Metabolic adaptations during lactogenesis. Fatty acid synthesis in rabbit mammary tissue during pregnancy and lactation

Abstract

1. Mammary tissue was obtained from rabbits at various stages of pregnancy and lactation and used for tissue-slice incubations (to measure the rate of fatty acid synthesis and CO(2) production) and to determine relevant enzymic activities. A biphasic adaptation in fatty acid synthetic capacity during lactogenesis was noted. 2. The first lactogenic response occurred between day 15 and 24 of pregnancy. Over this period fatty acid synthesis (from acetate) increased 14-fold and the proportions of fatty acids synthesized changed to those characteristic of milk fat (77-86% as C(8:0)+C(10:0) acids). 3. The second lactogenic response occurred post partum as indicated by increased rates of fatty acid synthesis and CO(2) production (from acetate and glucose) and increased enzymic activities. 4. Major increases in enzymic activities between mid-pregnancy and lactation were noted for ATP citrate lyase (EC 4.1.3.8), acetyl-CoA synthetase (EC 6.2.1.1), acetyl-CoA carboxylase (EC 6.4.1.2), fatty acid synthetase, glucose 6-phosphate dehydrogenase (EC 1.1.1.49), and 6-phosphogluconate dehydrogenase (EC 1.1.1.44). Smaller increases in activity occurred with glycerol 3-phosphate dehydrogenase (EC 1.1.1.8) and NADP(+)-isocitrate dehydrogenase (EC 1.1.1.42) and the activity of NADP(+)-malate dehydrogenase (EC 1.1.1.40) was negligible at all periods tested. 5. During pregnancy and lactation there was a close temporal relationship between fatty acid synthetic capacity and the activities of ATP citrate lyase (r=0.94) and acetyl-CoA carboxylase (r=0.90).

Metabolic adaptations during lactogenesis. Lactose synthesis in rabbit mammary tissue during pregnancy and lactation

“…The rabbit mammary gland first acquires the ability to synthesize detectable amounts of lactose (present study) and fatty acids Mellenberger & Bauman, 1974) approximately 9-10 days pre partum. Similarly investigations with Vol.…”

“…Cellular maturation, as indicated by development of the endoplasmicreticulum and Golgi apparatus, is also accelerated between days 19 and 21 of pregnancy (Bousquet et al, 1969). In addition, the rate of synthesis of fatty acids increases at approximately day 21 of pregnancy in rabbit mammary tissue, and the pattern of lipids synthesized changes to that characteristic of rabbit milk lipids Mellenberger & Bauman, 1974).…”

“…Mellenberger & Bauman (1974) have reported that the addition of acetate decreases glucose utilization for fatty acid biosynsynthesis. In the case of lactose synthesis, the addition of acetate to glucose incubations could possibly increase the availability of glucose for lactose synthesis.…”

“…However, there do not appear to have been any investigations with rabbit mammary tissue establishing the temporal relationships between lactose biosynthesis and the activity of relevant enzymes during pregnancy and lactation, although Denamur (1965) has reported the appearance of lactose in rabbit mammary tissue by day 22 of pregnancy. This would correspond to the first lactogenic stimulus given by fatty acid biosynthetic data Mellenberger & Bauman, 1974) and by cytological investigations (Bousquet et al, 1969). Since lactose is synthesized exclusively by the mammary gland and is closely related to total milk production (Wheelock & Rook, 1966), lactose biosynthesis would be indicative of the functional state of the mammary gland.…”

“…Investigations of fatty acid biosynthesis in rabbit mammary tissue during lactogenesis have suggested two lactogenic stimuli Mellenberger & Bauman, 1974). However, there do not appear to have been any investigations with rabbit mammary tissue establishing the temporal relationships between lactose biosynthesis and the activity of relevant enzymes during pregnancy and lactation, although Denamur (1965) has reported the appearance of lactose in rabbit mammary tissue by day 22 of pregnancy.…”