Koelreuteria paniculata invasiveness, yielding capacity and harvest date influence on biodiesel feedstock properties

Due to Koelreuteria paniculata Laxm., high abundance in Novi Sad (Serbia) and previously confirmed biodiesel feedstock suitability, this study aimed to assess generative potential and yield, assess K. paniculata invasive risk, and investigate the influence of harvesting periods on the oil content and quality. Fifty-five specimens present in the Novi Sad inner-city core exhibited very high scores in the conducted invasiveness risk assessment (score 35/39). Determined good overall adaptability, growth and development, vitality and decorativeness of K. paniculata specimens, as well as the absence of phytopathological and entomological damages, due to lack of natural enemies, provided this species high unhindered yielding. The majority of investigated trees reached 5-10 m in height and canopy volumes from 10.1 to 70 m³, with an estimated more than 130 000-700 000 seeds produced per canopy. Seeds from one representative specimen were collected on different harvesting dates, at the end of August, September and October of 2019, and analyzed for oil content and quality for biodiesel production. With the average oil percentage of 22.8 w%, determined in the representative specimen, investigated 55 seed-bearing K. paniculata trees merely in the inner city core of Novi Sad, could produce 115 kg of oil. Since oil properties (<1 w% of free fatty acids and the acid number <2 mgKOH.g^-1) and fatty acid profile (high content of monounsaturated fatty acids ≈72 w%) fit the requirements set in EN14214 biodiesel standard, regardless of the harvest date, harvest season can be extended to at least three months without compromising the oil quality for biodiesel production. Thus, intrinsic disservice of K. paniculata - high seed yielding can be shifted into a novel ecosystem service - quality biodiesel production. Aiming to avoid viable seed deposition in the ground and formation of the invasive seed bank, early August harvest can be recommended.

Comparative Study of Subcritical Water and Microwave-Assisted Extraction Techniques Impact on the Phenolic Compounds and 5-Hydroxymethylfurfural Content in Pomegranate Peel

Two environmentally friendly innovative extraction techniques - subcritical water (SWE) and microwave-assisted extraction (MAE) were applied for the extraction of phenolics from pomegranate peel. The impact of process conditions (SWE: temperature 100-220 °C, extraction time 5-30 min; MAE: solvent water and 50% ethanol, irradiation power 470 and 800 W) on the quality of extracts in terms of the content of total phenolics, total flavonoids, major phenolic constituents (gallic acid, ellagic acid, punicalin, punicalagin), as well as 5-hydroxymethylfurfural(HMF) amount was investigated. For SWE, temperature of 130 °C and 20 min extraction time were found optimal for obtaining high content of bioactive compounds and minimizing the yield of HMF. During MAE, phenolic compounds were effectively extracted by using lower microwave power and 50% ethanol. Comparing two techniques, MAE is more efficient than SWE for the extraction of phenolics from pomegranate peel while obtaining a HMF-free extracts.

Valorization of Yarrow (Achillea millefolium L.) By-Product through Application of Subcritical Water Extraction

In the present study, valorization of yarrow (Achillea millefolium) by-product from the filter tea industry was investigated through the application of subcritical water for the extraction of bioactive compounds. The influence of different process parameters (temperature 120-200 °C, extraction time 10-30 min, and HCl concentration in extraction solvent 0-1.5%) on extract quality in terms of content of bioactive compounds and antioxidant activity was investigated. Optimal conditions of the extraction process (temperature 198 °C, extraction time 16.5 min, and without acidifer) were determined and, when applied, the most efficient exploitation of by-products is achieved, that is, attainment of extracts rich in total phenols and flavonoids and high antioxidant activity. In addition, by applying the high performance liquid chromatographic analysis, the content of chlorogenic acid was determined as well as the hydroxymethylfurfural content in obtained extracts. The results demonstrated that subcritical water can be successfully used for utilization of yarrow by-products for obtaining extracts rich in antioxidants.

The preoperative management of dabigatran and its specific antidote idarucizumab in patients with nonvalvular atrial fibrillation: Case reports

Dabigatran is a novel oral anticoagulant preferred due to its ease of use, favorable pharmacokinetics, decreased potential for drug-drug interactions, and the lack of monitoring requirements. With the growing use of dabigatran, it is important to highlight that dabigatran increases the risk of hemorrhage after some procedures. Therefore, when dabigatran is used before the elective or urgent procedures, it is necessary to compare the thromboembolic event risk with the relative risk of bleeding. Before the approval of a reversal agent, the lack of specific antidotes had been the major limitation against the widespread utilization of dabigatran. In October 2015, idarucizumab, a humanized monoclonal antigen-binding antibody fragment capable of reversing the anticoagulant activity of dabigatran, has been introduced into the market to be used in lifethreatening bleeding or urgent surgery. In this manuscript, the preoperative management of dabigatran and the initial experience of using idarucizumab in a patient with nonvalvular atrial fibrillation were described. We propose that the option of dabigatran reversal needs to be considered in patients with nonvalvular atrial fibrillation. However, additional research is needed to define optimal perioperative management of dabigatran and other novel oral anticoagulants, especially in high bleeding risk patients, and to determine whether pre-procedure coagulation testing should be performed.

Spray Drying of a Subcritical Extract Using Marrubium vulgare as a Method of Choice for Obtaining High Quality Powder

White horehound (Marrubium vulgare L.), is a grey-leaved perennial herb, belonging to Lamiaceae family, distributed in Eurasia and northern Africa. Despite the fact that M. vulgare has been used since ancient times in treating diverse diseases, it is only in the last decade or so that scientists have been able to lay the foundation for its potential pharmacological actions from the results observed through the prism of ethnopharmacological use of this species. The novelty of this study was that subcritical water extraction, acknowledged as a powerful extraction technology to recover phenolic compounds, was coupled with spray drying. The subcritical horehound extract, obtained using optimal process parameters, was used as a liquid feed in spray drying. Maltodextrin was used as a carrier in a concentration of 10%. Thus, two M. vulgare powders, carrier-free and 10% MD, were produced. Comprehensive powders characterization was conducted in order to evaluate their quality. Results confirmed that spray drying can be used as a method of choice for obtaining high quality horehound powders which kept the amorphous structure constant after 6 months.

Publisher's Note: Effects of Lifshitz Transitions on Charge Transport in Magnetic Phases of Fe-Based Superconductors [Phys. Rev. Lett. 114, 097003 (2015)]

This corrects the article DOI: 10.1103/PhysRevLett.114.097003.

Autonomic nervous system function assessed by conventional and spectral analysis might be useful in terms of predicting retinal deterioration in persons with type 1 diabetes mellitus

AIMS

To determine whether cardiac autonomic dysfunction represents a risk factor for diabetic retinopathy (DR) development and progression in persons with type 1 diabetes mellitus (T1DM).

