Early Anoestrus Research Articles

Stimulation of Estrus and Ovulation by Resynchronization in Kangal Sheep during Early Anestrus.

A total of 100 Kangal sheep were divided into four groups with the aim of investigating the effectiveness of resynchronization during anestrus for the first time in the literature. The groups were then divided into two further subgroups, namely the resynchronization subgroup group (hCG+resynch) and group (resynch)) and the no resynchronization subgroup (Group (hCG) and group (control)). All the groups started with progesterone-containing sponge insertion on Day 7. The sponge was removed after 7 days (on Day 0), and 600 IU eCG + 131.5 µg PGF2α was injected. The animals in group (hCG+resynch) and group (hCG) received hCG injection at the time of sponge administration. Accordingly, four different groups were established, i.e., resynchronization + hCG administration group (hCG+resynch); n:25), no resynchronization + hCG administration (group (hCG); n:25), resynchronization + no hCG administration (group (resynch); n:25), and no resynchronization + no hCG administration (Group (control); n:25). Estrus rates at the first application in group (hCG+resynch), group (hCG), group (resynch), and group (control) groups were 76%, 88%, 96%, and 76%, respectively, and pregnancy rates were 52%, 64%, 72%, and 60%, respectively; there were no intergroup statistical differences in the two parameters above. It was concluded that resynchronization performed with two consecutive stimulations during anestrus could help save time and provide a pregnancy rate at a level that can provide economic returns.

Ovarian response is not affected by the stage of seasonal anestrus or breed of goats when using a progesterone injection plus human chorionic gonadotropin-based protocol

The aim of this study was to evaluate the effect of the stage of seasonal anestrus and breed on ovarian response in non-estrous cycling goats using a progesterone (P4) injection plus human chorionic gonadotropin (hCG)-based protocol. In Experiment 1, non-estrous cycling local Mexican goats were treated with 20 mg of P4 plus 100 IU of hCG injections 24 h apart during April (early anestrus, n = 13) or June (late anestrus, n = 12). The estrous response, interval from hCG-to-estrus, and interval to ovulation were not affected by season (P > 0.05). In addition, the size of the follicle from which ovulation occurred and the size of the corpus luteum were not different between the two stages of seasonal anestrus (P > 0.05). In Experiment 2, the estrous response was compared between multiparous non-estrous cycling local Mexican (n = 18) and Alpine (n = 19) goats in which stage of the estrous cycle was synchronized using the same P4+hCG protocol as in Experiment 1. Neither the onset of estrus nor the time of ovulation differed between breeds, and the estrus-to-ovulation interval also was similar for both breeds (P > 0.05). The diameter of the dominant follicle at the time of ovulation was similar between local and Alpine goats (P > 0.05). In addition, the pregnancy rate was not different for both local and Alpine goats (P > 0.05). In conclusion, results of this study indicate that the stage of seasonal anestrus or breed do not modify estrous and ovarian response in non-estrous cyclic goats synchronized with a P4 injection plus hCG-based protocol.

