Baroreflex control of heart rate and renal sympathetic nerve activity in rats with low brain angiotensinogen

The main objective of the present study was to evaluate baroreceptor control of heart rate (HR) and renal sympathetic nerve activity (RSNA) in transgenic rats (TG) with low angiotensinogen production in glial cells, TGR(ASrAogen)-680. In addition, the sympathetic and vagal autonomic tonus to the heart was investigated. As previously shown, TG rats presented a lower arterial pressure (AP) and HR. However, TG rats had decreased AP variability during the night (8.9 ± 0.4 mmHg vs 9.8 ± 0.3 mmHg, in SD) accompanied by an increase in HR variability (39 ± 1 beats/min vs 35 ± 1 beats/min, in SD) and augmented locomotor activity during the night (3.5 ± 0.3 counts/min vs 2.5 ± 0.2 counts/min, in SD). In addition, TG rats presented increased baroreflex sensitivity for the RSNA (slope of line that correlates decreases in RSNA and increases in AP = 1.36 ± 0.18 vs 0.77 ± 0.1, in SD) and an increased sensitivity for both the baroreflex bradycardia (0.79 ± 0.04 ms/mmHg vs 0.52 ± 0.04 ms/mmHg, in SD) and tachycardia (1.46 ± 0.1 ms/mmHg vs 0.93 ± 0.01 ms/mmHg, in SD). Further, TG rats had increased vagal tonus (25 ± 3 beats/min vs 11 ± 4 beats/min in SD) without significant change in the sympathetic tonus to the heart. These results confirm and extend previous observations showing that glial angiotensinogen, the main source of brain RAS peptides, importantly modulates sympathetic tonus, at least to the renal nerve, and vagal tonus to the heart.