Adrenergic control of lipid metabolism; in vitro studies

circulating hormones, and that catecholamine turnover in the circulation is rapid. Furthermore, the responses of the different fat storing tissues including the liver may be different. This problem is prevented when using isolated fat or liver tissue, or isolated adipocytes and hepatocytes. Migliorini et al. (1992) investigated lipolysis in adipose tissue slices of fish, toad, and snake. Remarkably, basal rates were much lower than those of mammals. Catecholamines had, however, no effect on lipolysis in fish and toad adipose tissue. Adrenaline decreased lipolysis in snake adipose tissue, while glucagon had a clear lipolytic effect on snake, both in-vivo and in-vitro. The release of FFA from all adipose preparations was stimulated by cAMP, xanthine derivatives and phosphodiesterase-inhibitors. Lipolysis was also stimulated by fluoride and forskolin, which also increased cAMP levels. These results, suggesting that lipolysis is mediated via phosphorylation of a lipase, did not support Farkas' idea that lipase is not regulated by cAMP . The advantage of working with isolated cells instead of chopped adipose tissue is that the influence of damaged cells is negligible, and that reproducible incubations from the same source can be made to study concentration dependent effects of different agonists and antagonists. To verify the hypothesis that β-adrenoceptor stimulation leads to inhibition of lipolysis in adipose tissue, we carried out experiments with isolated adipocytes from tilapia mesenteric fat tissue . The paper of Vianen et al. (2002) was the first to show in-vitro lipolysis in isolated fish adipocytes. Zhou et al. (1996) described the histology and size range of Atlantic salmon adipocytes. Christiansen et al. (1985) describing glucose uptake studies pointed to the fragility of adipocytes isolated from trout adipose tissue. Their adipocytes could not be incubated much longer than 4 minutes. The procedure of Vianen et al., however, allows incubations for 5 hours, in some cases overnight incubations were even performed. A general draw-back of working with lipolysis in fish adipose tissue appears the large variability in FFA release. The basal