilostazol produced a very slight increase in beating rate of the isolated atrium and a very slight increase in contraction of the papillary muscle of guinea pigs induced by cilostazol compared with that of isoproterenol (isoprenaline). The beating rate increasing effect was not antagonized by propranolol and it augmented isoproterenol's effect. When administered intravenously in anesthetized dogs, cilostazol increased blood flow in the coronary, internal carotid, vertebral and femoral arteries and transiently decreased blood flow in the renal and superior mesenteric arteries probably because of blood pressure fall. In anesthetized dogs, cilostazol decreased blood pressure by reducing the resistance in the peripheral blood vessels. An increase in heart rate, cardiac contractile force, myocardial oxygen consumption and respiration rate were also observed. In conscious rats, the drug increased heart rate. Cilostazol produced a slight relaxation of the smooth muscle of all organs except for blood vessels and slightly inhibited spontaneous motility of the isolated uterus of pregnant rats, the isolated ileum of rabbits and the ileum of rats in situ. It was considered that cilostazol had no specific effects against norepinephrine, serotonin, acetylcholine or histamine based on the results that the drug was only slightly antagonistic against the contraction of rabbit aorta induced by norepinephrine and serotonin, the contraction of isolated guinea-pig ileum induced by acetylcholine, histamine and barium chloride and the contraction of the isolated uterus of non-pregnant rats induced by oxytocin. The drug had little effect on the contraction of the nictitating membrane induced by stimulation of the preganglionic sympathetic nerve in the cat. These results suggest that cilostazol had little effect on the autonomic nervous system. Cilostazol slightly inhibited edema induced by carrageenin, but showed no diuretic effect and had little effect on neuromuscular transmission or the secretion of gastric juice, bile and pancreatic juice, and therefore it was considered to have no appreciable effect on the peripheral nervous system or organs except for its vasodilating and cardiac effects.