Role of sympathetic activity in blood pressure reduction with low calorie regimen

The pathogenesis of obesity

Body fat mass increases when energy intake exceeds energy expenditure. In the long term, a positive energy balance will result in obesity. The worldwide prevalence of obesity has increased dramatically, posing a serious threat to human health. Therefore, insight in the pathogenesis of obesity is important to identify novel prevention and treatment strategies. This review describes the physiology of energy expenditure and energy intake in the context of body weight gain in humans. We focus on the components of energy expenditure and the regulation of energy intake. Finally, we describe rare monogenetic causes leading to an impairment in central regulation of food intake and obesity.

Caloric restriction decreases orthostatic tolerance independently from 6° head-down bedrest

Astronauts consume fewer calories during spaceflight and return to earth with an increased risk of orthostatic intolerance. Whether a caloric deficiency modifies orthostatic responses is not understood. Thus, we determined the effects of a hypocaloric diet (25% caloric restriction) during 6° head down bedrest (an analog of spaceflight) on autonomic neural control during lower body negative pressure (LBNP). Nine healthy young men completed a randomized crossover bedrest study, consisting of four (2 weeks each) interventions (normocaloric bedrest, normocaloric ambulatory, hypocaloric bedrest, hypocaloric ambulatory), each separated by 5 months. Muscle sympathetic nerve activity (MSNA) was recorded at baseline following normocaloric and hypocaloric interventions. Heart rate (HR) and arterial pressure were recorded before, during, and after 3 consecutive stages (7 min each) of LBNP (-15, -30, -45 mmHg). Caloric and posture effects during LBNP were compared using two-way ANOVA with repeated measures. There was a strong trend toward reduced basal MSNA following caloric restriction alone (normcaloric vs. hypocaloric: 22±3 vs. 14±4 burst/min, p = 0.06). Compared to the normocaloric ambulatory, both bedrest and caloric restriction were associated with lower systolic blood pressure during LBNP (p<0.01); however, HR responses were directionally opposite (i.e., increase with bedrest, decrease with caloric restriction). Survival analysis revealed a significant reduction in orthostatic tolerance following caloric restriction (normocaloric finishers: 12/16; hypocaloric finishers: 6/16; χ2, p = 0.03). Caloric restriction modifies autonomic responses to LBNP, which may decrease orthostatic tolerance after spaceflight.

Mild caloric restriction reduces blood pressure and activates endothelial AMPK-PI3K-Akt-eNOS pathway in obese Zucker rats

Genetic obesity models exhibit endothelial dysfunction associated to adenosine monophosphate-activated protein kinase (AMPK) dysregulation. This study aims to assess if mild short-term caloric restriction (CR) restores endothelial AMPK activity leading to an improvement in endothelial function. Twelve-week old Zucker lean and obese (fa/fa) male rats had access to standard chow either ad libitum (AL, n=8) or 80% of AL (CR, n=8) for two weeks. Systolic blood pressure was significantly higher in fa/fa AL rats versus lean AL animals, but was normalized by CR. Endothelium-dependent relaxation to acetylcholine (ACh, 10(-9) to 10(-4) M) was reduced in fa/fa AL compared to control lean AL rats (p<0.001), and restored by CR. The AMPK activator AICAR (10(-5) to 8·10(-3) M) elicited a lower relaxation in fa/fa AL rings that was normalized by CR (p<0.001). Inhibition of PI3K (wortmannin, 10(-7) M), Akt (triciribine, 10(-5) M), or eNOS (L-NAME, 10(-4) M) markedly reduced AICAR-induced relaxation in lean AL, but not in fa/fa AL rats. These inhibitions were restored by CR in Zucker fa/fa rings. These data show that mild short-term CR improves endothelial function and lowers blood pressure in obesity due to the activation of the AMPK-PI3K-Akt-eNOS pathway.

