Inhibition of gonadotrophin release in mares during the luteal phase of the oestrous cycle by endogenous opioids

Transient suppression of ovulatory ovarian function in pony mares after treatment with slow-release deslorelin implants

Behavior during the estrous cycle of mares can affect their performance and therefore inhibition of cyclical ovarian activity is indicated. We hypothesized that implants containing the GnRH analog deslorelin downregulate GnRH receptors and inhibit ovulation in mares. The estrous cycles of Shetland mares were synchronized with 2 injections of a PGF_2α analog. One day after the second injection (day 0), mares received 9.4 (group D1, n = 6) and 4.7 mg deslorelin (D2, n = 5) as slow-release implants or 1.25 mg short-acting deslorelin as a control (C, n = 5). Ultrasonography of the reproductive tract and ovaries and observation of estrous behavior and collection of blood samples for analysis of progesterone and LH concentrations were performed every second day until day 10 and thereafter at 5-d intervals. Stimulation tests with the GnRH-agonist buserelin were performed on days 10 and 45. Until day 50, there were less spontaneous ovulations in group D1 (P < 0.01) and estrous behavior was reduced in groups D1 and D2 compared with group C (P < 0.05). The time until first ovulation (D1 62.0 ± 8.6, D2 44.2 ± 14.1, C 22.2 ± 3.1 d, P < 0.05) and the number of days with estrous behavior (P < 0.05) differed among groups. On day 10 after treatment, a GnRH stimulation test revealed interactions between group and time (P < 0.001) in plasma LH concentration that were no longer detectable on day 45 after treatment. In conclusion, long-acting deslorelin implants result in a transient downregulation of pituitary GnRH receptors that is associated with inhibition of ovulation and estrous behavior in Shetland mares.

Diestrous Ovulations in Pregnant Mares as a Response to Low Early Postovulatory Progestogen Concentration

Simple Summary

During early pregnancy in mares, progestogen is synthesized by the primary corpus luteum, which is the only source of progestogen until endometrial cup and accessory corpus luteum formation, from day 36 of pregnancy onwards. In the present study, we investigated the hormonal profile (gonadotrophin and progestogen concentrations) of 11 mares after experimental reduction of primary corpus luteum function. Two pregnancies of each mare were assigned to the control and treatment groups, respectively, and were analyzed until day 34. Low plasma progestogen concentration caused by the treatment reduced the negative feedback on the hypothalamic-pituitary axis, stimulating gonadotropin release, and luteal tissue response. Progestogen concentration restoration soon after treatment suggests a rebound effect and the resurgence of luteal function. In addition, diestrous ovulation was observed between days 11 and 15 in five treatment pregnancies (5/11), but none of the controls (0/11). Although the total luteal area increased after diestrous ovulations, corpus luteum size was not correlated to progestogen secretion. Results suggest that diestrous ovulations during early pregnancy in mares may reflect low progestogen concentrations in the early postovulatory period.

Abstract

Spontaneous prolongation of the luteal phase has been described in horses, but the underlying causes are still unclear. The present study investigated details of gonadotrophin and progestogen secretion in pregnant mares (n = 11) with or without experimentally reduced early postovulatory luteal function. From days 0 to 3 after ovulation, they were treated with the prostaglandin F_2α (PGF_2α) analogue cloprostenol or left untreated. After conceptus collection on day 34, they were assigned to the opposite treatment. Mares were affiliated to the group primary corpus luteum (n = 6) or diestrous corpus luteum (n = 5) depending on diestrous corpus luteum (CL) detection in the PGF pregnancy. For statistical comparisons, a p-value < 0.05 was significant. There was an effect of treatment (p < 0.01), but not of group on progestogen concentration. The concentration of LH was higher in PGF-treated than in untreated pregnancies (p < 0.05), but did not differ between groups. The FSH concentration did not differ between groups nor treatments. The total luteal tissue area was greater in mares with a diestrous ovulation during the PGF treatment pregnancy. Low progestogen concentration in the early postovulatory phase diminish the negative feedback on the hypothalamic-pituitary axis in early pregnancy and, thus, stimulate a luteal tissue response. Detection of secondary CL at the time of pregnancy examination in mares may reflect that early post-ovulatory progestogen concentrations were low.

Effects of estrogen and opioid blockade on blood pressure reactivity to stress in postmenopausal women

Estrogen may influence coronary heart disease risk in women through the effects of endogenous opioids on autonomic control of blood pressure. In a randomized, placebo-controlled trial, we examined the combined effects of estrogen and the opioid antagonist, naltrexone, on blood pressure responses to psychological stress in 42 postmenopausal women. After 3 months of estrogen or estrogen plus progestin (hormone replacement therapy; n = 27) or placebo replacement, participants completed a mental arithmetic task after administration of .7 mg/kg oral naltrexone or placebo. Systolic blood pressure (SBP), diastolic blood pressure, mean arterial pressure and heart rate (HR) were measured at rest and during the arithmetic stressor. Stress produced significant increases in circulatory measures regardless of estrogen condition or opioid blockade (p's < .001). Interestingly, there was an estrogen by naltrexone interaction on SBP reactivity scores [F(1,38) = 4.36, p < .05], where women on estrogen with intact opioid receptors showed the largest SBP responses to stress, compared with all other conditions. This is consistent with some studies of premenopausal women, suggesting that estrogens may alter opioid function during stress. The interaction between estrogen and endogenous opioids may explain sex differences in opioid effects on stress reactivity in younger premenopausal women.

