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 t issue and to study the interactions between mast cell mediators (hista mine and serotonin) and PGF2alpha in human myometrium contractile acti vity. Design Distribution of mast cells were analysed in cryostat sect ions of myometrium samples stained with Toluidine blue. Contractile ac tivity was evaluated in an isolated organ bath preparation on myometri al strips obtained from women whose pregnancies ended in elective caes arean section. Setting Biological Science Laboratories at the Universi ty of Concepcion. Subjects Twenty women undergoing elective caesarean and 10 women undergoing hysterectomy at the G. Grant Hospital. Main ou tcome measurements Cumulative concentration-response curves for histam ine and serotonin before and after the addition of subumbral concentra tions of the PGF2alpha 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, thres hold concentrations of serotonin (0.05 mumol/l) potentiated the contra ctile effect of histamine (EC50:0.3 (SE 0.06) mumol/l and 50% increase in E(max)). PGF2alpha had a poor contractile effect, but threshold co ncentrations (0.05 and 0.10 mumol/l) enhanced the contractile effect o f both serotonin and histamine. A population of mast cells was found i n close apposition to smooth muscle fibres. Conclusions It is postulat ed that the simultaneous release of mast cell mediators (histamine and serotonin) in myometrium could be an important stimulus for evoking s trong contractions in the human uterus. PGF2alpha may have indirect ef fects in myometrium by amplifying the effects of histamine and seroton in.