Myometrial regulation throughout pregnancy is key to understanding the processes involved in preterm labour and birth. Cholesterol depletion perturbs the membrane microenvironment by altering cell permeability and fluidity. Previous studies have also shown that cholesterol is able to modify myometrial contractility (Buxton & Vittori, 2005; Wray et al., 2005). Our hypothesis is that the cholesterol depleting agent simvastatin is able to inhibit myometrial contractions, accompanied by effects on lipid-raft associated proteins. The aim of this study was to investigate the effects of simvastatin on myometrium and the potential mechanism underlying any modulation. Myometrial biopsies were collected with written informed consent from patients undergoing elective caesarean section at term (> 37 weeks). Tissue strips were mounted for isometric tension recordings and effects of simvastatin (3.3nM – 0.1mM, n=20) on spontaneous myometrial contractility, both in the absence and presence of BayK 8644 (1µM, n=10), determined. Simvastatin treated cultured human myocytes were studied using immunofluorescence to investigate whether there is any effect on the localisation of the lipid raft markers caveolin-1 and flotillin-1 (n=4). Total cholesterol and protein were measured in untreated and treated cultured myocytes, using the Amplex red and bicinchinconic acid protein determination assay kits respectively (n=4). In all experiments, 15mM methyl-β-cyclodextrin (MCD) was used as a control cholesterol-depleting agent for comparison. Data are presented as means ± SEM and compared using ANOVA. Simvastatin significantly decreased myometrial contraction amplitude and frequency until a complete cessation was achieved at 100µM (p <0.0001). MCD treatment increased contraction amplitude and frequency (p <0.0001). BayK 8644 significantly increased contraction frequency (p <0.001), but was unable to abolish the effects of simvastatin in tissues preincubated with this calcium channel agonist. Immunofluorescence for both lipid raft markers was detected in cultured myometrial cell membranes. Time course (0-24hrs) analyses of cells incubated in simvastatin indicated a redistribution of the two raft markers, an effect not seen in myocytes treated with MCD. There was no difference in total cholesterol and protein concentration in simvastatin-treated myocytes (p >0.05) compared with MCD treatment where a significant decrease in total cholesterol only (p <0.001) was observed. These data demonstrating acute inhibition of human myometrial contractility by simvastatin and an altered distribution of raft associated proteins indicate mechanisms of statin action distinct from cholesterol depletion alone.