Increase In Prolactin Release Research Articles

Phase I clinical trial evaluating the safety, tolerance, pharmacokinetics and pharmacodynamics of HSK21542 injection in healthy volunteers.

HSK21542 injection is a new peripheral kappa opioid receptor (KOR) agonist. To evaluate its safety, tolerability, pharmacokinetics and pharmacodynamics, this study was conducted in healthy volunteers, consisting of two parts: a single ascending dose (0.2-3.375 μg/kg, 15-min infusion) and different infusion durations (0.2 and 1μg/kg, 2- or 15-min infusion). The area under the plasma concentration-time curve (AUC) and peak concentration (Cmax) of HSK21542 were dose-linear among 0.2-3.375 μg/kg. After intravenous injection, HSK21542 was rapidly eliminated with a half-life (t1/2) of 1.5h, and the majority (48.02%) of the dose was excreted unchanged in urine. Pharmacodynamic results showed that HSK21542 increased prolactin release and reached a peak at 1-2h after administration but had no significant effect on vasopressin levels. There was a brief increase in urine volume within the initial 2h after administration. HSK21542 was well tolerated; most of the adverse effects (AEs) in the trial group were grade 1, and only 2 cases (4.0%) were grade 2. The main AE was paresthesia, which appeared in 42% (21/50) in the trial group. No serious adverse event (SAE) was observed. No subject withdrew early due to AEs. These results suggest that HSK21542 may be a potential treatment for pain and pruritic conditions.

Calcium-Prolactin Secretion Coupling in Rat Pituitary Lactotrophs Is Controlled by PI4-Kinase Alpha

The role of calcium, but not of other intracellular signaling molecules, in the release of pituitary hormones by exocytosis is well established. Here, we analyzed the contribution of phosphatidylinositol kinases (PIKs) to calcium-driven prolactin (PRL) release in pituitary lactotrophs: PI4Ks - which control PI4P production, PIP5Ks - which synthesize PI(4, 5)P2 by phosphorylating the D-5 position of the inositol ring of PI4P, and PI3KCs – which phosphorylate PI(4, 5)P2 to generate PI(3, 4, 5)P3. We used common and PIK-specific inhibitors to evaluate the strength of calcium-secretion coupling in rat lactotrophs. Gene expression was analyzed by single-cell RNA sequencing and qRT-PCR analysis; intracellular and released hormones were assessed by radioimmunoassay and ELISA; and single-cell calcium signaling was recorded by Fura 2 imaging. Single-cell RNA sequencing revealed the expression of Pi4ka, Pi4kb, Pi4k2a, Pi4k2b, Pip5k1a, Pip5k1c, and Pik3ca, as well as Pikfyve and Pip4k2c, in lactotrophs. Wortmannin, a PI3K and PI4K inhibitor, but not LY294002, a PI3K inhibitor, blocked spontaneous action potential driven PRL release with a half-time of ~20 min when applied in 10 µM concentration, leading to accumulation of intracellular PRL content. Wortmannin also inhibited increase in PRL release by high potassium, the calcium channel agonist Bay K8644, and calcium mobilizing thyrotropin-releasing hormone without affecting accompanying calcium signaling. GSK-A1, a specific inhibitor of PI4KA, also inhibited calcium-driven PRL secretion without affecting calcium signaling and Prl expression. In contrast, PIK93, a specific inhibitor of PI4KB, and ISA2011B and UNC3230, specific inhibitors of PIP5K1A and PIP5K1C, respectively, did not affect PRL release. These experiments revealed a key role of PI4KA in calcium-secretion coupling in pituitary lactotrophs downstream of voltage-gated and PI(4, 5)P2-dependent calcium signaling.

Preclinical Evaluation of the Effects of Trazpiroben (TAK-906), a Novel, Potent Dopamine D2/D3 Receptor Antagonist for the Management of Gastroparesis.

