KINETICS OF PLASMA HOMOCYSTEINE IN HEALTHY-SUBJECTS AFTER PERORAL HOMOCYSTEINE LOADING

The kinetics of plasma homocysteine were determined in 13 healthy subj ects after peroral administration and in one person after intravenous injection. Various forms of homocysteine completely dissolved in an aq ueous solution were rapidly absorbed after peroral administration, and the bioavailability was estimated to be 0.53. The volume of distribut ion was 0.66 L/kg. The area under the plasma concentration curve (AUC0 -48 h) was proportional to the administered dose (33.5-134 mumol/kg bo dy wt), and showed small interindividual variations. Plasma homocystei ne showed first-order elimination kinetics for at least 6 h. The half- life (t1/2) was 223 +/- 45 min, and there was a significant correlatio n between t1/2 values determined on two different occasions in the sam e individual. The transient hyperhomocysteinemia was associated with a n increase in plasma methionine, which probably reflects intracellular remethylation of homocysteine. Less than 2% of the administered homoc ysteine dose was recovered in the urine. These findings may form the b asis for future studies on the regulation of plasma homocysteine in he alth and disease, and should motivate the evaluation of a homocysteine loading test as a diagnostic tool.