Evaluation of dimethoate-induced implantation delay and nidation by progesterone in albino mice

We investigated the effect of dimethoate, an organophosphorus insecticide, and progesterone on implantation. Virgin pregnant albino mice received dimethoate orally at a dose of 28 mg/kg body wt/d from days 1 to 7. Laparotomy on day 8 showed no implantation sites. Thereafter, graded doses of progesterone, 4, 9, and 12 mg/kg body wt/d, were administered up to day 15. A group of control mice received a similar quantity of distilled water. Autopsy on day 8 revealed that the control mice were pregnant, with a normal number of implantations and 8.08% pre-implantation loss, whereas treatment with dimethoate for 7 days or with dimethoate for 7 days followed by progesterone for 8 days totally abolished implantation, with a 100% pre-implantation loss. In all treated mice, a significant decrease occurred in body weight gain, as well as in the weight of the ovaries, uterus, and liver when compared with those of control mice. No significant changes were found in other organ weights (kidneys, adrenals, spleen, thymus, or thyroid). The observed effect of dimethoate could be due to an imbalance in the estrogen-progesterone ratio essential for implantation. Alternatively, dimethoate treatment could result in blastotoxicity or have an impact on the hypothalamic-pituitary axis.