In vitro effects of histamine on human pregnant myometrium contractility

The effects of histamine on pregnant human myometrium was examined by means of an in vitro technique. Samples of myometrium were taken from women delivered by elective caesarean section at various stages of gestation. Histamine (1 x 10(-6) to 1 x 10(-4) M) had good stimulant activity on all the strips examined. This contractile action was unaffected by H2 blockers but was competitively antagonised by H1-blockers. The H2-selective agonist, impromidine, was ineffective at molar concentrations between 1 x 10(-8) and 1 x 10(-3) while a specific full agonist of the H1 receptors, thiazole in the range of molar concentrations from 1 x 10(-6) to 3 x 10(-4), had an activity identical to that of histamine. The data obtained suggest that in the pregnant human myometrium the activation of H1-receptors is responsible for the contractile effect of histamine; a possible involvement of histamine in the pathophysiology of labour is discussed.