Heterogeneity of immunoreactive prolactin in the rat brain

Three immunoreactive prolactin proteins (24 Kd, 16 Kd, and 12 Kd) were identified in the rat brain using sodium dodecyl sulphate polyacrylamide gel electrophoresis, and western blot analyses. In male and female brains, the primary prolactin protein has a molecular weight of 24 Kd which is similar to that of pituitary prolactin. Two additional proteins with apparent molecular weights of 16 Kd and 12 Kd were also identified and were found in greater concentrations in the brain than in the pituitary, and were more predominant in the female brain. In addition, brain extracts proteolytically modify the 24K dalton PRL resulting in the formation of two fragments with apparent molecular weights of 16 and 8 Kd. These data indicate that the prolactin identified in the rat brain is similar to pituitary prolactin, and suggests, that like other PRL target tissues the brain may have the capacity to proteolytically modify prolactin.     

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

In order to investigate the effect of different doses of bromocriptine on plasma prolactin concentration and the interestrous interval, beagle bitches were treated twice daily with 5 microg (5-group), 20 microg (20-group), or 50 microg (50-group) bromocriptine per kg body weight orally, starting 28 days after ovulation. In the 5-group, the difference between the mean plasma prolactin concentration before and that during bromocriptine treatment was not significant. In contrast, mean plasma prolactin concentration decreased significantly after the start of bromocriptine treatment in the 20- and 50-groups. The mean interestrous interval was significantly shorter in all three groups than in untreated bitches in the same colony. The mean interestrous interval in the 20-group and that in the 50-group were similar, but both were significantly shorter than that in the 5-group. The results of this study indicate that bromocriptine shortens the interestrous interval in the bitch even when the dose is so low that it does not lower plasma prolactin concentration. Induction of estrus in the bitch by bromocriptine therefore involves a mechanism other than via the lowering of plasma prolactin concentration. Furthermore, this study shows that the extent of shortening of the interestrous interval by bromocriptine is dose dependent.     

Ovariectomy during the luteal phase influences secretion of prolactin, growth hormone, and insulin-like growth factor-I in the bitch

A decline in circulating progesterone concentration plays an important role in the ethiopathogenesis of pseudopregnancy in the bitch. Because growth hormone (GH) and prolactin (PRL) are essential for normal mammogenesis and the secretion of these hormones is influenced by changes in the circulating progesterone concentration, the purpose of this study was to investigate the effects of mid-luteal phase ovariectomy on the 6-h pulsatile plasma profiles of GH and PRL and the basal plasma concentrations of GH, PRL, and insulin-like growth factor-I (IGF-I) in six beagle bitches. Ovariectomy was followed by only mild or covert signs of pseudopregnancy. The sharp decrease of the plasma progesterone concentration was accompanied by decreased basal plasma concentrations of GH and IGF-I and a rise in basal plasma PRL concentration. GH and PRL were secreted in a pulsatile fashion both prior to and after ovariectomy. The mean basal plasma GH concentration was significantly higher before ovariectomy than on days 1 and 7 after ovariectomy. The mean area under the curve above the zero level (AUC(0)) for GH was significantly higher before than at 7 days after ovariectomy. The mean area under the curve above basal level (AUC(b)) and the frequency of GH pulses at 7 days after ovariectomy were significantly higher than before and 1 day after ovariectomy. Both the mean basal plasma PRL concentration and the mean AUC(0) for PRL increased after ovariectomy. In conclusion, ovariectomy of bitches in the mid-luteal phase stops progesterone-induced GH release from the mammary gland, as evidenced by the lowering of basal plasma GH levels, the recurrence of GH pulsatility, and the lowering of circulating IGF-I levels. The sudden lowering of plasma progesterone concentration is probably a primary cause of a prolonged increase in PRL secretion. These observations underscore the importance of similar, albeit less abrupt, hormonal changes in the cyclical physiological alterations in the mammary gland and in the development of pseudopregnancy.     

