The angiotensin II antagonist saralasin inhibits ovulation in the perfused rat ovary

Prorenin periconceptionally and in pregnancy: Does it have a physiological role?

Pregnancy demands major cardiovascular, renal and endocrine changes to provide an adequate blood supply for the growing fetus. The renin-angiotensin-aldosterone system plays a key role in this adaptation process. One of its components, prorenin, is released in significant amounts from the ovary and uteroplacental unit. This review describes the sources of prorenin in the periconception period and in pregnancy, including its modulation by in-vitro fertilization protocols, and discusses its potential effects, among others focusing on preeclampsia. It ends with discussing the long-term consequences, even in later life, of inappropriate renin-angiotensin-aldosterone system activity in pregnancy and offers directions for future research. Ultimately, a full understanding of the role of prorenin periconceptionally and during pregnancy will help to develop tools to diagnose and/or prevent reproductive complications.

Prorenin periconceptionally and in pregnancy: Does it have a physiological role?

Pregnancy demands major cardiovascular, renal and endocrine changes to provide an adequate blood supply for the growing fetus. The renin-angiotensin-aldosterone system plays a key role in this adaptation process. One of its components, prorenin, is released in significant amounts from the ovary and uteroplacental unit. This review describes the sources of prorenin in the periconception period and in pregnancy, including its modulation by in-vitro fertilization protocols, and discusses its potential effects, among others focusing on preeclampsia. It ends with discussing the long-term consequences, even in later life, of inappropriate renin-angiotensin-aldosterone system activity in pregnancy and offers directions for future research. Ultimately, a full understanding of the role of prorenin periconceptionally and during pregnancy will help to develop tools to diagnose and/or prevent reproductive complications.

Localized accumulation of angiotensin II and production of angiotensin-(1-7) in rat luteal cells and effects on steroidogenesis

These studies aim to investigate subcellular distribution of angiotensin II (ANG II) in rat luteal cells, identify other bioactive angiotensin peptides, and investigate a role for angiotensin peptides in luteal steroidogenesis. Confocal microscopy showed ANG II distributed within the cytoplasm and nuclei of luteal cells. HPLC analysis showed peaks that eluted with the same retention times as ANG-(1-7), ANG II, and ANG III. Their relative concentrations were ANG II >or= ANG-(1-7) > ANG III, and accumulation was modulated by quinapril, an inhibitor of angiotensin-converting enzyme (ACE), Z-proprolinal (ZPP), an inhibitor of prolyl endopeptidase (PEP), and parachloromercurylsulfonic acid (PCMS), an inhibitor of sulfhydryl protease. Phenylmethylsulfonyl fluoride (PMSF), a serine protease inhibitor, did not affect peptide accumulation. Quinapril, ZPP, PCMS, and PMSF, as well as losartan and PD-123319, the angiotensin receptor type 1 (AT1) and type 2 (AT2) receptor antagonists, were used in progesterone production studies. ZPP significantly reduced luteinizing hormone (LH)-dependent progesterone production (P < 0.05). Quinapril plus ZPP had a greater inhibitory effect on LH-stimulated progesterone than either inhibitor alone, but this was not reversed by exogenous ANG II or ANG-(1-7). Both PCMS and PMSF acutely blocked LH-stimulated progesterone, and PCMS blocked LH-sensitive cAMP accumulation. Losartan inhibited progesterone production in permeabilized but not intact luteal cells and was reversed by ANG II. PD-123319 had no significant effect on luteal progesterone production in either intact or permeabilized cells. These data suggest that steroidogenesis may be modulated by angiotensin peptides that act in part through intracellular AT1 receptors.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Angiotensin II reverses the inhibitory action produced by theca cells on bovine oocyte nuclear maturation

