Effects of midodrine on experimentally-induced postural hypotension in dogs

Effects of alpha-(2,5-dimethoxyphenyl)-beta-glycinamide-ethanol hydrochloride (midodrine, ST-1085) on experimental postural hypotension was examined in hexamethonium (20 mg/kg s.c.)-treated anesthetized dogs. The dogs were tilted 30 degrees to a head-up position. A 30 degree-tilt caused a significant decrease in blood pressure. Midodrine, 0.3 mg/kg, attenuated the decrease in blood pressure induced by the tilt significantly at 10 and 30 min after administration of the drug. The heart rate increased following the tilt, but the degree of the increase was rather small. Cerebral tissue blood flow significantly decreased by the tilt. Midodrine, 0.3 mg/kg, significantly attenuated the decrease in cerebral tissue blood flow induced by the tilt at 10 and 30 min. Vertebral arterial blood flow significantly decreased by the tilt. Midodrine reduced the decrease in vertebral arterial blood flow induced by the tilt significantly at 10 and 30 min. Cardiac output also decreased significantly by the tilt. Midodrine attenuated the decrease in cardiac output significantly at 10 min. Femoral arterial blood flow decreased significantly by the tilt. Midodrine tended to reduce the decrease in femoral arterial blood flow induced by the tilt at 30 min. Therefore, midodrine via vasoconstriction seems to be useful for the decrease in blood flows due to the postural hypotension.