Cardiovascular effects of intrathecally administered bradykinin in the rat: characterization of receptors with antagonists.

1. The effects of intrathecal (i.t.) pretreatment with selective B1 or B2 kinin receptor antagonists were studied on the cardiovascular response to i.t. injection of bradykinin (BK) in conscious freely moving rats. 2. BK (81 pmol) produced an increase in mean arterial pressure (MAP: 9-13 mmHg) and decrease in heart rate (HR: 20-30 beats min-1) that reached a maximum 2 min after injection. 3. The BK-induced cardiovascular responses were dose-dependently and reversibly reduced by four antagonists with the following rank order of potency: Tyr, D-Arg[Hyp3,D-Phe7,Leu8]-BK = D-Arg[Tyr3,D-Phe7,Leu8]-BK = D- Arg[Hyp3,D-Phe7,Leu8]-BK > D-Arg[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe 140). These compounds failed to alter the cardiovascular response to i.t. injection of 8.1 nmol of substance P. 4. Other compounds acting on the B2 receptor, namely D-Arg[Hyp3,Gly6,Leu8]-BK, D-Arg[Hyp3,D-Phe7]-BK, D-Arg[Hyp2,Thi5,8,D-Phe7]-BK and D-Arg[Hyp3,Gly6,D-Phe7,Leu8]-BK or on the B1 receptor, [Leu8]-desArg9-BK, did not influence the cardiovascular responses to BK at doses devoid of intrinsic activity on MAP and HR. 5. None of the kinin receptor antagonists caused motor impairment, respiratory arrest or persisting cardiovascular changes. 6. These results confirm that the cardiovascular effects induced by i.t. BK are mediated by the activation of a B2 receptor in the rat spinal cord. However, the rank order of potency of antagonists does not conform to the classical B2 functional site characterized in peripheral tissues.