Yvonne M. O'Brien

17 alpha-hydroxyprogesterone caproate vehicle, castor oil, enhances the contractile effect of oxytocin in human myometrium in pregnancy.

OBJECTIVE The possibility exists that the vehicle for 17-alpha-hydroxyprogesterone caproate, castor oil, exerts an effect on human uterine contractility. The aim of this study was to evaluate its effects on contractility of myometrial preparations that were obtained during pregnancy. STUDY DESIGN Myometrial strips were suspended under isometric conditions. Contractility was induced with oxytocin. Strips were incubated in castor oil or physiologic salt solution and suspended for a further oxytocin challenge. Contractile integrals were compared between both groups. RESULTS Strips that were exposed to castor oil demonstrated increased contractile activity that was elicited by oxytocin (mean contractility value, 165.53%+/-17.03%; n=8; P=.004), compared with control strips (mean contractility value, 72.57%+/-7.48%; n=8; P=.003). There was a significant increase in contractile activity of the castor oil-exposed strips, compared with those that were exposed to physiologic salt solution (n=8; P<.001). CONCLUSION Exposure of human myometrial preparations to castor oil results in enhanced oxytocin-induced contractility.

Stereology of human myometrium in pregnancy: influence of maternal body mass index and age

OBJECTIVE Knowledge of the stereology of human myometrium in pregnancy is limited. Uterine contractile performance may be altered in association with maternal obesity and advanced maternal age. The aim of this study was to investigate the stereology of human myometrium in pregnancy, and to evaluate a potential influence of maternal body mass index (BMI) and age. STUDY DESIGN Biopsies of human myometrium were obtained from 57 women at cesarean section (n = 26, n = 13, n = 18 normal, overweight and obese BMI, respectively), and volume fractions of smooth muscle and extracellular matrix were assessed using stereologic techniques. RESULTS The smooth muscle constituted 65.2% ± 8.9% (standard deviation) and the extracellular matrix 32.6% ± 7.7% (standard deviation) (n = 57). There was no correlation observed between maternal BMI, age, or parity with the fractional volumes of either smooth muscle or extracellular matrix. CONCLUSION These results outline the stereology of human myometrium in pregnancy. Putative functional differences in contractility, pertaining to obese or older mothers, are not related to smooth muscle content.

The influence of smooth muscle content and orientation in dissected human pregnant myometrial strips on contractility measurements.

This study examined the hypothesis that the force generated by myometrial strips from pregnant women is influenced by the smooth muscle content and fibre orientation of the strips and that correcting for these structural variables will provide a more accurate measure of contractility. Myometrial strips (n=72) were contracted by exposure to KCl, oxytocin, U44619 and phenylephrine and maximum responses were recorded. Morphological techniques were used to determine the cross-sectional area of the strips, the area occupied by smooth muscle and the area occupied by smooth muscle longitudinal in the strip. Maximum responses to contractile agents were expressed in terms of these three variables. The mean cross sectional area of strips was 2.01 ± 0.06 mm(2), of which 50% was smooth muscle, and 18% was smooth muscle longitudinal in the strip (n=72). There was much heterogeneity in responses, smooth muscle content and fibre orientation. Correction for morphological variability did not improve the heterogeneity in responses where coefficients of variation among strips from the same donor ranged from 43% to 63% when expressed in relation to longitudinal smooth muscle cross-sectional area. The standard method of preparation of myometrial strips for in vitro recording results in samples that are not structurally uniform. Correcting for the known structural variables does not provide a more accurate measure of maximum contractile responses. Because of the heterogeneity shown here, experiments that are dependent upon accurate estimation of maximum contractile responses require a large number of replicates to reach meaningful conclusions.

Human uterine lower segment myometrial cell and nuclear volume at term: influence of maternal age.

Little is known about the cytoarchitecture of human myometrial cells in pregnancy, and whether or not this may be influenced by maternal characteristics such as age, parity and body mass index (BMI). The aim of this study was primarily to evaluate human myometrial smooth muscle cell (SMC) and nuclear volume in the third trimester of human pregnancy, and secondarily to investigate if these parameters are altered in relation to the maternal characteristics outlined above. Myometrial biopsies were obtained from 30 women undergoing elective caesarean delivery at term. One‐micrometer sections were prepared for light microscopy and 100‐nm sections for electron microscopy. The nucleator technique was used to assess nuclear volume from the light microscopy images. Point‐counting methodology was used on transmission electron micrographs to assess the percentage of the cell volume occupied by the nucleus. Cell volume was calculated from these measurements. The euchromatin to heterochromatin (Eu/Het) ratio was determined to ascertain whether differences in nuclear volume were due to an increased range of genes being transcribed. The mean (± SEM) nuclear volume was 175 ± 10 μm3, the nucleus occupied 1.5 ± 0.1% of the SMC and the mean cell size was 14 047 ± 1352 μm3. The Eu/Het ratio was 7.54 ± 0.4. The mean volume of heterochromatin and euchromatin in the nucleus was 21.5 ± 1.7 and 149 ± 9 μm3, respectively. A multivariate regression analysis revealed that advanced maternal age was associated with an increase in the percentage of the cell occupied by nucleus (R2 = 0.32, P = 0.004). There were no other significant effects of maternal age, BMI or parity on the measured parameters. These findings provide reliable volumes for human myometrial cells and their nuclei at term gestation, and show that nuclear volume fraction may be influenced by maternal age.