Low doses of bromocriptine shorten the interestrous interval in the bitch without lowering plasma prolactin concentration

Relationship between clinical signs and hormonal analytical findings in bitches with lactatio sine graviditate

OBJECTIVE

Lactatio sine graviditate of the bitch can become clinically relevant in particularly severe manifestations. The aim of the study was to relate the hormone pattern consisting of progesterone (P4), estradiol 17β (E2) and prolactin to the time of occurrence of lactatio sine graviditate in the course of metoestrus and anoestrus as well as to its symptomatology.

MATERIAL AND METHODS

Sixty-eight bitches with apparent lactatio sine graviditate were divided into 3 groups according to their cycle status. All bitches were examined for gynaecological findings. Furhtermore, their blood progesterone, oestrogen, and prolactin concentrations were determined and compared with the 133-day hormone profile of 7 control animals.

RESULTS

Lactatio sine graviditate occurring in early metoestrus was characterised more by a shifted P4:E2 ratio than by hyperprolactinaemia. Overall, the prolactin concentration in the peripheral blood was significantly increased. Analysis of the individual cases revealed that hyperprolactinaemia was present to varying degrees. It could be detected in almost all bitches that showed full symptomatology at the end of metoestrus or at the beginning of anoestrus. Only then clinical signs correlated with an increased prolactin concentration in the peripheral blood. In most cases, the estradiol-17β concentration was within the reference range.

CONCLUSION AND CLINICAL RELEVANCE

The study indicates that the administration of prolactin inhibitors alone is not indicated in all cases of lactatio sine graviditate and that the timepoint of onset of the clinically relevant symptoms and the current prolactin level should be taken into account in the treatment of affected bitches.

Malignant ventricular tachycardia in acromegaly: a case report

CONTEXT

In patients with acromegaly, cardiovascular complications are the main cause of death; sudden death has been associated with ventricular tachyarrhythmias. In other patients with life-threatening malignant ventricular tachyarrhythmias, surgical placement of an implantable cardioverter-defibrillator (ICD) has proved highly effective in reducing sudden death rates.

CASE REPORT

The present article reports the case of a 50-year-old male acromegalic patient who presented symptoms of syncope induced by ventricular tachycardia. An ICD was surgically implanted and a pituitary adenoma, which was responsible for the acromegaly, was completely removed in the same procedure. The surgery was successful and the ventricular arrhythmias were effectively terminated. During six months of follow-up, no documented arrhythmic episodes occurred.

CONCLUSION

In patients with acromegaly, malignant ventricular tachyarrhythmia might be effectively controlled by implantation of an ICD and surgical removal of the pituitary adenoma.

Induction of fertile oestrus in the bitch using Deslorelin, a GnRH agonist

Oestrus induction in various canine breeds was attempted in 32 bitches. A group of 8 bitches were treated 80-160 d following their previous oestrus (G1) whereas a second group of 24 bitches (G2) were implanted 200-590 d following their previous oestrus. The treatment for each bitch consisted in one Deslorelin implant (Suprelorin® 4,7 mg, Virbac, France), inserted subcutaneously in the post-umbilical region. Ovulation, pregnancy rate and litter size were recorded. All bitches came in heat 4.3 ± 1.4 d after implantation (2-7 d). Ovulation was reported in 62.5% in G1 and 87.5% in G2. One bitch refused mating and since no AI was performed, she was not considered for further analysis. Pregnancy was obtained in 25% in G1 versus 78.3% in G2. Mean litter size was 6.7 ± 3.5 puppies (1-14). Luteal failure was suspected in 3 bitches, two that remained non-pregnant and one which aborted 58 d post-ovulation since the owner refused progesterone supplementation. Deslorelin implants can therefore be considered as a valuable alternative to induce fertile oestrus in bitches in anoestrus. Follow-up of the luteal phase is recommended, since some bitches might encounter luteal failure.

