The anatomy, chemical composition and maximum glycolytic capacity of adipose tissue in wild Svalbard reindeer (Rangifer tarandus platyrhynchus) in winter



Adipose tissue was dissected completely from 21 female and two male Svalbard reindeer killed in the wild in December 1989. The gross mass, mean adipocyte volume, collagen content, the maximum activities of hexokinase and phosphofructokinase and the fatty acid composition of triacylglycerols were measured in samples of adipose tissue from at least 14 superficial, intraabdominal, cardiac and intermuscular depots homologous to those of other terrestrial mammals. The total adipocyte complement was calculated from the mass of each depot and its site-specific adipocyte volume. Almost all the adipose depots found in other terrestrial mammals were present. Site-specific differences in adipocyte volume were pronounced but, in contrast to other mammals, the glycolytic capacity of intermuscular adipose tissue was only slightly greater than that of other metabolically active depots, possibly because this subspecies does not naturally perform prolonged, strenuous exercise. All metabolically active depots except the cardiac adipose tissue enlarged with increasing fatness, but the superficial depots expanded more than any of the internal depots. Partitioning between anterior and posterior superficial depots was variable, with the posterior depots enlarging slightly more than the anterior depots. The adipose tissue in the hoof and around the eye was metabolically inert, but that of the bone marrow and the knee had low but detectable glycolytic capacity. The hoof and knee depots contained a high proportion of collagen, suggesting that they are load-bearing structures.

There was no statistically significant correlation between fatness and mean adipocyte volume and differences in fatness were due mainly to differences in adipocyte complement. Cell proliferation may be the principal mechanism of adipose tissue expansion in all superficial, intraabdominal and intermuscular depots studied. The total adipocyte complement was about twice that predicted from allometric equations relating adipocyte complement to body mass in other mammals and did not increase with age. There were no significant differences between lactating and non-lactating females in any of the parameters measured. The mean volume of intra-orbital adipocytes corresponded closely to that predicted from allometric equations. There were more unsaturated triacylglycerol fatty acids in the outer sides of the superficial depots and in other peripheral sites such as hoof, eye and distal marrow, indicating some biochemical adaptation to cooler peripheral tissues.