The presence of prorenin, renin, angiotensinogen, angiotensin-converting enzyme, angiotensin II (Ang II) and Ang II receptors in the ovary is suggestive of a functional ovarian renin-angiotensin system (RAS). In cattle, the expression of Ang II is greatest in large follicles, suggesting that it is important during follicular growth and maturation. The present study was designed to investigate the role of Ang II in bovine oocyte nuclear maturation. Bovine cumulus-oocyte complexes (COCs) were cultured with or without follicular cells and Ang II or saralasin (Ang II antagonist). In the absence of follicular cells, Ang II at 0, 10(-11), 10(-9) and 10(-7) M did not affect the percentage of oocytes reaching the germinal vesicle breakdown (GVBD), metaphase I (MI) and metaphase II (MII) stage after 7-h (41.3 +/- 4.3, 35.3 +/- 4.0, 31.3 +/- 9.7, 38.7 +/- 8.6), 12-h (31.6 +/- 7.0, 34.7 +/- 6.1, 31.7 +/- 5.3, 28.9 +/- 9.1; mean +/- S.E.M.) and 18-h (44.9 +/- 7.3, 58.4 +/- 8.4, 53.1 +/- 7.4, 44.9 +/- 7.3) of culture, respectively. Similarly, saralasin at 0, 10(-11), 10(-9) and 10(-7) M did not affect the percentage of oocytes reaching MII stage after 18-h of culture (37.6 +/- 7.4, 34.4 +/- 7.7, 30.0 +/- 10.8 and 31.2 +/- 5.1, respectively). The theca cells (MII = 22.9%) or medium conditioned with follicular cells (GV = 65.5%, MI = 23.6%) inhibited oocyte maturation; however, theca cells (MII = 35.5 +/- 4.9; P < 0.05) or medium conditioned with follicular cells (GV = 34.6%, MI = 52.7%; P < 0.01) were not able to inhibit nuclear maturation when Ang II (10(-11) M) was present in the culture system. Theca cells remained viable during the culture period when Ang II was present. Therefore, results supported the idea of a role of Ang II in blocking the inhibitory effect of theca cells on nuclear maturation of bovine oocytes.

Immunocytochemical localization of angiotensin II receptor subtypes 1 and 2 in the porcine fetal, prepubertal and postpubertal ovary

There is considerable evidence for a mammalian ovarian renin-angiotensin system, which may influence ovulation, angiogenesis and steroidogenesis via the autocrine and/or paracrine actions of the biologically active product of the cascade, angiotensin II (AngII). There are two characterized AngII receptors--type 1, AT1 and type 2, AT2. We report the localization of these receptor subtypes within porcine fetal, prepubertal and postpubertal ovaries. Positive staining for AT1 and AT2 receptors was observed in egg nests in all fetal ovaries studied, as well as in a defined two-cell layer at the ovarian periphery. In prepubertal tissue, positive AT1 and AT2 staining was localized to granulosa cells adjacent to the basement membrane of pre-antral and antral follicles, with no staining in the thecal layer. There was immunostaining for both receptors in prepubertal oocytes and zona pellucida. In postpubertal tissue, positive AT1 and AT2 immunostaining was localized to areas of putative neovascularization, the zona pellucida and the oocyte. Further AT1 staining was located to the postpubertal antral follicle granulosa cells. The results indicate that there are higher densities of AT1 receptors than AT2 receptors in the porcine fetal, prepubertal and postpubertal ovary, and this has profound implications for the role of AngII in ovarian development.

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.

Periovulatory changes in the local release of vasoactive peptides, prostaglandin f(2alpha), and steroid hormones from bovine mature follicles in vivo

