Luteal Phase Of Estrous Cycle Research Articles

Ultrasonographic evaluation of canine pyometra

Pyometra is the most common disease found in adult intact female dogs, caused by acute or chronic suppurative bacterial infection of the uterus and is characterized by accumulation of inflammatory exudates in the uterine lumen with diverse clinic-pathological manifestation either locally or systemically. Disease is frequently noticed in adult female dog in luteal phase of estrous cycle during which progesterone level is high (progesterone sensitized uterus) and thus playing key role in pathogenesis. The preliminary diagnosis of pyometra is determined by case history, physical examination findings and laboratory test results in combination with radiography or/and ultrasonography showing a fluid-filled enlarged uterus. A late diagnosis of pyometra, when kidney failure has already occurred, may result in irreversible damage to the kidneys. Effects of sepsis and endotoxaemia can further cause multi-organ dysfunctions, but despite being a potentially life-threatening illness. In this communication, ultrasonography as an accurate procedure for the qualitative and quantitative examination and diagnosis of canine pyometra has been described.

Gene expression in the amygdala and hippocampus of cyclic and acyclic gilts.

Age at first estrus is the earliest phenotypic indicator of future reproductive success of gilts. Prebreeding anestrus is a major reason for reproductive failure leading to culling of replacement gilts. The two types of prebreeding anestrus are delay in attaining puberty (prepubertal anestrus, PPA) and silent ovulation (behavioral anestrus, BA). Neural tissues such as amygdala and hippocampus play a major role in regulating sexual behavior, social interactions, and receptivity to males. Differences in gene expression in the amygdala and hippocampus of gilts were analyzed in three comparisons: 1) PPA cases and cyclic controls at follicular phase of estrous cycle, 2) BA cases and cyclic controls at luteal phase of estrous cycle, and 3) gilts at different stages of the ovarian cycle (cyclic gilts at follicular phase and luteal phase of estrous cycle) to gain functional understanding of how these rarely studied tissues may differ between pubertal phenotypes and different stages of the estrous cycle of gilts. Differentially expressed genes (DEG) between PPA and BA cases and their respective cyclic controls were involved in neurological and behavioral disorders as well as nervous system functions that could directly or indirectly involved in development of behaviors related to estrus. The comparison between cyclic follicular and luteal phase control gilts identified the greatest number of DEG in the hippocampus and amygdala. These DEG were involved in adult neurogenesis and neural synapse (e.g., GABAergic, dopamine, cholinergic), suggesting that these tissues undergo structural changes and synaptic plasticity in gilts. This is the first report to demonstrate that the stage of estrous cycle is associated with dynamic changes in gene expression within porcine hippocampus and amygdala and indicates a role of gonadal steroids in regulating their biology.

Assisted reproductive technologies in cattle reproduction and selection

In vitro technology is one of the most dynamically developing and more and more stable biotechnological methods today accelerating selection, intensifying reproductive and genetic potential of breeding animals, allowing to increase breeding young animals production by one champion cow up to 5–10 calves per year, reduce generation interval and significantly accelerate process of updating and qualitative improvement of livestock. However, obtaining oocytes competent for in vitro development is one of the critical factors determining success of the method and depending on a number of biological and technical factors. This paper presents results of studies on effect of biological factors of direct and indirect impact on efficiency of obtaining oocytes in the system of transvaginal aspiration for the first time conducted in the Republic of Belarus. Yield of excellent and good quality oocytes increased during aspiration during the luteal phase of estrous cycle and remained almost unchanged during aspiration into the follicular phase. Presence of follicles with diameter over 8 mm in the ovaries during aspiration reduced yield of excellent and good quality oocytes averagely by 9.4 percentage points. Removing the dominant follicle 72 hours prior to aspiration allowed increasing the number of aspirated follicles by 41 %, and yield of oocytes – by 22.9 %. Microstimulation of ovaries prior to aspiration by follicle-stimulating hormones FSG-super and Plusset increased efficiency of aspiration in terms of the main indicators by 19.2–45.9 %. Follicular cyst or persistent corpus luteum in one of the ovaries reduced both quantitative and qualitative indicators of aspiration. The data obtained are of practical importance for development of technology for in vitro embryo production in the system of transvaginal aspiration of oocytes which will help to accelerate breeding process and increase efficiency of breeding work in livestock production in general.Acknowledgments. The research was conducted within the two state research programs: “Biotechnology”, subprogram “Development of biological science, biological education and biological industry for 2007–2011 and for the period up to 2020”, “High technologies and equipment for 2016-2020”, subprogram 1 “Innovative biotechnologies–2020”.