Immunohistochemical study of angiogenesis and angiogenic factors in equine granulosa cell tumours

The first part of our study (Müller et al., 2009) characterized angiogenesis in the equine cycling ovary through histomorphological and immunohistochemical examinations (vascular endothelial growth factors A and B [VEGF A, VEGF B], vascular endothelial growth factor receptors 1 and 2 [VEGF-R1, VEGF-R2], vascular angiopoietins 1 and 2 [Ang1, Ang2], angiopoietin receptor [Tie2], and von Willebrand Factor). Since angiogenesis plays an important role in development and growth of numerous tumours, the second part of our study involved a similar examination of 70 equine granulosa cell tumours (GCTt). The results of the second study were compared with those of the normal equine ovary. Certain similarities in the expression pattern could be detected between normal, cyclical ovaries (Müller et al., 2009) and GCTt. The immunoreactivity of granulosa cells and Leydig-like cells in GCTt resembles granulosa cells and luteinized thecal cells in periovulatory cycling ovaries. The neoplastic cells support circulation, supply and growth of GCTt by contributing to angiogenesis.

Comparison of Two Different Programmes of Ovulation Synchronization in the Treatment of Ovarian Cysts in Dairy Cows

It was the aim of this field study to evaluate two different protocols of ovulation synchronization for the treatment of ovarian cysts and their effect on reproductive performance in dairy cows. In addition, factors with a possible influence on treatment success and pregnancy outcome as well as costs per pregnancy were analysed. The study was performed with 130 German Holsteins with ovarian cysts diagnosed on days 55 to 60 postpartum. Cows belonging to group 1 (n = 65) received a modified ovsynch protocol [day 0: 0.15 mg cloprostenol (PGF) + 0.02 mg buserelin acetate (GnRH); day 14: PGF; day 16: GnRH]. Group 2 (n = 65) was treated with the conventional ovsynch protocol (day 0: GnRH; day 7: PGF; day 9: GnRH). Timed artificial insemination was performed 20 to 24 h later. Cows without ovarian cysts served as controls. Treatment success (disappearance of the ovarian cyst) after the first ovsynch cycle was higher in group 1 (66.2%) than in group 2 (23.1%, p < 0.05). Reproductive measures in group 1 were comparable with those of the control group and, compared with group 2, were conspicuously better (66.2%, 76.9%, 83.1%, 59.5% vs. 40.0%, 50.7%, 60.0%, 27.5% for cumulative pregnancy rate after treatment cycle 1 to 3 and second service conception rate, respectively, p < 0.05). Overconditioned cows and cows with larger ovarian cysts showed a diminished treatment and pregnancy success. In group 1, costs per pregnancy were only slightly higher than in the control group (group 1: €352.44, group 2: €484.59, control group: €333.77). In conclusion, our results suggest that ovsynch protocols can be used in the treatment of ovarian cysts. The modified ovsynch protocol led to a better cure rate as well as a better reproductive performance, and was economically beneficial compared with a conventional ovsynch protocol.

Uterine involution and endometrial function in postpartum pony mares

OBJECTIVE

To determine endometrial regeneration in postpartum mares by analysis of histologic features, apoptosis and cell proliferation markers, lectin binding, cytokines, and progesterone and estrogen receptors in endometrial biopsy specimens.

ANIMALS

9 postpartum mares.

PROCEDURES

Mares were examined on postpartum days 1, 9, and 16, and uterine biopsy specimens were obtained for histologic examination. Lectin binding was analyzed histochemically, and expressions of Ki-67 antigen (proliferation marker), lysozyme, and caspase 3 (apoptosis marker) were studied immunohistochemically. Gene expressions for cytokines (interleukin-1beta, -6 and -8 and tumor necrosis factor-alpha), cyclooxygenase 2, prostaglandin-E-synthase, and estrogen and progesterone receptors were determined by use of quantitative real-time PCR assay.

RESULTS

On day 1, neutrophils predominated but by day 9 had largely been replaced by lymphocytes and macrophages. High numbers of cells with staining for caspase 3 were found on day 1, but numbers decreased by day 9. In contrast, the number of cells with staining for Kiel 67 antigen increased between days 1 and 9. Lectin binding to the endometrium changed over time. Relative mRNA expressions for cytokines and prostaglandin-E-synthase did not differ among days. Expressions of progesterone and estrogen receptors were minimal on day 1 and increased by day 9.

CONCLUSIONS AND CLINICAL RELEVANCE

Early postpartum endometrial cells underwent apoptosis, but during the second week, postpartum proliferation of cells predominated. Lectin binding reflected changes in endometrial glycocalyx patterns. Increased expression of estrogen receptors allowed the endometrium to respond to estrogen during foal heat, and in subsequent diestrus, the endometrium was able to respond to progesterone.

Embryo transfer induces a subclinical endometritis in recipient mares which can be prevented by treatment with non-steroid anti-inflammatory drugs

We tested the hypothesis that subclinical endometritis occurs after embryo transfer (ET) in the horse. Recipient mares were treated with meclofenamic acid (M) or flunixin meglumin (F) after ET or were left untreated (n=9 per group). Embryos were re-collected 4 days after transfer. Endometrial biopsies were taken for histology and analysis of cyclooxygenase-2 (COX-2) by immunohistochemistry and for PCR. Bacteriological swabs were collected from the uterus and lavage fluid of donor and recipient mares. Progesterone and prostaglandin F(2alpha) release was analysed in recipient mares after ET. Four days after ET, four embryos were recovered from group M and three from group F and untreated mares, each. The number of polymorph nuclear neutrophils was reduced in treated mares (p<0.05). Expression of mRNA for inflammatory cytokines did not differ between groups. In group M, expression of endometrial prostaglandin-E-synthase was higher than in group F (p<0.05). Three out of nine control mares underwent preterm luteolysis (p<0.05 vs. treatment groups), prostaglandin release (p<0.05) and the number of COX-2 positive cells (p<0.01) were significantly higher than in treated mares. Only few bacteriological swabs were positive. In conclusion, treatment of embryo recipient mares with non-steroid anti-inflammatory drugs inhibits the inflammatory response of the endometrium after ET. Meclofenamic acid may have advantages in comparison to flunixin meglumin due to a different influence on prostaglandin synthesis that may not result in inhibition of embryonic mobility.

