On the hormonal regulation of lipolysis in isolated reindeer adipocytes

The effects of insulin and bovine growth hormone (bGH) on lipolysis (basal and/or adrenaline-stimulated) were investigated in isolated adipocytes from the Norwegian reindeer. Addition of 100 nmol l-1 adrenaline to the cells increased lipolysis 20-fold above basal lipolytic rate. Insulin (0.I and I nmol l-I) depressed lipolysis significantly at submaximal adrenaline stimulation but had no effect when lipolysis was stimulated maximally. Bovine GH (25 and 100 ng ml-I) inhibited basal lipolysis during the first 2 h of incubation, whereas refractoriness to this action was induced during the third and fourth hour of incubation. These effects were not influenced by inclusion of a small amount of glucocorticoid (dexamethasone, 25 ng ml-I). Addition of 0.I and I nmol l-I insulin together with bGH (100 ng ml-I) prevented the initial antilipolytic effect of the latter and resulted in the expression of normal basal lipolytic rates. Preincubation with bGH (100 ng ml-I) for 2 h did not alter the lipolytic response of the adipocytes to adrenaline. These findings lend support to the conclusion that insulin exerts a major control of lipolysis in reindeer adipose tissue. The significance of the antilipolytic effect of bGH is difficult to evaluate since this effect was transient and was abolished during the third and fourth hour of incubation.