Effects of β2 Adrenergic Receptor on Coronary Blood Flow and Cardiovascular Responses during Exercise and Metaboreflex in Men and Women

Abstract

Redundant mechanisms modulate coronary blood flow (CBF) matched to the metabolic demand.However, the possible sex differences in the mechanisms of CBF control are not fully understood. In addition, the effect of skeletal muscle metaboreflex on CBF in humans is unclear. Thus, 9 men (26 ± 4 yr; 23 ± 2 kg/m2) and 7 women (24 ± 4 yr; 24 ± 3 kg/m2) had their heart rate (HR) and blood pressure recorded. Mean arterial pressure (MAP), cardiac index (CI), total vascular resistance index (TVRI), femoral blood flow (FBF) and myocardial oxygen consumption (MVO2) were estimated. CBF was calculated as average of maximal blood flow velocity on the diastolic phase of ten cardiac cycles. The protocol consisted in 3 minutes rest, 3 minutes of handgrip exercise at 40% of the maximal voluntary force, 3 minutes of peripheral circulatory occlusion (metaboreflex) and recovery, before and after β2‐AR blockade (propranolol). Effects were statistically tested by two‐way ANOVA in men and women, followed by multiple comparisons with Bonferroni correction. HR increased during exercise in men and women (MΔ24 ± 22 BPM; WΔ23 ± 10 BPM; mean ± SD), and the β2‐AR blockade blunted the increase (MΔ 10 ± 6 BPM; WΔ 13 ± 5 BPM). MAP increased during exercise (MΔ36 ± 5 mmHg; WΔ36 ± 11 mmHg); the β2‐AR blockade reduced MAP in men, with no effect on the response during exercise (MΔ36 ± 5 mmHg; WΔ36 ± 11 mmHg). MAP decreased during metaboreflex activation compared to exercise, but was increased compared to rest (M Δ26 ± 9 mmHg; W Δ22 ± 8 mmHg), and β2‐AR blockade did not change this effect. CI increased during exercise in men and women (MΔ0.96 ± 1.2 L.min.m2; WΔ1.5 ± 0.6 L.min.m2), which was blunted by β2‐AR blockade (MΔ0.5 ± 0.6 L.min.m2; WΔ0.8 ± 0.6 L.min.m2). Compared to rest, metaboreflex increased CI only in women (MΔ −0.01 ± 0.7 L.min.m2; WΔ0.88 ± 0.6 L.min.m2), the β2‐AR blockade did not change the CI. TVRI increased during exercise (MΔ0.96 ± 1.6 mmHg/11·min/m2; WΔ −0.18 ± 0.9 mmHg/11·min/m2) and metaboreflex activation (MΔ2.0 ± 1.5 mmHg/11·min/m2; WΔ −0.13 ± 0.8 mmHg/11·min/m2) only in men. With β2‐AR blockade TVRI increased in women during exercise (MΔ1.95 ± 1.4 mmHg/11·min/m2; WΔ1.26 ± 1.9 mmHg/11·min/m2) and metaboreflex (MΔ2.2 ± 1.5 mmHg/11·min/m2; WΔ0.5 ± 0.8 mmHg/11·min/m2). FBF increased during exercise (MΔ564 ± 706 ml/min1; WΔ 573 ± 438 ml/min1) and metaboreflex activation (MΔ74 ± 253 ml/min1; WΔ 280 ± 487 ml/min1) and β2‐AR blockade prevented the increase in both groups. CBF increased during exercise (MΔ11 ± 8 cm/s1; WΔ 6 ± 8 cm/s1) and metaboreflex activation (MΔ0.3 ± 2 cm/s1; WΔ −0.8 ± 3 cm/s1) in men; after β2‐AR blockade CBF did not change in either groups in both conditions. MVO2 increased during exercise (MΔ6.5 ± 3.6; WΔ 5.0 ± 2.0) and metaboreflex activation (MΔ3.2 ± 1.0; WΔ 3.0 ± 1.2) in men and women and β2‐AR blockade blunted the increase. β2‐AR seems to play an import role to the lower TVR observed in women in response to exercise and metaboreflex activation. The increase of CBF during exercise and metaboreflex was higher in men and the β2‐AR blockade prevented the increase.Support or Funding InformationCAPES, CNPQ, FAPERJ, National Institute for Science & Technology ‐ INCT (In)activity & ExerciseThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.