The significance of the ovarian arteriolar vasodilatation in pathogenesis of the ovarian hyperstimulation syndrome

: Ovarian hyperstimulation syndrome is a complication of the ovulation stimulation, most commonly by gonadotrophins. It frequently occurs in patients included in in vitro fertilization program. The exact mechanism of development of this syndrome has not been elucidated yet. The basic pathogenic mechanism of development of this syndrome is vasodilation of the ovarian blood vessels. Dilated ovarian blood vessels become permeable. Permeability of dilated ovarian blood vessels is more increased by released ovarian mediators. Due to increased permeability of the blood vessels, there is leakage of the intravascular fluid into the extravascular areas resulting in hypovolemia, edema and ascites. Hypovolemia leads to renal perfusion decrease. Increased salt and water reabsorption occurs in the renal tubules so oliguria develops. Decreased arterial blood volume results in stimulation of the renin-angiotensin-aldosterone system, the sympathetic nervous system as well as the antidiuretic hormone. The activation of the sympathetic nervous system via beta adrenergic receptors stimulates renin release and aldosterone secretion. Renin stimulates release of angiotensin I which transforms into angiotensin II. Angiotensin II increases the pressure and stimulates aldosterone secretion. In patients with this syndrome, there is an elevated plasma endothelin and natriuretic peptide level. Endothelin is an important vasoconstrictor. It increases secretion of renin, aldosterone, catecholamines, antidiuretic hormone, and atrial natriuretic peptide, and enhances the vasoconstrictive effect of norepinephrine and angiotensin II. The platelet number increase together with the elevated factor of blood coagulation and hyperviscosity in a severe form of this syndrome may result in development of intravascular thrombosis. The treatment consists of maintenance of circulatory function, i.e. the increase of effective arterial blood volume by applying the plasma volume expanders.