Stimulation of lipogenesis in bovine adipose tissue by insulin and insulin-like growth factor.

The present study was undertaken to determine if insulin and insulin-like growth factor 1 (IGF-1) stimulated lipogenesis in bovine adipose tissue and determine the effects of insulin on lipogenic capacity in adipose tissue cultured for 48 h. In contrast to previous studies, insulin markedly stimulated lipogenesis in short-term (2 h) incubations. The stimulation of lipogenesis by insulin was dependent upon the source of bovine serum albumin used in the buffer. Insulin-like growth factor 1 also stimulated lipogenesis; however, the potency was 80- to 100-fold lower than for insulin. Lipogenic capacity was decreased approximately 75% after 48 h of culture in the absence of insulin. When insulin was present in the culture medium, the reduction in lipogenic capacity was attenuated in a dose-dependent manner. However, insulin alone did not totally maintain lipogenic capacity after 48 h. In contrast, inclusion of hydrocortisone (HC; 50 ng/ml) and insulin (10 ng/ml) in the medium completely prevented the decline in lipogenic capacity of cultured bovine adipose tissue. In summary, these results indicate that bovine adipocytes are quite sensitive to insulin in short-term in vitro incubations and that insulin plays a predominant role in maintenance of lipogenic capacity of bovine adipose tissue during culture. Furthermore, the marked potentiation of insulin's effects of lipogenesis after 48 h of culture by HC suggests that the glucocorticoid is involved in regulation of insulin receptor number and(or) other cellular proteins (e.g., enzymes) which are important for lipogenesis to occur.