Lactose and fatty acid synthesis in lactating-rat mammary gland. Effects of starvation, re-feeding, and administration of insulin, adrenaline, streptozotocin and 2-bromo-α-ergocryptine

Abstract

Lactose synthesis and fatty acid synthesis in intact lactating-rat mammary gland were measured simultaneously by incorporation of [U-14C]glucose and of both [U-14C]glucose and 3H2O respectively. Both processes were almost abolished by overnight starvation. Self-re-feeding caused recovery of lipogenesis to 100% of normal by 2 h and to 170% by 5 h. Lactose synthesis recovered to 80% of normal by 5 h. Food intubated to starved rats caused partial recovery in 3 h, standard diet favouring lactose synthesis and sugars favouring lipogenesis. Casein and starch were ineffective. Olive oil intubated to fed rats suppressed lipogenesis greatly and lactose synthesis slightly. Paraffin oil or water partly mimicked these effects. Adrenaline (subcutaneous) decreased lipogenesis from glucose, whereas insulin (subcutaneous) caused hypoglycaemia associated with loss of lactose synthesis but unchanged fatty acid synthesis. Streptozotocin and 2-bromo-alpha-ergocryptine (CB-154) impaired lipogenesis but not lactose synthesis. The results are interpreted in terms of competition for intracellular glucose by biosynthetic pathways for lactose and fat, and the possible implications for variations in milk composition are discussed.