LTF4 is a cysteinyl-leukotriene produced in vitro, but not reported to date in vivo. It is formed by the incubation of LTE4 with γ-glutamyl transpeptidase and glutathione. LTF4 is a weak agonist in its ability to contract vascular smooth muscle. [1] The rank order of potency of the cysteinyl-leukotrienes to contract vascular smooth muscle is LTD4 > LTC4 > LTE4 >> LTF4. [1] [2]
Reference:
[1]. Bernstrom, K., and Hammarström, S. A novel leukotriene formed by transpeptidation of leukotriene E4. Biochemical and Biophysical Research Communications 109, 800-804 (1982).
[2]. Lord, A., Charleson, S., and Letts, L.G. Leukotriene F4 and the release of arachidonic acid metabolites from perfused guinea pig lungs in vitro. Prostaglandins 29, 651-660 (1985).