METHODS

The study comprised 154 normoalbuminuric persons with T1DM divided into two groups according to the DR presence: with and without DR. Cardiovascular autonomic functioning was measured at baseline using conventional and spectral analysis. Participants were re-examined for the DR presence 18months after.

RESULTS

The group with DR had longer disease duration compared to the group without DR (20 vrs 11.5years, p<0.001), heart rate coefficient of variation (HRV-CV) at rest and during deep breathing were lower in participants with DR (p=0.001 and 0.004), as well did spectral indices of HRV: low frequency (LF) band, high frequency (HF) band (p=0.003 and 0.022) while LF/HF ratio indicating sympathovagal balance was higher (p=0.037). No difference in glycaemic control or blood pressure value were observed. Twenty-one (13.36%) participants developed non proliferative DR or progressed to proliferative DR. Cox proportional regression showed that the 18months risk from retinal deterioration was reduced by 33.4% by each increase in the HRV-CV of 1%, 12.7% for the same HRV-CV increase during deep breathing while LF band of 1ms(2) results in 8.6% risk reduction.

CONCLUSIONS

This study provides evidence that DR should not be considered merely a metabolic control manifestation and that HRV-CV as well as spectral indices of HRV might serve as a practical tool to identify a subgroup of T1DM patients with higher risk of retinal deterioration.

Effects of Lifshitz transition on charge transport in magnetic phases of Fe-based superconductors

The unusual temperature dependence of the resistivity and its in-plane anisotropy observed in the Fe-based superconducting materials, particularly Ba(Fe_{1-x}Co_{x})_{2}As_{2}, has been a long-standing puzzle. Here, we consider the effect of impurity scattering on the temperature dependence of the average resistivity within a simple two-band model of a dirty spin density wave metal. The sharp drop in resistivity below the Néel temperature T_{N} in the parent compound can only be understood in terms of a Lifshitz transition following Fermi surface reconstruction upon magnetic ordering. We show that the observed resistivity anisotropy in this phase, arising from nematic defect structures, is affected by the Lifshitz transition as well.

Absence of metallicity in K-doped picene: importance of electronic correlations

Potassium-doped picene (K(x)picene) has recently been reported to be a superconductor at x=3 with critical temperatures up to 18 K. Here we study the electronic structure of K-doped picene films by photoelectron spectroscopy and ab initio density functional theory combined with dynamical mean-field theory (DFT+DMFT). Experimentally we observe that, except for spurious spectral weight due to the lack of a homogeneous chemical potential at low K concentrations (x≈1), the spectra always display a finite energy gap. This result is supported by our DFT+DMFT calculations which provide clear evidence that K(x)picene is a Mott insulator for integer doping concentrations x=1, 2, and 3. We discuss various scenarios to understand the discrepancies with previous reports of superconductivity and metallic behavior.

Dependence of the excitability of pituitary cells on cyclic nucleotides

Cyclic 3',5'-adenosine monophosphate and cyclic 3',5'-guanosine monophosphate are intracellular (second) messengers that are produced from the nucleotide triphosphates by a family of enzymes consisting of adenylyl and guanylyl cyclases. These enzymes are involved in a broad array of signal transduction pathways mediated by the cyclic nucleotide monophosphates and their kinases, which control multiple aspects of cell function through the phosphorylation of protein substrates. We review the findings and working hypotheses on the role of the cyclic nucleotides and their kinases in the control of electrical activity of the endocrine pituitary cells and the plasma membrane channels involved in this process.

Dependence of spontaneous electrical activity and basal prolactin release on nonselective cation channels in pituitary lactotrophs

All secretory anterior pituitary cells fire action potentials spontaneously and exhibit a high resting cation conductance, but the channels involved in the background permeability have not been identified. In cultured lactotrophs and immortalized GH(3) cells, replacement of extracellular Na(+) with large organic cations, but not blockade of voltage-gated Na(+) influx, led to an instantaneous hyperpolarization of cell membranes that was associated with a cessation of spontaneous firing. When cells were clamped at -50 mV, which was close to the resting membrane potential in these cells, replacement of bath Na(+) with organic cations resulted in an outward-like current, reflecting an inhibition of the inward holding membrane current and indicating loss of a background-depolarizing conductance. Quantitative RT-PCR analysis revealed the high expression of mRNA transcripts for TRPC1 and much lower expression of TRPC6 in both lactotrophs and GH(3) cells. Very low expression of TRPC3, TRPC4, and TRPC5 mRNA transcripts were also present in pituitary but not GH(3) cells. 2-APB and SKF-96365, relatively selective blockers of TRPC channels, inhibited electrical activity, Ca(2+) influx and prolactin release in a concentration-dependent manner. Gd(3+), a common Ca(2+) channel blocker, and flufenamic acid, an inhibitor of non-selective cation channels, also inhibited electrical activity, Ca(2+) influx and prolactin release. These results indicate that nonselective cation channels, presumably belonging to the TRPC family, contribute to the background depolarizing conductance and firing of action potentials with consequent contribution to Ca(2+) influx and hormone release in lactotrophs and GH(3) cells.

The antihyperalgesic effect of levetiracetam in an inflammatory model of pain in rats: mechanism of action

BACKGROUND AND PURPOSE

Levetiracetam, a novel antiepileptic drug, has recently been shown to have antinociceptive effects in various animal models of pain. The purpose of this study was to investigate the antihyperalgesic effect of levetiracetam and its mechanism of action, by examining the involvement of GABAergic, opioidergic, 5-hydroxytryptaminergic (5-HTergic) and adrenergic systems in its effect, in a rat model of inflammatory pain.

EXPERIMENTAL APPROACH

Rats were intraplantarly injected with the pro-inflammatory compound carrageenan. A paw pressure test was used to determine: (i) the effect of levetiracetam on carrageenan-induced hyperalgesia; and (ii) the effects of bicuculline (selective GABA(A) receptor antagonist), naloxone (non-selective opioid receptor antagonist), methysergide (non-selective 5-HT receptor antagonist) and yohimbine (selective alpha(2)-adrenoceptor antagonist) on the antihyperalgesic action of levetiracetam.

RESULTS

Levetiracetam (10-200 mg.kg(-1); p.o.) significantly reduced, in a dose-dependent manner, the inflammatory hyperalgesia induced by carrageenan. The antihyperalgesic effect of levetiracetam was significantly decreased after administration of bicuculline (0.5-2 mg.kg(-1); i.p.), naloxone (1-3 mg.kg(-1); i.p.), methysergide (0.25-1 mg.kg(-1); i.p.) and yohimbine (1-3 mg.kg(-1); i.p.).

