Role of insulin on the control of postnatal increase in ornithine transcarbamylase activity in rat liver.

Repeatedly supplementing glucose after birth abolishes postnatal increase in ornithine transcarbamylase activity and increases the plasma insulin level. A single administration of actinomycin D does not affect this activity. When glucose and actinomycin D are administered in association at birth or 13 hours after birth, actinomycin D overcomes the inhibitory effect of glucose on ornithine transcarbamylase activity and decreases insulinemia at the level found in normal neonate. Insulin supply 20 hours after birth to neonates, which previously received glucose and actinomycin D, decreases the enzyme activity and increases plasma insulin level. It is concluded that the postnatal increase in ornithine transcarbamylase activity is bound to the normal postnatal decrease in insulinemia. Furthermore, the paradoxical effect of actinomycin D on enzyme activity might be due to an inhibition of insulin synthesis or a decrease in insulin release.