The vascular system of the rabbit ovary and its relationship to ovulation

Using Machine Learning to Construct the Blood-Follicle Distribution Models of Various Trace Elements and Explore the Transport-Related Pathways with Multiomics Data

Permeabilities of various trace elements (TEs) through the blood-follicle barrier (BFB) play an important role in oocyte development. However, it has not been comprehensively described as well as its involved biological pathways. Our study aimed to construct a blood-follicle distribution model of the concerned TEs and explore their related biological pathways. We finally included a total of 168 women from a cohort of in vitro fertilization-embryo transfer conducted in two reproductive centers in Beijing City and Shandong Province, China. The concentrations of 35 TEs in both serum and follicular fluid (FF) samples from the 168 women were measured, as well as the multiomics features of the metabolome, lipidome, and proteome in both plasma and FF samples. Multiomics features associated with the transfer efficiencies of TEs through the BFB were selected by using an elastic net model and further utilized for pathway analysis. Various machine learning (ML) models were built to predict the concentrations of TEs in FF. Overall, there are 21 TEs that exhibited three types of consistent BFB distribution characteristics between Beijing and Shandong centers. Among them, the concentrations of arsenic, manganese, nickel, tin, and bismuth in FF were higher than those in the serum with transfer efficiencies of 1.19-4.38, while a reverse trend was observed for the 15 TEs with transfer efficiencies of 0.076-0.905, e.g., mercury, germanium, selenium, antimony, and titanium. Lastly, cadmium was evenly distributed in the two compartments with transfer efficiencies of 0.998-1.056. Multiomics analysis showed that the enrichment of TEs was associated with the synthesis and action of steroid hormones and the glucose metabolism. Random forest model can provide the most accurate predictions of the concentrations of TEs in FF among the concerned ML models. In conclusion, the selective permeability through the BFB for various TEs may be significantly regulated by the steroid hormones and the glucose metabolism. Also, the concentrations of some TEs in FF can be well predicted by their serum levels with a random forest model.

Morphological and scanning electron microscopic study of the gonadal arterioles in the Tibetan sheep

This research aimed at revealing the structural features of Tibetan sheep's testicular and ovarian vasculature and providing theoretical basis for Tibetan sheep's physiological adaptability in plateau and low-oxygen environments. Through scanning electron microscopy, corrosion casts of the feature of the gonad arterioles were observed and analysed. The results of this study found that centrifugal arteries, centrifugal and centripetal arterioles were distributed in a 'dendritic' fashion in the testis lobule, the ovarian arteries and arterioles, which had a spiral shape. Testicular Tibetan Sheep knot-like artery had a denser spiral structure, and there were more branches in the microarteries. On the testis lobule and arteriole of caput epididymidis, the arteriole surface shows the 'fusiform' indentation to be more shallower. The ovarian artery had a higher degree of helix; its surface was distributed like a 'bark-like' indentation; and the ring was narrower and denser. Nevertheless, the arteriole network had a high concentration and a wide number of branches, as that of the ovarian arteriole network which had more end branches, the surface of the arterioles of ovaries and testicles was scarred and denser. The studies indicate that the structural features of testicular lobule, epididymal arterioles and ovarian arterioles are more conducive to increase the oxygen supply to the gonads tissue and controlling blood flow velocity and metabolism to respond to high altitudes and low-oxygen environments.

Ramification Pattern of the Arteries Supplying the Rabbit Female Genital Organs

Uterine adenocarcinoma occurs in more than 60% of female rabbits aged 4 years and over. To cure or prevent this uterine disorder, ovariohysterectomy should be performed. Although knowledge of the arterial supply to the ovary, uterus, and vagina is required, few studies have described the arterial anatomy. Therefore, we dissected ovarian, uterine, and vaginal arteries in 15 New Zealand White and 15 Japanese White rabbits to clarify the anatomy. The ovarian artery arose from the abdominal aorta, and in 50% of cases, the left artery emerged more cranially than the right artery. The ovarian artery provided the ovarian, uterine, and tubal branches with three branching types. The most frequent type (67% of the halves on the right and 63% of the halves on the left) exhibited three branches that independently arose from the ovarian artery. The uterine artery usually originated from the umbilical artery, with its ramification pattern divided into two types, having one or two uterine arteries, respectively. The most frequent type (all halves on the right and 83% of the halves on the left) had one uterine artery that originated from the umbilical artery. We observed three types of vaginal artery origins, with the branching type where the vaginal artery arose from the internal iliac artery being the most frequent (97% of the halves on the right and 90% of the halves on the left). The detailed arterial supply pattern of the rabbit female genital organs determined in the present study will be helpful when performing rabbit gynecological surgeries. Anat Rec, 303:1478-1488, 2020. © 2019 American Association for Anatomy.

