Conditions altering plasma concentrations of urea cycle and other amino acids in elderly human subjects

Describe plasma amino acid concentrations and total urinary amino acid excretion in subjects from an elderly female population.

Fasting plasma samples, complete 24-hour urine samples, and 3-day diet records were obtained from 96 healthy postmenopausal women in one study and fasting plasma samples were obtained from an additional 44 subjects in 3 separate studies. In one study, nonfasting plasma samples were also collected. The subjects ranged in age from 49 to 80 years of age. Samples were obtained to allow the evaluation of the effects of fasting vs. nonfasting, normal vs. Alzheimers subjects, and level of protein intake effects.

Heparinized plasma samples were deproteinized with a 5-sulfosalicylic acid solution and centrifuged at 14,900 x g. Deproteinized plasma and urine samples were analyzed for free amino acids on a Beckman System 6300 analyzer using a postcolumn reaction with ninhydrin to quantitate the amino acids.

It is concluded that: 1) From fasting plasma samples, 1 or 2 sampling days are sufficient to establish a characteristic concentration for most plasma amino acids. 2) Fasting amino acid concentrations do not reflect levels of dietary protein intake when dietary amino acid composition is similar. Shifts in fasting amino acid concentrations would be more indicative of changes in relative amounts of amino acids absorbed rather than level of dietary protein per se. 3) Totals of fasting plasma concentrations of arginine, citrulline and ornithine were relatively constant, but fluctuations occurred in the ratio of ornithine to arginine in the different populations; and 4) Patients with Alzheimers disease exhibited altered plasma ornithine and arginine concentrations relative to active or sedentary controls.