Morphological and biochemical action of dipyrone on rat placenta

1. The morphological and biochemical action of dipyrone (N-[2,3-dimethyl-5-oxo-1-phenyl-3-pyrazolin-4-yl] methylamino methanesulfonate, sodium monohydrate) on the placenta of albino rats was studied by means of karyometry of trophoblastic giant cells and by determinations of DNA, RNA and total protein contents. 2. The animals were treated with a single daily dose of 50 mg/kg body weight during 5 different periods: from the 9th to the 12th, 11th to the 14th, 13th to the 16th, 15th to the 18th or 17th to the 20th day of pregnancy, 3. Karyometric results showed that the nuclear volumes of placental cells in rats treated with dipyrone during the first 3 periods were significantly greater than in control animals and that, closer to term, no differences were observed in this regard. Only the animals treated from the 9th to the 12th day of pregnancy had higher placental contents of DNA, RNA and protein than the corresponding controls. 4. Our results showed that dipyrone had a blocking effect on placental cell division which occurs mainly in the initial steps of placental development.