Progesterone mediated increase in monoamine stores and the regulation of enzymes of biosynthesis and metabolism in the adrenal gland during late pregnancy in the rat.

The influence of repeated injections of progesterone to pregnant rats upon monoamine storage and regulation of enzymes phenylethanolamine-N-methyltransferase (PNMT), monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) was studied. All the pregnant females received progesterone (4 mg/100 g body weight) on 19, 20 and 21 days post-coitum but one group was killed at 21 days of pregnancy and the other one at 0 h parturition. Adrenal epinephrine demonstrated highly significant increase in progesterone treated rats. At the same time norepinephrine content declined significantly from the control value. The activity of enzyme PNMT also showed marked increase in the adrenals of progesterone treated females. Activity of enzyme MAO showed a slight decline after progesterone treatment to pregnant rats. Enzyme COMT in progesterone treateed animals showed decline at 0 h parturition but at 21 days post-coitum it was significantly higher from non-injected females. All the increases and decreases in monoamines and the three enzymes were significant when the results were expressed per adrenal gland or per gram of adrenal. The results suggest that exogenous progesterone administration during late pregnancy increases epinephrine stores by declining monoamine metabolism by MAO and COMT and increasing their synthesis by PNMT which is responsible for N-methylation of norepinephrine to epinephrine.