Current therapies for gastroparesis metoclopramide and domperidone carry risks of extrapyramidal symptoms and life-threatening cardiac arrhythmias. Trazpiroben, a novel, potent dopamine D2/D3 receptor antagonist, has low brain permeation and very low affinity for human ether-à-go-go-related gene (hERG) channel inhibition, potentially improving on safety profiles of existing therapies. Trazpiroben demonstrated the following receptor affinities: high for D2 and D3, moderate for D4, and minimal for D1 and D5 It demonstrated moderate affinity for adrenergic α 1B (α 1B) and 5-hydroxytryptamine (5HT) 2A receptors and low potential for off-target adverse events (AEs). Trazpiroben potently inhibited dopamine-activated D2L receptor activation of cognate G-proteins in human embryonic kidney 293 cell membranes and was a neutral D2L receptor antagonist. In vivo, trazpiroben dose-dependently increased prolactin release in orally dosed rat (0.1-1 mg/kg). Additionally, multiple oral doses in the rat (100 mg/kg) and dog (50 mg/kg) for 3 days produced robust plasma exposures and prolactin increases in both species. Trazpiroben inhibited retching/vomiting in the dog with apomorphine-induced emesis with a potency (0.1-1 mg/kg) like that of trazpiroben-mediated prolactin increases in rat. Oral trazpiroben (1, 10, and 30 mg/kg) did not affect rat rotarod performance, suggesting low brain penetration. Trazpiroben concentrations were low in cerebrospinal fluid versus plasma after multiple oral doses for 4 days in rat and dog. Trazpiroben weakly inhibited the hERG channel current (concentration causing half-maximal inhibition of control-specific binding of 15.6 µM), indicating little potential for disrupting cardiac rhythm. Overall, trazpiroben is a potent D2/D3 receptor antagonist designed to avoid the serious potential AEs associated with current gastroparesis therapies. SIGNIFICANCE STATEMENT: Trazpiroben is a novel, potent dopamine D2/D3 selective receptor antagonist designed to avoid adverse effects associated with the current pharmacological therapies metoclopramide and domperidone. Preclinical studies have demonstrated low brain penetration and weak affinity for the hERG channel, indicating that trazpiroben is not expected to be associated with central nervous system or cardiovascular safety issues. With these pharmacological properties, trazpiroben may represent a viable new treatment option for gastroparesis because of a potentially improved safety profile relative to existing therapies.

Kisspeptin Stimulation of Prolactin Secretion Requires Kiss1 Receptor but Not in Tuberoinfundibular Dopaminergic Neurons.

Kisspeptin has been shown to stimulate prolactin secretion. We investigated whether kisspeptin acts through the Kiss1 receptor (Kiss1r) to regulate dopamine and prolactin. Initially, we evaluated prolactin response in a Kiss1r-deficient mouse line, in which Kiss1r had been knocked into GnRH neurons (Kiss1r-/-R). Intracerebroventricular kisspeptin-10 (Kp-10) increased prolactin release in wild-type but not in Kiss1r-/-R female mice. In ovariectomized, estradiol-treated rats, the Kiss1r antagonist kisspeptin-234 abolished the Kp-10-induced increase in prolactin release but failed to prevent the concomitant reduction in the activity of tuberoinfundibular dopaminergic (TIDA) neurons, as determined by the 3,4-dihydroxyphenylacetic acid/dopamine ratio in the median eminence. Using whole-cell patch clamp recordings in juvenile male rats, we found no direct effect of Kp-10 on the electrical activity of TIDA neurons. In addition, dual-label in situ hybridization in the hypothalamus of female rats showed that Kiss1r is expressed in the periventricular nucleus of the hypothalamus (Pe) and arcuate nucleus of the hypothalamus (ARC) but not in tyrosine hydroxylase (Th)-expressing neurons. Kisspeptin also has affinity for the neuropeptide FF receptor 1 (Npffr1), which was expressed in the majority of Pe dopaminergic neurons but only in a low proportion of TIDA neurons in the ARC. Our findings demonstrate that Kiss1r is necessary to the effect of kisspeptin on prolactin secretion, although TIDA neurons lack Kiss1r and are electrically unresponsive to kisspeptin. Thus, kisspeptin is likely to stimulate prolactin secretion via Kiss1r in nondopaminergic neurons, whereas the colocalization of Npffr1 and Th suggests that Pe dopaminergic neurons may play a role in the kisspeptin-induced inhibition of dopamine release.

Milk yield loss in response to feed restriction is associated with mammary epithelial cell exfoliation in dairy cows

In dairy cows, feed restriction is known to decrease milk yield by reducing the number of mammary epithelial cells (MEC) in the udder through a shift in the MEC proliferation-apoptosis balance, by reducing the metabolic activity of MEC, or both. The exfoliation of MEC from the mammary epithelium into milk is another process that may participate in regulating the number of MEC during feed restriction. The aim of the present study was to clarify the mechanisms that underlie the milk yield loss induced by feed restriction. Nineteen Holstein dairy cows producing 40.0 ± 0.7 kg/d at 77 ± 5 d in milk were divided into a control group (n = 9) and a feed-restricted group (n = 10). Ad libitum dry matter intake (DMI) was recorded during a pre-experimental period of 2 wk. For 29 d (period 1), cows were fed either 100 (control) or 80% (feed-restricted) of their ad libitum DMI measured during the pre-experimental period. Then, all cows were fed ad libitum for 35 d (period 2). Milk production and DMI were recorded daily. Blood and milk samples were collected once during the pre-experimental period; on d 5, 9, and 27 of period 1; and on d 5, 9, and 30 of period 2. Mammary epithelial cells were purified from milk using an immunomagnetic method to determine the rate of MEC exfoliation. Mammary tissue samples were collected by biopsy at the end of each period to analyze the rates of cell proliferation and apoptosis and the expression of genes involved in synthesizing constituents of milk. Feed restriction decreased milk yield by 3 kg/d but had no effect on rates of proliferation and apoptosis in the mammary tissue or on the expression of genes involved in milk synthesis. The daily MEC exfoliation rate was 65% greater in feed-restricted cows than in control cows. These effects in feed-restricted cows were associated with reduced insulin-like growth factor-1 and cortisol plasma concentrations. When all cows returned to ad libitum feeding, no significant difference on milk yield or MEC exfoliation rate was observed between feed-restricted and control cows, but refeeding increased prolactin release during milking. These results show that the exfoliation process may play a role in regulating the number of MEC in the udders of dairy cows during feed restriction without any carryover effect on their milk production.