Urinary protein as a marker for systolic blood pressure reduction in patients with type 2 diabetes mellitus participating in an in-hospital diabetes education program

Increased blood pressure (BP) and urinary protein (UP)/microalbuminuria are risk factors for cardiovascular disease in patients with diabetes. Although the management of BP in patients with diabetes should involve a multidisciplinary therapy, there are no reports in which modulators have been identified in an in-hospital diabetes education program. The aim of the present study was to investigate the change in BP levels in patients with type 2 diabetes mellitus (T2DM) during a short-term (2-week) in-hospital education program on lifestyle modifications. A total of 167 patients with T2DM (101 men, 66 women; mean age, 61.1 years; glycated hemoglobin, 9.2%) were divided into 2 groups on the basis of their urinary albumin levels: 1 group without UP (urinary albumin level < 30 mg/day) and 1 group with UP (urinary albumin level ≥ 30 mg/day). We defined efficacy in reducing BP as a 20-mm Hg reduction in systolic BP (SBP) and a 10-mm Hg reduction in diastolic BP, and compared the changes between the 2 groups. Although the group with UP had higher SBP levels than the group without UP at baseline, this difference disappeared at the end of the program. Adjusted multivariate logistic regression analysis showed that UP at baseline was associated with a reduction in SBP (odds ratio, 3.361; 95% confidence interval, 1.29-8.79; P = 0.013). The data suggest that UP may be a marker related to the management of SBP through lifestyle modifications in patients with T2DM.

Calorie restriction and stroke

Stroke, a major cause of disability and mortality in the elderly, occurs when a cerebral blood vessel is occluded or ruptured, resulting in ischemic damage and death of brain cells. The injury mechanism involves metabolic and oxidative stress, excitotoxicity, apoptosis and inflammatory processes, including activation of glial cells and infiltration of leukocytes. In animal models, dietary energy restriction, by daily calorie reduction (CR) or intermittent fasting (IF), extends lifespan and decreases the development of age-related diseases. Dietary energy restriction may also benefit neurons, as suggested by experimental evidence showing that CR and IF protect neurons against degeneration in animal models. Recent findings by our group and others suggest the possibility that dietary energy restriction may protect against stroke induced brain injury, in part by inducing the expression of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF); protein chaperones, including heat shock protein 70 (Hsp70) and glucose regulated protein 78 (GRP78); antioxidant enzymes, such as superoxide dismutases (SOD) and heme oxygenase-1 (HO-1), silent information regulator T1 (SIRT1), uncoupling proteins and anti-inflammatory cytokines. This article discusses the protective mechanisms activated by dietary energy restriction in ischemic stroke.

Fasting-induced reductions in cardiovascular and metabolic variables occur sooner in obese versus lean mice

It is not uncommon for laboratory animals to be fasted prior to experimentation. Fasting evokes marked reductions in heart rate (HR), blood pressure (BP), heat production and oxygen consumption (VO(2)) in rodents. Mice with diet-induced obesity exhibit elevated HR and BP, and lower VO(2) and heat production in the fed condition versus their lean counterparts. It is unknown whether body composition alters the tempo of response to fasting. We tested the hypothesis that cardiovascular and metabolic responses to fasting are delayed in obese versus lean male C57BL/6J mice. In the fed condition, mice that consumed high-fat (HF, 45% fat) chow for 98 ± 5 days had elevated (P < 0.05) body fat percentage (DEXA), serum leptin (ELISA), HR and BP (72-h biotelemetry), and lower (P < 0.05) heat production and VO(2) (72-h metabolic chamber) versus animals that consumed standard chow (CON, 10% fat; n = 16 per group). HR, BP, VO(2), heat production and serum leptin decreased (all P < 0.05) in response to a 16-h fast (16:00-08:00 h) in both groups. Although the overall fold changes in cardiovascular and metabolic parameters were similar in magnitude among animals, fasting-induced reductions in cardiovascular and metabolic variables occurred ∼4 and ∼7 h earlier (P < 0.05), respectively, in HF versus CON mice. These findings indicate that while metabolic and cardiovascular stress evoked by a 16-h fast at 22°C is not different between HF and CON mice, fasting-induced responses occur sooner in obese animals.

Caloric restriction and heart function: is there a sensible link?

Calorie restriction (CR) is defined as a reduction in calorie intake below the usual ad libitum intake without malnutrition. Ample of clinical and experimental evidence has demonstrated that CR is capable of retarding aging process and development of cardiovascular disease. Although suppression of reactive oxygen species production and inflammation plays a central role in the favorable cardiovascular effects of CR, the health benefit of CR is believed to be ultimately mediated through a cadre of biochemical and cellular adaptations including redox homeostasis, mitochondrial function, inflammation, apoptosis and autophagy. Despite the apparent beneficial cardiovascular effects of CR, implementation of CR in the health care management is still hampered by apparent applicability issues and health concerns. Here we briefly review the cardiac consequence of CR and discuss whether CR may represent a safe and effective strategy in the management of cardiovascular health.

