Patterns Of Prolactin Secretion Research Articles

Prolactin secretion pattern among female flight attendants.

Epidemiological observations indicate that female flight attendants are exposed to some reproductive and endocrine system disturbances. The aim of the study was to determine the incidence of hyperprolactinemia among female flight attendants, and to identify factors affecting the secretion of prolactin in female flight attendants working within 1 time zone as well as on long-distance flights. The cross-sectional study covered 103 women aged 23-46 years. The study group (I) was divided into 2 subgroups: subgroup Ia comprising female flight attendants flying within 1 flight zone, and subgroup Ib composed of female flight attendants working on long-distance flights. The control group (II) included women of reproductive age who sought medical assistance due to marital infertility in whom the male factor was found to be responsible for problems with conception in the course of the diagnostic process. The assessment included: age, the body mass index, menstrual cycle regularity, the length of service, the frequency of flying, the prolactin, estradiol and progesterone concentrations, and the result of endometrial biopsy. Descriptive and inferential statistics methods were used to compile the data. The incidence of hyperprolactinemia in the female flight attendants (46%) was significantly higher than in the control group (9%), p < 0.001. Differences between subgroups Ia and Ib regarding individual concentrations were not statistically significant (p = 0.425). Hyperprolactinemia among the female flight attendants working ≥15 years is present slightly more often than in those working <15 years: 46% vs. 45% (p > 0.05). No significant difference was revealed in the secretion of prolactin between the study participants spending <60 h/month flying and those spending ≥60 h/month flying (p > 0.05). Hyperprolactinemia is more common in female flight attendants than in the general population. High values of prolactin concentration in flight attendants are rarely manifested in clinical symptoms. The frequency of flying and the length of service do not affect the development of hyperprolactinemia or the mean prolactin concentration. Int J Occup Med Environ Health. 2021;34(3):351-61.

Patterns of prolactin secretion

Prolactin is pleotropic in nature affecting multiple tissues throughout the body. As a consequence of the broad range of functions, regulation of anterior pituitary prolactin secretion is complex and atypical as compared to other pituitary hormones. Many studies have provided insight into the complex hypothalamic-pituitary networks controlling prolactin secretion patterns in different species using a range of techniques. Here, we review prolactin secretion in both males and females; and consider the different patterns of prolactin secretion across the reproductive cycle in representative female mammals with short versus long luteal phases and in seasonal breeders. Additionally, we highlight changes in the pattern of secretion during pregnancy and lactation, and discuss the wide range of adaptive functions that prolactin may have in these important physiological states.

Abstract A18: A novel, human-compatible mouse model for preclinical research on prolactin in breast cancer

Abstract Over 90% of all human breast cancers express receptors for prolactin (PRL). This mitogenic hormone has been associated with an increased risk for breast cancer (as supported by epidemiological and molecular biology research). Despite this evidence, knowledge of the precise mechanisms of action for PRL in human breast cancer is limited. This is likely due to the lack of a suitable experimental model for studying the potential role of PRL in breast cancer growth and metastasis in vivo. For other reproductive hormones, the research model that has proven to be critical for preclinical studies of cancer is the grafting of human cancer cells into immunodeficient mice. Currently, no such xenograft model exists for the study of human PRL (hPRL) in breast cancer. The primary reason for this is the significant structural differences between rodent and hPRL. The mouse PRL (mPRL) hormone does not activate the hPRL receptor. Thus, grafted human cancer cells cannot respond to circulating PRL produced by the mouse host. To address this void in the repertoire of research tools, we have generated a novel set of mouse strains that have been “humanized” with regard to the structural gene, tissue expression, and secretory patterns of PRL. These mice were created using bacterial artificial chromosome technology and have been crossed onto the mouse PRL knockout background, resulting in mice that synthesize and secrete hPRL in the absence of mPRL. Our characterization studies demonstrate that the hPRL within the mice is: (1) expressed in a human-like pattern (including local production in the mammary gland), (2) secreted in a physiological fashion, and (3) controlled by known regulators (estrogen / dopamine). Further, we have shown that the hPRL produced in the mice is fully bioactive at the hPRL receptor within human breast cancer cells (T47D). We propose that these innovative models will be superior tools for examining the effects of hPRL on the growth and metastasis of human breast cancer xenografts. To this end, we have bred these mice onto the NOD/SCID immunodeficient background to allow for such preclinical studies of PRL in cancer. These novel mouse lines represent a major advancement in the research models available for the study of human breast cancer. As such, we expect that their use will have a significant impact on future diagnosis, prognosis and treatment of hormone-dependent breast cancers. Citation Format: Heather R. Christensen, Michael K. Murawsky, Karen A. Gregerson. A novel, human-compatible mouse model for preclinical research on prolactin in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr A18.

