Bradykinin in reflex cardiovascular responses to static muscular contraction

We examined the contribution of bradykinin to the reflex hemodynamic response evoked by static contraction of the hindlimb of anesthetized cats. During electrical stimulation of ventral roots L7 and S1, we compared the cardiovascular responses to hindlimb contraction before and after the following interventions: inhibition of converting enzyme (kininase II) with captopril (3-4 mg/kg, n = 6); inhibition of kallikrein activity with aprotinin (Trasylol, 20,000-30,000 KIU/kg, n = 8); and injection of carboxypeptidase B (500-750 U/kg, n = 7). Treatment with captopril augmented the rise in mean arterial blood pressure and maximal time derivative of pressure (dP/dt) caused by static contraction from 21 +/- 3 to 39 +/- 7 mmHg and 1,405 +/- 362 to 2,285 +/- 564 mmHg/s, respectively. Aprotinin attenuated the contraction-induced rise in mean arterial blood pressure (28 +/- 4 to 9 +/- 2 mmHg) and maximal dP/dt (1,284 +/- 261 to 469 +/- 158 mmHg/s). Carboxypeptidase B reduced the cardiovascular response to static contraction. Thus the mean arterial blood pressure response was decreased from 36 +/- 12 to 24 +/- 11 mmHg, maximal dP/dt from 1,618 +/- 652 to 957 +/- 392 mmHg/s, and heart rate from 12 +/- 2 to 7 +/- 1 beats/min. These data suggest that stimulation of muscle afferents by bradykinin contributes to a portion of the reflex cardiovascular response to static contraction.