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  • Title: Endogenous bradykinin in the thoracic spinal cord contributes to the exercise pressor reflex.
    Author: Stebbins CL, Bonigut S.
    Journal: J Appl Physiol (1985); 1996 Sep; 81(3):1288-94. PubMed ID: 8889765.
    Abstract:
    This investigation tested the hypothesis that bradykinin causes excitatory effects in the thoracic spinal cord that augment the exercise pressor reflex. Thus we performed 30 s of electrically stimulated static contraction of the hindlimb in the anesthetized cat (alpha-chloralose) to provoke reflex-induced increases in mean arterial pressure, maximal rate of rise of left ventricular pressure (dP/dt), and heart rate (i.e., the exercise pressor reflex). These three responses were compared before and 15 min after intrathecal injection of 2 micrograms (n = 3), 10 micrograms (n = 6), or 50 micrograms (n = 3) of the selective bradykinin B2- receptor antagonist HOE-140 into the thoracic spinal cord or 10 micrograms of this antagonist into the lumbar (n = 3) spinal cord. In three of the six cats in which 10 micrograms of HOE-140 were injected into the thoracic spinal cord, an additional contraction was performed 60-90 min after treatment. The 2-microgram dose of HOE-140 had no effect on the exercise pressor reflex. Injection of 10 micrograms of this antagonist into the thoracic spinal cord reduced the contraction-evoked pressor, maximal dP/dt, and heart rate responses by 49 +/-7, 58 +/- 4, and 64 +/- 13%, respectively (P < 0.05). Fifty micrograms of HOE-140 failed to attenuate these responses further. In the three cats in which an additional contraction was performed 60-90 min after treatment with 10 micrograms of the antagonist, blood pressure and dP/dt responses had returned, in part, toward initial values. Neither intravenous (n = 3) nor intrathecal injection of 10 micrograms of HOE-140 into the lumbar spinal cord had any effect on the contraction-induced cardiovascular responses. Thoracic injection of 50-200 ng of bradykinin provoked a pressor response of 26 +/- 5 mmHg that was abolished by a similar injection of 10 micrograms of HOE-140. These data suggest that endogenous bradykinin contributes to the exercise pressor reflex by an excitatory action in the thoracic spinal cord.
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