Pregnancy management in the bitch

Pregnancy management to optimize maternal and neonatal health begins with breeding management and the selection of normal, healthy brood stock in ideal body condition. After breeding, a commercial diet appropriate for reproduction and lactation should be fed. Typically these contain 29-32% protein of animal source, at least 18% fat, 20-30% carbohydrate, and essential vitamins, minerals and fatty acids. Pregnancy is confirmed approximately 25 d after breeding. A "maternity ward" and whelping box should be provided. Steady increases in caloric intake and body weight are expected as pregnancy progresses. Weight loss should not occur. Throughout pregnancy, changes in the bitch's attitude, activity, appetite, body weight, and physical findings should be monitored by the owner. If appetite and body weight do not continue to increase, or if any signs of illness develop, maternal health should be assessed with a complete physical examination and a CBC, biochemical profile, and free-catch urinalysis. Fetal health should be assessed with ultrasonography. Maternal or fetal abnormalities will put the pregnancy at risk. Impending parturition and the progress of labor and delivery can be monitored by assessing rectal temperature, serum concentrations of progesterone, and/or uterine and fetal monitors. This article reviews the physiology of canine pregnancy and parturition, and typical schemes used to manage normal canine pregnancy to optimize maternal and puppy health.     

Circadian rhythm of circulating corticosterone and prolactin levels in spontaneously hypertensive rats

Circulating levels of corticosterone and prolactin were measured by radioimmunoassay at hourly intervals during a 24 h period to establish the diurnal rhythm of these hormones in spontaneously hypertensive rats (SHR). Corticosterone levels exhibited a distinct circadian variation with concentrations reaching a zenith at 2000 h and a nadir at 1200 h in male and female SHR. Corticosterone levels in females were consistently greater than males. Circulating prolactin levels were greater during the light h than dark in the female; the opposite occurred in males. Measurement of pituitary prolactin content tended to be low when serum prolactin levels were high and vice versa. The circadian rhythm of circulating corticosterone and prolactin in the hypertensive SHR was found to be similar to the day-night patterns established for normotensive rats. However, these measurements were made under quiescent conditions. It is suggested that because SHR are hyper-responsive to stress and because corticosterone and prolactin have synchronous effects on stress-induced adrenal steroidogenesis, further investigation of prolactin and corticosterone may reveal a participatory role of these hormones in the pathogenesis of the genetically-programmed hypertension of SHR.     

Hypoluteoidism in a bitch

Hypoluteoidism is characterized by insufficient secretion of progesterone by the corpora lutea during pregnancy. The resulting failure to maintain progesterone concentration above a critical level presumably could lead to fetal resorbtion as well as frank abortion. This report concerns a 2.5-year-old Bernese Mountain dog with a history of two previous pregnancies ending in abortion around Day 50 of pregnancy. The bitch was initially presented 2 days after mating. Physical and gynecological examination revealed no abnormalities. The infectious causes of abortion in the bitch, Brucella canis and herpesvirus, were excluded using serology. On Day 26 after mating, ultrasonography confirmed a pregnancy with at least four living fetuses. During the remaining part of the pregnancy repeated transabdominal ultrasonography and plasma progesterone measurements, using a RIA, were performed. On Day 42, ultrasonography revealed living fetuses but plasma progesterone concentration had decreased to 8.3 nmol/L, which is just above the threshold necessary to maintain a vital pregnancy. Oral treatment with 0.1mg medroxyprogesterone acetate (MPA) per kg body weight, once daily, was started and continued until Day 58 in order to prevent abortion due to progesterone deficiency. The endogenous plasma progesterone concentration decreased further, but pregnancy was maintained. On Day 59 a cesarean section was performed because of dystocia and four living and one dead pup were delivered. One puppy had severe facial malformations and was euthanised. The premature decrease in plasma progesterone concentration while ultrasonography demonstrated that the fetuses were still alive, and the maintenance of pregnancy during administration of MPA, strongly support the diagnosis of hypoluteoidism.     

Luteal function in the bitch: changes during diestrus in pituitary concentration of and the number of luteal receptors for luteinizing hormone and prolactin

The concentration of unoccupied luteal receptors for luteinizing hormone (LH) and prolactin, and the concentration of these two hormones in the pituitary was determined in 11 groups of bitches (n = 3 or 4/group) representing stages from proestrus through Day 80 of diestrus. Despite dramatic changes in serum concentrations of progesterone, the concentration of luteal receptors for LH and prolactin was quite constant throughout the entire luteal phase. In association with the ovulatory surge of LH, pituitary concentration of LH decreased abruptly from proestrus to Day 2 of diestrus, and was then gradually replenished during the remainder of diestrus. The concentration of prolactin in the pituitary did not vary significantly from proestrus through late diestrus.     

