Excretion and disposition of [14C]carbaryl in pregnant, non-pregnant and foetal tissues of the rat after acute administration.

1. Non-pregnant or pregnant Sprague-Dawley rats on the 18th and 19th days of gestation were injected i.p. with a tracter dose (2.8 microCi/kg) of either [ring-14C]carbaryl or [carbonyl-14C]carbaryl. Distribution of total 14C was examined in foetal, maternal and non-pregnant rat tissues. Pregnancy alters the disposition and excretion of carbaryl. 2. Carbaryl crossed the placenta and was rapidly distributed in all foetal tissues. Highest concentrations were seen in foetal kidney. At 8 h after injection, foetal brain, heart and lung all contained more 14C, on a weight basis, than their maternal organ counterparts. Elimination from the whole foetus was biphasic, and after 8 h approx. 3% of the dose was still present in the whole foetus. 3. Significantly more 14CO2 was exhaled by the pregnant rat during 8 h than by non-pregnant. Urinary excretion of 14C after dosage with [ring-14C]carbaryl was significantly less in pregnant than in non-pregnant rats. 4. Kinetically, the tissue distribution of 14C from carbaryl or metabolites was biphasic in pregnant and non-pregnant animals. [14C]carbaryl concn. declined rapidly for 1 to 2 h. After 2 h the 14C levels from animals dosed with [ring-14C]carbaryl declined more slowly. 5. The pattern of 14C distribution was more complicated after injection of [carbonyl-14C]carbaryl. The 14C activity increased in the animal tissues after 2 h, in contrast to animals dosed with [ring-14C]carbaryl. Non-pregnant animals treated with [carbonyl-14C]carbaryl did not show a similar pattern of distribution. Carbamylated tissue proteins may, after time, release some bound carbonyl-14C label, causing the increase in 14C activity seen between 2 and 8 h. However, this does not necessarily imply uptake of the intact carbamate.