INTERCELLULAR INTERACTIONS IN THE ENDOMETRIAL HYPERPLASIA-RELATED INFLAMMATION DEVELOPMENT

Proliferation and apoptosis play an important role in cyclic changes in the healthy canine endometrium. Proteins of the Bcl-2-family are known to be involved in the regulation of apoptosis. However, only few reports mention their expression patterns during cystic endometrial hyperplasia (CEH). In order to correlate proliferative and apoptotic processes, expression of the apoptosis-regulatory proteins Bcl-2 (anti-apoptotic) and Bax (pro-apoptotic) in healthy and cystic hyperplastic endometrial tissue as well as in pyometra was investigated. Uteri from 33 bitches were assigned to three groups: group 1 - healthy endometrium (n = 12), group 2 – CEH (n = 17) and group 3 - pyometra (n = 4). Markers for proliferation (Ki-67) and apoptosis (activated caspase-3 and TUNEL-method) as well as expression of Bcl-2 and Bax were determined in all endometrial layers. For groups 1 and 2 this was done during endometrial gland secretion in mid and late luteal phase (mLP, lLP), endometrial reparation in early anestrus (eAE) and in the regenerated endometrium in late anestrus (lAE). For group 3 only the late luteal phase was investigated.In group 1, cyclic proliferation patterns were found predominantly in superficial glands (SG) and stroma, whereas progesterone-mediated low expression levels coincided with high apoptosis rates in the basal glands (BG). In eAE, higher apoptotic activity was detected compared to lLP and lAE. Bcl-2 and Bax expression levels showed an inverse cyclic relationship in all tissue layers. In the stroma, in eAE, a rise in proliferative activity and concomitant increase in anti-apoptotic Bcl-2 expression levels was found, indicating that this layer serves as a source for endometrial regeneration.In CEH, no or limited cyclic patterns of proliferation, apoptosis, Bcl-2 and Bax were found. Increased proliferation rates coincided with deregulated apoptosis. Besides the glandular compartments, the stroma played an important role in the pathogenesis of canine CEH. In case of pyometra, both proliferation and apoptosis increased, indicating irreversible damage of the inflamed canine endometrium.In conclusion Bcl-2 and Bax play a role both in the physiological regenerative processes of the cyclic canine endometrium and in deregulating proliferation and apoptosis in CEH and pyometra.

Proliferative and apoptotic changes in the healthy canine endometrium and in cystic endometrial hyperplasia

Proliferation and apoptosis play an important role in cyclic changes in the healthy canine endometrium. Proteins of the Bcl-2-family are known to be involved in the regulation of apoptosis. However, only few reports mention their expression patterns during cystic endometrial hyperplasia (CEH). In order to correlate proliferative and apoptotic processes, expression of the apoptosis-regulatory proteins Bcl-2 (anti-apoptotic) and Bax (pro-apoptotic) in healthy and cystic hyperplastic endometrial tissue as well as in pyometra was investigated. Uteri from 33 bitches were assigned to three groups: group 1 - healthy endometrium (n = 12), group 2 – CEH (n = 17) and group 3 - pyometra (n = 4). Markers for proliferation (Ki-67) and apoptosis (activated caspase-3 and TUNEL-method) as well as expression of Bcl-2 and Bax were determined in all endometrial layers. For groups 1 and 2 this was done during endometrial gland secretion in mid and late luteal phase (mLP, lLP), endometrial reparation in early anestrus (eAE) and in the regenerated endometrium in late anestrus (lAE). For group 3 only the late luteal phase was investigated.In group 1, cyclic proliferation patterns were found predominantly in superficial glands (SG) and stroma, whereas progesterone-mediated low expression levels coincided with high apoptosis rates in the basal glands (BG). In eAE, higher apoptotic activity was detected compared to lLP and lAE. Bcl-2 and Bax expression levels showed an inverse cyclic relationship in all tissue layers. In the stroma, in eAE, a rise in proliferative activity and concomitant increase in anti-apoptotic Bcl-2 expression levels was found, indicating that this layer serves as a source for endometrial regeneration.In CEH, no or limited cyclic patterns of proliferation, apoptosis, Bcl-2 and Bax were found. Increased proliferation rates coincided with deregulated apoptosis. Besides the glandular compartments, the stroma played an important role in the pathogenesis of canine CEH. In case of pyometra, both proliferation and apoptosis increased, indicating irreversible damage of the inflamed canine endometrium.In conclusion Bcl-2 and Bax play a role both in the physiological regenerative processes of the cyclic canine endometrium and in deregulating proliferation and apoptosis in CEH and pyometra.

In this issue – September 2017

In this issue – September 2017

Use of cabergoline for oestrus induction in multiparous anoestrous Beagle bitches.

The purpose of this study was to examine the efficacy of daily cabergoline administration on oestrus induction in bitches. Of 20 multiparous Beagle bitches, 15 were not mated with sires in their last oestrus and 5 bitches that had been mated whelped. All bitches were in early or mid-anoestrus and received 5 μg/kg/day cabergoline PO. Oestrus was induced in the mid-anoestrus bitches at a higher rate than in the early anoestrus bitches. Comparing the different histories of previous pregnancy among the mid-anoestrus bitches, the rate of oestrus induction in the non-pregnant bitches was higher than in the bitches that whelped. Cabergoline is effective for oestrus induction in mid-anoestrus bitches.

