Masato Mikuni

The transcription factor C/EBP-beta and its role in ovarian function; evidence for direct involvement in the ovulatory process.

Gonadotropins are responsible for maturation of the ovarian follicle and the oocyte. Ovulation is the ultimate step in this process and involves disintegration of the follicular wall and subsequent release of an oocyte into the oviduct. These events are triggered by a surge of luteinizing hormone (LH). Genes expressed in the ovary, that respond to LH, are likely to be involved in the biochemical pathways that regulate ovulation. The transcription factor C/EBP‐β is induced promptly in the ovary, as a response to an ovulatory dose of gonadotropins. We used an ex vivo perfusion system to demonstrate that a specific reduction in ovarian C/EBP‐β expression inhibits ovulation. In such ovaries the oocytes appeared to be entrapped within the follicle. We have found a correlation between the expression level of the activating isoform of C/EBP‐β and the number of oocytes ovulated in response to gonadotropins. Since a reduction in C/EBP‐β expression does not affect the level of the ovulatory mediator prostaglandin endoperoxide synthase‐2 (PGS‐2), these findings support the view of C/EBP‐β as an important factor in the ovulatory process and highlight a C/EBP‐β‐dependent and PGS‐2‐independent pathway that takes part in regulation of ovulation.

Time-dependent ovulation inhibition of a selective progesterone-receptor antagonist (Org 31710) and effects on ovulatory mediators in the in vitro perfused rat ovary.

Abstract Progesterone (P) is one of several local mediators in the ovulatory cascade in the rat. The precise mechanisms of action for P in ovulation and in what phase of the ovulatory process P is critical, however, need to be clarified. The present study used a selective P-receptor antagonist, Org 31710, in the in vitro perfused rat ovary model to examine the local role of P and possible effects on prostaglandin (PG) and plasminogen-activator (PA) release in ovulation. Ovaries from eCG (15 IU)-primed rats were perfused for 20 h with LH (0.2 μg/ml) and 3-isobutyl-1-methylxanthine (IBMX, 200 μM) to induce ovulation (median = 10.0, 25%–75% range = 8.5–13). Org 31710 was added at either 0, 3.5, 7, or 9 h after LH+IBMX, resulting in significant suppression of ovulation after addition at 0 and 3.5 h (1.0, 1–5.5; and 5.0, 2.5–7.75 ovulations, respectively) but no suppressive effect when added at later time points. Progesterone and estradiol levels in the perfusion media were increased after LH+IBMX but were not affected by the presence of Org 31710. Ovarian tissue levels of PGE2, PGF2α, and PA activity were measured in ovaries that had been perfused for 10 h, a time that was 2 to 5 h before anticipated ovulation. The presence of Org 31710 significantly decreased the levels of PGE2, PGF2α, and PA activity. These results suggest that P is essential in ovulation during the initial stages of the ovulatory process. The effect of P to facilitate ovulation seems to relate to stimulation of the PG- and PA-mediator systems.

Ectopic ovary: A case of autoamputated ovary with mature cystic teratoma into the cul-de-sac

An ovary with a mature cystic teratoma which was autoamputated into the cul‐de‐sac and confirmed by laparoscopy is described. A 24‐year‐old woman with a history of chronic pelvic pain for 5 years presented with left abdominal pain. Magnetic resonance imaging revealed a left ovarian mass of 5 cm in diameter. The pain was relieved spontaneously after a few weeks. Laparoscopy was performed 5 months later. The mass was identified in the cul‐de‐sac partly enveloped in the omentum without any ligamentous or direct connection with the pelvic organs. There was no left ovary in its proper anatomical location. Histopathologic study revealed a mature cystic teratoma with viable ovarian tissue. These findings suggested autoamputation of the ovary either by inflammation or torsion, which is one of the mechanisms for the formation of an ectopic ovary.

Saralasin-induced inhibition of ovulation in the in vitro perfused rat ovary is not replicated by the angiotensin II type-2 receptor antagonist PD123319

