S-Adenosylmethionine (AdoMet) is an important biologic methylating agent for nucleic acids, phospholipids, biologic amines, and proteins. Previous studies indicated that hepatic AdoMet synthetase and hepatic levels of AdoMet are subnormal in patients with alcoholic cirrhosis. This abnormality limits the patients' capacity to convert phosphatidylethanolamine to phosphatidylcholine by way of phosphatidylethanolamine-N-methyltransferase (PEMT). Because alcoholic consumption appears to be associated with hepatic hypoxia, we previously measured AdoMet concentration in liver cells under acute hypoxia and found the level to be decreased substantially. In the present study, we determined whether a similar metabolic abnormality was also observed in rats maintained under physiologic hypoxia for 9 days and administered standard rat chow. The study showed that AdoMet levels in hypoxic rat (ave +/- SD) were significantly lower than those in the control (36.8 +/- 11.6 vs. 60.4 +/- 2.3 nmol/g liver; P < 0.05). Also significantly lower in the hypoxic group were the activities of AdoMet synthetase (0.60. +/- 0.07 vs. 0.97 +/- 0.20 U; P < 0.05) and PEMT (26.2 +/- 4.2 vs. 35.6 +/- 5.8 U; P < 0.02). The mRNA levels of AdoMet synthetase also declined in hypoxia indicating that hypoxia may modulate the gene expression of hepatic AdoMet synthetase. Thus, in vivo hypoxia may have an important effect on 1-carbon metabolism.