Lipolytic response of rat adipocytes to epinephrine: effect of age and cell size.

Isolated fat cells from 3, 12 and 28 month old rats were compared intheir lipolytic response to various doses of L-epinephrine. With increasing age a progressive decline in the response occurred when comparing rats with unmatched mean adipocyte diameters. However, this apparently age-related decrease was no longer evident if the diameters were matched since the 28 month old animals had a lipolytic response less than the 3 month old rats but greater than the 12 month olds. Body weight differences between these ages may account for these observations. The biphasic dose response curve to hormone stimulation in the 3 and 12 month olds was monophasic at 28 months. Within each age group the initial lag in glycerol release decreased and the lipolytic response increased as mean cell size increased. The rate of hormone stimulated glycerol release varied inversely with incubations of 3,700 to 25,000 cells/ml and aging had no effect on this parameter. DNA content per fat cell remained constant with age.