Animals : Male Wistar rats purchased from the National Laboratory Animal Centre, Mahidol University, weighing between 275-300 g were maintained under standardized laboratory conditions (temperature 22 ± 2˚C, 12/12 hr light/dark cycle) for one week acclimatization. They were allowed free access to drinking water and commercial standard rodent pellets. The study protocol including number of animal use was approved by the Animal Ethics Committee of the Faculty of Medicine, Chiang Mai University.