Pattern of Prolactin Secretion after Normal Vaginal Delivery and in Cesarean Delivery

ABSTRACTProlactin (PRL) is hormone of multiple biological actions and is best known for its role in milk production. This hospital-based study was undertaken to review the impact of PRL hormone in vaginal delivery and cesarean delivery. Our study is meant to create awareness in the society to promote breast feeding and the importance of promoting normal vaginal delivery whenever possible. In this study, we investigated the serum PRL values using enzyme-linked immunoflow assay method in 101 women who underwent normal (56) and cesarean delivery (45) in obstetrics and gynecology department of Kannur Medical College, Anjarakandy. Serum PRL at 24 and 48 hours blood sample was estimated among the two groups, mean PRL in vaginal delivery 24 hours 359.46 ± 119.70 ng/ml, 48 hours 386.67 ± 135.66 ng/ ml and in cesarean delivery 24 hours 245.49 ± 115.49 ng/ml, 48 hours 282.92 ± 69.59 ng/ml. The values of serum PRL are found to be significantly higher in the vaginal delivery group (p &lt; 0.001) as compared with the cesarean section group. Through this study, we concluded that the mothers who delivered by cesarean section had decreased PRL levels than the women who delivered vaginally which may have a significant role in establishment of breastfeeding.How to cite this articleManapatt AK, Anoop L, Tharammal D, Sathyapal A, Muneer Y. Pattern of Prolactin Secretion after Normal Vaginal Delivery and in Cesarean Delivery. Int J Infertility Fetal Med 2014;5(1):15-17.

Corticosterone Predicts Foraging Behavior and Parental Care in Macaroni Penguins

Corticosterone has received considerable attention as the principal hormonal mediator of allostasis or physiological stress in wild animals. More recently, it has also been implicated in the regulation of parental care in breeding birds, particularly with respect to individual variation in foraging behavior and provisioning effort. There is also evidence that prolactin can work either inversely or additively with corticosterone to achieve this. Here we test the hypothesis that endogenous corticosterone plays a key physiological role in the control of foraging behavior and parental care, using a combination of exogenous corticosterone treatment, time-depth telemetry, and physiological sampling of female macaroni penguins (Eudyptes chrysolophus) during the brood-guard period of chick rearing, while simultaneously monitoring patterns of prolactin secretion. Plasma corticosterone levels were significantly higher in females given exogenous implants relative to those receiving sham implants. Increased corticosterone levels were associated with significantly higher levels of foraging and diving activity and greater mass gain in implanted females. Elevated plasma corticosterone was also associated with an apparent fitness benefit in the form of increased chick mass. Plasma prolactin levels did not correlate with corticosterone levels at any time, nor was prolactin correlated with any measure of foraging behavior or parental care. Our results provide support for the corticosterone-adaptation hypothesis, which predicts that higher corticosterone levels support increased foraging activity and parental effort.

