Prostacyclin is a specific effector of adipose cell differentiation. Its dual role as a cAMP- and Ca(2+)-elevating agent.

The mitogenic-adipogenic activity of carbaprostacyclin (cPGI2), a stable analogue of prostacyclin (PGI2), has been proposed to be related to its ability to elicit cAMP production and to activate the protein kinase A cascade (Négrel, R., Gaillard, D., and Ailhaud, G. (1989) Biochem. J. 257, 399-405). In the present study, cPGI2 has been compared with other activators of the cAMP pathway, namely isoproterenol, forskolin and 8-bromo-cAMP, with respect to adipose cell differentiation. Carbaprostacyclin behaved as a much more potent and efficient effector of mouse Ob1771 preadipocyte differentiation than the latter agents. Moreover, cPGI2 also exerted a specific amplifying mitogenic-adipogenic role, as compared with isoproterenol in rat as well as human adipose precursor cells in primary culture, suggesting that the prostanoid was able to generate an additional second messenger. The fact that ionomycin was able to potentiate and amplify the differentiation induced by 8-bromo-cAMP led us to give evidence, using preadipocytes preloaded with the fluorescent calcium chelator Indo-1, that cPGI2, besides its ability to activate adenyl cyclase, was also able to induce a transient increase in intracellular free calcium. This phenomenon was independent of cAMP production or inositol phospholipid breakdown and appeared to be mediated after binding to a single class of PGI2 receptor. The potential to generate simultaneously two synergistic intracellular signals allows us to ascribe to PGI2 a key and specific role in the differentiation of adipose precursor cells in vitro that would likely lead in vivo to the recruitment of "dormant" preadipocytes to become adipocytes.