Mechanism of increased alpha adrenergic vasoconstriction in human essential hypertension.

Abstract

Multiple components of vascular alpha adrenergic responsiveness were investigated in twenty-four men with mild hypertension and eighteen age-and weight-matched normotensive controls. Arterial plasma norepinephrine (paNE), an index of sympathetic drive, was increased in hypertensives compared to normotensives (mean±SE), 199±24 vs. 134±11 pg/ml, P < 0.02. The effective concentration of intra-arterial (iaNE) We interpret these data as evidence for normal vascular alpha-receptor sensitivity to norepinephrine in mild hypertensives. Consequently, the increased sympathetic drive in mild hypertensives explains the elevated vascular alpha-tone. Although vascular alpha-receptor sensitivity to iaNE was normal, the FAVR responses at high doses (reactivity) were greater in hypertensives to regional infusion of both NE and angiotensin II. This "nonspecific" enhancement of vascular reactivity is probably explained by structural vascular changes in hypertensives.

Non-esterified fatty acids and blood pressure elevation: a mechanism for hypertension in subjects with obesity/insulin resistance?

“…These observations in favour of an a 1 -adrenergic-mediated action of NEFAs are in agreement with previous findings from Egan et al in humans. This group reported an increase in vascular tone and vascular responsiveness in a 1 -adrenergic stimulation in obese hypertensive patients, [28][29][30] which could not be explained from resistance in the vasodilating action of insulin. 31 Assuming that this increase is caused by NEFA elevation, the investigators studied the infusion of Intralipid and heparin in hand veins of two groups of normotensive subjects.…”

Sympathetic Vascular Tone in Human Obesity

“…These studies indicate that lean hypertensive and mostly hypertensive overweight subjects have increased forearm vasodilator response to α-adrenergic blockade by phentolamine as compared with lean normotensive controls, likely reflecting increased sympathetic vascular tone in hypertension [Egan et al, 1987[Egan et al, , 1989. The results in overweight subjects may also reflect increased sympathetic vascular tone associated with increased adiposity.…”

“…Two previous studies by Egan et al [1987; demonstrated increased forearm vasodilatation to phentolamine, a non-selective α-adrenergic receptor antagonist, in lean hypertensive subjects compared to normotensive controls [Egan et al, 1987], and in overweight, mostly hypertensive subjects compared with lean individuals [Egan et al, Figure II.7. Sympathetic neurovascular junction.…”

“…This observation suggests that the increased activation of α-adrenergic receptor causes more vasoconstriction in subjects with excess adiposity than in lean controls. Nevertheless, hypertension independent of obesity could have caused increased responses to phentoalmine [Egan et al, 1987].…”

“…Egan et al demonstrated elevated sympathetically mediated vascular tone in hypertensive compared to normotensive subjects [Egan et al, 1987] and in obese hypertensive compared to lean normotensive individuals [Egan et al, 1989]. The work of Egan et al demonstrates that hypertension is associated with increased α-adrenergic vascular tone.…”