OBJECTIVE Our aim was to explain the effect of the nonspecific angiotensin II antagonist saralasin and the specific angiotensin II type-2 receptor antagonist PD123319 on ovulation. STUDY DESIGN Saralasin, 1 micromol/L (n = 5), and PD123319 10 micromol/L (n = 6), were administered to in vitro perfused rat ovary. Prostaglandin (prostaglandin E2, prostaglandin F2alpha, 6-keto-prostaglandin F1alpha), hydroxy-eicosatetraenoic acid (12-hydroxy-eicosatetraenoic acid, 15-hydroxy-eicosatetraenoic acid), estradiol, and progesterone levels in the perfusate and the ovulation rate were compared (Mann-Whitney U test) with controls. RESULTS Saralasin significantly (P < .01) inhibited the ovulation rate (3.0 +/- 1.4) versus control (13.1 +/- 1.0) and reduced prostaglandin E2 (at 3 hours P < .01 and 20 hours P < .05) and 6-keto-prostaglandin F1alpha (at 20 hours P < .05) levels. Saralasin did not alter prostaglandin F2alpha, hydroxy-eicosatetraenoic acids, or steroid levels. PD123319 decreased 15-hydroxy-eicosatetraenoic acid levels at 3 hours (P < .05) but had no effects on other eicosanoids, steroid levels, or the ovulation rate. CONCLUSION Angiotensin II plays an important role in ovulation in the rat and is associated with ovarian prostaglandin synthesis. This effect is not selectively regulated via the angiotensin II type-2 receptor.

Alterations of follicular microcirculation and apex structure during ovulation in the rat.

OBJECTIVE We utilized methods for intravital microscopy and microcirculation measurements to study changes during ovulation. STUDY DESIGN Immature gonadotrophin-primed rats were laparotomized and one ovary was examined for morphological alterations during a 3 h period (covering a period from 1h before to 27 h after hCG) through water-immersion lenses (maximum magnification 812×). Microcirculatory blood flow was assessed by measurements of blood cell velocity and laser Doppler flowmetry. RESULTS Follicular hyperaemia was observed 30 min after hCG and then vasomotion was observed. A gradual decline of apical blood flow was seen, which later was associated with an avascular area over the top of the apex. Cells from the surface over the follicular apex were then detached from the exterior of the follicle and this phenomenon was initiated more than one hour prior to follicular rupture. The subsequent structural alterations varied with or without formation of a cone over the stigma. In ovulations with a stigma-cone, a translucent, irregular mass formed over the stigma. Prior to follicular rupture, granulosa cells and follicular fluid were extruded from the follicular cavity at a velocity of around 70 μm/s. Occasionally, intra-antral haemorrhage occurred prior to or during follicular rupture. CONCLUSION Characteristic features of ovulation in the rat are microcirculatory vasomotion, gradual formation of apical avascular area, specific changes of the stigma, and extrusion of the oocyte-granulosa cell complex with or without haemorrhage.

Visualization of the Periovulatory Follicle: Morphological and Vascular Events

The rapid development of molecular biology methods have led to a considerable increase in the understanding of ovarian physiology. In parallel, several in vitro techniques have been utilized to investigate the morphological and vascular changes during the ovulatory process. Although there has been a comparative development of technical equipment to capture dynamic morphology changes, there are very few in vivo observations regarding morphological changes that occur during the ovulatory process. This is most likely due to the technical difficulties involved in following a delicate prolonged physiological process that occurs intraabdominally. In this chapter we will discuss observations of changes in and around the follicle during ovulation as seen during in vitro perfusion (1, 2) and in vivo (3) in relation to earlier studies in this field.

Glucocorticoid suppression of intraovarian levels of prostaglandins and plasminogen activator activity at ovulation in the rat ovary

Aim:  Ovulation is a local physiological inflammatory process with active participation of inflammatory mediators and immune cells. To prevent extensive inflammatory injury to the follicle at ovulation there is also a local anti‐inflammatory system at ovulation, converting the inactive glucocorticoid cortisone to the more potent cortisol. The aim of this study was to examine the effects of the potent glucocorticoid analogue, dexamethasone (DEX), on ovulation rate and the ovarian production of the ovulatory mediators prostaglandins (PG) and plasminogen activators (PA).

The Ovarian Renin Angiotensin System Viewed Through Ovarian Perfusion

In 1898, Tiegerstadt and Bergman noted that the crude saline extracts of the kidney had a powerful pressor activity, which they named renin (1). This discovery eventually lead to the understanding of the circulating renin angiotensin system (RAS) as a unique endocrine appendage with a clear role in blood pressure control. In the classical circulating RAS system, the JG cells secrete prorenin that is subsequently converted by endopeptidases to renin, a 347 amino acid (Fig. 12.1). Prorenin is secreted from the renal juxtaglomerular cells at 10 times the concentration of renin. Prorenin, which was originally considered a unique product of the kidney, has now been located in chorion, tumor cells, and blood vessels, as well as the adrenal gland, brain, testis, and ovary. In fact, these extrarenal sources, or tissue-based renin angiotensin systems, may account for up to 10% of the total plasma prorenin concentration.