Short-term dietary regulation of lipogenesis in the lactating mammary gland of the rat.

Short-term (6 hr) withdrawal of chow diet from lactating rats decreases the rate of lipogenesis in mammary gland by 87%. This inhibition is in part explained by a 60% decrease in the extraction of glucose (the major lipogenic precursor) by the mammary tissue. These changes are not accompanied by any significant alteration in the arterial concentrations of glucose, lactate or insulin; the concentration of acetoacetate did increase by about 30%. Removal of food for 6 hr did not alter the activation state of acetyl-CoA carboxylase or the total activity of the enzyme. Glucose utilization by mammary gland acini from short-term starved rats was not depressed although a higher proportion of the glucose appeared as lactate in the medium and consequently less glucose was converted to lipid. Insulin was able to reverse these changes. Glucagon, adrenaline or cAMP did not inhibit glucose utilization or lipogenesis in isolated acini. It is concluded that the inhibition of lipogenesis in mammary gland after short-term withdrawal of food is mainly due to decreased extraction of glucose. The signal for this change does not appear to be an alteration in plasma insulin and it is postulated that there may be an intestinal factor(s) which acts synergistically with insulin.