Abstract
The antihypertensive effect of $\alpha-Methyldopa$ administered concurrently with timolol or labetalol were studied with spontaneously hypertensive rats (SHR). Every drugs were administered orally once a day after prechecking the systolic blood pressure and heart rate of SHR. The blood pressure and heart rate of SHR were significantly decreased in groups of combination while those of non-combination groups were fallen slightly. Compared with control group, the significant changes of blood pressure was obseved in group of $\alpha-methyldopa$ with timolol(100mg+2mg/kg)and $\alpha-methyldopa$ with labetalol (100mg+12.5mg/kg). The group of $\alpha-methyldopa$ with timolo 1 (100mg + 1.0mg/kg) reduced blood Pressure in similar degree as manifested in group of $\alpha-methyldopa$ with labetalol (100mg + 50mg/kg). In the group that $\alpha-methyldopa$ was administered concurrently with timolol, the maximum antihypertensive effect and heart rate decreasing effect were appeared after 3hr and 1hr of administration respectively and those effects in group of $\alpha-methyldopa$ with labetalol were appeared after 6hr of administration. The acute oral toxicity test was performed using albino mice with $\alpha-methyldopa$ alone, $\alpha-methyldopa$ with timolol (100:1) and $\alpha-methyldopa$ with labetatol (4:1), and was found that the $LD_{50}$ of $\alpha-methyldopa$ alone was 1104 mg/kg, $\alpha-methyldopa$ with timolol (100:1) was 1115 mg/kg and $\alpha-methyldopa$ with labetalol (4:1) was 354mg/kg.