Sympathetic regulation of coronary circulation during handgrip exercise and isolated muscle metaboreflex activation in men

Effects of alpha-adrenergic receptor blockade on coronary circulation in postmenopausal women

We sought to investigate the effect of the α1-adrenergic receptor blockade during handgrip exercise (Grip), isolated metaboreflex activation (Metabo), and cold pressor test (CPT) on coronary circulation in young (YW) and postmenopausal women (PMW). Ten YW and 9 PMW underwent two protocols: (1) 3 min of baseline followed by 3 min of CPT and (2) 3 min of rest, 3 min of Grip followed by 3 min of Metabo. Protocols were carried out under control conditions and α1-adrenergic receptor blockade (oral prazosin 0.03 mg·kg-1). Coronary blood velocity (CBV) and vascular conductance (CCI) were lower in PMW. Grip increased CBV only in YW (YW: Δ18.0 ± 21.1% vs. PMW: Δ4.2 ± 10.1%; p < 0.05), and the blockade did not change the CBV response to Grip in YW and PMW. During the Metabo, CBV returned to resting levels in YW and was unchanged from rest in PMW, before (YW:Δ1.7 ± 8.7% vs. PMW: Δ- 1.5 ± 8.6) and under the blockade (YW: Δ4.5 ± 14.8% vs. PMW: Δ9.1 ± 29.5%). CPT did not change CBV in both groups (YW: Δ3.9 ± 8.0 vs. PMW: Δ- 4.1 ± 6.2%), following the α1-blockade, CPT increased CBV only in YW (YW: Δ11.2 ± 12.8% vs. PMW: Δ2.2 ± 7.1%; p < 0.05 for group and condition). CCI decreased during Grip, Metabo, and CPT in YW and PMW, while the blockade prevented that decrease only in YW. The α1-adrenergic receptor plays a role in the control of coronary circulation in young women, evoking stronger vasoconstriction during CPT than Grip and Metabo in YW. PMW have impaired vasomotor control in the coronary circulation, which seems not to be caused by the α1-adrenergic receptor.

Sympathetic control of the coronary circulation during trigeminal nerve stimulation in humans

PURPOSE

We sought to investigate the sympathetic mechanism controlling coronary circulation during trigeminal nerve stimulation in healthy women.

METHODS

The protocol consisted of 3 min of trigeminal nerve stimulation (TGS) with cold stimuli to the face, in two conditions: (1) control and β-blockade (oral propranolol), and (2) control and α-blockade (oral prazosin).

RESULTS

Thirty-one healthy young subjects (women: n = 13; men: n = 18) participated in the study. By design, TGS decreased heart rate (HR), and increased blood pressure (BP) and cardiac output (CO). Before the β-blockade coronary blood velocity (CBV-Δ1.4 ± 1.3 cm s-1) increased along with the decrease of coronary vascular conductance index (CVCi-Δ-0.04 ± 0.04 cm s-1 mmHg-1) during TGS and the β-blockade abolished the CBV increase and a further decrease of CVCi was observed with TGS (Δ-0.06 ± 0.07 cm s-1 mmHg-1). During the α-blockade condition before the blockade, the CBV increased (Δ0.93 ± 1.48 cm s-1) along with the decrease of CVCi (Δ-0.05 ± 1.12 cm s-1 mmHg-1) during TGS, after the α-blockade CBV (Δ0.98 ± cm s-1) and CVCi (Δ-0.03 ± 0.06 cm s-1 mmHg-1) response to TGS did not change.

CONCLUSION

Coronary circulation increases during sympathetic stimulation even with a decrease in heart rate.

The exercise pressor reflex: An update

The exercise pressor reflex is a feedback mechanism engaged upon stimulation of mechano- and metabosensitive skeletal muscle afferents. Activation of these afferents elicits a reflex increase in heart rate, blood pressure, and ventilation in an intensity-dependent manner. Consequently, the exercise pressor reflex has been postulated to be one of the principal mediators of the cardiorespiratory responses to exercise. In this updated review, we will discuss classical and recent advancements in our understating of the exercise pressor reflex function in both human and animal models. Particular attention will be paid to the afferent mechanisms and pathways involved during its activation, its effects on different target organs, its potential role in the abnormal cardiovascular response to exercise in diseased states, and the impact of age and biological sex on these responses. Finally, we will highlight some unanswered questions in the literature that may inspire future investigations in the field.

The coronary vascular response to the metaboreflex at low-altitude and during acute and prolonged high-altitude in males

Myocardial oxygen delivery is primarily regulated through changes in vascular tone to match increased metabolic demands. In males, activation of the muscle metaboreflex during acute isocapnic hypoxia results in a paradoxical coronary vasoconstriction. Whether coronary blood velocity is reduced by metaboreflex activation following travel and/or adaptation to high-altitude is unknown. This study determined if the response of the coronary vasculature to muscle metaboreflex activation at low-altitude differs from acute (1/2 days) and prolonged (8/9 days) high-altitude. Healthy males (n=16) were recruited and performed isometric handgrip exercise (30 % max) followed by post-exercise circulatory occlusion (PECO) to isolate the muscle metaboreflex at low-altitude and following acute and prolonged high-altitude (3,800 m). Mean left anterior descending coronary artery blood velocity (LADv_mean, transthoracic Doppler echocardiography), heart rate, mean arterial pressure (MAP), ventilation, and respired gases were assessed during baseline and PECO at all time-points. Coronary vascular conductance index (CVC_i) was calculated as LAD_Vmean/MAP. The change in LADv_mean (acute altitude: -1.7 ± 3.9 cm/s, low-altitude: 2.6 ± 3.4 cm/s, P = 0.01) and CVC_i (acute altitude: -0.05 ± 0.04 cm/s/mmHg, low-altitude: -0.01 ± 0.03 cm/s/mmHg, P = 0.005) induced by PECO differed significantly between acute high-altitude and low-altitude. The change in LAD_Vmean and CVC_i induced by PECO following prolonged high-altitude was not different from low-altitude. Our results suggest that coronary vasoconstriction with metaboreflex activation in males is greatest following acute ascent to high-altitude and restored to low-altitude levels following 8-9 days of acclimatization.