Ovulation and the mechanism of follicle rupture. VI. Ultrastructure of theca interna and the inner vascular network surrounding rabbit graafian follicles prior to induced ovulation

ACTH impairs the migratory and secretory profile of mononuclear cells during proestrus in cattle

The aim was to evaluate the effect of ACTH on the mechanisms involved in peripheral blood mononuclear cells (PBMCs) infiltration into the ovary during dairy cattle proestrus. Regarding this, proper expression pattern of adhesion molecules must take place both in PBMCs and in endothelial cells. Argentinian Holstein cows (n = 12) were treated with 100 IU of ACTH every 12 h for 4 days before ovulation when ovariectomy was performed (day 18). Blood samples were taken on day 15 (0 h) and immediately before (72 h) and after (74 h) the last ACTH administration. In PBMCs, flow cytometry was performed to analyze CD44, CD11b and CD62-L expression along with gene expression of chemokines' receptors. Interleukin (IL)-4 and tumor necrosis factor-α (TNF-α) production was analyzed by flow cytometry after exposing PBMCs to autologous follicular fluid. In ovarian blood vessels, expression of the vascular endothelium cell adhesion-1 (VCAM-1) and the platelet endothelial cell adhesion molecule-1 was evaluated by immunohistochemistry. In T-lymphocytes, the expression of CD44 and CD11b was lower at 72 h in ACTH-treated cows (P < 0.05). In monocytes, the expression of CD11b and CD62-L was lower at 72 h in ACTH-treated cows (P < 0.05). Also, the percentage of IL-4+ cells was higher in ACTH-treated cows, meanwhile, the percentage TNF-α+ cells was lower in ACTH-treated cows (P < 0.05). Finally, in the vessels associated with the preovulatory follicle VCAM-1 immunoexpression was lower in ACTH-treated cows (P < 0.05). Here, we present novel insights into the effect of stress during the preovulatory period on the inflammatory pathway necessary for ovulation.

Modulation of microvascular permeability in the preovulatory rat ovary by an ovulatory gonadotropin stimulus

OBJECTIVE

To characterize the size selectivity of the rat ovarian vasculature and its changes after gonadotropin induction of ovulation.

DESIGN

Experimental study.

SETTING

Obstetrics and Gynecology Department.

ANIMAL(S)

Immature, female Sprague-Dawley rats.

INTERVENTION(S)

Rats were pretreated with equine chorionic gonadotropin, and ovaries were retrieved either 48 hours later or at any of several time points during ovulation induced by hCG. Fluorescein isothiocyanate-labeled Ficoll was injected 10 minutes before ovarian sampling, and the distribution of Ficoll was measured in plasma and ovarian extracts.

MAIN OUTCOME MEASURE(S)

The Ficoll data were analyzed according to a two-pore model to acquire information on small (rS) and large (rL) pore radii as well as the number of large pores reflected by the large pore fraction of the hydraulic conductance (LpS%) at each periovulatory time interval.

RESULT(S)

Before hCG, rS and rL were 54.7 ± 1.2 Å (mean ± SEM) and 149.3 ± 5.3 Å, respectively. At this preovulatory stage, LpS% was 7.1% ± 3.2%. Stimulation with hCG caused close to a three-fold increase in LpS% at 2 and 4 hours (20.9% ± 1.8% and 20.7% ± 2.5%, respectively) and approximately 15% enlargements of rS and rL. Thus, the change in LpS% represents a dramatic increase in the number of large pores and not an increased size of preexisting large pores, since the small and large pore radii changed in parallel.

CONCLUSION(S)

These results indicate that capillary permeability of the ovarian blood-follicle barrier is modulated by gonadotropin, mainly through increased numbers of large pores, similar to a classical inflammatory response.