CONCLUSIONS AND IMPLICATIONS

These results show that levetiracetam produced antihyperalgesia which is at least in part mediated by GABA(A), opioid, 5-HT and alpha(2)-adrenergic receptors, in an inflammatory model of pain. The efficacy of levetiracetam in this animal model of inflammatory pain suggests that it could be a potentially important agent for treating inflammatory pain conditions in humans.

Role of alpha2-adrenoceptors in the local peripheral antinociception by carbamazepine in a rat model of inflammatory mechanical hyperalgesia

The anticonvulsant carbamazepine was recently shown to possess local peripheral antinociceptive properties. In this study, we investigated whether alpha2-adrenergic receptors are involved in the local peripheral antihyperalgesic effects of carbamazepine and determined the type of interaction between carbamazepine and clonidine, an alpha2-adrenoceptor agonist. Intraplantar (i.pl.) coadministration of either carbamazepine (100-1000 nmol/paw) or clonidine (1.9-3.7 nmol/paw) with the proinflammatory compound concanavalin A (Con A; 0.8 mg/paw) caused a significant dose- and time-dependent reduction of the difference between the forces exerted by a rat's hind paws in a modified paw-pressure test. The coadministration of 260 and 520 nmol/paw (i.pl.) yohimbine, an alpha2-adrenoceptor antagonist, with carbamazepine, significantly depressed the local antihyperalgesic effect in a dose- and time-dependent manner whereas yohimbine by itself did not have any effect. The administration of a mixture of carbamazepine and clonidine at fixed dose fractions (1/4, 1/2 and 3/4) of ED50 caused a significant and dose-dependent reduction of Con A-induced hyperalgesia. Isobolographic analysis revealed an additive interaction. These results suggest that alpha2-adrenoceptors play a role in the local peripheral antihyperalgesic effects of carbamazepine and that local peripheral coadministration of carbamazepine with clonidine results in an additive antihyperalgesic effect.

Dependence of hyperpolarisation-activated cyclic nucleotide-gated channel activity on basal cyclic adenosine monophosphate production in spontaneously firing GH3 cells

The hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels play a distinct role in the control of membrane excitability in spontaneously active cardiac and neuronal cells. Here, we studied the expression and role of HCN channels in pacemaking activity, Ca(2+) signalling, and prolactin secretion in GH(3) immortalised pituitary cells. Reverse transcriptase-polymerase chain reaction analysis revealed the presence of mRNA transcripts for HCN2, HCN3 and HCN4 subunits in these cells. A hyperpolarisation of the membrane potential below - 60 mV elicited a slowly activating voltage-dependent inward current (I(h)) in the majority of tested cells, with a half-maximal activation voltage of -89.9 +/- 4.2 mV and with a time constant of 1.4 +/- 0.2 s at -120 mV. The bath application of 1 mM Cs(+), a commonly used inorganic blocker of I(h), and 100 microM ZD7288, a specific organic blocker of I(h), inhibited I(h) by 90 +/- 4.1% and 84.3 +/- 1.8%, respectively. Receptor- and nonreceptor-mediated activation of adenylyl and soluble guanylyl cyclase and the addition of a membrane permeable cyclic adenosine monophosphate (cAMP) analogue, 8-Br-cAMP, did not affect I(h). Inhibition of basal adenylyl cyclase activity, but not basal soluble guanylyl cyclase activity, led to a reduction in the peak amplitude and a leftward shift in the activation curve of I(h) by 23.7 mV. The inhibition of the current was reversed by stimulation of adenylyl cyclase with forskolin and by the addition of 8-Br-cAMP, but not 8-Br-cGMP. Application of Cs(+) had no significant effect on the resting membrane potential or electrical activity, whereas ZD7288 exhibited complex and I(h)-independent effects on spontaneous electrical activity, Ca(2+) signalling, and prolactin release. These results indicate that HCN channels in GH(3) cells are under tonic activation by basal level of cAMP and are not critical for spontaneous firing of action potentials.

[Dermatomyositis and malignant disease--case report]

The case of patients with dermatomyositis and malignant disease has been described. The diagnosis of malignant disease was made after death of the patient, when the malignant undifferentiated cells were found in the ascites. We think that dermatomyosistis was caused by malignant disease. The similar cases of disease were described and published in the literature.

Effect of Helicobacter pylori eradication on extent of duodenal gastric metaplasia and grade of gastritis

The extent of the regression of duodenal gastric metaplasia (DGM) after the eradication of Helicobacter pylori infection is controversial. Therefore, we decided to assess the degree of DGM before, sex weeks and one year after H. pylori eradication. 105 consecutive Helicobacter pylori positive patients with endoscopically proven duodenal ulcer, with DGM and Helicobacter pylori infection were recruited for this study. The diagnosis of Helicobacter pylori infection was based on CLO-test and histology, and DGM was assessed on four bulb biopsies taken before, sex weeks and one year after Helicobacter pylori eradication. Histological assessment of Helicobacter pylori associated gastritis was performed according to the Sydney classification. Follow up study on 98 patients before, six weeks and one year after the eradication of Helicobacter pylori showed that the mean extent of DGM did not change significantly after eradication and did not differ when compared with 14 patients with persisting infection. Our results show that the inflammatory process related to Helicobacter pylori does not play the main role in the development of DGM.

Regulation of Ca2+-sensitive adenylyl cyclase in gonadotropin-releasing hormone neurons

In immortalized GnRH neurons, cAMP production is elevated by increased extracellular Ca2+ and the Ca2+ channel agonist, BK-8644, and is diminished by low extracellular Ca2+ and treatment with nifedipine, consistent with the expression of adenylyl cyclase type I (AC I). Potassium-induced depolarization of GT1-7 neurons causes a dose-dependent monotonic increase in [Ca2+]i and elicits a bell-shaped cAMP response. The inhibitory phase of the cAMP response is prevented by pertussis toxin (PTX), consistent with the activation of G(i)-related proteins during depolarization. Agonist activation of the endogenous GnRH receptor in GT1-7 neurons also elicits a bell-shaped change in cAMP production. The inhibitory action of high GnRH concentrations is prevented by PTX, indicating coupling of the GnRH receptors to G(i)-related proteins. The stimulation of cAMP production by activation of endogenous LH receptors is enhanced by low (nanomolar) concentrations of GnRH but is abolished by micromolar concentrations of GnRH, again in a PTX-sensitive manner. These findings indicate that GnRH neuronal cAMP production is maintained by Ca2+ entry through voltage-sensitive calcium channels, leading to activation of Ca2+-stimulated AC I. Furthermore, the Ca2+ influx-dependent activation of AC I acts in conjunction with AC-regulatory G proteins to determine basal and agonist-stimulated levels of cAMP production.

