BIOCHEMICAL ASPECT OF DIMETHYL SULFIDE BREATH TEST IN THE STUDIES ON METHIONINE METABOLISM

Abstract

Dimethyl sulfide concentration in expired alveolar gas (alv-DMS) was determined following oral or i.v. administration of DL-, L- or D-methionine in healthy volunteers. Fasting level of alv-DMS was 1.9 .+-. 1.3 ng/dl (mean .+-. SD) in all 38 experimental subjects. Following ingestion of 2.0 g of DL-methionine, alv-DMS increased to a peak of 37.1 .+-. 21.7 ng/dl. Following administration of 1.0 g of D-methionine, the peak values of alv-DMS were 66.0 .+-. 42.1 ng/dl (mean .+-. SD) (orally) and 60.0 .+-. 19.9 ng/dl (i.v.). In contrast, 2.0 g of L-methionine administration caused a small increase in alv-DMS; 4.6 .+-. 2.6 ng/dl (orally) and 4.2 .+-. 2.1 ng/dl (i.v.). The increase in alv-DMS following administration of methionine is apparently related to D-methionine metabolism. The threshold level for DMS exhalation in normal subjects was between 0.5-1.0 g for the D-isomer and more than 2.0 g for the L-isomer of methionine. Since the behavior of methyl mercaptan in expired alveolar gas (alv-MM) was different from and disproportionate to that of alv-DMS, the increase in alv-DMS following D-methionine administration seemed to be caused by the mechanisms other than MM formation.