On the contribution of prostaglandin-like substances to the action of bradykinin on intestinal motility and blood flow in canine jejunal loop in situ.

Abstract

Blood flow and motility were studied in a canine jejunal loop in situ with intact innervation. Bradykinin was administered into a side branch of the supplying artery and indomethacin was infused intravenously 1 h before experiments. In the control group without indomethacin infusion, bradykinin 1-10 nmol/l gradually increased blood flow without significantly altering motility. Higher concentrations of bradykinin (20-100 nmol/l) augmented rhythmic contractions of the intestine. Phasic blood flow decreased during contraction and increased after relaxation, and mean blood flow increased. Bradykinin (0.2-1.0 mumol/l) caused tonic intestinal contractions. Blood flow initially increased but was soon impeded in proportion to the amplitude and duration of the tonic contractions. With intestinal muscle relaxation, blood flow increased to values markedly higher than control. In the group pretreated with indomethacin, blood flow did not increase after bradykinin administration. However, administration of PGE2 produced significant increase in flow, similar to that observed after bradykinin. Acetylcholine or isoprenaline also markedly increased blood flow. Increased intestinal motility caused by bradykinin mechanically impeded blood flow through the intestine, thus masking its direct vasodilating action. The action of bradykinin on the intestinal vascular bed is probably mediated or modulated by endogenous prostaglandin-like substances.