Effects of theophylline on small human placental arteries in vitro

Effects of theophylline on contractions induced by relevant physiological agents in tubular segments of small human placental arteries were measured in an isometric myograph. Theophylline 10(-7) - 3 X 10(-3)M caused marked relaxation of steady contractions produced by prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), vasopressin or potassium. EC50 for theophylline relaxation of the PGF2 alpha - contraction was 1.6 X 10(-4) M. Emax was 91.5% relaxation. Theophylline was less potent in relaxing the potassium induced contraction. Pretreatment experiments with 10(-4) and 10(-3)M theophylline showed a pronounced decrease in contractile Emax-values for PGF2 alpha, PGE2 and vasopressin as a possible indication of non-competitive antagonism. The results motivate further studies to elucidate possible effects of theophylline and other xanthines on the vascular resistance and blood flow in placenta.