Prolactin secretory rhythm in women: immediate and long-term alterations after sexual contact

Prolactin (PRL) is one of the most versatile hormones in the mammalian body, affecting reproductive, sexual and other functions. In rats, mating or vaginocervical stimulation activates a characteristic PRL secretory pattern for several days, which is essential for successful reproduction. Although the underlying mechanisms appear to be different, PRL is also crucial for human fertility. We have detected a PRL increase in women induced by sexual intercourse. Extending these findings, the current study aimed at analyzing the PRL secretory rhythm after sexual contact, in order to elucidate whether human females also show long-term alterations of the PRL secretory pattern. In a pilot study, serial blood samples were taken from women (n= 7) in mid-cycle to assess changes in PRL secretory rhythm induced by sexual intercourse, during a period of 32 h. Compared with control condition, sexual intercourse with orgasm induced not only the well-established immediate PRL increase of ~300% but also an additional PRL elevation around noon of the next day (P< 0.05). These fluctuations were measured on top of the regular circadian rhythm of PRL, manifested as a surge early in the morning. We are able to demonstrate a long-term change in the PRL secretory rhythm after sexual intercourse with orgasm in females, suggesting memory effects. We hypothesize that the additionally secreted PRL could be beneficial for decidualization and implantation. Further studies with more participants are required to investigate in detail the implications of such effects on reproductive success in humans.

Evidence that hyperprolactinaemia is associated with ovarian acyclicity in female zoo African elephants

African elephants of reproductive age in zoos are experiencing high rates of ovarian cycle problems (>40%) and low reproductive success. Previously, our laboratory found that 1/3 of acyclic females exhibit hyperprolactinaemia, a likely cause of ovarian dysfunction. This follow-up study re-examined hyperprolactinaemia in African elephants and found the problem has increased significantly to 71% of acyclic females. Circulating serum progestagens and prolactin were analysed in 31 normal cycling, 13 irregular cycling and 31 acyclic elephants for 12 months. In acyclic females, overall mean prolactin concentrations differed from cycling females (P < 0.05), with concentrations being either higher (n = 22; 54.90 ± 13.31 ngmL(-1)) or lower (n = 9; 6.47 ± 1.73 ngmL(-1)) than normal. No temporal patterns of prolactin secretion were evident in elephants that lacked progestagen cycles. In cycling females, prolactin was secreted in a cyclical manner, with higher concentrations observed during nonluteal (34.38 ± 1.77 and 32.75 ± 2.61 ngmL(-1)) than luteal (10.51 ± 0.30 and 9.67 ± 0.42 ngmL(-1)) phases for normal and irregular females, respectively. Of most concern was that over two-thirds of acyclic females now are hyperprolactinemic, a dramatic increase over that observed 7 years earlier. Furthermore, females of reproductive age constituted 45% of elephants with hyperprolactinaemia. Until the cause of this problem is identified and a treatment is developed, reproductive rates will remain suboptimal and the population nonsustaining.

Prolactin secretion patterns: basic mechanisms and clinical implications for reproduction

Prolactin (PRL) is one of the most versatile hormones in the mammalian body affecting reproductive, sexual, metabolic, immune, and other functions. It is therefore not surprising that the neural control of PRL secretion is complex, involving the coordinated actions of several hypothalamic nuclei. A plethora of experimental data exists on the hypothalamic control of hormone secretion under various physiological stimuli. There have been even mathematical models and computer studies published, which help to understand the complex hypothalamic-pituitary network. Nevertheless, the putative role of PRL for human reproduction still has to be clarified. Here, we review data on the underlying mechanisms controlling PRL secretion using both experimental and mathematical approaches. These investigations primarily focus on rhythmic secretion in rats during early pregnancy or pseudopregnancy, and they point to the important role of oxytocin as a crucial PRL-releasing factor. Recent data on human studies and their theoretical and clinical implications are reviewed as well. In particular, studies demonstrating a sustained PRL surge after sexual climax in males and females are presented, indicating possible implications for both sexual satiation and reproductive functions. Taking these data together, there is evidence for the hypothesis that the PRL surge induced by sexual activity, together with the altered PRL rhythmic pattern, is important for successful initialization of pregnancy not only in rodents but also possibly in humans. However, further investigations are needed to clarify such a role in humans.

