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Effects of aging on catecholamine metabolism
The Journal of Clinical Endocrinology and Metabolism
|March 1, 1985
Summary
Elderly individuals exhibit higher plasma norepinephrine (NE) levels due to increased NE entry into circulation, not altered production. This suggests changes in sympathetic neuronal NE handling with aging.
Area of Science:
- Physiology
- Gerontology
- Neuroscience
Background:
- Aging is associated with elevated plasma norepinephrine (NE) concentrations.
- The underlying mechanisms contributing to this phenomenon remain unclear.
Purpose of the Study:
- To investigate the determinants of high plasma NE in elderly subjects.
- To differentiate between NE secretion, clearance, and production in young versus elderly individuals.
Main Methods:
- Isotope dilution analysis to estimate apparent NE secretion.
- Measurement of NE plasma clearance.
- Estimation of NE production via urinary metabolite excretion (normetanephrine, vanillylmandelic acid, dihydroxmandelic acid).
Main Results:
- Apparent NE secretion was significantly higher in elderly subjects compared to young subjects.
- NE plasma clearance did not differ between age groups.
- NE production rates were similar in both young and elderly groups.
- Elderly subjects showed increased normetanephrine excretion and decreased deaminated metabolite excretion.
Conclusions:
- The elevated plasma NE in the elderly is attributed to an increased rate of NE entering the circulation.
- Normal NE production suggests that the aging process affects the local handling or disposition of sympathetic neuronal NE rather than its synthesis.
- These findings point to an alteration in sympathetic neuronal NE metabolism with advancing age.