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This study examines the effect of a low sulfur amino acid diet (LTD) and a high taurine diet (HTD), compared with a normal diet, on the plasma, urine, muscle, brain and renal cortex levels of taurine in immature and adult rats. Milk taurine from lactating dams reflected the taurine content of the diet, being low in LTD-fed and high in HTD-fed animals. Nursing pups (7, 14 and 21 d old) often had plasma, urine and tissue--renal cortex, heart, skeletal muscle--levels of taurine related to dietary exposure, a situation also found in adult animals. These diets did not influence the urinary excretion of the sulfur-containing alpha-amino acids methionine and cystine but a sulfur aminoaciduria of immaturity was evident. By contrast, the content of taurine in brain was constant regardless of dietary intake of sulfur amino acids. An age-related decline in brain taurine content was found--as noted by others--but this too was influenced by diet. This dual finding of brain taurine constancy despite wide differences in sulfur amino acid intake and changes in the renal handling of taurine as influenced by diet suggest that the renal adaptive response serves to maintain the stability of brain taurine content.

The relative contributions have been determined of taurine derived from the mother in utero, via milk during nursing, and from endogenous biosynthesis to the total taurine content of the rat pup between birth and weaning. At birth, 32% of the taurine in the pup has been biosynthesized, and this proportion rises to 83% by day 20 of life. At birth, 67% has been derived from the mother in utero, and by day 20 this has fallen to 4% of the total. This maternal taurine is lost with a half-life of 16 days. There is wide variation in the turnover from different tissues, the pancreas having a half-life of 7 days, and the brain 50 days. However, the amount of maternal taurine in the brain actually increases by 38% over the first 8 days of life. By day 20, 13% of the taurine content of the pup has been obtained from the milk. Taurine turnover in the suckling pup differs from turnover after weaning in that whole-body turnover from the suckling rat is not slower than exchange between organs. In other words, tissues are not in kinetic equilibrium. After animals are weaned, regardless of the taurine content of the diet, taurine is interchanged between organs faster than it is excreted from the animal.

The quantitative importance of diet versus biosynthesis as sources of taurine has been established in mice receiving dietary levels of 0.062% [3H]taurine and 0.74% [35S]methionine as sole sulfur-containing amino acids. After 15 days on diets radiolabeled with these levels of taurine and methionine, 16% of total-body taurine had been derived from diet and 24% from biosynthesis. By 30 days, these contributions had risen to 29% and 33%, respectively, and by 61 days to 46%. The half-life of turnover of taurine in the mouse was 18.6 days. These findings indicate that, like the rat and guinea pig, but unlike the cat and human, the mouse exhibits considerable biosynthetic capacity for taurine.

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