Pressor factors and cardiovascular pressor responsiveness in lean and overweight normal or hypertensive subjects

Adipose tissue as an endocrine organ: role of leptin and adiponectin in the pathogenesis of cardiovascular diseases

Obesity, the most common nutritional disorder in industrial countries, is associated with increased cardiovascular mortality and morbidity. Nevertheless, the molecular basis linking obesity with cardiovascular disturbances have not yet been fully clarified. Recent advances in the biology of adipose tissue indicate that it is not simply an energy storage organ, but also a secretory organ, producing a variety of bioactive substances, including leptin and adiponectin, that may influence the function as well as the structural integrity of the cardiovascular system. Leptin, besides being a satiety signal for the central nervous system and to be related to insulin and glucose metabolism, may also play an important role in regulating vascular tone because of the widespread distribution of functional receptors in the vascular cells. On the other hand, the more recently discovered protein, adiponectin, seems to play a protective role in experimental models of vascular injury, in probable relation to its ability to suppress the attachment of monocytes to endothelial cells, which is an early event in the atherosclerotic process. There is already considerable evidence linking altered production of some adipocyte hormones with the cardiovascular complications of obesity. Therefore, the knowledge of alterations in the endocrine function of adipose tissue may help to further understand the high cardiovascular risk associated with obesity.

Obesity, hypertension, and the heart

Hypertension occurs more commonly in obese than in lean persons at virtually every age. A variety of endocrine, genetic, and metabolic mechanisms have been linked to the development of obesity hypertension. These include insulin resistance and hyperinsulinemia, increased serum aldosterone levels, salt sensitivity and expanded plasma volume in the presence of increased peripheral vascular resistance, a genetic predisposition, and possibly increased leptin levels. Pressure and volume overload are present in obese hypertensives. This leads to a mixed eccentric-concentric form of left ventricular hypertrophy and increases the predisposition to congestive heart failure. Weight loss, even in modest decrements, is effective in reducing obesity-hypertension, possibly by ameliorating several of the proposed pathophysiologic mechanisms. There are currently no specific recommendations concerning pharmacotherapy of obesity-hypertension because each drug group has pros and cons.

Obesity-hypertension: the effects on cardiovascular and renal systems

Longitudinal and cross-sectional studies suggest that a large number of obese patients have a high prevalence of hypertension. This association causes the following changes: insulin and leptin resistance with a suppressed biologic activity of natriuretic peptide, which contributes to sodium retention with concomitant expanded cardiopulmonary volume and increased cardiac output. The cellular metabolism of cations may be altered in obesity and may lead to changes in vascular responsiveness and increased vascular resistance. These changes lead to structural adaptations in the heart characterized by concentric-eccentric left ventricular hypertrophy. The hypertrophic condition provides the basis for the development of congestive heart failure and cardiac arrhythmias that may explain the higher rates of cardiac sudden death in those patients. In the kidneys, obesity hypertension may initiate a derangement of renal function. The increased deposit of interstitial cells and of extracellular matrix between the tubules induces higher interstitial hydrostatic pressure and tubular sodium reabsorption. The consequent increase in renal flow and glomerular filtration enhances albuminuria excretion and the susceptibility to the development of renal damage. In summary, the hemodynamic and structural adaptations related to obesity hypertension is the cause of greater risk for adverse cardiovascular and renal events.

Resting metabolic rate and substrate use in obesity hypertension

There is substantial evidence that obesity is a prime risk factor for the development of hypertension. Although hyperinsulinemia and an increased activity of the sympathetic nervous system have been implicated in the pathogenesis of "obesity hypertension," their effects on energy metabolism have not been studied thus far. In the present study, we therefore examined resting metabolic rate (RMR) and basal substrate oxidation in subjects with obesity and obesity-related hypertension. A total of 166 subjects were characterized for RMR and basal substrate use through indirect calorimetry. Blood pressure was measured at rest and with 24-hour ambulatory monitoring. Blood samples were collected for the measurement of plasma catecholamines, leptin, and the insulin response to an oral glucose load. In our study population, 116 subjects were defined as hypertensive and 91 were defined as obese. Hypertensive patients under beta-adrenergic blockade (n=42) had a significantly lower RMR than did patients without beta-blockade (P<0. 05) and were therefore excluded from further analyses. Univariate regression analysis revealed a significant relationship between RMR and body fat mass, as well as body fat-free mass, in both groups. Compared with obese normotensive control subjects (n=27), obese hypertensives (n=43) had a 9% higher RMR (P<0.05), higher plasma catecholamine (P<0.05) and leptin (P<0.05) levels, and an increased insulin response to oral glucose (P<0.01). Together, these findings are compatible with the idea that chronic neurogenic and metabolic adaptations related to obesity may play a role in the development of obesity hypertension in susceptible individuals.