We previously proposed that an endothelin-angiotensin-atrial natriuretic peptide system may contribute to inducing ovulation of mature bovine follicles by modulating follicular secretion of steroids and prostaglandins (PGs). Thus, this study aimed to determine the real-time changes in the local release of angiotensin II (Ang II), endothelin (ET), atrial natriuretic peptide (ANP), PGF(2alpha), and steroid hormones from bovine mature follicles during the periovulatory period in vivo. Seven cows were treated for superovulation using FSH and PGF(2alpha) injections. Two dialysis capillary membranes per follicle were surgically implanted into the theca layer of mature follicles and connected to a microdialysis system (MDS). Fractions of the perfusate were collected from Day -1 (Day 0 = LH surge) to Day 3. Five out of seven treated cows were normally ovulated, and the newly formed corpora lutea were observed at the end of the experiment. In these five ovulated cows, the release of estradiol, androstenedione, and progesterone in the theca layer increased (P < 0.05) synchronously with the LH surge. Acute increases in PGF(2alpha) and Ang II concentrations in the ovarian venous plasma (OVP) were observed at 24-48 h after the peak of the LH surge, when multiple ovulations were expected to occur. The follicular Ang II release was low during the pre-LH surge period and rose (P < 0.05) at the beginning of the increase in the LH surge. On the other hand, ET-1 release dropped (P < 0.05) when plasma LH started to increase. However, no clear changes in ANP concentration in the MDS perfusate and plasma were observed. The above local changes in Ang II, PGF(2alpha), as well as steroid hormones were not observed in cows (n = 2) that did not show an LH surge and ovulation. The present results demonstrate for the first time the local release of Ang II, ET-1, and ANP from the bovine mature follicle in real-time in vivo and show that Ang II and PGF(2alpha) concentrations in the OVP acutely increase around the time of ovulation. The overall results support the concept of a local functional ET-Ang-ANP system in the bovine mature follicle that may be involved in the ovulatory process.

Clinical implications of the ovarian/endometrial renin-angiotensin-aldosterone system

New organ-specific functions of angiotensin II have recently been described: the importance of its role in the regulation of secretory epithelial function in many tissues including components of the reproductive tract has been documented. The source of angiotensin II in these tissues is the reproductive tract itself, and there is considerable evidence to suggest a distinct renin-angiotensin-aldosterone system in the ovary and uterus. Two main subtypes of angiotensin II receptors are recognized as angiotensin-receptor I and II, according to their sensitivity to the angiotensin II antagonists. However, the presence of angiotensin II receptors in the male and female reproductive tract suggests a multiplicity of roles that are unrelated to their primary functions or to each other. The renin-angiotensin-aldosterone system is a major determinant of sodium balance in pregnancy. More recently RT-PCR methods have revealed angiotensinogen transcription in the smooth muscle of spiral anteries of the decidua; a specific allele of this gene may be associated with hypertension in pregnancy as well as in pre-eclampsia. We investigated the evolution of plasma renin activity and aldosterone levels during normal and hypertensive pregnancy. Both were found to increase progressively during all three trimesters of normotensive pregnancy. Plasma renin activity in hypertensive women remained unchanged during all three trimesters of pregnancy. Plasma aldosterone levels in hypertensive women increased progressively during all three trimesters of pregnancy. However, plasma aldosterone levels remained significantly lower than the ones of normotensive pregnant women. These increased aldosterone levels were noticed despite unchanged renin levels. Further clinical studies investigating the renin-angiotensin-aldosterone system in the pathogenesis of pregnancy hypertension are needed. A renin-independent role of aldosterone in this pathological entity is suggested.

Angiotensin II: a reproductive hormone too?

It has long been known that angiotensin II (Ang II) can affect reproductive tissues such as the uterus. However, the existence of a local renin-angiotensin system (RAS) in female as well as male reproductive tissues is a relatively recent observation. Of great interest is the discovery that all components of the RAS are present in the ovary, that the ovary secretes components of the RAS into the bloodstream, and that the ovary itself is responsive to Ang II. Recent studies suggest that the primary role of Ang II in the ovary is to cause atresia in non-ovulatory follicles; however, there is also compelling data to suggest that Ang II facilitates ovulation. Male reproductive structures also contain all of the components of the RAS, gonadotropins regulate the activity of these components, and these tissues have Ang II receptors. Of great interest is the expression of testis-specific angiotensin-converting enzyme (ACE), which is located on germ cells. Recent studies using gene knock-out techniques indicate that testis ACE plays an important role in male fertility. However, the overall significance of the RAS for normal reproductive function remains questionable. There is now a body of evidence implicating the RAS in pathophysiologies associated with reproductive function, which gives rise to the possibility that drugs acting on the RAS might ameliorate some of these disorders. Considerable work remains to determine the role of Ang II in reproductive functions.

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.

