The Lack of Bimodality in the Effects of Endogenous and Exogenous Prostaglandins on Fat Cell Lipolysis in Rats

The aim of this study was to investigate and clarify the role of prostaglandins (PG) on fat cell lipolysis in female rats. Incubations with adenosine deaminase (ADA) were used for the deamination of endogenous adenosine and increased basal (155%) and isoproterenol (10 −9 M) (348%) stimulation of glycerol release from adipocytes. Indomethacin and aspirin increased the effects of ADA while indomethacin further increased isoproterenol (with ADA) stimulation of lipolysis ( p ≤ 0.05). Exogenous PGE 2 and PGI 2 inhibited the isoproterenol and ADA stimulation of fat cell lipolysis ( p ≤ 0.05). The expected stimulatory effect of high concentrations of PGE 2 and of low concentrations of PGI 2 was not observed in the presence of ADA. Dose-response curves revealed that the inhibitory effects of PGs were reached at lower concentrations for PGE 2 than for PGI 2 ( p ≤ 0.05). In conclusion, this study showed that endogenous and exogenous PGs of adipose tissue only express an antilipolytic action on fat cell lipolysis. This effect appears to be highly significant when the β-adrenergic pathway is stimulated. Our results also stress the need to control the antilipolytic effects of adenosine to study the regulation of fat cell lipolysis by PGs.