Urinary 3-methylthiopropionate excretion and the effect of D- or L-methionine ingestion studied in healthy subjects.
After overnight fasting, the urinary concentrations of 3-methylthiopropionate in 23 healthy male subjects aged from 17 to 72 were studied by gas chromatography and flame photometry. The urinary 3-methylthiopropionate concentrations after fasting showed an approximately normal distribution in the logarithmic scale (M +/- SD = 0.953 +/- 0.394): 10M = 8.97, 10M-SD = 3.62 and 10M + SD = 22.23 ng/mg Creatinine. In 6 volunteers, a 2g D- or L-methionine loading test was also performed. Following D-methionine ingestion, urinary 3-methylthiopropionate concentrations over a 1-hour period increased 22- to 95-fold above those of the pre- loading values and then decreased in an approximately linear manner on semilogarithmic graph paper during a further 2- or 3-hour observation period, after which the examination ended. The mean amount of 3-methylthiopropionate excreted in the urine 3 hrs after loading was 147.7 micrograms (n = 6). Following L-methionine ingestion, by contrast, the increases in 3-methylthiopropionate concentrations over a 1-hr period were 0.3- to 8.3-fold above those of the preloading values. The mean urinary excretion of 3-methylthiopropionate 3 hrs after loading was 3.58 micrograms (n = 4). Because of the simple and specific analytical procedure, quantitative determination of urinary 3-methylthiopropionate is useful in the study of human methionine metabolism.