Characterization of purinergic receptors and receptor-channels expressed in anterior pituitary cells

Purinergic G protein-coupled receptors (P2YR) and ion-conducting receptor-channels (P2XR) are present in the pituitary. However, their identification, expression within pituitary cell subpopulations, and the ability to elevate intracellular Ca2+ concentration ([Ca2+]i) in response to ATP stimulation were incompletely characterized. Here we show that mixed populations of rat anterior pituitary cells express messenger RNA transcripts for P2Y2R, P2X2aR, P2X2bR, P2X3R, P2X4R, and P2X7R. The transcripts and functional P2Y2R were identified in lactotrophs and GH3 cells, but not in somatotrophs and gonadotrophs, and their activation by ATP led to an extracellular Ca2+-independent rise in [Ca2+]i in about 40% of cells tested. Lactotrophs and GH3 cells, but not somatotrophs, also express transcripts for P2X7R, P2X3R, and P2X4R. Functional P2X7R were identified in 74% of lactotrophs, whereas 50% of these cells expressed P2X3R and 33% expressed P2X4R. Coexpression of these receptor subtypes in single lactotrophs was frequently observed. Purified somatotrophs expressed transcripts for P2X2aR and P2X2bR, and functional receptors were identified in somatotrophs and gonadotrophs, but not in lactotrophs. Consistent with the cell-specific expression of transcripts for P2X2R and P2X3R, the expression of their functional heteromers was not evident in pituitary cells. Receptors differed in their capacities to elevate and sustain Ca2+ influx-dependent rise in [Ca2+]i during the prolonged ATP stimulation. These results indicate that the purinergic system of anterior pituitary is extremely complex and provides an effective mechanism for generating a cell- and receptor-specific Ca2+ signaling pattern in response to a common agonist.

Characterization of calcium signaling by purinergic receptor-channels expressed in excitable cells

ATP-gated purinergic receptors (P2XRs) are a family of cation-permeable channels that conduct Ca(2+) and facilitate voltage-sensitive Ca(2+) entry in excitable cells. To study Ca(2+) signaling by P2XRs and its dependence on voltage-sensitive Ca(2+) influx, we expressed eight cloned P2XR subtypes individually in gonadotropin-releasing hormone-secreting neurons. In all cases, ATP evoked an inward current and a rise in [Ca(2+)](i). P2XR subtypes differed in the peak amplitude of [Ca(2+)](i) response independently of the level of receptor expression, with the following order: P2X(1)R < P2X(3)R < P2X(4)R < P2X(2b)R < P2X(2a)R < P2X(7)R. During prolonged agonist stimulation, Ca(2+) signals desensitized with different rates: P2X(3)R > P2X(1)R > P2X(2b)R > P2X(4)R >> P2X(2a)R >> P2X(7)R. The pattern of [Ca(2+)](i) response for each P2XR subtype was highly comparable with that of the depolarizing current, but the activation and desensitization rates were faster for the current than for [Ca(2+)](i). The P2X(1)R, P2X(3)R, and P2X(4)R-derived [Ca(2+)](i) signals were predominantly dependent on activation of voltage-sensitive Ca(2+) influx, both voltage-sensitive and -insensitive Ca(2+) entry pathways equally contributed to [Ca(2+)](i) responses in P2X(2a)R- and P2X(2b)R-expressing cells, and P2X(7)R operated as a nonselective pore capable of conducting larger amounts of Ca(2+) independently on the status of voltage-gated Ca(2+) channels. Thus, Ca(2+) signaling by homomeric P2XRs expressed in an excitable cell is subtype-specific, which provides an effective mechanism for generating variable [Ca(2+)](i) patterns in response to a common agonist.

[New diagnostic criteria and classification of diabetes mellitus]

World Health Organisation (WHO) has recently proposed new diagnostic criteria and classification of diabetes mellitus. A major change in diagnostic criteria is lowering of diagnostic fasting plasma glucose level: level of 7.0 mM/L or more in two separate samples is sufficient for the diagnosis. Diagnostic criteria for plasma glucose in 120-min. of oral glucose tolerance test are unchanged. Newly recommended fasting level seems to correlate better with 120-min. value and to be a good marker of increased cardiovascular risk. The new classification describes impaired glucose regulation with two stages: impaired fasting glycaemia (plasma glucose of 6.1-7.0 mM/L) which is a new category and impaired glucose tolerance. Both subcategories are not real clinical entities, but markers of diabetic and cardiovascular risk. Diabetes mellitus, as a clinical entity, is separated in four classes: type 1, type 2, other specific types and gestational diabetes. Gestational diabetes includes any glucose intolerance in pregnancy. The Croatian Board for Diabetes Mellitus recommends acceptance of these criteria and classification for clinical use in the country and suggests that OGTT be performed for metabolic syndrome detection in cases of impaired fasting glycaemia.

Local Regulation of Gonadotroph Function by Pituitary Gonadotropin-Releasing Hormone

Cultured rat pituitary cells and immortalized pituitary gonadotrophs (alphaT3-1 cells) express specific messenger RNA transcripts for GnRH and exhibit positive immunostaining for the GnRH peptide. Each cell type released GnRH during both static culture and perifusion, albeit in lesser amounts than cultured hypothalamic cells and GT1-7 neurons. In perifused pituitary cells, exposure to a GnRH agonist stimulated the release of GnRH as well as LH. In contrast, treatment with a GnRH receptor antagonist or with GnRH antiserum decreased basal LH release. In pituitary cell cultures, a small proportion of gonadotrophs exhibited high amplitude and low frequency baseline Ca2+ oscillations in the absence of GnRH stimulation. Such spontaneous oscillations were comparable to those induced by picomolar concentrations of GnRH and could be abolished by treatment with a GnRH antagonist. These in vitro findings indicate that locally produced GnRH causes low level activation of pituitary GnRH receptors, induces spontaneous intracellular Ca2+ oscillations, and contributes to basal LH secretion in cultured pituitary cells. In vivo, such autocrine or paracrine actions of pituitary-derived GnRH could provide a mechanism for the maintenance of optimal responsiveness of the gonadotrophs to pulses of GnRH arising in the hypothalamus. The presence and actions of GnRH in the anterior pituitary gland, the major site of expression of GnRH receptors, suggest that local regulatory effects of the neuropeptide could supplement the primary hypothalamic mechanism for the control of episodic gonadotropin secretion.

Psychotomimetics moderately affect dopamine receptor binding in the rat brain

The hypothesis that psychotomimetics induce a rapid dopamine receptor regulation that could participate in the expression of the brain dopaminergic overactivation and in the early signs of psychotic-like behaviour, was checked by radioligand binding on rat brain cryosections. For this purpose, subchronic 7-day-d-amphetamine pretreatment was combined with acute amphetamine, phencyclidine or LSD challenge. Acute application of psychotomimetics affected only striatal and accumbens but not nigral and olfactory dopamine receptor binding after 40 min, while subchronic amphetamine expressed no effect, as revealed by two-way ANOVA. Post-hoc statistical analysis showed that only striatal and accumbens[3H]SCH 23390 binding decrease (10-12%) following phencyclidine and striatal [3H]spiperone binding increase (11%) after acute amphetamine were significant. It is assumed that such moderate dopamine receptor binding changes probably reflect the fast receptor regulation responses without important influence on a proposed drug-induced dopaminergic overactivity. The registered alterations of D1 receptor binding after phencyclidine are suggested to be capable to modify the activity of some other neural pathways in the basal ganglia and thus participate in a psychotic-like behaviour.