Signs of impending parturition in the laboratory bitch

The most consistent and reliable physical sign of impending parturition in pregnant laboratory beagle bitches was palpable relaxation of pelvic and abdominal musculature. A drop in rectal temperature was of some value but was found to be too variable between individuals to use as the sole criterion. Abrupt changes in attitude or appetite were the chief behavioral changes observed. Since the institution of a standardized record form for all pregnant dogs, 15 consecutive term litters have been successfully derived from pregnant dogs into gnotobiotic life isolation units.     

Inhibition of lactation in the Beagle bitch with the prolactin inhibitor cabergoline (FCE 21336): Dose response and aspects of long-term safety

Sixteen healthy, lactating Beagle bitches with litters of three to six pups were assigned to four treatment groups for one daily oral treatment of cabergoline in an oily solution (0, 1.25, 2.50 or 5.0 mcg/kg body weight (BW) for 5 d, commencing on Day 8 of lactation. Bitches and all their puppies were weighed daily for 2 d before treatments started, and for 10 d thereafter. Technicians rated daily treatment effects on maternal health, maternal behavior and mammary glands, using a scoring system. Treatments had no effect on maternal health, maternal body weight, and maternal behavior. Treatments with the two higher doses caused a reaction and a regression of the mammary glands in a dose-related fashion, resulting in cessation of lactation with 5 mcg/kg BW. Maternal treatment did not adversely affect the puppies' health, and no puppy was lost during the trial. However, average daily weight gains of puppies declined with increasing levels of cabergoline, causing significant weight losses in the 2.5 and 5 mcg/kg treatment group. This became evident after 2 d of treatment. To save the puppies in the highest dosage group, hand-feeding, and later, crossfostering, had to be used with all litters, starting on Day 3 or 4 of treatment. Weight losses were dose-related with an ED(50) of 1.5 mcg/kg/d and persisted for at least 24 h after treatment had ceased. Since puppies were left with their mothers to provide a continued suckling stimulus, lactation rebounded in all bitches treated with 2.5 mcg/kg, but only in two of four bitches treated with 5 mcg/kg. All bitches returned to estrus at their normal intervals. Fertility and fecundity at the next breeding were undisturbed.     

High-risk pregnancy and hypoluteoidism in the bitch

High-risk pregnancies are those in which the prevalence of maternal, fetal and/or perinatal morbidity or mortality is likely to be higher than that of the general obstetrical population. Some maternal characteristics associated with risk to maternal, fetal and/or perinatal health are readily identifiable prior to conception, such as advanced maternal age, brachycephalic breed, or a previous history of pregnancy loss. Others, such as gestational diabetes or a singleton litter, are recognized after conception. Early recognition of the problem (i.e. the risk), anticipation of the potential sequelae, and development of an aggressive management scheme are essential for a successful outcome of a high-risk pregnancy. A previous history of pregnancy loss is a high-risk factor for recurrence during subsequent pregnancies. Infection is a common cause. In some instances, recurrent pregnancy loss is associated with low serum concentrations of progesterone. Although the mechanism(s) by which this occurs is not fully understood, the situation has been called hypoluteoidism. Whatever the cause of the risks to pregnancy, the goals of managing high-risk pregnancies are to optimize maternal, fetal and perinatal health, so as to maintain maternal health throughout pregnancy and lactation and maximize the number of healthy pups surviving to weaning age.     