Plasma epinephrine levels in hypertension and across gender and ethnicity

Epinephrine (E) infusions raise blood pressure and there is an excess incidence of hypertension among males and blacks. However, reports of E levels by ethnicity, gender, and blood pressure status are inconsistent. Insensitive assays, variability in plasma E levels within individuals, and the small size of most studies have contributed to these conflicting reports. We measured plasma E levels in a large diverse sample of subjects, using a highly sensitive assay. A total of 361 individuals participated in the study: 61% were men and 39% women, 74% were normotensive and 26% hypertensive, 59% were white and 41% were black. Except for difference in blood pressure and body mass index between the normotensives and hypertensives, subjects had similar baseline characteristics and took no antihypertensive medications for at least five days prior to sampling. All blood samples were collected after resting for a least 30 minutes following the insertion of an indwelling i.v. catheter. Catecholamine levels were determined using a radioenzymatic assay (assay sensitivities for E and norepinephrine were 6 pg/ml and 10 pg/ml, respectively). An ethnicity by gender interaction was found (F(1,315) = 5.126, p = .024). Subsequent analysis revealed that white women had significantly lower basal plasma E levels than white men (p <0.001) and black women (p = 0.036). There were no significant differences in E levels between black men and women or between white men and black men. Uncorrected E levels were lower in normotensive than hypertensive subjects (p = .009) but this difference was not significant when corrected for body mass index (BMI). Uncorrected norepinephrine levels were higher in women than men (p = .03) but the difference was no longer significant when corrected for BMI. Plasma E levels were significantly lower among white women than men or black women. In contrast to prior studies, E levels were lower in hypertensives, but this may reflect obesity among hypertensives.

Visceral obesity and insulin resistance are associated with plasma aldosterone levels in women

OBJECTIVE

Both obesity and insulin resistance increase the risk of hypertension and other cardiovascular diseases, but the mechanisms linking these abnormalities are unknown. The current study was undertaken to examine the effects of obesity, fat distribution, and insulin resistance on plasma levels of aldosterone and other adrenal steroids that might contribute to sequelae of obesity.

RESEARCH METHODS AND PROCEDURES

Twenty-eight normotensive premenopausal women and 27 normotensive men with a wide range of body fat underwent measurements of visceral adipose tissue by CT scan, total fat mass by dual energy X-ray absorptiometry, blood pressure, insulin sensitivity, and plasma levels of three adrenal steroid hormones.

RESULTS

Plasma aldosterone in women correlated directly with visceral adipose tissue (r=0.66, p<0.001) and inversely with insulin sensitivity (r=-0.67, p<0.001), and these associations were independent of plasma renin activity. There were no corresponding correlations in men. Plasma aldosterone was significantly correlated with plasma cortisol and dehydroepiandrosterone sulfate in women. Seventeen women and 15 men completed a weight-reduction regimen, losing an average of 15.1+1.2 kg. After weight loss, plasma aldosterone was significantly lower and insulin sensitivity higher; however, the correlations of aldosterone with visceral adipose tissue and insulin sensitivity in women persisted (p = 0.09 and 0.07, respectively). Although none of the women were hypertensive, blood pressure correlated with plasma aldosterone both before and after weight loss.

DISCUSSION

We conclude that visceral adiposity and insulin resistance are associated with increased plasma aldosterone and other adrenal steroids that may contribute to cardiovascular diseases in obese women.

Effects of past history of major depression on smoking characteristics, monoamine oxidase-A and -B activities and withdrawal symptoms in dependent smokers

