AGE, EXERCISE, THERMOGENESIS AND POSTPRANDIAL HYPOTENSIO

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In young adult humans, acute energy intake (feeding) evokes an integrative "postprandial" physiological response which includes an increase in metabolic rate (thermic effect of food intake--TEF) and a number of autonomic nervous system (ANS) and cardiovascular adjustments aimed at providing increased blood flow for digestion (splanchnic vasodilation) while maintaining arterial blood pressure (BP) at preprandial levels. Some older adults with chronic diseases demonstrate a reduced TEF and/or a postprandial fall in BP ("postprandial hypotension"), but it is unknown whether this occurs with age in healthy adults. If the latter is true, some evidence suggests that these changes may not occur with age in adult humans who exercise regularly. The specific aims of the present proposal are to determine if: (1) TEF is lower and postprandial BP declines occur in middle-aged and/or older sedentary adults compared with young adult controls; (2) the lower TEF is due to attenuated postprandial increases in sympathetic nervous system (SNS) activity associated with reduced CNS sympathoexcitatory responsiveness to acute hyperinsulinemia; (3) the postprandial hypotension also is associated with: a) an attenuated or absent whole-limb and skeletal muscle vasoconstriction; b) a smaller reduction in cardiac vagal modulation of heart rate and an attenuated tachycardia; and c) a lower baseline cardiac vagal tone and arterial baroreflex sensitivity; (4) middle-aged and older adults who exercise regularly do not demonstrate the lower TEF and postprandial hypotension observed with age in sedentary humans, and whether this is associated with augmented SNS responses, CNS sympathetic responsiveness to circulating insulin, limb vasoconstriction, vagally-mediated tachycardia, baseline cardiac vagal tone and baroreflex sensitivity; and (5) the reduced TEF and postprandial hypotension associated with sedentary aging are related to elevated adiposity. Because TEF contributes significantly to daily energy expenditure and, therefore, energy balance, the expected results should provide new and clinically important information concerning the effects of sedentary aging, regular exercise and adiposity on TEF in the context of age-related obesity and its metabolic and cardiovascular co-morbidities. Moreover, postprandial hypotension is associated with post-meal dizziness, weakness, syncope, cerebrovascular ischemia, and angina pectoris. As such, the expected results should provide new insight into the effects of sedentary aging, habitual exercise and body fatness on this clinically-important cardiovascular disorder.