Immunohistochemical localization of estrogen receptor alpha (ERα) in the oviduct of Indian buffalo during follicular and luteal phases of estrous cycle.

The localization and distribution of estrogen receptor alpha (ERα) in different segments of oviduct of buffalo during follicular and luteal phases of estrous cycle were investigated using immunohistochemistry. Tissue samples from the different segments of oviduct from 12 buffaloes (six each during follicular and luteal phases of estrous cycle) were collected from slaughter house after assessing the gross morphology of ovaries. In addition, blood samples were collected from the animals before slaughter to estimate levels of estrogen and progesterone hormones. The tissue distribution of estrogen receptor was determined by immunohistochemical technique using one-step polymer HRPO staining system. The estrogen receptor was localized in the lamina epithelialis, propria submucosa, tunica muscularis, and tunica serosa. The maximum localization was observed in the lamina epithelialis, where both ciliated and secretory cell types were positive for ERα. Percentage of positive cells varied during the follicular and luteal phases of estrous cycle. The lining epithelium of oviductal glands was also intensely positive for ERα. No immunostaining was observed in any tunic of the oviduct when the primary antibody was replaced by antibody diluent or buffer, and it served as negative control. The data showed that highest immune positive cells were observed in the ampulla region of the oviduct and these cells were lowest in the utero-tubal junction (p < 0.05). Infundibulum, ampulla, and isthmus showed a higher percentage of ERα-positive cells during follicular phase of estrous cycle as compared with those of the luteal phase of estrous cycle (p < 0.05). There was no significant difference in the percentage positive cells during the two phases of estrous cycle in the utero-tubal junction. Immunogold labeling with anti-ERα antibody confirmed the findings of immunohistochemical study at subcellular level. The higher expression during the follicular phase was directly correlated with the level of estrogen hormone.

Immuno Localization of Estrogen Receptor (ERα) and Progesterone Receptor (PR) in Uterus of Buffalo during Follicular and Luteal Phases of Estrous Cycle

The tissue distribution of estrogen receptor alpha (ERα) and progesterone receptor (PR) was examined using immunohistochemical technique. Image analysis was done to quantify the immune reactivity. The ERα and PR was localized in luminal epithelium, glandular epithelium, stromal cells, endothelial cells and myometrium and few cells in perimetrium. The immuno staining was observed in the nuclei of cells, however, faint cytoplasmic staining for PR was also observed. Variations were seen in the different tissue compartments of the uterus and during the different phases of the estrous cycle. Significantly higher number of ERα positive cells was observed in lamina epithelialis as compared to stromal cells and smooth muscle cells in myometrium. Significantly higher percentage of ERα positive cells was observed in the lamina epithelialis and lining epithelium of endometrial glands during follicular phase as compared to the luteal phases of estrous cycle (P < 0.05). Higher number of PR positive cells was observed in lamina epithelialis as compared to stromal cells and smooth muscle cells in myometrium (P < 0.05). Higher percentage of PR positive cells was observed in the lamina epithelialis during follicular phase as compared to the luteal phases of estrous cycle (P < 0.05). There was no significant difference in the immuno reactivity in stromal cells, lining epithelium of endometrial glands and smooth muscle cells of myometrium during the phases of estrous cycle. The study concluded that ERα and PR expressions were higher during follicular phase as compared to the luteal phase.

