Summary:In the present work certain parameters of the lipid metabolism of the Southern elephant seal (Mirounga leonina) are investigated using biochemical and electrophoretical methods and electronmicroscopy. Further it will be discussed whether the results indicate that the lipid metabolism has been adapted specifically to the polar environment. Earlier investi-gations on Weddell seals (Leptonychotes weddellii) showed that in this species, choles-terol levels were comparatively high (400-1000 mg/dl), while levels of triacylglycerides were comparatively low (30-90mg/dl), despite high dietary fat intake. However, no evi-dence of arteriosclerotic degeneration was detected in the arteries of Weddell seals and one elephant seal studied. In humans, however, a number of epidemiological studies have indi-cated a strong correlation between disorders in the lipid metabolism and coronary disease. Therefore, a number of laboratory methods have been established for routine and specia-lised diagnostics in human medicine. In the present study a number of these methods were used for investigations on Southern elephant seals and discussed.Field studies were carried out during two expeditions in 1995/96 and 1996/97 to the German-Argentinian Dallmann field laboratory on King George Island, Antarctica. For blood sampling, adult seals were either immobilised with ketamin or a ketamine/xylazine combination. Juvenile seals were not immobilised. Three different methods of drug ad-ministration were used, depending on field conditions. Three of 79 immobilisations were terminated using yohimbine.Laboratory analyses were carried out in the field laboratory, in the Klinikum Groß-hadern (LMU München), and in the Anatomische Anstalt, Lehrstuhl II (LMU München).In total, 182 blood samples were obtained from 40 seals, from 4 different animal groups: lactating cows, sucking pups, weaned pups, and adult seals during the annual moult. Each of the following parameters were analysed regularly in the 4 animal groups (value profiles):1) ultracentrifugation of blood serum to obtain lipoproteinfractions and determination of cholesterol concentration in each lipoprotein fraction2) concentration in the blood serum of: esterified and non-esterified cholesterol, phospho-lipids, triacylglycerides, non-esterified fatty acids, b-hydroxybutyrate (b-HBA), blood glucose, and a-tocopherole3) in each animal group and for each parameter the value profiles were calculated statis-tically using Kendall's coefficient of concordance. Value profiles with p < 0.05 were also checked statistically with the Spearman rank order correlation coefficient.4) in addition, following laboratory methods were applied to single samples of each animal group: quantitative lipoproteinelectrophoresis, fast protein liquid chromatography (FPLC) with concentrations of cholesterol in each FPLC fraction, high performance liquid chro-matography (HPLC)electron microscopy of lipoprotein particles in the blood serum and in the lipoprotein fractions separated by ultracentrifugation (Anatomische Anstalt, Lehrstuhl II).In lactating cows all parameters showed a significant coincidence with stage of lactation (p < 0.05). In sucking pups, coincidence with the sucking period (p < 0.05) was noted for the value profiles of cholesterol, esterified and non-esterified cholesterol, phospholipids and triacylglycerides. In weanlings coincidence with the weaning period (p < 0.05) was noted in the value profiles of phospholipids, b-HBA, and blood glucose (p < 0.05). During the moulting period, no coincidence was noted of any parameter (p > 0.05). In all animal groups, comparatively high levels of cholesterol and phospholipids were found. In all animal groups, an unknown tocopherol peak (called gML-peak) occurred in the HPLC, close to and of similar shape to the g-tocopherol peak as known in humans. It was noted that the diameters of some lipoprotein particles as found in the electron microscope photographs differ widely from those in humans.When ultracentrifugation is compared with the FPLC and the quantitative lipoprotein-electrophoresis, the HDL-cholesterol appears to be the predominant fraction. The HDL-binding SR-BI-receptor might play a central role in eliminating unnecessary cholesterol from the lipoprotein metabolism in order to avoid arteriosclerotic disease, as it has been found in mice. However, an high amount of disposable cholesterol might be necessary to ensure sufficient fluidity of cell membranes in blood vessels during deep diving. Chol-esterol might also be necessary as a source of precursors for aldosterone synthesis in order to save water during the lactation (and fasting) period in lactating cows. It is possible that the comparatively high levels of serum phospholipids are necessary for the synthesis of sufficient quantities of lung surfactant factor. In elephant seals, surfactant factor is assumed to be an essential substrate for the expansion of the lungs during the ascent from deep dives (over 1500m).The particular aspects of lipid metabolism to be discussed are changes occuring as a result of changes in the nutritional status during the fasting periods in elephant seals. The value profiles of the investigated parameters indicate that the fasting periods of lactating cows, weaned pups, and moulting seals differ considerably from each other. Thus, it appears that there is a characteristic limit determining maximum fasting duration for each group. However, the minimum of fasting duration in each group is assumed to be a matter of behaviour and ontogenesis of elephant seals and of the development of weaned pups respectively. Because a lactating cow requires a minimum of 22 days to nurse the pup, she must remain in the breeding colony ashore. While undergoing the transition from sucking to nutritional independence, the weaned pup continues to develop body tissues, such as musculature, lungs and nervous system. The moulting seals probably do not fast per-manently. Their onshore period is supposed to be due to the reduced thermoregulatory capabilities during the moulting process when the blood circulation of the body surface and thus, the thermosteresis is increased.In summary, the lipid metabolism in all ages is directly and variously involved in the adaptation to the polar environment.