HISTAMINE, A NEUROMODULATOR OF NORADRENERGIC TRANSMISSION IN UTERINE HORNS FROM MICE IN DIESTRUS

The effect of histamine on [H-3]norepinephrine ([H-3]NE) release in ut erine horns from mice in estrous and diestrous states was studied unde r two different experimental conditions: resting NE release and stimul us-evoked NE release. It was found that [H-3]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 s timulus-evoked [H-3]NE outflow in uterine horns from mice in the diest rous state and from ovariectomized mice treated with progesterone. Thi s effect was dose dependent and was antagonized by H-1 but not by H-2 or H-3 antagonists. R-alpha-Methylhistamine, a H-3 agonist, had no eff ect on stimulus-evoked [H-3]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 heterologou s regulation depends on progesterone predominance and on terminal depo larization; and (c) presynaptic H-1 receptors located on noradrenergic terminals could be responsible for such an effect.