The Influence of Glucose on Amino Acid Carbon Incorporation into Proteins, Fatty Acids, and Carbon Dioxide by Lactating Rat Mammary Gland Slices.

It has been shown that the capacity of epididymal fat pads (l), diaphragm (2, 3), and liver slices (2) to incorporate amino acid carbon into proteins is lower when those tissues are excised from unfed rather than from fed rats. The addition of glucose to the incubation media containing those tissues from unfed rats increases the incorporation to about the level observed when the same tissues are obtained from fed rats (l-3). The stimulating effect of glucose has also been observed in experiments with epididymal fat pads (1) and heart slices (4) from nonfasted rats, but here the effects were less pronounced than those with the tissues from fasted rats (1). This latter finding suggests that tissues with low glycogen content are best suited for studying the influence of glucose on amino acid incorporation into protein. Since the glycogen content of the lactating rat mammary gland is quite low (5), and since this gland is a very active site for protein synthesis, we chose it for the study of the interrelation between carbohydrate and amino acid metabolism. Lactating mammary gland slices have a high capacity for fatty acid synthesis. Previous work, from this (6-9) and other laboratories (lo), has shown that the addition of glucose to the incubation medium has a pronounced stimulatory effect on fatty acid synthesis from acetate, pyruvate, lactate, and propionate. It was of interest, therefore, to determine whether such an effect could be demonstrated on the conversion of amino acids into lipids by this gland.