Impact of NTRK2, DRD2 and ACE polymorphisms on prolactin levels in antipsychotic-treated patients with first-episode psychosis.

Hyperprolactinemia is a common side-effect of antipsychotics (APs), which may trigger serious secondary problems and compromise the adherence to treatment which is crucial for prognosis, especially in patients presenting with a first-episode of psychosis (FEP). We evaluated, in some cases for the first time, the effect of polymorphisms in multiple candidate genes on serum prolactin (PRL) levels in an AP-treated FEP cohort recruited in the multicenter PEPs study (Phenotype - genotype and environmental interaction; Application of a predictive model in first psychotic episodes). PRL concentration was measured in serum from 222 patients. A total of 167 polymorphisms were selected in 23 genes. Genetic association analysis was performed in the whole sample and also in homogenous subgroups of patients treated with APs with a high (N = 101) or low risk (N = 95) of increasing PRL release, which showed significant differences in their PRL levels. After Bonferroni correction, polymorphisms in NTRK2, DRD2 and ACE genes were associated with PRL concentration. Our results give more support to the impact of DRD2, but also of other genes related to dopamine availability such as ACE. Moreover, this study provides the first evidence for the involvement of NTRK2, which suggests that pathways other than the ones related to dopamine or serotonin may participate in the AP-related PRL levels.

P.3.c.006 - Association of polymorphism in the dopamine receptors and transporter genes with hyperprolactinemia in patients with schizophrenia

Association of polymorphism in the dopamine receptors and transporter genes with hyperprolactinemia in patients with schizophrenia D. Osmanova(1), A.S. Boiko(1), O.Y. Fedorenko(1), I.V. Pozhidaev(1), M.B. Freidin(2), E.G. Kornetova(3), S.A. Ivanova(1), B. Wilffert(4), A.J.M. Loonen(5) (1)Mental Health Research Institute- Tomsk NRMC, Laboratory of Molecular Genetics and Biochemistry, Tomsk, Russia (2)Research Institute of Medical Genetics, Tomsk NRMC, Laboratory of Population Genetics, Tomsk, Russia (3)Mental Health Research Institute- Tomsk NRMC, Department of Clinical and Social Psychiatry and Addiction, Tomsk, Russia (4)Groningen Research Institute of Pharmacy, Pharmacotherapy and Clinical Pharmacology, Groningen, The Netherlands (5)Groningen Research Institute of Pharmacy, Pharmacotherapy in Psychiatric Patients, Groningen, The Netherlands Background: Long-term antipsychotic drug use remains the mainstay of treatment for patients with schizophrenia. However, pharmacotherapy with these drugs is complicated by several troublesome side effects, including hyperprolactinemia (HP). Prolactin secretion is persistently inhibited by dopamine, and antipsychotic drugs are believed to increase prolactin release by blocking dopamine receptors in the pituitary gland. Genetic factors play an important role in the development of antipsychotic induced HP [1,2]. Genes coding for dopamine receptors and transporters are considered to be responsible for HP in schizophrenia [3]. The present study aimed to investigate the role of polymorphisms of the dopamine receptors and transporters genes (DRD1, DRD2, SLC6A3) in the pathogenesis of antipsychotic-related HP in patients with schizophrenia. Methods: 431 Russian patients with schizophrenia were examined. The average age of patients was 42.1 ± 1.4 years. Evaluation of serum prolactin level was performed by ELISA using reagents set PRL Test System (USA). Genotyping was carried out on 17 polymorphic variants of the dopamine receptors and transporters genes DRD1 (rs4532, rs936461), DRD2 (rs4245147, rs6279, rs2734842) and SLC6A3 (rs3756450, rs2550956, rs6347, rs2617605, rs3863145, rs250686, rs464049, rs4975646, rs1048953, rs11133767, rs27048, rs40184). The SPSS software was used for statistical analysis. The Hardy-Weinberg equilibrium (HWE) of genotypic frequencies was tested by the chi-square test. Results: We studied the association between HP and a set of SNPs from DRD1, DRD2 receptor genes and neurotransmitter transporter SLC6A3 in patients from Siberia with a clinical diagnosis of schizophrenia who were treated with classical and/or atypical antipsychotic drugs. All patients with schizophrenia were divided into two groups: those with and without HP. Physiological normal results for the serum prolactin levels are less than 20 ng/ml in men, and less than 25 ng/ml in women. Statistically significant result was obtained for polymorphic variant rs2550956 of the gene SLC6A3 (χ2 = 9.992; p = 0.007), which suggests its involvement in the development of HP. The heterozygous genotype TC of rs2550956 was significantly less common in patients with elevated levels of prolactin and it presumably has protective properties (OR 0.54; 95% CI: 0.36–0.81). We did not find any statistically significant associations for other polymorphisms DRD1 (rs4532, rs936461), DRD2 (rs4245147, rs6279, rs2734842) and SLC6A3 (rs3756450, rs6347, rs2617605, rs3863145, rs250686, rs464049, rs4975646, rs1048953, rs11133767, rs27048, rs40184). The group of dopamine receptors is heterogeneous and only some of them participate in the formation of psychotic symptoms and, accordingly, in the antipsychotic action of neuroleptics. The effect of neuroleptics on other groups of dopamine receptors leads to the development of different side effects including extrapyramidal disorders [4], and their role is extremely low in the formation of the actual therapeutic response. Conclusion: Our results indicate that genetic variants of SLC6A3 may have functional consequences on the modulation of prolactin secretion. Neurotransmitter systems are involved in the mechanisms of action of antipsychotic drugs; therefore, a further search for genetic markers associated with the development of antipsychotic-related hyperprolactinemia in schizophrenic patients is needed.

