Obesity and daytime pulse pressure are predictors of left ventricular hypertrophy in true normotensive individuals

OBJECTIVE

To investigate predictors of left ventricular mass corrected for height2.7 (LVMI) and left ventricular hypertrophy in patients who were found to be normotensive with both office and 24-h ambulatory blood pressure (BP) measurements.

METHODS

A total of 805 consecutive patients were analyzed. All patients underwent office BP measurements, 24-h ambulatory BP monitoring, laboratory measurements for cardiovascular risk factors and echocardiography. Individuals with both office and ambulatory normotension were characterized as true normotensive.

RESULTS

LVMI was found to be 34.5 +/- 10.9 g/m2.7 in normal-weight patients and 48.7 +/- 13.0 g/m2.7 in obese patients (P < 0.0001). LVMI was found to be 41.7 +/- 10 g/m2.7 in overweight patients, significantly lower than the values of obese patients (P < 0.005) and higher than the values of normal-weight patients (P < 0.001). These results remained significant even after adjustment for age, sex, daytime and nighttime SBP, daytime and nighttime DBP, daytime and nighttime BP variability and daytime and nighttime pulse pressure (PP). In a multivariate analysis model, in which LVMI was the dependent variable and office SBP, office DBP, daytime and nighttime SBP and DBP, daytime and nighttime PPs and variabilities, day-night SBP ratio, fasting serum glucose, triglycerides, total cholesterol, age and BMI were inserted as independent variables with weighted least squares regression by sex, the predictors of LVMI were age, BMI and daytime PP (r2 = 0.31). Left ventricular hypertrophy was 17.67 times more likely in obese patients as compared with normal-weight true normotensive individuals.

CONCLUSION

Obesity may represent a significant cardiovascular risk factor even in normotensive individuals. Other predictors of LVMI were ageing and daytime PP.

Mechanisms of obesity-induced hypertension

The relationship between obesity and hypertension is well established both in children and adults. The mechanisms through which obesity directly causes hypertension are still an area of research. Activation of the sympathetic nervous system has been considered to have an important function in the pathogenesis of obesity-related hypertension. The arterial-pressure control mechanism of diuresis and natriuresis, according to the principle of infinite feedback gain, seems to be shifted toward higher blood-pressure levels in obese individuals. During the early phases of obesity, primary sodium retention exists as a result of increase in renal tubular reabsorption. Extracellular-fluid volume is expanded and the kidney-fluid apparatus is resetted to a hypertensive level, consistent with a model of hypertension because of volume overload. Plasma renin activity, angiotensinogen, angiotensin II and aldosterone values display significant increase during obesity. Insulin resistance and inflammation may promote an altered profile of vascular function and consequently hypertension. Leptin and other neuropeptides are possible links between obesity and the development of hypertension. Obesity should be considered as a chronic medical condition, which is likely to require long-term treatment. Understanding of the mechanisms associated with obesity-related hypertension is essential for successful treatment strategies.

A sensitizing regimen of amphetamine that disrupts attentional set-shifting does not disrupt working or long-term memory

Exposure to an intermittent, escalating dose of amphetamine induces a sensitized state that, both behaviourally and neurochemically, mirrors several features linked to the positive symptoms of schizophrenia. Increasingly it is being realized that cognitive deficits are a core component of schizophrenia; therefore we sought to assess the effects of inducing an amphetamine-sensitized state on memory (working and long-term) and cognitive flexibility, two cognitive domains impaired in schizophrenia. Rats were exposed to a sensitizing regimen of amphetamine (1-5 mg/kg; three times per week for 5 weeks; escalating at 1mg/kg per week) or saline. In experiment 1, animals were tested on an operant delayed non-match to position task (working memory). Experiment 2 used a standard fixed-platform location water maze task (long-term memory), while experiment 3 used a variable-platform location water maze task (long-term memory and working memory). Amphetamine-sensitized animals were not impaired on any of these tasks. In experiment 4, animals were assessed on a strategy selection task in which they were first required to learn to locate a food reward using a particular learning strategy (place or response) then to learn to shift to an alternate learning strategy (response or place). Amphetamine-sensitized animals were not impaired on this task. In the final experiment animals were found to be impaired in performance of the extra-dimensional shift component of an attentional set-shifting task. These results suggest that while amphetamine sensitization does not produce memory impairments similar to those seen in schizophrenia, it does produce strong impairments in set-shifting, suggesting changes in prefrontal function similar to those seen in schizophrenia.

Hypertension and hypothyroidism: results from an ambulatory blood pressure monitoring study

OBJECTIVE

To examine differences between hypothyroid patients and healthy volunteers in 24-h ambulatory blood pressure parameters.

METHODS

The study population consisted of 100 individuals who were recently diagnosed for hypothyroidism. These patients had never been treated before with antihypertensive treatment or received drugs for hypothyroidism. All participants underwent 24-h ambulatory blood pressure monitoring. The control group consisted of 100 healthy volunteers matched one to one for gender and age with the hypothyroid participants.