Histomorphological and Immunohistochemical Characterization of Equine Granulosa Cell Tumours

Benign (n=33) and malignant metastasizing (n=1) granulosa cell tumours (GCTs) from 34 mares aged 3-21 years, and normal (control) ovaries from nine mares aged 3-10 years, were examined histologically and immunohistochemically (for inhibin alpha, glutathione S-transferase alpha [GSTalpha], c-erbB-2 oncoprotein [cerb], cytokeratin, vimentin, desmin and alpha-actin), the results being related where appropriate to clinical signs and endocrinological data. Availability permitting, serum samples from GCT-affected mares before and several weeks after ovariectomy were examined for the following hormones: oestradiol, progesterone and testosterone (by radioimmunoassay); and inhibin B (by a cross-reactive ELISA). Histological examination revealed that the GCTs were predominantly well differentiated neoplasms. The metastasizing GCT differed immunohistochemically from the benign GCTs in respect of the expression patterns of vimentin, cerb and GSTalpha in the granulosa cells. A notable feature was the presence of Leydig-like cells in mares with stallion-like behaviour or elevated serum testosterone, or both. GSTalpha immunolabelling indicated that the Leydig-like cells were potential producers of steroid hormone. From the immunohistochemical and endocrinological findings it was concluded that GCTs produce abnormally high concentrations of inhibin, which reduce the release of follicle-stimulating hormone, leading to atrophy of the contralateral ovary-a finding in 27 of the mares.

Pregnancy rates, LH and progesterone concentrations in mares treated with a GnRH agonist

The aim of the study was to investigate the effect of the GnRH agonist Buserelin given on day 10 after ovulation on pregnancy rate and concentrations of progesterone and LH. Altogether 191 warmblood mares were used for two trials. Fresh or frozen/thawed semen from 27 stallions was used for A.I. In trial A 171 mares received either Buserelin (Receptal, Hoechst, Germany, 40 microg/animal) or 10 ml 0.9% NaCl (placebo). On day 16 after A.I. pregnancy diagnosis was performed by ultrasound scanning of the uterus. For statistical analysis, data were analyzed by a mixed model, with four fixed factors (treatment, type of spermatozoa, A.I. number, reproductive status of the mare) and a random factor (stallion). Least Square Means (LSM) for pregnancy rate were 46.0% in GnRH agonist treated mares and 36.4% in the control group (P=0.22). In trial B 20 lactating and cycling mares were used for endocrine studies. Blood samples were recovered for analyses of progesterone and LH from days 0 to 11. The mean progesterone concentrations increased continuously from days 0 to 8 after ovulation in both groups (GnRH group: from 0.81+/-0.48 to 5.47+/-0.48 ng/ml, control group: from 0.63+/-0.68 to 5.83+/-0.68 ng/ml). Moreover, the progesterone concentrations from days 9 to 11 were not different between the GnRH and the control group. In contrast to this LH concentrations were markedly influenced by the GnRH agonist. On day 10 LH concentrations were significantly higher in GnRH agonist treated than in placebo treated animals. From the data obtained from individual animals it can be concluded that GnRH agonist, given during luteal phase may have different effect on luteal function.

Progesterone receptors, oestrogen receptor alpha and glucocorticoid receptors in the bovine intercaruncular uterine wall around parturition

The bovine intercaruncular uterine wall expresses steroid hormone receptors throughout pregnancy. Concentrations of specific hormones undergo massive changes during the peripartal period and modulate the synthesis of their own receptors. This is well documented for the placentome, but respective data concerning the intercaruncular uterine wall are completely lacking. Thus, intercaruncular uterine wall segments from cows (I) being 8 and 9 months pregnant (slaughtered cows) and (II) cows undergoing a premature caesarean section 269-282 days after artificial insemination (AI) with (IIa, b) or without (IIc) induction of birth with PGF(2alpha) agonist or (III) receiving a caesarean section during severe dystocia (n=6, 5, 5, 5, 6 and 4 animals, respectively) were studied. In four naturally calving cows (IV) endometrial biopsies were obtained within 30 min after the expulsion of the calf. All tissue probes were fixed for 24h in 4% formaldehyde, routinely embedded in paraffin, and cut at 4 microm. Progesterone receptors (PR), estrogen receptor alpha (ERalpha) and glucocorticoid receptors (GR) were assessed using specific antibodies and staining intensities were documented employing an immunoreactive score (IRS). PR, ERalpha and GR exhibited cell type- and location-specific distribution patterns. IRS for PR and ERalpha did not differ between groups. GR-IRS of endometrial stromal cells, however, were higher in animals undergoing premature caesarean section after induction of birth compared to animals slaughtered during month 8 or 9 of pregnancy or animals receiving caesarean section following dystocia. Results of the present study indicate that steroid hormone receptor amounts within the intercaruncular uterine wall do not (PR, ERalpha) - or in a tissue-specific manner (GR) only - change during the peripartal period, although respective hormones undergo massive changes during this period. This is in strict contrast to the placentome. Comparatively lower local tissue estrogen concentrations around term may be one cause for this difference.