Neuroprotective potential of the Bahadori leanness program: A “mini-fast with exercise” strategy

The Bahadori Leanness Program (BLP) is a multi-step strategy for weight control, the most innovative feature of which is "mini-fast with exercise" - every 24h includes a fast of 12-14 h duration within which is nested a session of aerobic exercise. Low-fat, low-glycemic-index foods choices help to insure that diurnal levels of glucose and insulin remain relatively low. Clinical experience demonstrates that clients can achieve good compliance with this protocol, and the long term impact on body weight is gratifying. Rodent studies demonstrate that alternate-day feeding is even more effective than caloric restriction for promoting neuroprotection, suggesting that intermittent periods of mild metabolic stress induce protective adaptations in the brain; exercise training is also neuroprotective in these models. Mattson has raised the possibility that regular meal-skipping might be a feasible strategy for achieving similar - though perhaps less potent - protection in humans. Thus, it is suggested that exercise superimposed on regular short-term fasts, as in the BLP, might provide meaningful neuroprotection. Studies assessing CSF levels of brain neurotrophic hormones might be useful for evaluating the impact of such a strategy on brain neurochemistry. It should not be overlooked that leanness, good insulin sensitivity, and regular exercise are likely to be neuroprotective in their own right. The episodic metabolic stress associated with BLP may also have potential for prevention and therapy of cancer, inasmuch as down-regulation of systemic IGF-I activity during the mini-fasts would be expected to boost the rate of apoptosis in IGF-I-responsive neoplastic or pre-neoplastic tissues. Moreover, the relatively low-diurnal insulin levels and exercise training associated with BLP would be expected to down-regulate sympathetic activity while boosting cardiac parasympathetic tone - effects that should decrease risk for hypertension and sudden-death arrhythmias. Thus, it is conceivable that BLP will provide a range of health benefits extending beyond those attributable to its favorable impact on body composition.

A case of sleep apnea syndrome manifesting severe hypertension with high plasma norepinephrine levels

A 55-year-old female was admitted to our hospital with severe hypertension (274/140 mmHg). Endocrinological examination revealed that her plasma levels of norepinephrine (NE) was elevated with high levels of urinary NE, normetanephrine and vanillylmandelic acid (VMA), suggesting the presence of pheochromocytoma. However, neither computed tomography nor MIBG scintigraphy detected any catecholamine-producing tumor in or outside the adrenal glands. She was screened with full polysomnography because of heavy snoring, and the diagnosis of severe obstructive sleep apnea syndrome (OSAS) was made. She was treated with calcium channel blocker for three weeks, but severe hypertension persisted. After treatment with nasal continuous positive airway pressure (CPAP) was added, her blood pressure gradually lowered week by week. Concomitantly, the levels of plasma and urinary NE, urinary normetanephrine and urinary VMA were normalized following nasal CPAP therapy for 2 weeks. Additional treatments with alpha-adrenergic blocker further decreased her home blood pressure. After a year, she continued nasal CPAP therapy and her blood pressure was nearly below 160/100 mmHg. Urinary NE level was slightly above normal range and other catecholamines stayed within the normal range. This case shows that patients with OSAS could develop severe hypertension through elevated sympathetic tone, mimicking pheochromocytoma. Nasal CPAP therapy is recommended not only to improve hypertension and catecholamine excess but also to distinguish the condition from pheochromocytoma.

Caloric restriction in humans: potential pitfalls and health concerns

To date, the only intervention that has consistently been shown to slow the rate of aging, and to increase mean and maximum lifespan in short-lived species, is life-long calorie restriction. It is yet unclear whether long-term calorie restriction in longer lived species (i.e. primates and humans) will have a similar effect. In humans, several studies investigating short-term calorie restriction or "weight loss" programs suggest beneficial outcomes on parameters of cardiovascular disease. Studies on long-term calorie restriction are performed on a self-selected group of human subjects and show similar effects. However, few studies are currently investigating the quality of life and potential pitfalls of long-term calorie restriction in humans. It is likely that some of the physiological and psychological effects of caloric restriction that occur in animals may impact the human life very differently. For certain, calorie restriction has a plethora of health benefits in mammals, such as a reduction in age-related diseases such as cancer. However, despite the "magic" of CR, this intervention in humans may present itself with a number of health concerns, which may not be applicable to or impact the life of experimental animals, but may do so in humans. These potential pitfalls and "side effects" are not clearly addressed in the literature and will be a focus of this review.