Changes in Biochemical Profile of Superovulated Sahiwal Cows through Hormonal Manipulation at Mid Luteal Phase of Estrous Cycle

Changes in Biochemical Profile of Superovulated Sahiwal Cows through Hormonal Manipulation at Mid Luteal Phase of Estrous Cycle

Review on canine pyometra, oxidative stress and current trends in diagnostics

Pyometra is one of the most important and common disorders in canine. The disease results in life threatening condition associated with septicemia and toxemia. The condition commonly occurs during luteal phase of estrous cycle, generally 4 weeks to 4 months of estrous cycle. The age, parity, breeds, administration of hormones are some predisposing factors of the condition. However, interaction between potentially pathogenic bacteria and hormonally primed uterus is believed to result in pyometra. The disease is initiated in the form of cystic endometrial hyperplasia, which later progresses into purulent uterine content following bacterial infection resulting in pyometra. The disturbance in antioxidant and pro-oxidant balance succeeding bacterial infection results in oxidative stress. The resultant stress further induces endometrial degeneration, immunosuppression and additionally aggravates the condition. An important clinical sign is malodorous, sanguineous or mucopurulent vaginal discharge with general symptoms such as vomiting, polyuria, polydipsia, depression, anorexia and occasionally fever. Till date, ultrasonography is the best diagnostic method while radiology and serological test are also helpful. Recently, the estimation of inflammatory mediators (acute phase proteins and prostaglandin metabolites) has appeared as marker for diagnosis of the pyometra. Determination of levels of inflammatory mediators has emerged as an important diagnostic method because it can be helpful in prognosis of the condition. The pyometra can be best treated by surgical manipulation (ovariohysterectomy); however, hormonal treatment can be given in less severe cases which aimed at reducing the effect of progesterone on the reproductive tract. Together, provision of antioxidants could be helpful in disease recovery along with the determined treatment. In this review, incidence, predisposing factors, etio-pathogenesis, oxidative stress associated with condition, diagnostic methods and treatment are discussed.

Endometrial Alterations After the Transfer of Embryonic Remains

In this study, we investigated the expression of mucin 1 (MUC1) mRNA and protein in sheep endometrium at different time points during follicular and luteal phases of estrous cycle, and also determined the effect of steroid hormone treatments and interferon tau (IFNτ) on MUC1 mRNA expression in endometrial cell culture in vitro. In experiment one, 15 Welsh mountain ewes were synchronized to a common estrus and killed at precise stages of estrous cycle corresponding to (1) pre-LH peak, (2) LH peak, (3) post-LH peak, (4) early luteal, and (5) mid-luteal. Reproductive tracts were harvested and mRNA was extracted from the endometrial tissues. Parts of the uterine horns were fixed for immunohistochemistry. In experiment two, mixed populations of ovine endometrial cells (from slaughterhouse material collected at the postovulatory stage of the estrous cycle) were cultured to 70% confluence before treatment with (1) progesterone (P4, 10 ng/mL, for 48 hours), (2) estradiol (E2, 100 pg/mL, for 48 hours), or with (3) E2 priming for 12 hours (100 pg/mL) followed by P4 (10 ng/mL) for 36 hours. These were compared with: (4) IFNτ (10 ng/mL, for 48 hours), and (5) basic medium (Dulbecco Modified Eagle Medium /F12) as control. The results showed that MUC1 mRNA and protein expression in sheep endometrium were highest during the midluteal stage and very low during the post-LH period compared with the other stages (P < 0.05). MUC1 immunostaining in the luminal epithelium was apically restricted and was not significantly different across all stages of estrous cycle except at the post-LH peak where it was significantly low. In cell culture, MUC1 mRNA expression was significantly upregulated by both steroids either singly or in combination (P < 0.05), and downregulated in the presence of IFNτ. In conclusion, endometrial MUC1 expression is cyclically regulated by both E2 and P4 in vivo and in vitro, and directly downregulated by IFNτ treatment in vitro.

