Effects of temperature and diets on magnesium, calcium and potassium metabolism in sheep and rats

Several biological and environmental interactions appear to be involved in the etiology of hypomagnesemic tetany. Effects of ambient temperature and diet on magnesium status of six ewe lambs and 72 adult male rats were studied in this investigation. Percentage absorption and fecal endogenous magnesium excretion were higher and urinary magnesium was lower in sheep fed a low magnesium diet than those fed normal magnesium diets. Effects of low dietary magnesium on fecal endogenous and urinary magnesium were increased by cold. Magnesium absorption was elevated by high dietary protein in sheep fed low magnesium, especially in cold, but with low magnesium intake, total radiomagnesium excretion by sheep fed the high protein level was 80% higher than when normal protein was fed. In general, magnesium concentrations in bone epiphysis, heart, muscle, liver, spleen, and certain other tissues were higher in cold exposed sheep than in those at room temperature. Tissue turnover rate of magnesium in sheep was higher in cardiac muscle and lower in skeletal muscle. Feed efficiency was decreased and feed consumption increased (P<.001) in rats by cold exposure. Total magnesium excretion by rats was increased by cold except when certain high potassium diets were fed but high potassium alone increased urinary magnesium. Urinary magnesium was also increased by high dietary iodine. High dietary protein appeared to counteract high magnesium excretion. Rats fed diets high in both potassium and protein had lower (P< .05<.001) plasma magnesium levels in cold than at room temperature. Bone magnesium levels were reduced (P<.05<.01) by high dietary protein, and increased by cold exposure in rats fed the low iodine control diet. Cold exposure also increased magnesium deposition in liver (P<.01) and heart (P<.05) but did not change skeletal muscle magnesium levels of rats.