Age, race, diagnosis, and sodium effects on the pressor response to infused norepinephrine

Autonomic function in hypertension. Are there racial differences?

Previous biochemical assessment of sympathetic nervous system activity including plasma catecholamines, plasma renin activity, and plasma dopamine-beta-hydroxylase levels has suggested racial differences in the contribution of the sympathetic nervous system to the pathogenesis or maintenance of hypertension. We, therefore, performed physiological and pharmacological studies in white and black subjects with essential hypertension and their age-matched normotensive counterparts to assess autonomic and sympathetic nervous system function. One hundred one male subjects (47 white hypertensive, 17 black hypertensive, 22 white normotensive, and 15 black normotensive subjects) were evaluated for baroreceptor reflex sensitivity to low-pressure (amyl nitrite inhalation) and high-pressure (phenylephrine infusion) stimuli; cold pressor test heart rate and blood pressure responses; and blood pressure response to phentolamine alpha-adrenergic blockade. Hypertensive subjects exhibited an increase in resting heart rate, a decrease in baroreceptor reflex sensitivity, and an exaggerated decline in mean arterial pressure in response to phentolamine. These abnormalities were present to a comparable degree in black and white hypertensive subjects. Cold pressor testing revealed greater increases in heart rate in blacks as compared with whites; however, this racial difference was present regardless of blood pressure status, occurring in black normotensive and black hypertensive subjects to a comparable degree. Cold pressor test blood pressure increments were similar in the four groups. We conclude that both white hypertensive and black hypertensive subjects demonstrate similar abnormalities in autonomic and sympathetic nervous system function including blunting of baroreceptor reflex sensitivity and an increased alpha-adrenergic receptor participation in blood pressure maintenance. The results do not suggest major racial differences in autonomic pathogenetic mechanisms in hypertension.

Pressor response to norepinephrine in essential hypertension. A study in families

Study of pressor response to graded, increased doses of infused norepinephrine in patients with essential hypertension, their normotensive siblings, and normotensive control subjects unrelated to the patients and without a family history of hypertension indicated an increased response in the two former groups. Comparison of the dose-response curves in the three groups showed that the difference in response was due to a reduced threshold to norepinephrine in patients and their siblings and not to differences in the slopes of the dose-response curves. These alterations were not paralleled by differences in heart rate responses.

Effect of chronic sodium loading on cardiovascular response in young blacks and whites

The effect of long-term oral sodium loading on blood pressure and on stress-induced cardiovascular response was studied in normotensive and marginally hypertensive young adults. The 121 subjects, 18-23 years old, included 38 whites and 83 blacks. Blood pressure and heart rate response to the stress of mental arithmetic was measured before and after 14 days of sodium load, which consisted of 10 g NaCl/day added to the usual diet. A sodium-sensitive response to sodium load occurred in 18.4% of whites and 37.3% of blacks. Sodium-insensitive subjects had a higher rate of sodium excretion (p less than 0.001). Sodium-sensitive hypertensive subjects had a significantly greater weight gain (p less than 0.001). A significant correlation between blood pressure change and sodium excretion (r = -0.28, p less than 0.01) occurred in the sodium-sensitive group. The high sodium intake did not augment the blood pressure or heart rate response to the beta-adrenergic-mediated stimulus of mental arithmetic in the population when grouped by blood pressure, race, or sodium sensitivity. These results suggest that blood pressure increase in response to sodium load, particularly in blacks, is related to functional changes in peripheral vascular resistance.

A mechanism for the development of fixed primary (essential) hypertension: insights from population-based studies using echocardiography

Two recent observations based on echocardiographic studies in large population-based studies may have far-reaching implications: The concentric form of left ventricular hypertrophy emerges prominently in white Framingham (MA) men aged 40-49 years, and ten years later in white Framingham women. This parallels the pattern of emergence of fixed primary hypertension in white Framingham adults. Normotensive black teenage boys in Bogalusa have an echocardiographic profile that parallels more closely the profile of middle-aged white Framingham men and women than white teenage boys and girls. As noted, the former echocardiographic profiles are strongly associated with fixed primary hypertension in older adults and may be the harbingers of the premature development of fixed primary hypertension in the young black boys. These findings fit into a chain of observations that: (1) give new insight into the mechanism for premature development of primary hypertension and that should ultimately lead to closing the loop needed to characterize the cause of such hypertension: (2) may ultimately help to explain the excess of premature cardiovascular, renal, and cerebrovascular morbidity and mortality in the U.S. black population compared with the white population; and (3) may lead to new, more effective strategies for reducing such excess morbidity and mortality.

Cardiovascular responsiveness to norepinephrine in mild essential hypertension

The responses of blood pressure, heart rate and forearm vascular resistance to exogenous norepinephrine (NE) were measured in 40 normotensive and 65 mildly hypertensive subjects (mean blood pressure 117/72 and 146/92 mm Hg, respectively). Both groups received low incremental doses of NE: 15, 30 and 60 ng/kg/min for 8 minutes each. In contrast to previous studies that compared the dose-response curves in normo- and hypertensive subjects, this study corrected the cardiovascular responses for the increment of plasma NE to account for differences in metabolic clearance of NE. Although age and sex appeared to play a role, the corrected cardiovascular responses did not differ significantly between normo- and hypertensive subjects. Thus, an increased cardiovascular sensitivity to exogenous NE was not demonstrated in mildly hypertensive subjects. This finding confirms some but not all previous studies of the dose-response relation.

Race, parental history of hypertension, and patterns of cardiovascular reactivity in women

This study examined the interaction of race and parental history of hypertension on patterns of cardiovascular responses among women. Two stressors were used that produce different patterns of cardiovascular reactivity: mental arithmetic, primarily a beta-adrenergic stimulus, and the cold face stimulus, which evokes alpha-adrenergic (i.e. vascular) activity. Systolic and diastolic blood pressure, heart rate, forearm blood flow, and forearm vascular resistance were assessed before, during, and after arithmetic and cold face stimulus. Both tasks produced the expected patterns of cardiovascular adjustment, although no Black-White differences occurred during arithmetic. However, Black subjects did show a slower recovery of diastolic blood pressure following arithmetic. The cold face stimulus produced significantly greater changes in systolic blood pressure in the Black than in the White women. Parental history of hypertension did not relate significantly to reactivity. The results provide limited support for the idea that Black females exhibit a greater pressor response than White females to a stimulus that produces primarily vascular rather than cardiac changes. These findings are discussed in relation to previous findings with males and with respect to their implications for the role of reactivity in Black-White differences in hypertension prevalence.