Scanning Electron Microscopic Studies on Uterus of Jaffarabadi Buffalo during Follicular and Luteal Phases of Estrous Cycle

The study was conducted on uterus of 20 adult Jaffrabadi buffaloes. Scanning electron microscopic observation showed that the surface of endometrium was folded. Lining epithelium of horn and body consist of ciliated and nonciliated cells. During follicular phase cells were flat, formed hexagonal structure with numerous microvilli, whereas, cells were narrow and polygonal in shape during luteal phase. More number of well-developed ciliated cells were found in follicular phase as compared to luteal phase. Numerous secretory blabs were observed on surface of secretory cells during luteal phase. The folds in the cervix were narrow and deep. The lining epithelium of cervix had ciliated and nonciliated cells. The cilia were more in cranial part than the caudal part of the cervix and present in the form of bunch, which were overlapping the secretory cells. Ciliated cells were more in number during follicular phase. Cervical glands were distributed on the cervical mucosa and ciliated cells were present around the openings of these glands.

Scanning electron microscopic study on the oviduct of buffalo during follicular and luteal phases of estrous cycle

The present investigation was conducted on different segments of oviduct of six buffaloes each during follicular and luteal phases of estrous cycle. The mucosa of different segments of oviduct was thrown into folds which were oriented as primary and secondary folds. The lamina epithelialis was lined with ciliated and non-ciliated cells. Ciliated cells had many kinocilia during the follicular phase. The non-ciliated cells were of two types, viz. secretory and non-secretory type. The infundibulum during the follicular phase had large number of ciliated cells as compared to that of luteal phase. The secretory cells had short, thick and stubby microvillous processes. The ampulla had almost similar ciliation as that of infundibulum. The luminal surface of secretory cells had secretory blebs and secretory material over it. The extent of ciliation decreased towards the uterotubal junction. The ciliated cells were more during the follicular phase as compared to that of the luteal phase.

Scanning Electron Microscopic Studies on the Uterus of Buffalo during Follicular and Luteal Phases of Estrous Cycle

Scanning Electron Microscopic Studies on the Uterus of Buffalo during Follicular and Luteal Phases of Estrous Cycle

In vivo and in vitro studies of MUC1 regulation in sheep endometrium

In this study, we investigated the expression of mucin 1 (MUC1) mRNA and protein in sheep endometrium at different time points during follicular and luteal phases of estrous cycle, and also determined the effect of steroid hormone treatments and interferon tau (IFNτ) on MUC1 mRNA expression in endometrial cell culture in vitro. In experiment one, 15 Welsh mountain ewes were synchronized to a common estrus and killed at precise stages of estrous cycle corresponding to (1) pre-LH peak, (2) LH peak, (3) post-LH peak, (4) early luteal, and (5) mid-luteal. Reproductive tracts were harvested and mRNA was extracted from the endometrial tissues. Parts of the uterine horns were fixed for immunohistochemistry. In experiment two, mixed populations of ovine endometrial cells (from slaughterhouse material collected at the postovulatory stage of the estrous cycle) were cultured to 70% confluence before treatment with (1) progesterone (P4, 10 ng/mL, for 48 hours), (2) estradiol (E2, 100 pg/mL, for 48 hours), or with (3) E2 priming for 12 hours (100 pg/mL) followed by P4 (10 ng/mL) for 36 hours. These were compared with: (4) IFNτ (10 ng/mL, for 48 hours), and (5) basic medium (Dulbecco Modified Eagle Medium /F12) as control. The results showed that MUC1 mRNA and protein expression in sheep endometrium were highest during the midluteal stage and very low during the post-LH period compared with the other stages (P < 0.05). MUC1 immunostaining in the luminal epithelium was apically restricted and was not significantly different across all stages of estrous cycle except at the post-LH peak where it was significantly low. In cell culture, MUC1 mRNA expression was significantly upregulated by both steroids either singly or in combination (P < 0.05), and downregulated in the presence of IFNτ. In conclusion, endometrial MUC1 expression is cyclically regulated by both E2 and P4in vivo and in vitro, and directly downregulated by IFNτ treatment in vitro.