Identification of hepsin and protein disulfide isomerase A3 as targets of gelatinolytic action in rat ovarian granulosa cells during the periovulatory period

The matrix metalloproteinase (MMP) family is believed to play a role in the ovulatory process because MMP inhibitors block oocyte release. However, little is known about the mechanisms by which the MMPs affect ovulation. The present study investigated the degradomic actions of the gelatinases, MMP2 and MMP9, by identifying gelatinolytic targets in periovulatory granulosa cells. Granulosa cells were collected from immature rats 48 h after equine chorionic gonadotropin treatment and were cultured with human chorionic gonadotropin (hCG) in the absence or presence of a specific MMP2/9 inhibitor ((2R)-2-[(4-biphenylylsulfonyl)amino]-3-phenylpropionic acid) for an additional 24 h. The conditioned media was analyzed for gelatinolytic activity, progesterone, and peptide profiles. Gelatinolytic activity and progesterone were induced in response to hCG; however, there was no difference in progesterone between cells treated with or without the inhibitor. Peptide fragments of proteins altered in the presence of the gelatinase inhibitor were identified by two-dimensional gel electrophoresis and mass spectrometry. Protein disulfide isomerase A3 (PDIA3), which plays a role in protein folding, was identified as a peptide that decreased in the presence of inhibitor while the serine protease hepsin, was found to increase with inhibitor treatment. Subsequent experiments established that PDIA3 and hepsin were targets of MMP2/9 action by cleavage with MMP2 and Western blot analysis, respectively. Additionally, hepsin was identified as a gelatinolytic target in ovarian cancer cells. In the present study, proteomics has identified proteins that may be involved in novel ways in the complex cascades that are mediated by gelatinolytic MMPs during the periovulatory period.

Stereo-electron microscopy of the ovarian follicles of cat and mouse

Three dimensional structure of developing ovarian follicles in the cat and the mouse were examined to clarify the cellular and the extra cellular components during follicular maturation by scanning electron microscopy. Epithelial cells of the membrana granulosa (MG) and the cumulus oophorus (CO) show variable morphology, which depends on the location of the cells in the follicle. In the small antral follicle, there is no morphological difference between the surface structure of the MG and the CO lining cells. In the large antral follicle, however, the lumenal lining cells of the MG change their spherical shape to a rather flattened one showing numerous pseudopodial processes creeping over the surrounding lumenal cells. The CO cells remain rounded with fine cytoplasmic protrusions on their outer surfaces which seem to make a network. The outer surface view of the zona appears as composed of labyrinthine canals with relatively large pores of various sizes, however, the inner surface is rather compact with a number of small pores.

Fundamental roles of reactive oxygen species and protective mechanisms in the female reproductive system

Controlled oxidation, such as disulfide bond formation in sperm nuclei and during ovulation, plays a fundamental role in mammalian reproduction. Excess oxidation, however, causes oxidative stress, resulting in the dysfunction of the reproductive process. Antioxidation reactions that reduce the levels of reactive oxygen species are of prime importance in reproductive systems in maintaining the quality of gametes and support reproduction. While anti-oxidative enzymes, such as superoxide dismutase and peroxidase, play a central role in eliminating oxidative stress, reduction-oxidation (redox) systems, comprised of mainly glutathione and thioredoxin, function to reduce the levels of oxidized molecules. Aldo-keto reductase, using NADPH as an electron donor, detoxifies carbonyl compounds resulting from the oxidation of lipids and proteins. Thus, many antioxidative and redox enzyme genes are expressed and aggressively protect gametes and embryos in reproductive systems.

An intravital microscopy method permitting continuous long-term observations of ovulation in vivo in the rabbit

BACKGROUND

A method for intravital microscopy of the rabbit ovary was developed to enable observations of real-time changes during ovulation in vivo. The aim was to correlate these events to biochemical events at specific stages of ovulation.

METHODS

Virgin, female rabbits were primed with equine chorionic gonadotrophin (CG) (30-100 IU) then HCG (100 IU) 2 days later to induce ovulation. During anaesthesia, the right ovary was surgically exteriorized and submerged in an organ chamber with a microscopy lens positioned close to the ovary. Continuous video recordings were performed.

RESULTS

Initial equine CG priming experiments revealed the highest ovulation rate, without premature luteinization, after 30 IU equine CG. This priming protocol subsequently demonstrated follicular ruptures 11.5-14 h after HCG. Numbers of ovulations from the exteriorized and contralateral non-exteriorized ovary were similar. The sequence of typical features of ovulation was: shutdown of microcirculation in the follicular apex, formation of petechiae in the follicular wall and a cone-shaped structure over the future rupture site, marked bleeding in connection with follicular rupture and a fairly steady extrusion velocity of granulosa cells and the oocyte.

