Age-related norepinephrine induced lipolytic response of isolated rat adipocytes

1. Groups of male Long Evans rats were sacrificed at the ages of 10, 16, 20, 24, 28, 32, 38 and 45 weeks. 2. The two epididymal fat pads from each rat in each group (4-5 rats) were excised for the preparation of adipocytes. 3. Cell suspensions were incubated in triplicate with each of seven norepinephrine concentrations ranging from 0.5694 to 569,400 nM. 4. Lipolytic responses are expressed as nmol glycerol released/microgram DNA/90 min. 5. The animals reached a peak response between the ages of 20 and 32 weeks. 6. Aging resulted in a gradual increase in the apparent affinity (Km) of the response yielding system for norepinephrine. 7. Initially an increase in the lipolytic capacity of the cells in response to norepinephrine, is observed, as reflected by the Vmax values up to an age of 20 weeks. 8. Vmax then stays relatively constant at elevated levels up to an age of 32 weeks, followed by an abrupt decrease with further aging.