Immunocytochemical evidence for the presence of oxytocin and neurophysin in the large cells of the bovine corpus luteum

Evidence for existence of insulin-like factor 3 (INSL3) hormone-receptor system in the ovarian corpus luteum and extra-ovarian reproductive organs during pregnancy in goats

Insulin-like factor 3 (INSL3), initially described as a male hormone, is expressed in female reproductive organs during the estrous cycle and pregnancy but its function has not yet been established. This study explores the function of INSL3 in pregnant Saanen goats by characterizing the expression dynamics of INSL3 and its receptor, relaxin family peptide receptor 2 (RXFP2) and by demonstrating specific INSL3 binding in reproductive organs, using molecular and immunological approaches and ligand-receptor interaction assays. We demonstrate that the corpus luteum (CL) acts as both a source and target of INSL3 in pregnant goats, while extra-ovarian reproductive organs serve as additional INSL3 targets. The expression of INSL3 and RXFP2 in the CL reached maximum levels in middle pregnancy, followed by a decrease in late pregnancy; in contrast, RXFP2 expression levels in extra-ovarian reproductive organs were higher in the mammary glands but lower in the uterus, cervix and placenta and did not significantly change during pregnancy. The functional RXFP2 enabling INSL3 to bind was identified as an ~ 85 kDa protein in both the CL and mammary glands and localized in large and small luteal cells in the CL and in tubuloalveolar and ductal epithelial cells in the mammary glands. Additionally, INSL3 also bound to multiple cell types expressing RXFP2 in the uterus, cervix and placenta in a hormone-specific and saturable manner. These results provide evidence that an active intra- and extra-ovarian INSL3 hormone-receptor system operates during pregnancy in goats.

Effects of hCG and ovarian steroid hormones on vasotocin levels in the female catfish Heteropneustes fossilis

Effects of hCG, ovariectomy and estradiol replacement on brain, plasma and/or ovarian vasotocin in vivo, and estradiol, progesterone, 17alpha, 20beta-hydroxy-4-pregnen-3-one and hCG on ovarian vasotocin in vitro were investigated in the catfish. A 100IU/fish of hCG induced ovulation and elicited both periovulatory and post-ovulatory changes in vasotocin concentrations with a significant increase up to 8h in the brain and up to 16h in both plasma and ovary. After stripping the fish at 16h, the peptide concentration decreased significantly with time, up to 4 days. Ovariectomy in early pre-spawning phase resulted in a duration-dependent significant reduction of both brain and plasma vasotocin. Estradiol replacement in 3-week ovariectomized fish produced dosage-dependent biphasic effects: the lower dosage (0.1microg/g) restored the vasotocin level while the higher dosage (0.5microg/g) decreased it significantly below the control level. In vitro incubation of ovarian tissues with estradiol produced season-dependent effects on vasotocin. The incubation of pre-vitellogenic ovarian pieces with estradiol (1, 10, and 100ng/ml) elevated vasotocin level in a dose- and duration-dependent manner while that of post-vitellogenic follicles resulted in a significant decrease. The incubation of intact post-vitellogenic follicles or follicular envelope with progesterone and 17alpha, 20beta-hydroxy-4-pregnen-3-one (1microg/ml) or hCG (20IU/ml) for 8 and 16h significantly increased vasotocin in a duration-dependent manner. The results show that both gonadotropin and ovarian steroids modulate vasotocin titer, which may influence follicular growth, ovulation and spawning in the catfish.

Oxytocin and vasopressin expression in the ovine testis and epididymis: changes with the onset of spermatogenesis

