Noradrenaline levels and morphologic alterations of myocardium in experimental protein-calorie malnutrition

Characterization of Myocardial Repolarization Reserve in Adolescent Females With Anorexia Nervosa

BACKGROUND

Patients with anorexia nervosa exhibit abnormal myocardial repolarization and are susceptible to sudden cardiac death. Exercise testing is useful in unmasking QT prolongation in disorders associated with abnormal repolarization. We characterized QT adaptation during exercise in anorexia.

METHODS AND RESULTS

Sixty-one adolescent female patients with anorexia nervosa and 45 age- and sex-matched healthy volunteers performed symptom-limited cycle ergometry during 12-lead ECG monitoring. Changes in the QT interval during exercise were measured, and QT/RR-interval slopes were determined by using mixed-effects regression modeling. Patients had significantly lower body mass index than controls; however, resting heart rates and QT/QTc intervals were similar at baseline. Patients had shorter exercise times (13.7±4.5 versus 20.6±4.5 minutes; P<0.001) and lower peak heart rates (159±20 versus 184±9 beats/min; P<0.001). The mean QTc intervals were longer at peak exercise in patients (442±29 versus 422±19 ms; P<0.001). During submaximal exertion at comparable heart rates (114±6 versus 115±11 beats/min; P=0.54), the QTc interval had prolonged significantly more in patients than controls (37±28 versus 24±25 ms; P<0.016). The RR/QT slope, best described by a curvilinear relationship, was more gradual in patients than in controls (13.4; 95% confidence interval, 12.8-13.9 versus 15.8; 95% confidence interval, 15.3-16.4 ms QT change per 10% change in RR interval; P<0.001) and steepest in patients within the highest body mass index tertile versus the lowest (13.9; 95% confidence interval, 12.9-14.9 versus 12.3; 95% confidence interval, 11.3-13.3; P=0.026).

CONCLUSIONS

Despite the absence of manifest QT prolongation, adolescent anorexic females have impaired repolarization reserve in comparison with healthy controls. Further study may identify impaired QT dynamics as a risk factor for arrhythmias in anorexia nervosa.

Food restriction impairs myocardial inotropic response to calcium and beta-adrenergic stimulation in spontaneously hypertensive rats

Although long-term food restriction (FR) has been shown to induce cardiac remodeling and dysfunction, there are few data on the effects of FR on pressure-overloaded hearts. The aim of this study was to examine the effects of FR on cardiac muscle performance during inotropic stimulation in the myocardium of spontaneously hypertensive rats (SHRs). Male 60-day-old SHRs were subjected to FR for 90 days. Food-restricted animals received 50% of the ad libitum amount of food consumed by the control group. Myocardial function was studied in isolated left ventricular papillary muscle under isometric contraction in basal condition (1.25 mmol/L extracellular Ca(2+) concentration) and after 3 inotropic maneuvers: (1) at postrest contraction of 30 seconds, (2) at extracellular Ca(2+) concentration of 5.2 mmol/L, and (3) after beta-adrenergic stimulation with 10(-6) mol/L isoproterenol. At basal condition, time from peak tension to 50% relaxation was greater in the food-restricted group (P < .05). Inotropic stimulation with postrest contraction and isoproterenol promoted a significant lower increase of developed tension, maximum rate of tension development, and maximum rate of tension decline in the food-restricted compared to the control group. The elevation of extracellular Ca(2+) concentration induced a lower increase of developed tension, maximum rate of tension development, and time from peak tension to 50% relaxation in the food-restricted than in the control group. In conclusion, long-term FR promotes impairment of myocardial inotropic response to calcium and beta-adrenergic stimulation in SHRs.

QT interval dispersion in young women with anorexia nervosa

OBJECTIVES

To evaluate the degree of QT dispersion in a group of young women in the starvation phase of anorexia nervosa (AN) and its relation to left ventricular (LV) mass.

STUDY DESIGN

Sixteen patients with self-induced starvation were matched with 16 women of normal weight and 16 constitutionally thin women (body mass index <20 kg/m2). Starving patients and control patients underwent an electrocardiogram and echocardiogram. QT intervals were measured from surface electrocardiograms and QT dispersion was defined as the difference between maximum QT and minimum QT occurring in any of the 12 leads.

RESULTS

LV-chamber mass was significantly less in women with AN than in thin and normal-weight women. QT dispersion was significantly greater in AN than in the thin and control groups (QT dispersion: 50 +/- 14 vs 34 +/- 9 and 37 +/- 11 ms, P <.001; QT interval dispersion corrected for heart rate: 49+12 vs 34 +/- 9 and 36 +/- 7 ms, P <.01, respectively). A significant relation between QT dispersion and LV-mass index (r = -0.726, P <.01), and between QTc dispersion and LV mass index (r = -0.693, P < 0.01) were found only in the patients with AN.

CONCLUSION

Starving patients show an increased QT dispersion related to reduced LV mass. This result could represent a useful indicator of arrhythmic risk and sudden death in AN.

