Ovarian derived prorenin-angiotensin cascade in human reproduction

Comparison between resveratrol and cabergoline in preventing ovarian hyperstimulation syndrome in a rat model

OBJECTIVE

The aim of this study is to investigate the effects of resveratrol in a rat model of ovarian hyperstimulation syndrome (OHSS) and compare with cabergoline.

DESIGN

Randomized controlled, animal study.

ANIMAL(S)

Female Wistar rats.

MATERIAL AND METHODS

A rat OHSS model was used to investigate the effects of resveratrol compare with cabergoline administration for preventing OHSS. Body weight, ovary weight, diameter, vascular permeability (VP), vascular endothelial growth factor (VEGF), cyclooxygenase-2 (COX-2) expression (immunohistochemistry), and serum estradiol (E2) levels were then compared.

RESULTS

The ovarian VEGF concentration was significantly increased in the OHSS Groups (Groups 3-5) compared with the control groups (1 and 2). But vascular permeability, VEGF, and COX-2 expressions were reduced in animals treated with the resveratrol group compared with the cabergoline group (group 5) and the severe OHSS (group 3) group. Blood E2 levels were decreased in group treated with the resveratrol group compared with the cabergoline group (group 5) and severe the OHSS (group 3) group.

CONCLUSION(S)

Our results in a rat model suggest that resveratrol has a beneficial effect on OHSS by reducing the increases in ovarian daimeter, VP, and VEGF expression associated with OHSS. These effects may be mediated by the COX-2 inhibitory capacity of resveratrol.

Ovarian hyperstimulation syndrome

Ovarian hyperstimulation syndrome (OHSS) is an iatrogenic complication of assisted reproduction technology. The syndrome is characterized by cystic enlargement of the ovaries and a fluid shift from the intravascular to the third space due to increased capillary permeability and ovarian neoangiogenesis. Its occurrence is dependent on the administration of human chorionic gonadotrophin (hCG). β-hCG and its analogs, estrogen, estradiol, prolactin, histamine and prostaglandins have all been implicated in OHSS but now it is increasingly better understood that the vasoactivesubstances such as interleukins, tumor necrosis factor-α, endothelin-1, and vascular endothelial growth factor (VEGF) secreted by the ovaries have been implicated in increasing vascular permeability. Enlargement of the ovaries causes abdominal pain, nausea and vomiting. Leakage of fluid from follicles, increased capillary permeability leading to third spacing (due to the release of vasoactive substances), or frank rupture of follicles can all cause ascites. Due to leakage of fluid through the impaired blood vessels both within and outside the ovary there is massive fluid-shift from the intra-vescular bed to the third compartment results in intravascular hypovolemia with concomitant development of edema, ascites, hydrothorax and/or hydropericardium. Low-dose gonadotrophin protocols have been implemented to reduce the risks of fertility treatment in polycystic ovary syndrome patients. Prophylactic albumin administration may interrupt the development of OHSS by increasing the plasma oncotic pressure and binding mediators of ovarian origin. OHSS is significantly lower in an antagonist protocol than in an agonist protocol. Cabergoline inhibits partially the VEGF receptor 2 phosphorylation levels and associated vascular permeability without affecting luteal angiogenesis reduces the 'early' (within the first 9 days after hCG) onset of OHSS. To prevent thrombosis, subcutaneous heparin 5000-7500 U/d is begun on the first day of admission. These patients need a hospital ward where the clinical picture is well understood and the personnel have expertise in its treatment and follow-up. Admission to an intensive care unit is necessary when critical OHSS develops.

