The heart and skeletal muscle in experimental protein malnutrition in rhesus monkeys

Susceptibility of female rats to cardiac arrhythmias following refeeding after severe food restriction

Background

Many studies have shown malnutrition and inadequate caloric consumption have adverse acute effects on cardiovascular structure and function.

Methods

To determine the adverse long term cardiovascular effects, we studied cardiac morphology and function in female (F) and male (M) severe food restricted rats 3 months after refeeding (sFR-Refed).

Results

Two weeks of a normal chow diet in which calories were reduced by 60% decreased body weight (BW) by approximately 15% in both sexes. Within 2 weeks of refeeding, no differences in BW were detected between CT and sFR-Refed groups. However, male rats gained almost 3 times more BW than the females over the 3-month refeeding period. Sex differences were also observed in cardiac pathology. Hearts from F-sFR-Refed rats exhibited more atrophy and less hypertrophy, while M-sFR-Refed rats predominantly exhibited hypertrophic remodeling. While there were no differences in the frequency of ventricular arrhythmias induced by ischemia/reperfusion (I/R) in the isolated heart between M-CT and M-sFR-Refed rats, I/R induced twice as many arrhythmias in the F-sFR-Refed rats compared to F-CT.

Conclusions

These findings indicate the female heart is more susceptible to the long term adverse cardiovascular effects of sFR months after refeeding. Thus, this study provides a rationale for studying sex differences in cardiovascular risk in individuals who experience sFR for voluntary (e.g., very low-calorie dieting) or involuntary (e.g., poverty) reasons earlier in life.

What are the long-term effects of a 2-week period of severe food restriction (sFR) on cardiac structure and function months after refeeding (sFR-Refed) in male and female rats?

This study shows sex differences exist in cardiac pathology months after refeeding. A majority of cardiomyocytes were atrophied in F-sFR-Refed rats, while in M-sFR-Refed rats, the cardiomyocytes predominantly exhibited hypertrophic remodeling.

While there were no differences in the frequency of ventricular arrhythmias induced by ischemia/reperfusion (I/R) in the isolated heart between M-CT and M-sFR-Refed rats, I/R induced twice as many arrhythmias in the F-sFR-Refed rats compared to the controls.

Our findings have implications for the long-term risk of developing cardiovascular disease in individuals who have voluntarily or involuntarily experienced periods of sFR earlier in their lives, and that woman may be at greater cardiovascular risk than men.

Short-term very low caloric intake causes endothelial dysfunction and increased susceptibility to cardiac arrhythmias and pathology in male rats

New Findings

What is the central question of this study?

What are the effects of a 2 week period of severe food restriction on vascular reactivity of resistance arteries and on cardiac structure and function?

What is the main finding and its importance?

This study showed, for the first time, that a 2 week period of severe food restriction in adult male Fischer rats caused endothelial dysfunction in mesenteric arteries and increased the susceptibility to ischaemia–reperfusion‐induced arrhythmias and cardiac pathology. Our findings might have ramifications for cardiovascular risk in people who experience periods of inadequate caloric intake.

Abstract

Severe food restriction (sFR) is a common dieting strategy for rapid weight loss. Male Fischer rats were maintained on a control (CT) or sFR (40% of CT food intake) diet for 14 days to mimic low‐calorie crash diets. The sFR diet reduced body weight by 16%. Haematocrits were elevated by 10% in the sFR rats, which was consistent with the reduced plasma volume. Mesenteric arteries from sFR rats had increased sensitivity to vasoconstrictors, including angiotensin II [maximum (%): CT, 1.30 ± 0.46 versus sFR, 11.5 ± 1.6; P < 0.0001; n = 7] and phenylephrine [maximum (%): CT, 78.5 ± 2.8 versus sFR, 94.5 ± 1.7; P < 0.001; n = 7] and reduced sensitivity to the vasodilator acetylcholine [EC₅₀ (nm): CT, 49.2 ± 5.2 versus sFR, 71.6 ± 6.8; P < 0.05; n = 7]. Isolated hearts from sFR rats had a 1.7‐fold increase in the rate of cardiac arrhythmias in response to ischaemia–reperfusion and more cardiac pathology, including myofibrillar disarray with contractions and cardiomyocyte lysis, than hearts from CT rats. The sFR dietary regimen is similar to very low‐calorie commercial and self‐help weight‐loss programmes, which provide ∼800–1000 kcal day⁻¹. Therefore, these findings in rats warrant the study of cardiovascular function in individuals who engage in extreme dieting or are subjected to bouts of very low caloric intake for other reasons, such as socioeconomic factors and natural disasters.

