Author(s): OUE, A., IIMURA, Y., MIYAKOSHI, Y., OTA, M., Institution: TOYO UNIVERSITY, Country: JAPAN, Abstract-ID: 669

INTRODUCTION:
Postural change from supine to upright causes translocation of blood from the upper body and thorax to the lower body due to the hydrostatic effects of gravity, causing decreases in venous return and cardiac preload. On the other hand, because these decreases can be counterbalanced by some compensatory responses (e.g., the elevation of sympathetic nerve activity and skeletal muscle pump activity), blood pressure (BP) and cardiac output can normally be maintained. Recently, dietary nitrate (NO₃⁻) supplementation with beetroot juice (BRJ) has been used to increase nitric oxide (NO) production via chemical reduction from NO₃⁻ and nitrite (i.e., the NO₃⁻ → nitrite → NO pathway). It has been reported that enhanced NO activity via this pathway could attenuate sympathetic nerve activity and act as a dilator at rest or during exercise, contributing to control of blood pressure and tissue blood flow. However, it is not clear the extent to which increased NO via the NO₃⁻ → nitrite → NO pathway contributes to the venous vascular response during postural change and subsequent skeletal muscle pump activity. Thus, the purpose of this study was to clarify the effects of acute intake of BRJ on venous blood pooling due to postural change from supine to upright and subsequent venous return by the tiptoe maneuver.
METHODS:
Fifteen healthy young adults (9 men, 6 women, 22.1 ± 1.5 years, 166.7 ± 9.5 cm, 65.8 ± 15.1 kg) volunteered for this study. At 2.5 h after intake of BRJ or prune juice (control beverage: CON), the postural change from supine to upright and the subsequent tiptoe maneuver on the right side (skeletal muscle pump test) were carried out. During performance of the protocol, the change in right calf volume was measured by venous occlusion plethysmography. The change in calf volume from supine to upright position was defined as the total venous volume (VV), which is an index as the volume of venous blood pooling. The decrease in calf volume during the tiptoe maneuver was defined as the venous ejection volume (Ve).
RESULTS:
Plasma nitrate concentration was higher in the BRJ group than in the CON group at 2.5 h after beverage intake (p < 0.05). Postural change in both the groups caused significant increases in BP and heart rate and a decrease in stroke volume (all p < 0.05). However, these parameters did not differ between the CON and BRJ groups. Cardiac output did not differ between the supine and upright positions in either the CON or BRJ group. Ve (CON: 3.91 ± 0.80 mL/dL of tissue; BRJ: 4.04 ± 1.01 mL/dL of tissue, p > 0.05) and VV (CON: 5.95 ± 1.18 mL/dL of tissue; BRJ: 6.06 ± 1.36 mL/dL of tissue, p > 0.05) was not different between CON and BRJ.
CONCLUSION:
The increase in NO activity with intake of BRJ did not alter calf venous pooling during postural change from supine and upright or the subsequent calf venous return by skeletal muscle pump activity in healthy young adults.