Animals and diets
Twenty four, male, Dunkin Hartley guinea pigs (Cavia porcellus) weighing 700–1000 g were used in this experiment. They were housed individually and were given commercial rabbit chow pellets (Gold Coin Company, Malaysia) daily and a once weekly, vegetable diet of mustard leaves, cabbage and carrot. The animals were divided equally into four groups, i.e. untreated (control), high cholesterol diet-treated (hypercholesterolemic animal), C. domestica plus high cholesterol diet-treated and solely C. domestica diet-treated group.
The control group was given the commercial rabbit chow and vegetable diet through out the experiment. Hypercholesterolemia was induced in the animals by giving cholesterol (Sigma Chemical Co., St. Louis, USA) mixed with the rabbit chow pellet (2% cholesterol, w/w, in food pellet) . For each 100 g of ground rabbit chow pellet, 2 g of cholesterol were added and mixed with a little sterile distilled water. This mixture was made into pellet form and dried in an oven (50°C), overnight. To study the effect of C. domestica, powdered C. domestica was mixed in the rabbit chow (4% C. domestica, w/w, in food pellet) . C. domestica rhizome was purchased from a local market in Kuala Lumpur Malaysia. Powdered C. domestica was prepared by drying the sliced rhizome in an oven at 45°C for 12 hours and grinding it into powder with a blender. The powdered C. domestica was mixed in the rabbit chow in the same way as described for cholesterol.
Collection of serum and aorta
After five weeks of diet treatment, the animals were fasted overnight in preparation for serum and aorta collection. At 8.00 in the morning, the animals were weighed, anesthetized under chloroform and the thoracic abdominal cavity was opened. Blood was collected by heart puncture and serum was separated by centrifugation of the blood. The heart together with the aorta (2–3 cm length) was excised from each animal. The aorta was cut at the origin and removed from the heart. A 2 mm section of the aorta of each animal was soaked in a 10 % (v/v) formal saline solution for H & E staining and another 2 mm section was placed in kriomatrix and kept at -20°C for frozen sections. The remaining aorta was soaked in deionized water and homogenized for biochemical analysis.
Triglyceride level in the serum and aorta were determined using Fletcher's method . Lipid was first extracted from serum and aorta using the method of Folch et al.  before the cholesterol and phospholipid levels were determined. The cholesterol level was determined by carrying out gas chromatography (Chemo 8610HT) as previously described  and detected by FID 8 61 detector. Estimation of cholesterol levels in both samples were calculated using the internal standard method . Phospholipid level was determined according to the method of Murison et al. .
The aorta sections that were soaked in 10% formal saline solution were processed for normal histological section. The tissue samples were ultrasectioned (5–6 μm thickness), stained with hematoxylin and eosin (H&E) and examined under a light microscope for observation of structural abnormality. For frozen sections, ultra-thin sections of the aorta (8 μm thickness) were stained with Schultz stain  and examined for cholesterol deposits.
Mean values obtained in the biochemical analyses were analysed for statistical difference with the Student's t-test.