Antipsychotic drugs for the acute treatment of patients with a first episode of schizophrenia: a systematic review with pairwise and network meta-analyses

The first episode of schizophrenia is a pivotal phase of this debilitating illness. Which drug to use remains controversial without a summary of all direct or indirect comparisons of drugs. We did a systematic review with pairwise and network meta-analyses of efficacy and tolerability. We searched MEDLINE, Embase, PsycINFO, Cochrane Library, PubMed, Biosis, and ClinicalTrials.gov for randomised controlled trials of antipsychotics for the acute treatment of first-episode schizophrenia, published up to Nov 17, 2016. Our primary outcome was overall change in symptoms. Secondary outcomes were change in positive and negative symptoms, categorical response to treatment, study dropout for any reason and for inefficacy of treatment, use of drugs to treat parkinsonian symptoms, weight gain, sedation, increase in prolactin release, overall functioning, and quality of life. We did the meta-analyses with a random-effects model to calculate standardised mean differences (SMDs) or odds ratios (ORs) with 95% CIs. We identified 19 relevant randomised controlled trials of 12 antipsychotic drugs that involved 2669 participants. 13 of the studies presented data on the primary outcome. For overall reduction of symptoms, amisulpride (SMD -0·37, 95% CI -0·61 to -0·14), olanzapine (-0·25, -0·39 to -0·12), ziprasidone (-0·25, -0·48 to -0·01), and risperidone (-0·14, -0·27 to -0·01) were significantly more efficacious than haloperidol, but the evidence was very low to moderate quality. Amisulpride was superior for reduction of symptoms to quetiapine (SMD -0·25, 95% CI -0·50 to -0·01). Olanzapine was superior to haloperidol and risperidone for reduction of negative symptoms. Several second-generation antipsychotics were superior to haloperidol in terms of all-cause discontinuation. Olanzapine was associated with at least one use of drugs to treat parkinsonian symptoms and quetiapine with less akathisia than haloperidol, aripiprazole, risperidone, and olanzapine, but, again, evidence was very low to low quality. Molindone was superior to risperidone, haloperidol, and olanzapine in terms of weight gain, and superior to risperidone in terms of increase in prolactin release. Haloperidol seems to be a suboptimum treatment option for acute treatment of first-episode schizophrenia, but we found little difference between second-generation antipsychotics. The evidence was generally of low quality and the numbers of patients for each drug were small. Thus, the choice of treatment should be guided primarily by side-effects. German Federal Ministry of Education and Research.

Effect of stress on prolactin release in nulliparous and primiparous rats

Reproductive experience modifies seric concentration of prolactin. In adition, stress is known to modulate this neurohormone release. Taken together, these facts are suggestive of a possible interaction. The objective of the present study was to analyze the influence of acute and prolonged stress on prolactin secretion in nulliparous and experienced rats. Wistar nulliparous (n= 12) and primiparous (n= 12) female rats were submitted to a chronic jugular vein catheterization surgery. Both groups were submitted to acute stress induced by formalin (4%) subcutaneous injection or restrained stress in a PVC tube. One hour stress sessions were performed during proestrous morning. Blood samples were obtained in 2, 5, 10, 15, 30 and 60 minutes after acute or during restrained stress. Seric prolactin concentration was measured by radioimmunoassay. The results showed an increased prolactin release at 10 and 15 minutes in primiparous compared to nulliparous during restrained stress (Repeated Measures Anova, F 5,15 = 9,65; p< 0,001). No differences between groups were observed in prolactin release after formalin injection. In conclusion, we can suggest that prolactin secretory stress response can be modulated by reproductive experience although further studies are necessary to elucidate oestrus cycle and different contribution of stress types.

α-Estrogen and Progesterone Receptors Modulate Kisspeptin Effects on Prolactin: Role in Estradiol-Induced Prolactin Surge in Female Rats.

