Norepinephrine and forearm vascular resistance responses to tilt and cold pressor test in essential hypertension: effects of aging.

Heart rate, blood pressure, forearm vascular resistance (FVR), and catecholamine and renin responses to head-up tilt at 80 degrees and cold pressor test were investigated in 15 hypertensive men aged less than fifty-five (mean 44 +/- 7 years; M +/- SD) and 13 similarly hypertensive men aged more than fifty-five (mean 62 +/- 4 years; M +/- SD). Baseline plasma norepinephrine levels, as well as norepinephrine responses to tilt and cold pressor stress, were similar in the two groups, suggesting a lack of age-related increase in plasma norepinephrine (NE) responses in patients with essential hypertension. Normalized FVR responses (% change) to tilting (28 +/- 21 vs 95 +/- 36; M +/- SE) and cold pressor test (33 +/- 12 vs 64 +/- 21; M +/- SE) were significantly less (p less than 0.01) in older hypertensives. These results, but not the plasma NE responses to reflex sympathetic activation by tilt and cold pressor testing in older hypertensives, suggest an impaired forearm vasoconstriction.