title: An investigation of the effects and mechanism of adenosine triphosphate (ATP) on labouring and non-labouring human myometrial contractility.
Creators: name: Zafrah, Hind
Publisher: name: University of Liverpool Repository
Year: 2023

description: Dysfunctional labour is defined as uncoordinated myometrial contractions associated with a lack of cervical dilatation. Currently, oxytocin is the only treatment available, and approximately 50% of women who have dysfunctional labour do not respond to oxytocin administration. This results in a large proportion of women requiring an emergency caesarean delivery which comes with associated risks. Adenosine triphosphate (ATP) has been shown to increase rat uterine contractions via purinergic receptors (P), mainly P2X1 or P2X7 receptors. Therefore, this study aimed to investigate the effects of ATP on human myometrial contractile activity, and its potential role in dysfunctional labour, with the hypothesis being that expression of P2X1 and/or P2X7 receptors in women's myometrial tissues is up-regulated at term, and ATP binding to one of these receptors would potentiate myometrial contraction during the onset of labour. On the other hand, the depletion of one or both receptors would lead to dysfunctional labour. Quantitative immunoblotting studies measured the expression level of P2X1Rs and P2X7Rs and determined their location in myometrial tissue obtained from 1) non-labouring term pregnant, 2) normally labouring, 3) dysfunctionally labouring and 4) non-pregnant women. The effect of ATP and its analogues, ATPγS (a non-hydrolyzing form of ATP) and BzATP (a more potent agonist at the P2X7R), on labouring and non-labouring human myometrial contractility was also measured in organ bath assays. To further determine the role of P2X7R in mediating this action, selective antagonists, A-438079 and A-740003, were used. Immunoblotting studies demonstrated that P2X1Rs were expressed in human myometrium, but that the pattern and quantity of expression did not differ between groups. P2X7R expression was also detected in human myometrium and interestingly, was significantly greater in the normal labouring group (32845±8655%, n=3, P= 0.0025) than non-pregnant (4911±751%, n=3), term pregnant non-labouring (12256± 2118%, n=10), and dysfunctionally labouring (15599±3146%, n=5) groups. In non-labouring tissues, ATP produced a significant increase in contractile frequency (230±38.7%, n=7). All three agonists increased the frequency of spontaneous contractions significantly with the rank order of ATPγS&gt; BzATP&gt; ATP (656±102.4% (n=6) &gt; 250.2±38.8%(n=9) &gt; 230±38.7%(n=7)), respectively. Selective P2X7R antagonists, A-438079 and A-740003, were unable to inhibit the stimulatory effects of ATP. Furthermore, there were no significant differences in the effect of ATP on myometrial activity between non-labouring and dysfunctionally labouring women. It is concluded that the increased P2X7R expression observed in the normal labouring group could potentially be implicated in the myometrial contractility response to ATP and help in the augmentation of contraction during the onset of labour, although no normally-labouring tissues were available to confirm this in the contractility studies. The data do not support a major role for P2X7R in human myometrial responses to purinergic stimulation, at least in non-labouring women; however, comparisons still need to be made with normal labouring myometrial tissue.