Kisspeptin (Kp) regulates prolactin (PRL) in an estradiol-dependent manner. We investigated the interaction between ovarian steroid receptors and Kp in the control of PRL secretion. Intracerebroventricular injections of Kp-10 or Kp-234 were performed in ovariectomized (OVX) rats under different hormonal treatments. Kp-10 increased PRL release and decreased 3,4-dihydroxyphenylacetic acid levels in the median eminence (ME) of OVX rats treated with estradiol (OVX+E), which was prevented by tamoxifen. Whereas these effects of Kp-10 were absent in OVX rats, they were replicated in OVX rats treated with selective agonist of estrogen receptor (ER)α, propylpyrazole triol, but not of ERβ, diarylpropionitrile. Furthermore, the Kp-10-induced increase in PRL was two times higher in OVX+E rats also treated with progesterone (OVX+EP), which was associated with a reduced expression of both tyrosine hydroxylase (TH) and Ser40-phosphorylated TH in the ME. Kp-10 also reduced dopamine levels in the ME of OVX+EP rats, an effect blocked by the progesterone receptor (PR) antagonist RU486. We also determined the effect of Kp antagonism with Kp-234 on the estradiol-induced surges of PRL and luteinizing hormone (LH), using tail-tip blood sampling combined with ultrasensitive enzyme-linked immunosorbent assay. Kp-234 impaired the early phase of the PRL surge and prevented the LH surge in OVX+E rats. Thus, we provide evidence that Kp stimulation of PRL release requires ERα and is potentiated by progesterone via PR activation. Moreover, alongside its essential role in the LH surge, Kp seems to play a role in the peak phase of the estradiol-induced PRL surge.

Pharmacological characterization of a novel potent, selective, and orally active phosphodiesterase 10A inhibitor, PDM-042 [(E)-4-(2-(2-(5,8-dimethyl-[1,2,4]triazolo[1,5-a]pyrazin-2-yl)vinyl)-6-(pyrrolidin-1-yl)pyrimidin-4-yl)morpholine] in rats: potential for the treatment of schizophrenia.

Recently, we identified a novel phosphodiesterase 10A (PDE10A) inhibitor, PDM‐042 ((E)‐4‐(2‐(2‐(5,8‐dimethyl‐[1,2,4]triazolo[1,5‐a]pyrazin‐2‐yl)vinyl)‐6‐(pyrrolidin‐1‐yl)pyrimidin‐4‐yl)morpholine). PDM‐042 showed potent inhibitory activities for human and rat PDE10A with IC 50 values of less than 1 nmol/L and more than 1000‐fold selectivity against other phosphodiesterases. Tritiated PDM‐042, [3H]PDM‐042, had high affinity for membranes prepared from rat striatum with a K d value of 8.5 nmol/L. The specific binding of [3H]PDM‐042 was displaced in a concentration‐dependent manner by PDM‐042 and another structurally unrelated PDE10A inhibitor, MP‐10. In rat studies, PDM‐042 showed excellent brain penetration (striatum/plasma ratio = 6.3), occupancy rate (86.6% at a dose of 3 mg/kg), and good oral bioavailability (33%). These data indicate that PDM‐042 is a potent, selective, orally active, and brain‐penetrable PDE10A inhibitor. In behavioral studies using rat models relevant to schizophrenia, PDM‐042 significantly antagonized MK‐801‐induced hyperlocomotion (0.1–0.3 mg/kg) without affecting spontaneous locomotor activity and attenuated the conditioned avoidance response (CAR) (0.3–1 mg/kg). In tests for adverse effects, PDM‐042 had a minimal effect on catalepsy, even at a much higher dose (10 mg/kg) than the minimal effective dose (0.3 mg/kg) in the CAR. Furthermore, PDM‐042 had no effect on prolactin release or glucose elevation up to 3 mg/kg, while risperidone increased prolactin release and olanzapine enhanced glucose levels at doses near their efficacious ones in the CAR. Our results suggest that PDM‐042 is a good pharmacological tool that can be used to investigate the role of PDE10A and may have therapeutic potential for the treatment of schizophrenia.

Opioid modulation of prolactin secretion induced by stress during late pregnancy. Role of ovarian steroids

BackgroundThe opioid system modulates prolactin release during late pregnancy. Its role and the participation of ovarian hormones in this modulation are explored in ether stress-induced prolactin release. Methods/ResultsEstrous, 3-day and 19-day pregnant rats were used. We administered the antagonist mifepristone (Mp) and tamoxifen to evaluate progesterone and estradiol action in naloxone (NAL, opioid antagonist) or saline treated rats. Ether stress had no effect on serum prolactin levels in controls but increased prolactin release in NAL-treated rats. Prolactin response to stress in NAL-treated rats was blocked by l-DOPA administration. Mp treatment on day 18 of pregnancy increased prolactin levels after stress without alterations by NAL. Tamoxifen on days 14 and 15 of pregnancy completely blocked Mp and NAL effects on prolactin release at late pregnancy. In contrast, stress significantly increased prolactin levels in estrous rats and pretreatment with NAL prevented this. On day 3 of pregnancy, at 6.00 p.m., stress and NAL treatment inhibited prolactin levels in saline-treated rat. No effect of stress or NAL administration was detected on day 3 of pregnancy at 9.00 a.m. icv administration of specific opioids antagonist, B-Funaltrexamine but not Nor-Binaltorphimine or Naltrindole, caused a significant increase in stress-induced prolactin release. ConclusionsOpioid system suppression of prolactin stress response during late pregnancy was observed only after progesterone withdrawal, involving a different opioid mechanism from its well-established stimulatory role. This mechanism acts through a mu opioid receptor and requires estrogen participation. The opioid system and progesterone may modulate stress-induced prolactin release, probably involving a putative prolactin-releasing factor.

