Plasma Levels of the Endocannabinoid Anandamide in Women—A Potential Role in Pregnancy Maintenance and Labor?

0021-972X/04/$15.00/0 Printed in U.S.A. The Journal of Clinical Endocrinology & Metabolism 89(11):5482–5487 Copyright © 2004 by The Endocrine Society doi: 10.1210/jc.2004-0681 Plasma Levels of the Endocannabinoid Anandamide in Women—A Potential Role in Pregnancy Maintenance and Labor? OSAMA M. H. HABAYEB, ANTHONY H. TAYLOR, MARK D. EVANS, MARCUS S. COOKE, DAVID J. TAYLOR, STEPHEN C. BELL, AND JUSTIN C. KONJE Although exposure to exocannabinoids (e.g. marijuana) is associated with adverse pregnancy outcome, little is known about the biochemistry, physiology, and consequences of endocannabinoids in human pregnancy. In these studies, we measured the levels of the endocannabinoid anandamide (Narachidonoylethanolamine, AEA) by HPLC-mass spectrometry in 77 pregnant and 25 nonpregnant women. The mean ⴞ SEM plasma AEA levels in the first, second, and third trimesters were 0.89 ⴞ 0.14, 0.44 ⴞ 0.12, and 0.42 ⴞ 0.11 nM, respectively. The levels in the first trimester were significantly higher than those in either the second or third trimester. During labor, E NDOGENOUS CANNABINOIDS, endocannabinoids, are unsaturated fatty acid derivatives that act as ligands for the cannabinoid receptors (1). Arachidonoylethanolamide or anandamide (AEA) was the first endocannabinoid isolated from brain tissue (2). It is enzymatically released from cell membrane phospholipid precursors in response to depolarizing agents, hormones, and neurotransmitters (3, 4). The levels of AEA are considered to be controlled by its cellular uptake through an AEA transporter (5, 6) and its subsequent enzymatic degradation by a membrane-bound fatty acid amide hydrolase (FAAH) (7–10) and other enzymes (11–13). AEA exerts its effects through interaction with plasma membrane cannabinoid receptors. Two subtypes of cannabinoid receptors, CB1 and CB2, belonging to the superfamily of G protein-coupled receptors (14) have been reported (15–18). They have been localized in different tissue types including the reproductive tract. The CB1 receptor is referred to as the central receptor because it was first localized in the central nervous system (19), whereas the CB2 receptor is referred to as the peripheral receptor because it was first localized in the spleen and other sites (18, 20, 21). Several epidemiological and observational studies have been published on the adverse effects of exogenous cannabinoids present in marijuana on pregnancy in the human and Abbreviations: AEA, N-Arachidonoylethanolamine (anandamide); AEA-d0, unlabeled AEA; AEA-d8, deuterium-labeled AEA; BMI, body mass index; FAAH, fatty acid amide hydrolase; IVF, in vitro fertilization; MS, mass spectrometry. JCEM is published monthly by The Endocrine Society (http://www. endo-society.org), the foremost professional society serving the endocrine community. AEA levels were 3.7 times nonlaboring term levels (2.5 ⴞ 0.22 vs. 0.68 ⴞ 0.09 nM, P < 0.0001). During the menstrual cycle, levels in the follicular phase were significantly higher than those in the luteal phase (1.68 ⴞ 0.16 vs. 0.87 ⴞ 0.09 nM, P < 0.005). Postmenopausal and luteal-phase levels were similar to those in the first trimester. These findings suggest that successful pregnancy implantation and progression requires low levels of AEA. At term, AEA levels dramatically increase during labor and are affected by the duration of labor, suggesting a role for AEA in normal labor. (J Clin Endocrinol Metab 89: 5482–5487, 2004) animal models. These effects vary from early fetal loss, fetal growth restriction, and premature birth (22–26). By contrast, there are relatively few reports on the role of endocannabinoids in pregnancy. In the mouse, it has been proposed that AEA plays an important role in the local regulation of uterine implantation (27), because AEA was shown to be embryotoxic and arrests embryo development (28). In the implantation site, tissue AEA levels are only 25% of those in the nonimplantation site (29). This is considered to be due to local tissue levels of FAAH, which is expressed at higher levels in the implantation site compared with the nonimplantation site (30). More recent studies have suggested a further potential role for endocannabinoids (e.g. AEA) in myometrium because CB1 receptor is expressed in the human myometrium and in vitro stimulation of this receptor by AEA results in relaxation of myometrial strips (31). CB1 receptor and FAAH immunoreactivity have also recently been identified in the human placenta and fetal membranes (32), suggesting that the endocannabinoid system may also be important in these tissues during gestation. Little information is available on the systemic levels of AEA during human pregnancy. However, during early pregnancy, blood AEA levels are inversely correlated with FAAH levels in peripheral blood mononuclear cells (33), and, since FAAH levels at 8 wk gestation were lower in women who subsequently miscarried compared with those who progressed beyond the first trimester, this suggested that low AEA levels are required for successful pregnancy progression (34). Plasma AEA levels have also been shown to be higher in patients who fail to achieve an ongoing pregnancy after in vitro fertilization (IVF) treatment and embryo transfer 5482 Reproductive Sciences Section (O.M.H.H., A.H.T., D.J.T., S.C.B., J.C.K.) and Genome Instability Group (M.D.E., M.S.C.), Department of Cancer Studies and Molecular Medicine, University of Leicester, Leicester Royal Infirmary, Leicester LE2 7LX, United Kingdom Habayeb et al. • Anandamide in Pregnancy Maintenance and Labor Subjects and Methods Subjects All subjects gave signed informed consent to take part in the study, which was approved and conducted according to the guidelines of the institute’s research ethics committee. For the purposes of determining the changes in the levels of AEA during pregnancy, we studied crosssectionally five groups of women in the first, second, and third trimesters; term nonlaboring; and term laboring. To minimize the potential influence of a wide gestational window on AEA levels, we restricted our sampling to 6 –11 postmenstrual weeks in the first trimester, 15–27 postmenstrual weeks in the second trimester, and 28 –35 postmenstrual weeks in the third trimester. Term was defined as 37– 42 completed postmenstrual weeks. The inclusion criteria for the pregnant women were body mass index (BMI) less than 27 kg/m2, accurately dated pregnancies from firsttrimester ultrasound scans performed between 6 and 8 postmenstrual weeks, uncomplicated singleton pregnancies, and no coexisting maternal or gestational diseases. None were on any medication or known to have taken recreational drugs. Only women in established labor (defined as cervical dilatation of at least 4 cm and three to four regular uterine contractions every 10 min) were included in the term laboring group. The nonpregnant women were divided into two groups: pre- and postmenopausal. The inclusion criteria for the premenopausal wome (...truncated)