Dissociation of 24-hour catecholamine levels from blood pressure in older men

Increased plasma norepinephrine levels have been observed in some persons with early essential hypertension. Although both plasma norepinephrine level and mean arterial blood pressure rise with age, little is known about the state of catecholamine secretion in elderly patients with essential hypertension. We studied the 24-hour cycle levels of plasma norepinephrine, epinephrine, and dopamine in 12 elderly hypertensive subjects and 13 age-matched normotensive controls (mean ages, 63.8 ± 1.2 yr and 64.8 ± 1.8 yr [SEM] respectively). Blood samples were obtained at bihourly intervals from 0900 to 2100 hours and every 30 minutes from 2100 to 0900 hours, during which time sleep and breathing were continuously monitored. A circadian rhythm was displayed in both groups by plasma epinephrine levels (mesor, 49 ± 2 pg/ml and 38 ± 1 pg/ml; amplitude, 15 ± 2 pg/ml and 11 ± 1 pg/ml; acrophase, 12.20 ± 0.40 hr and 14.41 ± 0.34 hr in the normotensive and hypertensive groups respectively) but not by plasma norepinephrine or dopamine levels. During the 24-hour cycle plasma epinephrine, but not norepinephrine or dopamine, levels were positively related to mean arterial blood pressure (r = 0.60 for the normotensive subjects, r = 0.57 for the hypertensive subjects, p < 0.01 for both). Mean 24-hour plasma norepinephrine (377 ± 9 pg/ml vs 455 ± 9 pg/ml; p < 0.001), epinephrine (34 ± 2 pg/ml vs 45 ± 2 pg/ml; p < 0.01), and dopamine (40 ± 2 pg/ml vs 62 ± 3 pg/ml; p < 0.01) levels were lower in the hypertensive group, although groups did not differ in parameters known to affect catecholamine secretion such as body weight, sodium intake, sleep efficiency, or sleeprelated breathing disorders. Mean 24-hour plasma norepinephrine level was inversely related to the 24-hour mean arterial blood pressure (r =-0.48, p < 0.05). High norepinephrine levels in the elderly may reflect decreased baroreceptor sensitivity as well as compensatory response to decreased /3-adrenergic receptor sensitivity. It is unclear why elderly hypertensive persons, unlike younger hypertensive persons, have lower plasma catecholamine levels than do elderly normotensive persons.