Heart Rate Variability and Baroreceptor Function in Chronic Diabetic Rats

Abstract

Abstract In conscious chronic (12 to 18 weeks) streptozotocin diabetic rats, we examined the changes in basal heart rate, with particular attention to heart rate variability assessed by evaluating the standard deviation (bpm) of the lengths of adjacent pulse pressure. We also investigated in anesthetized rats the ability of the aortic baroreceptors to acutely (30 minutes) reset to hypertensive levels. For this purpose, pressure-nerve activity curves for the baroreceptors were obtained, and gain (slope of the curve) and mean arterial pressure at 50% of maximal baroreceptor activity were calculated. The shift of the pressure-nerve activity curve was used as an index of resetting. Conscious diabetic rats (n=6) exhibited lower mean arterial pressure (93±6 versus 109±4 mm Hg), heart rate (272±25 versus 359±11 bpm), and heart rate variability (18±7 versus 36±6 bpm) than control rats (n=7). Under anesthesia, diabetic rats (n=7) and control rats (n=8) exhibited similar mean arterial pressure (113±6 versus 109±7 mm Hg in control rats ), mean arterial pressure at 50% of maximal baroreceptor activity (117±5 versus 107±6 bpm), gain (1.66±0.08 versus 1.81±0.05%/mm Hg), and extent of resetting (44±12 versus 49±9%) to hypertensive levels. The present study demonstrated that conscious chronic diabetic rats presented lower heart rate variability than control rats. On the other hand, chronic diabetes was not associated with alterations in baroreceptor function or its ability to rapidly reset to hypertensive levels.