Characteristics of prolactin-releasing response to salsolinol in vivo in cattle

The aims of the present study were to clarify the effect of salsolinol (SAL), a dopamine (DA)-derived endogenous compound, on the secretion of prolactin (PRL) in cattle. The experiments were performed from April to June using calves and cows. A single intravenous (i.v.) injection of SAL (5 mg/kg body weight [BW]) or sulpiride (a DA receptor antagonist, 0.1 mg/kg BW) significantly stimulated the release of PRL in male and female calves ( P < 0.05), though the response to SAL was smaller than that to sulpiride. The secretory pattern of PRL in response to SAL or sulpiride in female calves resembled that in male calves. A single i.v. injection of SAL or sulpiride significantly stimulated the release of PRL in cows ( P < 0.05). There was no significant difference in the PRL-releasing response between the SAL- and sulpiride-injected groups in cows. A single intracerebroventricular injection of SAL (10 mg/head) also significantly stimulated the release of PRL in castrated calves ( P < 0.05). These results show that SAL is involved in the regulatory process for the secretion of PRL, not only in male and female calves, but also in cows. The results also suggest that the potency of the PRL-releasing response to SAL differs with the physiological status of cattle.

The effect of 6-hydroxydopamine infusion into the third cerebral ventricle on the plasma prolactin levels in anoestrous ewes subjected to prolonged and repeated stress.

The effect of 6-hydroxydopamine (6-OHDA) infusion into the third cerebral ventricle on the secretion pattern of prolactin in anoestrous sheep, subjected to repeated and prolonged stress-stimuli was followed. On the 12-15 th day after the infusion of 6-OHDA into the third cerebral ventricle and after having tested the effect of this infusion on plasma prolactin concentration, the animals were subjected to mild electric footshocks 9 hrs daily (9 a.m.-6 p.m.) for 3 consecutive days. Infusion of 6-OHDA induced a very high rise of plasma prolactin values by about 3 times as compared to those found before infusion (from 118.2 +/- 39.5 to 338.9 +/- 81.7 ng/ml mesor 24 h). On the other hand, the response of the animals pretreated with 6-OHDA to electric stimulation was characterized by the lack of changes in plasma prolactin concentration; their plasma hormone concentrations were neither raised during stimulation nor decreased after the stimulation and were maintained during all these days nearly at the same level as after the infusion of 6-OHDA. Central mechanisms which could account for the so high and prolonged elevation of plasma prolactin concentration after the infusion of 6-OHDA and for the lack of its rise under conditions of prolonged stress are discussed.

Differential behavioural and hormonal responses to two different stressors (footshocking and immobilization) in sheep.

Two different stressors footshocking and immobilization applied for 3 days induced in sheep differential behavioural and hormonal responses in cortisol and prolactin secretion. Immobilization drastically disturbed rumen motoric activity (significantly attenuated its contractions), caused loss of appetite and severe general depression. Footshocking did not induce any of these symptoms. Immobilization induced 2-3 fold higher rise of plasma cortisol mesors on the days of stressing as compared to footshocking. On the poststressing days after footshocking as well as after immobilization plasma cortisol mesors fell to 50% of the prestimulatory values. The rise of plasma prolactin mesors in footshocked and in immobilized animals on the days of stressing was nearly of the same magnitude. However, a significant difference in the response of prolactin secretion between footshocked and immobilized animals occurred in the circadian rhythmicity of the hormone secretion. Footshocking induced circadian rhythmicity with characteristic acrophases, while immobilization did not induce the circadian pattern of prolactin secretion. An attempt of interpretation of the described phenomena has been undertaken.

Effect of an Injectable Cabergoline Formulation on Serum Prolactin (PRL) and Milk Secretion in Early Postpartum Beagle Bitches

This study was conducted in order to evaluate effects on prolactin (PRL) concentration and mammary milk secretion of an injectable cabergoline formulation administered to five lactating Beagle bitches during early postpartum (PP). Bitches were bled twice daily (from PP day 3 to PP day 12) and then daily (from PP day 13 to PP day 16) to assay serum PRL. On PP day 6, a subcutaneous (SC) injection of 0.1 ml/kg of placebo was administered. On PP day 9, a SC 0.1 ml/kg dose of injectable cabergoline was administered. All bitches were checked for milk production, using a clinical scoring in order to quantify milk expression from each teat. A circadian variation of serum PRL was evident during the 6 days of pre-treatment monitoring. The day after cabergoline injection, an 80% decrease of PRL serum concentration was observed (p < 0.05). The circadian oscillatory pattern of PRL secretion disappeared after administration of cabergoline, and PRL values remained significantly lower than in the previous days for the first 60 h following treatment (p < 0.001). Milk production was drastically reduced when comparing pre-treatment to post-treatment scores (p < 0.001). A single dose of injectable cabergoline caused a significant reduction in serum PRL concentration and a significant reduction in milk flow. The injectable formulation of cabergoline appeared to be safe and well tolerated.

