GROWTH AND METABOLISM OF FETAL AND MATERNAL MUSCLES OF ADOLESCENT SHEEP ON ADEQUATE OR HIGH FEED INTAKES - POSSIBLE ROLE OF PROTEIN-KINASE-C-ALPHA IN FETAL MUSCLE GROWTH

From days 4-104 of pregnancy, adolescent sheep, weighing 43.7 (SE 0.87 ) kg were offered a complete diet at two different intakes (approximat ely 5 or 15 kg/week) designed to meet slightly, or well above, materna l maintenance requirements. The fetal and maternal muscles were taken on day 104 of pregnancy and analysed for total DNA, RNA and protein. E wes offered a high intake to promote rapid maternal weight gain, weigh ed more (76.5 (SE 4.5) v. 50.0 (SE 1.7)kg) and had muscles with a grea ter fresh weight, whilst their fetuses had smaller muscles, than those fed at a lower intake. Plantaris muscle of the ewes fed at the high i ntake contained more RNA and protein; again the opposite situation was found in the fetal muscle. On the higher maternal intakes, the DNA, R NA and protein contents of the fetal plantaris muscle were less than i n fetuses of ewes fed at the lower intake. To investigate the possible mechanisms involved in this decrease in fetal muscle mass, cytosolic and membrane-associated muscle proteins were subjected to Western immu noblotting with antibodies to nine isoforms of protein kinase C (PKC), a family of enzymes known to play an important role in cell growth. F ive PKC isoforms (alpha, epsilon, theta, mu and zeta) were identified in fetal muscle. One of these, PKC-alpha, was located predominantly in the cytosolic compartment in the smaller fetuses of the ewes fed at a high plane of nutrition, but was present to a greater extent in the m embranes of the more rapidly growing fetuses of the ewes fed at the lo wer intake. This was the only isoform to demonstrate nutritionally rel ated changes in its subcellular compartmentation suggesting that it ma y mediate some aspects of the change in fetal growth rate.