Naturally occurring lipid that stimulates angiogenesis. Secreted by differentiating adipocytes; stimulates blood vessel formation and causes vasodilation. The (R)-isomer is bioactive. Prepn of optical isomers: E. Abderhalden, E. Eichwald, Ber. 48, 1847 (1915); of l-form: E. Baer, H. O. L. Fischer, J. Am. Chem. Soc. 67, 2031 (1945); S. Gronowitz et al., Chem. Phys. Lipids 14, 174 (1975). Purification from adipocytes and identification of angiogenic activity: D. E. Dobson et al., Cell 61, 223 (1990). Biosynthesis: W. O. Wilkison et al., J. Biol. Chem. 266, 16886 (1991); W. O. Wilkison, B. M. Spiegelman, ibid. 268, 2844 (1993). Effect on retinal circulation and probable role in pathology of diabetes: Y.-D. C. Halvorsen et al., J. Clin. Invest. 92, 2872 (1993).