Effects of angiotensin converting enzyme inhibitor cilazapril and angiotensin II antagonist saralasin in ovarian hyperstimulation syndrome in the rabbit

We investigated the possible effects of the angiotensin converting enzyme (ACE) inhibitor cilazapril and angiotensin II antagonist saralasin on ovulation, ovarian steroidogenesis and ascites formation in the ovarian hyperstimulation syndrome (OHSS) in the rabbit model. OHSS was induced in rabbits by human menopausal gonadotropin (hMG) and intermittent human chorionic gonadotropin (hCG). In the cilazapril group (n = 10), animals also received cilazapril 2 mg/kg intraperitoneally daily for 7 days. In the saralasin group (n = 8), animals received saralasin intraperitoneally 1 h before or 1 h after hCG administration. Control animals (n = 8), received intraperitoneal saline solution. Serial blood samples were drawn on days 1, 5, 7 and 9 to measure serum estradiol and progesterone levels. On day 9, all rabbits underwent surgical exploration. Peritoneal and pleural fluid formation, ovarian weights and number of ovulations were determined. The volume of the ascitic and pleural fluids after hyperstimulation were not statistically different between the control, cilazapril and saralasin groups. The weight gains and ovarian weights of animals were similar between treatment and control groups. Saralasin significantly (p < 0.05) inhibited ovulation, but cilazapril did not. Cilazapril and saralasin did not affect progesterone production. Only cilazapril significantly decreased estradiol production (p < 0.05). In conclusion, the ACE inhibitor cilazapril and angiotensin II antagonist saralasin did not prevent ascites formation in OHSS. The ovarian renin-angiotensin system may not be the only factor acting in ascites formation in the OHSS.

The ovarian renin-angiotensin system in reproductive physiology

The identification of the presence of prorenin, renin, angiotensinogen, angiotensin-converting enzyme, angiotensin II (Ang II), and Ang II receptors in the ovary suggests that there is a functional ovarian renin-angiotensin system (RAS). It could play a significant role in such areas of ovarian physiology as follicular development, steroidogenesis, oocyte maturation, ovulation, and follicle atresia. Expression of the ovarian RAS is regulated by gonadotropins. Ang II, a bioactive octapeptide of RAS, has important effects as a paracrine/autocrine regulator at different stages of the reproductive cycle. Ang II modulates ovarian steroidogenesis and formation of the corpus luteum and also stimulates oocyte maturation and ovulation via Ang II receptors on granulosa cells. In addition, increasing evidence demonstrates that Ang II is a major factor in regulating the function of atretic follicles. In any physiologic system, aberrations result in the development of pathologic states. Disturbances in the ovarian RAS can be the cause or the result of such reproductive disorders as polycystic ovary syndrome, ovarian hyperstimulation syndrome, ovarian tumors, and ectopic pregnancy. Data support the concept of an active and regulated RAS in ovarian follicles. Species differences observed in the expression of ovarian RAS suggest varying functional roles among species with respect to ovarian physiology.

High densities of angiotensin II subtype 2 (AT2) receptors in the porcine placenta and fetal membranes

The present study was undertaken in order to characterize and determine angiotensin (Ang) II receptors and renin in the porcine placenta and fetal membranes. High densities of Ang II receptors of subtype 2 (AT2 receptors) were demonstrated in all parts of the placenta and fetal membranes throughout gestation. AT1 receptors (subtype 1) were only found in the first part of the gestation and only in the allantochorion-endometrium at low densities. The total Ang II receptor density was increased in the allantochorion-endometrium in the last stage of gestation. Except for this finding the Ang II receptor density did not vary during gestation. Some of the highest receptor densities were found in the allantoamnionic membrane. The Ang II receptor densities did not correlate with the duration of the gestation in any part of the placenta. Enzymatically active renin was found in all parts of the porcine placenta and fetal membranes in concentrations similar to those found earlier in the blood plasma. The renin concentrations did not correlate with the Ang II receptor densities or the duration of the gestation in any part of the placenta. Compared with the human placenta, where the Ang II receptors are almost exclusively AT1 receptors and low receptor densities are found in the fetal membranes, the present results indicate profound species differences in the expression and function of the renin-angiotensin system in the placenta and fetal membranes.

