Stimulus of leucine incorporation into perfused liver protein by insulin

Livers from 24-hr fasting sham-operated or partially pancreatectomized rats were perfused at 38 C with heparinized blood from normal 24-hr fasting rats. Leucine-1-C14, 1.6 x 105 counts/min per ml, and glucose to make the initial total concentration 2 mg/ml were added to the blood. Incorporation of leucine-1-C14 into protein proceeded linearly for 2 hr, then at a decreased rate. The leucine-1-C14 incorporated into protein over the initial 2-hr perfusion period decreased progressively as the time after partial pancreatectomy of the liver donors increased, up to 6 months. Insulin, 0.01 unit/ml, added to the perfusing blood stimulated leucine incorporation into protein of livers from rats partially pancreatectomized 3 months before (mean terminal blood sugar 160 mg/100 ml) but not into that of livers from the 6-month series (mean terminal blood sugar 315 mg/100 ml). No significant effect of insulin was obtained in any of the sham-operated groups. It is concluded that insulin added in vitro can stimulate incorporation of leucine into protein in livers from mildly diabetic, but not severely diabetic, rats.