The role of nitric oxide in passive leg movement-induced vasodilatation with age: insight from alterations in femoral perfusion pressure

We sought to better understand the contribution of nitric oxide (NO) to passive leg movement (PLM)-induced vasodilatation with age, with and without a posture-induced increase in femoral perfusion pressure (FPP). PLM was performed in eight young (24 +/- 1years) and eight old (74 +/- 3years) healthy males, with and without NO synthase inhibition via intra-arterial infusion of N-G-monomethyl-(L)-arginine ((L)-NMMA) into the common femoral artery in both the supine and upright-seated posture. Central and peripheral haemodynamic responses were determined second-by-second with finger photoplethysmography and Doppler ultrasound, respectively. PLM-induced increases in heart rate, stroke volume, cardiac output and reductions in mean arterial pressure were similar between age groups and conditions. In the young, (L)-NMMA attenuated the peak change in leg vascular conductance (LVCpeak) in both the supine (control: 7.4 +/- 0.9; (L)-NMMA: 5.2 +/- 1.1mlmin(-1)mmHg(-1), P<0.05) and upright-seated (control: 12.3 +/- 2.0; (L)-NMMA: 6.4 +/- 1.0mlmin(-1)mmHg(-1), P<0.05) posture, with no significant change in the old (supine control: 4.2 +/- 1.3; supine (L)-NMMA: 3.4 +/- 0.8; upright-seated control: 4.5 +/- 0.8; upright-seated (L)-NMMA: 3.4 +/- 0.8mlmin(-1)mmHg(-1), P>0.05). Increased FPP augmented the LVCpeak in the young control condition only (P<0.05). In the upright-seated posture, NOS inhibition attenuated the FPP-induced augmentation of rapid vasodilatation in the young (control: 1.25 +/- 0.23; (L)-NMMA: 0.74 +/- 0.11mlmin(-1)mmHg(-1)s(-1); P<0.05), but not the old (control: 0.37 +/- 0.07; (L)-NMMA: 0.25 +/- 0.07mlmlmin(-1)mmHg(-1)s(-1); P>0.05). These data reveal that greater FPP increases the role of NO in PLM-induced vasodilatation in the young, but not the old, due to reduced NO bioavailability with age. Therefore, PLM involving alterations in posture may be useful to determine changes in NO bioavailability with age.