Abstract
We investigated the influence of pharmacological dose (5 mg/kg of body weigh) of exogenous melatonin on morphological changes and morphometric indexes of thyroid gland functional activity in young rats. It was shown a decrease in thyroid gland functional activity after influence of melatonin, namely: decrease of cross- section area of the follicular epithelium, decrease in thyrocytes heigh, observed presence of a dense colloid without expressed resorption vacuoles, decrease amount of interfollicular epithelium, decrease in a follicle-colloid index and increase in a colloid accumulation index, increase in amount of connective tissue elements in thyroid gland. Thus, 28 days melatonin exposure, in dose 5 mg/kg of body weigh, decreased regenerative and functional thyroid gland activity in 3-mounth rats.