Prolactin and fMRI response to SKF38393 in the baboon.

Background. This study’s goal was to provide dose–response data for a dopamine agonist in the baboon using standard methods (replicate measurements at each dose, across a range of doses), as a standard against which to subsequently validate a novel pharmacological MRI (phMRI) method. Dependent variables were functional MRI (fMRI) data from brain regions selected a priori, and systemic prolactin release. Necessary first steps included estimating the magnitude and time course of prolactin response to anesthesia alone and to various doses of agonist. These first steps (“time course studies”) were performed with three agonists, and the results were used to select promising agonists and to guide design details for the single-dose studies needed to generate dose–response curves.Methods. We studied 6 male baboons (Papio anubis) under low-dose isoflurane anesthesia after i.m. ketamine. Time course studies charted the changes in plasma prolactin levels over time after anesthesia alone or after an intravenous (i.v.) dose of the dopamine D1-like agonists SKF82958 and SKF38393 or the D2-like agonist pramipexole. In the single-dose dopamine agonist studies, one dose of SKF38393 (ranging from 0.0928–9.28 mg/kg, N = 5 animals) or pramipexole (0.00928–0.2 mg/kg, N = 1) was given i.v. during a 40-min blood oxygen level dependent (BOLD) fMRI session, to determine BOLD and plasma prolactin responses to different drug concentrations. BOLD response was quantified as the area under the time-signal curve for the first 15 min after the start of the drug infusion, compared to the linearly predicted signal from the baseline data before drug. The ED50 (estimated dose that produces 50% of the maximal possible response to drug) for SKF38393 was calculated for the serum prolactin response and for phMRI responses in hypothalamus, pituitary, striatum and midbrain.Results. Prolactin rose 2.4- to 12-fold with anesthesia alone, peaking around 50–90 min after ketamine administration and gradually tapering off but still remaining higher than baseline on isoflurane 3–5 h after ketamine. Baseline prolactin level increased with age. SKF82958 0.1 mg/kg i.v. produced no noticeable change in plasma prolactin concentration. SKF38393 produced a substantial increase in prolactin release that peaked at around 20–30 min and declined to pre-drug levels in about an hour. Pramipexole quickly reduced prolactin levels below baseline, reaching a nadir 2–3 h after infusion. SKF38393 produced clear, dose-responsive BOLD signal changes, and across the four regions, ED50 was estimated at 2.6–8.1 mg/kg.Conclusions. In the baboon, the dopamine D1 receptor agonist SKF38393 produces clear plasma prolactin and phMRI dose–response curves. Variability in age and a modest sample size limit the precision of the conclusions.

The pharmacology of Adrenomedullin 2/Intermedin

Adrenomedullin 2 (AM2) or intermedin is a member of the calcitonin gene-related peptide (CGRP)/calcitonin family of peptides and was discovered in 2004. Unlike other members of this family, no unique receptor has yet been identified for it. It is extensively distributed throughout the body. It causes hypotension when given peripherally, but when given into the CNS, it increases blood pressure and causes sympathetic activation. It also increases prolactin release, is anti-diuretic and natriuretic and reduces food intake. Whilst its effects resemble those of AM, it is frequently more potent. Some characterization of AM2 has been done on molecularly defined receptors; the existing data suggest that it preferentially activates the AM(2) receptor formed from calcitonin receptor-like receptor and receptor activity modifying protein 3. On this complex, its potency is generally equivalent to that of AM. There is no known receptor-activity where it is more potent than AM. In tissues and in animals it is frequently antagonised by CGRP and AM antagonists; however, situations exist in which an AM2 response is maintained even in the presence of supramaximal concentrations of these antagonists. Thus, there is a partial mismatch between the pharmacology seen in tissues and that on cloned receptors. The only AM2 antagonists are peptide fragments, and these have limited selectivity. It remains unclear as to whether novel AM2 receptors exist or whether the mismatch in pharmacology can be explained by factors such as metabolism.

