Pre-eclampsia (PE) is a disease of pregnancy with maternal hypertension as one of its defining symptoms. The aetiology of PE may involve a disturbance of arachidonic acid (AA) metabolism reflected by altered levels of circulating AA and its metabolites that are known to affect Ca²⁺ mobilisation and will cross the placental barrier. We have investigated the effect of AA on [Ca²⁺]_i in human umbilical artery smooth muscle cells (HUASMC) isolated and cultured from cords obtained with ethical approval and informed consent. We measured the fluorescence ratio (R_f) of fura-2 at 340/380 nm excitation in single or small groups of 3Ð5 cells as a measure of cytosolic [Ca²⁺].

Both normal and PE HUASMC responded to 50 mM AA with an in increase in R_f that was larger in PE (2.99 ± 0.47, n = 19) than normal (1.44 ± 0.28, n = 16) (means ± S.E.M., n = number of cords, P < 0.009, Student’s unpaired t test). The response in PE cells was also qualitatively different, often showing a secondary increase in R_f that was delayed by up to 600 s. The increased response in PE cells could be the result of altered AA metabolism via the cyclo-oxygenase (COX) or lipoxygenase (LOX) pathways. To test this we used indomethacin and NDGA (10 mM, 20 min pre-incubation) as COX and LOX inhibitors, respectively. Neither significantly affected the response of PE cells to AA (2.97 ± 0.93, n = 8; 3.80 ± 1.33, n = 8; P > 0.4), but both induced a secondary increase in R_f in normal cells to 3.12 ± 0.87 (n = 3, P < 0.04) and 8.05 ± 1.71 (n = 3, P < 0.001), respectively, so that the final R_f was no less than that that seen in PE. As exposure to AA induces a strong contraction, the secondary rise in R_f could be an artifact of a delayed contraction. However, fluorescence ratio imaging showed that in 11/18 cells the secondary rise in R_f preceded the contraction.

AA can also be metabolised by a monoxygenase (MOX). Thus the effect of COX or LOX inhibition on [Ca²⁺]_i could be explained by metabolites of the COX and LOX pathways interacting to inhibit the secondary [Ca²⁺]_i increase, or an increase in the effective [AA] potentiating Ca²⁺ mobilisation either directly or indirectly via a MOX metabolite. The potentiated AA response seen in normal cells after indomethacin pretreatment (4.55 ± 1.4, n = 3) was inhibited by also pretreating with the MOX inhibitors metyrapone (50 mM: 26 ± 6 %, n = 3; P < 0.001) and isoniazid (200 mM: 19 ± 7 %, n = 3; P < 0.001). We conclude that in pre-eclampsia the activities of COX or LOX are reduced or that of MOX increased, diverting more AA through the MOX pathway to cause a secondary [Ca²⁺]_i rise in response to AA.

This work was supported by The Community Fund and Tommy’s, The Baby Charity.

All procedures accord with current local guidelines and the Declaration of Helsinki.