The Role of Growth Hormone on Ovarian Functioning and Ovarian Angiogenesis

Although not yet well-understood, today it is clear that Growth Hormone (GH) exerts a relevant role in the regulation of ovulation and fertility; in fact, fertility is lower in women with GH deficiency (GHD), and GH receptors (GHR) and GH mRNA have been found in the ovary since the onset of follicular development in humans. However, despite the strong evidence of GH in the regulation of fertility, many aspects of GH actions at this level are still not well-established, and it is likely that some controversial data depend on the species analyzed, the dose of the hormone and the duration of use of GH. Folliculogenesis, ovulation, and corpus luteum formation and maintenance are processes that are critically dependent on angiogenesis. In the ovary, new blood vessel formation facilitates oxygen, nutrients, and hormone substrate delivery, and also secures transfer of different hormones to targeted cells. Some growth factors and hormones overlap their actions in order to control the angiogenic process for fertility. However, we still know very little about the factors that play a critical role in the vascular changes that occur during folliculogenesis or luteal regression. To promote and maintain the production of VEGF-A in granulosa cells, the effects of local factors such as IGF-I and steroids are needed; that VEGF-A-inducing effect cannot be induced by luteinizing hormone (LH) or chorionic gonadotropin (CG) alone. As a result of the influences that GH exerts on the hypothalamic-pituitary-gonadal axis, facilitating the release of gonadotropins, and given the relationship between GH and local ovarian factors such as VEGF-A, FGF-2, IGF-1, or production of sex steroids, we assume that GH has to be a necessary factor in ovarian angiogenesis, as it happens in other vascular beds. In this review we will discuss the actions of GH in the ovary, most of them likely due to the local production of the hormone and its mediators.

The blood-follicle barrier (BFB) in disease and in ovarian function

The blood-follicle barrier (BFB) is one of the blood-tissue barriers in mammalian body found in developing follicles in the ovary. The BFB, besides the tight junction (TJ)-permeability barrier of the endothelial cells in the microvessels that surround the developing follicle, is constituted and contributed significantly by the basement membrane of the developing follicle which alters its composition rapidly during follicle development. While the concept of the BFB and its ultrastructure were described more than six decades ago, fewer than 20 reports are found in the literature that were dedicated to investigate the biology, regulation, and function of the BFB either in health or in disease. Furthermore, detailed analysis of the adhesion protein complexes and the regulation of the junction dynamics at the BFB are still missing in the literature. The goal of this short chapter is to provide an update on this important blood-tissue barrier, it is obvious that future investigation is much needed in the field to understand this ultrastructure better in order to treat and better ovarian disorders including ovarian cancer.

Existence of the lymphatic system in the primate corpus luteum

To date, there have been no detailed studies on the lymphatic system in the primate corpus luteum (CL); early reports suggested that the presence of this "secondary circulation" in luteal tissue is species-dependant. Therefore, studies were designed to determine if (a) lymphatic vessels exist, and (b) recently discovered lymphangiogenic factors and their receptor are expressed in the macaque CL during the menstrual cycle. Immunohistochemistry (IHC) detected the lymphatic endothelial cell marker, lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), in some endothelial cells and vessels within the ovarian stroma and theca layer of preovulatory follicles and in the CL. Dual fluorescent IHC demonstrated that LYVE1 co-localized with another lymphatic endothelial cell marker D2-40, but a blood vascular endothelial cell marker (von Willebrand Factor, VWF) was in different cells. The numbers and staining intensity of LYVE1-positive cells in the CL appeared to increase from early to mid luteal phase, and remained elevated thereafter. RT-PCR detected cDNA fragments for mRNAs encoding VEGFC, FIGF, and their receptor FLT4 in CL. Real-time PCR analyses revealed similar patterns of VEGFC and FLT4 expression during the luteal lifespan; mRNA levels increased (p < 0.05) from early to mid luteal phase and decreased (p < 0.05) by late luteal phase. In contrast, FIGF levels were elevated initially, declined (p < 0.05) at mid luteal phase, and then increased (p < 0.05) to very late luteal phase. The data strongly suggest that lymphatic vessels are present in the primate CL, and that the VEGFC/FIGF-FLT4 system regulates lymphangiogenesis and luteal structure-function during the menstrual cycle.

