Older hypertensive humans had a greater norepinephrine metabolic clearance rate (1100 vs 900 ml/m2; P=0.004) and enhanced alpha-adrenergic responsiveness compared with normotensive subjects.
Observational (n=44)
Is sympathetic nervous system activity and alpha-adrenergic responsiveness altered in older hypertensive humans compared to normotensive controls?
Older hypertensive humans exhibit enhanced alpha-adrenergic responsiveness and increased norepinephrine metabolic clearance compared to normotensive controls, suggesting a mechanism for elevated blood pressure.
Absolute Event Rate: 1100% vs 900%
p-value: p=0.004
We have previously demonstrated in normotensive humans an age-associated increase in sympathetic nervous system (SNS) activity combined with appropriate downregulation of alpha-adrenergic responsiveness. Impaired downregulation of alpha-adrenergic responsiveness, despite a comparable level of SNS activity, could contribute to higher blood pressure in older hypertensive humans. We measured arterial plasma norepinephrine (NE) levels and the extravascular NE release rate (NE2) derived from 3HNE kinetics (to assess systemic SNS activity), and platelet and forearm arterial adrenergic responsiveness in 20 normotensive (N) and in 24 hypertensive (H), otherwise healthy, older subjects (60-75 yr). Although plasma NE levels were similar (N 357 +/- 27 vs. H 322 +/- 22 pg/ml; P = 0.37), NE2 tended to be greater in the hypertensive group (H 2.23 +/- 0.21 vs. N 1.64 +/- 0.20 microgram. min-1. m-2; P = 0. 11), and the NE metabolic clearance rate was greater (H 1,100 +/- 30 vs. N 900 +/- 50 ml/m2; P = 0.004). In the hypertensive group, there was a greater alpha-agonist-mediated inhibition of platelet membrane adenylyl cyclase activity and a NE- but not ANG II-mediated decrease in forearm blood flow. Compared with normotensive subjects, in older hypertensive subjects 1) NE metabolic clearance rate is increased, 2) systemic SNS activity tends to be increased, and 3) arterial and platelet alpha-adrenergic responsiveness is enhanced. These results suggest that heightened SNS activity coupled with enhanced alpha-adrenergic responsiveness may contribute to elevated blood pressure in older hypertensive humans.
Supiano et al. (Mon,) conducted a observational in Hypertension (n=44). Hypertension vs. Normotension was evaluated on Norepinephrine (NE) metabolic clearance rate (p=0.004). Older hypertensive humans had a greater norepinephrine metabolic clearance rate (1100 vs 900 ml/m2; P=0.004) and enhanced alpha-adrenergic responsiveness compared with normotensive subjects.