Effects of Ingestion of High Protein or Excess Methionine Diets by Rats for Two Years

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Abstract
Eighteen male Wistar rats weighing 230 g (9 wk old) were fed casein diets containing 10% protein (HC), 50% protein (HP) or 10% protein plus 2% DL-methionine (MET) for 2 yr. In HC rats, mean body weight was 570 g; the carcass contained 13.5% protein and 37% lipid. The HP-fed rats had a 100 g lower body weight than HC rats due solely to a smaller amount of body lipid. Liver urea concentration and kidney weight were higher in HP rats than in HC rats. The body weight of MET-fed rats was lower than the other two groups and body lipid was only 30% that of HC rats. Histologic examination showed a normal aspect of the thoracic aorta from HC rats, whereas in HP, moderate signs of vascular aging—thicker intima and media with hypertrophy of smooth muscular cells (smc) with collagen enrichment and diffuse fibrosis—were observed. Aortas from MET rats also exhibited thicker intima and media due to smc hypertrophy. Some smc presented degenerative aspects and necrosis; other smc were replaced by chondrold cells and foci of fibrosis, resulting in a loss of the distension capacity of the aorta. Such an advanced stage of vascular aging is not normally found in 2-yr-old rats.