Morphological effects of acetylcarvacrol on thyroid of Wistar rats subjected to repeated dose dermal and oral toxicity tests.

Acetylcarvacrol is a semi-synthetic product derived from carvacrol and has known activity against ticks. In vertebrates, the thyroid has been used as a bioindicator in toxicity studies due to its sensitivity to external factors. Thus, the objective of this study was to evaluate the toxic effects of acetylcarvacrol in Wistar rats subjected to repeated dose dermal and oral toxicity tests by means of histopathological analysis of the thyroid. For each test, the rats were divided into 4 groups containing 5 animals. In the topical treatment test, acetylcarvacrol was applied to the trichotomized back of each animal at concentrations of 26, 52 and 104 μL/mL for 21 days. In the oral test, the animals were fed acetylcarvacrol by gavage at concentrations of 26, 52 and 104 μL/mL for 30 days. The control groups were treated only with the vehicles. A significant increase in interstitial tissue vascularization was observed in the group treated topically with the highest concentration of acetylcarvacrol compared to the control. No significant changes were observed between the treatment and control groups in the oral experiment. The comparison between the treated groups and their respective controls also showed no differences in the colloid, the follicle and the follicular cells. The reduced occurrence of changes in this tissue suggests relative safety for use in the control of ticks, although caution is needed when using it at high concentrations or for long periods of time.