Hypotension and bradycardia during caloric restriction in mice are independent of salt balance and do not require ANP receptor

We hypothesized that caloric restriction (CR)-induced hypotension would correlate with increased sodium excretion through an atrial natriuretic peptide (ANP)-dependent mechanism. To test this hypothesis, the cardiovascular parameters of c57/Bl mice were measured with radiotelemetry while urine was collected. The 23-h mean blood pressure (BP) dropped from 108.6 ± 1.8 to 92.7 ± 2.4 mmHg, and 23-h heart rate dropped from 624 ± 5 to 426 ± 13 beats/min over 7 days of CR at 29°C. Contrary to our hypothesis, urine sodium excretion decreased by 55% by day 7 of CR. Consistent with decreased sodium excretion was the drop in plasma ANP (from 82.4 ± 4.3 to 68.0 ± 5.8 pg/ml). To explore the possibility that CR lowers BP through an ANP receptor-dependent mechanism that is independent of its effect on sodium retention, we measured the cardiovascular parameters of mice deficient in the ANP receptor (NPR1−/−) or the ANP clearance receptor (NPR3−/−). Mean BP fell from 117.1 ± 3.9 to 108.0 ± 4.7 mmHg in the NPR1−/− mice and from 87.0 ± 2.4 to 78.4 ± 1.7 mmHg in the NPR3−/− mice during CR. These data indicate that the hypotension induced by CR does not depend on increased sodium excretion. Rather, it appears that the mouse responds to the low BP induced by CR with an increase in sodium reabsorption. Furthermore, circulating ANP levels and data from NPR1−/− and NPR3−/− mice suggest that the ANP pathway may not be involved in the cardiovascular response to CR.

Effect of long-term body weight change on the incidence of hypertension in Japanese men and women

OBJECTIVE

To elucidate the effect of long-term body weight changes on the subsequent incidence of hypertension in a large sample of community-residing Japanese males and females.

METHODS

Subjects were 3431 men and 2409 women, between 30 and 69 y old, who underwent annual periodic health examinations from 1987 (baseline year) until 1996. They were free from hypertension during the first 5 y from the baseline year. Body weight change index between 1987 and 1992 was the body mass index (BMI) (weight (kg) over height (m) squared) slope. Multiple logistic analysis was performed to assess the effect of BMI slope on the incidence of hypertension during the subsequent 5 ys (1992-1996), while controlling for baseline age, BMI, systolic blood pressure (SBP), diastolic blood pressure (DBP) and smoking habit.

RESULTS

During the first 5 y, the prevalence of overweight males (25.0< or =BMI<30.0) significantly increased from 18.4 to 23.5% in males and from 10.4 to 14.1% in females. In all, 11.7% of the males and 8.9% of the females developed hypertension between 1992 and 1996. Those who developed hypertension had a significantly higher baseline age, BMI, SBP and DBP both in males and females. The baseline smoking rate among the females who developed hypertension was significantly lower than those who did not develop the hypertension. After adjustment of these covariables by the multiple logistic analysis, the BMI slope was positively correlated with the incidence of hypertension both in females and males significantly.

CONCLUSIONS

Weight gain increased the risk of developing hypertension independent of age and blood pressure level among relatively lean Japanese men and women.

Dbh(-/-) mice are hypotensive, have altered circadian rhythms, and have abnormal responses to dieting and stress

We used mice deficient in dopamine beta-hydroxylase [Dbh(-/-)] and their littermate controls [Dbh(+/-)] to examine the role of epinephrine (Epi) and norepinephrine (NE) in the maintenance of cardiovascular parameters during 7 days of caloric restriction and acute exposure to environmental stress. Cardiovascular parameters of the mice were monitored using blood pressure radiotelemeters at an ambient temperature of 29 degrees C. Under normal conditions, Dbh(-/-) mice had a low heart rate, were severely hypotensive, and displayed an attenuated circadian blood pressure rhythm. Upon 50% caloric restriction, Dbh(+/-) mice exhibited decreases in heart rate and mean blood pressure. However, the blood pressures of Dbh(-/-) mice did not fall significantly in response to caloric restriction, and the bradycardia associated with caloric restriction was attenuated in these mice. In response to an open-field test, the blood pressure and heart rate of Dbh(+/-) mice increased substantially and rapidly, whereas Dbh(-/-) mice had blunted changes in blood pressures and no change in heart rate. These data suggest a primary role of Epi and NE in mediating the hypotension induced by dieting. Furthermore, Epi and NE play a smaller, but still significant, role in the bradycardia induced by caloric restriction. In contrast, Epi and NE are required for the tachycardia in an open field but are not required for the increase in blood pressure.

