II-85Posters
EFFECT OF CYTOCHROME P450 INHIBITION ON BASELINE
BLOOD FLOW AND ON ACETYLCHOLINE-INDUCED
VASODILATION IN THE HUMAN SKIN MICROCIRCULATION
Helena Lenasi, Martin Štrucl
Institute of Physiology, Faculty of Medicine, University of Ljubljana; helena.lenasi.ml@mf.uni-lj.si
Background Cytochrome P450 (CYP) epoxygenase expressed in endothelial cells has been shown to be
involved in the generation of epoxyeicosatrienoic acids (EETs). EETs are known to induce
endothelial cell hyperpolarization and as such are suggested to be one of the mechanisms
for the action of yet undefined endothelium-derived hyperpolarizing factor (EDHF). EDHF
induces vasodilatation, independent of nitric oxide (NO) and prostacyclin (PGI2), of nu-
merous vessels from different species. The identity of EDHF in the human circulation re-
mains controversial. In coronary arterioles, EDHF appears to be CYP 2C9-derived metabo-
lite, whereas there are no data for human skin microcirculation. Skin microcirculation is
of interest because it is easily accessible and might reflect functional changes of other parts
of the circulation. Therefore, the aim of our study was to determine whether or not a CYP-
dependent mechanism contributes to the regulation of blood flow in skin microcirculation.
To this end, we studied the effects of sulphaphenazole, a selective CYP 2C9 inhibitor, on
baseline skin blood flow (SkBF) and on endothelium-dependent vasodilatation, in the pres-
ence and absence of combined eNOS and COX inhibition, respectively.
Methods and We measured SkBF at four independent skin sites on the volar aspect of the forearm in 12
results  healthy subjects using laser-Doppler fluxmetry (LDF). Endothelium-dependent vasodilata-
tion was assessed by an iontophoretical application of acetylcholine (ACh), whereas we
used sodium-nitroprusside (SNP) to assess endothelium-independent vasodilatation. To
study the NO/PGI2-independent vasodilatation, potentially attributable to an EDHF, we
inhibited endothelial NO synthase (eNOS) and cyclooxygenase (COX) by an intradermal
injection (10 µl) of the eNOS inhibitor, L-NMMA (40 mM) and the COX inhibitor, diclofen-
ac (30 mM); saline (10 µl) was injected as a control. To test the involvement of CYP in the
EDHF-mediated vasodilatation, sulfaphenazole (10mM) was applied intradermally.
Combined eNOS and COX inhibition had no effect on baseline LDF (10.8±2.1 PU in con-
trol vs. 8.3±1.2 PU in treated site). On the other hand, the ACh-stimulated increase in LDF
was significantly attenuated after eNOS and COX inhibition (35.7±5.5 PU), compared to
the control (60.5±8.2 PU, p < 0,05). Nevertheless, at least 60 % of ACh-mediated vasodilata-
tion was preserved after combined eNOS and COX inhibition. On the contrary, eNOS and
COX inhibition had no impact on the SNP-stimulated increase in LDF (71.1±8.3 PU in
control vs. 63.5±5.8 PU increase in the treated site). Sulfaphenazole had no significant
effect on baseline LDF (10.8±2,1 PU for saline and 11.6±2.6 PU for sulfaphenazole) as
well as on the ACh-induced LDF increase (60.5±8.2 PU in saline and 63.6±6.9 PU in treat-
ed site). Also, when sulfaphenazole was coinjected to sites, pretreated with L-NMMA and
diclofenac, there were no statistical differences between saline and sulfaphenazole-treated
sites either in baseline LDF values (8.3±1.2 PU for saline vs. 10.4±2.7 PU for the sul-
faphenazole-treated site) or in the responses to ACh. (35.7±5.5 PU for saline vs. 34.2±5.6
PU for the sulfaphenazole-treated site).
Conclusion Our investigation showed that a non-NO-, non-prostanoid-dependent mechanism, poten-
tially attributable to EDHF, contributes substantially to the regulation of baseline blood
flow as well to the ACh-provoked vasodilatation in the human skin microcirculation. Fur-
thermore, the results indicate that CYP 2C9 is probably not involved in the generation of
the putative EDHF in cutaneous microcirculation. Further studies are needed to clarify the
exact nature of EDHF in human skin.