Systemic oxytocin induces a prolactin secretory rhythm via the pelvic nerve in ovariectomized rats

We have shown previously that an intravenous injection of oxytocin (OT) in ovariectomized (OVX) rats initiates a circadian rhythm of prolactin (PRL) secretion similar to that observed after cervical stimulation (CS). In this study, we investigated the pathway through which OT triggers the PRL rhythm. We first tested whether an intracerebroventricular injection of OT could trigger the PRL secretory rhythm. As it did not, we injected OT intravenously while an OT receptor antagonist was infused intravenously. This antagonist completely abolished the PRL surges, suggesting that a peripheral target of OT is necessary for triggering the PRL rhythm. We hypothesized that OT may induce PRL release, which would be transported into the brain and trigger the rhythm. In agreement with this, OT injection increased circulating PRL by 5 min. To test whether this acute increase in PRL release would induce the PRL rhythm, we compared the effect of intravenously administered thyrotropin-releasing hormone (TRH) and OT. Although TRH injection also increased PRL to a comparable level after 5 min, only OT-injected animals expressed the PRL secretory rhythm. Motivated by prior findings that bilateral resection of the pelvic nerve blocks CS-induced pseudopregnancy and OT-induced facilitation of lordosis, we then hypothesized that the OT signal may be transmitted through the pelvic nerve. In fact, OT injection failed to induce a PRL secretory rhythm in pelvic-neurectomized animals, suggesting that the integrity of the pelvic nerve is necessary for the systemic OT induction of the PRL secretory rhythm in OVX rats.

Kisspeptin Regulates Prolactin Release through Hypothalamic Dopaminergic Neurons

Prolactin (PRL) is tonically inhibited by dopamine (DA) released from neurons in the arcuate and periventricular nuclei. Kisspeptin plays a pivotal role in LH regulation. In rodents, kisspeptin neurons are found mostly in the anteroventral periventricular and arcuate nuclei, but the physiology of arcuate kisspeptin neurons is not completely understood. We investigated the role of kisspeptin in the control of hypothalamic DA and pituitary PRL secretion in adult rats. Intracerebroventricular kisspeptin-10 (Kp-10) elicited PRL release in a dose-dependent manner in estradiol (E2)-treated ovariectomized rats (OVX+E2), whereas no effect was found in oil-treated ovariectomized rats (OVX). Kp-10 increased PRL release in males and proestrous but not diestrous females. Associated with the increase in PRL release, intracerebroventricular Kp-10 reduced Fos-related antigen expression in tyrosine hydroxylase-immunoreactive (ir) neurons of arcuate and periventricular nuclei in OVX+E2 rats, with no effect in OVX rats. Kp-10 also decreased 3,4-dihydroxyphenylacetic acid concentration and 3,4-dihydroxyphenylacetic acid-DA ratio in the median eminence but not striatum in OVX+E2 rats. Double-label immunofluorescence combined with confocal microscopy revealed kisspeptin-ir fibers in close apposition to and in contact with tyrosine hydroxylase-ir perikarya in the arcuate. In addition, Kp-10 was not found to alter PRL release from anterior pituitary cell cultures regardless of E2 treatment. We provide herein evidence that kisspeptin regulates PRL release through inhibition of hypothalamic dopaminergic neurons, and that this mechanism is E2 dependent in females. These findings suggest a new role for central kisspeptin with possible implications for reproductive physiology.

Venous plasma nicotine correlates of hormonal effects of tobacco smoking

The present study resolves some of the discrepancies in the literature by correlating the effects of tobacco smoking on hormone release with venous plasma nicotine levels. Cortisol, prolactin, and β-endorphin concentrations were measured. Habitual male tobacco users smoked denicotinized (very low nicotine) and average nicotine cigarettes in the morning after overnight tobacco abstinence. Several venous blood samples were withdrawn before and during the smoking sessions for subsequent analyses. The increases in plasma nicotine correlated well with plasma cortisol and prolactin levels (correlation coefficients r = 0.66 and 0.53, respectively, p < 0.05). This study quantifies the well known increase in plasma cortisol and prolactin after nicotine postsmoking for about 1 h with peak plasma levels up to 35 ng/ml. Contrary to most abused drugs which release dopamine and decrease prolactin, nicotine concentration correlated with increased prolactin release. Increases in maximal plasma β-endorphin levels following tobacco smoking were barely statistically significant with insufficient data to obtain a correlation coefficient.

Membrane estrogen receptor-α-mediated nongenomic actions of phytoestrogens in GH&lt;sub&gt;3&lt;/sub&gt;/B&lt;sub&gt;6&lt;/sub&gt;/F&lt;sub&gt;10&lt;/sub&gt; pituitary tumor cells