Skeletal muscle expression of LDH and monocarboxylate transporters in growing rats submitted to protein malnutrition

BACKGROUND

In different circumstances such as infant malnutrition, old age or chronic disease, decline of muscular strength, particularly anaerobic power, is shown. In this context, our laboratory, has demonstrated a decrease in anaerobic glycolytic power in pre-pubertal Bolivian children living at low and high altitude and suffering from marginal protein malnutrition.

AIM OF THE STUDY

To bring molecular support to the relationship between protein malnutrition and anaerobic glycolytic metabolism, we studied the impact of prolonged protein malnutrition on lactate metabolism in different muscles of growing rats. Lactate dehydrogenase (LDH), monocarboxylate transporters (MCT1, MCT4) and membrane protein CD147 were chosen as specific markers of anaerobic glycolytic metabolism.

METHODS

Two groups of 10 weaning male rats were fed for 10 weeks either ad libitum with a well-balanced diet containing 18% protein or an isocaloric-diet containing 8% protein. LDH activity and mRNA amounts of LDH isoforms, MCT, CD147 were measured.

RESULTS

Protein deprivation during rat growth induced a decrease of LDH specific activity in skeletal muscles (mean value of -41%), accompanied by isoform distribution modifications in soleus, but not in glycolytic muscles (extensor digitorum longus (EDL) or plantaris). A reduction in mRNA amounts encoding the LDH A and B subunits was observed in EDL. A decrease in LDH B mRNA amounts was monitored in plantaris, whereas no modification in both LDH isoform mRNA quantities was observed in soleus. MCT1 mRNA quantities were decreased in EDL but MCT4 mRNA quantities remained stable. CD147 mRNA amounts were unchanged except for EDL with a 42% increase.

CONCLUSIONS

The global decreases of LDH activity, LDH and MCT gene expressions in growing rat skeletal muscles support the observed alterations of lactate metabolism associated with lowered muscular anaerobic performances in protein malnutrition.

The ultrastructure of skeletal and smooth muscle in experimental protein malnutrition in rats fed a low protein diet

Light microscopy of the pectoralis muscle of rats on a low protein diet did not show such morphological alterations as atrophy, degeneration, or sarcoplasmic edema, but electron microscopy occasionally demonstrated ultrastructural changes only in the sarcomeres of myofibrils. In the affected sarcomeres, the Z-line was disrupted and often showed a jagged structure. The Z-substance with electron opacity was frequently present flowing along the long axis of myofibrils, here referred to as the streaming of Z-lines. In addition, regular striations formed by the reciprocal arrangement of thick and thin filaments disappeared from the affected sarcomeres, though these filaments were still discernible. Two or more consecutive sarcomeres in a single myofibril were occasionally involved in these changes. A further two or more neighboring sarcomeres at the same level of myofibrils were affected transversely by these structural alterations. On the other hand, the ultrastructure of the intestinal smooth muscle was not affected by protein deficiency. The study suggests that the ultrastructural damage induced by a low protein diet is attributed to the activation of endogenous protease by the excess leaking of Ca2+ into the cytosol as a result of lipid peroxidation of cell membrane by raised free radicals, owing to the depletion of glutathione production by protein deficiency. It also suggests that the smooth muscle cells differ in their susceptibility to protein deficiency from the skeletal muscle cells.