RESULTS

Clinic systolic and diastolic blood pressures were significantly higher in patients with hypothyroidism compared with volunteers. The mean 24-h systolic blood pressure and 24-h pulse pressure were significantly higher in patients with hypothyroidism compared with volunteers. The 24-h systolic blood pressure variability was also significantly higher in patients with hypothyroidism. Fasting serum cholesterol tended to be higher in patients with hypothyroidism compared with volunteers but the difference was not statistically significant, while fasting serum triglycerides were significantly higher. Body mass index was also significantly higher in patients with hypothyroidism.

CONCLUSIONS

These findings indicate that hypothyroidism may be an important predictor of higher mean 24-h systolic blood pressure, 24-h pulse pressure and 24-h systolic blood pressure variability, parameters of ambulatory blood pressure monitoring that have been previously associated with higher cardiovascular target organ damage.

Gestational methylazoxymethanol acetate treatment impairs select cognitive functions: parallels to schizophrenia

Gestational methylazoxymethanol acetate (MAM) exposure has been suggested to produce neural and behavioral abnormalities similar to those seen in schizophrenia. In order to assess MAM treatment as a model of schizophrenia, pregnant female rats were injected with MAM (22 mg/kg) on gestational day 17 and their offspring were assessed in adulthood on a series of cognitive tasks. The first experiment involved an attentional set-shifting task, a rodent analog of the Wisconsin card sort task. In experiment 2, animals were tested on the 5-choice serial reaction time task, a rodent analog of the continuous performance task. In the final experiment animals were assessed on a differential reinforcement of low rate of responding 20 s schedule of reinforcement (DRL-20), a task that is sensitive to changes in inhibitory control. In the first experiment, MAM-treated animals required a greater number of trials than controls to successfully learn an extradimensional shift on the set-shifting task, and had difficulties in learning to reverse a previously acquired discrimination. In contrast, MAM-treated animals showed little impairment on the 5-choice task, aside from a modest but consistent increase in premature responding. Finally, MAM exposed animals showed substantial impairments in DRL performance. Post-mortem analysis of brain tissue showed significant decreases in tissue weight in the hippocampus, parietal cortex, prefrontal cortex, and dorsal striatum of MAM-treated animals. These results support the notion that MAM treatment may simulate some aspects of schizophrenic cognition.

The role of medial prefrontal cortex in context-specific inhibition during reversal learning of a visual discrimination

Rats with medial prefrontal cortex or sham lesions were trained on a visual discrimination task designed for the eight-arm radial maze. After reaching asymptotic performance on this task, both groups were divided into sub-groups that would experience reversal learning in the same or different context from original training. The results showed that both groups reversed in the different context had accelerated learning compared to the groups reversed in the same context. Reversal learning in rats with medial prefrontal cortex damage was faster than sham animals in the same context. These and other results from a transfer test suggest that the medial prefrontal cortex participates in the behavioral effects of a context-specific inhibitory association acquired during visual discrimination learning.

Reconditioning of heroin place preference requires the basolateral amygdala

To investigate the role of the basolateral amygdala (BLA) in the reacquisition of heroin seeking, we studied the effect of BLA inactivation after heroin re-exposure in the presence of drug-conditioned cues. We employed a heroin conditioned place preference task [Leri F, Rizos Z, 2005. Reconditioning of drug-related cues: a potential contributor to relapse after drug re-exposure. Pharmacol Biochem Behav 2005;80:621-30.], where after initial conditioning and subsequent extinction, rats received a single reconditioning session (explicit compartment-heroin re-pairing), followed by a test of heroin seeking 24 h later. Rats were infused with GABA(A)/GABA(B) agonists (muscimol and baclofen, 0.03 and 0.3 nmol, respectively/0.3 microl) or vehicle, either 15 min or 6 h following the heroin reconditioning session. Animals that received vehicle infusions, whether they were given 15 min or 6 h following reconditioning, showed a significant preference for the heroin-paired compartment 24 h later. However, inactivation of the BLA 15 min post-reconditioning, but not 6 h following reconditioning, completely blocked the reacquisition of heroin seeking. These results suggest that the BLA plays an important role in a putative learning process initiated by drug re-exposure which may underlie the process of relapse.

Reconditioning of drug-related cues: A potential contributor to relapse after drug reexposure

To investigate the process of relapse to drug seeking caused by reexposure to drugs, we studied the consequences of recurring instances of stimuli-drug associations using heroin conditioned place preference (CPP) in rats. After original conditioning and extinction, rats received either a single compartment-heroin pairing (reconditioning) or were primed with heroin and tested for reinstatement of CPP. It was found that the session of reconditioning, but not the session of reinstatement, caused the reappearance of a preference for the heroin-paired compartment on a test given 24 h later, in drug-free conditions. The effect of reconditioning was found to be dependent on heroin doses, and was not seen when heroin injections were given outside the conditioning environment. Furthermore, a single session of reconditioning elevated heroin seeking even on a test given 96 h later. Finally, heroin seeking was found to be significantly elevated on a test given 28 days after the last extinction session whether animals received 1 or 3 reconditioning sessions. These results suggest that the motivational value of cues associated with heroin is not eliminated by extinction and, importantly, that these cues can rapidly regain their ability to promote drug seeking behavior if they are re-associated with the effect of heroin.