Date of Award

8-1970

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nutrition

Major Professor

John T. Smith

Committee Members

Frances A. Schofield, Mary Rose Gram, Bernadine Meyer

Abstract

The relationship of dietary sulfate to the efficiency of feed utilization, excretion of 35S-cysteine sulfur as 35S-taurine sulfur, and sulfation of lung tissue by the rat was investigated.

The feed efficiencies of animals fed diets from weaning that contained 0.10 per cent of inorganic sulfate and 0.47 per cent of organic sulfur as sulfate were significantly higher at the end of a six-week feeding period than were those of littermates fed diets that contained higher or lower levels of inorganic sulfate but comparable levels of total sulfur as sulfate. These findings showed that equivalent levels of sulfur as sulfate supplied by amino acids did not compensate for the omission of sulfate from the diet of the rat.

Results of a subsequent experiment revealed that the excretion of 35S-cysteine sulfur as 35S-taurine at the end of a 17-day feeding period was 58 and 82 per cent lower, respectively, among adult rats fed normal and high levels of inorganic sulfate than among those fed low levels of inorganic sulfate in diets that contained equal levels of total sulfur as sulfate. Reductions of 50 and 45 per cent, respectively, from the level of 35S-taurine excreted by the animals fed the low sulfate diet were observed when normal and high levels of sulfate were fed in diets that contained equal levels of 35S-cysteine.

When 18 groups of rats were fed different levels of inorganic sulfate in diets supplemented with 0.40 per cent of cysteine, differences could be detected neither in 35S-cysteine sulfur as 35S-taurine sulfur excreted in the urine nor in the total sulfur as sulfate in the lungs at the end of the six-week feeding period.

After the experimental diets had been consumed for one week, the excretion of 35S-cysteine sulfur as 35S-taurine sulfur was significantly higher among weaning rats fed a low sulfate diet than among those fed a normal sulfate diet that contained the same level of cysteine, but no differences could be detected by the end of week 2. Adult rats fed the low sulfate diet excreted significantly higher levels of 35S-cysteine sulfur as 35S-taurine sulfur at the end of weeks 1 and 2 of the study than did the animals fed the normal sulfate diet, but not at the end of week 3.

Dietary adaptation, which results in reduction in the excretion of 35S-cysteine sulfur as 35S-taurine sulfur to the level excreted by the animal fed the normal sulfate diet, occurs when low sulfate diets are fed to rats for extended periods. The initial rise in cysteine sulfur as taurine sulfur in the urine illustrates an inefficiency in the oxidation of amino acid sulfur to sulfate. The significance of the adaptation to the low sulfate diet, demonstrated by decreased 35S-taurine excretion, as a means of conserving the sulfur-containing amino acids is not revealed by the present findings.

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