Characterization of a plasma membrane calcium oscillator in rat pituitary somatotrophs

In excitable cells, oscillations in intracellular free calcium concentrations ([Ca(2+)](i)) can arise from action-potential-driven Ca(2+) influx, and such signals can have either a localized or global form, depending on the coupling of voltage-gated Ca(2+) influx to intracellular Ca(2+) release pathway. Here we show that rat pituitary somatotrophs generate spontaneous [Ca(2+)](i) oscillations, which rise from fluctuations in the influx of external Ca(2+) and propagate within the cytoplasm and nucleus. The addition of caffeine and ryanodine, modulators of ryanodine-receptor channels, and the depletion of intracellular Ca(2+) stores by thapsigargin and ionomycin did not affect the global nature of spontaneous [Ca(2+)](i) signals. Bay K 8644, an L-type Ca(2+) channel agonist, initiated [Ca(2+)](i) signaling in quiescent cells, increased the amplitude of [Ca(2+)](i) spikes in spontaneously active cells, and stimulated growth hormone secretion in perifused pituitary cells. Nifedipine, a blocker of L-type Ca(2+) channels, decreased the amplitude of spikes and basal growth hormone secretion, whereas Ni(2+), a blocker of T-type Ca(2+) channels, abolished spontaneous [Ca(2+)](i) oscillations. Spiking was also abolished by the removal of extracellular Na(+) and by the addition of 10 mM Ca(2+), Mg(2+), or Sr(2+), the blockers of cyclic nucleotide-gated channels. Reverse transcriptase-polymerase chain reaction and Southern blot analyses indicated the expression of mRNAs for these channels in mixed pituitary cells and purified somatotrophs. Growth hormone-releasing hormone, an agonist that stimulated cAMP and cGMP productions in a dose-dependent manner, initiated spiking in quiescent cells and increased the frequency of spiking in spontaneously active cells. These results indicate that in somatotrophs a cyclic nucleotide-controlled plasma membrane Ca(2+) oscillator is capable of generating global Ca(2+) signals spontaneously and in response to agonist stimulation. The Ca(2+)-signaling activity of this oscillator is dependent on voltage-gated Ca(2+) influx but not on Ca(2+) release from intracellular stores.

Expression and responsiveness of P2Y2 receptors in human endometrial cancer cell lines

In single endometrial carcinoma HEC-1A and Ishikawa cells, ATP induced a rapid and extracellular Ca2+-independent rise in cytosolic Ca2+ concentration ([Ca2+]i) in a dose-dependent manner, with an ED50 of about 10 microM. The spike phase was followed by a sustained plateau phase that was dependent on Ca2+ influx through voltage-insensitive Ca2+ channels, whose gating was controlled by a capacitative Ca2+ entry mechanism. ADP was less potent in raising the cystolic Ca2+ concentration, and AMP and adenosine were ineffective. The order of agonist potency for this receptor was ATP = UTP > ATP-gamma-S >> ADP. Several other agonists, including beta,gamma-methylene-ATP, 2-MeS-ATP, and BzATP were ineffective. This ligand-selective profile indicates the expression of the P2Y2R subtype in endometrial cells. Accordingly, reverse transcription-PCR using P2Y2 primers amplified the expected transcript from both cell lines. The coupling of these receptors to phospholipase C was confirmed by the ability of ATP to increase inositol 1,4,5-trisphosphate and diacylglycerol productions. These receptors are also coupled to the phospholipase D-1 pathway, leading to accumulation of phosphatidic acid. Activation of P2Y2 receptors by a slowly degradable ATP analog, ATP-gamma-S, was associated with a significant suppression of cell proliferation without affecting the cellular apoptosis. These results indicate that P2Y2 receptors may participate in control of the cell cycle of endometrial carcinoma cells.

Expression of Ca(2+)-mobilizing endothelin(A) receptors and their role in the control of Ca(2+) influx and growth hormone secretion in pituitary somatotrophs

The expression and coupling of endothelin (ET) receptors were studied in rat pituitary somatotrophs. These cells exhibited periods of spontaneous action potential firing that generated high-amplitude fluctuations in cytosolic calcium concentration ([Ca(2+)](i)). The message and the specific binding sites for ET(A), but not ET(B), receptors were found in mixed pituitary cells and in highly purified somatotrophs. The activation of these receptors by ET-1 led to an increase in inositol 1,4,5-trisphosphate production and the associated rise in [Ca(2+)](i) and growth hormone (GH) secretion. The Ca(2+)-mobilizing action of ET-1 lasted for 2-3 min and was followed by an inhibition of action potential-driven Ca(2+) influx and GH secretion to below the basal levels. As in somatostatin-treated cells, the ET-1-induced inhibition of spontaneous electrical activity and Ca(2+) influx was accompanied by the inhibition of adenylyl cyclase and by the stimulation of inward rectifier potassium current. In contrast to somatostatin, ET-1 did not inhibit voltage-gated Ca(2+) channels. During prolonged agonist stimulation a gradual recovery of Ca(2+) influx and GH secretion occurred. In somatotrophs treated with pertussis toxin overnight, the ET-1-induced Ca(2+)-mobilizing phase was preserved, but it was followed immediately by facilitated Ca(2+) influx and GH secretion. Both somatostatin- and ET-1-induced inhibitions of adenylyl cyclase activity were abolished in pertussis toxin-treated cells. These results indicate that the transient cross-coupling of Ca(2+)-mobilizing ET(A) receptors to the G(i)/G(o) pathway in somatotrophs provides an effective mechanism to change the rhythm of [Ca(2+)](i) signaling and GH secretion during continuous agonist stimulation.

