RESUMO
Objective:To investigate the therapeutic effect of levo-thyroxine ( L-T 4) gel on hypothyroidism in rat model. Methods:A total of 30 Wistar rats (15 males, 15 females, 2-month age) were completely randomized into 6 groups ( n=5 per group) with one group as the normal control and the other 5 groups were established as the hypothyroidism models by intraperitoneal injection of 18.5 MBq 131I. Of the 5 hypothyroidism groups, 3 groups were given 0.2 g (high-dose group), 0.1 g (medium-dose group) and 0.05 g (low-dose group) L-T 4 gel per 100 g body mass on alternate days, respectively, one group was given 0.1 g blank gel per 100 g body mass daily and the other group was given 5 μg levo-thyroxine sodium tablets (Euthyrox) per 100 g body mass daily. The levels of total thyroxine (TT 4), free triiodothyronine (FT 3), free thyroxine (FT 4) and thyroid stimulating hormone (TSH) in serum were determined by radioimmunoassay and chemiluminescence immunoassay at 2, 4 and 8 weeks after administration, respectively. One-way analysis of variance and Bonferroni test were used for data analysis. Results:At 2 weeks after administration, compared with the normal control group, TT 4, FT 4 decreased and TSH increased in the oral Euthyrox group (TT 4: (65.04±8.20) vs (40.34±1.41) nmol/L, FT 4: (29.63±4.03) vs (18.03±2.76) pmol/L, TSH: (6.04±0.80) vs (10.07±1.01) mU/L; F values: 60.081-108.128, t values: from -4.44 to 4.86, all P<0.05). However, TT 4 ((67.88±14.27) nmol/L), FT 3 ((4.04±0.84) vs (4.45±0.34) pmol/L), FT 4 ((33.76±7.71) pmol/L) and TSH ((8.20±0.40) mU/L) in the L-T 4 gel low-dose group showed no significant differences with the normal control group ( t values: 0.44-2.61, all P>0.05). At 4 weeks after administration, there were no significant differences of TT 4, FT 3, FT 4 and TSH between the L-T 4 gel low-dose group/the oral Euthyrox group and the normal control group ( F values: 34.527-90.976, t values: from -0.95 to 0.35, all P>0.05). The differences of TT 4, FT 3, FT 4 and TSH were not significant between the L-T 4 gel low-dose group and the oral Euthyrox group ( t values: from -0.71 to 1.03, all P>0.05), which was still not significantly different at 8 weeks ( F values: 47.239-160.679, t values: from -0.58 to 1.02, all P>0.05). Conclusions:L-T 4 gel has obvious therapeutic effect on hypothyroidism in rats. Its effect is fast and stable, and its therapeutic effect is better than L-T 4 sodium tablets (Euthyrox).