Factors affecting gestation duration in the bitch

A retrospective analysis was performed to determine the effects of age, breed, parity, and litter size on the duration of gestation in the bitch. Bitches at two locations were monitored from breeding to whelping. A total of 764 litters whelped from 308 bitches (36 large hounds, 34 Golden Retrievers, 23 German Shepherd Dogs (GSD), and 215 Labrador Retrievers). By breed, the number of whelpings was 152, 72, 58, and 482 for the hounds, Golden Retrievers, German Shepherd Dogs, and Labrador Retrievers, respectively. Whelping was predicted to be 57 d from the first day of cytologic diestrus in the hounds or 65 d from the initial progesterone rise in the other breeds. The average gestation duration (calculated as 8 d prior to Day 1 of cytologic diestrus in hounds or measured from the initial progesterone rise in other breeds) by breed (days +/- S.D.) was 66.0 +/- 2.8, 64.7 +/- 1.5, 63.6 +/- 2.1, and 62.9 +/- 1.3 for the hounds, Golden Retrievers, German Shepherd Dogs, and Labrador Retrievers, respectively. The relationship of age, breed, parity, and litter size with the difference in gestation duration was evaluated using log linear modeling. Age or parity had no effect on gestation duration. Compared to Labrador Retrievers, the German Shepherd Dogs, Golden Retrievers and hounds were more likely to have a longer gestation duration; three, four and nearly eight times as likely, respectively. Bitches whelping four or fewer pups were significantly more likely to have a longer gestation duration than those whelping five or more pups; the prolongation averaging 1 d.     

Effects of TRH on circulating growth hormone, prolactin and triiodothyronine levels in the bovine.

The effects of administration of synthetic thyrotropin-releasing hormone (TRH) on circulating growth hormone (GH), PROLACTIN (PRL) and triiodothyronine (T3) levels of lactating dairy cows, non-lactating dairy heifers, and beef cows were studied. Intravenous administration of 0.1, 1, and 5 microgram of TRH per kg of body weight (bw) elevated plasma GH and PRL levels of lactating cows within 5 min. The plasma GH and PRL levels increased in proportion to the dose of TRH and reached a peak 10 to 30 min after TRH injection. Intravenous administration of 1 microgram of TRH per kg of bw to 7 non-lactating heifers, 14 lactating dairy cows, and 5 non-lactating beef cows elevated plasma GH level to peak values after 15 min, the increase rates being 6.9, 5.6, and 3.8 times as high as those in the pretreatment levels. The mean maximum vale was also in that order. Plasma T3 levels of non lactating dairy heifers at pre- and post-injection of TRH were significantly higher than those of lactating cows. The peak values of plasma PRL were obtained between 5 to 30 min after TRH administration. The increase rates of lactating dairy cows, heifers, and beef cows were 19.2, 13.9, and 20.9 times as high as those in the pretreatment. In contrast to GH and T3, plasma PRL levels of both pre- and post-injection with TRH in lactating cows and heifers were significantly higher in May than in October, though the increase rates were similar. Plasma PRL levels of lactating dairy cows at pre- and post-injection with TRH were significantly higher than those of non-lactating heifers. Subcutaneous administration of TRH was also effective to increase plasma TH, rl, and T3 levels in lactating cows. No significant change of GH or PRL response to TRH was observed after a short-term pretreatment of thyroid hormones.     

Effects of prolonged artificial photoperiod on circulating prolactin and melatonin levels in seasonal ewes

Crossbred ewes exposed to long days for 46 months prior to photoperiod reversal showed no alteration in the duration or amplitude of the circulating melatonin peak between 24 and 46 months of continuous long day exposure. By 3 months after photoreversal to short days, both the amplitude and duration of the peak had adapted to the new scotophase. In short day treated ewes, the melatonin peak was abolished by 46 but not 24 months of short day exposure, and was not fully restored in all ewes 3 months after photoreversal. Mean prolactin levels over 24 h remained high up to 46 months of long day treatment, and declined 3 months after short day exposure. Conversely, mean prolactin levels remained low up to 46 months of short day treatment, increasing 3 months after exposure to long days. Thus: (i) depletion of the melatonin-synthesizing capability of the ovine pineal gland by prolonged exposure to long nights is not completely reversed after 3 months of continuous long day exposure, and (ii) a nocturnal melatonin peak is not essential for maintenance of plasma prolactin levels under these conditions.Special issue dedicated to Dr. Lawrence Austin.     

