Body weight is frequently the most sensitive indicator of the adverse effects of xenobiotics, so it is considered as a determined parameter of toxicity testing. Administration of tested extracts decreased body weight gain in normal animals, in agreement with other researchers [
10,
11] who reported that green tea suppressed the body weight gain as well as the gain of intraperitoneal adipose tissues. However, DMN enhanced that gain. Administration of licorice to DMN-injected animals augmented DMN effect by enhancing that gain, while the mixture or green tea markedly attenuated that effect. This change may be related to the hypertriglyceridemic effect of green tea, which caused the release of lipids from their depots, liver and adipose tissues, and its lowering effect on weight of various adipose tissue [
11,
12]. Administration of tested extracts and DMN had insignificant increase in liver weight/body weight % ratio. The increase was more pronounced in DMN-injected rats. Administration of green tea showed no effect on marked increase induced by DMN intoxication on that ratio, while licorice or mixture augmented this effect. So, it can be concluded that DMN might cause mild liver hypertrophy. However, while licorice or the mixture enhanced that effect, green tea exerted no change on it. In view of the present study, DMN caused substantial decreases in plasma levels of T
3 and T
4 concentrations consistent with a tremendous increase in plasma level of thyroid-stimulating hormone (TSH). DMN also increased the hepatic activity of thyroxine 5'-monodeiodinase (thyroxine 5'-DI). Thus, the stimulatory effect of DMN on 5'-DI was not accompanied with an increase of plasma T
3 level. Not only the hepatic 5'-DI activity, but also the continuous release from thyroid gland and uptake of the hormone by the tissues can control T
3 level in plasma [
13]. Based on this assumption, it is worth mentioning that the decreased level of plasma T
3 concentration in DMN-injected animals may be attributed to a decreased secretion and/or an increased uptake or extraction of the hormone by the tissues. Moreover, in parallel with the decrease in T
3 and T
4 levels in DMN intoxicated animals pathological examination of thyroid tissue, showed degeneration, desquamation and atrophy of many acini as indicated in recent study. Green tea decreased T
3 level, although that decrease was statistically insignificant, while it increased the plasma levels of TSH and T
4. On the other hand, green tea attenuated the lowering effect of DMN on T
3 and T
4 levels by increasing these levels, the values are still below the normal control ones. In parallel with amelioration of T
3 and T
4 levels induced by green tea administration in respect to DMN lowering effect histopathological examination revealed that green tea improved the thyroid perturbations produced by DMN intoxication. Green tea profound the DMN rising effect on TSH level by inducing a slight increase in its level. This is logically accepted because green tea antagonized DMN effect and increased T
3 and T
4 levels. Green tea induced a decrease in hepatic thyroxine-5'-DI activity but it was statistically insignificant. Also, green tea suppressed the rising effect of DMN on 5'-DI activity by decreasing it, so it is suggested that green tea decreased the rate of conversion of T
4 into T
3 and the increase of T
3 and T
4 levels may be attributed to increased secretion and the improvement of thyroid tissue architecture. These observations agree with findings reported by Satoh
et al[
14]., Licorice induced a decrease in T
3 level, while it had no significant change on T
4 level. On the other hand, licorice induced a substantial increase in TSH level. Licorice profound the elevated effect of DMN on TSH level. It was remarkable that the effect of licorice and DMN on TSH level was additive. The co-administration of DMN and licorice did not affect the lowering effect of DMN on T
3 and T
4 levels. Licorice induced an increase in thyroxine 5'-DI activity, but it attenuated the rising effect of DMN on that activity. Linking rise of 5'-DI activity induced by licorice with its lowering effect on T
3 level, showing an impression that the stimulated hepatic 5'-DI may be stressed to acclimatize the decrease of T
3 level, a kind of compensatory mechanism. Consistent with these results, Martinez-deMena
et al.,[
15] stated that T
3 up regulates 5' DI (type II) in brown adipose tissues. It was obvious that the tremendous increase in TSH level exerted by the mixture was a result of synergistic effect between licorice and green tea. The increase in TSH level was concomitant with the decrease of T
3 and T
4 levels by the mixture. Surprisingly, although the mixture profound the DMN rising effect on TSH level, the increase was not additive. On the other hand, the co-administration of the mixture with DMN did not significantly affect the lowering effect of DMN on T
3 and T
4 levels. The mixture decreased thyroxine 5'-DI activity and inhibited the rising effect of DMN on that activity.
In conclusion, these results indicated that administration of green tea alone in DMN-injected animals was more pronounced in increase of T3 and T4 levels than concomitant administration of green tea and licorice. Also this study revealed that the treatment of the DMN intoxicated animals with green tea and/or licorice induced marked amelioration of pathological lesions induced in thyroid tissue manifested by increase in the number and size of follicles which become more organized and appeared to have higher amount of colloid.