Involvement of adenosine in vanadate-stimulated release of lipoprotein lipase activity.

A short-term incubation of isolated rat fat pads with vanadate showed the stimulated release of lipoprotein lipase (LPL) activity and suppression of the rise in extracellular adenosine level. The addition of adenosine to the medium showed inhibition of both the stimulated release of LPL activity and an increase in intracellular cAMP content by vanadate. A progressive increase in 5'-nucleotidase activity in the particulate fraction containing plasma membrane was suppressed by vanadate in a time- and dose-dependent manner, suggesting that vanadate inhibits, in part, the production of adenosine based on a dephosphorylation of AMP. In adipocytes, the inhibition of adenylate cyclase via A1 adenosine receptor is more predominant than the stimulation of adenylate cyclase via A2 adenosine receptor (Londos C. et al., Proc. Natl. Acad. Sci. U.S.A., 75, 5362-5366 (1978)). Therefore, vanadate may stimulate the release of LPL activity from the fat pads by suppressing the rise in extracellular adenosine level, accompanied by the activation of adenylate cyclase activity.