Intermittent food deprivation improves cardiovascular and neuroendocrine responses to stress in rats

Stressful events may trigger disease processes in many different organ systems, with the cardiovascular system being particularly vulnerable. Five-mo-old male rats had ad libitum (AL) access to food or were deprived of food every other day [intermittent food deprivation (IF)] for 6 mo, during which time their heart rate (HR), blood pressure (BP), physical activity and body temperature were measured by radiotelemetry under nonstress and stress (immobilization or cold-water swim) conditions. IF rats had significantly lower basal HR and BP, and significantly lower increases in HR and BP after exposures to the immobilization and swim stressors. Basal levels of adrenocorticotropic hormone (ACTH) and corticosterone were greater in the IF rats. However, in contrast to large stress-induced increases in ACTH, corticosterone and epinephrine levels in AL rats, increases in these hormones in response to repeated immobilization stress sessions were reduced or absent in IF rats. Nevertheless, the IF rats exhibited robust hypothalamic/pituitary and sympathetic neuroendocrine responses to a different stress (swim). The IF treatment improved glucose metabolism, as indicated by lower basal levels of circulating glucose and insulin, but with maintenance of glucose and insulin responses to stress. We concluded that improvements in cardiovascular risk factors and cardiovascular and neuroendocrine stress adaptation occur in response to IF.

Intermittent fasting and dietary supplementation with 2-deoxy-D-glucose improve functional and metabolic cardiovascular risk factors in rats

Hypertension and insulin resistance syndrome are risk factors for cardiovascular disease, and it is therefore important to identify interventions that can reduce blood pressure and improve glucose metabolism. We performed experiments aimed at determining whether intermittent fasting (IF) can improve cardiovascular health and also tested the hypothesis that beneficial effects of IF can be mimicked by dietary supplementation with 2-deoxy-D-glucose (2DG) a non-metabolizable glucose analog. Four-month-old male rats were implanted with telemetry probes to allow continuous monitoring of heart rate, blood pressure, physical activity, and body temperature. Rats were then maintained for 6 months on one of three different dietary regimens: ad libitum feeding, IF, or 2DG supplementation. Rats on the IF regimen consumed 30% less food over time and had reduced body weights compared with rats fed ad libitum, whereas rats on the 2DG regimen did not reduce their food intake and maintained their body weight. Heart rate and blood pressure were significantly decreased within 1 month in rats on IF and 2DG diets and were maintained at reduced levels thereafter. Body temperature was significantly decreased in group IF, but not in group 2DG. Levels of serum glucose and insulin were significantly decreased in rats maintained on IF and 2DG-supplemented diets, suggesting that IF and 2DG diets affect insulin sensitivity in a similar manner. Finally, rats in groups IF and 2DG exhibited increased levels of plasma adrenocorticotropin and corticosterone, indicating that these diets induced a stress response. We conclude that reductions in blood pressure, heart rate, and insulin levels, similar to or greater than those obtained with regular physical exercise programs, can be achieved by IF and by dietary supplementation with 2DG by a mechanism involving stress responses.

Body mass index is a good predictor of hypertension and hyperlipidemia in a rural Japanese population

OBJECTIVE

The association between body mass index (BMI) and cardiovascular risk factors, widely recognized in Western populations, was evaluated on subjects living in a rural Japanese area.

DESIGN

A cross-sectional survey.

SUBJECTS

A total of 16 871 subjects aged 40-59 y, from a rural area in Japan, participated in an annual health examination. All of the subjects were required to answer six items in a questionnaire on health behavior and provide blood samples.

MEASUREMENTS

Quetelet's index, blood pressure, total cholesterol, high-density lipoprotein cholesterol, health practices on exercise, drinking and smoking.

RESULTS

The mean BMI in the population was 23.1+/-2.9. After adjustment for sex, age and six health habits, the BMI was found to be significantly associated with blood pressure and the serum lipid levels by multivariate logistic regression analysis. The adjusted odds ratio for hypertension (> or =140/90 mmHg) against the lowest quartiles of BMI (separated by 20, 25 and 28) were 1.6, 2.8 and 5.2, respectively. The adjusted odds ratio for hypercholesterolemia (> or =240 mg/dl) against the lowest quartiles of BMI were 2.1, 3.3 and 4.6, respectively.

CONCLUSION

There was a significant relationship between the BMI and cardiovascular risk factors in a rural Japanese population. This association could be extended to lower BMI levels than those in Western populations.

