Effect of melengestrol acetate on growth and reproduction in rats.

Effects of melengestrol acetate on reproductive performance of 48 female rats and 20 of their female progeny were evaluated in two experiments. Treatments of 0, .01, and .1 mg in .1 ml of propylene glycol were given three groups of 16 rats for 7 days. From day 7 following sperm detection (10-day breeding period), half from each group received .1 mg per day for 14 days. Experiment 2 tested performance of 10 progeny exposed or unexposed to in utero treatment. Cyclic changes in Experiment 1 were inhibited only in animals receiving daily initial treatment of .1 mg. Estrus was detected in 61.5% of animals within 48 h of treatment withdrawal. Synchronization caused no significant changes in conception rates or postbreeding results of treatment. Treatment during gestation lowered weight gain for dams, increased gestation length, and decreased number of pups per litter. Treatment lowered mean weight per litter and weight per pup. It also caused high mortality among pups. In Experiment 2, there were no differences between progeny groups in gestation length, litter size, weight per litter, weight per pup, or mortality rate.