Changes in activities of urea cycle enzymes in early stages of liver regeneration after partial hepatectomy in rats.

The activities of urea cycle enzymes were measured during the first 24 hours of regeneration after partial hepatectomy. In animals fed normal rat chow (22% protein), there was an initial 40-60% decrease in the specific activities of all urea cycle enzymes, to reach a low point 4 hours after the operation. Thereafter, the specific activities increased again, approximating zero time values by 24 hours after partial hepatectomy. In this and all subsequent experiments all urea cycle enzymes responded in a very similar fashion. On diets containing 0% or 10% protein, the drop was delayed for approximately 12 hours; during this time, the specific activities were above zero time values. The minimum level was reached at about 18 hours, with a return to normal or above at 24 hours. On a diet containing 75% protein, there was an initial decrease to a low level at 4 hours, followed by a more pronounced increase, with a peak above zero time levels at 12 hours.