Microscopic and histochemical characterization of the bovine uterine tube during the follicular and luteal phases of estrous cycle

The morphometrical and morphological features of the infundibulum and ampulla of the uterine tubes of adult cattle were studied. The materials used in this study were consisted of 12 pairs of uterine tube of healthy cows at age of 16–36 months, collected from Assiut slaughterhouses. Through observations of the ovaries, follicular and luteal phases of estrous cycle of each cattle were specified. Semithin sections of ampulla and infundibulum at follicular and luteal phases were made and histochemical analysis of the ampulla by use of PAS, Alcian Blue, Sudan Black B was also done. In addition, acid phosphatase activity of the ampullar epithelium was demonstrated. Histological analysis of the epithelium of bovine oviduct revealed that it was consisted of non-ciliated secretory cells, two populations of ciliated cells (CC), basal cells and Peg cells. At the luteal phase, the secretory cells possessed many cytoplasmic protrusions that extended beyond the luminal borders of the ciliated cells and exocytosis of secretory materials was observed. While at the follicular phase, the ciliated cells were predominated. The histochemistry of the ampullar epithelium revealed increase in secretions of neutral, acidic mucopolysaccarides and lipid from the secretory cells at the luteal phase with moderate acid phosphatase activity. Histomorphometric examinations of infundibulum and ampulla indicated that the mean number and height of primary folds as well as the thickness of the epithelium were increased significantly at the follicular phase.

Transcriptional profile of endometrial TLR4 and 5 genes during the estrous cycle and uterine infection in the buffalo (Bubalus bubalis)

Endometritis is one of the leading causes of infertility in the cattle and buffalo and innate immune mechanism plays an important role in clearing the infection. In this regard, endometrial expression and function of Toll Like Receptors (TLR) are focus of investigation in the recent years. In this study, we report the transcriptional profiles of TLR4 and 5 in the buffalo endometrium during the follicular, early, mid and late luteal phases of estrous cycle and 'subclinical and clinical endometritis' and also at true anestrus (n = 10 for each stage) using RT-PCR and qRT-PCR as they are the ligands for the lipopolysaccharide and flagellin components of E.coli, the most common cause of postpartum endometritis. We found a significant positive correlation between TLR4 and 5 in all the groups (r = 0.696-0.803; P < 0.05) except late luteal phase (r = 0.522; P > 0.05). Chi-square analysis showed that the qualitative expression of endometrial TLR4 and 5 transcripts was significantly associated with the phase of estrous cycle and also with uterine infection (P < 0.05). Further, using true anestrus category as a calibrator group, relative quantitation of TLR4 and 5 revealed that the transcriptional expression of TLR4 and 5 genes were highly upregulated (24.6-83.3 folds) during endometritis conditions and moderately upregulated during mid-luteal phase (6.8-16.2) of the estrous cycle (P < 0.05). The results suggested a role of progesterone in the expression of TLR4 and 5.

Effect of transient high-energy diets just after ovulation on ovarian performance and metabolic status in cyclic ewes

The aim of this study was to investigate the influence of short-term treatment of high-energy diet after ovulation on ovarian function and metabolic status in ewe. Cycling ewes Ossimi were divided into treatment group (TG; n=6) and control group (CG; n=6). After ultrasonographic detection of ovulation (day 0), a high-energy diet (12.55MJ DE/kg diet; 125% of maintenance) was fed to TG from day 1 to day 4 after ovulation (4days). The high-energy diet consisted of 850g concentrate mixture and 150g alfalfa hay, plus ad libitum access to wheat straw. The CG was offered as maintenance diet (10MJ DE/kg diet) throughout the experiment. Follicular development was observed ultrasonographically every other day while blood samples were collected daily throughout the experiment for the analysis of glucose, total cholesterol, urea, triglycerides, total proteins, aspartate aminotransferase (AST), alanine transaminase (ALT) and glutamate oxaloacetate transaminase (GOT). Transient feeding of high-energy ration during early luteal phase of estrous cycle significantly influenced the concentration of glucose and some metabolic profiles. Total proteins were greater at first, third and fourth day after ovulation (ovulation is day 0) in TG when compared to CG ewes. Blood glucose concentration was greater in TG than that of CG at days 1, 2, 3 and 4 postovulation. The average number of small follicles (2–2.9mm) of the first follicular wave after ovulation was greater in TG ewes (23.3 follicles) than that of CG (2.2). There was no difference in the number of medium (3–5mm) and large sized follicles (>5mm) between CG and TG ewes. Moreover, the maximum size of large follicles did not differ between CG (5.6mm) and TG ewes (5.9mm). In conclusion, high-energy diet may improve number of small follicles and alter energy metabolite during early luteal phase in cycling ewes.

