Haemodynamic effects of bradykinin in rats

The intravenous infusion of bradykinin (20 micrograms/kg X min) induced an initial fall in blood pressure and total peripheral resistance in anaesthetized rats. These changes were accompanied with an increase in cardiac output and stroke volume. These effects were transient and after 20 min of infusion blood pressure and total peripheral resistance were much less decreased than initially. Cardiac output and stroke volume had completely normalized. Lower doses of bradykinin (1 microgram/kg X min), which did not affect blood pressure, induced a reduction in mesenteric and renal vascular resistance. After higher doses (4 or 20 micrograms/kg X min) mesenteric vascular resistance was further decreased but renal vascular resistance was unchanged or markedly increased. This renal vasoconstrictor response was almost absent in rats which were pretreated with indomethacin (4 mg/kg i.v.). Hence the increase in renal vascular resistance was most probably due to the stimulation of the synthesis of prostaglandins, which act as renal vasoconstrictors in the rat.