Running Title: Measurement of anandamide in human plasma Abbreviations: AEA, N-arachidonoylethanolamine (anandamide); AEA-d8, octo-deuterated anandamide; LOD, limit of detection; LOQ, limit of quantification; RSD, relative standard deviation; UPLC, ultra performance liquid chromatography, HPLC, high performance liquid chromatography; MS/MS, tandem mass spectrometry Keywords: anandamide, endocannabinoid, liquid chromatography, mass spectrometry, plasmaThe authors affirm that they have no conflicts of interest.

Running Title: Extraction of AEA from human bio-matrices Abbreviations: AEA, N-arachidonoylethanolamine (anandamide); AEA-d8, deuterated anandamide; LOD, limit of detection; LOQ, limit of quantification; LPE, liquid-phase extraction; SPE, solid-phase extraction; UPLC-MS/MS, ultra performance liquid chromatography tandem mass spectrometry.Keywords: Endocannabinoid, anandamide, solid phase extraction.The authors affirm that they have no conflicts of interest. samples from labouring and non-labouring women were analysed using both techniques no extraction method-dependent differences were observed.Consequently, we provide evidence for a robust SPE technique for the extraction of AEA from bio-matrices to replace the existing liquid extraction methods which is superior in terms of speed, extraction efficiency and sample size required.

Objective Plasma anandamide (AEA) levels have previously been shown to be elevated in labour and defective cannabinoid receptor type 1 signalling in mice has been shown to be associated with elevation of corticotrophin-releasing hormone and spontaneous onset of preterm labour. We measured plasma AEA levels in women undergoing induction of labour to define the changes during the transition from the nonlabouring to labouring state.Design A longitudinal observational study.Setting A large UK teaching hospital.Population Term pregnant women undergoing induction of labour.Methods Blood was collected from women before induction of labour and again when they were in active labour. Plasma AEA was extracted and measured using ultraperformance liquid chromatography-tandem mass spectrometry.Main outcome measures The primary outcome variable was change in plasma AEA levels from the nonlabouring to the labouring state. The secondary outcome was induction-to-delivery interval.Results There was a 1.5-fold increase in mean plasma AEA levels from 1.20 ± 0.57 nm in the nonlabouring state to 1.82 ± 0.87 nm in the labouring state (P < 0.0001). Induction-to-delivery interval was predicted by both Bishop's score (P < 0.0001) and percentage change in plasma AEA levels (P < 0.0001). There was a negative correlation between the percentage change in plasma AEA level and the induction-to-delivery interval (r = -0.28; P = 0.0481). This means that the greater the rise in the plasma AEA levels the shorter the duration of labour.Conclusions Plasma AEA levels increase with active labour and the negative correlations between percentage change in plasma AEA levels and induction-to-delivery interval suggest that AEA is likely to be involved in the physiological mechanisms of labour. Whether this increase is essential for myometrial contraction is unclear and needs further investigation.