Cardiovascular responses to caloric restriction and thermoneutrality in C57BL/6J mice

We utilized variations in caloric availability and ambient temperature (T(a)) to examine interrelationships between energy expenditure and cardiovascular function in mice. Male C57BL/6J mice (n = 6) were implanted with telemetry devices and housed in metabolic chambers for measurement of mean arterial pressure (MAP), heart rate (HR), O(2) consumption (VO(2)), and locomotor activity. Fasting (T(a) = 23 degrees C), initiated at the onset of the dark phase, resulted in large and transient depressions in MAP, HR, VO(2), and locomotor activity that occurred during hours 6-17, which suggests torporlike episodes. Food restriction (14 days, 60% of baseline intake) at T(a) = 23 degrees C resulted in progressive reductions in MAP and HR across days that were coupled with an increasing occurrence of episodic torporlike reductions in HR (<300 beats/min) and VO(2) (<1.0 ml/min). Exposure to thermoneutrality (T(a) = 30 degrees C, n = 6) reduced baseline light-period MAP (-14 +/- 2 mmHg) and HR (-184 +/- 12 beats/min). Caloric restriction at thermoneutrality produced further reductions in MAP and HR, but indications of torporlike episodes were absent. The results reveal that mice exhibit robust cardiovascular responses to both acute and chronic negative energy balance. Furthermore, we conclude that T(a) is a very important consideration when assessing cardiovascular function in mice.

Altered leptin signaling is sufficient, but not required, for hypotension associated with caloric restriction

Caloric restriction of mammals leads to decreases in blood pressure and heart rate. Although relevant clinically, the mechanisms involved, in terms of hormones and signaling pathways invoked, are currently not known. Circumstantial evidence suggests that leptin signaling may be involved with the bradycardia and hypotension associated with caloric restriction. This hypothesis was specifically tested using leptin-deficient mice (ob/ob) or leptin-receptor rats (Koletsky). Ob/ob mice were hypertensive during the light cycle relative to littermate controls (108 +/- 2 vs. 100 +/- 2 mmHg, respectively). Both ob/ob mice and wild-type mice exhibited hypotension and bradycardia on initiation of a 50% caloric restriction regime, suggesting that the loss of leptin during caloric restriction is not required to explain the cardiovascular effects. Blood pressure in Koletsky rats did not drop in response to caloric restriction during the light cycle, whereas blood pressure in littermate control rats significantly dropped. These data suggest that at least two pathways are involved with cardiovascular effects of caloric restriction: one dependent on leptin signaling and the other independent of the leptin axis.

Association between blood pressure and insulin resistance in obese females during weight loss and weight rebound phenomenon

The purpose of this study was to investigate the effect of weight loss on blood pressure and its related variables in moderately obese Japanese females, including an investigation of the rebound phenomenon. Study I examined the effects of weight loss on blood pressure in 138 moderately obese, nondiabetic females (BMI 29.3+/-0.3 kg/M2; age, 46.3+/-0.8 years) during a 3-month therapeutic dietary and exercise program. Study II investigated the effect of weight rebound on blood pressure over an additional 21 months of exercise in 48 subjects from Study I subjects. After 3 months, the BMI significantly decreased to 27.9+/-0.3 kg/m2. Abdominal total fat, visceral fat (V), and subcutaneous fat (S) also decreased significantly. In addition, the summation of insulin (sigmaIRI), plasma glucose (sigmaPG) and HOMA during 75 g oral glucose tolerance test also all significantly decreased. Significant decreases in both the SBP and DBP were observed after the 3 month weight reduction program. Multiple regression analysis revealed that the reduction in SBP was significantly and positively associated with the reduction in log sigmaIRI and the reduction in log 24h-urinary norepinephrine excretion at the end of Study I. The DBP showed a significantly positive association with the log sigmaIRI. With regard to the weight rebound phenomenon, Study II showed that the SBP, DBP and sigmaIRI all increased significantly, and a positive correlation was observed between the changes in the SBP and those in the log sigmaIRI. However, no such correlation was observed regarding the abdominal total fat and visceral fat during both periods. These results suggest that weight loss therefore caused the BP to decrease due to both an improvement in hyperinsulinemia and a decrease in the adrenergic activity which may be involved in the urinary catecholamine. As a result, hyperinsulinemia is thus considered to play an important role in the pathogenesis of blood pressure due to obesity not only during weight loss, but also during the weight rebound phenomenon.