Contractions of seminiferous tubules and epididymal duct walls promote spermiation and sperm transfer, and they are thought to be stimulated by the related peptides oxytocin and vasopressin. This study tested the hypothesis that if oxytocin and/or vasopressin play a physiological role in sperm shedding and transport, then local or circulating concentrations of these peptides would increase during puberty. Testes, epididymides, and trunk blood of sheep at stages during the first spermatogenic wave were collected, and radioimmunoassay measured significant increases in testicular and epididymal oxytocin during spermatogenesis. No changes were measured in circulating oxytocin or in local or circulating vasopressin. Localization and synthesis was investigated by immunohistochemistry and Western blot analysis employing antibodies recognizing epitopes of either oxytocin, oxytocin-associated neurophysin, vasopressin, or vasopressin-associated neurophysin. Marked expression of both oxytocin and its associated neurophysin in testicular Leydig and epididymal principal cells was seen, and weak neurophysin immunoreactivity was also identified in Sertoli cells. The intercellular distribution of oxytocin varied between regions of the epididymis, suggesting several roles for oxytocin. Vasopressin synthesis was not apparent in either tissue. These results confirm the presence and development of paracrine oxytocinergic systems in the ram testis and epididymis of ram during puberty while questioning the physiological importance of vasopressin.

Oxytocin in the semen and gonads of the stallion

It has been suggested that oxytocin is involved in sperm transport and motility in domestic animals. Immunoreactive oxytocin was measured in seminal fractions (pre-ejaculatory fluid, seminal plasma, gel and sperm) and in extracts of testis and epididymis from stallions. In addition, sections of gonadal tissue from stallions were immunostained for the presence of oxytocin and its neurophysin. Oxytocin was detected in all of the seminal fractions, being highest in the gel. It was also present in washed, lysed sperm and in extracts from the testis and epididymis. Immunostaining for oxytocin was present in occasional interstitial cells in the testis and in the epididymal epithelium and smooth muscle. However, immunostaining for neurophysin was detected in a few interstitial cells in the testis of only 1 of 8 stallions and was absent from all areas of the epididymis. These data demonstrate for the first time the presence of oxytocin in stallion semen and gonadal tissue; however, lack of immunostaining for neurophysin indicated that it was unlikely that there was local synthesis within the gonads.

Immunolocalization of neurophysin in cytokeratin-positive luteal cells of cows

We have recently detected a subgroup of cytokeratin (CK)-positive luteal cells in the bovine corpus luteum of the early and mid-luteal phase, but not in that of pregnancy. Since, according to the literature, neurophysin (NP)-positive luteal cells behave comparably, simple immunohistochemistry and double labeling were used to identify in serial sections whether the presence of NP co-incided with that of CK. The numbers of CK-positive cells and NP-positive luteal cells were comparable throughout the estrous cycle, decreasing from early to late luteal phase. While few CK-positive cells were found in the former thecal layer during the early luteal phase, many CK-positive cells appeared in the former granulosal layer. NP-positive cells were only detected in the former granulosal layer. During the mid-luteal phase, the CK-positive cells consisted of small and large luteal cells, but only large NP-positive cells were found. Roughly 80% of the large CK-positive cells contained NP, whereas CK was lacking in more than 50% of the NP-positive cells. The corpora lutea of pregnancy contained neither CK-positive nor NP-positive cells. The significance of the simultaneous occurrence of CK and NP remains to be elucidated.

Cytokeratin expression in bovine corpora lutea

Cytokeratin (CK)-positive cells were obtained from bovine corpora lutea. When cultured, these cells behave like CK-positive endothelial cells obtained from bovine large blood vessels. The origin of CK-positive cells has now been studied in 45 bovine corpora lutea of different estrous cycle stages. Additionally, 7 corpora lutea of pregnant cows were examined. The tissues were grouped into early stage (days 2 to 4), secretory stage (days 5 to 17) and late stage (days 18 to 21) according to gross morphology, wet weight and total progesterone content. One portion of a corpus luteum was used for immunohistochemistry, and another for Western blot analysis. Twenty-six of the 45 corpora lutea showed CK expression, as confirmed by immunostaining and Western blotting. Cytokeratin expression was found in all corpora lutea from the early stage, in 14 of 26 corpora lutea from the secretory stage, and 3 of 10 from the late stage. Early stage corpora lutea displayed "zonation" such that a high number of CK-positive luteal cells occurred in the region of the previous granulosa layer and a very low number in the previous thecal layer. Secretory CK-positive corpora lutea showed uniformly distributed, predominantly large luteal cells. In secretory corpora lutea of group A, CK-positive cells and a distinct microvascular tree were seen, the latter visualized by factor VIII-related antigen immunolabelling of endothelial cells. Group B showed none or very few CK-positive cells. Corpora lutea of pregnant cows behaved like corpora lutea of group B. Roughly 1% of CK-positive cells closely associated with the capillary wall were sometimes reminiscent of endothelial cell sprouts.

