Monica Marabini

Mechanisms responsible for sympathetic activation by cigarette smoking in humans.

The pressor and tachycardic effects of cigarette smoking are associated with an increase in plasma catecholamines, suggesting the dependence of these effects on adrenergic stimulation. Whether the stimulation occurs at a central or a peripheral level and whether reflex mechanisms are involved is unknown. Methods and ResultsIn nine normotensive healthy subjects (age, 33.0±3.5 years, mean±SEM), we measured blood pressure (Finapres device), heart rate (ECG), calf blood flow and vascular resistance (venous occlusion plethysmography), plasma norepinephrine and epinephrine (high-performance liquid chromatography assay), and postganglionic muscle sympathetic nerve activity (microneurography from the peroneal nerve) while subjects were smoking a filter cigarette (nicotine content, 1.1 mg) or were in control condition. Cigarette smoking (which raised plasma nicotine measured by highperformance liquid chromatography from 1.0±0.9 to 44.2±7.1 ng/mL) markedly and significantly increased mean arterial pressure (+13.2±2.3%), heart rate (+30.3±4.7%), calf vascular resistance (+ 12.1±4.9%), plasma norepinephrine (+34.8±7.0%), and plasma epinephrine (+90.5±39.0%). In contrast, muscle sympathetic nerve activity showed a marked reduction (integrated activity −31.8±5.1%, P < .01). The reduction was inversely related to the increase in mean arterial pressure (r= −.67, P < .05), but the slope of the relation was markedly less (−54.1±7.5%, P < .05) than that obtained by intravenous infusion of phenylephrine in absence of smoking. The hemodynamic and neurohumoral changes were still visible 30 minutes after smoking and occurred again on smoking a second cigarette. Sham smoking was devoid of any hemodynamic and neurohumoral effect. ConclusionsThese data support the hypothesis that in humans the sympathetic activation induced by smoking depends on an increased release and/or a reduced clearance of catecholamines at the neuroeffector junctions. Central sympathetic activity is inhibited by smoking, presumably via a baroreceptor stimulation triggered by the smoking-related pressor response. The baroreflex is impaired by smoking, however, indicating that partial inability to reflexly counteract the effect of sympathetic activation is also responsible for the pressor response.

Cardiac and carotid structure in patients with established hypertension and white-coat hypertension

Aim The introduction of ambulatory blood pressure monitoring in the clinical practice has defined a new subgroup of hypertensive patients called white-coat hypertensives. It has been reported that white-coat hypertensives have less cardiac involvement than established hypertensive patients. This study was designed to examine the extent of cardiac and vascular involvement in patients with white-coat hypertension and established hypertension. Patients and methods We studied 82 patients with mild essential hypertension, never previously treated, using 24-h ambulatory blood pressure monitoring and an echocardiographic and vascular ultrasonographic study. Left ventricular dimensions and mass were obtained according to the Penn convention. The intima–media thickness of the posterior wall of both common carotid arteries was measured 5, 10 and 20 mm caudally to the flow-divider and the average value was used for analysis. Results Of the 82 patients, 31 (mean ± SD age 35 ± 10 years) had average, 24-h systolic/diastolic blood pressure values of below 132/85 mmHg white-coat hypertensives) and 51 (aged 42 ± 2. years) had a consistently elevated diastolic blood pressure. Both groups had similar body surface area (1.82 ± 0.22 versus 1.81 ± 0.22 m2), sex distribution (20 males and 11 females versus 32 males and 19 females), duration of hypertension, metabolic parameters and smoking habit. The 24-h ambulatory blood pressure monitoring values were, by definition, significantly higher in established hypertensives than in white-coat hypertensives (142 ± 10/94 ± 6 versus 127 ± 6/79 ± 4 mmHg, P < 0.001). The left ventricular mass index and intima–media thickness were significantly higher in the established hypertensives (112 ± 17 g/m2, 0.67 ± 0.11 mm, respectively) than in the white-coat hypertensives (98 ± 18g/m2, 0.58 ± 0.09 mm; P < 0.001 for both). Conclusions The prevalence of left ventricular hypertrophy and cardiac remodeling was significantly more frequent in established hypertensives (51%) compared to white-coat hypertensives (19%). These confirm that structural changes in the left ventricle in white-coat hypertensives are more limited than in established hypertensives and show that in white-coat hypertensives there is significantly less involvement of the conductance vessels than in established hypertensives.

