Studies on the autonomic nervous system in borderline hypertension

Altered Cardiovascular Reactivity to and Recovery from Cold Face Test-Induced Parasympathetic Stimulation in Essential Hypertension

Essential hypertension is associated with increased sympathetic and diminished parasympathetic activity as well as impaired reactivity to sympathetic stimulation. However, reactivity and recovery from parasympathetic stimulation in hypertension are unknown. We investigated reactivity and recovery to primarily parasympathetic stimulation by Cold Face Test (CFT) in essential hypertension. Moreover, we tested whether chronic stress modulates CFT-reactivity dependent on hypertension status. The CFT was conducted by applying a cold face-mask for 2 min in 24 unmedicated, otherwise healthy hypertensive men and in 24 normotensive controls. Systolic and diastolic blood pressure (BP) and heart rate (HR) were measured repeatedly. Chronic stress was assessed with the Trier-Inventory-for-Chronic-Stress-Screening-Scale. Hypertensives did not exhibit diastolic BP decreases after CFT-cessation (p = 0.59) as did normotensives (p = 0.002) and failed to show HR decreases in immediate response to CFT (p = 0.62) when compared to normotensives (p < 0.001). Systolic BP reactivity and recovery patterns did not differ between hypertensives and normotensives (p = 0.44). Chronic stress moderated HR (p = 0.045) but not BP CFT-reactivity (p's > 0.64) with chronically stressed normotensives showing similar HR reactivity as hypertensives. Our findings indicate impaired diastolic BP and HR reactivity to and recovery from CFT in hypertensives and a moderating effect of chronic stress on HR reactivity potentially reflecting reduced relaxation ability of the cardiovascular system.

Increased pressor response to noradrenaline in pituitary dependent Cushing's syndrome

OBJECTIVES

The mechanism of hypertension in Cushing's syndrome remains undetermined. Some studies have demonstrated an increased sensitivity to pressor agents but it is not clear if patients with Cushing's syndrome of different aetiologies demonstrate this finding. We have examined pressor sensitivity in a group of patients with Cushing's disease (pituitary dependent hypercortisolism) by measuring blood pressure during incrementally increasing infusions of noradrenaline.

METHODS

Eight subjects (7 female, 1 male), aged 42.2 +/- 4.5 years (mean +/- SEM) with Cushing's disease were studied. Eight age- and sex-matched control subjects were also studied. Four of the eight controls and five patients with Cushing's disease had elevated blood pressure. All medication for this had been stopped at least seven days prior to the study. After subjects ate a light breakfast, ECG leads and a sphygmomanometer were attached, an intravenous cannula was inserted and all subjects then rested quietly for 60 minutes. Noradrenaline was then infused intravenously for 10-minute periods at concentrations of 0.01, 0.03, 0.07, 0.11 and 0.18 microg/kg/minute.

RESULTS

On the day of the study the baseline blood pressures and pulse rates in the patients with Cushing's disease (blood pressure; 138/87 +/- 6/3 mmHg, pulse 76.5 +/- 4.8 beats/minute) and controls (blood pressure; 126/86 +/- 6/6 mmHg, pulse 71.2 +/- 3.7 beats/minute) were not significantly different. The mean change in diastolic blood pressure from baseline at the time of the peak increase or when the test was stopped was 21. 5 +/- 4.7 mmHg in Cushing's disease compared to 7.0 +/- 2.5 mmHg in controls (P = 0.03). The mean change in mean arterial pressure from baseline at the time of the peak increase or when the test was stopped was 22.0 +/- 4.0 mmHg in Cushing's disease compared to 13.0 +/- 2.4 mmHg in controls (P = 0.03). No significant difference in mean change of systolic pressure (26.0 +/- 4.6 vs. 25 +/- 4.0 mmHg) or pulse rates (- 11.1 +/- 1.8 vs. - 4.7 +/- 2.6) was seen in the group with Cushing's disease as compared to the control group.