Influences of oxytocin on the synthesis of prostaglandins by uterus from rats in different stages of the estrous cycle

We explored the oxytocin-prostaglandin interactions during the rat estrous cycle. The experiments were done with uterine preparations isolated from rats in different stages of the sex cycle incubated 'in vitro' with oxytocin (O) (50 mU/ml). We found that the effect of O on prostaglandin (PG) synthesis was associated to the sex hormones, and varied during the estrous cycle. Indeed, during the estrogenic influence (i.e. at proestrus and estrus) O diminished the synthesis of PGE2 and with the highest estradiol concentration (i.e. during estrus) the hormone also augmented the synthesis of PGF2 alpha. During metestrus, no changes in PG synthesis after treatment were found. Likewise, during diestrus, when progesterone levels fall, O enhanced PGF2 alpha uterine synthesis. In this study an inhibitory action of O on the uterine production of 6-keto-PGF1 alpha at proestrus was also seen. The present results indicate that when estrogen concentration increases (during estrus) 6-keto-PGF1 alpha synthesis also increases. In summary, we have observed that sex hormones exert a modulating action on the influences of O on uterine PGs synthesis.

Synthesis of oxytocin in amnion, chorion, and decidua may influence the timing of human parturition

Despite the widespread clinical use of oxytocin (OT) as a potent and specific stimulant of labor, previous research data have not supported a role for OT in the physiology of normal human parturition. We have demonstrated synthesis of OT mRNA in amnion, chorion, and decidua using Northern blot analysis, ribonuclease protection assays, and in situ hybridization. Probes directed towards both the 3' and 5' ends of the gene have been used. Levels were highest in decidua with considerably less in chorion and amnion and very low levels in placenta. The transcript size in decidua appears to be 60-80 nucleotides smaller than the transcripts in amnion and chorion. OT gene expression in chorio-decidual tissues increased three- to fourfold around the time of labor onset. Estradiol stimulated synthesis of OT mRNA during in vitro incubation. These results support the hypothesis of a paracrine system involving OT and sex steroids within intrauterine tissues wherein significant changes could occur without being reflected in the maternal circulation. Such a paracrine system could rationalize a long-sought role for oxytocin in the physiology of human labor. These data may lead to novel approaches towards prevention or treatment or preterm labor.

Immunohistochemical evidence for the presence of oxytocin in the opossum corpus luteum

Corpora lutea from opossums late in pregnancy were examined by immunohistochemistry for the presence of oxytocin. Oxytocin-immunoreactivity was observed in all corpora lutea examined but not elsewhere in ovarian tissue. The immunoreactive staining observed was confined primarily to the perinuclear cytoplasm of reactive luteal cells. Not all luteal cells showed oxytocin-immunoreactivity. The immunohistochemical localization of oxytocin in the pregnant opossum corpus luteum demonstrates for the first time this peptide in a metatherian ovary. Its presence in this primitive species suggests that oxytocin has a fundamental role in the physiology of the mammalian ovary.

Effects of gonadotropins, insulin and insulin-like growth factor I on ovarian oxytocin and progesterone production

Oxytocin is produced in the granulosa-derived cells of the ruminant corpus luteum where its gene is dramatically up-regulated within days of ovulation. Regulation of these processes is poorly understood but oxytocin release can be increased by insulin, insulin-like growth factor I (IGF-I), and gonadotropins. Here we have assessed interactions between these regulatory systems. Follicle-stimulating hormone (FSH), luteinizing hormone (LH) and human chorionic gonadotropin (hCG) caused dose-dependent release of oxytocin from bovine granulosa cells cultured in medium containing 100 ng/ml insulin. The gonadotropins also increased oxytocin mRNA levels and their effects were mimicked by forskolin. The effects of these stimuli on oxytocin and progesterone release were synergistically increased by insulin or IGF-I. Binding studies revealed separate binding sites with characteristics of insulin and IGF-I receptors. Insulin potentiated the effects of hCG and forskolin on oxytocin mRNA levels and release of oxytocin and progesterone in cells from follicles containing greater than 50 ng/ml estradiol. In cells from follicles containing less than 5 ng/ml estradiol these stimuli had little effect on oxytocin release although progesterone release was synergistically increased by insulin and forskolin. The data suggest that gonadotropins regulate oxytocin synthesis and release and that these effects are amplified by insulin or IGF-I acting via their own receptors. Changes associated with maturation of the target cells in vitro appear prerequisite for oxytocin production in response to increased cAMP levels in the presence of insulin or IGF-I.