Mechanical, biochemical, and morphological changes in the heart from chronic food-restricted rats

Food restriction (FR) has been shown to induce important morphological changes in rat myocardium. However, its influence on myocardial performance is not completely defined. We examined the effects of chronic FR on cardiac muscle function and morphology. Sixty-day-old Wistar–Kyoto rats were fed a control (C) or a restricted diet (daily intake reduced to 50% of the amount of food consumed by the control group) for 90 days. Myocardial performance was studied in isolated left ventricular (LV) papillary muscle. Fragments of the LV free wall were analysed by light microscopy, and the ultrastructure of the myocardium was examined in t...he LV papillary muscle. The myocardial collagen concentration was also evaluated. FR decreased body weight (BW) and LV weight (LVW); the LVW/BW ratio was higher in the restricted group (C, 1.86 ± 0.17 mg/g; FR, 2.19 ± 0.31 mg/g; p < 0.01). In the FR animals, the cardiac fibers were polymorphic, some of them were of small diameter and others presented lateral infoldings; the ultrastructural alterations were focal and included reduction of sarcoplasmic content, absence and (or) disorganization of myofilaments and Z line, numerous electron dense and polymorphic mitochondria, and deep infoldings of the plasma membrane. The hydroxyproline concentration was higher in the FR animals (p < 0.01). FR prolonged the contraction and relaxation time of the papillary muscle and did not change its ability to contract and shorten. In conclusion, although a 90-day period of FR caused striking myocardial ultrastructural alterations and increased the collagen concentration, it only minimally affected the mechanical function.Key words: diet, papillary muscle, undernutrition, myocardium, ultrastructure.

Cardiac function during protein malnutrition and refeeding in the isolated rat heart

In an attempt to elucidate the effect of protein restriction and subsequent refeeding on cardiac muscle function, 133 rat hearts were studied on a Langendorff perfusion apparatus: 19 normal controls, 55 rats during 6 weeks of protein restriction, and 59 rats during 6 weeks of refeeding following starvation. During starvation animals lost 14.3% of body weight and 12.8% in heart weight, both to be gained upon refeeding. Both developed force and force velocity tended to decrease in starving rats compared to control or refeeding rats. This trend was present at time 0, but more so after 60 min of perfusion. Furthermore, these differences became even more obvious and significantly different at the higher heart rates of 300 and 400 beats/min, and less so at 100 or 200 beats/min. These protein malnutrition-associated cardiac function derangements reversed almost completely to normal upon refeeding.

Effects of streptozotocin diabetes on the noradrenergic innervation of the rat heart: a longitudinal histofluorescence and neurochemical study

The effects of the age of induction and total duration of streptozotocin diabetes on the sympathetic noradrenergic innervation of the rat heart was examined with glyoxylic acid induced histofluorescence to demonstrate the distribution of noradrenergic fibers within the heart, and with high performance liquid chromatography with electrochemical detection to measure tissue levels of the neurotransmitter norepinephrine. Diabetes was induced in male Sprague-Dawley rats at 1, 2, and 4 months of age. Within each of these groups, diabetic rats survived for periods of 1, 2, and 4 months. Additional groups of diabetic rats survived to a chronological age of 8 months. Norepinephrine levels in the hearts of diabetic rats were increased over those of control rats in all groups at 1 month duration of diabetes. Ventricles were generally affected to a greater extent than atria. At 2 months duration of diabetes, ventricular levels remained elevated while atrial norepinephrine levels were at or below control levels. At 4 months duration of diabetes, and in all groups at 8 months of age, the norepinephrine levels were at or below control levels, except in the ventricles of rats induced at 4 months of age, which remained elevated. Histofluorescence studies demonstrated the presence of axon bundles and varicose noradrenergic profiles in the diabetic rat hearts, distributed in a pattern similar to that seen in controls. However, at 1 month duration of diabetes in all groups, the density of noradrenergic varicosities in diabetic rat hearts appeared increased with abundant branched profiles. These results are surprising, since studies on genetic models of diabetes have suggested decreased norepinephrine levels in the heart. The present study suggests that during the early phases of streptozotocin induced diabetes, noradrenergic nerves are still intact and may be susceptible to pharmacologic manipulation. The later fall of norepinephrine levels back to or below control levels may indicate actual neuronal damage, suggesting that early intervention may be necessary to protect these nerves from degeneration. This issue is potentially important in view of the reported toxic effects of high NE levels on the heart, and the high incidence of death from myocardial infarct in diabetic humans with autonomic neuropathy.

Effect of protein-calorie malnutrition on catecholamine levels and weight of heart in rats

Catecholamine levels and weight of heart were studied in rats subjected to protein-calorie malnutrition and after a period of nutritional rehabilitation. Rats given a protein deficient diet (4% protein) for periods of 6 and 12 weeks showed a severe restriction of body weight gain. Nevertheless, even though the measured heart weight of deficient rats was significantly lower than the respective controls (16% protein), the deficient rats incurred "real" cardiac enlargement since the mean heart weight of the equal body weight controls was significantly different from that of the deficient animals. The mean heart weight of rats fed a high-protein diet for 6 weeks thereupon a 6-week period of protein deprivation was still less than that of controls, and the heart ratio was still greater than that of controls. However, the heart weight of rehabilitated rats was not significantly different from that of equal body weight controls. Serum protein and albumin levels in dificient rats were significantly decreased in comparison to rats fed a high-protein diet. While the serum protein levels of rehabilitated rats were lower than those of controls, the albumin levels were not different. The protein-calorie malnourished rats, which received a low-protein diet for 6 and 12 weeks, showed a significant increase in myocardium noradrenaline concentration. After a period of nutritional rehabilitation this change did not persist. These catecholaminergic alterations in heart may be responsible, at least in part, for the different cardiac abnormalities described as a result of protein-calorie dietary deficiency. It may also explain the "real" cardiac enlargement observed in deficient rats, according to the hypothesis that noradrenaline may be the ultimate myocardial hypertrophy hormone.