MEASUREMENT AND SEASONAL-VARIATIONS OF BLACK BEAR ADIPOSE LIPOPROTEIN-LIPASE ACTIVITY

The black bear (Ursus americanus) provides a unique model for the stud y of adipose physiology because it exhibits seasonal periods of rapid weight gain and weight loss without marked changes in its metabolic ra re. To better understand fat cycling in this model, we obtained plasma and gluteal adipose tissue from five captive adult bears at approxima tely 20-day intervals from October 1 1992 through March 31 1993. The s tudy included a predenning and denning period for each animal. Samplin g during the predenning period followed a 12-h fast. Bears were anorec tic while denning. Adipose LPL activities and plasma insulin concentra tions were determined for each time point. Predenning LPL activities ( 4.83 +/- 0.64 mu mol/h/g) were significantly greater than those seen d uring the denning period (1.82 +/- 0.65, p < 0.001). A biphasic patter n of fasting LPL activity was seen in four of the five bears during th e predenning period. Fasting insulin concentrations showed no such pat tern of variation during the study period (mean = 25.1 +/- 1.36 pmol/l ; range 1.1-6.0). We found no evidence of a linear relationship betwee n LPL activity and insulin levels (p = 0.139). Neither LPL activity no r insulin concentrations were related to changes in weight (p = 0.257 and p = 0.7104, respectively). We conclude that LPL activity can be me asured in black bear adipose tissue and that fall (predenning) activit ies are significantly higher than those seen during the winter (dennin g period). Furthermore, the seasonal regulation of LPL involves some f actor(s) in addition to insulin.