W. A. Landmann

Suboptimal intake of magnesium in rats. Effects during growth and gestation

Abstract To investigate the interaction of magnesium depletion and source of protein and the effect of this interaction on growth, female weanling Sprague-Dawley rats were fed diets based on 20% casein or 20% soy protein isolate which contained eithe adequate (800 mg/kg) or suboptimal (200 mg/kg) levels of magnesium. The initial suboptimal level of approximately 100 mg/kg magnesium was increased to approximately 200 mg/kg magnesium on day 6 of the study. The nutritional stress of rapid growth resulted in clinical signs of deficiency including audiogenic seizures in the animals fed the casein diet which was low in magnesium. Some clinical manifestations of deficiency persisted through almost all of the 6-week growth period. The lower nutritional quality of soy protein isolate and/or the components of soy which depress mineral bioavailability resulted in a higher rate of alopecia and skin sores in the rats fed the soy low magnesium diet than in those fed the casein low magnesium one. Growth retardation in the magnesium deficient animals occurred during the post-weaning growth phase. Gestational weight gain was also depressed by low magnesium intake to a greater extent than has been previously reported in response to a mild magnesium restriction. Because of recent reports of suboptimal intakes of magnesium by humans, further research of combined effects of subacute magnesium deficiency and utilization of foods containing soy protein is needed.

Influence of magnesium deficiency and soy protein on magnesium and zinc status in rats

Abstract Female weanling Sprague-Dawley rats were fed casein or soy protein isolate based diets containing approximately 800 or 200 mg Mg/kg diet. Magnesium deficiency was reflected in reduced femur, carcass and plasma magnesium but not in hepatic concentration. Zinc concentration in bone was decreased in magnesium deficient animals. Plasma alkaline phosphatase and hemoglobin were depressed by magnesium deficiency. The enzyme levels were lowest in rats fed soy protein. The adverse effects on magnesium and zinc status were more pronounced than had previously been reported in response to mild magnesium deficiency for a shorter period of time.

Parturition and pregnancy outcome in rats as influenced by marginal intake of magnesium

Abstract Female Sprague-Dawley rats were fed 20% casein or 20% soy protein isolate diets which contained either adequate (800 mg/kg) or suboptimal (200 mg/kg) levels of magnesium from weaning through gestation. Reproductive performance was adversely affected by suboptimal magnesium levels and by consumption of soy protein. Number of implantation sites and number of live births were reduced in the low magnesium casein-based diet group. Neonatal mortality was highest in the low magnesium soy-based diet litters, perhaps because of additional nutrient deficiencies from use of soy protein. Intrauterine growth retardation occurred in both magnesium deficient groups. The length and difficulty of parturition and retention of conceptus in the postpartum uterus was increased for magnesium deficient groups. Nitrogen, fat, magnesium and zinc concentrations of pups were decreased in response to suboptimal magnesium intake. These effects were more pronounced than those which had been reported when a suboptimal magnesium level was fed only during breeding and/or gestation.

Urinary 3-methylhistidine as an index of dietary protein adequacy in the adult rat: Short term testing

Abstract Urinary excretion of 3-methylhistidine (3-MH) was evaluated as an indicator of dietary protein quality using adult rats with shortterm feeding. The effect of protein depletion and repletion on excretion of 3-MH was also studied. Four groups of 6 rats weighing between 250 and 300 grams were fed diets containing 10% protein from casein, wheat gluten, blood globin, or a complementary mixture of wheat gluten and globin. Daily variations of weight, 3-MH and creatinine, as well as 6-day means were observed. The correlation of PER with the 6-day means of urinary 3-MH was not high. Body weight changes and fractional rates of synthesis (based on estimated myofibrillar 3-MH pool size) appeared to be highly correlated to PER and sensitive to the influence of dietary protein and calorie deficiencies on body protein metabolism. 3-MH excretion, then, when used to determine fractional rates of catabolism and synthesis of myofibrillar protein, could be useful in short-term protein evaluation using adult rats.