Nuclear volume and chromatin conformation of small and large bovine luteal cells: effect of gonadotropins and prostaglandins and dependence on luteal phase

Change in nuclear volume and chromatin conformation are generally considered to reflect altered gene expression in eukaryotic cells. The present studies were undertaken to investigate whether these nuclear parameters of luteal cells can be altered by hormone treatment in vitro or change during the estrous cycle. The nuclear volume of small luteal cells was significantly lower than that of large luteal cells during the cycle and pregnancy. The nuclear volumes of small and large luteal cells from pregnancy did not change during incubation without any hormone or with 10 nM prostaglandin (PG)F 2 alpha. However, incubation with 1 nM human chorionic gonadotropin (hCG) or 10 nM PGE1 resulted in a significant increase of nuclear volume of small luteal cells by 4 h and that of large luteal cells by 6 h. Small luteal cells were more responsive to hCG than large luteal cells. The nuclear volumes of small and large luteal cells also significantly increased from early to mid luteal phase with no further change in late luteal phase. hCG and PGE1, as well as PGF2 alpha, treatment resulted in a change of chromatin conformation of small and large luteal cells. Dibutyryl cyclic AMP (10 mM) mimicked the hormones by increasing nuclear volumes and changing the chromatin conformation of small and large luteal cells. Chromatin conformation of small and large luteal cells also changed from early to mid luteal phase and mid to late luteal phase. In conclusion, in vitro, hCG and PGs can regulate nuclear volume and/or chromatin conformation of small as well as large bovine luteal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The regulation of oxytocin gene expression in early bovine luteal cells

The oxytocin gene is maximally expressed in the cells of the early bovine corpus luteum (1-5 days post-ovulation) and provides an excellent marker for luteinization, having been up-regulated in vivo at ovulation. However, it is down-regulated again later in the luteal phase. To help understand the mechanisms involved in regulating this gene, and hence differentiation in the early bovine corpus luteum, oxytocin secretion into the medium as well as oxytocin mRNA were measured in serum-free cultures of early luteal cells in the presence or absence of various effectors. Insulin-like growth factor I (IGF-I) deferred the endogenous down-regulation of the gene and hence increased oxytocin peptide secretion in the first days of culture. Prostaglandin F2 alpha had no influence on oxytocin mRNA levels but reduced the stimulatory effect of IGF-I on peptide secretion, indicating an effect at the post-transcriptional level. Oestradiol had no effect either on oxytocin mRNA levels or on oxytocin secretion.

Oxytocin and progesterone secretion by bovine granulosa cells of individual preovulatory follicles cultured in serum-free medium

To examine the secretion of oxytocin (OT) and progesterone (P) from a homogeneous population of cells during luteinization, we developed a serum-free culture technique for granulosa cells, obtained from individual preovulatory bovine follicles. Granulosa cells from earlier stages of the follicle development did not have the capability to secrete OT under the in vitro conditions used. For optimal stimulation of the cells the medium (a 1:1 mixture of Dulbecco's modified Eagle's medium and Ham's F-12) was supplemented with bovine serum albumin (BSA) and insulin. OT was detectable from day 1 of culture reaching a maximum level between days 2 and 4 and then declined towards day 5. In the absence of insulin OT declined from day 1 onwards and was undetectable from day 4. When cells were cocultured with theca tissue or theca-conditioned medium (TCM), there was an enhancement in OT secretion, but not in P secretion. Other tissues including liver, kidney, aorta, muscle and adrenal incubated with the cells induced a similar increase in OT production. In the presence of insulin progesterone secretion was increased and was correlated with OT production, but did not show a consistent pattern among follicles. We conclude that (a) culture of granulosa cells from an individual follicle in a serum-free medium can be used to study the secretion of OT and P from bovine granulosa cells, (b) insulin is essential for the optimal production of OT and P by these cells, and (c) the addition of theca or other tissues enhanced OT secretion by a mechanism not understood.

