In vitro lipolytic effect of bovine pituitary diabetogenic protein.

Bovine diabetogenic protein has been further purified by gel filtration yielding a fraction (Mr 25 000--28 000) having increased diabetogenic and in vitro lipolytic activity. Using rat epididymal fat pads, this fraction was shown to be lipolytic at concentrations as low as 1--10 mug/ml. The in vitro lipolytic effect was unaffected by the nutritional state of the animals, was not potentiated by dexamethasone, could be demonstrated in the presence and absence of glucose and was not mediated by alpha- and beta-adrenergic receptors. A lag phase of greater than 1 h was observed before diabetogenic protein induced lipolysis occurred, suggesting that protein synthesis might be involved. Cycloheximide (10 mug/ml), added initially, prevented the diabetogenic protein-induced lipolysis. This direct effect of the purified protein on adipose tissue helps explain the elevation of free fatty acids seen when bovine diabetogenic hormone is administered in vivo and suggests that this anterior pituitary protein may be a new lipid-mobilizing hormone.