Influence of reproductive stage at PRID insertion on synchronization of estrus and ovulation in mares

In the present study, we investigated the effects of reproductive status, size of follicles and plasma progesterone concentrations of mares at PRID insertion on the efficacy of the treatment, estrous cycle patterns, plasma concentrations of progesterone and LH. The progesterone-releasing device (PRID) was administered intravaginally to 28 Haflinger mares for 11 days at different reproductive stages: anestrus (n=6), estrus (n=11) and diestrus (n=11). Plasma concentrations of progesterone at insertion (Day 1) of PRID differed among treatment groups (anestrus: 0.2-0.6 ng mL(-1), estrus: 0.2-0.5 and diestrus: 1.6-10.8 ng mL(-1); P<0.001). Total secretion of progesterone (area under curve (AUC)) during treatment period revealed highest values in diestrus (38.2+/-3.1 ng mL(-1)h(-1)) followed by estrus (25.1+/-2.7) and anestrus (21.0+/-0.4 ng mL(-1)h(-1); P<0.05). Progesterone area under curve (AUC) was positively correlated with initial progesterone concentrations (R=0.5; P<0.05), but it did not correlate with the interval from PRID removal to ovulation. Plasma concentrations of LH during treatment period, were significantly lower in anestrous mares (184.6+/-28.6 ng mL(-1)h(-1)) when compared to estrous and diestrous mares (349.7+/-53.3 and 370.5+/-40.3 ng mL(-1)h(-1); P<0.05). Follicular size at PRID insertion had no effects on the intervals from PRID removal to subsequent estrus and ovulation. Follicle diameters at removal of PRID were significantly correlated with the interval from coil removal to estrus (R=-0.55, P<0.05) and ovulation (R=-0.72, P<0.0004) in cyclic mares. In anestrus 0 of 6 (0%) mares, in estrus 5 of 11 (45.5%) and in diestrus 6 of 11 (54.5%) mares ovulated within a defined interval of 1 day before to 1 day after mean interval from PRID removal to ovulation. In cyclic mares, response to treatment was significantly higher when compared to anestrous mares: almost all mares responded with estrus and ovulation independent from the stage of the estrous cycle at the start of treatment. However, accuracy of synchronization was still unsatisfactory. In cyclic mares, the plasma progesterone concentrations at insertion of PRID seem to be more important for the efficacy of the treatment than the assignment to estrous cycle stages.

Seasonal effects on attempts to synchronize estrus and ovulation by intravaginal application of progesterone-releasing device (PRID™) in mares

To investigate seasonal effects on the efficacy of estrus synchronization in mares, we administered a progesterone-releasing device (PRID) intravaginally to eight Haflinger mares for 11 days. In January 3 of 8 mares responded to the treatment with estrus and ovulation, in March 7 with estrus and 6 of 7 mares with ovulation, in June 6 of 7 and in October 7 of 8 mares with estrus and ovulation. Follicle distribution patterns at PRID insertion were different between January/October, March/June and June/October (P<0.05). Number of follicles decreased during PRID treatment in January, March and June (difference of number of follicles at Day 12 minus number of follicles at Day 1: -4.2+/-2.7, -0.9+/-0.9 and -4.9+/-1.5 follicles), while it increased in October (3.9+/-1.2 follicles; P<0.05). Mean progesterone concentrations were lowest in January (0.3+/-0.1 ng mL(-1)) when compared with March (3.5+/-1.8 ng mL(-1); P=0.063), June (4.4+/-1.4 ng mL(-1); P<0.05) and October (2.2+/-0.9 ng mL(-1); P<0.05). At Day 2 of PRID treatment, mean progesterone concentrations significantly increased in all mares. Except from January, mean LH concentrations decreased within one day after PRID insertion and remained at low levels during treatments in January and March. Total secretion of LH during PRID-treatment was significantly lower in January and March when compared with June and October. In the 5 of 7 mares that ovulated during PRID treatment a distinct increase of plasma LH concentrations after ovulation was detected. Administration of the progesterone releasing intravaginal device PRID combined with the PGF2alpha analogue cloprostenol was able to induce estrus and ovulation in mares at different times of the year. However, efficacy of the treatment was not satisfactory concerning effectiveness in relation to season and synchrony of intervals from removal of PRID to ovulation in mares.

LH and IGF-1 release during oestrus and early luteal phase in lactating and non-lactating horse mares

The aim of the present study was to determine effects of lactation on basal LH and IGF-1 concentrations and on the LH response to a GnRH-analogue at different stages of the oestrous cycle in mares. A total of 17 cyclic Haflinger mares were included in the study. Experiments were performed on lactating mares in first postpartum oestrus, the subsequent early luteal phase, and second postpartum oestrus. Non-lactating mares were used in oestrus and early luteal phase. Blood samples were taken for 1 h at 15 min intervals. Mares were then injected with the GnRH-analogue buserelin (GnRHa; 5 microg i.v.) and blood samples were drawn every 15 min for further 2 h. LH in all samples and basal IGF-1-concentrations were determined by RIA. In lactating mares, basal LH concentrations during the early luteal phase tended to be lower (p = 0.07) and the LH response to GnRHa, calculated as area under the curve, was significantly less pronounced compared to non-lactating mares (p < 0.01). As well in lactating mares, the basal LH concentration between first early luteal phase and second oestrus differed significantly (p < 0.05) and the net response to GnRHa was significantly lower between first oestrus as well as second oestrus and first early luteal phase (p < 0.05) but not between first and second oestrous postpartum. Within the group of non-lactating mares, the LH response to GnRHa was as well significantly lower during oestrus than during early luteal phase (p < 0.01). IGF-1 concentrations differed neither between groups nor stages of the cycle within groups. In conclusion, basal and GnRHa-stimulated LH release in lactating mares is lower than in non-lactating mares. This difference, however, occurs only in the early luteal phase. In lactating mares, concentrations of LH appear adequate to allow ovulation to occur.