Intravascular pressure and diameter profile of the utero-ovarian resistance artery network: estrous cycle-dependent modulation of resistance artery tone

Blood flow to the ovary varies dramatically in both magnitude and distribution throughout the estrous cycle to meet the hormonal and metabolic demands of the ovarian parenchyma as it cyclically develops and regresses. Several vascular components appear to be critical to vascular regulation of the ovary. As a first step in resolving the role of the resistance arteries and their paired veins in regulating ovarian blood flow and transvascular exchange, we characterized the architecture and intravascular pressure profile of the utero-ovarian resistance artery network in an in vivo preparation of the ovary of the anesthetized Golden hamster. We also investigated estrous cycle-dependent changes in resistance artery tone. The right ovary and the cranial aspect of the uterus in 26 female hamsters were exposed for microcirculatory observations. Estrous-cycle phase was determined in each animal before experimentation. The utero-ovarian vascular architecture was determined and resistance artery diameters were measured in each animal by video microscopy. Servo-null intravascular pressure measurements were made throughout the uteroovarian arterial network in 11 of the animals. Architectural data showed a complex anastomotic network jointly supplying the uterus and ovary. Resistance arteries showed a high degree of coiling and close apposition to veins, maximizing countercurrent-exchange capabilities. Arterial pressure dropped below 60% of systemic arterial pressure before the arteries entered the ovary. Both the ovarian artery and the uterine artery, which jointly feed the ovary, showed cycle day-dependent changes in diameter. Arterial diameters were smallest on the day following ovulation, during the brief luteal phase of the hamster. The data show that resistance arteries comprise a critical part of a complex network designed for intimate local communication and control and suggest that these arteries may play an important role in regulating ovarian blood flow in an estrous cycle-specific manner.

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.

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.

The formation of lymph in the ovary

The lymphatics of the ovaries of pregnant and non-pregnant ewes were outlined either by direct or retrograde injection of indian ink or Berlin blue and the distribution of these vessels within the ovary was determined. In active ovaries the mature follicles and corpora lutea contained a profuse network of lymphatics. In inactive ovaries the lymphatics were very small and poorly developed. Lymph was collected from the ovaries of conscious ewes for periods of several days. The flow of lymph from ovaries with corpora lutea averaged 4.15 ml./h; a maximum rate of flow of 14.9 ml./h was recorded in one ewe. The protein concentration of ovarian lymph was 73 % of the plasma concentration. When 131 I labelled albumin was injected intravenously into ewes it entered the ovarian lymph very rapidly and the specific activities of albumin in the plasma and lymph equilibrated within 10 to 20 min of injection. The structure of the ovarian blood capillaries provided an explanation for the very high rate of lymph flow and protein leakage in the ovary. The endothelium of the blood capillaries was discontinuous with gaps up to 1 to 2 μm in diameter through which red cells, indian ink particles and ferritin passed into the interstitial spaces. Where the basement membrane of the capillaries was deficient over gaps the surfaces of the luteal cells came into direct contact with the circulating plasma, and occasionally cytoplasmic extensions from the luteal cells projected into the lumen of the blood capillaries. The lymphatics which were associated with many of the blood capillaries had open intercellular junctions and material could enter these vessels readily from the interstitial spaces. The blood capillaries in the ovarian stroma and those around immature follicles appeared less permeable than the capillaries of the corpus luteum. The association between the development of the corpus and an increase in lymph production in the ovary suggests the possibility that the changes in capillary permeability may be related to the synthesis and secretion of steroid hormones.