Dietary protein or arginine deficiency impairs constitutive and inducible nitric oxide synthesis by young rats

Effects of dietary protein or arginine deficiency on constitutive and lipopolysaccharide (LPS)-induced nitric oxide (NO) synthesis were determined in young rats by quantifying urinary nitrate excretion. In Experiment 1, 30-d-old rats (n = 16) were divided randomly into two groups (n = 8/group) and pair-fed on the basis of body weight semipurified isocaloric diets containing 20 or 5% casein. In Experiment 2, 30-d-old rats (n = 24) were divided randomly into three groups (n = 8) and pair-fed on the basis of body weight purified isonitrogenous and isocaloric diets (composed of amino acids) containing 0.0, 0.3 or 1.0% L-arginine. In both experiments, daily collection of urine was initiated 10 d after the start of pair-feeding. On d 17 after the pair-feeding was initiated, LPS (1 mg/kg body wt) was injected intraperitoneally into rats, and urine was collected daily for an additional 7 d. In Experiments 3 and 4, activities of constitutive and inducible NO synthases were measured in macrophages and various tissues from protein- or arginine-deficient rats (n = 6). Body weight was lower in rats fed the 5% casein diet or the 0.0 and 0.3% arginine diets than in those fed 20% casein or 1% arginine, respectively. Dietary protein or arginine deficiency decreased serum concentrations of arginine and urinary nitrate excretion before and after LPS treatment, indicating impaired constitutive and inducible NO synthesis. Protein malnutrition reduced constitutive and inducible NO synthase activities in brain, heart, jejunum, lung, skeletal muscle and spleen, and inducible NO synthase activity in macrophages. Because NO is a mediator of the immune response and is the endothelium-dependent relaxing factor, impaired NO synthesis may help explain immunodeficiency and cardiovascular dysfunction in protein- or arginine-deficient subjects.

Left ventricular mass and function in children with severe protein energy malnutrition

We studied 25 children, aged 1-5 years (mean 2.65 +/- 0.8 years) with severe protein energy malnutrition, and compared their left ventricular mass and function to those of 26 healthy, age- and sex-matched normal children. The mean left ventricular mass in the patients was lower than that in the controls (25.75 +/- 8.09 g vs. 32.44 +/- 11.64 g; P less than 0.05, C.I. 2.08 to 11.30). However, left ventricular mass (g)/kg body weight was significantly increased in the patients (4.44 +/- 1.45 vs. 2.42 +/- 0.87; P less than 0.001, C.I. 1.28 to 2.76) suggesting relative cardiac "sparing". The systolic function indices like ejection fraction, percentage fractional shortening, and velocity of circumferential fiber shortening were not significantly different in the patients and in the normal children. The left ventricular end-diastolic volume, stroke volume and cardiac output were reduced in proportion to decrease in body size in the patients, so that the cardiac index was not reduced but slightly increased in the patients. (5.95 +/- 1.9 l/min/m2 in patients, 4.97 +/- 1.4 l/min/m2 in controls; P less than 0.05, C.I. 0.04 to 1.92). There was no significant difference in any of these parameters of left ventricular function or mass in patients with marasmus, as compared to those of patients with marasmic kwashiorkor. Amongst the 25 patients, however, 5 patients (20%) had an ejection fraction of less than 50%. Compared to the other 20 patients, these 5 patients had lower left ventricular mass (18.4 +/- 4.3 g vs. 27.5 +/- 7.8 g, P less than 0.05 C.I. 1.63 to 16.75), lower left ventricular mass (g)/kg body weight and a worse prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of maternal calorie-restricted diet on development of the foetal heart, as evaluated in primary cultures of rat myocardial cells

