Biosynthetic capacity and regulatory aspects of prostaglandin E₂ formation in adipocytes

In contrast to previous studies, Parker et al. (Diabetes (1989) 38, 1123) have recently found that isolated rat adipocytes alone were unable to synthesize prostaglandins (PG) and that the PG measured in adipocyte suspensions were due to contaminating non-adipocyte cells. In the present study the capacity of adipocytes to produce PGE₂ has further been explored. Preparations of isolated rat adipocytes were extensively washed in order to get rid of contaminating cells. The released PGE₂ was measured by radioimmunoassay (RIA) after high-performance liquid chromatography (HPLC) separation. We found that after repetive washing (up to 20 times) the isolated adipocytes were still able to synthesize PGE₂ and this process was fully activatable by epinephrine, which indicates that pure adipocytes, themselves, are able to produce PGE₂. However, addition of non-adipocyte material (from the adipose tissue) to 'pure' adipocytes (washed 10 times) enhanced the PGE₂ synthesis significantly (P < 0.001) as compared to 'pure' adipocytes alone. Thus, some kind of synergy exists between adipocytes and non-adipocyte cells in the adipose tissue in respect to PG formation. Some regulatory aspects of PG synthesis in 'pure' adipocytes were also investigated. Phospholipase A₂ (2 U/ml) enhanced PGE₂ synthesis significantly (119 ± 21 to 658 ± 85 pg/10⁶ cells, P < 0.001) without affecting lipolysis (glycerol release). The combined effect of epinephrine (5 μM) and phospholipase A₂ (2 U/ml) on PGE₂ formation was almost additive. Insulin inhibited the epinephrine-induced PG formation (P < 0.01) but had no effects on the action induced by phospholipase A₂. In conclusion, there is no doubt that isolated adipocytes cooperate with non-adipocyte cells from the adipose tissue in respect to PG synthesis. Isolated adipocytes seem, however, still to have the ability to synthesize PGs, at least PGE₂. Finally, both epinephrine and phospholipase A₂ have the capacity for inducing PGE₂ synthesis in isolated adipocytes.