Centrally infused bradykinin increases baroreceptor reflex sensitivity.

Kinins are present in the central nervous system, and central administration of bradykinin increases blood pressure and heart rate. In this study, we determined the effect of intracerebroventricular infusion of bradykinin on the baroreceptor reflex of conscious rats. Male Wistar rats were anesthetized with thiobarbital (40 mg/kg i.p.), and chronic intracerebroventricular cannulas (25 gauge) were implanted into the lateral ventricles. Baroreceptor control of heart rate was evaluated by recording reflex heart rate changes (beats per minute) in response to mean arterial pressure changes (mm Hg) produced by bolus injection of phenylephrine (0.5-20 micrograms/kg i.v.) or sodium nitroprusside (0.5-25 micrograms/kg i.v.). The ratio beats per minute/mm Hg or the mean slope of the individual regression lines of the relation between heart rate and mean arterial pressure changes for increases or decreases in arterial pressure was used as an index of baroreceptor reflex sensitivity. Baroreceptor control of heart rate was evaluated within 1 and 3 hours of intracerebroventricular infusion of bradykinin (7.5 micrograms/7 microliters/hr) or saline (7 microliters/hr). There was no change in basal mean arterial pressure or heart rate during central bradykinin infusion (112 +/- 2 mm Hg and 402 +/- 18 beats per minute in the control period). After 1 hour of central bradykinin infusion, there was a significant increase of baroreceptor reflex sensitivity for increments in mean arterial pressure (-2.91 +/- 0.26 versus -1.5 +/- 0.24 beats per minute/mm Hg in the control period; p less than 0.01, paired Student's t test). In contrast, no significant changes were observed for the reflex tachycardia. Similar results were obtained with 3 hours of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)