Pathophysiological role of leptin in obesity-related hypertension

To explore the pathophysiological role of leptin in obesity-related hypertension, we examined cardiovascular phenotypes of transgenic skinny mice whose elevated plasma leptin concentrations are comparable to those seen in obese subjects. We also studied genetically obese KKA(y) mice with hyperleptinemia, in which hypothalamic melanocortin system is antagonized by ectopic expression of the agouti protein. Systolic blood pressure (BP) and urinary catecholamine excretion are elevated in transgenic skinny mice relative to nontransgenic littermates. The BP elevation in transgenic skinny mice is abolished by alpha(1)-adrenergic, beta-adrenergic, or ganglionic blockers at doses that do not affect BP in nontransgenic littermates. Central administration of an alpha-melanocyte-stimulating hormone antagonist causes a marked increase in cumulative food intake but no significant changes in BP. The obese KKA(y) mice develop BP elevation with increased urinary catecholamine excretion relative to control KK mice. After a 2-week caloric restriction, BP elevation is reversed in nontransgenic littermates with the A(y) allele, in parallel with a reduction in plasma leptin concentrations, but is sustained in transgenic mice overexpressing leptin with the A(y) allele, which remain hyperleptinemic. This study demonstrates BP elevation in transgenic skinny mice and obese KKA(y) mice that are both hyperleptinemic, thereby suggesting the pathophysiological role of leptin in some forms of obesity-related hypertension.

Marked weight reduction lowers resting and exercise blood pressure in morbidly obese subjects

Obesity and high blood pressure (BP) often coexist. Weight reduction lowers resting BP but its effect on BP during exercise (a predictor of target organ damage) has not been evaluated. Blood pressure was measured at rest and during cycling, before and after weight reduction induced by gastric restriction. Nineteen subjects (4 male), 41 +/-2 (SEM) years of age and body mass index (BMI) of 43 +/- 0.9 kg/m2, were studied. On each occasion BP was measured at rest, at a steady state of 0 and 25 watts, at peak exercise and 1 min into recovery. Body weight was reduced by 28% +/- 6% and BMI decreased from 43.3 +/- 0.9 to 31.5 +/- 0.7 kg/m2 (P < .01). Both BP and heart rate, at rest and at all exercise intensities, were significantly lower after weight reduction. Resting BP decreased from 133 +/-4/87 +/- 3 mm Hg to 115 +/- 4/77 +/- 2 mm Hg (P < .001), and BP at peak exercise decreased from 181 +/- 8/98 +/- 4 to 162 +/- 6/83 +/- 5 mm Hg (P < .001). The change in resting systolic BP did not correlate with the change in body weight or with the change in heart rate, but it correlated with the baseline systolic BP (R = 0.61; P < .005). It is concluded that marked weight reduction reduces BP at rest and at all exercise intensities. Gastroplasty should be considered as an option in morbidly obese hypertensive patients who are not well controlled with conventional treatment, and who fail to lose or to maintain a reduced weight by calorie restriction alone.

Concurrent reductions in blood pressure and metabolic rate during fasting in the unrestrained SHR

Fasting produces multiple cardiovascular, metabolic, and behavioral responses. To examine the interrelationship between these responses, male spontaneously hypertensive rats (SHR; n = 8) implanted with cardiovascular telemetry devices were housed in metabolic chambers at 23 degrees C for 22-h daily measurements of physiological variables. The experimental apparatus was designed so that ingestive behavior was detected by photobeams and locomotion was detected by a load sensor. Cardiovascular and metabolic status were determined as both a function of the circadian cycle (12-h dark and 10-h light), as well as during periods of inactivity (no ingestion and minimal locomotion) within the dark and light phases. Data were obtained during baseline, 48-h of caloric deprivation, and 6 days of refeeding. Fasting produced significant reductions in mean arterial pressure (dark: -9.2+/-1.3 from 143.7+/-3.7 mm Hg; light: -8.6+/-1.8 from 140.1+/-3.7 mm Hg), heart rate (dark: -43.4+/-5.2 from 330.0+/-5.2 beats/min; light: -27.4+/-5.2 from 294.0+/-5.2 beats/min), and oxygen consumption (dark: -5.0+/-0.6 from 20.6+/-0.3 ml x min(-1) x kg (0.75); light: -2.7+/-0.2 from 14.9 +/-0.2 ml x min(-1) x kg(0.75)). Analysis of inactive periods during both light and dark phases revealed that these reductions were not dependent on behavioral effects. We conclude that fasting produces concurrent and interrelated reductions in cardiovascular and metabolic function in the SHR. The merging of cardiovascular telemetry, indirect calorimetry, and behavioral monitoring provides a powerful approach for investigation of the integrative physiological responses to energetic challenges.

