Gluconeogenesis from L-cysteine in the perfused rat liver

The effects of dietary and hormonal treatments on the rate of gluconeogenesis from L-cysteine have been investigated in the perfused rat liver in situ. In order to demonstrate gluconeogenesis from L-cysteine, rats were fed either a 90% casein diet, or this diet with 2 or 4% cysteine, added in place of casein, and perfused in the fed state; or fed stock diet and starved 48 or 72 hours; or fasted and injected with cortisol. The net rate of gluconeogenesis (in mumoles/min/g liver) from cysteine in rats fed 4%cysteine was 0.24; in 48-hour starved rats it was 0.10; in 72-hour starved rats it was 0.16; and in the cortisol injected rats it was 0.23. When [U-14C]cysteine plus carrier cysteine (10 mM) was added as the substrate for gluconeogenesis in 72-hour starved rats; 3.9% of the label appeared in glucose. The above dietary and hormonal treatments stimulated gluconeogenesis from L-cysteine.