THE INCREASE IN VASOMOTOR TONE INDUCED BY A PARENTERAL LIPID EMULSIONIS LINKED TO AN INHIBITION OF PROSTACYCLIN PRODUCTION

The aim of the study was to verify whether the infusion of a lipid emu lsion causes a rise in vascular pressure related to an imbalance in th e production of vasoconstricting and vasodilatating eicosanoids. Segme nts of umbilical veins were perfused with and without 1.5 mu M indomet hacin (cyclooxygenase inhibitor) in solutions differing only in their lipid content (control vs. lipid). The lipid-induced higher pressure ( p < 0.05) was associated with an inhibition (p ( 0.05) in the output o f the vasodilatator PGI(2), and an increase (p < 0.01) in the producti on of the vasoconstrictor PGF(2 alpha). Indomethacin abolished differe nces in pressure, but produced a rise (p < 0.01) in vascular tone of b oth the control and lipid-containing solutions by inhibiting PGI(2) sy nthesis. Prostacyclin was the only eicosanoid significantly correlated (p < 0.01) to vascular tone. The lipid emulsion was therefore linked to the inhibition of the conversion of PGH(2) to PGI(2). The ensuing g reater PGH(2) availability would result in vivo, in the increased synt hesis of vasoconstricting eicosanoids. The lipid-containing solution p roduced vasoactive responses similar to those reported with tert-butyl hydroperoxide, suggesting that hydroperoxides contaminating commonly used lipid emulsions could be causing a prostanoid-dependent vasoconst ricton.