Functional role of alternative splicing in pituitary P2X2 receptor-channel activation and desensitization

Although ATP-gated ion channel (P2XR) expression is high among anterior pituitary cells, identification of the receptor subtypes and their selective expression within subpopulations of cell types, as well as their physiological role(s), are incompletely characterized. In this study, we focused on the expression and activity of the P2X2R subtype in anterior pituitary cells. Our results indicate that the primary P2X2R gene transcript in pituitary cells undergoes extensive alternative splicing, with generation of six isoforms. Two of these isoforms encode functional channels when expressed in GT1 or HEK293 cells: the wild-type P2X2R and the spliced isoform P2X2-2R, which lacks a stretch of carboxyl-terminal amino acids (Val370-Gln438). Four other clones showed different alterations, including an interfered reading frame starting in the first transmembrane domain and a 27-amino acid deletion in the large extracellular loop. When expressed separately or in combination with wild-type channels, these clones were nonfunctional. In single cell Ca2+ current and cytosolic Ca2+ concentration ([Ca2+)i) measurements, the P2X2R and P2X2-2R had similar EC50 values for ATP and time courses for activation and recovery from desensitization but differed significantly in their desensitization rates. The spliced isoform exhibited rapid and complete desensitization, whereas the wild-type channel desensitized slowly and incompletely. The mRNAs for wild-type and spliced channels were identified in enriched somatotroph, but not gonadotroph or lactotroph fractions. Expression of a functional ATP-gated channel in somatotrophs was confirmed by the ability of ATP to increase the frequency of [Ca2+]i spikes in spontaneously active cells or initiate spiking in quiescent cells. When voltage-gated Ca2+ influx was blocked, ATP increased [Ca2+]i, with a similar profile and EC50 to those observed in GT1 cells heterologously expressing wild-type or spliced P2X2R. The ligand-selectivity profile of native channels was consistent with the presence of P2X2R in somatotrophs. Finally, the desensitization rate of P2X2R in a majority of somatotrophs was comparable to that observed in neurons coexpressing wild-type and spliced channels. These data indicate that alternative splicing of P2X2R and coexpression of P2X2R and P2X2-2R subunits provide effective mechanisms for controlled cationic influx in somatotrophs.

Identification of amino acid residues contributing to desensitization of the P2X2 receptor channel

The P2X2 receptor (P2X2R) is a member of the ATP-gated ion channels that mediate Ca2+ entry in several tissues, including the brain, adrenal medulla, and pituitary. Alternative usage of cryptic splice sites in the primary P2X2R transcript accounts for the existence of several transcript types, one of which (P2X2-2R) encodes a functional channel. P2X2-2R lacks a stretch of cytoplasmic C-terminal amino acids (Val370-Gln438) and exhibits rapid and complete desensitization, whereas P2X2R desensitizes slowly and incompletely. The role of the C terminus in P2X2R desensitization was studied by generating several channel mutants and monitoring intracellular free Ca2+ changes in transfected single GT1-7 neurons. Deletion studies indicated that the Arg371-Ile391 segment of the P2X2R is required for sustained Ca2+ influx. To identify the important residues within this segment, three contiguous amino acids were sequentially changed to alanine. Only two of these replacement mutants, at Arg371-Thr372-Pro373 and Lys374-His375-Pro376, had an enhanced rate of desensitization. Single amino acid deletions in the P2X2R C terminus and a series of insertions of wild-type sequences into the corresponding spliced site identified four residues, Pro373-Lys374-His375-Pro376, required for sustained Ca2+ influx through agonist-occupied wild-type channels. Thus, it is likely that the Pro373-Pro376 sequence of P2X2R represents a functional motif that is critical for the development of the slow desensitization profile observed in these channels. Consequently, deletion of this motif by alternative splicing provides an effective mechanism for generating a channel with controlled Ca2+ influx.

Acute amphetamine and/or phencyclidine effects on the dopamine receptor specific binding in the rat brain

Psychotic-like behaviour was induced in rats with a single i.p. injection of AMPH (20 mg/kg b.w.) and/or PCP (10 mg/kg b.w.). The D1 and D2 dopamine receptor (DAR) specific binding of [3H]SCH 23390 and [3H]spiperone, respectively, during the 120 min period upon the treatment was examined on cryosections using computerized scanning and image analysis. AMPH, alone or in combination with PCP, induced a transient decrease of the D1 receptor specific binding in the striatum (30 min; AMPH, -18%; AMPH+PCP, -31%) and nucleus accumbens (30 min; AMPH, -30%; AMPH+PCP, -40%), which was completely abolished at the 120 min point. Only AMPH persistently elevated nigral D1 receptor specific binding. PCP-induced striatal and accumbal D1 receptor down-regulation was intensive throughout the 120 min period, while in the s. nigra it was non-significant. A significant increase of the D2 receptor specific binding was observed only 30 min after the treatment in striatum (AMPH, 15%; PCP, 16%; AMPH+PCP, 13%) and n. accumbens (AMPH, 16%). These alterations of DAR specific binding may reflect a regulation of the DAR and the changes in nigrostriatal and mesolimbic DA-ergic neurotransmission during an intensive drug-induced psychotic-like behavioral expression.

Wortmannin-sensitive and -insensitive steps in calcium-controlled exocytosis in pituitary gonadotrophs: evidence that myosin light chain kinase mediates calcium-dependent and wortmannin-sensitive gonadotropin secretion

In cultured rat pituitary cells, increases in the cytosolic calcium concentration ([Ca2+]i) and LH release are induced by activation of GnRH receptors as well as by nonreceptor-mediated stimuli. Treatment of pituitary cells with the myosin light chain kinase (MLCK) inhibitor, wortmannin, attenuated GnRH-induced LH release. Wortmannin also reduced the LH responses to nonreceptor-mediated elevation of [Ca2+]i by ionomycin and activation of voltage-sensitive Ca2+ channels by Bay K 8644 or high K+, as well as Ca2+-induced LH release in permeabilized pituitary cells. The [Ca2+]i responses to these stimuli were unaltered in wortmannin-treated pituitary cells, indicating that this compound inhibits a Ca2+-dependent step in exocytosis without affecting Ca2+ signaling. In perifused pituitary cells, the GnRH-induced early spike phase of LH release was not affected by wortmannin, whereas the subsequent plateau phase was almost completely inhibited. No significant changes in GnRH-induced phospholipase D activity and diacylglycerol production were observed in wortmannin-treated pituitary cells during the sustained phase of agonist stimulation. Wortmannin also had no effect on LH responses to the protein kinase C activator, phorbol 12-myristate 13-acetate, further indicating that the attenuation of agonist-induced LH release is not related to inhibition of the diacylglycerol/protein kinase C pathway. In addition, agonist-induced LH release was attenuated by two other MLCK inhibitors, MS-347a and KT5926. These data suggest that MLCK mediates the downstream effects of Ca2+ on exocytosis, an action supported by the finding of wortmannin-sensitive phosphorylation of a 20-kDa protein in pituitary cells and alphaT3-1 gonadotrophs treated with GnRH, K+, and Bay K 8644. This protein was coprecipitated from pituitary extracts with a specific antibody to nonmuscle myosin IIB and comigrated with 20-kDa smooth muscle myosin light chain on SDS-PAGE. These results demonstrate that Ca2+ controls exocytosis through an initial wortmannin-insensitive step and a sustained wortmannin-sensitive step and suggest that the latter event in the cascade of cellular responses is dependent on phosphorylation of nonmuscle myosin IIB light chain by MLCK.