CONCLUSION

This method captured a sequence of structural changes during ovulation. It could be combined with blood and follicular fluid sampling for biochemical analysis and could be used in studies on biochemical reactions in relation to specific changes in the follicular structure during ovulation.

Morphodynamics of the follicular-luteal complex during early ovarian development and reproductive life

Female reproductive activity depends upon cyclic morphofunctional changes of the ovarian tissue during the female's fertile period, but the primum movens of an active gonadal rearrangement can be found from early phases of embryo development. To offer a basic account of the main steps of ovarian dynamics, we review the morphofunctional behavior of the follicular-luteal complex in an integrated study using light microscopy and transmission and scanning electron microscopy as well as through the use of numerous drawings. Particular emphasis is given to some reproductive aspects including (1) germ-somatic cell relationships and onset of folliculogenesis during early gonadal development; (2) follicular development and oocyte-follicle cell associations through adult folliculogenesis, finally leading to ovulation; (3) morphodynamics of corpus luteum formation, development, and regression, and (4) degenerative processes involving germ and somatic cells. The results reported, many of which originated in our laboratory, arise from some experiments on laboratory mammals but mostly from a large selection of human specimens. The data obtained are integrated and correlated with classic reports as well as with current views. Crucial biochemical, histophysiological, and clinical aspects are also emphasized.

The matrix metalloproteinase system: changes, regulation, and impact throughout the ovarian and uterine reproductive cycle

The ovary and uterus undergo extensive tissue remodeling throughout each reproductive cycle. This remodeling of the extracellular environment is dependent upon the cyclic hormonal changes associated with each estrous or menstrual cycle. In the ovary, tissue remodeling is requisite for growth and expansion of the follicle, breakdown of the follicular wall during the ovulatory process, transformation of the postovulatory follicle into the corpus luteum, as well as the structural dissolution of the corpus luteum during luteal regression. In the uterus, there is extraordinary turnover of the endometrial connective tissue matrix during each menstrual cycle. This turnover encompasses the complete breakdown and loss of this layer, followed by its subsequent regrowth. With implantation, extensive remodeling of the uterus occurs to support placentation. These dynamic changes in the ovarian and uterine extracellular architecture are regulated, in part, by the matrix metalloproteinase (MMP) system. The MMP system acts to control connective tissue remodeling processes throughout the body and is comprised of both a proteolytic component, the MMPs, and a regulatory component, the associated tissue inhibitors of metalloproteinases. The current review will highlight the key features of the MMPs and tissue inhibitors of metalloproteinases, focus on the changes and regulation of the MMP system that take place throughout the estrous and menstrual cycles, and address the impact of the dynamic tissue remodeling processes on ovarian and uterine physiology.

Follicular Microvasculature and Angiogenic Factors in the Ovaries of Domestic Animals

The genetic and molecular mechanisms that control the development of capillary blood vessels during follicular development are beginning to be elucidated. Ovarian follicles contain and produce angiogenic factors that may act alone or in concert to regulate the process of thecal angiogenesis. These factors are ultimately controlled by endocrine, paracrine and autocrine regulation. A recent study indicated that vascular endothelial growth factor (VEGF) plays an important role in the process of thecal angiogenesis during follicular development. We are developing a novel technology for the induction of follicular development using the technique of in vivo gene administration. Here, we summarize the recent progress of our research.

Chemokines and human reproduction

OBJECTIVE

To review the available information regarding chemotactic cytokines and their possible implications in human reproduction.

DESIGN

A thorough literature and MEDLINE search was conducted to identify studies relating to the role of chemokines in ovulation, menstruation, implantation, cervical ripening and preterm labor, and endometriosis.

RESULT(S)

Chemokines mediate leukocyte traffic through their specific receptors in various tissues. Although four families have been described to date, two remain the major subfamilies: alpha-chemokines (with interleukin-8 as representative for this group), and beta-chemokines (with monocyte chemotactic protein-1 as representative). Interleukin-8, monocyte chemotactic protein-1, and growth-regulated oncogene-alpha are involved in follicular development and atresia, ovulation, steroidogenesis, and corpus luteum function. Interleukin-8 showed cycle-dependent expression in human endometrium, and at the same time, stimulated endometrial stromal cell growth, acting as an autocrine growth factor. Interleukin-8 has been identified in human amnion, chorion, decidua, and villous placenta, and its level increases during labor. Levels of interleukin-8 correlate with the release of collagenases, a crucial step that regulates the process of cervical extracellular matrix remodeling. The levels of monocyte chemotactic protein-1; regulated on activation, normal T-expressed and secreted (RANTES); interleukin-8; and growth-regulated oncogene-alpha are elevated in the peritoneal fluid of women with endometriosis, and they correlate with the stage of the disease.