Cyclic Morphological Changes in the Beagle Mammary Gland

Interpretation of chemical-induced effects on the female beagle mammary gland can be difficult owing to the wide variation of normal glandular morphology. In this retrospective study, morphological features of the gland in four (proestrus, estrus, diestrus, and anestrus) phases of the cycle are described. The gland was quiescent (inactive) in proestrus and estrus. In diestrus, with the rise of progesterone, four (I-IV) distinct morphological changes were evident. In phase I, there was exuberant stromal and ductal proliferation. In phase II, there was early lobular development with branching ducts and alveolar proliferation. In phase III, there was an abundance of glandular tissue with large lobules containing secretory material, whereas phase IV had features of early regression, increased interlobular connective tissue, and eosinophilic secretions in distended ducts and acini. In early anestrus, ducts were distended, with eosinophilic secretions with alveolar regression, whereas regression was complete in late anestrus. Glandular morphology was slightly variable in the mammary chain within the same dog. Progesterone receptor expression was prominent in estrus and early diestrus, and peak estrogen receptor expression was noted in diestrus II. Expression of proliferation marker ki-67 was highest in diestrus I, followed by diestrus II. There was excellent concordance between the estrous stage and the glandular morphology.

Histological Study of Canine Mammary Gland During the Oestrous Cycle

The development of the mammary gland is a puzzling phenomenon and the research on this field has been focussed mostly on the carcinogenesis, with a less goal-oriented concern in basic histology. In order to determine the histological features of normal mammary gland in the different oestrous phases we used 39 non-pregnant female dogs of various breeds and ages. The animals were grouped in: pre-pubertal, pro-oestrous, oestrous, early and late dioestrous, early and late anoestrous phases. Major changes of the canine mammary histology throughout the oestrous cycle were identified in this study. A rudimentary gland with few ducts in the base of the nipple was observed in pre-pubertal female individuals and pubertal pro-oestrous female ones. In the oestrus, small inactive lobules associated with ductal branching and inconspicuous regressive changes were observed, while in early dioestrus, a ductal arborization was present. In late dioestrus, a complete lobuloalveolar differentiation and secretory capacity was achieved. The regressive histological features were abundant on early anoestrus, and markedly generalized on late anoestrus. The regressive process was longer in the more caudal gland pairs. This work provides baseline knowledge of canine mammary gland that may be relevant for interspecies comparative purposes and for pathologists dealing with mammary gland tumours.

The effect of nutrition on the seasonality of reproduction in ewes

The beneficial effects of nutrition on reproduction in sheep have been described, particularly on ovulation rate. However, the relationships between nutrition and reproductive seasonality are not well known. This review will deal with the effects of body fat or food intake on sexual and hypothalamic/pituitary activity in sheep, mainly focused on Mediterranean genotypes. Although only severe malnutrition can significantly extend the length of the seasonal anestrous period, the level of fat reserves can play a significant role on reproductive seasonality delaying the onset of seasonal anoestrus, particularly on the Mediterranean environment. The effect of overfeeding on LH secretion has also been reported, specially at short term. Several experimental approaches have elucidated that both high body fat and food intake are able to modify the sensitivity of the hypothalamus to oestradiol negative feedback during seasonal anoestrus, with those effects being associated to a reduced amount of NPY mRNA and to an increase of plasma insulin, glucose and leptin concentrations, particularly in the late scenario. However, the highest receptivity to nutritional stimulation in terms of increasing LH occurs when ewes are subjected to a photoperiodic state of early anoestrus or late breeding season rather than under a photoperiod characteristic of the end of anoestrus or the beginning of the breeding season.

