The Effects of Watermelon Juice Supplementation on Postprandial Vascular Endothelial Function

Overview

The purpose of this study is to test if watermelon juice supplementation improves vascular dysfunction experience during hyperglycemia.

The objective of this pilot study is to determine the potential for watermelon juice to attenuate the reduction postprandial endothelial function and skeletal muscle microvascular blood flow (MVBF) experienced during hyperglycemia. The investigators will attempt to answer the following hypotheses: Hypothesis 1: Watermelon juice supplementation will attenuate the reduction in endothelial dysfunction and microvascular blood flow during an oral glucose challenge. Hypothesis 2: Watermelon juice will increase L-arginine bioavailability during hyperglycemia and correlate with improved vascular response. Exploratory Aim: The postprandial period is defined by increased sympathetic nervous system activity (vasoconstriction) and NO• mediated vasodilation. Heart rate variability (HRV) is a measurement of the balance of parasympathetic to sympathetic activity. The investigators will measure HRV during the oral glucose challenge to interrogate the possibility that watermelon juice can modulate the balance of blood vessel constriction and relaxation during an oral glucose Procedures Involved There will be 1 screening visit, and 2 outpatient visits. Participants will consume watermelon juice or placebo for 2 weeks. The washout period will last 2 weeks prior to the cross-over to the opposite condition. Participants visits will be conducted at the Vascular and Resting Metabolism Lab located in the department of kinesiology at LSU. Screening Visit Participants will undergo consenting and fasting blood draws to measure glucose, lipids, and CBC. Vital signs (blood pressure, body weight, body composition (DXA), heart rate, etc) will be measured. For DXA procedure participants will undergo a whole body scan lasting approximately 10 minutes. Participants will remove all metal objects from their body and lie down on the table. The legs will be secured together using two Velcro straps. The participant will be instructed to remain completely still during the scan. Randomization will be performed to allocate the study participant for their initial group assignment to either the watermelon juice group or placebo. The initial six participants will be assigned treatment A for phase 1 and treatment B for phase 2, thereafter the following 6 will be assigned treatment B first then treatment A. The remaining participant will be randomly assigned either treatment A or B in a counterbalanced fashion. Daily Juice Drop-in visits Since the required supplementation duration is 14 days participants will be provided with 2 days (Saturday and Sunday) worth of watermelon juice or placebo to account for days when the LSU AG Center will not be open. To allow for scheduling conflicts and unforeseen circumstances a 3 day period of supplementation less then or greater than the 14 periods will be permitted. Participants will also be provided with juice or placebo for anticipated instances where they cannot be on campus. In order to monitor compliance participants will be asked return the juice container for the days where juice was consumed off premises. Visit 2 and 3: Oral Glucose Challenge - Postprandial FMD and MVBF Participants will arrive in morning at 6:00am fasted for 10-hours. Body composition will be measured by DXA. Next, participants will rest for 30 minutes in the supine positing while wearing a heart rate monitor (Zephyr, Bioharness) to measure heart rate and heart rate variability. Resting metabolic rate will be measured via indirect calorimetry for 20 minutes. Then fasting measures of blood glucose, FMD (ultrasound) and MVBF (near-infrared spectroscopy) will be taken followed by ingestion of 75 g of glucose (glucola). An IV line will be placed in the participants arm vein for blood draw purposes and will remain there throughout the testing. A blood sample will be drawn, and then the participant will drink a sugar solution consisting of 75 grams of glucose. Blood will be drawn at specific times after the participant consumes the drink. Each blood sample will be about 1 tablespoon. (6 tablespoons total for the test). During the IV procedure, a small amount of the participant's own blood (less than 1 teaspoon) will immediately be returned into the participants vein through the IV after each specimen is collected. Blood will be drawn at minute 15, 30, 60, 90, 120 minutes. Postprandial measurements of FMD and MVBF will be taken at 30, 60, 90, and 120 minutes.

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Outcomes