Gonadotropin-stimulated regulation of blood-follicle barrier is mediated by nitric oxide

Although initially described over 30 years ago, the blood-follicle barrier has remained a biological enigma. In this study, we characterize the blood-follicle barrier with respect to its regulation of intrafollicular inter-alpha-trypsin inhibitor protein (I alpha I) influx after an ovulatory stimulus. We have found that I alpha I is localized within the ovarian vasculature but is excluded from the follicular compartment until an ovulatory stimulus is given. Within minutes after an ovulatory dose of human chorionic gonadotropin, I alpha I is localized within the follicular fluid of responding follicles where this protein becomes associated with and stabilizes the newly synthesized hyaluronic acid-rich cumulus extracellular matrix. Analysis of this process has shown that intravenous injection of sodium nitroprusside or excess substrate for nitric oxide synthase, L-arginine, mimics the effect of gonadotropic hormones on the influx of I alpha I into the follicular compartment of preovulatory follicles. Moreover, intravenous injection of specific nitric oxide synthase inhibitors, NG-nitro-L-arginine methyl ester and NG-nitro-L-arginine, inhibits gonadotropin-mediated intrafollicular influx of I alpha I and also inhibits ovulation in the mouse.

The intraovarian progesterone modulation of follicle development in the rabbit ovary

Intraovarian progesterone levels were manipulated by surgically adjusting the number of corpora lutea (CL) present in rabbit ovaries and this model was used to study the local effect of luteal progesterone on growth of follicles. The results show that when a single CL or several CL were present, follicle growth was inhibited. However, when all CL on one ovary were removed, increased numbers of follicles grew even when a single CL was present in the contralateral ovary. These findings show that progesterone inhibits follicle growth and that at least part of its action is local, i.e., exerted within the ovary. Additionally, ovarian blood vessels and periovarian lymph ducts were cannulated, and samples were collected and analyzed for steroid and protein content. The results show that when CL were present, ovarian vein progesterone levels were elevated 10-30-fold over levels in ovaries without CL; this high concentration points to the blood vascular system as the principal carrier of the steroid within the ovary. Analysis of lymph showed that protein content was consistently high and that the progesterone concentration was not significantly altered with the presence of CL; these two findings show that ovarian capillaries are extremely permeable to proteins, but the unexpectedly low concentrations of progesterone in lymph may signal an intraovarian countercurrent mechanism by which it is returned to the blood.

The effect of reduced oxygen tension on progesterone accumulation in rat granulosa cell cultures

Studies were carried out on the effect of oxygen tension on progesterone (P) accumulation in rat granulosa cell cultures. At 1-2% oxygen, basal, luteinizing hormone (LH)-stimulated, and follicle stimulating hormone (FSH)-stimulated P accumulations were 20, 18, and 11%, respectively, of P levels at 20% oxygen. Basal P accumulation was also inhibited at 5% oxygen, but LH- and FSH-stimulated P levels were 50% and 40% higher, respectively, than at 20% oxygen. P levels at 10% oxygen were intermediate between those at 5% and 20% oxygen. The inhibitory effect of 1-2% oxygen on P accumulation was reversible: LH-stimulated P accumulation was inhibited in cultures incubated in 1-2% oxygen for 24 h, but rebounded during a subsequent 24 h period in 20% oxygen to the same level as that in cultures maintained continuously in 20% oxygen. We conclude that oxygen tension does influence granulosa cell steroidogenesis in vitro. Changes in blood flow and oxygen delivery to the ovary before and after ovulation could, therefore, effect the pattern of steroidogenesis during this period.

Electrophysiological properties of the follicle wall in the pig ovary

The transmural potential difference and short-circuit current of the porcine Graafian follicle have been measured in an attempt to test whether antral fluid accumulates as a result of active transport of salt. The values obtained by mounting explants of follicle wall in Ussing chambers were close to zero and the specific electrical resistance was only 59 delta.cm2. The elemental composition of the follicular fluid was similar to that of ovarian venous plasma with the exception of follicular Na+ which was slightly more abundant. Bicarbonate concentrations were slightly lower in follicular fluids. These findings were interpreted as evidence that the follicular wall is a leaky epithelium and, therefore, any charge resulting from net ion transport will be shunted along low resistance paracellular pathways.

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.