Hypercoagulability, high tissue factor and low tissue factor pathway inhibitor levels in severe ovarian hyperstimulation syndrome: possible association with clinical outcome

During ovarian gonadotrophin stimulation for ovulation induction or in vitro fertilization, a clinical severe ovarian hyperstimulation syndrome (OHSS) may occur. Only few studies have investigated the mechanism responsible for the alterations of the haemostatic system in women affected by severe OHSS. The aim of the present study was to investigate the correlation between the magnitude of ovarian stimulation and the increase in fibrin formation and degradation in severe OHSS. Twenty-five patients (age range 23-43 years) who were hospitalized for severe OHSS, 25 women undergoing in vitro fertilization who did not develop OHSS (case-control group) and 25 healthy age-matched women (healthy control group) were investigated. On the day of admission a number of haemostatic markers, including D-dimer, thrombin-antithrombin complexes (TAT), prothrombin fragment 1 + 2 (F1 + 2), plasmin-antiplasmin complexes (PAP), tissue factor (TF), tissue factor pathway inhibitor (TFPI) and von Willebrand factor antigen (vWF), were examined. In patients with severe OHSS, TF, D-dimer, TAT, F1 + 2, PAP and vWF antigen plasma levels were significantly higher than those observed both in the case-control group and in healthy controls, whereas TFPI levels were significantly lower (P < 0.005) with respect to both case-controls and healthy controls. D-Dimer levels were related with serum oestradiol levels and oocyte number recovered (r = 0.45, P < 0.001 and r = 0.47, P < 0.001, respectively). D-Dimer and TAT levels were significantly (P < 0.05 and P < 0.005, respectively) higher in OHSS patients with unsuccessful pregnancy outcome (D-dimer, 226.5, 56-1449 ng/ml; TAT, 19.8, 3.1-82.6 microg/l) with respect to those with successful outcome of pregnancy (D-dimer, 145, 29-330 ng/ml; TAT, 5.0, 1.0-19.6 microg/l). Our data indicate that a marked hypercoagulability with alterations of TF and TFPI levels is detectable in patients with severe OHSS and that it is related to the clinical outcome.

Effect of angiotensin-converting enzyme inhibitor on renal function in ovarian hyperstimulation syndrome in the rabbit

OBJECTIVE

To investigate renal function and whether captopril prevents alterations in the handling of sodium and water in the ovarian hyperstimulation syndrome (OHSS) in the rabbit.

DESIGN

Experimental study

SETTING

Physiology laboratory.

ANIMAL(S)

Six female New Zealand white rabbits were used as controls, and 13 were hyperstimulated with gonadotropins.

INTERVENTION(S)

Saline or captopril.

MAIN OUTCOME MEASURE(S)

Renal excretory and hemodynamic variables.

RESULT(S)

The 3% extracellular volume expansion in OHSS animals induced a significant elevation in mean arterial pressure by 27%, although increments in natriuresis and diuresis were similar to those observed in controls. The OHSS group had impaired pressure-natriuresis sensitivity compared with controls (0.36 +/- 0.07 microEq/min/g of Na excreted per mm Hg vs. 1.74 +/- 0.45 microEq/min/g of Na excreted per mm Hg; P<.05. Captopril significantly reduced mean arterial pressure (P<.05) and shifted the pressure-natriuresis response to the left by 0.85 +/- 0.17 microEq/min/g of Na excreted per mm Hg (P<.05).

CONCLUSION(S)

In OHSS in the rabbit model, pressure-natriuresis sensitivity is impaired. Angiotensin II may play a significant role in this phenomenon, since angiotensin-converting enzyme inhibition normalized the pressure-natriuresis relationship.

Influence of the angiotensinogen gene on the ovulatory capacity of mice

OBJECTIVE

The tissue-bound ovarian renin-angiotensin system (OVRAS) is critically involved in ovulation in humans and rodents. Mice with disruption and overexpression of the angiotensinogen gene (Agt) have been previously generated. We investigated the influence of varying Agt gene expression on the ovulatory capacity and early embryonic development in mice.

DESIGN

Observational study of genetically altered mice and their response to a superovulation protocol.

SETTING

Academic research institution.

ANIMAL(S)

Mice with varying copy numbers of Agt (one copy: n = 48; two copies: n = 51; three copies: n = 20; four copies: n = 24).

INTERVENTION(S)

Superovulation protocol, oocyte culture.

