AUTONOMIC MEDIATION OF SHORT-TERM CARDIOVASCULAR OSCILLATIONS AFTER ACUTE HEMORRHAGE IN CONSCIOUS RATS

The role of the autonomic and the renin-angiotensin (R-A) activities i n short-term cardiovascular control during the bradycardic phase follo wing severe hemorrhage was investigated in conscious rats. Spectral an alysis of beat-to-beat fluctuations of the R-R interval (RRI), systoli c (SEP) and diastolic (DBP) blood pressure in the 0.01-5-Hz range was carried out under control conditions and following a bleeding of 30% o f total blood volume, with and without i.v injection of atropine (2 mg /kg), prazosin (2 mg/kg), propranolol (5 mg/kg) or captopril (7 mg/kg) . The bradycardic stage was characterized by: (i) an increase of the t hree oscillatory components exhibited by RRI variability which appears driven by vagal activity and buffered by beta-adrenergic activity, wh ile the increase of the slower LF (0.01-0.2 Hz) oscillations seems dri ven by the slow alpha-adrenergic control; (ii) a decrease of SEP and D BP oscillations and absence of SBP-RRI correlation in the MF band (0.2 -0.6 Hz) possibly related to a decrease in the sympathetic drive of SB P-MF and DBP-MF oscillations and in RRI baroreflex control; (iii) an i ncrease in LF oscillations of SEP and even more of DBP that seems driv en by the slow alpha- and beta-adrenergic control and buffered by the R-A control, responses possibly related to an increase of LF oscillati ons of peripheral resistance; (iv) the persistence of high SBP-RRI cor relation in the LF band and in the respiratory band (1-3 Hz); the form er seem to reflect the existence of a slow baroreflex control mediated by beta-adrenergic activity, the latter appears to be caused by feedf orward mechanical effects of RRI changes on SEP.