Arterial baroreflex sensitivity, plasma catecholamines, and pressor responsiveness in essential hypertension.

Abstract

Arterial baroreflex sensitivity, plasma norepinephrine (NE) and epinephrine (E), and pressor and depressor responses were assessed in 25 patients with essential hypertension and 29 normotensive control subjects. Sensitivity of the cardiac limb of the baroreflex was determined by blood pressure and interbeat interval responses associated with the Valsalva maneuver, externally applied neck suction and pressure, and injection of phenylephrine and nitroglycerin. By all these techniques, patients with essential hypertension had significantly decreased baroreflex sensitivity, even after adjustment for age mismatching between the hypertensive and normotensive groups. Hypertensive patients also had significantly higher mean levels of plasma NE and E in both brachial arterial and antecubital venous blood (246 vs 154 pg/ml arterial NE, 286 vs 184 pg/ml venous NE, 99 vs 55 pg/ml arterial E, and 65 vs 35 pg/ml venous E) and significantly larger pressor responses to injected phenylephrine (30.9 mm Hg/100 ,)g vs 16.7 mm Hg/100 ,ug). When baroreflex-cardiac sensitivity values measured by the various techniques were averaged, there was a significant inverse relationship between sensitivity and venous NE and between sensitivity and pressor responsiveness. The results indicate that decreased baroreflex-cardiac sensitivity, increased sympathetic outflow, and pressor hyperresponsiveness tend to occur together in some patients with essential hypertension. Decreased arterial distensibility and altered central neural integration can account for these findings.Circulation 68, No. 2, 234-240, 1983. THE ARTERIAL baroreceptor reflex system constitutes one of the most powerful and rapidly acting homeostatic mechanisms for controlling blood pressure, and as such has attracted the interest of hypertension researchers for many years. Baroreflex sensitivity measured by the change in interbeat interval per unit change in systolic pressure after injection of a vasoconstrictor and after the Valsalva maneuver is significantly decreased in patients with essential hypertension. [1][2][3][4][5][6] However, in investigations in which externally applied neck suction has been used to increase carotid transmural pressure and thereby stimulate carotid baroreceptors, decreased baroreflex sensitivity in hypertension has not consistently been detected.7-9When directly compared, results obtained with these techniques have not agreed very well,'0 most likely because the techniques measure different aspects of baroreflex function. In this study, several different measurement techniques were used in each subject to determine if-and with what consistency across techniques patients with essential hypertension have decreased arterial baroreflex sensitivity. It was reasoned that averaging baroreflex sensitivities measured by all or several of the techniques might provide a more valid index of arterial baroreflex gain than relying on one technique alone.When baroreceptor afferents are stimulated, their reflexive circulatory effects result from vagal stimulat...

Ethanol-induced hypertension involves impairment of baroreceptors.

“…This is supported by the findings that there is an inverse correlation between BRS and plasma norepinephrine concentration 8 and a positive correlation between plasma norepinephrine levels and sympathetic neural activity. 17 Our data showing that /3-blockade produced a greater reduction in HR in ethanol-fed rats than in controls and the findings of Chan et al 7 that plasma norepinephrine levels were increased after 12 weeks of ethanol support the view that long-term ethanol administration is associated with enhanced sympathetic activity.…”

Increased pulse pressure is associated with reduced baroreflex sensitivity

“…24 In hypertensive subjects, an inverse relationship has been reported between BRS and plasma catecholamine levels. 25 However, in systo-diastolic and systolic hypertension, baroreceptor modulation of sympathetic nerve traffic is still present despite impaired baroreflex control of the heart rate and increased muscle sympathetic nerve activity. 26,27 Increased sympathetic modulation hardly explains our findings of reduced BRS and increased SAP variability in relation to increased PP, since the heart rate and HRV did not indicate varying sympathetic tone in relation to PP levels.…”

The effect of enalapril on baroreceptor mediated reflex function in normotensive subjects.

“…mean of the slopes of the individual regression lines for each vasoactive drug before and after enalapril. In addition, we calculated (a) the mean maximal variations (from control values) of systolic blood pressure and RR-interval induced, before and after enalapril, either by phenylephrine or by nitroglycerin (Goldstein, 1983) and (b) the total magnitude of the mean variations in mean arterial pressure and RR-interval from control values by integrating them over the time taken by these parameters to return to their control levels by planimetry. These products are referred to as 'pressure-time product' (mm Hg s) (McRitchie et al, 1976) and 'RR-interval-time product' (ms s).…”