Obesity and hypertension

Substantial evidence from epidemiological data supports a link between obesity and hypertension. However, the relationship between the two disorders is not straightforward and most likely represents an interaction of demographic, genetic, hormonal, renal, and hemodynamic factors. Age, race, and sex also modulate the strength of the association between obesity and hypertension. Hyperinsulinemia, which is characteristic of obesity, can contribute to the probability of developing hypertension by activating the sympathetic nervous system (SNS) and by causing sodium retention. The pressor effect of insulin in obesity may be further enhanced by the observation that its vasodilator action can be blunted in obese subjects. Preliminary data have shown that leptin, whose levels are increased in most obese individuals, can contribute to hypertension in obesity through its effects on insulin, SNS, and sodium excretion. The kidney may also have a role in the pathophysiology of hypertension in obesity. Abnormal renal sodium handling coupled with structural changes in the kidney of an obese patient can raise blood pressure. In addition, obesity is associated with distinct cardiovascular hemodynamic alterations and development of eccentric myocardial hypertrophy. Most of these obesity-associated abnormalities, as well as hypertension itself, can be reversed by weight loss. Furthermore, weight loss can prevent, or at least delay, the development of hypertension in patients with high-normal blood pressure. Weight reduction should be the first-line treatment in every obese hypertensive patient. However, the majority of patients will need pharmacologic intervention in conjunction with weight loss. Selection of antihypertensive agents in the overweight patient should take into account the mechanisms leading to hypertension and the metabolic abnormalities that characterize the obese patient.

Obesity, hypertension, and sympathetic nervous system activity

Several epidemiologic studies have shown that obesity represents an independent risk factor for the development of cardiovascular diseases, including hypertension, myocardial ischemic disease, and cardiac arrhythmias. One of the most appealing concepts in obesity-related hypertension is that a specific etiology can be identified. There is now substantial evidence that human obesity is characterized by abnormalities in sympathetic cardiovascular control. The application of sensitive techniques to assess sympathetic nervous system (SNS) activity in humans, including catecholamine levels, norepinephrine (NE) spillover techniques, and microneurography have furthered this concept. Catecholamine levels in obesity have been conflicting, with high, normal, and low levels reported. However, studies examining weight loss have found that the fall in blood pressure (BP) was highly correlated with reductions in plasma NE. Examination of NE spillover in obesity has shown regional overactivity in the kidneys. High renal SNS activity could lead to sodium retention and abnormal glomerular hemodynamics that could raise BP. Microneurography, which determines muscle sympathetic outflow, has shown consistent elevation in obesity, but no difference between normotensive and hypertensive obesity. However, the hyperinsulinemia of obesity may act in concert with the SNS to elevate BP, as the combination of the two seems to produce vascular constriction. Leptin also has several cardiovascular actions that may contribute to BP regulation. Epidemiologic studies also found that SNS activity predicts hypertension in obese subjects.

Factors that affect calorie-sensitive and calorie-insensitive reduction in blood pressure during short-term calorie restriction in overweight hypertensive women

This study was performed to elucidate the factors that affect the reduction in blood pressure produced by calorie restriction in overweight women with essential hypertension. Fifty-one subjects were admitted to the metabolic ward of the hospital. After being fed a standard diet (6.3 to 8.4 MJ/d) for 2 weeks, the calorie-restricted group (n=34) was fed a low-calorie diet (1.9 MJ/d) for an additional 2 weeks. The calorie-nonrestricted group (n=17) was fed the standard diet for 4 weeks. Sodium and potassium intake was kept constant, as was the level of exercise activity. The calorie-restricted group was subdivided into "calorie-sensitive" and "calorie-insensitive" groups based on an average 5 mm Hg reduction in mean blood pressure during the low-calorie diet. The mean age was 51+/-6 years (mean+/-SD) in the calorie-sensitive group (n=16), which was significantly lower than the mean age of 61+/-6 years in the calorie-insensitive group (n=18). Multiple regression analysis indicated that age and change in body weight exhibited significant correlations with blood pressure reduction produced by calorie restriction among 17 parameters. Findings suggest that age can predict the extent of blood pressure reduction that would be obtained during 2 weeks of calorie restriction in overweight hypertensive women. The reduction in blood pressure may be related in part to the amount of weight loss.