Toxic effects of methoxychlor administered subcutaneously on the hypothalamic-pituitary-testicular axis in adult rats

This study was undertaken to evaluate the effects of methoxychlor MTX at the hypothalamic-pituitary-testicular axis in adult male rats. This global objective comprises three major aims: (1) to analyze the possible differential MTX effects in norepinephrine and serotonin concentration an in serotoninergic metabolism in anterior, mediobasal and posterior hypothalamus and median eminence; (2) to evaluate effects induced by MTX exposure on gonadotropins and testosterone; 93 to elucidate whether the regulatory interactions in the hypothalamic-pituitary-testicular axis are modified by this pesticide. Animals were administered subcutaneously 25 mg/kg/day of MTX for 1 month. MTX increased norepinephrine and serotonin content in anterior hypothalamus (P ⩽ 0.05), but decreased serotonin concentration in posterior hypothalamus (P ⩽ 0.05). MTX diminished serotonin turnover in anterior hypothalamus (P ⩽ 0.01) and decreased plasma LH (P ⩽ 0.001) and testosterone (P ⩽ 0.05) levels but those of FSH remained unmodified. We can conclude that MTX exposure: (1) could exert differential effects in norepinephrine and serotonin concentration an in serotoninergic metabolism in anterior, mediobasal and posterior hypothalamus and median eminence, being the anterior hypothalamus the most sensitive region to the pesticide; (2) could inhibit LH and testosterone secretion without changing FSH; (3) four potential pathways might be involved in MTX effects on testosterone secretion (changing LH secretion; modifying serotonin and norepinephrine at the hypothalamic level; alterating the direct neural pathway between brain and testes; and/or by a direct effect in testes).