MAIN OUTCOME MEASURE(S)

Number of oocytes harvested, early embryonic development of zygotes, evaluation of ovarian histology, serum estradiol measurements.

RESULT(S)

The mean number of oocytes harvested was greatest in wild-type mice (two copies of Agt, 39.9 +/- 14) with a reduction of ovulatory capacity in mice overexpressing Agt (three copies [34.8 +/- 11.7] and four copies [31.2 +/- 12.4], P =.026). Mice with one copy of Agt showed a slight decrease of ovulatory capacity compared to wild-type mice (35.8 +/- 15.2, P =.29). Ovarian histology, serum estradiol levels, and early embryonic development were independent of the Agt genotype.

CONCLUSION(S)

Overexpression of Agt was associated with reduced ovulatory capacity, but with none of the other parameters that were evaluated. These findings support an important role of the ovarian renin-angiotensin system in the process of follicular rupture.

A rise of the serum level of von Willebrand factor occurs before clinical manifestation of the severe form of ovarian hyperstimulation syndrome

BACKGROUND

Ovarian hyperstimulation syndrome (OHSS) appears to be caused by increased capillary permeability in the vascular endothelial cells. Such cells secrete excess amounts of von Willebrand factor (vWF), a large adhesive glycoprotein.

METHODS

We retrospectively evaluated the circulating levels of vWF and of vascular endothelial growth factor (VEGF) twice, on the days of oocyte retrieval and embryo transfer, in 46 women who developed early-onset OHSS.

RESULTS

Nineteen, 14, and 13 women developed mild, moderate, and severe OHSS, respectively. Inconsistent changes were observed in the VEGF during oocyte retrieval and embryo transfer. However, the net increase in serum vWF during that period showed an increase in absolute value at the time of embryo transfer that paralleled an increase in the severity of OHSS. That is, in mild OHSS, the serum vWF increased from 140 +/- 44 to 164 +/- 28%; in moderate OHSS, it increased from 113 +/- 47 to 186 +/- 22%; and in severe OHSS, it increased from 120 +/- 35 to 274 +/- 63%. All 9 women with a vWF level > 230% at embryo transfer developed severe OHSS, while 9 of 13 women with severe OHSS exhibited a vWF > 230% at embryo transfer.

CONCLUSION

The results suggest that a rise of the serum level of vWF occurs prior to clinical manifestation of OHSS in patients with severe OHSS but not in patients with mild OHSS.

Serum total renin levels after ovarian electrocautery in women with polycystic ovary syndrome

Recent observations have suggested an enhanced activity of the ovarian renin-angiotensin system in polycystic ovary syndrome (PCOS). Owing to technical restrictions, the direct measurement of ovarian renin-angiotensin activity is impossible. The measurement of total renin (active renin + prorenin) in serum is particularly valuable for analyzing the ovarian renin-angiotensin system, as 90% of circulating renin is in the form of prorenin and ovaries are the major extrarenal source of prorenin in females. Also, the renin synthesized by ovaries is in the form of prorenin. In the present study we hypothesized that ovarian trauma caused by electrocautery 'impairs' the activity of the ovarian renin-angiotensin system, which in turn would interrupt the endocrine vicious cycle of PCOS, and restore normal ovarian function. To test this, we examined the effect of ovarian electrocautery on serum levels of total renin in 11 oligomenorrheic women, aged 25 to 36 years, with PCOS and anovulatory infertility. Against our basic hypothesis the serum total renin levels remained unaltered after ovarian electrocautery, while the serum levels of luteinizing hormone, testosterone and androstenedione declined. The mechanism that induces ovulation without altering total renin levels in serum remains to be resolved.