CONCLUSION(S)

Chemokines play a relevant role in many physiologic and pathologic situations, such as ovulation, menstruation, implantation, cervical ripening and preterm labor, and endometriosis. Their regulation soon may provide new therapeutic strategies.

Potential implications of chemokines in reproductive function: an attractive idea

Chemokines are a new family of cytokines specialised in attracting leukocytes, acting in physiological conditions and in pathological processes. A wide variety of cell types in response to exogenous irritants or endogenous mediators of the inflammatory reaction produce them. Pivotal parts of reproductive function are based on inflammatory like processes wherein different leukocytes subsets are recruited and activated to produce paracrine autocrine effects in which cytokines and growth factors are implicated. Since chemokines control leukocyte trafficking and belong to the cytokine superfamily, in this review we analyze the implications of these molecules and related cells in ovulation, embryonic implantation, menstruation, parturition and their role in pathological process such as preterm delivery, endometriosis, ovarian hyperstimulation syndrome and HIV infection.

Participation of nerve growth factor in the regulation of ovarian function

Nerve growth factor (NGF) belongs to a family of related target-derived proteins required for the survival and development of discrete neuronal populations in the central and peripheral nervous systems (Levi-Montalcini, 1987; Snider, 1994). Although initial observations led to the conclusion that the biological actions of neurotrophins are restricted to the nervous system (Thoenen, 1991; Raffioniet al.1993), new evidence suggests that they, and in particular NGF, can also affect non-neuronal cells.

Concentrations of steroids and biochemical constituents in follicular fluid of buffalo cows during different stages of the oestrous cycle

One of the factors controlling ovarian physiology in cattle is the alteration that occurs in the hormonal and biochemical composition of follicular fluid. Because they are ill-defined in buffaloes, the present study was aimed at determining changes in the follicular fluid collected from 197 pairs of buffalo ovaries after slaughter. Total oestrogens, progesterone, calcium, inorganic phosphorus and total protein were found to be higher before oestrus and reached their peak values during oestrus. Glucose concentrations were maximal before oestrus. Testosterone, total corticosteroids and acid phosphatase concentrations increased during metoestrus peaking during dioestrus. Alkaline phosphatase concentration was higher during dioestrus. Ratios and correlations between changes in concentrations of the different follicular steroids were determined.

The role of superoxide dismutase in the human ovary and fallopian tube

OBJECTIVES

To investigate the localization of manganese superoxide dismutase (Mn-SOD) and copper-zinc superoxide dismutase (Cu, Zn-SOD) in the human ovary and fallopian tube, and to examine the role of superoxide radicals and SODs in the human ovulatory process.

METHODS

Using immunohistochemical methods, we studied the localization of SODs in 22 human ovaries, in 18 fallopian tubes, and in aspirated granulosa cells. We measured, by enzyme-linked immunosorbent assay, the concentrations of SODs in follicular fluid taken from 94 IVF patients.

RESULTS

Mn-SOD was found in granulosa, in theca and luteal cells and in fallopian tubes. Cu, Zn-SOD was localized in theca and luteal cells. The concentration of Cu, Zn-SOD in follicular fluid in the high-progesterone group (11.3 + 4.2 ng/ml) was significantly less than in the low-progesterone group (24.5 + 19.5) (p < 0.05).

CONCLUSION

Mn-SOD and Cu, Zn-SOD have different localizations and actions in human ovaries and fallopian tubes. The superoxide radical-SOD system might play an important role in ovulation and in the luteal function of the human ovary.

