Distribution of mast cells and the effect of their mediators on contractility in human myometrium.

OBJECTIVE: To examine the distribution of mast cells in human uterine tissue and to study the interactions between mast cell mediators (histamine and serotonin) and PGF2 alpha in human myometrium contractile activity.
DESIGN: Distribution of mast cells were analysed in cryostat sections of myometrium samples stained with Toluidine blue. Contractile activity was evaluated in an isolated organ bath preparation on myometrial strips obtained from women whose pregnancies ended in elective caesarean section.
SETTING: Biological Science Laboratories at the University of Concepción.
SUBJECTS: Twenty women undergoing elective caesarean and 10 women undergoing hysterectomy at the G. Grant Hospital. MAIN OUTCOME MEASUREMENTS: Cumulative concentration-response curves for histamine and serotonin before and after the addition of subumbral concentrations of the PGF2 alpha or serotonin were performed.
RESULTS: Serotonin was more active than histamine to evoke contractions (EC50:0.20 (SE 0.02) mumol/l vs 1.5 (SE 0.2) mumol/l, respectively). Furthermore, threshold concentrations of serotonin (0.05 mumol/l) potentiated the contractile effect of histamine (EC50:0.3 (SE 0.06) mumol/l and 50% increase in E(max)). PGF2 alpha had a poor contractile effect, but threshold concentrations (0.05 and 0.10 mumol/l) enhanced the contractile effect of both serotonin and histamine. A population of mast cells was found in close apposition to smooth muscle fibres.
CONCLUSIONS: It is postulated that the simultaneous release of mast cell mediators (histamine and serotonin) in myometrium could be an important stimulus for evoking strong contractions in the human uterus. PGF2 alpha may have indirect effects in myometrium by amplifying the effects of histamine and serotonin.