Free fatty acids exert a greater effect on ocular and skin blood flow than triglycerides in healthy subjects

Background: Free fatty acids (FFAs) and triglycerides (TGs) can cause vascular dysfunction and arteriosclerosis. Acute elevation of plasma FFA and TG concentration strongly increase ocular and skin blood flow. This study was designed to discriminate whether FFA or TG independently induce hyperperfusion by measuring regional and systemic haemodynamics. Methods: In a balanced, randomized, placebo-controlled, double-blind, three-way, crossover study nine healthy subjects received either Intralipid® (Pharmacia and Upjohn, Vienna, Austria) with heparin, Intralipid® alone or placebo control. Pulsatile choroidal blood flow was measured with laser interferometry, retinal blood flow and retinal red blood cell velocity with laser Doppler velocimetry, and skin blood flow with laser Doppler flowmetry during an euglycaemic insulin clamp. Results: A sevenfold increase of FFA during Intralipid®/heparin infusion was paralleled by enhanced choriodal, retinal, and skin blood flow by 17 ± 4%, 26 ± 5% (P < 0.001), and 47 ± 19% (P = 0.03) from baseline, respectively. In contrast, a mere threefold increase of FFA by infusion of Intralipid® alone did not affect outcome parameters, despite the presence of plasma TG levels of 250-700 mg dL^-1; similar to those obtained during combined Intralipid®/heparin infusion. Systemic haemodynamics were not affected by drug infusion. Conclusions: Present findings demonstrate a concentration-dependent increase in ocular and skin blood flow by FFA independently of elevated TG plasma concentrations. As vasodilation of resistance vessels occur rapidly, FFA may play a role in the development of continued regional hyperperfusion and deteriorate microvascular function.