Methionine transsulfuration is increased during sepsis in rats

Methionine transsulfuration in plasma and liver, and plasma methionine and cysteine kinetics were investigated in vivo during the acute phase of sepsi s in rats. Rats were infected with an intravenous injection of live Escheri chia coli, and control pair-fed rats were injected with saline. Two days af ter injection, the rats were infused for 6 h with [S-35] methionine and [N- 15] cysteine. Transsulfuration was measured from the transfer rate of 35S f rom methionine to cysteine. Liver cystathionase activity was also measured. Infection significantly increased (P < 0.05) the contribution of transsulf uration to cysteine flux in both plasma and liver (by 80%) and the contribu tion of transsulfuration to plasma methionine flux (by 133%). Transsulfurat ion measured in plasma was significantly (P < 0.05) higher in infected rats than in pair-fed rats (0.68 and 0.25 mu mol.h(-1).100 g(-1), respectively) . However, liver cystathionase specific activity was decreased by 17% by in fection (P < 0.05). Infection increased methionine flux (16%, P < 0.05) les s than cysteine flux (38%, P < 0.05). Therefore, the plasma cysteine flux w as higher than that predicted from estimates of protein turnover based on m ethionine data, probably because of enhanced glutathione turnover. Taken to gether, these results suggest an increased cysteine requirement in infectio n.