Very-low-calorie diets have been implicated in causing ventricular arrhythmias and sudden cardiac death. Furthermore, studies indicate that maternal carbohydrate-restricted diets consumed during pregnancy and lactation reduce foetal growth, parturition and postnatal survival of rat pups. In this study, Sprague-Dawley rats were maintained on a semi-purified full-calorie or 50% carbohydrate-calorie-restricted diet throughout pregnancy. The function and integrity of myocardial cell cultures obtained from 3-5-day-old offspring from both groups of dams were evaluated after a drug-induced toxic challenge. After the myocytes had been in culture for 4 days, they were exposed to various concentrations of amitriptyline (1 x 10(-3) to 1 x 10(-5) M). Morphology, beating activity, lactate dehydrogenase release, glucose utilization, beta-adrenergic receptor [125I]iodopindolol binding, and cellular adenosine triphosphate content were evaluated for 24 hr after drug exposure. There were no significant differences in morphology, beating activity or glucose utilization between the full-calorie and calorie-restricted groups. When compared with the full-calorie group, lactate dehydrogenase release from the calorie-restricted group was significantly lower at 8 hr for the untreated controls and those cells exposed to 1 x 10(-4) and 1 x 10(-5) M-amitriptyline. Adenosine triphosphate levels were lower in untreated controls from the calorie-restricted group when compared with the full-calorie group at 4 hr. Within the calorie-restricted group, those cultures exposed to 1 x 10(-4) M-amitriptyline had significantly depressed adenosine triphosphate levels after 8 hr of drug treatment when compared with their respective untreated controls. Finally, the calorie-restricted group had significantly increased binding affinities of beta-receptors. Thus, maternal consumption of calorie-restricted diets during pregnancy may affect the myocardial functional capacity and integrity of the offspring.

[Striated muscle in protein malnutrition: an experimental study in albino rats]

The effects of undernutrition on the "gastrocnemius plantaris" muscle of young albino rats were observed with light and electronmicroscopy and were compared with controls. Pregnant rats received a diet containing 6.7% protein and the neonates had a 3.2% protein diet after weaning. A total number of 40 animals were distributed in two groups: one hypoproteic and one control. Half of the animals of each group were killed 15 days after birth and the remaining ones at 30 days. We could observe important reduction in the weight of the undernourished rats reaching about 50% when compared with the control animals. An important reduction in the diameter of muscle fibers was noted in undernourished rats. Histochemical reactions showed that not only the type I but also the type II fibers were involved, the latter being more severely reduced in size. Type II fibers os small diameter, resembling F (fetal) fiber were found in animals at 15 days indicating a delay in maturation. Ultrastructural evaluation of the muscle did not show specific changes except for a severe reduction in the caliber of fibers when compared with control animals. We concluded that there was hypoplasia and not atrophy of the muscular tissue in animals submitted to pre- and post-natal undernutrition. The present study, associated with others in which the spinal motor cells and peripheral nerves of undernourished rats were analysed, allow us to consider that with protein deprivation there is a delay in the development, a hypoplasia of the motor unit. We think that in infantile progressive spinal amyotrophy (Werdnig-Hoffmann disease) there is possibly hypoplasia and not atrophy of the type II fibers and we postulate that a metabolic proteic problem is involved in this disease.

Overzealous resuscitation of an extremely malnourished patient with nutritional cardiomyopathy

Overzealous resuscitation of the severely malnourished patient may be associated with life-threatening complications. A variety of electrolyte, hemodynamic, septic, and nutritional derangements may result in sudden decompensation and even death. We present a case that dramatically illustrates these complications and focuses on the key role of underlying nutritional cardiomyopathy.

