Dilated thin-walled blood and lymphatic vessels in human endometrium: a potential role for VEGF-D in progestin-induced break-through bleeding.

Progestins provide safe, effective and cheap options for contraception as well as the treatment of a variety of gynaecological disorders. Episodes of irregular endometrial bleeding or breakthrough bleeding (BTB) are a major unwanted side effect of progestin treatment, such that BTB is the leading cause for discontinued use of an otherwise effective and popular medication. The cellular mechanisms leading to BTB are poorly understood. In this study, we make the novel finding that the large, dilated, thin walled vessels characteristic of human progestin-treated endometrium include both blood and lymphatic vessels. Increased blood and lymphatic vessel diameter are features of VEGF-D action in other tissues and we show by immunolocalisation and Western blotting that stromal cell decidualisation results in a significant increase in VEGF-D protein production, particularly of the proteolytically processed 21 kD form. Using a NOD/scid mouse model with xenografted human endometrium we were able to show that progestin treatment causes decidualisation, VEGF-D production and endometrial vessel dilation. Our results lead to a novel hypothesis to explain BTB, with stromal cell decidualisation rather than progestin treatment per se being the proposed causative event, and VEGF-D being the proposed effector agent.

Observing three-dimensional human microvascular and myogenic architecture using conventional fluorescence microscopy.

Microangiography and vascular casting have previously been used to demonstrate the three-dimensional architecture of human uterine microvasculature. However, a limitation of these perfusion-dependent techniques is the difficulty in identifying surrounding tissue components. We have previously shown that it is possible to visualise microvascular networks on the cut surfaces of fresh tissue specimens by diffusive labelling of vascular endothelium with fluorescently conjugated UEA-1 lectin. Unlike perfusion methods that are limited to accessible vascular networks, diffusive fluorescence labelling (DFL) allows additional visualisation of extravascular cellular components, such as smooth muscle. Following UEA-1 DFL, smooth muscle-myosin and -actin were then visualised by immunolocalisation on the acetone-fixed tissue pieces. This allowed clear three-dimensional distinction between the vascular and muscle architecture of the myometrium and endometrium. This method can also be applied for studying the relative distribution of microvascular and muscle architecture in leiomyomas (fibroids). The techniques described in this methodological study provide a simple way of directly examining the uterine vasculature in three dimensions using conventional microscopy, while also distinguishing myometrial from endometrial parts of the network.

The levonorgestrel-releasing intrauterine system in modern gynaecology.

The levonorgestrel-releasing intrauterine system was initially developed for contraception but is now widely used for a variety of gynaecological conditions. Compliance can sometimes be hampered by troublesome side effects (principally breakthrough bleeding) but appropriate counselling can reduce unnecessary discontinuation.

Hormonally mediated disturbance of angiogenesis in the human endometrium after exposure to intrauterine levonorgestrel.

BACKGROUND: The levonorgestrel intrauterine system (LNG-IUS) is a contraceptive device that is used for treatment of menorrhagia. The system induces inter-menstrual bleeding within the first few months after insertion. We hypothesized that this bleeding might be associated with a change in vascular development. METHODS: A randomized, controlled study was undertaken on 48 women. RESULTS: Hysterectomy specimens were obtained and immunocytochemistry was carried out with antibodies to CD31, alpha-smooth muscle actin and myosin. Stereological measurement of blood vessels was also undertaken. Most vessels appeared normal, including the arterioles. Large thin-walled vessels were present in the superficial endometrium of the treated group but were almost completely absent in the controls. The distribution of cytoskeletal markers revealed well-formed basal arterioles with more widespread expression in the superficial stroma than was found in untreated tissue. The volume fraction of blood vessels (P = 0.0001), the number of vessel cross-sections per unit area (P = 0.0003) and the cross-sectional diameters of the largest vascular lumens (P = 0.0001) were significantly increased following treatment with LNG-IUS. However, there was no difference in the median values of vessel diameter or the vascular surface density. CONCLUSION: These findings suggest that the LNG has a localized effect on some vessels within the superficial endometrium.

The Mirena levonorgestrel system.

The levonorgestrel intrauterine system is a safe, efficacious, long-term contraceptive device. Additionally, it results in a decrease in the volume of menstrual blood loss in women with normal periods and those with menorrhagia. It may also have a role in the treatment of other benign gynecological disorders, such as adenomyosis or endometriosis, and it has been advocated as a means of delivering progestogen to the endometrium as part of combined hormone replacement therapy. Despite the beneficial effect on menstrual volume, compliance is sometimes limited by breakthrough bleeding during the first months of use. The precise mechanism of this bleeding is unclear, but it may be related to a direct effect of levonorgestrel on endometrial vascular development. Detailed counseling is crucial to explain this anticipated side effect in order to reduce unnecessary discontinuation of treatment.