Reproductive cycles of the domestic bitch

Domestic dogs are monoestrous, typically non-seasonal, polytocous, spontaneous ovulators and have a spontaneous luteal phase slightly longer (by approx 5 day) than the 64±1day luteal phases of a 65±1day pregnancy, a phase followed by an obligate anestrus before the next 2-3 week "heat" (proestrus-estrus). The resulting inter-estrus intervals of 5-12 months are variable among bitches, commonly 6-7 months, and range from highly variable to regular (to perhaps within±5-10 day of sequential 7 month cycle, for instance) within bitches, and across studies and do not vary significantly between pregnant and non-pregnant cycles. Hormone levels reported are those observed in this laboratory using previously reported assays and canine gonadotropin standards unless stated otherwise. Endocrine sequences for dog cycles are not unlike those of many other mammals, including selection of ovulatory follicles by increased LH pulsatility, the occurrence of estrus behavior and LH surge during a decline in the estrogen: progestin ratio, a pronounced preovulatory luteinization as in humans and rodents, and luteotrophic roles for both LH and prolactin. Non-pregnant bitches have a spontaneously prolonged luteal phase, often longer and with a more protracted decline in serum progesterone than in pregnancy as there is no uterine luteolytic mechanism. The obligate anestrus of 8-40 weeks is terminated by poorly understood interactions of environment (e.g. pheromones, possibly photoperiod) and a potential endogenous circannual cycle in sensitivities of hypothalamic dopaminergic, serotonergic and/or opioid pathways.     

True vaginal prolapse in a bitch

Frequently, vaginal fold prolapse is the protrusion of edematous vaginal tissue into and through the opening of the vulva occurring during proestrus and estrus stages of the sexual cycle. True vaginal prolapse may occur near parturition, as the concentration of serum progesterone declines and the concentration of serum oestrogen increases. In the bitch, this type of true vaginal prolapse is a very rare condition.

This short communication describes a 5-year-old female, cross-breed dog in moderate condition, weighing 33 kg, with distocia and true vaginal prolapse. Abdominal palpation and transabdominal ultrasonography revealed live and dead foetuses in the uterine horns. One dead and four live fetuses were removed from uterus by cesarean section. The ovariohysterectomy was performed after repositioning the vaginal wall with a combination of traction from within the abdomen and external manipulation through the vulva. Re-occurrence of a vaginal prolapse was not observed and the bitch recovered completely after the surgical therapy.

Compared to other vaginal disorders, vaginal prolapse is an uncommon condition in the bitch. In the present case, extreme tenesmus arising from distocia may have predisposed to the vaginal prolapse. The cause of dystocia was probably the disposition of the first foetus. We concluded that the vaginal prolapse was the result of dystocia in the present case.     

Luteal function of induced corpora lutea in the bitch

Nineteen anestrous bitches with a mean of 22 kg body weight and ranging from 2 to 4 years of age were induced to exhibit estrus and ovulate using PMSG and HCG. Twelve days after the first day of estrus, bitches were assigned to four treatment groups. Group (A) consisted of six bitches, Group (B) of five bitches and Groups (C) and (D) of four bitches each. At this time, bitches in Groups (A), (B) and (C) were laparotomized and those assigned to Groups (A) and (B) were bilaterally hysterectomized leaving the cervix and oviducts intact. Although bitches in Group (C) were laparotomized, they were not hysterectomized. Group (D) bitches were not subjected to any surgical procedures. Homologous uterine extract was prepared from each bitch in Group (A) and administered intramuscularly beginning on day 25 (day 0 = first day of estrus) and continued every other day for 61 days post-estrus. Bitches in Group (B) were similarly injected with equal volumes of 0.9% saline. Blood samples, obtained prior to laparotomy and every other day for 85 days thereafter, were assayed for plasma progesterone concentrations using radioimmunoassay. One bitch in each of Groups (A) and (D) did not form luteal tissue following treatment with PMSG and HCG although both bitches exhibited estrus following treatment. All other bitches showed an increase in progesterone levels (4 to 19 ng/ml) between the first day of estrus and 10 days post-estrus. Thereafter, progesterone levels progressively declined in all groups with levels below 1 ng/ml between 38 to 40 days post-estrus. Results of this study suggested that CL formed in the bitch following PMSG and HCG treatment have a reduced function compared to non-induced CL of a normal, non-fertile estrous cycle. Such premature CL regression appears to be independent of the presence or absence of the uterus.