CONCLUSIONS

We conclude that patients with pituitary-dependent Cushing's syndrome have enhanced pressor diastolic and mean arterial responses to noradrenaline and this may be an important underlying mechanism for the hypertension seen in this particular group of Cushing's syndrome patients.

Plasma adrenaline modulates alpha 1-adrenoceptor mediated pressor responses and the baroreflex control in patients with borderline hypertension

Plasma level of adrenaline has been reported to be elevated in borderline hypertension. However, its role in developing and maintaining hypertension is still not completely understood. This study aimed to estimate the role of plasma adrenaline in developing hypertension. Ten patients with borderline hypertension (BHT) and 10 age-matched normotensive subjects were included. We infused at least three graded doses of phenylephrine, an alpha-adrenoceptor agonist, into the antecubital vein of subjects lying quietly in a supine position. Mean blood pressure was measured continuously through the right radial artery. Cardiac output was measured by the thermodilution method before and after the administration of each dose of phenylephrine infusion. We obtained dose-response curves for mean blood pressure and total peripheral resistance to phenylephrine. Baroreflex sensitivity was calculated by plotting the longest R-R intervals against the elevated peak mean blood pressure after the infusion of each dose of phenylephrine. Plasma noradrenaline and adrenaline concentrations at rest were measured by high performance liquid chromatography coupled with trihydroxyindole fluorimetric detection. The plasma adrenaline level at rest was higher in patients with BHT than in normotensive subjects. With graded infusion of phenylephrine, both the pressor responses and the changes in total peripheral resistance were greater in patients with BHT than in normotensive subjects. The plasma adrenaline level was positively correlated with the slope of dose response curves for the increments of mean blood pressure to phenylephrine (r = 0.60, p < 0.01). Baroreflex sensitivity was reduced in patients with BHT as compared with normotensive subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between salivary growth factors, electrolytes and abnormal sodium transport in human hypertension

We have previously shown cheek cell Na+/H+ antiporter activity to be reduced in human hypertensives. We have now examined the relationship between abnormal antiporter activity and a variety of salivary factors. Total protein concentration and amylase activity were higher in hypertensives, but salivary flow rate and epidermal growth factor, transforming growth factor-alpha, calcium, and magnesium concentrations were not significantly different between hypertensives and normotensives. The lowered cheek cell Na+/H+ antiporter activity in those hypertensives with diastolic BP greater than 95 mmHg was accompanied by lowered salivary Na+/H+ ratios. In borderline hypertensives (diastolic BP between 90 and 95 mmHg), the Na+/H+ ratio was reduced to a similar extent to that seen in those hypertensives with a diastolic BP above 95 mmHg, however the cheek cell antiporter activity was not reduced, suggesting that these two differences are not related in a simple fashion in all hypertensives. It is concluded that it is unlikely that differences in salivary growth factors explain the lowered cheek cell Na+/H+ antiporter activity observed in human hypertension. Our findings indicate that salivary electrolyte composition may be related to cheek cell Na+/H+ antiporter activity and these parameters may be altered in hypertension.

Effects of sodium salts on pressor reactivity in salt-sensitive men

Blood pressure in patients with essential hypertension is raised by sodium chloride but not by nonchloride sodium salts. Although a high sodium chloride diet is known to augment the pressor response to norepinephrine and angiotensin II, the effect of nonchloride sodium salts on pressor responsiveness has not been studied so far. To examine whether sodium chloride and nonchloride sodium salts evoke different pressor responses to these agonists, we performed graded norepinephrine and angiotensin II infusions in salt-sensitive (n = 7) and salt-resistant (n = 8) normotensive subjects. The subjects were given a low salt diet (20 mmol/day) for 3 weeks, to which a supplement of 200 mmol sodium per day, provided as either sodium chloride or sodium citrate, or a placebo was added for 1 week each. We found that, although sodium chloride raised mean arterial blood pressure in the salt-sensitive subjects (p less than 0.005), sodium citrate did not. However, under both sodium salts pressor response to norepinephrine and angiotensin II was significantly greater than under placebo (p less than 0.02). Furthermore, with both sodium salts, pressor response in the salt-sensitive subjects was greater than in the salt-resistant subjects (p less than 0.01). This study thus demonstrates that, although blood pressure in salt-sensitive individuals is raised by sodium chloride only, both sodium chloride and sodium citrate evoke similar increases in pressor response to norepinephrine and angiotensin II. Since pressor response increased with both sodium salts but resting blood pressure increased only with sodium chloride, enhanced pressor responsiveness alone cannot account for the sodium chloride-induced rise in resting blood pressure.