Vasopressin release and water metabolism in patients with cirrhosis

Water retention is a complication in many patients with cirrhosis, usually attributed to excessive release of arginine vasopressin. To investigate the responsiveness of arginine vasopressin to osmotic and non-osmotic stimuli and its relationship to free water excretion, we studied 19 patients with cirrhosis under three different conditions: 45 min with legs raised to 60 degrees, to expand the central blood volume; infusion of 1000 ml of 0.45% saline solution to reduce plasma osmolality; and rapid injection of 50 ml of 2 M NaCl to increase plasma osmolality. Both expansion of central blood volume and decrease of plasma osmolality significantly reduced plasma vasopressin levels (from 2.1 +/- 0.6 to 1.39 +/- 0.3 pg/ml, p < 0.04; and from 1.09 +/- 0.25 to 0.41 +/- 0.13 pg/ml, p < 0.0001). The changes in free water excretion differentiated two subgroups of patients during each test: excretors and non-excretors. In the excretors, increased free water excretion was associated with suppressed vasopressin levels (below 0.5 pg/ml) and normal renal function. In the non-excretors, inability to improve free water excretion was associated with high vasopressin levels or with reduced distal delivery of the glomerular filtrate, except in some cases where vasopressin levels had fallen below 0.5 pg/ml and renal function was normal. For these cases the presence of other vasopressin-independent antidiuretic mechanisms is conceivable. The injection of hypertonic saline solution caused significant rises in plasma osmolality (from 287 +/- 1.9 to 292 +/- 1.6 mmol/kg, p < 0.05) and in plasma vasopressin levels (from 1.13 +/- 0.29 to 2.86 +/- 0.52 pg/ml, p < 0.05). These results suggest that vasopressin release in patients with cirrhosis is normally responsive to osmotic and non-osmotic stimuli, although our results show a lower theoretical osmolar threshold for suppression of vasopressin release in non-excretors than in excretors (276 vs 284 mmol/kg).

Reflex vasopressin and renin modulation by cardiac receptors in humans.

Animal studies have shown that vasopressin secretion is modulated by arterial baroreceptors and cardiopulmonary volume receptors. Whether this is the case also in humans is controversial, however. To determine whether vasopressin is reflexly modulated by cardiac volume receptors, we studied the effect on plasma vasopressin (venous blood, radioimmunoassay) of reducing venous return and left ventricular end-diastolic diameter (echocardiography) by producing a 20-minute lower body negative pressure in 14 healthy subjects (aged 49.3 +/- 3.8 years, mean +/- SEM). The data were compared with those of 14 age-matched heart-transplant recipients, i.e., subjects with cardiac denervation. In healthy subjects, lower body negative pressure at -15 mm Hg caused a modest reduction in left ventricular end-diastolic diameter (-5 +/- 3.4%) and no change in vasopressin, whereas lower body negative pressure at -37.5 mm Hg caused a more marked reduction in left ventricular end-diastolic diameter (-12 +/- 2.5%) and a small, variable, but overall statistically significant (p < 0.05) increase in vasopressin (+145 +/- 46%, p < 0.01). The left ventricular end-diastolic diameter changes induced by the two lower body negative pressure stimuli were similar in heart-transplant recipients, but the vasopressin increase seen with the lower body negative pressure at -37.5 mm Hg was abolished. The marked increase in plasma renin activity and forearm vascular resistance induced by lower body negative pressure in healthy subjects was also abolished or drastically attenuated in heart-transplant recipients.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of vasopressin release in moderately severe essential hypertension

Vasopressin plasma concentrations have been measured in two groups of subjects, 13 moderate essential hypertensive patients without target organ damage and eight control normotensive subjects, before and after the assumption of the upright position, and intravenous infusions of hypotonic saline (0.45% NaCl, 0.25 ml kg−1 min−1 for 1 h) and hypertonic saline (100 mmol NaCl in 50 ml). Plasma vasopressin in recumbent baseline conditions was not significantly different in the two groups. Upright posture and hypertonic challenge augmented, while hypotonic saline reduced plasma vasopressin levels, which were not significantly different between the two groups. Plasma renin activity increased in the upright position, was reduced by administration of hypotonic saline and unaffected by hypertonic saline, with no differences between the hypertensives and normotensives. After hypertonic saline, urinary flow rate and urinary sodium excretion in the hypertensive group increased to values significantly (p < 0.05) higher than in normotensive subjects. In conclusion our study excludes significant alteration of vasopressin regulation in moderate uncomplicated hypertension. In hypertensives although the response of vasopressin to an osmotic load is preserved, the data suggest that the renal handling of the osmotic load may be altered.

Osmoregulation of vasopressin during acute lowering of arterial pressure by clonidine in moderate hypertension

Hypertonic saline (100 mmol in 50 ml) was injected intravenously over 5 min in two groups of moderate essential hypertensive patients (group 1, n = 13; group 2, n = 6). In group 2, arterial pressure had been lowered by infusion of clonidine (0.3 mg in 100 ml saline), from 186 +/- 8/116 +/- 3 to 146 +/- 9/98 +/- 5 mmHg (mean +/- s.e.m.). The hypertonic stimulus increased the plasma osmolality of all subjects from 288 +/- 1 to 296 +/- 1 mosmol/kg (P less than 0.01). Plasma vasopressin increased from baseline values that were not significantly different (P less than 0.01) in each of the two groups. The increase in plasma vasopressin was significantly greater (P less than 0.05) in the group 2 hypertensives with a reduced arterial pressure (+7.81 +/- 1.79 pg/ml) than in the group 1 untreated hypertensives (+3.15 +/- 1.2 pg/ml). In our study, acute lowering of arterial pressure by clonidine did not significantly change baseline vasopressin, but facilitated osmotically induced vasopressin secretion.