Past history of major depression is more common in smokers than in non-smokers. We have shown in a previous study that lifetime prevalence of major depression is higher in dependent smokers and they have lower monoamine oxidase-A and -B activities than non-smokers. Because several studies have found an association between MAO-B activity and depression we analysed data of these smokers to assess whether past history of major depression is associated with reduced monoamine oxidase activities (A and B) or not. Further, we tried to characterize smokers with past history of major depression and its effect on withdrawal symptoms. The data of 88 dependent smokers (Fagerström Tolerance Questionnaire score > or = 6 and smoking > or = 20 cigarettes/day) who participated in a smoking cessation study were analysed. Smokers with past history of major depression but without current illness did not differ in demographic and smoking characteristics from smokers without past history of major depression. Smokers with past history of major depression were mainly women and had lower body mass index. Adjusted for gender and body mass index dependent smokers with or without past history of depression had similar MAO-A and MAO-B activities but smokers with past history of major depression had significantly lower resting plasma norepinephrine levels. Smokers with past history of depression had not significantly higher ratings for depression (Montgomery-Asberg Depression Rating Scales) and anxiety (Hamilton Anxiety Scales) and smoking cessation did not exacerbate these ratings (assessed up to 3 months) and none had depressive episode during the postcessation period up to one year. Past history of depression was associated with higher scores on 'expressed sadness' and 'depressive mood'. Abstinent smokers with past history of depression had significantly higher ratings in one of the seven ratings of a 6 months period for craving (day 28), anxiety (day 7) and total withdrawal symptom score (day 7) when compared to those who had no past history of major depression. It is concluded that (i) past history of major depression is more frequent in female smokers; (ii) smokers with past history of depression may have more intense withdrawal symptoms (craving and anxiety) at some time after cessation: and (iii) past history of depression does not affect monoamine oxidase activities, therefore, reduced monoamine oxidase activities found in previous studies are possibly characteristic features of smoking.

Blood pressure trend and cardiovascular events in nuns in a secluded order: a 30-year follow-up study

30-year data are presented on blood pressure and cardiovascular morbidity and mortality for 144 nuns living in a secluded order in six nunnerlie in Umbria, central Italy and 138 lay women from the same region. There were no significant differences at baseline regarding age, blood pressure, body mass index, race, ethnic background, menarche, family history of hypertension or 24-hour urinary sodium excretion. None of the women were smokers and none took birth control pills nor did they use estrogen replacement therapy. During the observation period blood pressure remained remarkably stable among the nuns. None showed a rise in diastolic blood pressure to above 90 mm Hg. On the contrary the lay women showed the expected rise in blood pressure with age. This resulted in a gradually greater difference (delta > 30/15 mm Hg) in blood pressure between the two groups, which was statistically significant. There were 31 fatal and 69 non-fatal cardiovascular events during the 30 years of follow-up. These were significantly more common in the lay women, 10 vs. 21 fatal and 21 vs. 48 non-fatal in the nuns and lay women respectively. It appears reasonable to assume that the difference in psychosocial stress is the main underlying factor for the observed findings.

Catecholamines and blood pressure in obstructive sleep apnea syndrome

To evaluate the release of catecholamines and their relationship with systemic blood pressure (BP) in normotensive patients with obstructive sleep apnea syndrome (OSAS), diurnal and nocturnal urinary norepinephrine (NE) and epinephrine (E) excretion in 12 normal subjects and in 10 OSAS patients were compared; in addition, nocturnal NE and E excretion were measured in the patients while receiving short-term CPAP. Blood pressure was continuously monitored in the patients during both nights of urine collection. In normal subjects, both NE and E excretion decreased from day to night. In the patients without CPAP, only NE excretion decreased at night, and BP increased from wakefulness to sleep; both NE and E excretion were higher in patients than in normal subjects. With CPAP, which prevented apneas, only E excretion decreased with respect to the previous night, while BP no longer increased during sleep. The extent of nocturnal E decrease with CPAP was not correlated to BP variations. These results suggest that in normotensive OSAS subjects, sympathetic nervous system activity, based on NE excretion, is continuously increased and is not affected by short-term CPAP treatment. Conversely, adrenal activity, based on E excretion, is also increased, but it tends to be normalized by short-term CPAP. No clear relationship could be found between sympatho-adrenal behavior and BP during sleep.

Effects of insulin on renal haemodynamics and the proximal and distal tubular sodium handling in healthy subjects

