Endothelium-dependent relaxation of arteries is mediated by nitric oxide, prostacyclin and endothelium-dependent hyperpolarizing factor (EDHF). Direct cell-to-cell electrical and/or chemical coupling via gap junctions may be involved in the EDHF response (Edwards et al. 1999). The functional characteristics of gap junctions are dependent upon the expression patterns of integral connexin proteins. Therefore, in human resistance arteries, we have investigated the effects of a putative gap junctional uncoupler, 18-α glycerrhetinic acid (18-α GA), on EDHF-mediated relaxations together with assessing mRNA expression encoding several connexins.

Resistance vessels were dissected from omental biopsies taken, following written informed consent (Central Manchester Ethics Committee CEN/00/203), at elective Caesarean section from women with uncomplicated pregnancies. Vessels were mounted on a wire myograph, normalised in physiological salt solution (37 °C, bubbled with 95 % air-5 % CO₂) and constricted with U46619 (10^-10-10^-6 M, n = 11). Upon a sustained constriction, incremental doses of bradykinin were added (10^-9 -10^-6 M). This was repeated in the presence of L-NNA (100 µM) and indomethacin (10 µM), to assess EDHF-dependent relaxation. The vessels were further incubated with 18-αGA (100 µM, 20 min) and responses of preconstricted vessels to bradykinin repeated.

Residual constriction to U46619 following the highest dose of bradykinin was 28 ± 4.0 % (mean ± S.E.M.) of control. After L-NNA/indomethacin incubation the residual constriction to U46619 was 47 ± 8.0 % (P < 0.05, Student’s unpaired t test). This EDHF-attributable relaxation was further attenuated following incubation with 18-α GA: residual constrictions to U46619 were 73 ± 6.3 % of control. RNA was extracted from omental arteries (n = 6) and RT-PCR performed with gene-specific nucleotide primers to β-actin and connexins 43, 40 and 37. mRNA encoding connexins 43 and 40 was observed in 5 of 6 patient samples and connexin 37 in 4 of 6 samples.

Thus, in omental arteries from pregnant women pre-constricted with U46619, EDHF-mediated relaxation is significantly blunted by the gap junctional uncoupler 18 α GA. Additionally, mRNA encoding the common vascular connexins 43, 40 and 37 is often observed. These data support the concept that EDHF-mediated vasodilatation in human resistance vessels may, at least partly, be mediated via connexin-containing gap junctions.

This work was supported by Tommys, the baby charity.