Acute Insulin-induced Hypoglycaemia does not alter IGF-1 and LH Release in Cyclic Mares

Lactation in the mare is associated with changes in the release of metabolic as well as reproductive hormones. Plasma glucose concentration is constantly reduced in lactating compared with non-lactating mares. Several metabolic signals have been proposed to link nutrition and somatic metabolism with reproductive function. The following experiment was performed to study the effect of acute hypoglycaemia on the release of insulin-like growth factor-1 (IGF-1) and luteinizing hormone (LH) in cyclic mares. Different doses of insulin (0.1 and 0.2 IU/kg body weight) were given to induce a decrease in plasma glucose concentration, as existent in lactating mares. All horses treated with insulin developed a hypoglycaemia over a time period of nearly 10 h. The IGF-1 and LH were analysed before and after insulin administration. At no point of time, a significant difference between the two insulin treatments and the control treatment was observed. Therefore, the hypoglycaemic horse is apparently able to provide the brain with sufficient glucose. Short-term hypoglycaemia does not affect the hypothalamo-pituitary-ovarian axis, and concentrations of IGF-1 and LH remained stable during insulin-induced hypoglycaemia. An acute change in plasma glucose concentration is thus not or at least not the only metabolic signal that links nutrition and somatic metabolism with reproductive function in the horse mare.

Morphological changes and proliferative activity in the oviductal epithelium during hormonally defined stages of the oestrous cycle in the bitch

The aim of the present study was to investigate morphological changes and proliferative activities in the epithelium of the canine oviduct with regard to the part of the oviduct - possibly indicating the existence of a locally restricted sperm reservoir - and the stage of the oestrous cycle. Nine healthy adult nulliparous bitches were submitted to ovariohysterectomy at three stages of the cycle: anoestrus (n = 3), late follicular phase (n = 3) and mid-luteal phase (n = 3). The whole oviduct ranging from the utero-tubal junction (UTJ) to the infundibulum (IN) was collected, divided into UTJ, IN plus six segments of equal length, i.e. eight oviductal specimens per animal were studied by light microscopy. Morphological characteristics of ovaries and endometrium were recorded macroscopically and verified histologically. The height of oviduct epithelial cells and percentage of ciliated cells (CC) were assessed and the respective data analysed statistically. Proliferative activity was immunohistochemically visualized by means of Ki-67 antigen detection. Blood was collected and concentrations of oestradiol-17beta and progesterone (P(4)) were measured. Within the IN and five of the six tissue samples collected from the ampulla and isthmus in anoestrous bitches, the oviductal surface epithelium consisted of low cuboidal cells demonstrating a uniform dark staining intensity. Only a very few scattered lighter staining CC could be detected. Under the influence of oestrogens during late follicular phase, the oviductal epithelium was highly differentiated. Lighter stained CC with apically located nuclei were easily distinguishable from basophilic secretory cells with apical cytoplasmic protrusions. Cell height and percentage of CC were significantly higher than in anoestrus (p <or= 0.05). During mid-luteal phase, high levels of P(4) were associated with differentiated and dedifferentiated cells as well as cells in regression seen in the mucosal folds of all samples. The percentage of CC and cell height were significantly lower than during late follicular phase (p <or= 0.05). Further signs of dedifferentiation consisted of a loss of cilia, a pinching off of the apical cytoplasm as well as the presence of debris and macrophages within the oviductal lumen. In the oviductal part of UTJ and the caudal isthmus hormone-dependent variations in cellular morphology were less distinct. Changes in cell height were minimal and did not differ significantly throughout the oestrous cycle. Hypertrophic cells with large nuclei were predominantly present at these sites, but did not consistently demonstrate signs of ciliation or secretion. Sporadic proliferating activity, visualized by means of Ki-67 antigen, was mainly seen in some cells of the late follicular phase samples. Thus, overall proliferative activity is generally very low or may occur within a relatively short period of time. It therefore cannot be excluded, that periods exhibiting higher mitotic rates are not included in the present study. It should, however, be mentioned that cells demonstrating morphological signs of apoptosis can only be seen very sporadically within a few specimens during mid-luteal phase, thus, reflecting low proliferative capacities and minimal cellular turnover found during this study. The results of the present study strongly indicate that oestrogens cause hypertrophy and differentiation, whereas P(4) induces gradual dedifferentiation or regression of the oviductal epithelium. Furthermore, they reveal clearly visible changes in the morphology of the tubal epithelium during the oestrous cycle. Depending on the tubal segment, these are, however, variably expressed. Whether the low degree of cellular variation of the UTJ and caudal isthmus is caused by specific hormone concentrations at these sites or specific regulatory mechanisms and may be associated with specific functional properties such as the formation of a locally restricted sperm reservoir needs further investigations.