Endothelial mitosis during the initial stages of corpus luteum neovascularization in the cycling adult rat

The initial stages of neovascularization of the corpus luteum were studied in cycling adult rats using light-microscopic autoradiography. The aim of this analysis was to determine whether endothelial mitosis is a factor in this vascular growth and whether there are differences in the amount of mitotic activity in various regions of the ovary. Ovaries were examined at two time intervals: 1-2 hr and 7-8 hr following ovulation. Animals received an intraperitoneal injection of tritiated-thymidine 20 min prior to perfusion fixation of the ovaries. Autoradiographic demonstration of tritiated-thymidine labeling in endothelial nuclei was considered an indication of DNA synthesis preceding mitosis. The percentage of labeled endothelial cells in the ovaries at both time intervals varied according to the region of tissue examined and the stage of differentiation of that region. Stromal vessels were less heavily labeled than thecal vessels. Thecal vessels surrounding growing follicles were more heavily labeled than those surrounding atretic follicles. The heaviest labeling was seen in the developing corpora lutea 7-8 hr following ovulation. Minimal labeling was evident in the corpora lutea which were formed in previous cycles. A regional difference was also detected in the ovarian mesothelium. The portion of the mesothelium overlying ovulated follicles and developing corpora lutea had the greatest percentage of labeled cells. The major findings of this study were: endothelial mitosis was elevated in the initial stages of luteal neovascularization; the heightened endothelial labeling was confined to specific regions of the ovary; and mesothelium in close proximity to the developing corpora lutea also displayed heightened DNA synthesis.

Histochemical investigation of the folliculogenesis in the ovary of the Mongolian gerbil (Meriones unguiculatus)

The ovaries of 70 mature Mongolian gerbils (Meriones unguiculatus) were investigated morphologically and enzyme histochemistry for the appearance of acid phosphatase, non-specific esterases, succinate dehydrogenase and thiamine pyrophosphatase. In the oocyte two particular enzyme active zones exist depending on the state of development. In young oocytes acid phosphatase, succinate dehydrogenase and thiamine pyrophosphatase can be found only in the perinuclear zone. From the late secondary follicle on, activity of acid phosphatase, succinate dehydrogenase and non-specific esterases can be detected only in a peripheral area of cytoplasm, whereas thiamine pyrophosphatase is present in the entire ooplasm. In the follicular epithelium a different pattern of enzyme distribution suggests a functional differentiation of the epithelial cells during folliculogenesis.

Surgical alteration of the mesosalpinx and its influence upon ovarian ovulatory function in the rabbit

Ovarian ovulatory function as correlated with the production of corpora lutea was studied in 58 rabbits that were subjected to unilateral surgical procedures. Initially, a resection of 50% of the isthmus and 50% (n = 8) or all (n = 8) of the corresponding mesosalpinx was performed. Next, 50% of the ampulla and 50% (n = 7) or all (n = 8) of the corresponding mesosalpinx was resected. Finally, a variable length, either one third, two thirds, or all, of the ampulla (n = 27) was dissected from the adjacent mesosalpinx. After natural copulation of the animals, without administration of gonadotropin, the numbers of corpora lutea on the operated and control sides were counted. A slight but nonsignificant overall reduction in corpora lutea on the operated side was observed. This showed no correlation either to the amount of mesosalpinx resected or the proximity of the surgical procedure to the ovary. Also, no correlation was observed with the length of dissected ampullary part.

Prostaglandins and preovulatory follicular maturation in mice

Experiments have been carried out in an effort to reverse the indomethacin-induced inhibition of preovulatory follicular development in immature superovulated mice utilizing prostaglandins E2 and F2 alpha. All mice were primed with 5 IU pregnant mare's serum gonadotropin followed 40 h later by 80 IU luteinizing hormone (LH). Animals were sacrificed 10 1/2 or 11 1/2-12 h post-LH, at which time ovaries were fixed and prepared for microscopic observation. Control mice receiving both indomethacin and prostaglandin (PG) vehicles averaged 92% germinal vesicle breakdown, and 82% of maturing oocytes were surrounded by an expanded cumulus oophorus. Ovarian weight increased by 29% and the apical walls of preovulatory follicles demonstrated appreciable thinning following LH administration. In mice receiving indomethacin plus PG vehicle, follicular maturation was suppressed in a dose-dependent manner; in mice receiving 10 mg/kg, less than 50% of the oocytes resumed meiosis and, of these, only 9% were accompanied by cumulus expansion. Ovarian weight gain was also inhibited, and the apical follicle wall exhibited few signs of preovulatory thinning. PGE2 and PGF2 alpha both reversed the inhibition of cumulus and oocyte maturation induced by indomethacin, though PGE2 was more effective. Only PGF2 alpha promoted apical follicular thinning, and neither PG had a significant effect on ovarian weight. We conclude that, in mice, PGs may play an integral role during preovulatory maturation of the oocyte and cumulus, as well as thinning of the apical wall.

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.