GnRH-induced calcium and current oscillations in gonadotrophs

The rat pituitary gonadotroph is a well-studied cell model for investigation of the oscillatory nature of calcium signaling in agonist-stimulated excitable cells. Cytosolic calcium levels ([Ca(2+)](i)) in gonadotrophs are controlled by two distinct oscillators, a plasma membrane oscillator that generates extracellular calcium-dependent low-amplitude [Ca(2+)](i) spiking in unstimulated cells and an endoplasmic reticulum oscillator that is activated by calcium-mobilizing receptors for GnRH, endothelin, and pituitary adenylate cyclase-activating polypeptide. In this review, the characteristics of the spontaneous and agonist-induced calcium oscillations in gonadotrophs and the coordinate actions of the two oscillators during GnRH action discussed.

Expression of purinergic receptor channels and their role in calcium signaling and hormone release in pituitary gonadotrophs. Integration of P2 channels in plasma membrane- and endoplasmic reticulum-derived calcium oscillations

The role of ATP as a positive feedback element in Ca2+ signaling and secretion was examined in female rat pituitary gonadotrophs. ATP and ADP, but not AMP or adenosine, induced a dose- and extracellular Ca2+-dependent rise in [Ca2+]i in identified gonadotrophs in a Mg2+- and suramin-sensitive manner. ATP, adenosine-5'-O-(3-thiotriphosphate), adenosine-5'-O-(1-thiotriphosphate), 2-methylthio-ATP, and 3'-O-(4-benzoyl)benzoyl-ATP were roughly equipotent in rising [Ca2+]i in gonadotrophs, while ADP was effective only at submillimolar concentration range, and none of these compounds permeabilized the cells. On the other hand, alpha,beta-methylene-ATP, beta,gamma-methylene-ATP, and UTP were unable to induce any rise in [Ca2+]i. This pharmacological profile is consistent with expression of P2X2 and/or P2X5 purinergic receptor channels. Patch-clamp experiments showed that ATP induced an inward depolarizing current in gonadotrophs clamped at -90 mV, associated with an increase in [Ca2+]i. The ATP-induced [Ca2+]i response was partially inhibited by nifedipine, a blocker of voltage-sensitive Ca2+ channels (VSCC), but was not affected by tetrodotoxin, a blocker of voltage-sensitive Na+ channels. Thus, the P2-depolarizing current itself drives Ca2+ into the cell, but also activates Ca2+ entry through VSCC. In accord with this, low [ATP] induced plasma membrane-dependent [Ca2+]i oscillations in quiescent cells, and increased the frequency of spiking in spontaneously active cells. ATP-induced Ca2+ influx also affected agonist-induced and InsP3-dependent [Ca2+]i oscillations by increasing the frequency, base line, and duration of Ca2+ spiking. In addition, ATP stimulated gonadotropin secretion and enhanced agonist-induced gonadotropin release. ATP was found to be secreted by pituitary cells during agonist stimulation and was promptly degraded by ectonucleotidase to adenosine. These observations indicate that ATP represents a paracrine/autocrine factor in the regulation of Ca2+ signaling and secretion in gonadotrophs, and that these actions are mediated by P2 receptor channels.

Gonadotropin-releasing hormone-induced sensitization of calcium-dependent exocytosis in pituitary gonadotrophs

Agonist-induced increases in cytoplasmic calcium concentration ([Ca2+]i) play a pivotal role in regulated exocytosis by promoting the fusion of secretory vesicles with the plasma membrane. In permeabilized and ATP-primed pituitary cells, increases in ambient [Ca2+]i stimulated the release of LH from gonadotrophs with an EC50 of 2-3 microM. In contrast, the responses of intact gonadotrophs to agonist stimulation by GnRH were characterized by transient [Ca2+]i elevations of up to 1.5 microM, followed by a plateau of 300-400 nM. The sensitivity of the exocytotic response of permeabilized cells to [Ca2+]i was significantly increased by GnRH, which reduced the EC50 for [Ca2+]i to the submicromolar concentration range. The stimulatory action of GnRH on LH release in permeabilized cells was not a consequence of intracellular Ca2+ release, but was associated with increased cytidine diphosphate diacylglycerol production. Activation of protein kinase C by phorbol esters caused a similar increase in the Ca2+ sensitivity of LH release from permeabilized cells, and this effect was not additive to that of GnRH. Furthermore, the GnRH-induced increase in the sensitivity of the exocytotic response to Ca2+ was attenuated by inhibitors of protein kinase C. These findings indicate that although elevated [Ca2+]i per se can promote LH release from permeabilized gonadotrophs, concomitant activation of protein kinase C is necessary to support exocytosis at the physiological [Ca2+]i levels that prevail in GnRH-stimulated intact cells. Such sensitization of the Ca(2+)-dependent secretory mechanism by protein kinase C may be an important step in the agonist-induced release of LH from pituitary gonadotrophs.

Calcium signaling in single rat Leydig cells

The steroidogenic activity of the Leydig cell is regulated by glycoprotein and peptide hormones with the potential to activate both adenylate cyclase and phospholipase C. Although the control of androgen production by LH is clearly mediated by cAMP, the extent to which Ca(2+)-mobilizing stimuli control Leydig cell function is less well defined. The basal level of intracellular calcium ([Ca2+]i) in adult rat Leydig cells was 70-160 nM and was unaffected by high K+ or the dihydropyridine calcium channel agonist, Bay K 8644. These findings are consistent with the absence of voltage-sensitive calcium channels in the Leydig cell. In addition, no increase in [Ca2+]i was observed in cells treated with LH, CRF, and serotonin. However, both GnRH and endothelin-1 (ET-1) induced rapid and transient elevations of [Ca2+]i that were not associated with a sustained plateau phase and were unaffected by removal of Ca2+ from the incubation medium. The amplitude of the [Ca2+]i response was not altered by increasing concentrations of GnRH and ET-1, but the number of responsive cells increased progressively to a maximum of about 30% of the Leydig cell population. The calcium-mobilizing actions of GnRH and ET-1 were abolished by the GnRH and ETA receptor antagonists, [Dp-Glu1,D-Phe2,D- Trp3,6]GnRH and BQ-123, respectively. The majority of the cells expressed solely GnRH or ETA receptors, and about 10% expressed both receptors. GnRH-induced Ca2+ responses were observed almost exclusively in medium-sized Leydig cells, whereas ET-induced responses were most frequent in large Leydig cells. These data demonstrate that single Leydig cells expressing GnRH and ETA receptors exhibit monophasic [Ca2+]i responses that are activated in an all-or-none fashion. Such transient Ca2+ signaling may trigger short term cellular responses or could modulate the actions of gonadotropins acting through the cAMP signaling pathway.

