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

ABSTRACT 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 PGF2α 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 PGF2α or serotonin were performed. Results Serotonin was more active than histamine to evoke contractions (EC50:0.20 (SE 0.02) μmol/l vs 1.5 (SE 0.2) μmol/l, respectively). Furthermore, threshold concentrations of serotonin (0.05 μmol/l) potentiated the contractile effect of histamine (EC50:0.3 (SE 0.06) μmol/l and 50% increase in Emax). PGF2α had a poor contractile effect, but threshold concentrations (0.05 and 0.10 μmol/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. PGF2α may have indirect effects in myometrium by amplifying the effects of histamine and serotonin.