The effects of insulin on renal haemodynamics and renal sodium handling were studied in 10 healthy males. Using the euglycaemic insulin clamp technique, insulin was infused on separate days resulting in two levels of hyperinsulinaemia (41 +/- 3 and 90 +/- 7 mU/l, respectively). Renal haemodynamics and the proximal and distal tubular sodium handling were studied using inulin, para-amino-hippuric acid, sodium and lithium clearances. Low- and high-dose insulin infusions were followed by a fall in sodium clearance from 1.6 +/- 0.1 ml/min to 1.2 +/- 0.1 and 1.0 +/- 0.1 ml/min, respectively. Both levels of hyperinsulinaemia resulted in increased distal tubular sodium reabsorption. The distal antinatriuretic effect of insulin was associated with dose- and time-dependent decline in proximal tubular sodium reabsorption. The changes in proximal tubular sodium handling occurred without any significant changes in natriuretic factors, such as renal dopamine and plasma atrial natriuretic peptide levels. However, hyperinsulinaemia resulted in time- and dose-dependent increases in renal plasma flow, and renal vasodilatation could, possibly via changes in renal interstitial pressure, have contributed to the fall in the proximal tubular sodium reabsorption. The results also suggest that decreased proximal sodium reabsorption may be a compensatory mechanism counteracting the insulin-induced sodium retention.

Relation of obesity and diet to sympathetic nervous system activity

The hypothesis that dietary intake and obesity stimulate the sympathetic nervous system was investigated in a cross-sectional study of 572 men aged 43-85 years from the Normative Aging Study. Habitus was represented by body mass index, as a measure of overall adiposity, and by the ratio of abdomen-to-hip circumference (abdomen/hip ratio), as a measure of centripetal fat distribution. Sympathetic activity was assessed by measurement of 24-hour urinary norepinephrine excretion. Increased body mass index and total caloric intake were independently associated with increased 24-hour urinary norepinephrine excretion (p = 0.0001 and p = 0.0055, respectively). In addition, mean urinary norepinephrine excretion was higher in subjects classified as either hyperglycemic (serum fasting glucose greater than or equal to 113 mg/dl) and hyperinsulinemic (serum fasting insulin greater than or equal to 19 microIU/ml) (p = 0.0023) or in subjects classified as either hyperglycemic or hyperinsulinemic (p = 0.0063) than the mean urinary norepinephrine excretion in normal subjects. These relations were demonstrated to be independent of age, smoking status, and physical activity. Our results are consistent with the hypothesis that insulin mediates sympathetic stimulation in response to dietary intake and increases sympathetic nervous system activity in the obese.

Effect of insulin on plasma norepinephrine and 3,4-dihydroxyphenylalanine in obese men

Increasing evidence relates serum insulin level and blood pressure in obese individuals. Although the connection between these two factors is not established, a common presumption is that the sympathetic nervous system is somehow involved, in part, because laboratory studies demonstrate insulin stimulation of sympathetic and cardiovascular activity. Because the obese may exhibit altered responsiveness to insulin action, the current investigation compared cardiovascular and neurohumoral responses to euglycemic insulin infusion (200 mU/m2/min) in obese and lean men. At baseline, obese men displayed higher glucose and insulin levels, faster pulse rates, and elevated mean arterial pressures (MAP) than lean controls; plasma norepinephrine (NE) and 3,4-dihydroxyphenylalanine (DOPA) concentrations, however, did not differ. During insulin infusion, pulse rate increased equally in obese and lean subjects (from 69 to 78 min-1 in obese and from 56 to 66 min-1 in lean subjects), while MAP remained unchanged in both groups. Elevations in plasma NE (+85 pg/mL in obese and +109 in lean pg/mL) and reductions in plasma DOPA (-233 pg/mL in obese and -376 pg/mL in lean) did not differ between groups. Sodium excretory rate decreased during insulin infusion in lean subjects by 2.2 mEq/h but increased in obese by 5.3 mEq/h (difference in response between groups, P = .024). Thus, in these obese men, cardiovascular and sympathetic responses to insulin persist despite evidence of moderate insulin resistance; increased sympathetic activity, as a cause for the resting tachycardia and borderline hypertension at baseline, seems unlikely.

Age and blood pressure changes. A 20-year follow-up study in nuns in a secluded order

In a prospective study, 144 white nuns belonging to a secluded monastic order and 138 white control laywomen were followed for 20 years to investigate whether living for a long time in a stress-free environment influences the effect of aging on blood pressure. Silence, meditation, and isolation from society are the distinctive features of the life-style examined. At study entry, blood pressure was not dissimilar in the nuns and the control group, but it increased over time only in the controls, with a mean slope of the regression line (beta coefficient) of 0.089 in the nuns (NS) and 2.171 in the controls (p less than 0.0001) for systolic blood pressure and of 0.054 in the nuns (NS) and 0.742 in the controls (p less than 0.0001) for diastolic blood pressure. Weight and body mass index increased similarly over time in the two groups. Family history of hypertension was not dissimilar between the groups. Serum cholesterol and triglycerides, higher at study entry in the nuns, increased similarly over time in the two groups. Twenty-four-hour urinary sodium excretion, collected randomly in both groups, did not differ over time between nuns and controls. None of the women smoked or used oral contraceptives. Educational level was higher in the control group, but subgroups of 48 nuns and 52 laywomen of comparable educational level maintained the same difference in the blood pressure trend over time as in the main cohort. Parity affected the increase of systolic, but not of diastolic, blood pressure with age among the laywomen, but nuns and no-childbirth controls maintained a significantly different blood pressure trend over time.(ABSTRACT TRUNCATED AT 250 WORDS)

