Effects of diet and selected hormones on the activities of hepatic malic enzyme and glucose-6-phosphate dehydrogenase in infant, prematurely weaned rats.

Male Sprague-Dawley rats were weaned on postnatal d 17 to isocaloric diets in which fat supplied either 10% (PWC group) or 65% (PWF group) of the available energy. Compared with animals left with the dams to be weaned spontaneously to the maternal low fat diet (SWC group), the PWC rats showed early increases in the activities of liver glucose-6-phosphate dehydrogenase (G-6-PD) and malic enzyme (ME). The activity of G-6-PD was diminished in the PWF group, but the early rise in liver ME activity attendant on premature weaning was not prevented. Premature weaning, regardless of diet, decreased plasma glucagon levels within 1 d. Hydrocortisone failed to evoke hepatic ME activity in SWC rats; similarly, corticosterone and insulin, separately or together, did not affect ME activity in SWC rats. However, triiodothyronine evoked hepatic ME appearance within 1 d. Glucagon suppressed the expected rise in hepatic ME activity in PWC rats; in contrast, injection of glucagon antiserum into SWC rats led to the appearance of liver ME within 2 d. The data indicated that interaction among diet, glucagon and thyroid hormones may be part of the mechanism regulating the first appearance of ME in rat liver.