Abstract
The effect of histamine on [ 3H]norepinephrine ([ 3H]NE) release in uterine horns from mice in estrous and diestrous states was studied under two different experimental conditions: resting NE release and stimulus-evoked NE release. It was found that [ 3H]NE release was higher for the diestrous state under both resting and stimulus-evoked (100 mM K + and electrical stimulus) conditions. Histamine only potentiated the stimulus-evoked [ 3H]NE outflow in uterine horns from mice in the diestrous state and from ovariectomized mice treated with progesterone. This effect was dose dependent and was antagonized by H 1 but not by H 2 or H 3 antagonists. R- α-Methylhistamine, a H 3 agonist, had no effect on stimulus-evoked [ 3H]NE release. According to these results, it could be concluded that: (a) histamine regulates the NE release from noradrenergic nerve terminals in uterine tissues; (b) this heterologous regulation depends on progesterone predominance and on terminal depolarization; and (c) presynaptic H 1 receptors located on noradrenergic terminals could be responsible for such an effect.
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