BackgroundEstradiol (E2) mediates various intracellular signaling cascades from the plasma membrane via several estrogen receptors (ERs). The pituitary is an estrogen-responsive tissue, and we have previously reported that E2 can activate mitogen-activated protein kinases (MAPKs) such as ERK1/2 and JNK1/2/3 in the membrane ERα (mERα)-enriched GH3/B6/F10 rat pituitary tumor cell line. Phytoestrogens are compounds found in plants and foods such as soybeans, alfalfa sprouts, and red grapes. They are structurally similar to E2 and share a similar mechanism of action through their binding to ERs. Phytoestrogens bind to nuclear ERs with a much lower affinity and therefore are less potent in mediating genomic responses. However, little is known about their ability to act via mERs to mediate nongenomic effects.MethodsTo investigate the activation of different nongenomic pathways, and determine the involvement of mERα, we measured prolactin (PRL) release by radio-immunoassay, MAPK activations (ERK1/2 and JNK1/2/3) via a quantitative plate immunoassay, and intracellular [Ca2+] by Fura-2 fluorescence imaging in cells treated with E2 or four different phytoestrogens (coumestrol, daidzein, genistein, and trans-resveratrol).ResultsCoumesterol and daidzein increased PRL release similar to E2 in GH3/B6/F10 cells, while genistein and trans-resveratrol had no effect. All of these compounds except genistein activated ERK1/2 signaling at 1–10 picomolar concentrations; JNK 1/2/3 was activated by all compounds at a 100 nanomolar concentration. All compounds also caused rapid Ca2+ uptake, though in unique dose-dependent Ca2+ response patterns for several aspects of this response. A subclone of GH3 cells expressing low levels of mERα (GH3/B6/D9) did not respond to any phytoestrogen treatments for any of these responses, suggesting that these nongenomic effects were mediated via mERα.ConclusionPhytoestrogens were much more potent in mediating these nongenomic responses (activation of MAPKs, PRL release, and increased intracellular [Ca2+]) via mERα than was previously reported for genomic responses. The unique non-monotonic dose responses and variant signaling patterns caused by E2 and all tested phytoestrogens suggest that complex and multiple signaling pathways or binding partners could be involved. By activating these different nongenomic signaling pathways, phytoestrogens could have significant physiological consequences for pituitary cell functions.

Fusion Pore Regulation of Peptidergic Vesicles

Neuroendocrine secretory vesicles discharge their cargo in response to a stimulus. This process begins with the formation of a fusion pore, an aqueous channel between a spherical vesicle and the nearly “flat” plasma membrane, through which cargo molecules diffuse into the cell exterior. After formation the fusion pore can expand, leading to the complete merger of the vesicle membrane and releasing all of the vesicle cargo (full fusion exocytosis). On the other hand, fusion pore can relatively swiftly close, allowing only partial release of vesicle cargo and retaining vesicle physical integrity (transient exocytosis). We studied the release of the pituitary hormone prolactin by hypotonicity, because this hormone also contributes to osmoregulation. Perifused cells spontaneously released prolactin at room temperature, and hypotonicity evoked a transient increase in prolactin release, followed by a sustained depression, as monitored by radioimmunoassay. In single cells imaged by confocal microscopy, hypotonicity elicited discharge of the fluorescently-labelled atrial natriuretic peptide cargo from ∼2% of vesicles/cell, while KCl-induced depolarization resulted in a response of ∼10% of vesicles/cell, with different unloading/loading time-course of the two fluorescent probes. High resolution changes of membrane capacitance were recorded in both, unstimulated and stimulated conditions, reflecting single vesicle fusion/fissions with the plasma membrane. In stimulated cells, the probability of occurrence of full fusion events was low and unchanged, since over 95% of fusion events were transient. However, stimulation prolonged the average pore dwell-time (hypotonicity and KCl depolarization for 25%, respectively), increased the frequency of occurrence (hypotonicity for 35%, KCl depolarization tenfold) and the fusion pore conductance (hypotonicity and KCl depolarization for 50%, respectively). Hypotonicity only rarely elicited new fusion events in silent membrane patches. The results indicate that transient exocytosis appears to be the dominant mode of exocytosis at spontaneous as well as at stimulated conditions.

Osmosensitivity of prolactin cells is enhanced by the water channel aquaporin-3 in a euryhaline Mozambique tilapia (Oreochromis mossambicus)

In teleost fish, prolactin (PRL) has important actions in the regulation of salt and water balances in freshwater (FW) fish. Consistent with this role, the release of PRL from the pituitary of the Mozambique tilapia is stimulated as extracellular osmolality is reduced. Stretch-activated calcium-permeant ion channels appear to be responsible for the initiation of the signal transduction that leads to increased PRL release when PRL cells are exposed to reductions in extracellular osmolality. In this study, we examined a possible involvement of the aquaporin-3 (AQP3) water channel in this osmoreceptive mechanism in PRL cells of the tilapia. AQP3 expression levels in the rostral pars distalis of the pituitary, consisting predominantly of PRL cells, were higher in fish adapted to FW than in seawater (SW)-adapted fish. Immunohistochemical studies revealed that AQP3 is located in the cell membrane and perinuclear region of PRL cells, with more intense immunosignals in PRL cells of FW-adapted fish than in those of SW fish. In FW PRL cells, the magnitude of hyposmoticity-induced cell volume increase was greater than that seen in SW PRL cells. Mercury, a potent inhibitor of AQP3, inhibited hyposmoticity-induced cell volume increase and PRL release from FW PRL cells. The inhibitory effect of mercury was partially restored by beta-mercaptoethanol, whereas no effect of mercury was observed on PRL release stimulated by a depolarizing concentration of KCl, which induces Ca2+ influx and stimulates the subsequent Ca2+-signaling pathway. These results indicate significant contribution of AQP3 to osmoreception in PRL cells in FW-adapted tilapia.