Effects of thiopentone or chlormethiazole on human placental stem villous arteries.

Small placental stem villous arteries were micro dissected from specimens obtained at normal term vaginal delivery (n = 25). Ring preparations of the vessels were mounted in organ baths and isometric tension was measured. Prostaglandin F2 alpha (PGF2 alpha) 10(-7)-10(-4) mol litre-1 produced concentration-dependent contractile responses that were inhibited by thiopentone 10(-4)-10(-3) mol litre-1 and by chlormethiazole 3 x 10(-4)-3 x 10(-3) mol litre-1. Thiopentone 10(-4)-10(-3) mol litre-1 and chlormethiazole 3 x 10(-4)-3 x 10(-3) mol litre-1 decreased the tension in vessels previously treated with PGF2 alpha 10(-5) mol litre-1. Chlormethiazole 3 x 10(-3) mol litre-1 inhibited, and thiopentone 10(-4)-10(-3) mol litre-1 abolished contractile responses to 5-hydroxytryptamine. Contractions induced by angiotensin II were inhibited by thiopentone 10(-3) mol litre-1 and chlormethiazole 3 x 10(-3) mol litre-1. The concentrations of the two drugs needed to affect contractile activation of isolated human stem villous arteries exceeded the free plasma concentrations reached during anaesthesia induced by the agents during Caesarean section, and the present results do not suggest any major effects of thiopentone or chlormethiazole on fetal placental vascular resistance during the clinical use of these drugs.