Development of the perifollicular capillary network. Autoradiographic and morphometric studies in the rabbit ovary

The published data give a report on systematic examinations on the development of the perifollicular capillary network in the theca interna in rabbit ovaries. The follicle size and the number of capillaries were investigated by means of morphometric methods. The extent of proliferation of granulosa and endothelial cells was studied autoradiographically by determining the labelling index (LI). The results show that the perifollicular capillary network is initiated only when the stratum granulosum has developed into a multilayered cell population. After that the number of capillaries increases linearly with increasing follicle size, independently of the oestrus cycle. During follicle growth at different times in the oestrus cycle the decrease and increase in the LI of granulosa cells is followed by a corresponding decrease and increase in the LI of endothelial cells several hours later. It should be noted, however, that the proliferation of endothelial cells in follicles with a diameter of 900 microns continues, although the decreasing LI of granulosa cells already indicates a reduced follicle growth. The number of labelled endothelial cells in atretic follicles decreases only after a decrease in proliferation of granulosa cells. In conclusion, it can be noted that the follicle growth and function is not influenced by variations in the number of capillaries in the theca interna. The curve of LI of granulosa and endothelial cells suggests that the granulosa cells have a certain regulatory function with respect to the growth of the capillary network in the theca interna.

Gonadotropin-induced ovulation in a reptile (Anolis carolinensis): histological observations

Although much is known about morphological changes in the apex of the mammalian ovarian follicle prior to its rupture (ovulation), information about this process in nonmammalian vertebrates is limited to only a few species. We describe here the histological changes in the stigma of the lizard (Anolis carolinensis) ovarian follicle preceding FSH-induced ovulation. Females with a large vitellogenic follicle received two injections, separated by 7 hr, of either porcine FSH (25 micrograms) or saline, and then were sampled at 6, 9, 12, 15, 18, and 24 hr after the first injection. Thus, all but the 6-hr group received two injections. By 12 hr, about half of the FSH-treated females had ovulated, and most had ovulated by 15 hr. In contrast, only 1 of 40 control females ovulated. Large unovulated follicles were fixed and bisected through the circular stigma; one hemisphere was embedded in paraffin and stained with Mallory's trichrome, and the other was embedded in plastic and stained with toluidine blue. FSH treatment produced marked histological changes in the stigma region, as well as alterations in nonstigmal areas of the follicle. The membrana granulosa of control follicles consisted of a single layer of squamous, darkly staining granulosa cells. After FSH treatment, nonstigmal granulosa cells separated slightly, and their nuclei became more clear and assumed an oval shape; in the stigma, these cells became widely separated, with round, light-staining nuclei containing one or two prominent nucleoli. The nonstigmal theca of FSH-treated follicles was similar to that of control follicles except that collagen fibers were more dissociated. In the stigma, collagen fibers were widely dissociated, and the theca swelled, presumably due to accumulation of extracellular fluid. Abundant fluid accumulated in the stigma, especially between the granulosa cells and their basement membrane and between the tunica albuginea and the theca externa. These changes in the lizard stigma are similar to those reported in mammals except that no marked inflammatory response occurs in the lizard stigma. We hypothesize that the Anolis follicle undergoes preovulatory luteinization, and that the stigma exhibits ischemic necrosis before rupture.

Studies on the mechanism of ovulation using the model of the isolated ovary

Using the isolated perfused rabbit and rat ovaries as experimental models, we have studied various biochemical aspects of the ovulatory process. In rabbits, ovulations were induced by injecting hCG prior to the perfusion or by adding LH directly to the medium. In PMSG-treated rats, ovulations were induced by adding LH to the perfusion system. Steroids and other metabolites were analyzed in the perfusate and in follicular fluid. Steroid levels in follicular fluid were high early in the preovulatory development, but declined to very low levels 4 hours after LH stimulation. Levels of prostaglandins E and F rose as ovulation approached. In both perfusion models, indomethacin blocked ovulation without affecting steroid release or oocyte maturation. In the rabbit, PGF2 alpha reversed the indomethacin-induced inhibition and was able to induce follicular rupture by itself. Manipulations of the follicular fluid content of progesterone and estradiol to supraphysiological levels did not affect follicular rupture or oocyte maturation in the rabbit model. When the initial increase in LH-induced steroidogenesis was blocked by a 3 beta-ol-dehydrogenase inhibitor, ovulation was not affected. In rats, inhibition of estradiol production by an aromatase blocker did not affect the ovulatory process. When the endogenous formation of cyclic AMP is increased by pretreatment with a phosphodiesterase inhibitor, the LH-induced ovulation frequency increases in rabbits. Furthermore, forskolin, which increased the adenylate cyclase activity, stimulated steroidogenesis and induced follicular rupture. Recent experiments in the rat indicate that cyclic AMP acts on the ovulatory process via an effect on prostaglandin synthesis.

