Lipolysis as a function of cell numbers and fat content: comparison between isolated rat and dog adipocytes

The lipolytic responses to dihydroergotamine (5 mug/mi) of isolated rat adipocytes andto epinephrine (50 ng/m1 and 1 mug/m1) of both rat and dog adipocytes were measured over a period of two hours. Glycerol release was calculated as a function of either glycerol ester content or of cell number per incubation vial. The conventional calculation based on glyceride content gave the following results: a) epididymal fat cells from rats weighing less than 160 gm were more sensitive to dihydroergotamine and epinephrine than were fat cells from heavier animals weighing close to 200 gm; b) dog adipocytes from abdominal subcutaneous tissue were less sensitive to eipnephrine than were rat adipocytes. No such differences were noted when the same data were calculated on the basis of cell numbers per incubation vial: the lipolytic response was uniform with rat adipocytes obtained either from the lighter or the heavier weight groups, and so was the response of dog and rat cells. These results indicate that in the type of studies where receptor-dependent hormone and drug effects are measured, the number of cells per incubation vial is an important parameter to be considered in evaluating a lipolytic response.