Selective alpha sub( 1)-adrenergic blockade disturbs the regional distribution of cerebral blood flow during static handgrip exercise

• Published in: American journal of physiology. Heart and circulatory physiology 2016-06, Vol.310 (11), p.H1541-H1541
• Main Authors: Fernandes, Igor A, Mattos, Joao D, Campos, Monique O, Machado, Alessandro C, Rocha, Marcos P, Rocha, Natalia G, Vianna, Lauro C, Nobrega, Antonio CL
• Format: Article
• Language: English
• ISSN: 0363-6135

Handgrip-induced increases in blood flow through the contralateral artery that supplies the cortical representation of the arm have been hypothesized as a consequence of neurovascular coupling and a resultant metabolic attenuation of sympathetic cerebral vasoconstriction. In contrast, sympathetic restraint, in theory, inhibits changes in perfusion of the cerebral ipsilateral blood vessels. To confirm whether sympathetic nerve activity modulates cerebral blood flow distribution during static handgrip (SHG) exercise, beat-to-beat contra- and ipsilateral internal carotid artery blood flow (ICA; Doppler) and mean arterial pressure (MAP; Finometer) were simultaneously assessed in nine healthy men (27 plus or minus 5 yr), both at rest and during a 2-min SHG bout (30% maximal voluntary contraction), under two experimental conditions: 1) control and 2) alpha sub( 1)-adrenergic receptor blockade. End-tidal carbon dioxide (rebreathing system) was clamped throughout the study. SHG induced increases in MAP (+31.4 plus or minus 10.7 mmHg, P < 0.05) and contralateral ICA blood flow (+80.9 plus or minus 62.5 ml/min, P < 0.05), while no changes were observed in the ipsilateral vessel (-9.8 plus or minus 39.3 ml/min, P > 0.05). The reduction in ipsilateral ICA vascular conductance (VC) was greater compared with contralateral ICA (contralateral: -0.8 plus or minus 0.8 vs. ipsilateral: -2.6 plus or minus 1.3 ml-min super( -1)-mmHg super( -1), P < 0.05). Prazosin was effective to induce alpha sub( 1)-blockade since phenylephrine-induced increases in MAP were greatly reduced (P < 0.05). Under alpha sub( 1)-adrenergic receptor blockade, SHG evoked smaller MAP responses (+19.4 plus or minus 9.2, P < 0.05) but similar increases in ICAs blood flow (contralateral: +58.4 plus or minus 21.5 vs. ipsilateral: +54.3 plus or minus 46.2 ml/min, P > 0.05) and decreases in VC (contralateral: -0.4 plus or minus 0.7 vs. ipsilateral: -0.4 plus or minus 1.0 ml-min super( -1)-mmHg super( -1), P > 0.05). These findings indicate a role of sympathetic nerve activity in the regulation of cerebral blood flow distribution during SHG.