Capillary sprouts in ovaries of immature superstimulated golden hamsters: a SEM study of microcorrosion casts

A new polyester resin of low viscosity was used to study the three-dimensional structure of capillary sprouts of mature follicles and of corpora lutea. Vascular microcorrosion casts were obtained from ovaries of immature golden hamsters between days 4 and 7 after stimulation with pregnant mares' serum gonadotrophin (PMSG). On days 4 and 5 after PMSG, a nodular appearance of the organ was due to mature follicles and corpora lutea. Capillary sprouts were seen as dead-ending structures originating from the thecal capillary network. The sprouts were either concentrated around (follicle type 1) or towards (follicle type 2) the center of the antrum. Increased vascular permeability resulted in resin leakage only in type 2. Intact corpora lutea were characterized by radially grown capillary sprouts. Regressing corpora lutea showed a marked reduction of the vascular bed as displayed by filling defects in casts on day 6 and 7 after PMSG. It is assumed that: 1. Dead-ending capillary structures, resin leakage, and filling defects are not always artifacts of the microcorrosion cast technique, but can express functional microcirculatory changes. 2. The concentric growth of thecal capillary sprouts may be related to the presence of an intact follicular basal membrane, and the radial growth of sprouts be taken as a sign of a digested basal membrane.

Alteration by histamine of the sympathetic nerve-mediated contractions in the bovine ovarian follicle wall in vitro

The histaminergic effect on electrically induced contractions and tritium release was studied in vitro, using strips from the wall of mature bovine ovarian follicles. Follicular fluid and blood plasma from the animals were analysed for electrolyte, bicarbonate, glucose and total protein concentrations in order to compare them with the concentrations of these components in the Krebs-Ringer solution used in the experiments. Electrical field stimulation (EFS) of the follicle strip caused a contraction which was completely blocked by tetrodotoxin and was predominantly of adrenergic origin since phentolamine, in contrast to atropine, blocked the response. The neurogenic response was inhibited by histamine in a concentration-dependent way via the H1-receptor since the H1-antagonist, pyrilamine, counteracted the inhibitory effect of histamine while the H2-antagonist, cimetidine, potentiated the effect. This histaminergic response of EFS-induced contractions could be reproduced in experiments where the H1-agonist, 2-methylhistamine, was inhibitory while the H2-agonist, 4-methylhistamine, had no obvious influence on the twitch response. Histamine reduced the contractile response to exogenous noradrenaline via the H1-receptor, because pyrilamine counteracted, and cimetidine potentiated the effect. The histamine-induced depression of the motor response to EFS and exogenous noradrenaline was probably due to a postjunctional effect mediated by the H1-receptor. Experiments utilizing [3H]noradrenaline release during EFS did not suggest prejunctional effects of histamine. Chemical determinations on follicle fluid and plasma showed that the artificial follicular fluid imitated well the environmental conditions the follicle wall is exposed to in situ.

Light and ultrastructure of intra-ovarian oocyte release in infantile rats

Follicular ruptures with intra-ovarian oocyte release (IOR) were studied in 17, 21 and 24-day-old rats by morphological methods. Using a light microscope, it was seen that IOR occurred at all times and the IOR frequency did not change. IOR developed in preantral follicles. Their oocytes were mostly found within the follicular compartment (incomplete IOR). Using an electron microscope, a circumscribed dissolution of the basal lamina was observed. IOR granulosa cells appeared activated. They rarely underwent typical necrosis after herniation into the extrafollicular area. Herniated granulosa cells tended either to stay intact or to shed cytoplasmic components into the extracellular space, whilst nuclei of active cell function were maintained. Tissue adjacent to an IOR seemed inactive with the exception of endothelial cells. Some endothelial cells underwent necrosis. Additionally, the endothelium was discontinuous. The morphological data support the hypothesis that the mechanism of follicular rupture represents an inside to outside process.