The enigma of insulin resistance and hypertension. Insulin resistance, blood pressure, and the circulation

The epidemiologic link between obesity and hypertension is more clearly emerging to be one between insulin resistance and hypertension. Relative insulin resistance occurs not only in obese hypertensive patients but also in non-obese lean essential hypertensive patients. Although insulin has complex actions on the circulation, plausible mechanisms by which insulin might raise blood pressure include renal sodium retention and stimulation of the sympathetic nervous system. However, the evidence that insulin can actually raise blood pressure in the long-term is lacking. Since hypertension does not develop in all obese or insulin-resistant subjects, the relationship must be modulated by other genetic or environmental factors. Obesity, diminished physical conditioning, aging, and diabetes are ubiquitous contributors to relative insulin resistance and all are associated with a tendency for blood pressure to rise. Conditions and agents associated with acquired insulin resistance and secondary forms of hypertension include pregnancy, oral contraceptives, acromegaly, and glucocorticoids. Although type 2 non-insulin-dependent diabetes is a state of increased insulin resistance, hypertension is partly sustained by secondary renal mechanisms. Future research should identify the genetic and environmental determinants of insulin resistance in hypertension and utilize these in therapy.

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.

Effects of alpha 1 inhibition on renal blood flow and sympathetic nervous activity in systemic hypertension

Doxazosin is a competitive inhibitor of norepinephrine at alpha 1 adrenoceptors on vascular smooth muscle, where it blocks vasoconstriction. Twenty-four patients with mild hypertension were treated with either doxazosin or placebo for 6 weeks. Supine and upright mean arterial pressures decreased by 9 and 12 mm Hg, respectively, in patients receiving doxazosin. This decrease was significantly more than the blood pressure change with placebo (p less than 0.05). Doxazosin therapy led to a small increase in weight (p less than 0.05). It was also associated with a statistically insignificant decrease in renal vascular resistance (568 dynes s/cm5) so that renal blood flow and creatinine clearance did not change. Doxazosin increased renin levels acutely and norepinephrine levels with 6-week treatment, but these changes were not significantly different from placebo. Norepinephrine clearance, measured after a 120-minute infusion of 3H norepinephrine, did not change. Heart rate increased acutely after doxazosin administration, but returned to baseline during 6-week therapy. Blood pressure, measured hourly for 14 hours after treatment, was consistently decreased in all patients. Doxazosin taken once daily lowers blood pressure without affecting renal blood flow or heart rate.

Effect of diet on energy expenditure and plasma norepinephrine in lean and obese Pima Indians

To assess whether thermogenesis or sympathetic nervous system (SNS) function might differ between lean and obese human subjects, studies of thermic and sympathetic responses to standard stimuli were undertaken in Pima Indians, an ethnic group with a high prevalence of obesity. Plasma levels of norepinephrine (NE) and energy expenditure at rest and in response to feeding, exercise, and graded infusions of NE were compared in five lean and five obese Indians during a period of weight maintenance (WM), after 3 weeks of overfeeding (OF) and, in the obese, also after 6 weeks of underfeeding (UF). Basal energy expenditure, when adjusted for fat free mass, was equivalent during WM and increased 3% with OF (P less than 0.01) in both groups. Thermic responses to exercise or a test meal did not differ in lean and obese and did not change with OF, while thermic responses to NE infusion fell during OF to a greater degree in obese than lean (P less than 0.05). A similar pattern (decreased effect in obese with OF) was also noted in the glycemic response to infused NE (P less than 0.05). Although not quantitatively different in lean and obese, the plasma NE concentration appeared to vary more in response to feeding or dietary alteration in the obese than lean, a finding that may reflect lower plasma clearance of NE in the obese. These studies, therefore, raise the possibility that overfeeding in obese Pima Indians may limit the contribution of sympathetically mediated thermogenesis to energy expenditure, though the implications of this for body weight regulation are speculative.