Cadmium exposure disrupts GABA and taurine regulation of prolactin secretion in adult male rats

This work was undertaken to evaluate the possible effects of cadmium exposure on 24 h changes of gamma-aminobutyric acid (GABA) and taurine median eminence and pituitary contents. Also the possible alterations of the regulatory mechanisms of GABA and taurine on prolactin secretion were evaluated. Adult male rats were given cadmium at a dose of 25 mg/l of cadmium chloride in the drinking water for 30 days. Control age-matched rats received cadmium free water. Metal exposure induced the appearance of a maximal value of prolactin at 08:00 h. In median eminence, cadmium abolished the GABA and taurine maximal values and decreased GABA and taurine mean levels. In the anterior pituitary, cadmium treatment phase advanced 12 h the peak observed in controls at 00:00 h for both amino acids. There was a positive correlation between GABA and taurine contents in median eminence and the anterior pituitary in both control and cadmium-exposed animals. However, the correlation between GABA or/and taurine with prolactin levels disappeared in cadmium-exposed animals. These results suggest that cadmium exposure affects GABA and taurine daily pattern in the median eminence and anterior pituitary, and those changes explain, at least in part, the modification in the regulatory pattern of prolactin secretion.

Pregnancy‐Induced Adaptation in the Neuroendocrine Control of Prolactin Secretion

During pregnancy, neuroendocrine control of prolactin secretion is markedly altered to allow a state of hyperprolactinaemia to develop. Prolactin secretion is normally tightly regulated by a short-loop negative-feedback mechanism, whereby prolactin stimulates activity of tuberoinfundibular dopamine (TIDA) neurones to increase dopamine secretion into the pituitary portal blood. Dopamine inhibits prolactin secretion, thus reducing prolactin concentrations in the circulation back to the normal low level. Activation of this feedback secretion by placental lactogen during pregnancy maintains relatively low levels of prolactin secretion during early and mid-pregnancy. Despite the continued presence of placental lactogen, however, dopamine secretion from TIDA neurones is reduced during late pregnancy. Moreover, the neurones become completely unresponsive to endogenous or exogenous prolactin at this time, allowing a large nocturnal surge of prolactin to occur from the maternal pituitary gland during the night before parturition. In this review, we describe the changing patterns of prolactin secretion during pregnancy in the rat, and discuss the neuroendocrine mechanisms controlling these changes. The loss of response to prolactin is an important maternal adaptation to pregnancy, allowing the prolonged period of hyperprolactinaemia required for mammary gland development and function and for maternal behaviour immediately after parturition, and possibly also contributing to a range of other adaptive responses in the mother.

Body weights and plasma prolactin levels in female rats treated subchronically with ziprasidone versus olanzapine

In a putative animal model of antipsychotic drug-induced weight gain, female rats received either vehicle, ziprasidone (2.0, 6.0, 10 mg/kg) or olanzapine (2.0 mg/kg), orally, twice daily, for 7 days. Body weights were assessed daily and prolactin assayed at the end of the regimen. Ziprasidone caused significant weight gain, as did olanzapine, while stimulating distinct patterns of prolactin secretion. Thus, assessment of body weight provides only limited predictive validity in differentiating between weight gain-inducing and weight-neutral drugs.

Toxic effects of methoxychlor on the episodic prolactin secretory pattern: possible mediated effects of nitric oxide production.