Effects of lactation on metabolic and reproductive hormones in Lipizzaner mares

In this study, growth hormone (GH), insulin-like growth factor 1 (IGF-1), leptin, luteinising hormone (LH) and prolactin were analyzed in mares from late pregnancy throughout lactation (group 1, n=46) and in non-lactating mares (group 2, n=11). Plasma GH concentrations in group 1 mares during gestation and lactation were lower than in mares of group 2 (P<0.05). Highest IGF-1 levels were found in lactating mares in the week of foaling. IGF-1 concentrations decreased continuously thereafter. Plasma leptin concentrations decreased after foaling and, for 4 weeks, were lower in lactating than in non-lactating mares (P<0.05). Reduced leptin concentrations may promote feed intake and allow lactating mares to avoid an energy deficit. In group 1 mares, prolactin concentrations reached a maximum in the week of foaling and decreased rapidly thereafter. Plasma LH concentrations in group 1 mares before foaling were lower than at corresponding times in group 2 (P<0.05). LH concentrations then increased and did no longer differ from group 2 until week 2 postpartum. This increase may contribute to the resumption of cyclic ovarian activity in postpartum mares. Subsequently, LH levels in lactating mares decreased again (P<0.05). Increased IGF-1 concentrations early postpartum might contribute to ovarian stimulation while reduced IGF-1 and GH concentrations later in lactation might cause reduced stimulation. The changes in somatotrophic hormones could thus explain, at least in part, a more pronounced stimulation of ovarian function early postpartum than during the following months of lactation.

Blood plasma concentrations of oestradiol-17beta, testosterone and testosterone/oestradiol ratio in dogs with neoplastic and degenerative testicular diseases

Oestradiol-17beta and testosterone blood plasma concentrations were measured in dogs with Leydig-cell tumours (n=20), Sertoli-cell tumours (n=6), seminomas (n=9), unilateral inguinal cryptorchidism (n=7), abdominal cryptorchidism (n=9, one bilateral), degenerate scrotal testicles (n=6, two bilateral), and animals with normal scrotal testicles (n=20). The testosterone/oestradiol ratio (testosterone concentration [ng/mL]x100/oestradiol concentration [pg/mL]) was calculated.A considerably higher oestradiol concentration was found in dogs with Sertoli-cell tumours (29.0, 14.4-48.3 pg/mL; median, minimum-maximum; P=0.0256, Mann-Whitney test) and lower oestradiol levels were found in animals with seminomas (12.0, 3.4-17.6 pg/mL; P=0.0025) compared to the healthy control group (18.0, 8.6-31.5 pg/mL). Testosterone concentration was decreased in dogs with Sertoli-cell tumours (0.08, 0.03-0.77 ng/mL) when compared to the control group (1.95, 0.05-3.70 ng/mL; P=0.0012). Testosterone/oestradiol ratios differed from the control (9.6, 0.58-35.8) only in dogs with Sertoli-cell tumours (0.32, 0.06-2.80; P=0.0005). Clinical signs of feminization were observed in five dogs with Sertoli-cell tumour and one dog with a Leydig-cell tumour, and were more often associated with decreased testosterone/oestradiol ratios than with an increased oestradiol-17beta concentration.

Dopaminergic and opioidergic regulation of gonadotropin and prolactin release in stallions

In the non-breeding season, LH release is reduced via dopaminergic systems in the ram. On the other hand, our previous studies demonstrated an opioidergic inhibition of LH release in stallions outside the breeding season. Thus, in the present study we investigated the dopaminergic regulation of LH and prolactin secretion in stallions, considering interactions between dopamine and opioids. To achieve this, stallions (n=8) were treated with the dopamine antagonist sulpiride (0.6 mg/kg), the opioid antagonist naloxone (0.5 mg/kg), sulpiride plus naloxone or saline in December, March and June. Two hours after the respective treatments, they received a GnRH agonist. Sulpiride induced a significant prolactin release which was most pronounced in December, indicating seasonal variations in the inhibition of prolactin secretion by dopaminergic systems. Prolactin concentrations were not changed by naloxone. Neither during nor outside the breeding season, a dopaminergic regulation of LH release could be demonstrated. In contrast, naloxone caused a significant (p < 0.05) LH release, confirming an opioidergic inhibition of LH release. In conclusion, opioidergic regulation of LH and dopaminergic inhibition of prolactin secretion undergo seasonal changes. Neither during nor outside the breeding season, dopaminergic effects on LH release exist in the stallion.

Social suppression in nonreproductive female Damaraland mole-rats, Cryptomys damarensis: no apparent role for endogenous opioid peptides

The role of endogenous opioid peptides (EOPs) on LH secretion was examined to investigate the neuronal mechanisms responsible for the inhibition of GnRH and the resultant infertility in nonreproductive female Damaraland mole-rats, Cryptomys damarensis. The endorphin antagonist naloxone was administered to five groups of females to determine its effect on plasma LH levels: Grouping was determined by social status, social environment, and whether the females were ovariectomized. A single injection of naloxone had no significant effect on LH secretion in either intact or hystero-ovariectomized females. Multiple injections with naloxone failed to affect basal LH concentrations but did result in a decrease in GnRH-stimulated LH secretion in ovariectomized nonreproductive and reproductive females. A significant response to a single naloxone injection following GnRH priming was obtained in both nonreproductive females and in nonreproductive females housed in the absence of the reproductive pair. These results suggest EOPs play a role in sexual function but that socially induced infertility is unlikely to be mediated through the EOP system.

Seasonal short-term effects of naltrexone on LH secretion in male carp (Cyprinus carpio L.)

In order to evaluate the influence of the season (the stage of gonad maturity) on the modulatory role of endogenous opioid peptides in LH secretion in fish, sexually mature male carp (Cyprinus carpio L.) were intravenously injected with naltrexone-opioid receptor antagonist (5 or 50 microg kg(-1)) in the period of natural spawning (June) or gonad recrudescence (December). Moreover, the possible involvement of the dopaminergic system was studied in fish pre-treated with pimozide (dopamine receptor antagonist) and in intact fish. Blood samples were taken every minute, up to 10 min after naltrexone injection. In June, naltrexone significantly lowered LH levels in comparison to saline injected males. In December, there were no differences between saline and naltrexone-injected carps. In fish pre-treated with pimozide, neither in June nor in December were any significant differences in LH levels between control group and the groups injected with naltrexone found. The results showed that, in male carp, LH secretion under the influence of naltrexone depends on the stage of gonad maturity what suggests that the feedback of gonadal steroids on LH release could be mediated by the endogenous opioids. The role of dopamine in these processes is also discussed.

