Purpose: The purpose of this study is to determine whether taste and/or trigeminal stimulation have a physiological effect on neuroendocrine levels in humans. The hypothesis we are testing in the present study is that bitter substances or carbonation alter the level of stress hormones in the blood through stimulation of trigeminal or taste stimulation. If this stimulation occurs, it could have adverse effects in patients with wasting. Unfortunately, many of the medications taken by patients, for example those with AIDS, are extremely bitter, and could cause trigeminal/taste stimulation that could increase stress hormones, and possibly metabolic rate and wasting. The neuroendocrine parameters being studied are epinephrine, norepinephrine, and cortisol. Chemosensory stimulation of the taste and smell receptors, which occurs during ingestive behavior, prompts cephalic phase responses which include increased salivation and gastric secretion, increased pancreatic exocrine secretion, increased secretion of insulin, and decreased blood levels of FFA. Carbonation (as in carbonated beverages), while not considered a taste, stimulates the trigeminal nerve. Bitter substances can also stimulate the trigeminal nerve by permeating through bilipid membranes of taste cells as well tight junctions between cells to stimulate free nerve endings. Methods: In this study subjects are screened in a 30-minute session and tested in one 4 1/2 hour session at least one day after the screening. Medical and dietary histories are taken and informed consents are signed at the screening. In the morning of the test session day, the subject is admitted to the CRU. The subject then has a saline lock placed in a peripheral arm vein. Sixty minutes later a baseline blood sample is taken. Then 10 ml of water is squirted into the subject's mouth, which he swishes and expectorates. Blood samples are taken at 5 minutes, 10 minutes, and 25 minutes after stimulus administration. There is a twenty-five minute break between each test stimulus. Three test stimuli are then tested in the same manner as the control stimulus (water) and blood draws are taken immediately before, and 5, 10, and 25 minutes after administration of the stimulus. The taste stimuli are delivered in a fixed order, from least to most intense: water, carbonated water, bitter water (Invirase), and capsaicin. The blood concentrations of epinephrine, norepinephrine, and cortisol are analyzed for each blood sample. Each subject has a total of 16 blood draws of 5 ml each (80 ml total per subject). Blood is centrifuged and the plasma is frozen at -70oC until assay. Cortisol is measured by radioimmunoassay, and catecholamines are separated by HPLC and quantitated electrochemically. The subject's pulse and blood pressure is taken immediately before stimulus administration, and 25 minutes after stimulus administration. Subjects rate the perceived overall intensity of the stimulus and the pleasantness of each stimulus, as well as their mood, alertness, and level of hunger on line scales. The levels of epinephrine, norepinephrine, and cortisol are compared before and after the administration of each taste stimulation. Results: The study is in progress. Eight subjects have been tested but plasma samples have not yet been analyzed. Future plans: The testing will ultimately be expanded to AIDS patients and the elderly.
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