Fat transfer and energetics during lactation in the hooded seal: the rolesof tissue lipoprotein lipase in milk fat secretion and pup blubber deposition

Hooded seals (Cystophora cristata) lactate for 3.6 days during which female s simultaneously fast and transfer large amounts of energy to their pups th rough fat-rich milk. Pups grow rapidly, principally due to blubber depositi on. Lipoprotein lipase (LPL), the primary enzyme responsible for tissue upt ake of triglyceride fatty acids, may strongly influence both maternal milk fat secretion and pup blubber deposition. We measured the energetic costs o f lactation (using hydrogen isotope dilution, (H2O)-H-3), milk composition, prolactin, and LPL activity (post-heparin plasma LPL [PH LPL], blubber, ma mmary gland and milk; U) in six females. PH LPL and blubber LPL were measur ed in their pups. Females depleted 216.3 MJ . day(-1) of body energy and fa t accounted for 59% of maternal mass loss and 90% of postpartum body energy loss, but maternal body composition changed little. Maternal blubber LPL w as negligible (0.0-0.2 U), while mammary LPL was elevated (1.8-2.5 U) and w as paralleled by changes in prolactin. Estimated total mammary LPL activity was high (up to 20,000 U . animal(-1)) effectively favoring the mammary gl and for lipid uptake. Levels of total blubber LPL in pups increased seven-f old over lactation. Pups with higher PH LPL at birth had greater relative g rowth rates (P = 0.025). Pups with greater blubber stores and total blubber LPL activity had elevated rates of fat deposition (P = 0.035).