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Effect of Dietary Protein and Magnesium on Selected ATP Phosphotransferases and Neuromuscular Behavior in Young Rats¹

Department of Pediatrics and Department of Biochemistry, St. Louis University School of Medicine, 1402 South Grand Boulevard, St. Louis, Missouri 63104

Weanling rats fed purified diets containing 0.5, 18, or 36% protein and 0, 5, or 200 mg of magnesium per 100 g diet were studied particularly in regard to neuromuscular behavior, growth, and activity of four magnesium-dependent ATP phosphotransferases. Rats fed diets limited only in magnesium (5 mg/100 g) had reduced food intake and growth and developed late edema and electrocardiogram changes. When rats were fed a diet designed to produce a state of malnutrition similar to proteincalorie malnutrition of childhood (0.5% protein, 5 mg magnesium/100 g, and 44% lactose), the plasma protein and magnesium values fell to about 50% of control values. When these malnourished animals were refed 36% protein with no added magnesium, they developed intense erythema, profound spiking of the T waves in the electrocardiogram, and 80% of them convulsed and died within 10 days; their plasma protein values had increased to 75% of control values, plasma magnesium had decreased to 20% of control values, and muscle and liver magnesium had decreased slightly. Similar malnourished rats refed 36% protein with 200 mg magnesium/100 g were clinically indistinguishable from control rats by day 60. Changes in enzyme activity appeared to be related to dietary carbohydrate, but could not be related to magnesium deficiency. Control rats fed purified diet had higher hexokinase, glucokinase, and pyruvate kinase activity than rats fed laboratory ration. Rats fed 0.5% protein and 88% sugar usually had decreased enzyme values per milligram tissue that increased when expressed per milligram soluble protein. These rats had increased muscle hexokinase values.

KEY WORDS: • weanling rats • neuromuscular behavior • growth • magnesium deficiency • protein-calorie malnutrition • electrocardiogram • ATP phosphotransferases

¹ This investigation was supported in part by USPHS grant-in-aid AM11044 and AM16219-01, from the National Institute of Arthritis and Metabolic Diseases, Dr. Caddell was a trainee of the National Heart and Lung Institute, supported by grant HE-5672.

Manuscript received 2 October 1972.

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				J. L. Caddell Magnesium in the Nutrition of the Child Clinical Pediatrics, March 1, 1974; 13(3): 263 - 272. [PDF]