Muscle Metaboreflex Modulation of Spontaneous Cardiac Baroreflex Sensitivity: Does Sex Matter?
Authors: Samora Milena , Teixeira André L. , Sabino‐Carvalho Jeann L. , Vianna Lauro C. 
Published: June 2021

It is well established that during exercise, the arterial baroreflex is reset to operate around the prevailing blood pressure in an exercise intensity‐dependent manner. This exercise‐induced modulation of baroreflex function is mediated by central signals and by afferent signals arising from working skeletal muscle that are composed of mechanically and metabolically sensitive afferents. Previous studies in humans examining the influence of metabolically sensitive skeletal muscle afferents (i.e., muscle metaboreflex) on cardiac baroreflex sensitivity (cBRS) have found equivocal results reporting increases, decreases, or no change in sensitivity. The reason behind these discrepancies could be attributable to variation in the methods used to assess baroreflex function, exercise modality and intensity, size of exercising muscle mass, and, less discussed, but also relevant, the inclusion of both men and women. This becomes important given a plethora of studies indicating that sex plays a pivotal role when it comes to blood pressure regulation. Given this, the aim of the present study was to investigate the effect of isolated muscle metaboreflex activation on cBRS and the potential sex‐related differences in this interaction. Forty healthy and physically active volunteers (20 men), aged 18–30 years were recruited. All women were non‐oral contraceptives users and performed experiments in the early follicular phase of the menstrual cycle. After 10 minutes rest period, the subjects performed 90s of isometric handgrip (IHG) at 40% of maximal voluntary contraction followed by 3‐min of post exercise ischemia (PEI) to isolate the muscle metaboreflex. Beat‐to‐beat heart rate (HR ‐ electrocardiography) and arterial blood pressure (finger photopletysmography) were continuously measured. Spontaneous cBRS was assessed for all combined sequences (Gainall), and also separately upward (Gainup) and downward (Gaindown) using the sequence technique. HR variability was measured in time (RMSSD ‐ standard deviation of the RR intervals) and frequency domains (LF – low and HF – high frequency power). Resting MBP was lower in women than men (P < 0.01). MBP increased from rest during IHG and remained elevated during PEI in both men and women. However, the magnitude of these responses was greater in men. Resting cBRS was similar between men and women. During PEI, men exhibited an increase in cBRS (Gainall: Δ3.0 ± 1.1 ms mmHg‐1, P = 0.03; Gainup: Δ4.4 ± 2.1 ms mmHg‐1, P = 0.04; and Gaindown: Δ3.3 ± 1.4 ms mmHg‐1, P = 0.03). In contrast, cBRS was unchanged during PEI in women (Gainall: Δ0.6 ± 0.7 ms mmHg‐1, P = 0.10; Gainup: Δ0.3 ± 0.7 ms mmHg‐1, P = 0.27; and Gaindown: Δ0.2 ± 1.1 ms mmHg‐1, P = 0.43). At rest, HF and LF power were lower in women compared with men, whereas RMSSD and LF/HF ratio were similar. During PEI, men exhibited a highest increase in RMSSD and HF compared to women, while LF power was unchanged in both groups. In addition, LF/HF ratio decreased in men and was unchanged in women. These findings indicate that the muscle metaboreflex activation modulates spontaneous cBRS in a sex dependent manner.Support or Funding InformationBrazilian National Council of Scientific and Technological Development (CNPq); Foundation for Research Support of Federal District (FAPDF); Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.