(755.6) Cholinergic-mediated Circulatory Responses at the Onset of Isometric Exercise: Does Sex Matter?

Poster Board Number: E443

Milena Samora (University of Texas, University of Brasilia), André Teixeira (University of Guelph), Jeann Sabino-Carvalho (University of Brasilia), Lauro Vianna (University of Brasilia)

Introduction: We have shown that handgrip exercise evokes an initial decrease in systemic vascular resistance (SVR), which was abolished by cholinergic blockade (glycopyrrolate) and, thereby, augmented the blood pressure (BP) response. These findings suggest that a cholinergic mechanism is important for the BP and SVR responses at the onset of isometric handgrip exercise in humans. Noteworthy, this previous study included men only, and was not designed to investigate the potential existence of sex-related differences in immediate BP and circulatory responses evoked at the exercise onset. Given this, the aim of this study was to test the hypothesis that women present an attenuated fall in SVR and increased pressor response compared to men at the onset of isometric handgrip exercise due to a blunted cholinergic vasodilation.

Methods: Ten healthy men (aged 21 ± 1 year) and 10 women (aged 24 ± 1 year) were recruited. Women were non-oral contraceptives users and performed experiments in the early follicular phase of the menstrual cycle. Participants performed 20s bout of isometric handgrip exercise at 40% of maximal voluntary contraction. Beat-to-beat heart rate (HR) (ECG) and mean BP (finger photopletysmography) were continuously measured. Beat-to-beat stroke volume (SV) was obtained with the Modelflow method and matched with HR to estimate cardiac output (CO) and SVR. The exercise responses were expressed as a change from 10s immediately before the onset of voluntary contraction.

Results: The BP response pattern appeared to be different between men and women at the onset of isometric exercise. While men presented a typical exercise-evoked biphasic BP response (3s: Δ2 ± 2 mmHg; 10s: Δ1 ± 1 mmHg; 20s: Δ5 ± 3 mmHg), women showed a progressive increase in mean BP (3s: Δ1 ± 1 mmHg; 10s; Δ3 ± 1 mmHg; 20s: Δ6 ± 1 mmHg; P=0.681). Men demonstrated a decrease in SVR at 3s (Δ-0.9 ± 0.3 mmHg.L-1.min), 10s (Δ -1.6 ± 0.4 mmHg.L-1.min) and 20s (Δ-1.9 ± 0.7 mmHg.L-1.min) following the exercise onset, and these responses tended to be attenuated in women (3s: Δ-0.3 ± 0.3 mmHg.L-1.min; 10s: Δ-1.2 ± 0.4 mmHg.L-1.min; 20s: Δ-0.6 ± 0.5 mmHg.L-1.min; P=0.131). There were no sex differences in HR, SV and CO responses to exercise.

Conclusion: These findings suggest a lack of sex differences in immediate BP and circulatory responses at the onset of isometric handgrip exercise, indicative of similar cholinergic-mediated vasodilation in skeletal muscle between men and women.

CAPES (to M. Samora, J.L. Sabino-Carvalho and L.C. Vianna) and CNPq, FAPDF and an American Physiological Society Arthur C. Guyton Awards for Excellence in Integrative Physiology (to L.C. Vianna).