The expression of the aryl hydrocarbon receptor in reproductive and neuroendocrine tissues during the estrous cycle in the pig

The aryl hydrocarbon receptor (AhR) has been recognized as a mediator of xenobiotic-induced toxicity. In addition, it was demonstrated that the AhR is able to influence the regulation of reproductive processes in females. The aim of this study was to examine AhR mRNA (real-time PCR) and protein (Western-blot) expression in ovarian follicles and stroma, corpora lutea (CL), oviducts, endometrium, myometrium as well as in medial basal hypothalami (MBH), and anterior (AP) and posterior (PP) pituitaries harvested during the follicular (days 17–19) and luteal (days 8–10) phase of the porcine estrous cycle. The AhR transcript and protein were found in all structures collected during both phases. AhR mRNA expression tended ( p = 0.06) to be higher in the CL than in follicles. The AhR protein expression in ovarian stroma was higher ( p ≤ 0.01) during the follicular than in the luteal phase. Endometrial expression of AhR mRNA was higher ( p ≤ 0.01), while AhR protein was lower ( p ≤ 0.01) during the follicular phase in comparison to the luteal phase. Within neuroendocrine tissues, AhR mRNA and protein content in hypothalamus were relatively low and did not differ ( p > 0.05) between phases. In contrast, higher AhR mRNA expression in AP ( p ≤ 0.001) and protein expression in PP ( p ≤ 0.01) were found during the luteal phase compared to the follicular phase. Differences in AhR expression observed in reproductive and neuroendocrine tissues during the follicular and luteal phase of the estrous cycle indicate the involvement of AhR in the regulation of reproductive function in pigs.

Characteristics of stimulation of gonadotropin secretion by kisspeptin-10 in female goats

The aims of the present study were to clarify the effect of kisspeptin-10 (Kp10) on the secretion of luteinizing hormone (LH), follicle stimulating hormone (FSH), growth hormone (GH) and prolactin (PRL) in goats, and compare the characteristics of any response with those of the response to gonadotropin-releasing hormone (GnRH). The experiments were performed using four female goats (4–5 years old) in the luteal phase of estrous cycle. A single intravenous (i.v.) injection of 1, 5 and 10 μg/kg b.w. (0.77, 3.85 and 7.69 nmol/kg b.w.) of Kp10 stimulated the release of LH. Maximum values were observed 20–30 min after the injection. On the other hand, Kp10 did not alter plasma GH and PRL concentrations significantly. Three consecutive i.v. injections of Kp10 (5 μg/kg b.w.) or GnRH (5 μg/kg b.w.: 4.23 nmol/kg b.w.) at 2-h intervals increased both plasma LH and FSH levels after each injection ( P < 0.05); however, the responses to Kp10 were different from a similar level of GnRH. The rate of decrease in LH and FSH levels following the peak was attenuated in Kp10-treated compared to GnRH-treated animals. These results show that Kp10 can stimulate the release of LH and FSH but not GH and PRL in female goats and suggest that the LH- and FSH-releasing effect of the i.v. injection of Kp10 is less potent than that of GnRH.