Pathogenetic and therapeutic relevance of cardiovascular pressor reactivity to norepinephrine in human hypertension

In normotensive humans with a positive family history of essential hypertension, blood pressure (BP) is often dysregulated. Body sodium, blood volume, plasma angiotensin II (AngII), epinephrine and norepinephrine (NE), their responses to changes in sodium intake or posture, as well as baroreflex function, beta-receptor-mediated cardiac responsiveness, and the responsiveness of BP to AngII appear to be largely unaltered. However, the responsiveness of BP to NE is commonly exaggerated. An increase in potassium intake may improve the NE hyperreactivity and concomitantly lower BP within the "normotensive" range. Therefore, a selective vascular NE hyperreactivity relative to existing sympathetic activity seems to be a common familial abnormality predisposing for the development of essential hypertension. In borderline or established essential hypertension, an inappropriate vascular reactivity relative to sympathetic activity probably complements other mechanisms contributing to the maintenance of hypertension. Various antihypertensive treatments may lower BP at least in part by improving cardiovascular NE (hyper)reactivity without provoking an equivalent rise in sympathetic activity. These include dietary potassium supplementation, thiazide-type agents, indapamide, calcium channel blockers, postsynaptic alpha 1-blockers, and AngII converting enzyme inhibitors.

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

We studied the blood pressure responses to infused norepinephrine in 34 normotensive and 21 unmedicated subjects with essential hypertension. The two groups were similar in age, relative body weight, and urinary electrolyte excretion. Patients were studied on two extremes of dietary salt (200 mEq Na and 10 mEq Na per day). The dose-response curves were highly linear (p less than 0.00001) for both systolic and diastolic blood pressures. There was no evidence for an increased sensitivity to infused norepinephrine among the hypertensive subjects. On the other hand, older subjects had steeper slopes (p less than 0.005). Subjects on a high salt diet had steeper slopes than those on low salt diets (p less than 0.0025); this trend was especially apparent among blacks (p less than 0.005). Black and white hypertensive subjects responded to the high salt diet in opposite fashion: The blacks showed an increased pressor sensitivity (p less than 0.05), whereas the whites demonstrated a nonsignificant decreased pressor sensitivity. These results indicate that age, race, and salt effects must be meticulously controlled in studies of sympathetic nervous system physiology.

Function of the autonomic nervous system in young, untreated hypertensive patients

The reactivity of the sympathetic nervous system was studied in 10 young, adult patients with labile hypertension and compared with a normotensive age-matched control group. Upon graded exercise on a constant speed bicycle ergometer, the hypertensive subjects reacted with an exaggerated blood pressure response and a significantly greater increase in the plasma adrenaline and noradrenaline levels. The basal catecholamine levels, however, were similar in both observation groups. This was in spite of an intact baroreceptor reflex in the hypertensives as indicated by a normal hemodynamic response to angiotensin II. This apparent discrepancy may be explained by an enhanced uptake of adrenaline during stress into the neuron, where it acts as a cotransmitter and facilitates the release of noradrenaline via presynaptic beta 2-adrenoceptors. Similar blood pressure and heart rate responses to isoproterenol and atropine were observed in both groups. This indicates normal beta-adrenoceptor sensitivity and vagal nerve activity in the hypertensive subjects.