BackgroundThis work addresses the issue of whether methoxychlor (MTX) exposure may modify the ultradian secretion of prolactin through changes in the synthesis of nitric oxide (NO) induced by Nω-nitro-L-arginine methyl ester (L-NAME) in the hypothalamic-pituitary axis. Associated changes in dopamine (DA) content in the anterior (AH), mediobasal (MBH) and posterior hypothalamus (PH) and median eminence (ME) were evaluated.MethodsTwo groups of animals (MTX and MTX+L-NAME treated) received subcutaneous (sc) injections of MTX at a dose of 25 mg/kg/day for one month. The other two groups of animals (control and L-NAME treated) received sc vehicle injections (0.5 mL/day of sesame oil), during the same period of time to be used as controls. Forty hours before the day of the experiment, animals were anaesthetized with intrapritoneal injections of 2.5% tribromoethanol in saline and atrial cannulas were implanted through the external jugular vein. Plasma was continuously extracted in Hamilton syringes coupled to a peristaltic bomb in tubes containing phosphate-gelatine buffer (to increase viscosity). The plasma was obtained by decantation and kept every 7 minutes for the measurement of plasma prolactin levels through a specific radioimmnunoassay and DA concentration by high-pressure liquid chromatography (HPLC).ResultsProlactin release in animals from all experimental groups analyzed was episodic. Mean plasma prolactin levels during the bleeding period, and the absolute pulse amplitude were increased after MTX or Nω-nitro-L-arginine methyl ester (L-NAME) administration. However MTX and L-NAME did not modify any other parameter studied with the exception of relative pulse amplitude in MTX treated rats. L-NAME administration to rats treated with the pesticide reduced mean plasma prolactin levels and the absolute amplitude of prolactin peaks. Peak duration, frequency and relative amplitude of prolactin peaks were not changed in the group of rats treated with MTX plus L-NAME as compared to either control or MTX treated rats. Whereas MTX decreased DA content in the ME and increased it in the AH, its content did not change in the MBH or PH, as compared to the values found in controls. Also, L-NAME administration decreased DA content in the ME as compared to controls. However, L- NAME administration to MTX exposed rats, markedly increased DA content in the ME as compared to either MTX treated or control rats. L-NAME administration increased DA content in the AH as compared to the values found in non-treated rats. However L-NAME administration to MTX exposed rats did not modify DA content as compared to either MTX treated or control rats. L-NAME administration did not modify DA content at the MBH nor in saline treated nor in MTX treated rats. However, the values of DA in the MBH in MTX plus L-NAME treated animals were statistically decreased as compared to L-NAME treated rats. In the PH, L-NAME administration increased DA content as compared to the values found in non-treated animals. L-NAME administration to MTX exposed rats also increased DA content as compared to either MTX treated or control rats.ConclusionThe results suggest the existence of an interaction between MTX and L-NAME in the modulation of the ultradian prolactin secretion at the pituitary levels. The possibility of an indirect effect mediated by changes in DA content at the ME requires further examination.

Prolactin secretory rhythm of mated rats induced by a single injection of oxytocin

Mating or vaginocervical stimulation [copulatory stimulus (CS)] induces two daily surges of the hormone prolactin (PRL) in rats. This unique secretory pattern of PRL surges is characteristic for the first half of pregnancy and is also present in ovariectomized (OVX) rats. Studies have shown that CS additionally provokes an acute release of the hormone oxytocin (OT). In this study, we tested whether a single injection of OT (iv) is sufficient to initiate the PRL secretion pattern of OVX/CS rats. Furthermore, we measured the 24-h profile of dopamine (DA) content in the anterior lobe of the pituitary gland, because DA is the major inhibitory factor of PRL secretion. The results indicated that a single injection of OT induces a PRL secretory rhythm and a DA release pattern similar to that initiated by CS. Immunocytochemical investigation showed that particular OTergic neurons in the hypothalamus express receptors for PRL, as well as for vasoactive intestinal polypeptide, which indicates an involvement in generating the PRL rhythm and entraining it to the ambient photoperiod. On the basis of this study, we suggest that the PRL-DA inhibitory feedback loop between lactotrophs and DAergic neurons plays a crucial role in generating the oscillatory PRL secretion pattern in CS rats. A timing signal, likely provided by the hypothalamic suprachiasmatic nucleus, entrains the autonomous PRL oscillation to a particular time of day. Mathematical modeling was used to illustrate the proposed network function. The experimental results further suggest an additional feedback mechanism in which certain hypothalamic OTergic neurons are influenced by PRL.