Evaluation of the reproductive and developmental toxicity of the AT1-selective angiotensin II receptor antagonist losartan in rats

Losartan, an AT1-selective angiotensin II receptor antagonist, was evaluated in female rats for effects on fertility, reproduction, and perinatal and postnatal development. In a range-finding study, pregnant rats were treated orally from gestation days 6-17 (GD 6-17) with doses of 25, 75, 150, 225, and 300 mg Losartan/kg/day. There were treatment-related decreases in maternal body weight gain, slight treatment-related decreases in hemoglobin concentration, and slight treatment-related increases in serum urea nitrogen in the 225 and 300 mg/kg/day groups. In a fertility study, female rats were treated for 15 days prior to mating, during mating, and GD 0-19 with doses of 25, 100, and 300 mg Losartan/kg/day. The initial dose of 300 mg/kg/day was lowered to 200 mg/kg/day at the start of mating due to excessive body weight loss during the premating treatment interval. There were no treatment-related effects on reproductive performance, mating, or fertility indices in the F0 generation. There was no evidence of treatment-related or dose-related fetal malformations. However, decreased F1 pup body weights were observed in all drug-treated groups. In the 100 and 300/200 mg/kg/day groups there were treatment-related increases in F1 pup mortality and alterations in the pattern of postweaning body weight gains. There was also a delay in developmental signs in the 100 and 300/200 mg/kg/day groups, which were likely secondary to the decreased weight of the pups in these groups. In a developmental toxicity study, pregnant rats were administered 50, 100, and 200 mg Losartan/kg/day on GD 6-17. There was no evidence of developmental toxicity in any dose group. Maternal toxicity was evident in the 200 mg/kg/day group as a treatment-related decrease in body weight gain during gestation. In a late-gestation/lactation study, pregnant rats were administered 10, 25, and 100 mg Losartan/kg/day on GD 15 through lactation day 20 (LD 20). There were treatment-related decreases in maternal body weight gain during gestation and lactation in the 100 mg/kg/day group. Decreased pup weights were noted in all dose groups, and pre- and postweaning pup deaths were observed in the high dose group which were comparable to those observed in the female fertility study. The lack of fetal body weight effects at 100 mg Losartan/kg/day in the developmental toxicity study, with treatment ending on GD 17, indicates that adverse effects observed in the F1 generation in the fertility and late-gestation/lactation studies were due to exposure during late gestation and/or lactation.(ABSTRACT TRUNCATED AT 400 WORDS)

Reproduction and the renin-angiotensin system

A unique aspect of the circulating renin-angiotensin system and the many independent tissue renin-angiotensin systems is their interactions at multiple levels with reproduction. These interactions, which have received relatively little attention, include effects of estrogens and possibly androgens on hepatic and renal angiotensinogen mRNA; effects of androgens on the Ren-2 gene and salivary renin in mice; the prorenin surge that occurs with but outlasts the LH surge during the menstrual cycle; the inhibitory effects of estrogens on thirst and water intake; the tissue renin-angiotensin systems in the brain, the anterior pituitary, and the ovaries and testes, that is, in all the components of the hypothalamo-pituitary-gonadal axis; the presence of some components of the renin-angiotensin system in the uterus and the fetoplacental unit; and the possible relation of renin and angiotensin to ovulation and fetal well-being. These interactions are described and their significance considered in this short review.

The distribution of angiotensin II type 1 receptors, and the tissue renin-angiotensin systems

Since its discovery, the functions of the renin-angiotensin system (RAS) have attracted a great deal of attention, and the roles it plays under normal conditions, and in disease, acquire a deepening significance with every year. In general, the RAS has been considered largely in terms of its roles in sodium and potassium homeostasis and the regulation of blood pressure. The continued acquisition of information on the distribution of angiotensin receptors, however, emphasizes that our interpretation needs to be widened, and it is now clear that angiotensin II has an array of functions in the tissues, which are unrelated to its systemic roles. This paracrine function is brought about by the existence of complete, localized tissue RASs, which respond to physiological demand independently from the systemic system.