Biochemical consequences of protein depletion in the rabbit heart

We showed previously that cardiac function was depressed in rabbits subjected to 6 weeks of protein depletion and was restored after 4 weeks of protein refeeding. To identify nutritional or metabolic factors that underlie cardiac dysfunction, we assessed the nutritional status and myocardial content of energy-providing substrates in three groups of rabbits: group I served as control; group II was fed a protein-free diet; and group III was fed a protein-free diet and then repleted. Animal weights were 2.73 +/- 0.22 kg in group I, 1.92 +/- 0.28 kg in group II, and 2.78 +/- 0.12 kg in group III. Serum albumin concentrations decreased from 3.70 +/- 0.12 g/dl in group I to 2.81 +/- 0.10 g/dl in group II, and returned to normal (3.71 +/- 0.11 g/dl) in group III. The heart weights; myocardial contents of water, nitrogen (N), total fat, and glycogen; skeletal muscle N concentrations; and liver N contents were measured. Protein depletion produced a reduction in total cardiac mass due to decreased nitrogen and glycogen contents, but there was an increased fat content. Comparison with other organs suggests that cardiac muscle plays a role in energy homeostasis, undergoing glycogenolysis and proteolysis similar to those of liver and skeletal muscle. Protein repletion restored normal mass of the heart, but not of the liver. We conclude that adequate nutrition may be important in maintaining cardiac function.

Muscle involvement during postnatal protein calorie malnutrition and recovery in rhesus monkeys

The effect of protein calorie malnutrition (PCM) and, thereafter, nutritional rehabilitation on neuromuscular dysfunction was evaluated electromyographically, histopathologically and biochemically in 24 young, growing, healthy rhesus monkeys. There were 2 control and 2 PCM groups with 6 animals in each group. Animals of one control and one PCM group were killed at 10-12 weeks and those of the second PCM group were rehabilitated and killed together with the second control group at 20-22 weeks. The animals with PCM demonstrated irritability, muscular wasting, weight loss and reduced physical activity. The electromyographic findings showed a myopathic pattern revealed by significant reduction in motor unit potential duration and amplitude, and amplitude of interference pattern at maximum effort. The histopathological abnormalities were non-specific and consisted of rare obliterations of cross striations and streaming fibrillar appearance, mild increase in epimysial and perimysial tissue and 29-34% reduction in fibre size. A statistically significant reduction in motor nerve conduction velocity of median, ulnar, common peroneal and tibial nerves was found. The muscle Na and K were evaluated in all groups of animals. Muscle K content was reduced and Na concentration was augmented following PCM. The change in concentration of electrolytes within the fibres and reduction in the diameter of muscle fibres could be related to the observed functional alterations. These changes returned to normal in rehabilitated group.

Effects of reduced left ventricular mass on chamber architecture, load, and function: a study of anorexia nervosa

We investigated the effects of reduction in left ventricular mass on cavity geometry, afterload, pump function, and exercise performance in 17 patients with anorexia nervosa and in 10 age-and sex-matched normal subjects. Left ventricular mass index determined by two-dimensional echo-cardiography was significantly lower than that in normal subjects (53 +/- 15 vs 79 +/- 18 g/m2; p less than .005). Left ventricular end-diastolic and end-systolic volume indexes were also reduced in patients with anorexia nervosa compared with normal subjects (49 +/- 11 vs 65 +/- 17 ml/m2, p less than .005; 14 +/- 5 vs 19 +/- 4 ml/m2, p less than .025). In spite of the reductions in left ventricular mass and volume indexes, left ventricular chamber architecture described as h/R ratio, mass to volume ratio, and short/long left ventricular axis ratio were normal. Left ventricular afterload assessed as end-systolic meridional and circumferential wall stress was normal (59 +/- 18 vs 79 +/- 19 dyne/cm2 X 10(3) and 170 +/- 26 vs 167 +/- 23 dyne/cm2 X 10(3)). Ejection fraction, percent fractional shortening, and the relationship between end-systolic wall stress and ejection fraction were all within normal limits. In seven patients restudied after a 15% to 20% weight gain, left ventricular mass and volume indexes increased significantly but end-systolic wall stress and ejection fraction did not change. Ten patients with anorexia nervosa and resting heart rates and systolic blood pressures significantly lower than control values underwent treadmill testing. Exercise duration, peak heart rate, peak systolic blood pressure, and peak oxygen consumption in these patients were all significantly lower than normal. The hypotensive effect of fasting resulted in an initial decrease in afterload, which was the stimulus for reduction in left ventricular mass. The left ventricular remodeling associated with the mass reduction occurred in such a way that (1) orthogonal, meridional, and circumferential wall stresses were normalized, (2) normal chamber shape and architecture were maintained, and (3) chamber function and stress-shortening relationships were preserved. Thus down-regulation of left ventricular mass per se, like up-regulation of left ventricular mass, is not associated with abnormal left ventricular function.