Pattern of prolactin secretion after administration of gonadotropin-releasing hormone agonist at the preovulatory phase of intrauterine insemination cycles

Administration of a gonadotropin-releasing hormone (GnRH) agonist at the preovulatory phase is an option for triggering ovulation in assisted reproductive technology cycles. The aim of this work was to investigate the pattern of prolactin secretion after the administration of a single dose of GnRH-agonist at the preovulatory phase. Descriptive study at a tertiary referral center. Fifteen normally ovulating patients undergoing ovarian stimulation for intrauterine insemination were studied. Ovarian stimulation was carried out using human menopausal gonadotropin (intramuscular 75 IU daily). When at least one follicle reached 17 mm (observed echographically), 0.5 mg of buserelin acetate was administered. Blood samples were taken to determine prolactin concentrations, at the time of agonist injection and 4, 8, 12, 24 and 48 hours later. A statistically significant increase in serum levels of prolactin was observed 4, 8 and 12 hours after GnRH-agonist administration, with a peak at 8 hours. The administration of a single dose of GnRH-agonist at the preovulatory phase in patients undergoing ovarian stimulation performed with human menopausal gonadotropin causes a significant increase in serum prolactin levels.

Characterisation of olanzapine-induced weight gain and effect of aripiprazole vs olanzapine on body weight and prolactin secretion in female rats

Atypical antipsychotic drug (APD)-induced weight gain causes non-compliance, increasing the risk of relapse and medical complications. In an animal model, we assessed body weights, food intake, body fat/lean body mass contents and blood serum levels of glucose and lipids in female rats treated with olanzapine (Experiment 1). Also, we investigated the effect of aripiprazole vs olanzapine treatment on weight gain (WG) and plasma prolactin secretion in two strains (Wistar and Sprague-Dawley) and in two housing conditions (singly and group housed; Experiment 2). In Experiment 1, Wistar females received either vehicle or olanzapine (5.0 mg kg(-1), p.o.) twice daily for 14 days. In Experiment 2, female rats (Wistar or Sprague-Dawley), housed singly or in groups, received either vehicle, aripiprazole (2.0-8.0 mg kg(-1), p.o.), or olanzapine (1.0-10 mg kg(-1), p.o.) twice daily for 7 days. Body weights and food intake were assessed daily. Body composition and blood assays were analyzed at the end of the treatment. WG induced by chronic olanzapine treatment was characterised by hyperphagia, increased body fat, and serum free fatty acid content and reduced lean tissue and serum glucose content. Subchronic aripiprazole treatment resulted in rapid and robust WG similar to those observed with olanzapine. In spite of similar effects on body weight, aripiprazole and olanzapine stimulated markedly different patterns of prolactin secretion. Body weight changes and prolactin secretion induced by these APDs were significantly modulated by housing and by strain. Assessment of body weight in the present model may not have predictive validity, and other measures may be needed to differentiate between WG-inducing and weight-neutral drugs.

Differences in reproductive pattern between wild and domestic rams are not associated with inter-specific annual variations in plasma prolactin and melatonin concentrations

This study compares morphological changes, performed with real-time transrectal ultrasonography, of testis and accessory glands and seasonal endocrine changes in a wild (Mouflon) and a domesticated (Spanish Merino) breed of sheep. In Mouflons, the maximum plasma testosterone concentrations, testicular diameter and vesicular gland size occurred synchronously during autumn ( P < 0.001). In Merino rams the highest circulating levels of testosterone ( P < 0.05) and maximum testicular diameter ( P < 0.001) occurred during summer, with no seasonal variations in vesicular and bulbourethral glands. The seasonal changes in plasma concentrations of prolactin were not correlated with annual variations in testicular and glandular size in neither wild nor domestic species. No differences were observed between both species for the seasonal pattern of prolactin secretion and mean amplitude of melatonin. Wide differences in reproductive patterns between wild and domestic types of rams do not appear to be attributed to seasonal changes in prolactin and melatonin secretion.