Effect of progesterone on norepinephrine release from mouse adrenergic terminals in vitro

1. The in vitro effect of progesterone on norepinephrine (NE) release and contractile activity was analyzed in uterine horns from estrogen-primed and progesterone-primed mice. 2. Progesterone (6-10 nmol/ml) evoked the release of [3H]NE above basal levels from uterine horns in both experimental conditions, the effect of progesterone on estrogen-primed being more important than on progesterone-primed mice uterus. 3. Progesterone also increased electrically evoked [3H]NE release in estrogen-primed uterine tissue, nevertheless no effect was observed in progesterone-primed ones. 4. Progesterone (0.6-10 nmol/ml) inhibited uterine horn isometric contractions only in estradiol-primed mice. This effect was partially blocked in uterine horns from reserpine-treated mice and when propanolol (1 microM) was added to the preparation of estradiol-primed mice uterus.