INFLUENCE OF AGE ON ORTHOSTATIC CHANGES IN PLASMA-RENIN ACTIVITY AND URINARY CATECHOLAMINES IN MAN

  • 1 January 1975
    • journal article
    • research article
    • Vol. 24  (6) , 481-488
Abstract
Plasma renin activity [PRA], urinary epinephrine, norepinephrine and dopamine excretion were studied in 54 healthy subjects with respect to age-related orthostatic changes. The test subjects were divided into six 10-yr groups, according to their year of birth [1901-1910 to 1951-1960]. In the oldest groups [1901-1910 and 1911-1920], both basal PRA values and norepinephrine and epinephrine excretion and their orthostatic increase were smaller than in younger subjects. Conversely, urinary dopamine excretion and the dopamine/norepinephrine and epinephrine ratio rose with advancing age. There were no significant differences between the plasma Na and K concentrations in the various groups. Urinary aldosterone excretion was slightly higher in the oldest group than in the others, but was still within the control value limits. The i.v. administration of Inderal reduced both resting PRA values and the orthostatic increase in the youngest age groups, so that their PRA approached the values in older subjects. Higher norepinephrine and epinephrine excretion and the lower dopamine/norepinephrine and epinephrine ratio in young subjects may play a role in their higher PRA, especially in the orthostatic reaction. Diminution of sympathetic activity, with lower norepinephrine and epinephrine excretion and relatively high dopamine excretion, may have a direct bearing on the lower PRA values in older subjects. The diminished capacity of older subjects for catecholamine mobilization and raised renin secretion during an orthostatic stress may be related to the higher incidence of orthostatic forms of hypotension in old age.