Angiotensin II induces acrosomal exocytosis in bovine spermatozoa

Ejaculated mammalian spermatozoa must reside in the female genital tract for some time before gaining the ability to fertilize the egg. During this time, spermatozoa undergo some physiological changes that collectively are called capacitation. Capacitation of mammalian spermatozoa is a prerequisite for acrosome reaction, which is an exocytotic event occurring before fertilization. The specific biophysical and biochemical changes that accompany sperm capacitation and the agonists inducing acrosome reaction are not fully understood. Using SDS-gel electrophoresis and immunoblotting, we demonstrate the existence of a class of angiotensin receptors (AT1) in bovine spermatozoa. In capacitated sperm, we show that angiotensin II (ANG II) AT1 receptors are localized in the head and tail, whereas in noncapacitated cells the receptors are localized in the tail only. We find that ANG II markedly stimulates acrosomal exocytosis of capacitated bovine spermatozoa in vitro in a concentration range of 0.1-10 nM. No effect of ANG II was found in noncapacitated cells. The ability of ANG II to stimulate the acrosome reaction depends on the presence of calcium ions in the incubation medium. The ANG II-induced acrosome reaction was markedly inhibited by a selective AT1 receptor antagonist, losartan (DUP 753). PD-123319, a selective antagonist of the ANG II AT2 receptor, had no effect on the ANG II-induced acrosome reaction. Thus ANG II via activation of AT1 receptors may play a regulatory role in the induction of the acrosome reaction.

The human placental renin-angiotensin system

The human placenta and related tissues are considered to be examples of the recently accepted local renin-angiotensin systems (RAS). The brain is another example of a system that is thought to be regulated independently of the kidney and the role of angiotensin within the CNS as a neural mediator has drawn considerable attention. It has been known for a long time that many of the neuroendocrine mediators and receptors are expressed in the placenta and it has been suggested that there are many parallels between the classical neuroendocrine system and the placental one. The present review summarizes information that components of the RAS are expressed in uteroplacental tissues, are regulated by endogenous substances, and have important biological functions within this reproductive system. A comparison of similarities and differences between the classical and the placental RAS may provide clues to functions in other endocrine and neuroendocrine systems. The major components of the placental RAS that are considered are renin, prorenin, angiotensin I, angiotensin II, angiotensin converting enzyme (ACE), angiotensin receptors, and angiotensinogen (renin substrate). The factors that regulate these components at the cellular and the nuclear level are described. It is concluded that prorenin via angiotensin-dependent and angiotensin-independent mechanisms influences functions within uteroplacental tissues. Some of these actions are direct and others are mediated by the release of different signalling molecules. These features are similar to many neuroendocrine systems and utilize some of the same messengers.

Subpopulations of human granulosa-luteal cells obtained during early timed and during normally timed follicular aspiration in in-vitro fertilization-embryo transfer cycles

OBJECTIVE

To find the differences between human granulosa-luteal cells obtained during early timed follicular aspiration to prevent severe ovarian hyperstimulation syndrome (OHSS) and during normally timed follicular aspiration.

DESIGN

Retrospective analysis of clinical laboratory data.

SETTING

In vitro fertilization unit, University Department of Obstetrics and Gynecology, Ljubljana, Slovenia.

PATIENT(S)

Twenty women undergoing IVF-ET at high risk for OHSS.

INTERVENTION(S)

Cells were obtained from the follicles of women who were stimulated with hMG and hCG during an early timed follicular aspiration of one ovary, 10-12 hours after hCG, and during a normally timed follicular aspiration of the contralateral ovary, 32-36 hours after hCG administration.

MAIN OUTCOME MEASURE(S)

Subpopulations of granulosa-luteal cells were observed by computerized image analysis in which hCG was localized using immunoperoxidase staining.

RESULT(S)

Early timed follicular aspirates contained no oocytes and only a scant number of granulosa cells. Granulosa-luteal cells were smaller than those from normally timed follicular aspirates. We identified three subpopulations in early timed follicular aspirates: nonluteinized, small luteinized, and medium luteinized cells. In normally timed follicular aspirates, four subpopulations were identified, including large luteinized cells. The normally timed follicular aspirates contained more hCG-stained cells. Three staining types of hCG localization were found: on the surface membrane, on the surface membrane and within the cytoplasm, and only within the cytoplasm of cells from normally timed follicular aspirates. Early timed follicular aspirates contained only cells with membrane hCG localization.