An intrabursal injection procedure for the in vivo study of ovulation in hamsters

A new procedure for studying the effect of various drugs on ovulation in vivo is described. In golden hamsters (Mesocricetus auratus), each ovary is enclosed within a complete bursa that is continuous with the oviduct. Drugs can be applied topically to ovaries by injection of a solution into a bursal cavity of an anesthetized hamster several hours before ovulation; the contralateral ovary serves as an in vivo control and receives no treatment. After ovulation, the number of ruptured follicles on experimental and control ovaries are compared. Data presented show that: (1) the operation and injection procedure per se do not affect ovulation; (2) normal saline is a suitable vehicle for administration of drugs by this route; (3) compounds with molecular weights of less than 1,000 daltons rapidly penetrate all layers of the follicle wall; (4) solutions injected into the bursal cavity 6 hours before ovulation remain there until ovulation. The advantages and limitations of this technique are discussed.

A scanning electron microscopic study of the luteo-follicular complex. II. Events leading to ovulation

Morphological changes on the ovarian surface of different mammals both before and during ovulation have been examined by scanning electron microscopy. Preovulatory follicles were blisterlike structures that protruded markedly from the ovarian surface. Basal areas of preovulatory follicles were covered with polyhedral cells containing numerous microvilli, whereas on the lateral surfaces, superficial cells were elongated and possessed few microvilli. At the apex of the follicle, cells were very flattened and possessed few microvilli, which were present only in regions of intercellular contact. In some apical areas, cells appeared to be degenerating, whereas in other regions, groups of cells had "sloughed off." In addition, a fluidlike material was observed to exude from intercellular spaces of the superficial epithelium and to cover some apical cells. By transmission electron microscopy, the same fluidlike material was observed to (1) infiltrate the connective tissue of the tunica albuginea, (2) accumulate under the basal lamina, and (3) distend intercellular spaces of the superficial epithelium. Just prior to ovulation, large, irregular areas of the apex were ruptured and the oocyte, covered with a large amount of fluid, appeared to emerge from the follicle. At ovulation, the oocyte was not completely covered with follicle cells and the zona pellucida was clearly evident. The surface of the zona was quite irregular and contained numerous infoldings, channels and crypts. Follicle cells had polyhedral or star shapes and possessed large cytoplasmic evaginations that obliquely penetrated the zona. Both the zona pellucida and corona cells were covered with a fine layer of granular material. The SEM results and parallel TEM observations suggest that a local increase of fluids (edema) may be an important factor in the final decomposition of the distended and weakened apex of the preovulatory follicle. In addition, the participation of follicle cells, smooth muscle cells and the oviduct in the escape of the oocyte from the ruptured follicle is discussed.

The development of rabbit ovarian follicles following copulation

The morphologic development of rabbit ovarian follicles was studied by means of light and electron microscopy 0, 2, 4, 6, 8, and 10 hours after copulation. The progressive changes at the apex of the follicle included extensive edema, hyperemia, and rupture of blood vessels, and then rupture of the follicular wall. Ovulation occurred when the cohesive forces in the cellular layers of the follicular apex became less than the physical forces within the follicle. Most of the morphologic changes in the follicle as it approached ovulation could be related to the effects of locally produced estrogens.

Permeability of ovarian follicles and capillaries in mice

The permeability of ovarian capillaries and follicles in prepubertal and sexually mature (proestrus and metestrus) randomly bred Swiss Albino female mice (SCH:ARS HA ICR strain) was studied by intravenous injection of either ferritin or horseradish peroxidase (HRP), followed by examination with light and electron microscopes. The study revealed that capillaries in the interstitial and perifollicular regions were provided with a continuous endothelium that had constant permeability characteristics irrespective of sexual maturity or phase of the estrous cycle. Horseradish peroxidase left the capillaries primarily through interendothelial cell junctions and was present in all follicles within 30 seconds after administration of the tracer. Ferritin, on the other hand, was absent from endothelial cell junctions, and left the capillaries, at a slower rate than HRP, via cytoplasmic vesicular transport. Both tracers were found in the granulosa cells but rarely in the oocytes. The tracers reached the oocyte through the intercellular spaces between granulosa cells. These findings demonstrate that the follicular apparatus of the mouse is permeable to ferritin and HRP, and that follicular regions such as the basal lamina of the follicle and the zona pellucida do not stop or retard the passage of either tracer.