Toxic synergism of methylmercury with sodium nitrite and ethylurea on reproduction and survival of progeny in rats

Abstract

Sodium nitrite and ethylurea were administered to pregnant rats that had been fed 10 ppm dietary methylmercury from weaning, to determine the effect of this combination of treatments on reproduction and the survival of progeny. Prolonged consumption of dietary methylmercury plus ingestion of sodium nitrite (2 g/litre in the drinking-water) and ethylurea (0.636% in the diet) from day 14 of the breeding period decreased litter rate, litter size, birth weight and weanling weight to about 30, 60, 60 and 30% of control values, respectively. The percentage of stillborn pups was 5–10 times higher than in the controls and only four pups survived to weanling from the six litters derived from 18 possible matings. In methylmercury-treated rats administration of sodium nitrite and ethylurea (50 and 100 mg/kg body weight/day, respectively) by stomach tube on days 17, 18 and 19 of gestation did not reduce litter rate and litter size markedly, but only six pups from eight litters survived to weaning. Reduction of the nitrite-ethylurea exposure improved most breeding parameters and survival. The combination of methylmercury and nitrite-ethylurea increased the number of deaths at the foetal and the pre- and post-weanling stages of development.