Ovulation as a tissue remodelling process. Proteolysis and cumulus expansion

Ovulation, recurring every midcycle of the mammalian female and triggered by a surge of luteinizing hormone (LH) released from the pituitary, is an essential prerequisite for fertilization and subsequent embryonic development. Here we shall describe two of the biological components of the ovulatory response, cumulus expansion (frequently denoted as cumulus maturation) and the rupture of follicular wall, both crucial for the release of a fertilizable ovum. The role of a proteolytic cascade and its regulation by eicosanoids will be emphasized in relation to follicle rupture. The new data implicating cumulus maturation as an essential step for the release of the ovum and the apparent mediatory role of interleukin-1 in this process will be presented. LH/hCG stimulates, in the preovulatory follicles, a cascade of proteolytic enzymes, including plasminogen activator (PA), plasmin and matrix metalloproteinase 1 (MMP-1). These enzymes bring about the degradation of perifollicular matrix and, most notably, the decomposition of the meshwork of collagen fibers which provides the strength to follicular wall. Furthermore, pharmacological blockage of any of these enzymes resulted in inhibition of follicle rupture. LH/hCG stimulates, in addition, an increase in ovarian production of eicosanoids. These include prostaglandins, obtained from arachidonic acid via the cyclooxygenase pathway and leukotrienes, the products of lipoxygenase. Previous studies from our and other laboratories have demonstrated the ability of inhibitors of cyclooxygenase and of lipoxygenases to suppress ovulation in several mammalian species. MK-886, which inhibits the translocation of 5-lipoxygenase (5-LO) from the cytosol and its binding to the membranal 5-LO activating enzyme, suppressed dose-dependently follicular rupture from the treated ovary. Zymographic analysis of ovarian extracts from PMSG/hCG-stimulated rats revealed a band of collagenolytic activity at 52kD, corresponding to human MMP-1 and at 72kD, corresponding to human MMP-2. Both activities were markedly stimulated by administration of hCG and were significantly inhibited by indomethacin, NDGA or MK-886. Thus, eicosanoids seem to mediate LH stimulation of follicular collagenase. Interleukin-1 (IL-1) has been recently implicated in ovulation. The ability of an IL-1 receptor antagonist (ra) to block ovulation in vivo and in vitro has been demonstrated recently. Morphological examination of the ovulatory follicles failing to ovulate suggests that this effect is exerted by inhibiting cumulus oophorus expansion and detachment from mural granulosa cells. In vitro, IL-1ra attenuated the action of hCG and FSH on cumulus expansion and follicular hyaluronic acid synthesis. Thus, IL-1 seems to mediate and/or facilitate gonadotropin action on cumulus expansion, and hence on ovulation.

Regulation of angiotensin II receptor expression in ovarian follicles. A review

The regulation of angiotensin (Ang) II receptor expression in ovarian follicles was reviewed. Ang II receptor expression, assessed as the Ang II binding capacity, varied with the animal species and the developmental stage of the follicle. In cows, the expression correlated positively with follicular size and negatively with the active renin concentration in the follicular wall tissue. No relations were found to the follicular fluid concentrations of prorenin, estradiol or progesterone. In cell cultures, luteinizing hormone up-regulated Ang II receptor expression in cows, whereas it was decreased by follicle-stimulating hormone, Ang II and testosterone in rats. These data support the concept of an active and regulated RAS in ovarian follicles. The species differences in Ang II expression suggest varying functional roles of the RAS between species.

Prorenin and active renin concentrations in ovarian follicular fluid increase after the LH peak in superovulated heifers

1. The aim was to analyse the in vivo variations with time of prorenin and active renin and their relationship to steroid hormones in ovarian follicular fluid during follicular growth in heifers. 2. Thirty one beef heifers were assigned to two groups after oestrous synchronization: an unstimulated and a follicle-stimulating hormone (FSH)-treated (superovulated) group. Within each group, animals were slaughtered at different times of the follicular phase of the oestrous cycle. Ovarian follicular fluids were aspirated and analysed for the concentrations of active renin, prorenin, oestradiol-17 beta (E2) and progesterone (P4). 3. Prorenin and active renin concentrations in follicular fluid remained constant until the luteinizing hormone (LH) peak, after which time they increased four- and two-fold, respectively, in superovulated heifers. 4. In follicular fluid, prorenin and active renin correlated negatively with oestradiol and E2/P4 ratio but positively with progesterone during follicular growth in superovulated heifers. Prorenin also correlated negatively with oestradiol and E2/P4 ratio in unstimulated heifers. 5. The increase of renin concentrations in ovarian follicles after the LH peak and the correlations to steroid hormones suggest an important role of the ovarian renin-angiotensin system in bovine follicular growth and maturation.