Immunohistochemical localization of VEGF and its receptors in the corpus luteum of the bitch during diestrus and anestrus

The corpus luteum (CL) is a temporary endocrine gland, whose life span depends on the interaction of luteotrophic and luteolytic factors. Since development and maintenance of CL is based on angiogenesis, angiogenic growth factors may play a role in CL-function of the bitch, as described for other species. The aim of this study was to detect the presence of the vascular endothelial growth factor (VEGF) system in the bitch CL throughout diestrus and early anestrus. For that purpose, blood samples from 24 bitches were collected and analyzed for progesterone to determine ovulation time and the animals were subjected to ovariosalpingohysterectomy 10, 20, 30, 40, 50, 60 or 70 days after ovulation. The corpora lutea were fixed in formalin and embedded in Paraplast ® resin. Five micrometers sections were submitted to standard immunohistochemistry protocol using three primary antibodies (SC-315, SC-316 and VG76e) for detection of kinase domain region (KDR), fms-like tyrosine kinase 1 (Flt-1) and VEGF, respectively. The VEGF system expression could be detected in all diestrus stages in endothelial as well as luteal cells (responsible for blood vessel formation and progesterone production, respectively), indicating time dependent changes: immunostaining tended to increase from Day 10 to 50 and to decrease until Day 70 post-ovulation. In the CL of the bitch, structure related cells, like pericytes and stroma cells, expressed it in determined time points of diestrus with little intensity variation. We concluded that VEGF might have a modulatory effect in the CL of the dog acting as paracrine and autocrine factor through its receptors, Flt-1 and KDR.

Degeneration and apoptosis of endometrial cells in the bitch

The relationships between changes in plasma progesterone concentrations, degeneration of the luminal epithelium, the occurrence of apoptosis of endometrial cells and endometrial leucocyte populations in the bitch were determined. Mature bitches ( n = 15) were euthanized and necropsied when in diestrus (Days 7–75, n = 12) or in anestrus (Days 10, 32 and 53). Degeneration of the luminal epithelium was observed in bitches in late diestrus (Days 38–75, n = 5) when plasma progesterone concentrations were decreasing and in anestrus (Days 10 and 32, n = 2) when plasma progesterone concentrations were <0.5 ng/mL. Endometrial leucocyte populations increased after degeneration of the luminal epithelium (around Day 42 of diestrus). Apoptosis was mainly observed in the basal glandular epithelial cells and endothelial cells of blood capillaries in all except anestrous bitches. Very few apoptotic cells were found in the superficial glandular epithelial cells and stromal cells. Higher apoptotic indices were detected in the basal glandular epithelium on Days 12–42 of diestrus than at other stages. Therefore, apoptosis of glandular basal epithelial cells occurred mainly in early diestrus, degeneration of cells of the luminal epithelium occurred from mid-diestrus to early anestrus, and the increase in leucocyte numbers may have been a consequence and not a cause of luminal epithelial degeneration.

Shortening of Interestrous Intervals With Cabergoline in Bitches: A Clinical Trial

Two consecutive interestrous intervals (n=46) were recorded in 23 bitches of different breeds. At varying times after day 100 from the onset of the second proestrus, cabergoline (5 microg/kg per os q 24 hours) was administered from early (n=11), mid- (n=10), and late (n=2) anestrus until 2 days after the beginning of the following proestrus. Interestrous intervals (IEI) were significantly shorter in the cabergoline-treated time periods when compared to the nontreated IEI (184+/-4.5 days versus 239+/-4.5 days; P<0.01). The mean number of days of cabergoline treatment until the onset of proestrus was 21.4+/-2.9 (least square means and standard error of the mean [LSM+/-SEM]). Mean cabergoline treatment durations beginning in early, mid-, and late anestrus were 27.4+/-3.7, 17.6+/-3.8, and 5+/-3 days (LSM+/-SEM), respectively. A significant correlation was found between the stage of anestrus in which the treatments began and the duration of the treatments required to induce estrus (0.51, P=0.01).