Ovarian oxytocin and neurophysin concentrations in the cynomolgus monkey (Macaca fascicularis)

The neurohypophysial hormone oxytocin has previously been found in the ovaries of several animal species. In ruminants ovarian oxytocin is postulated to have a luteolytic function, because of its high concentrations in the corpus luteum. In primates the role of ovarian oxytocin is not known. In the present study we measured the immunoreactive oxytocin and oxytocin-neurophysin content in paired ovaries removed from cynomolgus monkeys (Macaca fascicularis) during the late luteal phase of the cycle (Days 12-14 of the luteal phase or Days 26-28 of a menstrual cycle). Each animal was pulsed with synthetic gonadotropin-releasing hormone to maintain normal menstrual cyclicity. The concentration of oxytocin and its neurophysin during the late luteal phase was greater in the non-corpus luteum than corpus luteum-bearing ovary. By high pressure liquid chromatography and bioassay the oxytocin in both the corpus luteal and non-corpus luteal ovaries was similar to synthetic and posterior pituitary oxytocin. The finding of high concentrations of immunoreactive oxytocin in the non-corpus luteum-bearing ovary suggests that the function of ovarian oxytocin in primates may not be confined specifically to the corpus luteum.

Regulatory peptides in the mammalian urogenital system

By immunocytochemistry a number of the gut/brain peptides have been demonstrated in nerve fibers of the mammalian urogenital tract. These peptides are localized to large vesicles in nerve terminals of afferent fibers or efferent nerves innervating blood vessels, non-vascular smooth muscle, lining epithelium and glands. There is evidence that some neuropeptides (VIP, NPY) participate in the local non-cholinergic, non-adrenergic nervous control of smooth muscle activity and blood flow, while other peptides (substance P, CGRP) seem to be sensory transmitters. It is likely that impaired function of the peptidergic nerves is involved in sexual dysfunction such as male impotence.

Ovarian oxytocin and progesterone are secreted independently of one another

Experiments were performed with cultured bovine granulosa cells to examine the relationship between the secretions of oxytocin and progesterone and to determine whether progesterone could be responsible for the progressive refractoriness of these cells to stimulation by ascorbic acid. Aminoglutethimide suppressed progesterone secretion by 95% but it neither reduced oxytocin secretion nor restored the cellular response to delayed ascorbate treatment. Addition of a high concentration of progesterone to the culture medium also failed to affect oxytocin secretion, its stimulation by ascorbate, or the endogenous secretion of the steroid. It is concluded that oxytocin and progesterone can be independently secreted and that progesterone regulates neither its own secretion nor that of oxytocin.

Immunohistochemical localization of oxytocin and vasopressin in the adrenal glands of rat, cow, hamster and guinea pig

The distribution of oxytocin and vasopressin in the adrenals of rat, cow, hamster and guinea pig has been studied by use of immunohistochemical techniques. In all the species studied the adrenal cortex contained both peptides; the staining in the zona glomerulosa being more intense than that in zona fasciculata or zona reticularis. The medulla, however, showed considerable species variation. In the cow, both peptides appear to be present in the adrenergic and noradrenergic cells, though staining was particularly prominent in cortical islands interspersed within the medullary tissue. In the rat, groups of medullary cells positive for both peptides were found, though it was not possible to associate these groups with particular chromaffin cell types. In the hamster oxytocin was present only in adrenaline-containing cells, whereas vasopressin was present in all medullary cells. The guinea pig medulla, which contains only adrenaline-secreting cells, was positive for both peptides. The possibilities that vasopressin and oxytocin have an autocrine or paracrine role in functioning of the adrenal gland is discussed.