In vitro incubation of bovine ovarian follicles: indications for an active and regulated renin-angiotensin system

1. The ovarian follicular renin-angiotensin system was investigated by using an in vitro incubation method, based on tissue incubation of individual bovine follicles. 2. Very high and varying concentrations of active renin (median 18.0 GU/kg, range 2.1-107 GU/kg; n = 101) and prorenin (11.7 GU/kg, range < 2.6-142 GU/kg; n = 101) existed in unincubated ovarian follicular tissue. 3. Active renin and prorenin increased 35 and 959%, respectively, in follicular wall tissue and incubation medium during 72 h of in vitro incubation. The protein synthesis inhibitor cyclohexamide inhibited active renin and prorenin formation. No activation of prorenin occurred in incubation medium or follicular fluid in vitro. Active renin was degraded during incubation. 4. Primarily prorenin but also active renin were secreted into the incubation medium. Secretion was directed both to the internal and external surface of the follicular wall. 5. Follicle-stimulating hormone (FSH) slightly stimulated the synthesis and secretion of prorenin in vitro. 6. The synthesis and secretion rates of active renin and prorenin varied markedly between individual follicles. 7. The finding of very high and varying concentrations of active renin in follicular wall tissues together with the formation and secretion of active renin during in vitro incubation provide further evidence for an active and regulated renin-angiotensin system in ovarian follicles.

Angiotensin II receptor density in bovine ovarian follicles relates to tissue renin and follicular size

1. The purpose of this study was to investigate angiotensin II (AII) receptors in isolated bovine ovarian follicles and the relationship of their density to follicular concentrations of prorenin, active renin, oestradiol and progesterone. 2. Displacement of [125I]-[Sar1-Ile5-Ile8]-AII binding by the AII receptor antagonists PD 123319 and Losartan (DuP 753) confirmed that follicular AII receptors are of subtype 2 (AT2 receptor). 3. The dissociation constant (Kd) for [Ile5]-AII (human AII) was 0.84 (range 0.51-1.47) nmol/L. The receptor density varied between 90 and 5990 (mean 1640) fmol/mg membrane protein. 4. The follicular AII receptor density correlated positively with follicular diameter (Spearman's rho = 0.518; P < 0.003) and tissue weight (Spearman's rho = 0.636; P < 0.0001), and negatively with the active renin concentration in the follicular wall (Spearman's rho = -0.399; P < 0.02). The AII receptor density did not correlate with the follicular fluid concentrations of prorenin, active renin, oestradiol (E2), progesterone (P4) or the E2/P4 ratio. The follicular fluid concentrations of prorenin correlated negatively with the E2/P4 ratio (Spearman's rho = -0.716; P < 0.0001). 5. The inverse relationship between AII receptor density and the high active renin concentrations in the follicular wall suggests an active regulated tissue renin-angiotensin system. A high AII receptor density is a general feature of large bovine ovarian follicles.

The basis and evidence of a role for the ovarian renin-angiotensin system in health and disease

OBJECTIVE

We reviewed the evidence for an intrinsic ovarian renin-angiotensin system (OVRAS), highlighting potential diverse signaling in this system through different bioactive angiotensin peptides, their specific receptors, and second messengers. In addition, sites of action for OVRAS in the regulation of ovarian function in health and disease were reviewed.

DATA SOURCES

We used published journals and abstracts from national scientific meetings. Current developments in the renin-angiotensin field are historically set.

STUDY SELECTION

One hundred referenced articles provided studies on renin-angiotensin systems in mammalian species, including humans.