Serum estradiol-17β, progesterone and respective uterine cytosol receptor concentrations in bitches with spontaneous pyometra

The role of serum estradiol-17β (E2) and progesterone (P4) in relation to uterine estrogen (ER) and progesterone receptors (PR) was investigated in canine cystic endometrial hyperplasia—pyometra (CEH-P). Blood and uterine samples were collected pre- and post-ovariohysterectomy, respectively, from 54 bitches presenting spontaneous CEH-P and 25 healthy control bitches. Competitive enzyme immunoassays (EIA) and enzyme ligand immunoassays (ELIA) were applied to estimate serum hormones and uterine cytosol active receptors, respectively. Animals were classified in the stages of first half of diestrus, second half of diestrus and early anestrus on the basis of reproductive history, clinical signs, uterine and ovarian macro- and microscopic inspection and serum P4 concentration. Bitches with CEH-P, compared to their respective stage controls, exhibited (a) similar P4 fluctuations, (b) higher E2 concentrations, (c) lower PR concentrations during diestrus first and second half and (d) lower ER concentrations during diestrus first half and early anestrus. Negative correlation was detected between P4 and ER within both CEH-P and control groups. It was concluded that P4 was the main uterine receptor regulator for both PR and ER during diestrus and early anestrus in healthy and affected uteri. However, in CEH-P bitches, high P4 levels in diestrus appeared to over-activate uterine PRs, leading to stronger PR self-down regulation and ER suppression. These findings indicate an increased sensitivity of CEH-P uterus to P4 action. During early anestrus, a complementary role of endogenous E2 was considered, since reduction of P4 action appeared to permit uterine ER replenishment and activation by relatively high E2 levels.

Morphological changes of the endometrial epithelium in the bitch during metoestrus and anoestrus.

Although cyclic changes of the endometrium in dogs involving both stromal and glandular compartments have been described, the fate of the surface epithelium after progressive growth and secretion is still unclear. In the present study, uteri of 43 healthy bitches in metoestrus and anoestrus were examined macroscopically and histologically. Tissue biopsies were taken from three different locations (cranial and middle parts of uterine horns and bifurcation). The stage of the oestrous cycle was determined by evaluation of progesterone and oestradiol levels in plasma hormone and was also confirmed clinically. Crypts formed in the luteal phase were covered with a columnar epithelium which gradually underwent fatty degeneration. In addition, the stromal part of the crypts disappeared and finally, in early anoestrus, epithelial sheaths desquamated and shed off into the uterine lumen. The surface epithelium was replaced by new cuboidal cells proliferating and migrating from the glandular openings. These findings were confirmed by oil red O staining and immunohistochemical detection of proliferation with Ki-67 marker.

Regulation of LH secretion during seasonal anestrus by dopaminergic pathways in Rasa Aragonesa ewes treated or not with melatonin

The involvement of the dopaminergic system in the steroid-dependent inhibition of luteinizing hormone (LH) secretion during anestrus in ovariectomized, estradiol-implanted adult Rasa Aragonesa ewes was investigated in both ewes treated with melatonin on 8 March (n = 10) and in control (n = 8) ewes. Melatonin implants did not significantly increase LH secretion. However, treatment with pimozide induced a significant increase (P &lt; 0.05) in LH pulse frequency in both groups during early anestrus. We conclude that, in the absence of males, the dopaminergic system is clearly involved in the inhibition of LH secretion during anestrus in both melatonin-treated and control ewes. Key words: Sheep, melatonin, pimozide

Investigations on the re-establishment of the positive feedback of oestradiol during anoestrus in the bitch.

To test for the re-establishment of the positive feedback of oestradiol (E2) during anoestrus in the dog, the hypothalamo-pituitary-ovarian axis of five beagle bitches was challenged by treatments with oestradiol benzoate (EB), mimicking the course of the pro-oestric E2 secretion. Treatments in anoestrus started 7 days following the decline of progesterone (P) <1 ng/ml; they were repeated in 5 week intervals until onset of pro-oestrus; another treatment was performed during dioestrus 50 days after onset of the preceding pro-oestric bleeding. Each dog served as its own control by receiving vehicle-treatments in one of the following cycles. Each observation period covered a time window of 168 h and blood samples were collected for the determination of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and E2 in 6 (0-24 h) and 8 h (24-168 h) intervals. In the control periods and as indicated by the parameters area under curve (AUC), basal and maximal values, the availability of LH, FSH and E2 decreased from dioestrus to early anoestrus to increase again during the course of anoestrus (p < 0.05), indicating a gradual desensitization of the hypothalamus towards the negative feedback of oestradiol. At all times treatments with EB lowered the availability of FSH (decreased AUC and basal levels). A delay in the occurrence of the first LH peak after treatments with EB (p < 0.001) and decreased maximal values (p < 0.001) indicated a suppression of the LH-release. In no case treatment with EB led to a pre-ovulatory like LH-surge. In each dog the last trial with EB in anoestrus passed over into pro-oestrus/oestrus, with a reduced AUC and peak value of the pre-ovulatory LH-surge being the only differences to the control group. The observed differences in the response of LH and FSH to treatments with EB point towards subtle differences in the mechanisms controlling the release of these two hormones during anoestrus. From the data obtained, it may be concluded that the time window for E2 to act via a positive feedback seems to be very small and restricted to the end of anoestrus, and that full follicular function is a pre-requisite to allow for this phenomenon.

