Role of vascular endothelial cell growth factor in Ovarian Hyperstimulation Syndrome

Evaluation and management of infertility in women: the internists' role

Interventions for infertility have greatly increased in number and sophistication. Women with multiple medical problems and women near or beyond menopause are now able to conceive. The internist will be called on to assess the risk that infertility interventions pose and to counsel patients accordingly. Knowledge of the medical illnesses associated with infertility, the types of infertility treatments available, and the medical complications of these interventions are required to properly assess this risk. Medical complications of infertility interventions can be direct effects of related drugs and technologies and indirect consequences of the induced pregnancy, multiple gestation, or associated medical conditions. This article reviews the definitions and scope of infertility, the interventions used for treatment of infertility, the medical complications of these interventions, the potential risks of fertility treatment in women unable to conceive spontaneously, and important issues for preconception counseling.

The ovarian hyperstimulation syndrome

OBJECTIVE

To review the up-to-date literature concerning the pathogenesis of, risk factors for, prevention of, and therapy for the ovarian hyperstimulation syndrome, and to provide suggestions for management of this syndrome.

DESIGN

Literature review combined with on-site clinical experiences at the authors' institution of practice.

PATIENT(S)

Women who have risk factors for or manifest the ovarian hyperstimulation syndrome.

INTERVENTION(S)

Intravenous fluid management, thrombosis prevention techniques, paracentesis techniques, and critical care management protocols.

MAIN OUTCOME MEASURE(S)

Staging system of the ovarian hyperstimulation syndrome, criteria for outpatient versus hospitalization management, and indications for varying levels of interventional management.

RESULT(S)

The ovarian hyperstimulation syndrome, unique to the field of assisted reproductive technology, remains a largely elusive and unpredictable iatrogenic physiologic complication in the course of pharmacologic ovarian stimulation. Reliable information on risk factors, possible physiologic mechanisms, prevention techniques, and management is fortunately progressing, and overall advances are being made in this field. The present review is an attempt to summarize the modern literature regarding this syndrome and to use this current knowledge to provide a basis for acceptable management regimens.

CONCLUSION(S)

Ovarian hyperstimulation syndrome is a serious complication of assisted reproductive technology, with potential for critical morbidity and death. Physicians who prescribe medications known to be associated with this syndrome should be familiar with identifiable risk factors, means of prevention, and a system for staging and treating the disease and have a current knowledge base for putative models of pathogenesis.

Importance of angiogenesis in reproductive physiology

The cyclic angiogenesis that occurs uniquely within the female reproductive tract is critical for normal reproduction. Two families of endothelial cell-specific growth factors and their receptors have been identified in the ovary, uterus, and placenta: vascular endothelial growth factor/vascular permeability factor and the angiopoietins. These appear to have complementary actions on the vasculature and to be involved during intrauterine development as well as in the adult. Within the ovary, a complex cascade of events required for angiogenesis may play a role in follicular maturation and selection as well as in normal corpus luteum function. Aberrant expression of angiogenic factors plays a role in a wide variety of abnormalities in the ovary. In the uterus, angiogenesis is required for endometrial growth and remodeling. Peptide growth factors such as vascular endothelial growth factor may serve as local mediators of the effects of reproductive hormones on the endometrial vasculature. Disease states such as dysfunctional uterine bleeding, endometriosis, and endometrial hyperplasia or cancer may be associated with aberrant uterine angiogenesis.

The vascular endothelial growth factor/fms-like tyrosine kinase system in human ovary during the menstrual cycle and early pregnancy

In human ovaries, angiogenesis is known to be associated with the development of follicles and the formation of the corpus luteum (CL). A complex vascular network is formed within the thecal cell layer during follicular growth, and rapid neovascularization occurs toward the granulosa cell layer after ovulation. Vascular endothelial growth factor (VEGF) is a multifunctional cytokine, stimulating endothelial cell growth and enhancing microvascular permeability. A specific receptor for VEGF, fms-like tyrosine kinase (Flt-1), is expressed in vascular endothelial cells that mediates the action of VEGF. We examined the localization and expression of VEGF and Flt-1, using an immunohistochemical technique and RT-PCR analysis, in human follicles and corpora lutea during the normal menstrual cycle and early pregnancy. We measured concentrations of VEGF in extracts of human CL using an enzyme-linked immunosorbent assay during the luteal phase and early pregnancy. Immunostaining for VEGF was observed in granulosa cells from small antral follicles to preovulatory follicles. The staining was detected in thecal cells from medium-sized to preovulatory follicles. The intensity of the staining was gradually increased as a follicle grew. Flt-1 was localized in granulosa and thecal cells of preovulatory follicles as well as in endothelial cells. In the human CL, the intense staining for VEGF was observed in granulosa and thecal lutein cells, especially in the midluteal phase. The immunostaining for Flt-1 was faint in endothelial cells in the CL, whereas it was distinct in granulosa and thecal lutein cells. The concentrations of VEGF in lutein extracts were high in the early and midluteal phases and tended to decrease toward the late luteal phase. During early pregnancy, a measurable amount of VEGF was detected. RT-PCR analysis demonstrated that messenger ribonucleic acids encoding VEGF121, VEGF165, and Flt-1 were expressed in the CL. These results suggest that VEGF might have an autocrine role in the ovulatory process and luteal function as well as a paracrine role in angiogenesis.

Vascular endothelial growth factor in reproductive biology

The critical role of angiogenesis in embryology and tumor biology has been recognized for more than 20 years. However, the fact that neovascularization is essential to processes in mammalian female reproduction has only recently been appreciated widely. In this review we focus on a single angiogenic growth factor, vascular endothelial growth factor. As scientists have discovered in many aspects of cell biology, multiple and redundant signaling pathways have evolved in nature, presumably to protect essential biological functions from inactivating diseases or mutations. Despite this redundancy, some factors are of hierarchical importance. Vascular endothelial growth factor appears to be such a factor in the regulation of angiogenesis.