Monoamine oxidase activity in rat organs during pregnancy

To elucidate the involvement of MAO activity in rat pregnancy, female rats exhibiting at least 3 consecutive 4-day estrous cycles were used. The day of sperm-positive smears was designated as day 0 of pregnancy. The rats were sacrificed on day 2 of diestrus (diestrus-2) and days 7, 14 and 21 of gestation. The organs were collected and weighted, and mitochondrial fractions were prepared for MAO analysis with kynuramine dihydrobromide as substrate. Specific activity (pmol/mg of protein/min) in the ovary is significantly lower in rats on diestrus-2 (792 +/- 127) (mean +/- S.D.) than on day 14 (1,038 +/- 140) and day 21 (1,580 +/- 61) of pregnancy. However, the levels of MAO activity in the uterus of rats on diestrus-2 (899 +/- 266) is higher than on day 21 (570 +/- 80) of pregnancy. The MAO activity in the placenta on day 21 (644 +/- 82) was higher than day 14 (356 +/- 88) of pregnancy. Total MAO activity per organ (nmol/min) of ovary on day 21 (27.2 +/- 5.2) is higher than on diestrus-2 (8.7 +/- 3.0) and on day 14 (14.2 +/- 3.6). Our results suggest that MAO activity in rat reproductive organs such as uterus, ovary, and placenta might fluctuate significantly near term, in correlation with steroid levels, tissue catecholamine contents and so on, in order to maintain pregnancy.