Effects of short-term hyper- and hypoprolactinaemia on hormones of the pituitary, gonad and -thyroid axis and on semen quality in male Beagles

Effects of a short-term hyper- and hypoprolactinaemia on serum concentrations of LH, testosterone and semen quality in six male Beagles were investigated. Blood samples were collected at 3-day intervals for 12 weeks. The time span was divided into five 3-week periods: pre-treatment, metoclopramide (MCP) treatment (0.2 mg/kg orally three times daily), cabergoline (CAB) treatment (5 microg/kg orally once daily), post-treatment 1 and post-treatment 2. In the latter, only semen characteristics were evaluated. Semen parameters were analyzed once per week during the whole 15-week investigation time. At the end of each period, the effects of a single intravenous injection of thyrotropin-releasing hormone (TRH; 10 microg/kg) on the secretion of prolactin (PRL), LH, testosterone, thyroid-stimulating hormone and thyroxine (T4) were investigated. Pre-treatment serum PRL concentration increased under MCP (p < 0.05), followed by a decrease under CAB administration (p < 0.05). Luteinizing hormone and testosterone concentrations were not affected. Except for straight-line sperm velocity, semen quality did not differ between collection periods. A single iv TRH injection induced a significant PRL increase at 20 min in all experimental periods except during CAB treatment. Luteinizing hormone and testosterone did not show clear TRH-related changes. Basic T4 levels were significantly reduced after CAB treatment (p < 0.05). The results of the present study demonstrate that MCP-induced short-term hyperprolactinaemia in male beagles does not seriously affect the hypothalamo-pituitary axis and semen quality.

Physiology of the canine anoestrus and methods for manipulation of its length

Progression from early to late anoestrus is characterized by the appearance of a larger number of gonadotrophin-releasing hormone (GnRH) pulses with a higher amplitude, an increase in the sensitivity of the pituitary to GnRH, an increase in ovarian responsiveness to gonadotrophins, and an increase in basal plasma follicle-stimulating hormone (FSH) concentration. A period of increased luteinizing hormone (LH) pulsatility has been observed shortly before the onset of pro-oestrus. Apart from these changes in the hypothalamus-pituitary-ovary axis, the initiation of a new follicular phase in the bitch is also stimulated by dopaminergic influences other than the accompanying plasma prolactin decrease. Metergoline, a drug which in a low dosage lowers the plasma prolactin concentration via a serotonin-antagonistic pathway, does not shorten the anoestrus; while bromocriptine, in a dosage insufficient to cause a decrease in the plasma prolactin concentration, does prematurely induce a follicular phase. These observations indicate that it is not the decrease in the plasma prolactin concentration, but another dopamine-agonistic influence that plays a crucial role in the transition to a new follicular phase. The dopamine-agonist induced oestrus is associated with a rapid rise in the basal plasma FSH concentration, similar to what is observed during the physiological late anoestrus. Administration of GnRH, eCG and oestrogens may also be used to induce oestrus but with variable results. Oestrus can be prevented surgically or medically, for which purpose progestagens are the most important drugs. The mechanism is still unclear, although it has been demonstrated that with continuing medroxyprogesterone acetate (MPA) treatment the FSH response to GnRH stimulation decreases and changes occur in the pulsatile release of the gonadotrophins. In general, LH pulses coincide with a FSH pulse, but during MPA treatment, LH pulses were observed while there was such a small increase in FSH that it was not recognized as significant FSH pulse.

Follicular development and plasma concentrations of LH and prolactin in anestrous female dogs treated with the dopamine agonist cabergoline