Estradiol-17beta and progesterone in the peripheral blood plasma of goats following superovulation with a single dose of pFSH, hMG or eCG

During the breeding season, 42 adult German Improved Fawn nanny goats were superovulated with a single dose of pFSH, hMG or eCG at the end or a single application of pFSH 36h before the end of synchronization treatment using flugestone acetate (FGA). Plasma sampling was performed immediately before and 1h after gonadotrophin treatment, twice daily during pre-estrus and estrus and once daily during post-estrus in order to determine peripheral estradiol-17beta and progesterone levels. During that period, ovarian dynamics was followed by serial ultrasound scans (8h interval during pre-estrus and estrus and once daily during post-estrus). Estradiol-17beta profiles differed between the treatment groups exhibiting significantly positive correlations between the mean estradiol-17beta concentrations and the numbers of developing large and medium-sized follicles during estrus. The early bolus application of FSH 36h before the end of synchronization treatment induced an additional advanced estradiol-17beta peak during gestagen dominance. A sharp decrease of estradiol-17beta at the end of estrus seems to play a major role for normal luteal development. Progesterone profiles during the early luteal phase revealed high premature luteal regression. An early progesterone increase was accompanied by low premature regression rates.Although simple B-mode ultrasonography is suitable to follow follicular growth patterns and to determine the ovulation rate following different superovulation regimen endocrinological supervision is required in order to detect a premature corpus luteum insufficiency.

Ultrasonic study of follicular dynamics following superovulation in German Merino ewes

Ewes are commonly superovulated with a single dose of eCG or multiple doses of pFSH. It would be convenient and less expensive to use a single dose of FSH, but results of various trials have been controversial. We wished to investigate ovarian dynamics using ultrasonography after superovulation with a single dose of pFSH and hMG as compared with a single dose of eCG. Estrus was synchronized during the breeding season with fluorogestone acetate-containing intravaginal sponges in adult German Merino ewes (n = 38). They were superovulated with single doses of pFSH (17 mg; n = 10), hMG (600 IU FSH and 600 IU LH; n = 9) or eCG (1250 IU; n = 10) given at the time of sponge removal, or pFSH (17 mg; n = 9) given 36h before sponge removal. Follicular and luteal development were observed by ultrasonic scanning every 8 h from the gonadotrophin injection until the end of estrus, and then once daily until Day 6 after estrus. Jugular venous blood was collected starting immediately before and 1 h after superovulation treatment, then twice daily until the end of estrus and once daily for the following 7 days. Concentrations of estradiol-17beta (E2) and progesterone (P4) were measured in plasma. Differences in the follicular dynamics of the 4 superovulation groups were obvious. The functional duration of the pFSH action was estimated to last approximately 48 h, whereas eCG and hMG were active for up to 72 h. The diameter of the ovulatory follicles proved to be smaller than it was described for unstimulated ewes. Single applications of pFSH or hMG can induce a superovulatory response, although the post-estrus progesterone profile revealed a high premature luteal regression rate in the different superovulation groups. Premature corpus luteum regression could not be seen by ultrasonography at this early stage of the luteal phase, indicating that the technique may fail to detect these corpora lutea in an embryo transfer program. However, ultrasonography represents a suitable method to observe follicular dynamics following different superovulation regimens in sheep.

Neuroendocrine regulation of gonadotropins in the male and the female

For the past decade, neuroendocrinology, in general, and neuroendocrine regulation of reproduction, in particular, were strongly dominated by molecular genetics and molecular endocrinology. In very recent years, however, neuroendocrinology is taking back its place. Beyond doubt GnRH is the neuroendocrine signal for ovulation. But there are still many unexplored pathways within the 'black box' triggering and regulating this signal. Neuroendocrine control of reproduction starts very early in life, well before birth. Hypophyseal gonadotropin secretion is under hypothalamic control at around mid-gestation in the fetal sheep and the fetal pig. These two species could be considered as best-studied farm animals considering neuroendocrinology. This minireview thus will give in the first part a short survey of developmental processes of some of the neuroendocrine systems in the pig and sheep. In the second part, the opioidergic and catecholaminergic control of gonadotropins in adults will be briefly discussed. The last part will focus on the new less known pathways mediating effects on hormones which regulate the reproductive functions.

Seasonal variation and opioidergic regulation of growth hormone release in cyclic, ovariectomized, and pregnant pony mares

Modulation of reproductive functions is one of the multiple effects of growth hormone (GH). To investigate effects of reproductive functions on GH release in the horse, plasma GH concentrations in ovary-intact (n = 7) and ovariectomized (n = 8) mares during the anovulatory and breeding seasons and in pregnant mares (n = 6) at various stages of gestation were determined. To analyze an opioidergic regulation of GH release, repeated blood samples were taken over 3 h, and mares were injected with the opioid antagonist naloxone (0.5 mg/kg i.v.) or saline. GH was determined by RIA with an antiserum raised against porcine GH and equine GH as standard. In ovariectomized and ovary-intact, cyclic mares, GH concentrations were low and not different between the two groups in November and December. GH concentrations increased significantly (P < 0.05) in cyclic mares during May and June but were not affected by stage of the cycle and were low in ovariectomized mares. In pregnant mares, plasma GH concentrations remained high throughout pregnancy and did not decrease during winter but increased significantly (P < 0.05) postpartum. Naloxone induced a significant GH release in ovary-intact mares; this response was most pronounced (P < 0.05) during the breeding season. Naloxone did not affect GH in ovariectomized mares. During pregnancy, naloxone induced a significant release of GH around Day 280 (P < 0.05) but not at other times of pregnancy. In conclusion, GH release is influenced by season. The seasonal changes depend on ovarian factors, are absent in ovariectomized mares, and can be modulated by pregnancy. GH release is regulated at least in part by opioidergic pathways.

