**3.1.2 OAT activity assay**

The renal cortex of male and female mice was dissected and prepared to quantify OAT activity. To determine the conditions for assay of OAT activity, the incubation time was tested every 5 min up to 30 min and the protein concentration varied from 0 to 400 µg per sample. OAT activity increased linearly with the concentration of soluble proteins up to 400 µg in male mouse cortex and 300 µg in that of the female when the incubation time was fixed at 30 min (Fig.2 left, male: r2=0.99809 and female: r2=0.99583, *P* < 0.01). OAT activity increased linearly in proportion with the incubation time up to 30 min when the concentration of soluble proteins was fixed at 140 µg in both male and female mice (Fig. 2 right, male: r2=0.99352 and female: r2=0.9972, *P* < 0.01). Constantly, OAT activity was more than three-fold higher in female than in male mouse kidney. The sex-differential OAT activity found in the present results is in good agreement with published data (Levillain et al., 2007; Ventura et al. 2009).

Fig. 2. Technical verifications to determine the conditions for OAT assay.

Closed circles: female mouse kidney and closed triangles: male mouse kidney. In all cases, the coefficient of correlation was statistically significant (*P* < 0.01 or less).
