The implantation receptive luteal phase of the endometrium. On the current status of molecular and cell biology research

Abstract

The biological aim of the differentiation and maturation of endometrial tissue compartments during any menstrual cycle is the achievement of suitable conditions for blastocyst implantation and the establishment of pregnancy. Infertility and early embryonic loss are frequently caused by insufficient endometrial differentiation. Even any incomplete receptivity stage of the luteal phase endometrium will prevent attachment and implantation. We have studied the physiological changes throughout an endometrial cycle to elucidate causes of endometrial insufficiency leading to subfertility or infertility. Up to now, the histological changes described by Noyes et al. are understood as classical diagnostic approaches. However, evidence is accumulating that molecular deficits of endometrial differentiation are by no means detectable histologically, and consequently ask for the research on new diagnostic methods and parameters. There are histochemical localizations of specific protein molecules, adhesion molecules and cytokines, which permit by far more detailed and significant molecular analyses than any classical morphological means could yield. Moreover, there are convincing arguments to use further biochemical assessments on proteins of the uterine secretions as specific diagnostic parameters. The electrophoretical resolution presents typical protein patterns, which in turn can be interpreted as characteristic reflexions of the functional phases of the endometrial cycle. What is demonstrated as the so-called adequate luteal phase protein pattern clearly is the product of the receptive endometrium, reflecting the "implantation window". This is established already two days after ovulation and persists usually eight further days, if the endometrial cycle is undisturbed (15th to 24th day of the cycle).