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Pteroylglutamic Acid Balance Studies on Monkeys¹

Two Figures

Department of Biochemistry, School of Medicine, University of Arkansas, Little Rock

Young rhesus monkeys were given a diet known to produce the anemia, leukopenia, and other manifestations of pteroylglutamic acid (PGA) deficiency. Daily urine and fecal collections were made and these excreta assayed for PGA, using Streptococcus faecalis. Suitable conjugase preparations were employed in the fecal analyses. Each experimental period lasted 21 days or longer.

The following daily additions were made to the diets of such animals, under suitably controlled conditions: 100 µg of synthetic PGA (which is the approximate minimum daily requirement); 100 µg of synthetic pteroic acid; 2.5 gm of yeast extract, containing approximately 100 µg of PGA, largely in the form of the conjugate. The average daily urinary and fecal PGA excretions of these monkeys, when expressed on a body weight basis, were not significantly different from the excretions of a control monkey receiving the deficient diet only. In this series the average daily urinary outputs were approximately 1 µg, and the average fecal outputs were between 8 and 10 µg, expressed in terms of synthetic PGA per kilogram of body weight. These may be considered "basal" levels of excretion.

It is concluded that neither synthetic PGA, synthetic pteroic acid, nor crude yeast PGA conjugate, when fed at the 100 µg level, pass through the intestinal tract of the young rhesus monkey unchanged.

Increasing the daily intake of synthetic PGA to 1000 µg resulted in a three-fold increase in urinary and fecal output over the "basal" level. Notwithstanding, the actual urinary increase was only about 1% of the oral dose and the fecal increase much less than 1% of the dose. Obviously, even at high levels of intake, synthetic PGA does not, to any significant extent, pass through the intestinal tract of the monkey unchanged.

The low percentage urinary return of large daily oral doses of synthetic PGA by the monkey is in sharp contrast to the response of the normal adult human, who excretes 30–50% of a 5 mg oral dose within 24 hours.

Manuscript received 26 July 1948.