Abstract
Plasma norepinephrine (NE) and epinephrine (E) levels are indicators of peripheral sympathetic and adrenomedullary activities, respectively. The sympathoadrenomedullary system is involved in the metabolic response to carbohydrate intake and is affected by aging; however, the relationship between glucose metabolism and adrenomedullary activity in older adults remains poorly defined. The objective of this study was to examine the changes in the impact of carbohydrate-rich meals on circulating catecholamines with aging. After iv glucose tolerance testing and 1 d of habituation, blood samples were collected every 10-30 min for 24 h. Daytime hours were spent at bed rest. Sleep was scheduled between 2300 and 0700 h with polygraphic monitoring. The study was performed at a general clinical research center. Nine young (age, 20-28 yr) and eight older (age, 50-69 yr) healthy men participated in this study. Identical mixed meals (62% carbohydrate) were given at 0900, 1400, and 1900 h. The main outcome measures were 24-h plasma E and NE measurements. The profiles of E and NE were characterized by clear day-night differences, which were preserved in the older group. Young subjects showed a clear dissociation between postprandial adrenomedullary and sympathetic activities characterized by a rapid decline in plasma E and increased NE levels. There was an overall increase in NE levels and markedly dampened postprandial variation in plasma E in the older men. In young adults, postprandial E levels follow a biphasic pattern that is inversely related to that of glucose and insulin. Aging is associated with a dysregulation of this response.
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