Histamine, a neuromodulator of noradrenergic transmission in uterine horns from mice in diestrus.

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 H1 but not by H2 or H3 antagonists. R-alpha-Methylhistamine, a H3 agonist, has 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 H1 receptors located on noradrenergic terminals could be responsible for such an effect.

Histamine content and mast cells distribution in mouse uterus: the effect of sexual hormones, gestation and labor.

The histamine content of uteri from mice was analyzed in terms of both concentration and total amount per uterine horn a) at two stages of the estrous cycle (estrous and diestrous), b) under sex hormone treatment, c) during pregnancy and after delivery. Histamine concentration and mast cell density were greater during diestrous and in mice treated with progesterone (p less than 0.001). This effect was attributed to a reduction in uterine mass weight, since the amount of histamine per uterine horn remained constant throughout the estrous cycle. During pregnancy, both concentration and amount of histamine per uterine horn were increased, values were significantly higher than in estrous (p less than 0.001) from day 14-17 until day 21 when labor occurred. After six to eight hours post-partum an abrupt reduction on histamine content was observed. Mast cells were more abundant in myometrium than in endometrium, their density followed the same pattern as histamine concentration throughout the estrous cycle.