Changes in uterine protein secretion during luteal and follicular phases and detection of phosphatases during luteal phase of estrous cycle in buffaloes ( Bubalus bubalis)

Changes in uterine proteins during different reproductive states and their functional significance though known in other species have not been established in buffaloes. An attempt has been made to unravel the changes in composition of buffalo uterine secretion with growth and regression of corpora-lutea during early, mid and late luteal and follicular phase of estrous cycle using gel filtration and electrophoresis techniques. Also the phosphatases activities in luteal phase uterine secretions have been studied. Gel filtration chromatography analysis revealed a protein peak in void volume of the column, the intensity of which was more in all the luteal phase samples than follicular phase samples. Alkaline phosphatase was also found eluted in the void volume. The other three uterus-specific peaks (Peaks V–VII) were detected below 13.7 kd molecular weight. There were at least five peaks of acid phosphatases activity in chromatogram. Silver staining of SDS-PAGE gel detected as many as 40 protein bands in the uterine fluid of which nine proteins were glycoproteins. Molecular weight (MW) comparison revealed the major protein band at 66 kd which could be serum albumin. Comparison of uterine proteins with serum protein bands revealed a 93.5 kd glycoprotein in buffalo serum that did not appear in uterine fluid and at least 11 uterus-specific protein bands (506, 470, 241, 114, 49, 38, 33, 26, 19.2, 16, and 14.3 kd). The 38 and 19.2 kd bands were luteal-stage specific. Intense periodic acid Schiff's (PAS) stained bands in uterine proteins compared to serum indicated glycosylation process in endometrial epithelial cells. The study suggested that buffalo uterine secretion contained mainly serum and several uterus-specific proteins of which few were luteal phase specific. Further study on characterizing the unique or most abundant proteins and defining their role in uterine functions would help to address the cause of low reproduction rate in buffaloes.

Colocalization of progesterone receptors in parvicellular dynorphin neurons of the ovine preoptic area and hypothalamus.

Recent evidence suggests that the dynorphin-kappa receptor opioid system acts to mediate the inhibitory effect of progesterone (P) on GnRH pulse frequency during the luteal phase of the ovine estrous cycle. It is known that progesterone receptors (PRs) are required for the actions of P on GnRH secretion. Therefore, if P acts directly on dynorphin (DYN) neurons, then these neurons should contain PRs. To test this hypothesis, we used a dual-label immunoperoxidase procedure to visualize PRs and DYN in the preoptic area (POA) and hypothalamus of ovary-intact ewes killed during the luteal phase of the estrous cycle. The PR was colocalized in more than 90% of parvicellular DYN neurons in the POA, anterior hypothalamus (AHA), and arcuate nucleus (ARC). By contrast, none of magnocellular DYN cells of the paraventricular and supraoptic nuclei coexpressed immunoreactive PRs. The high percentage of colocalization of PRs in parvicellular DYN cells of the POA, AHA, and ARC suggests that these cells are prime targets of P. In addition, DYN cells in the ARC, but not the POA or AHA, were found to receive synaptic inputs from DYN-positive axon terminals. This observation raises the possibility that an ultrashort feedback loop controls the release of DYN from ARC neurons.

Follicular growth and atresia during the last half of the luteal phase of the guinea pig estrous cycle: relation to serum progesterone and estradiol levels and utero-ovarian blood flow.

The relationships among follicular growth, changes in serum progesterone (P) and estradiol (E) levels, and utero-ovarian blood flow (OBF) through the guinea pig ovary were examined during days 7-16 of the luteal phase (day 0 = estrus) of the estrous cycle and during the subsequent ovulatory (proestrous-estrous) period. Follicles were classified as either viable or atretic based on strict criteria and grouped according to diameter. No changes in follicular growth were observed between days 7-9 of the cycle when serum P levels were elevated and OBF was at low rates. Between days 13-15 when serum P levels were low and both OBF and serum E levels were rising, there was a dramatic increase in the number of viable follicles present in all follicle classes. As the percentage of viable follicles increased, the number of atretic follicles in each size population decreased. Peaks in the number of large follicles (300-450 microns), OBF, and serum E levels were observed during the subsequent ovulatory period. These data suggest that as luteal activity declines during the last half of the estrous cycle, follicular recruitment and growth are stimulated. The concomitant elevations in OBF suggest a supportive role for this parameter in follicular development. In turn, the subsequent elevation in serum E levels serves as an index of follicular maturation. These data suggest that the elevated P levels during the luteal phase of the estrous cycle may either directly or indirectly, through the regulation of gonadotropin secretion, regulate follicular growth in the guinea pig.