EVIDENCE FOR PREADIPOCYTE PROLIFERATION DURING CULTURE OF SUBCUTANEOUS AND INTRAMUSCULAR ADIPOSE TISSUES FROM ANGUS AND WAGYU CROSSBRED STEERS

The primary objective of this study was to provide evidence for preadi pocyte proliferation during culture of adipose tissue explants; a seco ndary objective was to compare the lipogenic activity and cellularity of adipose tissues from American Wagyu crossbred steers. Subcutaneous (s.c.) and intramuscular (i.m.) adipose tissues were obtained at slaug hter from the 2nd to 6th lumbar region of the loin from Angus (n = 10) and Wagyu crossbred steers (n = 10) that had been fed for 552 d by ty pical Japanese production standards. Adipose tissue explants were incu bated 36 h with [H-3]thymidine in the absence and presence of aphidico lin (a specific inhibitor of genomic DNA replication). Adipocytes were liberated by collagenase treatment and [H-3]thymidine incorporation i nto DNA was measured. Whereas there were no significant differences be tween adipose tissue depots, Wagyu s.c. and i.m. preadipocytes and vas cular cells exhibited greater (P < .05) [H-3]thymidine incorporation i nto DNA than adipocytes from Angus steers. Intramuscular adipose tissu e from both breeds exhibited lower (P < .05) rates of lipogenesis from acetate both before and after longterm (36-h) incubation than s.c. ad ipose tissue. Furthermore, i.m. adipocytes were smaller (P < .05) than s.c. adipocytes. The activities of fatty acid synthetase and glucose- 6-phosphate dehydrogenase were greater (P < .05) in Wagyu s.c. adipose tissue and less in Wagyu i.m. adipose tissue than in corresponding An gus tissues. There were no differences between breed types (P = .17) i n rates of lipogenesis from acetate, either before or after explant cu lture. These data suggest that lipid-filling cells that have the capac ity to proliferate exist in bovine s.c. and i.m. adipose tissues. The smaller size and greater rates of DNA synthesis indicate that Wagyu s. c. and i.m. adipose tissues are less mature and more proliferatively a ctive than Angus adipose tissues.