The effect of a daily administration of a dopamine agonist (cabergoline, 5 microg/kg) for 4 weeks, starting about 95 days after the end of estrus on follicular development and its relationship with LH and prolactin secretion has been investigated in two groups of anestrous bitches (Beagles and Greyhounds). Pro-estrus was detected in 80% (8/10) of beagles and 50% (3/6) of treated greyhounds. The mean inter-estrus interval of treated animals was 132+/-5.0 and 169+/-7.0 days for beagles and greyhounds, respectively, and in both this differed significantly from the cycle preceding treatment (192+/-9.0 and 198+/-12.0 days) and from that in untreated bitches (194+/-11.0 and 196+/-11.0 days for beagles and greyhounds, respectively (all comparisons at P<0.001). The interval from the beginning of treatment to pro-estrus in responding animals was 13.3+/-1.90 days in beagles and 20.3+/-1.70 days in greyhounds. Cabergoline increased (P<0.001) the length of pro-estrus (10.6+/-0.50 and 11.7+/-0.50 days) in the treated estrus cycle compared to the previous estrus cycle (8.4+/-0.30 and 8.8+/-0.40 days for in beagles and greyhound, respectively). Ovarian enlargement and follicle development was detected by ultrasound in 90% of treated beagles and in 83% of greyhound between the second and third weeks of treatment, but only 80% of beagles and 66% of treated greyhound displayed pro-estrus and estrus. In the treated bitches, mean plasma LH increased (P<0.001) before pro-estrus. There was high variability in mean plasma prolactin levels between animals. These data indicate that the administration of the dopamine agonist cabergoline to anestrous bitches increases mean LH plasma levels and induces follicular development shortly before pro-estrus but this activity is not always followed by pro-estrus and estrus. Finally, prolactin per se does not have a prominent role in the control of folliculogenesis in the bitch.

Estrus induction and synchronization in canids and felids

Indications for estrus induction in the dog and cat include potential missed breeding opportunities or conception failure, the treatment of primary or secondary anestrus, out-of-season breeding (feline) and synchronization of ovulation for embryo transfer programs. Reported methods for estrus induction in bitches and queens include the use of synthetic estrogens (diethylstilbesterol), dopamine agonists (bromocriptine and cabergoline), GnRH agonists (lutrelin, buserelin, fertirelin, deslorelin, and leuprolide), exogenous gonadotropins (LH, FSH, hCG, PMSG, and human menopausal gonadotropin) and opiate antagonists (naloxone). These methods vary widely in efficacy of inducing estrus as well as in the fertility of the induced estrus. The applicability of some of these methods for clinical practice is questionable. This review will summarize published reports on estrus induction in canids and felids, both wild and domestic, and provide an update on research using a long-acting injectable deslorelin preparation in bitches.

The effects of a low dose of cabergoline on induction of estrus and pregnancy rates in anestrous bitches

This is the first report of successful induction of normal estrus and ovulation in breeder bitches with as a low dose as 0.6 microg/kg/day of cabergoline formulation marketed for use in women. Sixty-one pure breed bitches from various breeds were used in the study at their already determined periods of anestrus. Twenty-four dogs formed the control group, while 37 bitches were administered with two different doses of cabergoline (recommended dose group, n=10, 5 microg/kg/day and low dose group, n=27, 0.6 microg/kg/day). Induced estrus rates and mean treatment and proestrus durations of dogs in these two dose groups were compared. At the second phase of the study, the effects of 500 IU human chorionic gonadotropin (hCG) administered on days 1 and 3 of estrus induced by the low dose of cabergoline, on the duration of behavioral estrus, ovulation rates, pregnancy rates and the number of offspring were investigated. For this purpose, the dogs with signs of proestrus (22/27) following the treatment in the low dose group were assigned into two subgroups. Five hundred IU of hCG (Pregnyl, Organon, Turkey) was intramuscularly administered to eight of these dogs [low dose (hCG+) group] on days 1 and 3 of estrus. The remaining 14 dogs were not treated with hCG [low dose (hCG-) group]. An aqueous solution of cabergoline (Dostinex, Pharmacia, Italy) was orally administered until 2 day after the onset of proestrus or for a maximum of 42 days. Blood samples were taken daily from all treatment and 11 control bitches during the first five days of behavioral estrus to measure progesterone concentrations. In the recommended dose and low dose groups, estrus was induced between days 8-45 and 4-48 (mean: 23.63+/-14.33 and 24.41+/-14.31 days), in the ratio of 80.0 and 81.5%, respectively (p>0.05). In both dose groups, post-treatment interestrous intervals were significantly shorter than both those of the control group and their own pre-treatment interestrous intervals (p<0.05). Ovulation rates, pregnancy rates and mean number of offspring delivered by the dogs in the recommended dose, low dose (hCG-), low dose (hCG+) and control groups were found to be similar (p>0.05). However, the mean duration of behavioral estrus of the dogs in the low dose (hCG+) group was found to be significantly longer compared to dogs in all other groups (p<0.05). In both dose groups, no correlation could be found between the anestrus stages and treatment durations (p>0.05). Shortly, it has been concluded from the study that (1) normal and fertile estrus can be induced more economically in bitches during different stages of anestrus using as a low dose of 0.6 microg/kg of cabergoline formulation marketed for use in women, and that (2) hCG injections on days 1 and 3 of the estrus induced by this method has no positive effects on the ovulation rates, pregnancy rates and the number of offspring per pregnancy.

