The bovine cervix explored : the cow as a model for studies on functional changes in the cervix uteri

Abstract

The cervix uteri is a rigid tube which connects the uterus with the vagina and during most of the time it is firmly closed. During oestrus, late pregnancy and parturition, the morphological appearance in the cervix changes markedly, resulting in a softer cervix, which during parturition can even be stretched open to a diameter that is more than a tenfold larger than before. During gyneacological interventions, such as artificial inseminations in several animal species, or in women it would be beneficial to penetrate the cervix with ease. Clinical obsterical problems occur when insufficient closure of the cervix during pregnancy causes premature birth, or when the cervix fails to dilate during birth. Collagen is one of the most important components of the cervix that causes the rigidness of the cervix and during softening of the cervix, collagen has been shown to undergo significant changes in its structure. Several hormones are involved in regulating these changes, by stimulating or depressing processes that are mostly associated with the inflammation cascade. So far studies that aimed to get more insight into the many factors involved in cervical softening have been using cross-sectional study protocols. Ethical and practical considerations in the subjects that are mostly used (women, small laboratory animals or small ruminants) make it almost impossible to perform longitudinal studies in these species. Another limiting factor in these type of studies is the fact that functional changes in the cervix are usually related to the gestational age, rather than the stage of gestation, relative to parturition. The hormonal changes in the maternal blood and the changes that take place in the cervix during parturition are more dramatic compared towhat happens during late pregnancy or the oestous phase of the cycle. It is therefore, logic to assume that during parturition functional changes in the cervix are differently regulated than during the other two stages, that they may differ in several biochemical and cellular aspects, and that timing of these changes relative to the moment of birth is critical. With the studies described in this thesis we aimed to find out if the cow could be a more suitable model for longitudinal studies of the cervix. By using a newly described biopsy technique to study samples that were repeatedly obtained from cows during different stages of gestation we were able to differentiate the biochemical changes that occur in the collagen of the bovine cervix during cervical ripening and during parturition. By adapting an ultrasound cervimetry technique, previously used in women, combining it with frequent blood-sampling and electromyographic (EMG) measurements of the uterus, we were able to continuosly monitor cervical dilatation during parturition and relate this to temporal changes in hormone levels and myometrial activity. In addition, studies of the cervix of the non-pregnant cow have shown that regional differences exist in biochemical aspects of collagen and expression of oestrogen and progesterone receptors, indicating that it is critical for the interpration of studies on cellular or biochemical changes, to describe in detail the area were samples were obtained.