The role of nutrition in the regulation of LH secretion during anestrus by the serotoninergic and dopaminergic systems in Mediterranean ewes treated with melatonin

The steroid-dependent inhibition of LH secretion involves dopaminergic and serotoninergic systems but it is unclear how the plane of nutrition affects this inhibition during anestrus in melatonin treated ewes. Melatonin implants (18 mg) were inserted (Day 0) into ovariectomized, estradiol treated adult Rasa Aragonesa ewes on a high (H; n=8) or low energy diet (L; n=6) which were applied in early anestrus (Day 29–57) and late anestrus (Day 90–104). Cyproheptadine (0.1 mg/kg), a serotoninergic (5HT 2) receptor antagonist, was administered in early and late anestrus (Day 50 and 107) followed by pimozide (0.08 mg/kg), a dopaminergic 2 receptor antagonist (Day 57 and 114). The H ewes had significantly higher LH concentrations ( P<0.05) before cyproheptadine treatment in early anestrus. The H and L ewes responded in a similar way to the antagonists in both early and late anestrus, except for L ewes who had a higher LH pulse amplitude after pimozide treatment in both periods ( P<0.05). During early anestrus, cyproheptadine tended to increase ( P=0.06) LH pulse frequency in L ewes and LH concentrations in H ewes. The LH secretion also increased in L ewes after pimozide administration during early anestrus ( P<0.05 for mean LH concentrations and LH pulse frequency and amplitude). However, pimozide dramatically increased LH secretion during late anestrus (Day 114) irrespective of the plane of nutrition ( P=0.06–0.08 for LH pulse frequency and P<0.05 for LH concentrations and pulse amplitude). In melatonin treated Mediterranean ewes, the plane of nutrition appeared to modify the effect of dopaminergic and serotoninergic systems on the steroid-dependent inhibition of LH secretion throughout anestrus.

Thyroid hormones mediate steroid-independent seasonal changes in luteinizing hormone pulsatility in the ewe.

Thyroid hormones permit the increase in response to estradiol negative feedback in ewes at the transition to anestrus. In this study, we tested whether the thyroid hormones are also required for steroid-independent seasonal changes in pulsatile LH secretion. In experiment 1, Suffolk ewes were ovariectomized and thyroidectomized (THX) or ovariectomized only (controls) in late November. LH pulse frequency and amplitude were measured for 4 h in December, April, May, June, and August. Pulse frequency was also measured in the presence of estradiol-containing implants during the breeding (December) and early anestrus (March) seasons. As expected, in the presence of estradiol, pulse frequency declined between December and March in control but not THX ewes. In the absence of estradiol, a seasonal decline in frequency and an increase in amplitude occurred in control ewes, concurrent with lengthening photoperiod. A similar trend was seen in THX ewes, but the seasonal changes were lower in magnitude and not significant. In experiment 2, the same protocol was used (pulse measurements in December, May, and June) with a larger THX group size (n = 7). Results were similar to those of experiment 1 for controls. In THX ewes, pulse frequency did not change over time and was significantly elevated relative to that of controls during the summer. Pulse amplitude in THX ewes tended to increase during summer and did not differ from pulse amplitudes in control ewes. These results demonstrate that thyroid hormones are required for steroid-independent cycles in LH pulse frequency; however, some seasonal changes in amplitude still occur in the absence of thyroid hormones. This finding contrasts with the changes in estradiol negative feedback at the transition to anestrus, which are entirely thyroid hormone dependent.