Immunocytochemical localization of oxytocin and neurophysin in human corpora lutea

Corpora lutea, corpora albicantia, and ovarian stroma from normal human premenopausal ovaries were examined for the presence of oxytocin and neurophysin by using highly specific antisera and peroxidase-antiperoxidase light-microscopic immunohistochemistry. Oxytocin and neurophysin immunoreactivity was found in some but not all cells of the corpora lutea obtained on days 19 to 24 of the menstrual cycle. Stromal tissue and corpora albicantia did not give a positive reaction for either of these peptides, and negative results were also obtained with corpora lutea of mid- and term-pregnancy and preovulatory follicles. Specificity of the immunohistochemical reaction was confirmed by immunoabsorption tests. The specific localization of immunoreactive oxytocin and neurophysin in corpora lutea of the human menstrual cycle directly demonstrates the presence of oxytocin- and neurophysin-positive cells within the human corpus luteum.

Expression of the oxytocin gene in the large cells of the bovine corpus luteum

In the bovine ovary there is a delay of 4-6 days between the observed maximum of oxytocin mRNA and the peak in the luteal levels of oxytocin nonapeptide. This implies a maturation process involving components of the post-translational processing pathway. In situ hybridization shows the oxytocin gene to be transcribed exclusively in the large cells of the corpus luteum at the beginning of the estrous cycle.

Prostaglandin F2 alpha and oxytocin interactions in ovarian and uterine function

The oxytocin-neurophysin gene is expressed in several nontraditional sites within the endocrine system. In the ovary its expression in the corpora lutea is initiated by ovulation. Ovarian oxytocin concentrations reach maximal levels around day 11 of luteal cycle and fall to a nadir at estrus. PGF2 alpha has the capacity to release oxytocin from the corpus luteum, and oxytocin in turn releases PGF2 alpha from the uterine endometrium or decidua. This positive feedback loop between the ovary and the uterus ensures the completion of luteolysis in species that depend on the presence of the uterus for the termination of luteal lifespan. Immunization against oxytocin has been shown to disrupt this loop, resulting in much-prolonged luteal cycles. In primates and other species in which luteal life span is independent of the uterus, an oxytocin PGF2 alpha interaction may take place within the ovary itself. At parturition a related interaction takes place which ensures the expulsion of the fetus and placenta in an orderly manner. Oxytocin of both pituitary and ovarian origin reaches the uterus via its blood supply and binds to two types of receptors: one on myometrial cells, the occupation of which initiates contractions, and the other on decidual cells, the occupation of which initiates prostaglandin generation. This prostaglandin diffuses into the adjacent myometrium and augments the oxytocin-induced contractions. In conjunction with a direct softening effect by prostaglandins on the cervix the augmented contractions achieve the force needed to dilate the cervix and expel the fetus. An additional source of oxytocin during labor may be the placenta, another non-traditional site for the occurrence of oxytocin.

Ultrastructural localisation of oxytocin and neurophysin in the ovine corpus luteum

Polyclonal rabbit antisera raised against oxytocin, bovine neurophysin I and vasopressin were used, together with an immunogold complex, to localise the peptides in ultrathin sections of ovine corpus luteum. The only organelle which consistently showed gold labelling was the secretory granule of the large luteal cell. In non-consecutive sections of the same large luteal cell all the granules showed a similar level of labelling after oxytocin or neurophysin I antisera: however no immunolabelling was detected for vasopressin. Oxytocin and neurophysin seem to be rapidly lost after secretion since exocytosed granule cores showed no labelling above background levels.

Ovulation triggers oxytocin gene expression in the bovine ovary

The gene for the nonapeptide neurohormone oxytocin is highly expressed in the bovine corpus luteum. Measurements of oxytocin-specific mRNA through the oestrous cycle of non-pregnant cows show that transcription is maximal accompanying ovulation and decreases rapidly thereafter. In contrast, immunohistochemistry shows neurophysin peptide levels to be greatest at mid-cycle. Low levels of oxytocin mRNA are detected in follicles and in the luteolytic half of the cycle. This mRNA is virtually absent in the corpus luteum of pregnant cattle. No cyclicity is evident in hypothalamic oxytocin mRNA levels.