Watermelon Supplementation and Arterial Stiffness
| Status: | Archived |
|---|---|
| Conditions: | High Blood Pressure (Hypertension) |
| Therapuetic Areas: | Cardiology / Vascular Diseases |
| Healthy: | No |
| Age Range: | Any |
| Updated: | 7/1/2011 |
| Start Date: | August 2010 |
| End Date: | April 2011 |
Effects of Oral L-citrulline/L-arginine in Watermelon on Central Blood Pressure and Arterial Stiffness in Individuals With Obesity-related High Blood Pressure
Increased abdominal obesity (waist circumference) and systolic blood pressure (BP) are main
risk factors for the metabolic syndrome. Approximately 60% of adults in the United States
are prehypertensive or hypertensive. Hypertension has been associated with abnormal
endothelial and autonomic function, the two main mechanisms of BP regulation. Endothelial
dysfunction, as a result of reduced NO (a vasodilator), and increased sympathetic nervous
system activity contribute to arterial stiffness by enhancing the vasomotor tone. Because BP
variations are sensed by baroreceptors in the wall of large arteries, increased stiffness of
arteries may attenuate the control of BP by the autonomic nervous system leading to
hypertension. High production of proinflammatory cytokines and low adiponectin (vascular
protective molecule), are considered the underlying mechanisms leading to endothelial
dysfunction and arterial stiffness. The recommended intervention for controlling BP in
overweight/obese individuals with pre- and stage 1- hypertension is lifestyle modifications
and not drug therapy. Among the dietary regimens that are reported to reduce BP is
L-arginine, the substrate for endothelial NO production. Recently, oral L-citrulline has
been shown to be more effective than L-arginine in improving circulating NO levels because
is not affected by enzymatic degradation. Watermelon, the leading US melon crop, is one of
the few natural foods rich in L-citrulline which is efficiently transformed to arginine in
humans. The investigators long-term goal is to provide feasible and effective dietary ways
to reduce cardiovascular risk factors in individuals with high abdominal fat and BP. The
overall objective of this study is to bring forth evidence that watermelon supplementation
will reduce BP and cardiovascular risk factors such as arterial stiffness, autonomic
dysfunction and endothelial dysfunction. The investigators postulate that watermelon
supplementation will reduce BP and arterial stiffness by enhancing endothelial function and
reducing vascular inflammation. The findings of this study will provide a foundation for
disseminating feasible, safe approaches for preventing and combating obesity-related
hypertension at its early stage which does not require drug therapy.
The purpose of the study is to examine the effect of 12 weeks of L-citrulline/L-arginine in
the form of watermelon supplementation on arterial function and autonomic neural control of
the heart rate and blood pressure in older overweight/obese men and women with pre- and
stage 1- hypertension. The specific aims of the study are:
1. To investigate the extent to which daily consumption of watermelon supplementation
containing L-citrulline/L-arginine (4/2 g) will reduce BP and arterial stiffness. This
aim will examine the working hypothesis that watermelon supplementation will reduce BP
and improve arterial function. This aim will be tested by measuring brachial and
central (aortic and carotid) BP at rest and during physiological stress (head-up tilt
test and cold pressor test), and by evaluating arterial stiffness using pulse wave
velocity of the aorta and legs as primary variables.
2. To determine the effect of watermelon supplementation on endothelial function. There is
evidence that watermelon improves endothelial function in rats. Hence, we postulate
that watermelon in part exerts its vascular protective effects by modulating indices of
endothelial function. This aim will be tested by measuring flow-mediated dilation using
vascular ultrasound and circulating levels of vasodilators, vasoconstrictors, and
markers of vascular inflammation (adiponectin, leptin, endothelin-1, angiotensin II,
prostaglandin F2α, sVCAM-1, sICAM-1, and 8-isoprostane).
3. To determine whether watermelon supplementation will improve the autonomic control of
BP and heart rate in individuals with high abdominal obesity and BP. There is evidence
that food high in L-arginine improves baroreflex sensitivity (BRS) in individuals with
pre-hypertension. This aim will examine the working hypothesis that watermelon will
improve cardiovascular autonomic control of BP by measuring heart rate variability, BP
variability and BRS at rest and during physiological stress as secondary variables.
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