CONCLUSION(S)

We found differences in morphometric characteristics and hCG localization between human granulosa-luteal cells obtained during early timed follicular aspiration to prevent severe OHSS and during normally timed follicular aspiration.

Rare occurrence of ovarian hyperstimulation syndrome in oocyte donors

OBJECTIVES

To define the incidence and severity of ovarian hyperstimulation syndrome (OHSS) occurring in oocyte donors.

METHODS

Women (n = 149) aged 31.3 +/- 4.8 years (mean +/- S.D., range 21-41 years) participated as designated oocyte donors and underwent 400 consecutive cycles of controlled ovarian stimulation using human menopausal gonadotropin following pituitary downregulation with gonadotropin-releasing agonist. Patients were monitored by serial transvaginal ultrasound examinations and serum estradiol (E2) determinations. Oocytes (15.6 +/- 7.5 per aspiration; range 2-57) were harvested by ultrasound-directed transvaginal follicle aspiration 36 h following the intramuscular injection of human chorionic gonadotropin (hCG). Follow-up examination occurred 1 and 2 weeks post-aspiration.

RESULTS

On the day of hCG injection E2 levels ranged from 512 to 13,502 pg/ml (mean 2902.7 +/- 1486.9 pg/ml). Over the next few weeks the degree of hyperstimulation in donors was staged: mild 65% (grade I, n = 98; grade II, n = 162); moderate 33.5% (grade III, n = 120; grade IV, n = 14); severe 1.5% (grade V, n = 6; grade VI, n = 0). Associated preaspiration E2 levels were: grade I, 1120 +/- 424 pg/ml; grade II, 2084 +/- 613 pg/ml; grade III, 3785 +/- 1713 pg/ml; grade IV, 5370 +/- 1264 pg/ml; grade V, 4286 +/- 1100 pg/ml. Worsening OHSS was associated with increasing levels of E2. There were no serious complications and hospitalization was not required. All symptoms resolved within 30 days of aspiration, disappearing by the time of the first menstrual flow in women of grade-III or lower stage.

CONCLUSION

Although oocyte donors commonly experienced exaggerated levels of serum E2 they rarely (< 2%) developed severe OHSS. This may be attributable to their lack of embryo transfer which avoids exacerbating the illness.

Angiotensin converting enzyme inhibition of the gonadotropin-stimulated rabbit: effect on estradiol production

PURPOSE

Our purpose was to determine whether angiotensin converting enzyme (ACE) inhibitors affect gonadotropin-stimulated estradiol (E2) production.

DESIGN

This was a prospective, masked, randomized, placebo-controlled animal trial. Twenty female New Zealand White rabbits were hyperstimulated with gonadotropins. One-half of the rabbits received concomitant treatment with the ACE inhibitor, enalapril; one-half received concomitant treatment with a placebo.

RESULTS

Baseline peripheral E2 (13 +/- 4 vs 11 +/- 2 pg/ml) and angiotensin II (Ang II) (22 +/- 5 vs 27 +/- 7 pg/ml) levels were similar in both groups. Significant inhibition of peripheral Ang II levels was achieved in the enalapril group (32 +/- 6 vs 93 +/- 15 pg/ml; P = 0.005). E2 was significantly higher in the rabbits receiving enalapril versus placebo (369 +/- 58 vs 183 +/- 35 pg/ml, P < 0.03), respectively. By day 10, peripheral E2 had returned to normal levels in both groups (13 +/- 1 vs 13 +/- 1 pg/ml). However, E2 levels in the ovarian effluent were 2.8 times higher in the enalapril rabbits.

CONCLUSION

Peripheral Ang II levels increase after gonadotropin stimulation and ACE inhibitors are able to blunt this increase significantly. ACE inhibition has a significant stimulatory effect on ovarian E2 production. This implies that Ang II may normally inhibit ovarian E2 production in stimulated cycles.