Diuretic-induced hypokalemia

Diuretic therapy is the most common cause of potassium deficiency. Although the extent of potassium deficiency usually does not exceed 200 or 300 mEq, under appropriate circumstances such modest deficiency may have important consequences. Factors that tend to increase the incidence or severity of potassium deficiency in patients who take diuretics include high salt diets, large urine volumes, metabolic alkalosis, increased aldosterone production, and the simultaneous use of two diuretics that act on different sites in the renal tubule. There are many serious complications of potassium deficiency, including cardiac arrhythmias, muscle weakness, rhabdomyolysis, glucose intolerance, and several complications that result directly from increased ammonia production, such as protein and nitrogen wasting and hepatic coma. Emphasized herein are those conditions that impose potential danger in patients with mild hypokalemia. Important factors that identify specific causes of potassium deficiency and its treatment are discussed briefly.

Myocardial inotropic responses and adrenoceptors in protein-deficient rats

Inotropic effects of isoprenaline, phenylephrine and calcium were studied in left atria of 5 weeks old rats fed a low (5%) or a normal (21%) protein diet for 3 weeks. Rats maintained on a low (5%) protein diet consume about half the amount of food eaten by the same rats maintained on a normal (21%) protein diet and thus suffer from protein-calorie malnutrition (PCM). Body weight did not increase in PCM, but heart weight adjusted to body weight was slightly increased compared to normal rats. Atrial resting tension and peak developed tension in response to isoprenaline, phenylephrine or calcium were not diminished by PCM. The number of alpha and beta-adrenoceptors and the receptor affinity in ventricular membranes were not reduced by PCM.

Muscle changes in protein-deprived young rats. A morphometrical, histochemical and ultrastructural study

Rats were reared on a standard diet up to the age of 6 weeks when they were divided into two groups. One was fed on a diet containing 14% protein and the other on a diet with only 1.5% protein. The size of the various fibre types of the EDL muscle of both groups was assessed at 6 and 25 weeks of age. All the fibre types of protein-deprived rats were smaller compared to the age-matched controls, the difference being most evident in the 2B fibres. In the protein-deprived rats the 2B fibres atrophied while the type 1 and type 2A fibres simply failed to grow. Histochemical and ultrastructural examination revealed a marked reduction of the subsarcolemmal mitochondria after prolonged protein deprivation; normally large accumulations of mitochondria are seen preferentially in type 2A fibres.

Chronic tubulointerstitial nephritis and wasting disease in marmosets (Callithrix jacchus)

Six marmosets (Callithrix jacchus), 20 months to 16 years old, died from a disease characterized by weakness and paralysis of the hind legs, weight lose, anemia and transient diarrhea. The lesions most prominent at necropsy were subacute to chronic tubulointerstitial nephritis, subacute to chronic pancreatitis, and generalized hemosiderosis. Chronic protein deficiency is believed to be the underlying pathogenic mechanism, since the diet contained no more than 15% animal protein during the last two years, and increasing the amount of protein was accompanied by disappearance of the syndrome.

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.

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

Experimental protein-calorie malnutrition was produced in rats by giving them a low-protein diet for 6 weeks. Control animals were fed a high-protein diet. The deficient rats showed severe restriction of body weight gain, fatty liver and hypoproteinaemia. In addition the present study demonstrates that the experimentally induced protein-calorie malnutrition brings about marked pathological changes and increased catecholamine levels in the hearts of rats. Based on this demonstration, and considering the synchronism of morphological and biochemical data, we postulate that the nutritional stress to the heart raises the myocardium noradrenaline concentration and the continued exposure to high levels of catecholamines may play a role in the development of cardiac changes in protein-energy malnutrition.

Conducting tissue of the heart in kwashiorkor

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