DATA ABSTRACTION

Interpretation of the reviewed publication was in line with the original authors' conclusions and statistical analysis.

DATA SYNTHESIS

Techniques in molecular biology, biochemistry, and immunohistochemistry have identified an OVRAS in mammalian species. Ovarian tissues contain all the elements for the production of angiotensin, including prorenin/renin, angiotensinogen, and angiotensin-converting enzyme. In addition, angiotensin II is present in ovarian compartments, and receptors for angiotensin II are demonstrated on specific ovarian cells. Angiotensin II is implicated to play a role in ovulation, steroidogenesis, follicular atresia, and hyperandrogenic syndromes.

CONCLUSIONS

The newly identified OVRAS may have important actions in the ovary that range from regulation of ovulation to ovarian dysfunction, such as hyperandrogenic syndromes in women. In this respect, the OVRAS is a putative paracrine/autocrine regulator in the ovary, and pharmacologic regulation of the OVRAS may provide new methods for the management of fertility and reproduction.

Tumor necrosis factor-alpha inhibits ovulation and steroidogenesis, but not prostaglandin production in the perfused rat ovary

OBJECTIVE

We tested the null hypothesis that tumor necrosis factor-alpha (TNF-alpha) does not decrease ovulation, estradiol and progesterone production, or prostaglandin (PG) E2, PGF2alpha, or 6 keto-PGF1alpha production in the open bursa rat ovarian perfusion model.

METHODS

Experimental animals were controlled for age, weight, litter, and pregnant mare's serum gonadotropin (PMSG) aliquot. Female Sprague-Dawley rats, 26-27 days old, were injected with 25 IU PMSG. Forty-eight hours later, the right ovary was dissected, the bursa removed, and the specimen placed in the perfusion chamber with defined media. Luteinizing hormone and isobutylmethylxanthine were given as an ovulatory trigger. Test perfusions also received TNF-alpha in 0.8-nmol/L, -pmol/L, and -fmol/L doses. Samples were collected at 0, 1, 3, 5, 7, 10, and 20 hours. Ovulations were counted at 20 hours. Steroids and PGs were measured.

RESULTS

The addition of TNF-alpha to the rat ovarian perfusion model resulted in a dose-dependent decrease in ovulations (mean +/- standard deviation): 16.14 +/- 6.2 in controls (n = 7) versus 2.38 +/- 3.4 with TNF-alpha 0.8 nmol/L (n = 7), and 4.3 +/- 1.5 with TNF-alpha 0.8 pmol/L (n = 3), both P < .001. Tumor necrosis factor-alpha also inhibited estradiol (P < .005) and progesterone production (P < .05) throughout, but produced no significant changes in PG production.

CONCLUSIONS

Tumor necrosis factor-alpha inhibits ovulation in a dose-dependent fashion, and inhibits estradiol and progesterone production without altering PG production in the open bursa rat ovarian perfusion model.

Angiotensin-converting enzyme inhibitors have no effect on ovulation and ovarian steroidogenesis in the perfused rat ovary

The null hypothesis of this study was that the angiotensin-converting enzyme inhibitors, captopril and teprotide, would not reduce the number of ovulations in vivo and in vitro in the rat. Captopril (in three regimens) was administered continuously beginning prior to pregnant mare's serum gonadotropin and hCG to trigger ovulation. The number of in vivo ovulations were counted. Ovaries similarly primed with pregnant mare's serum gonadotropin were dissected and perfused in media with hCG and captopril (two regimens) or teprotide (one regimen). The number of in vitro ovulations and steroid production in the perfusions were evaluated. The results were evaluated by the Student's t test. Power calculations gave only a 20% chance of missing a 16% difference in ovulations or steroidogenesis. There was no inhibition of ovulation or change in steroid production in angiotensin-converting enzyme treated rats in vivo or in vitro. While angiotensin II has been shown to be an important mediator in the mechanism of ovulation, angiotensin-converting enzyme inhibition via captopril or teprotide does not result in angiotensin II antagonistic effects. Hypothetical mechanisms to explain this paradox are presented.