Table 2.

4 × 4 Latin square design

Animal no.	Treatment I	Treatment II	Treatment III	Treatment IV
1	V	L	H	M
2	L	M	V	H
3	M	H	L	V
4	H	V	M	L

V: vehicle control group; L: low dose group; M: middle dose group; H: high dose group; at least 3 days washout period between two treatments.