Some enzyme patterns of Morris hepatoma 9618A under controlled feeding schedules.

The growth rate of Morris hepatoma 9618A showed marked variation in 130 rats under different controlled feeding conditions, and a highly significant decrease in the growth rate was observed in rats adapted to a schedule of 8 hours feeding in each 48-hour cycle, compared to a schedule of 8 hours feeding in each 24-hour cycle. Low levels of tyrosine-a-ketoglutarate transaminase and serine dehydratase activities in the hepatomas were not changed by such dietary manipulations. On the other hand, glucose-6phosphate dehydrogenase activity of the hepatomas was maintained at a 10to 20-fold higher level than in the host liver; in addition, this enzyme activity exhibited a somewhat different pattern between the 3rd and 4th transplantation generations and was significantly increased in rats adapted to a schedule of 8 hours feeding in each 48-hour cycle. The activities of malic enzyme and tryptophan pyrrolase in the hepatomas were not affected by feeding schedules but were much higher in the former and much lower in the latter than in the host livers. The activity of citrate cleavage enzyme did not vary with diet in the hepatomas although the activity of this enzyme responded to diet in the host livers. Glycogen levels in hepatomas were higher than those in the host liver from rats which were killed at late fasting periods in controlled feeding schedules. Slightly decreased levels of glycogen were observed in hepatomas in the fourth generation compared with the levels in the previous generation. The results clearly indicate the difficulties inherent in attempting to correlate enzyme activities with growth rate in a slowly growing highly differentiated Morris hepatoma. It is