Chronic vagal nerve stimulation improves baroreflex neural arc function in heart failure rats

We tested whether 6-wk vagal stimulation (VS) treatment improved open-loop baroreflex function in rats after myocardial infarction (MI). The following three groups of Sprague-Dawley rats were examined: normal control (NC, n = 9), MI with no treatment (MI-NT, n = 8), and MI treated with VS (MI-VS, n = 7). Under anesthesia, a stepwise input ranging from 60 to 180 mmHg was imposed on isolated carotid sinus baroreceptor regions, while the responses in splanchnic sympathetic nerve activity (SNA) and arterial pressure (AP) were measured. The response range of percent SNA was greater in the MI-VS than in the MI-NT group (63.8 ± 4.9% vs. 33.1 ± 3.8%, P < 0.01). The slope of the AP response to percent SNA was not different between the MI-VS and MI-NT groups (0.611 ± 0.076 vs. 0.781 ± 0.057 mmHg/%). The difference in the response range of AP between the MI-VS and MI-NT groups did not reach statistical significance (40.7 ± 6.2 vs. 26.4 ± 3.5 mmHg). In conclusion, the 6-wk VS treatment significantly improved the baroreflex control of SNA, but the effect was limited for the baroreflex total-loop function due to the lack of significant improvement in the AP response to percent SNA.