The effect of maternal progesterone injections on fetal development of brain monoamine oxidase of rats

Abstract

The activity of mitochondrial type A and B monoamine oxidase (MAO) in the brain of rats has been shown to increase during the first 3 weeks of lifeL The type A form of MAO develops more rapidly with adult levels being reached by 14 days of age 3 while the activity of the B-type continues to rise through the third week after birth 7. Few studies have been undertaken to assay MAO activity in rat fetal brain. Using histochemical methods, Shimizu and Morikawa s detected low levels of MAO activity in certain brain areas at 15 days of gestation. Bennett and Giarman I assayed MAO activity towards 5-hydroxytryptamine at 20 days of gestation, and found it to be already at 30 ~ of adult levels. Recently, we have demonstrated an increase in both A and B MAO activity in the brains of 7-day-old rats whose mothers were treated with progesterone before and after parturition 8. Prenatal progesterone alone had no effect on MAO activity in newborn (1-day-old) rats; however, progesterone was not administered for 5 days prior to birth, so as not to interfere with parturition. Since the newborn rat pups were not exposed to progesterone for 5 days, it cannot be determined what influence progesterone had on brain MAO activity prenatally. Accordingly, the present study was undertaken to determine whether progesterone stimulates one or both types of MAO activity in the brains of fetuses exposed to progesterone via the mother. Thirty-six female rats of the Long-Evans strain (obtained from Charles River Laboratories) were time-mated and housed in individual plastic cages with ad libitum food pellets and water. Animals were injected daily with either progesterone (3.3 mg/kg) or the olive oil vehicle alone starting day 7 of gestation and continuing until the day of sacrifice. Fetuses were removed on days 14, 17, 20 and 22 of gestation, following decapitation of the mother. Their brains were rapidly removed, weighed and placed in small vials which were kept on ice for periods of up to 2 h prior to homogenization. The procedure used was a radioisotope assay using 0.1 mM [14C]5-hydroxytryptamine (5-HT) as the substrate for type A and 0.26 mM [14C]phenylethylamine (PEA) for type B MAO, essentially as described previously z. Brains of 14-20-day-old