Session SA2.6

Temporal Analysis of the Spontaneous Baroreceptor Reflex during Acute and Chronic Shaker Stress in Freely Moving Rats

O Sarenac, S Drakulic, M Lozic, T Loncar-Turukalo*,
D Bajic, N Japundzic-Zigon

University of Belgrade
Belgrade, Yugoslavia

Radiotelemetred male Wistar conscious rats were exposed to acute and chronic shaker stress (18 times/day 200 cycles/min for 3 days) and the baroreceptor reflex (BRR) functioning was evaluated using the method of sequences. Systolic and diastolic blood pressure (SBP and DBP), pulse interval (PI) and heart rate (HR) were derived from arterial pulse pressure as maximum, minimum and inter-beat interval and its inverse, respectively. SBP and PI beat-to-beat sequences were low-pass filtered by a moving average on 10 cardiac cycles to filter out respiration induced fluctuations. To evaluate the spontaneous BRR, the following parameters were calculated: BRR sensitivity (BRS); BRR effectiveness index (BEI=nšof sequences/nšof ramps); number of ramps per minute (NR); number of sequences per minute (N); average sequence length (NB); average ramp length (NBR); sequence SBP and PI increment and swing; contour coverage area (CCA, area embedding the sequence points in PI-SBP plain) and coordinates of baricentre (mass center of CCA). Rats exposed to acute shaker stress exhibited increased vigilance, moderate HR increase without significant changes in BP, BEI, BRS, NR, N, NBR, NB, SBP or PI increments and swings. However, the CCA was significantly decreased as well as the PI coordinate of the baricentre indicating reduced BRR operating range and resetting toward lower PI values. In the post-stress period acute stress induced reduction of NB indicating that the BRR works in the faster frequency range, probably associated with the observed faster breathing. Chronic shaker stress evoked no changes in recorded parameters except for the reduction of the CCA, without changes in baricentre coordinates. This suggests that the BRR range is reduced without resetting. In the post-stress period chronic stress induced the shortening of NB and NBR, as well as of SBP and PI increments and swings, indicating that the BRR functioning is shifted toward faster BP changes. It can be concluded that acute and chronic shaker stress does not affect the BRS and BEI and reduces BRR operating range with and without BRR resetting, respectively.

(Abstract Control Number: 185)