The effect of maternal progesterone on brain monoamine oxidase activity of neonatal rats.

Monoamine oxidase activity was measured in the brains and uteri of neonatal rats exposed to preand/or postnatal progesterone. Daily doses of progesterone were injected subcutaneously into pregnant females on gestational days 8-17 and postpartum days 2-6. On postpartum day 1, half of the pups of each litter were crossfostered to a female in the opposite experimental condition. Pups were sacrificed on postpartum days 1, 3 and 7, and whole brain type A and B MAO activity was determined by a radioisotope assay utilizing 14C-labelled 5-hydroxytryptamine (5-HT) and phenylethylamine (PEA), respectively. Postnatal progesterone elevated both types of MAO activity in the brains of both sexes by day 7. Deamination of both substrates was highest in those animals receiving both preand postnatal progesterone. No sex differences in MAO activity were obtained for either control or progesterone-treated rat pups. Uterine MAO activity was not affected by maternal progesterone administration. Progesterone levels measured in blood plasma of 7-day-old animals were significantly higher in those animals receiving postnatal progesterone. These results support the observation that progesterone elevates brain MAO activity in vivo, and that progesterone administered to a lactating female elevates MAO activity in her suckling young. Implications for possible behavioral consequences of MAO alterations are discussed.