Effects of Ghrelin on Sympathetic Nerve Activity in Humans
- UT Southwestern-Other
Wanpen Vongpatanasin, M.D.
We plan to recruit 36 otherwise healthy subjects. each subject will participate in 3 studies, which will be separated by at least 4 weeks apart, using randomized crossover design.
Part 1: During the first study, subjects will be randomized to receive one of the 3 treatments a) intravenous saline, or b) intravenous ghrelin (inD# 74,065) at the dose of 5 pmol/kg/min, or c) i.v. ghrelin at the dose of 10 pmol/kg/min each for 180 minutes. We will collect venous endothelial cells, measure Sna by microneurography, skeletal muscle blood flow by high-resolution ultrasonography, total body energy expenditure (ee) by indirect calorimetry (determining changes in concentration of oxygen and carbon dioxide from the exhaled air), hunger scale by questionnaire, plasma glucose, leptin, ghrelin, and insulin at baseline, after infusion of ghrelin or saline alone for 60 minutes, and after ingestion of 800-kcal liquid meal while the subjects continue to receive i.v. saline or ghrelin for 120 minutes. To collect endothelial cells from the superficial veins a thin wire will be inserted in the vein to collect cells from the inner lining of the vein. The cells collected will be processed and stained for several proteins involved in endothelial cell function, using immunofluorescent technique. To measure skeletal muscle blood flow, ultrasound probe will be placed over the forearm to obtain images while octafluoropropane microbubbles (Definity) are infused intravenously at the rate of 0.20 to 0.27 ml/min. We will dilute 1 vial of Definity to 30 cc of normal saline and the total dose of Definity use will not exceed 2 vials per study subject per day or visit. Sna will be measured from the peroneal nerve in the leg. This is done by inserting a tiny needle directly into the nerve. We will begin by stimulating electrically over the skin with a pencil-sized blunt probe to localize the nerve and its branches. When we stimulate over the nerve, subject will notice either involuntary twitching of the leg or arm muscles, or a tingling sensation. These tingling sensations are annoying but not painful and disappear when the stimulation is stopped. once we have localized the nerve, we will introduce a tiny, sterile wire needle (an electrode) through the skin at the same location. When the tip of the needle enters the nerve, subjects will once again notice either involuntary muscle twitches or tingling in the leg or arm. at this point, we will turn the electrical stimulator off and make minor adjustments in the position of the needle until we begin to record the nerve signals. The recording needle will remain in this position for the duration of the study. after infusion of ghrelin or placebo, skeletal muscle blood flow and Sna will be measured during handgrip exercise at 30% of maximal effort for 3 minutes and during lower body negative pressure (LBnP) at -20 mm Hg and -40 mm Hg (each for 3 minutes) to simulate orthostatic stress. Peripheral venous line insertion and laboratory assay for glucose and other routine chemistries will be performed at the cardiovascular physiologylaboratory (room H4.136). We plan to obtain 150 cc or 10 tablespoons of blood to assess changes in the hormones during the study.
Part 2: During the second studies, subjects will be randomized to one of the remaining 2 arms and the same procedure will be repeated.
Part 3: During the third studies, subjects will be randomized to the last arm of the study and the same procedure will be repeated.
Sna, ee, changes in endothelial cell expressions, and hormone changes during treatment with 2 doses of ghrelin will be compared to those during saline infusion.
We plan to study 36 otherwise healthy subjects. Experiments will be performed in 2 groups of nondiabetic human subjects (age 18-65): 1) 18 lean healthy subjects (BMI 18.5-24.9) and 2) 18 obese healthy subjects (BMI >=30).