The effect of administering a dopamine agonist (Cabergoline) on follicular and luteal development during pro-estrus and estrus in the female greyhound

To study the effect of the dopamine agonist Cabergoline, on ovarian activity in the female dog during pro-estrus and estrus, 6 greyhounds were treated with 5 microg/kg per os of Cabergoline for 20 days beginning on the first day of pro-estrus; 6 animals were left untreated (controls). Ovarian morphology was determined by ultrasound examination once a day during pro-estrus and twice a day during estrus. Follicles were divided into three classes on the basis of their diameter: F1 (<3mm), F2 (3-6mm) and F3 (>6mm). The presence and diameters of post-ovulatory follicles (F-POST) and corpora lutea (CL) were also recorded. Blood samples were taken once a day during pro-estrus and twice a day during estrus. The plasma was assayed for LH, prolactin and progesterone by radioimmunoassay. There were no differences between Cabergoline-treated and control dogs in the duration of pro-estrus or estrus. There was a progressive increase in follicle diameter from the start of pro-estrus when follicles were mainly class F1 to the day of estrus when follicles were mainly class F3. Three days after the start of estrus, the first F-POST follicles were detected. This pattern of development continued and on day 5 the first CLs were detected. By day 9, only CLs were detected. The peak of pre-ovulatory LH was within 3 days of estrus and ovulation was detected in all animals within 3 days of the LH peak. There were no differences in LH concentrations between groups. Plasma prolactin levels varied between animals and were reduced in treated dogs, however, this was not statistically significant (P=0.12). Plasma progesterone levels were below 1.0 ng/ml before the LH surge and thereafter gradually increased. There were no differences in plasma progesterone concentrations between treated and control dogs. In conclusion these results show that the administration of the dopamine agonist Cabergoline during pro-estrus and estrus did not affect the duration of pro-estrus or estrus or the pattern of follicular and luteal development in female dogs.

Anoestrus in the Dog: a Fascinating Story

In the bitch, progression from early to late anoestrus is characterized by a higher amplitude and a larger number of gonadotrophin-releasing hormone (GnRH) pulses generated by the hypothalamus, an increase in the sensitivity of the pituitary to GnRH, and an increase in ovarian responsiveness to gonadotrophins. An increase in basal plasma follicle-stimulating hormone (FSH) concentration is a critical event required for initiation of folliculogenesis. A period of increased luteinizing hormone pulsatility has been reported shortly before the onset of pro-oestrus. Apart from these changes in the hypothalamic-pituitary-ovarian axis, there is also involvement of dopaminergic influences in the initiation of a new follicular phase in the bitch. Administration of the dopamine-agonists bromocriptine and cabergoline shortens the anoestrus and is associated with a decrease in the plasma prolactin concentration, suggesting that the shortened anoestrus is the result of suppression of prolactin secretion. Yet, the anoestrus is not shortened in bitches treated with metergoline, a drug, which in a low dosage lowers the plasma prolactin concentration via a serotonin-antagonistic pathway. In addition, under physiological conditions low plasma prolactin concentrations are found during the entire anoestrus. Furthermore, a low dosage of bromocriptine, insufficient to cause a decrease in the plasma prolactin concentration, prematurely induces folliculogenesis. These observations indicate that not the decrease in the plasma prolactin concentration, but another dopamine-agonistic influence plays a critical role in the transition to a new follicular phase. The dopamine-agonist induced shortening of the anoestrus is associated with a rapid rise in the basal plasma FSH concentration, similar to what is observed during the physiological late anoestrus. This observation underlines the importance of an increase in the circulating plasma FSH concentration in the initiation of folliculogenesis in the bitch.