Effect of stage of anestrus on the induction of estrus by the dopamine agonist cabergoline in dogs

Beagle bitches were administered the dopamine D 2 receptor agonist cabergoline in 3 groups of 5 animals each, starting on known days of the estrous cycle. Cabergoline treatment was started in either early anestrus (Days 93 to 108), mid-anestrus (Days 123 to 156), or late anestrus (Days 161 to 192) at doses of 5 ug/kg/d, per os, and was continued until the confirmation of induced proestrus or for 40 d. Reproductive parameters were compared with those in 5 control anestrous bitches (Days 90 to 150). In control bitches, the mean (± SEM) interval to the next proestrus (73 ± 11 d) resulted in an interestrus interval (192 ± 9 d) similar to that of the previous cycles (196 ± 11 d). In 14 of the 15 cabergoline-treated bitches, the next proestrus occurred within 4 to 30 d, was premature in early and mid-anestrous bitches and developed with low variability within groups. The resulting intervals to proestrus in bitches treated with cabergoline in early anestrus (20 ± 2 d), mid-anestrus (14 ± 3 d) and late anestrus (6 ± 1 d) resulted in interestrus intervals in those groups of 131 ± 5, 166 ± 7 and 196 ± 2 d, respectively. In response to treatment, interestrus intervals were reduced (P<0.05) and more synchronous (P<0.05) in early and mid-anestrus bitches, and were more synchronous (P<0.05) in late-anestrous bitches compared with those of control bitches or those of the previous cycle. Periovulatory estradiol and progesterone profiles of induced cycles in treated bitches were similar to those of spontaneous cycles in control bitches. Four of 5 control bitches and 12 of the 14 responding cabergoline-treated bitches became pregnant and produced normal litters. Plasma prolactin concentrations at Days 2 and 5 of treatment (0.3 ± 0.1 ng/mL) and at the onset of proestrus shortly before the end of treatment (0.4 ± 0.1 ng/mL) were lower (P<0.05) than those present in anestrus prior to treatment (1.7 ± 0.6 ng/mL) or in control bitches. Prolactin was also low at the onset of proestrus in control bitches (0.5 ± 0.2 ng/mL). The results demonstrate that prolactinlowering doses of the dopamine agonist cabergoline can terminate the normal obligate anestrus in dogs, and that the effect occurs more slowly in early anestrus than in mid or late anestrus.

Concurrent pulsatile secretion of luteinizing hormone and follicle-stimulating hormone during different phases of the estrous cycle and anestrus in beagle bitches.

The 6-h secretory profiles of LH and FSH and the possible concordance between the episodic release of LH and FSH were studied in 6 beagle bitches during early, mid-, and late anestrus and during the follicular and luteal phases of the estrous cycle. Plasma samples were obtained at 10-min intervals via jugular venipuncture. In all stages of anestrus and in the luteal phase, FSH and LH secretion was pulsatile. All FSH pulses coincided with LH pulses. However, the mean duration of the FSH pulse (115 min) was significantly longer than that of the LH pulse (72 min). The basal plasma LH concentration was low compared with the maximum peak levels, whereas FSH pulses were characterized by relatively low peaks compared with the basal levels. In contrast to the basal plasma LH levels and the area under the curve (AUC) for LH, the basal plasma FSH levels and the AUC for FSH increased significantly as anestrus progressed. During the follicular phase, the secretory pattern of LH was characterized by frequent increases of short duration. During this phase, the basal plasma FSH concentration was relatively low, whereas the basal plasma LH level was high in comparison with that in the other phases of the estrous cycle. The luteal phase was characterized by an increased frequency of LH pulses, a shorter duration of the LH peaks, and a tendency to a lower amplitude of both LH and FSH peaks compared with values observed during anestrus. It is concluded that in the bitch, FSH and LH pulses are released in concordance and that progression from early to late anestrus is associated with an increase in basal plasma FSH concentration without a concomitant rise in basal plasma LH concentrations. The latter suggests that in the bitch an increase in circulating FSH should be considered to be a critical event required for the initiation of ovarian folliculogenesis and consequently for the termination of anestrus.