Microvasculature of preovulatory follicles: comparison of in situ and in vitro perfused rabbit ovaries following stimulation of ovulation

Perifollicular vasculature undergoes significant morphologic changes as ovulation approaches. These vascular changes were observed in in vitro perfused and in situ rabbit ovaries by means of scanning electron microscopy of microcorrosion casts. Casts were made in in situ unstimulated ovaries, in situ ovaries stimulated with human chorionic gonadotropin, in vitro perfused unstimulated ovaries, and in vitro perfused ovaries after an ovulation-inducing dose of human chorionic gonadotropin, prostaglandin F2 alpha, histamine, or norepinephrine. Dilated vessels, extravasation of resin from weakened vessels, and filling defects at the apex of the follicle were observed in in situ ovaries 9 to 12 hours after stimulation and in in vitro perfused ovaries 4 to 6 hours after human chorionic gonadotropin. In vitro perfused ovaries stimulated with prostaglandin F2 alpha or histamine demonstrated dilated capillaries with extravasation of the resin and filling defects at the apex of large follicles. Norepinephrine-stimulated ovaries showed incomplete filling of vessels, although some large follicles showed extravasation of resin. The occurrence of dilated vessels, extravasation of resin, and filling defects is indicative of preovulatory vascular changes in both in situ and in vitro perfused ovaries, regardless of the ovulatory stimulus.

Studies on the morphology of the isolated perfused rabbit ovary. II. Ovulation in vitro after HCG-treatment in vivo

Ovulation was induced in rabbits by intravenous administration of human chorionic gonadotrophin (HCG), and 4-5 h later the ovaries were isolated and introduced into an in-vitro perfusion system containing synthetic medium with albumin. Rupture of follicles occurred in vitro within the physiological time range (mean 11.3 h after injection of HCG), although with a reduced frequency. Preovulatory and ruptured follicles were studied in detail by light and electron microscopy. In the granulosa layer of ruptured or preovulatory follicles cytoplasmic blebbing activity, disappearance of Call-Exner bodies and differentiation toward luteinized cells were found. Perhaps the most important sign of normal preovulatory development in vitro was that the basement membrane surrounding the granulosa layer was penetrated by projections of granulosa cells. In the absence of this penetration phenomenon the granulosa layer prolapsed out of the follicle. Immediately before rupture, follicles showed marked degeneration, restricted to the outer layers of the apical wall, which is compatible with the hypothesis that degradative enzymes are released close to the surface of preovulatory follicles. Although the majority of follicles that ovulated under in-vitro conditions showed the same kind of morphological alterations as can be seen in vivo, occasional atypical ruptures occurred without any overt signs during perfusion. Also technical manipulations of the perfusion system, e.g., nonphysiological increase of perfusion pressure, could force follicles to rupture. This illustrates the importance of careful morphological study of all ovaries perfused in vitro before conclusions are drawn.

Studies on the morphology of the isolated perfused rabbit ovary. I. Effect of long-term perfusion

Isolated ovaries from untreated, sexually mature rabbits were introduced into an in vitro perfusion system and perfused with a chemically defined medium containing albumin. The ovaries were perfused for up to 15 h (mean 11.5 h) and then processed for morphological investigation. Both at the light- and electron-microscopical levels, most of the ovaries exhibited a normal structure comparable with ovaries in situ. In two cases, however, marked accumulations of bacteria were found, although not inside the follicles. Since ovulation in the rabbit normally occurs between 9.5-13 h after mating or human chorionic gonadotrophin treatment, this model seems adequate for studies of ovulation in vitro. It is, however, important to study the ovaries microscopically after the perfusion to detect artifacts, e.g., bacterial infection, that may have influence on the process of ovulation.

An ultrastructural study of ovarian perifollicular capillaries in the indomethacin-treated rabbit

The perifollicular capillaries of the rabbit ovary were observed by light and electron microscopy following administration of human chorionic gonadotropin (hCG) and indomethacin (IM). Fenestrations and interendothelial gaps were not observed at 4, 10, or 12 hours, at which times carbon particles were confined to capillary lumina. By 24 hours, dilated capillaries were noted among granulosa cells and theca. In the theca, interendothelial gaps permeable to carbon particles were observed. At 48 hours, ribosome-rich, newly developed capillaries were noted. Many collagen fibrils were observed in the tunica albuginea and theca externa in hCG/IM-treated rabbits in contrast to those treated with hCG alone. Ovarian prostaglandins normally produced in response to gonadotropins may be responsible for alterations in perifollicular capillaries and degradation of collagen in the follicle wall, changes considered essential for ovulation.