Effects of the dopamine agonist cabergoline on the pulsatile and TRH-induced secretion of prolactin, LH, and testosterone in male beagle dogs

In the present study, the pulsatile serum profiles of prolactin, LH and testosterone were investigated in eight clinically healthy fertile male beagles of one to six years of age. Serum hormone concentrations were determined in blood samples collected at 15 min intervals over a period of 6 h before (control) and six days before the end of a four weeks treatment with the dopamine agonist cabergoline (5 microg kg(-1) bodyweight/day). In addition, the effect of cabergoline administration was investigated on thyrotropin-releasing hormone (TRH)-induced changes in the serum concentrations of these hormones. In all eight dogs, the serum prolactin concentrations (mean 3.0 +/- 0.3 ng ml(-1)) were on a relatively constant level not showing any pulsatility, while the secretion patterns of LH and testosterone were characterised by several hormone pulses. Cabergoline administration caused a minor but significant reduction of the mean prolactin concentration (2.9 +/- 0.2 ng ml(-1), p < 0.05) and did not affect the secretion of LH (mean 4.6 +/- 1.3 ng ml(-1) versus 4.4 +/- 1.7 ng ml(-1)) or testosterone (2.5 +/- 0.9 ng ml(-1) versus 2.4 +/- 1.2 ng ml(-1)). Under control conditions, a significant prolactin release was induced by intravenous TRH administration (before TRH: 3.8 +/- 0.9 ng ml(-1), 20 min after TRH: 9.1 +/- 5.9 ng ml(-1)) demonstrating the role of TRH as potent prolactin releasing factor. This prolactin increase was almost completely suppressed under cabergoline medication (before TRH: 3.0 +/- 0.2 ng ml(-1), 20 min after TRH: 3.3 +/- 0.5 ng ml(-1)). The concentrations of LH and testosterone were not affected by TRH administration. The results of these studies suggest that dopamine agonists mainly affect suprabasal secretion of prolactin in the dog.

Dopamine agonists, anti-progestins, anti-androgens, long-term-release GnRH agonists and anti-estrogens in canine reproduction: a review

Over the last 10 years, new drugs have been applied to canine reproduction, widening the spectrum of therapeutic possibilities for diseases that were previously surgically treated, and facilitating better control of the estrous cycle and fertility. Some are not approved for use in dogs; their use is experimental and further clinical trials are necessary. Dopamine agonists such as cabergoline, bromocriptine or metergoline are ergoderivative alkaloids that exert an anti-prolactinergic effect via stimulation of D2 pituitary receptors or inhibition of central serotoninergic ones. Their main indication is suppression of lactation. Anti-prolactinergic compounds have also been successfully used for pregnancy termination and shortening of interestrous intervals. Anti-progestins, (e.g. mifepristone and aglepristone) are synthetic steroids that bind with high affinity to progesterone (P4) receptors, preventing P4 from exerting its biological effects. Anti-progestins have been indicated in P4-dependent conditions, such as pregnancy termination, induction of parturition and the medical treatment of pyometra. Several groups of drugs have been described to have anti-androgenic properties through different mechanisms of action: progestins, receptor binding anti-androgens (e.g. flutamide), competitive enzyme inhibitors (e.g. finasteride), aromatase inhibitors, and GnRH agonists. Their main application is medical treatment of benign prostatic hyperplasia. Long-term release formulations of GnRH agonists (e.g. leuprolide or deslorelin acetate) postponed puberty and reversibly suppressed reproductive function in male and female dogs for periods exceeding 1 year. Anti-estrogens (e.g. clomiphene and tamoxifen citrate) are synthetic non-steroidal type I anti-estrogenic compounds that competitively block estrogen receptors with a combined antagonist-agonistic effect. In dogs, their action is more agonistic than antagonistic.