Plasma beta-endorphin around parturition and its relationship to cortisol level and resumption of pituitary and ovarian functions in dairy cows

The objectives were to evaluate the concentrations of beta-endorphin in peripheral circulation around parturition and to investigate their relationship to the concentrations of cortisol and postpartum resumption of pituitary and ovarian functions in dairy cows. Subjects were 21 Holstein-Friesian cows in late pregnancy. Blood samples were collected from these animals from day 270 in pregnancy until the first ovulation after calving. Average immunoreactive (IR) beta-endorphin concentrations in cows with dystocia (n = 8) in periparturient period (from day 270 of pregnancy until 24 h after calving) were slightly higher than those in cows with normal calving (n = 13) in the same period although the difference was not significant. During the periparturient period, the peak level of IR beta-endorphin was seen at the time of rupture in cows with normal calving and it was observed at the time of parturition in cows with dystocia. The trend of IR beta-endorphin secretion appeared to be concomitant with cortisol secretion in the periparturient period but not in postpartum period (from 24 h after calving until the first ovulation). Average IR beta-endorphin concentrations in cows with dystocia in the postpartum period were not significantly different from those in cows with normal calving. There was no significant association between average IR beta-endorphin concentrations in early postpartum period (from 24 h until 7 days after calving) and the responsiveness of luteinising hormone (LH) to exogenous GnRH administered on day 7 postpartum. However, a negative correlation (r = -0.593; n = 21; P = 0.004) was observed between average IR beta-endorphin concentrations and LH concentrations during the period from day 1 until the first ovulation in the 21 cows. In addition, a positive correlation (r = 0.498; n = 21; P = 0.020) was seen between the beta-endorphin concentrations and time to the first ovulation after calving. The results from this study suggest that beta-endorphin may release into peripheral blood differently from cortisol and that it may be involved in regulating LH secretion and thus the resumption of ovarian cyclicity in postpartum dairy cows.

Histomorphological endometrial status and influence of oxytocin on the uterine drainage and pregnancy rate in mares

The aim of this field study was to examine the influence of the uterotonic substance oxytocin in 2 different therapeutic dosages of 15 and 25 i.u., respectively on the uterine drainage of oestrous mares and on their fertility. In addition endometrial biopsies of mares with and without intrauterine fluid accumulations around the time of ovulation were evaluated histomorphologically regarding the aetiology of susceptibility to uterine infection. A population of 59 Hanoverian Warmblood mares was used in this study. The mares were divided into Group A (mares with intrauterine fluid accumulations [n = 49]) and Group B (controls [n = 10]). Group A was further subdivided into 3 groups according to varying oxytocin administrations (none, 15 i.u., 25 i.u.). Prior to insemination, all mares were examined by rectal palpation, ultrasonography and vaginal inspection. In addition, hormone plasma concentrations were evaluated at the time of ovulation, namely oestradiol and progesterone concentrations. Endometrial biopsies were obtained from all mares. Endometrial samples for microbiological and cytological evaluation were taken from mares of Group A only. All mares were inseminated close to ovulation during the first cycle. This study shows that intravenous oxytocin treatment of mares with intrauterine fluid accumulations results in better pregnancy rates than no treatment.

Gonadal sex hormones and dystonia: experimental studies in genetically dystonic hamsters

In some kinds of idiopathic dystonia, including paroxysmal dystonia, a role of sex hormones has been suggested because of female predominance and onset, recurrence, or exacerbation of dystonic symptoms with pregnancy. Similar effects of pregnancy have recently been reported in a model of paroxysmal dystonia, the genetically dystonic hamster. Dystonia in mutant hamsters of both genders is transient, i.e., exhibits spontaneous remission at around puberty, strongly suggesting involvement of gonadal sex hormones. For exploration of the role of sex hormones in dystonia, we undertook a series of ontogenetic experiments in male and female dystonic hamsters. Mutant animals of both genders exhibited the same postnatal development of dystonia with maximum severity of dystonic attacks between weaning and approximately 40 days of age and spontaneous remission thereafter. As shown by plasma sex hormone determinations and, in females, vaginal cytology, spontaneous improvement of the movement disorder coincided with puberty in both genders. Male and female hamsters had about the same plasma levels of progesterone. Compared with nondystonic hamsters, onset of puberty was significantly retarded in both male and female dystonic hamsters. Furthermore, body weight gain was lower in dystonic animals, indicating retarded postnatal development. Gonadectomy at time of weaning did not alter the age-dependent development and remission of dystonia, suggesting that gonadal sex hormones are not critically involved in the disease in hamsters. We propose that transient paroxysmal dystonia in mutant hamsters is caused by postnatal retardation of brain development resulting in a temporary impairment of brain functions with spontaneous remission independent of gonadal sex hormones. In view of the fact that the brain can synthesize steroids such as progesterone independent of peripheral glands in both genders, such neurosteroids might be involved in the postnatal brain maturation that leads to remission of dystonia at around puberty in mutant hamsters.