Investigation of mammalian ovulation with an in vitro perfused rabbit ovary preparation

An in vitro perfused rabbit ovary preparation has been developed to study local factors responsible for the ovulatory process. This preparation enables: (1) isolation of the ovary from systemic influences, (2) direct serial observations of follicle development and ovulation, (3) addition to the perfusing medium of substances that may influence ovulation acting at the level of the ovary, and (4) correlation of the times of individual follicle rupture with ovarian contractile patterns. With this model the temporal requirements for human chorionic gonadotropin in the process of ovulation have been studied. The direct effects on ovulation of prostaglandin F3 alpha (PGF 2 alpha), the antihistamine chlorpheniramine, and calcium deprivation were also investigated. Chlorpheniramine and EDTA each led to inhibition of ovulation and depressed ovarian contractility. The use of the isolated in vitro ovary preparation permits characterization of the local requirements for ovulation.

Hormonal control of oocyte meiosis, ovulation and luteinization in mammals

The ovulatory process can be regarded as a series of biochemical and morphological changes ultimately leading to the release of a mature oocyte and the transformation of the Graafian follicle into the corpus luteum. This process involves acute changes in steroidogenesis, resumption of oocyte meiosis, and finally rupture of the follicular wall and luteinization of the granulosa cells. Normally, all of these changes are induced synchronously by the pre-ovulatory LH surge. Experimentally, however, these changes in steroidogenesis, oocyte maturation and follicular rupture can be dissociated from each other showing that the LH effect is mediated via different cellular messengers. The gonadotrophins act in an orderly sequence to induce follicular maturation. The granulosa cells increase their number of LH receptors and respond to LH with increased stimulation of cyclic AMP accumulation and progesterone secretion. Concomitantly, they decrease in their FSH receptors and their response to FSH diminishes in terms of ability to stimulate cyclic AMP accumulation. The ovulatory process is associated with increased uptake of LH by the follicle; when granulosa cells are obtained from pre-ovulatory follicles and cultured they luteinize spontaneously. Steroid hormones modulate the actions of gonadotrophins on follicular maturation. In addition, there are non-steroidal factors in follicular fluid which regulate follicular maturation: an oocyte maturation inhibitor keeps the oocyte in meiotic arrest; a luteinizing inhibitor prevents the granulosa cells from luteinizing prior to follicular rupture; a folliculostatin inhibits FSH release from the pituitary gland. The functional activity and the lifespan of the corpus luteum depend on adequate pre-ovulatory as well as post-ovulatory gonadotrophic stimulation. Its lifespan may also be regulated by an LH binding inhibitor.

Mechanism of action of luteinizing hormone and follicle-stimulating hormone on the ovary in vitro

The mechanism of action of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) upon various cell types of the mammalian ovary is reviewed. Emphasis is placed upon in vitro studies using organ and cell culture as well as short-term incubations. FSH and LH actions upon the following ovarian functions are discussed: steroidogenesis and metabolism of the ovary as a whole and of the isolated follicle and its component cell types, the granulosa and thecal cells, as well as folliculogenesis and follicular growth, oocyte maturation, follicular rupture, and corpus luteum maintenance and steroidogenesis. The roles of gonadotropin receptors, AMP, prostaglandins, protein kinase, and protein synthesis in these LH and FSH actions are discussed. Intra-ovarian regulation of LH and FSH action is reviewed, including a discussion of the possible roles of follicular fluid inhibitors upon oocyte maturation and granulosa cell luteinization.

Mast cell histamine and ovarian follicular growth in the lizard Anolis carolinensis

The hypothesis is proposed that histamine released from mast cells in the theca of ovarian follicles increases thecal hyperemia and vessel permeability, and thus plays a role in follicular growth in Anolis carolinensis. Mast cells are present in the stroma and theca, and the number of thecal mast cells increases as follicles grow. The levels of histamine in follicular walls varies with follicular size. Histamine causes vasodilatation of thecal vessels. Antihistamine blocks the effects of histamine and, when given alone, stimulates vasoconstriction. Antihistamine also blocks estradiol-induced growth of large follicles. These findings are consistent with the above hypothesis.