Effects of endothelin-1 on Ca2+ signaling and secretion in parathyroid cells

It has been previously reported that parathyroid cells express endothelin (ET) receptors and secrete ET-1 in an extracellular Ca2+ concentration ([Ca2+]e)-dependent manner. Here, we examined the effects of ET-1 on intracellular signaling and parathyroid hormone (PTH) secretion in dispersed bovine parathyroid (bPT) cells, which comprise several cell types including epithelial and endothelial cells, in two cell lines, the rat parathyroid epithelial (PT-r) and the bovine parathyroid endothelial (BPE-1) cells. An RNA-polymerase chain reaction analysis revealed that both ETA and ETB receptors are expressed in bovine parathyroid tissue and BPE-1 cells, and only the ETA receptor is expressed in PT-r cells. PT-r cells also expressed an inositol 1,4,5-trisphosphate (Ins[1,4,5]P3) receptor, and ionomycin induced an increase in the intracellular Ca2+ concentrations ([Ca2+]i) in a Ca(2+)-deficient medium, indicating the presence of an operative intracellular Ca2+ pool in these cells. In cells bathed in 1 mM [Ca2+]e, ET-1 induced a rapid and transient increase in the Ins(1,4,5)P3 production, which was associated with a similar profile of increase in [Ca2+]i and with a peak response of about 800 nM. No changes in the profile of [Ca2+]i responses were observed in ET-1-stimulated cells in the presence of Ca2+ channel blockers, or in Ca(2+)-deficient medium, indicating that Ca2+ mobilization was not associated with Ca2+ entry. Furthermore, a sustained stimulation with ET-1 induced a decrease in [Ca2+]i below the prestimulatory level in a large population of cells, and the percentage of the cell population that shows the sustained decrease of [Ca2+]i increased in higher ET-1 concentrations. [Ca2+]i in PT-r cells was also controlled by a [Ca2+]e-dependent mechanism that changed [Ca2+]i from 28 to 506 nM in a 0.1-3 mM concentration range with an EC50 of 1.2 mM, which is comparable to that reported for bPT cells. In the same range of [Ca2+]e, PTH secretion from bPT cells was inhibited with an IC50 of 1 mM, and ET-1 increased PTH release in a dose-dependent manner but without affecting the IC50 for the [Ca2+]e-dependent inhibition. Thus, the parathyroid epithelial cells appear to respond to ET-1 in a unique way, and the ET autocrine system can be regarded as a possible mechanism to modulate the sensitivity of [Ca2+]e-dependent PTH release.

Effects of the phospholipase-C inhibitor, U73122, on signaling and secretion in pituitary gonadotrophs

The effects of inhibition of phosphoinositide hydrolysis by U73122 [1-(6-[17 beta-3-methoxyestra-1,3,5- (10) triene-17-yl] amino/hexyl) 1H-pyrroledione] and neomycin on agonist-stimulated intracellular signaling and secretory responses were analyzed in cultured pituitary cells and alpha T3-1 gonadotrophs. GnRH (100 nM)- and endothelin-1 (ET-1; 100 nM)-induced inositol (1,4,5)-trisphosphate and diacylglycerol formation in normal cells and immortalized gonadotrophs were reduced by U73122 in a concentration-dependent manner, with IC50 values of about 2 microM and complete inhibition at 10 microM U73122. Neomycin also reduced GnRH- and ET-induced inositol phosphate production in both cell types. Agonist-induced intracellular Ca2+ responses were also inhibited in both cell types by U73122 and neomycin at the same concentrations that inhibited their inositol phosphate responses. In cultured pituitary cells, agonist-induced LH release was inhibited by U73122 and neomycin in a dose-dependent manner. In perifused pituitary cells, U73122 completely inhibited GnRH- and ET-1-induced LH release, but after 10 min caused a progressive and substantial increase in basal LH release. In static cultures, U73122 inhibited agonist-induced LH response at low concentrations (up to 3 microM), but stimulated LH release at higher concentrations due to direct activation of exocytosis by the compound. When added alone, U73122 caused a concentration-dependent increase in LH release with an EC50 of about 7 microM and a maximum response similar that that elicited by GnRH. The stimulatory action of U73122 on LH release was not reduced in the absence of extracellular Ca2+. In contrast to cultured pituitary cells, alpha T3-1 gonadotrophs showed only constitutive exocytosis that was not affected by either neomycin or U73122. These results demonstrate that GnRH and ET(A) receptors are coupled to the phosphoinositide/Ca2+ transduction system in pituitary gonadotrophs, and provide evidence for the dependence of agonist-regulated exocytosis on this signaling pathway. The ability of U73122 to stimulate LH release could reflect an additional action of the compound at late steps in the exocytic pathway.

Developmental and physiological aspects of Ca2+ signaling in agonist-stimulated pituitary gonadotrophs

GnRH-induced Ca2+ signaling was analyzed in gonadotrophs from pituitary glands of neonatal, prepubertal, peripubertal, cycling, and ovariectomized female and adult male rats. In all cases, single cell studies showed three types of Ca2+ responses to increasing GnRH concentrations: subthreshold, baseline oscillatory, and biphasic (an early transient followed by sustained oscillations or a plateau). An increase in the frequency, but not the amplitude, of spiking, and the presence of both baseline oscillatory and biphasic Ca2+ responses were observed in single cells from all groups exposed to low and subsequently to higher GnRH concentrations. Thus, modulation of the frequency of Ca2+ spiking at low to medium GnRH concentrations and suppression of the oscillatory response at high agonist concentrations are characteristics of the gonadotroph that are not affected by age, sex, stage of the estrous cycle, or gonadectomy. Ca2+ influx through plasma membrane channels contributed to both baseline oscillatory and biphasic responses, and both types of Ca2+ signaling were associated with LH release. The sensitivity of gonadotrophs to GnRH stimulation was similar in cells from single and multigland preparations from the same group of donors, but varied according to age and physiological status. Thus, sensitivity was low in neonatal gonadotrophs and progressively increased in postnatal cells. In cycling females, gonadotrophs from proestrous animals were more sensitive than those from estrous and diestrous animals. Ca2+ signaling was more uniform in gonadotrophs from ovariectomized than in those from normal females. During prolonged culture there was an increase in the frequency of Ca2+ spiking in response to 1 nM GnRH over the first 3 days, followed by a gradual decrease over 7-10 days and loss of the response in older cultures. These changes in Ca2+ signaling were accompanied by similar changes in the GnRH-induced secretory responses. These data indicate that frequency-controlled spiking, with suppression of the oscillatory mechanism at high agonist concentrations, is a characteristic of Ca2+ signaling in rat gonadotrophs. In addition, developmental, physiological, and in vitro changes in pituitary sensitivity to GnRH are expressed through modulation of the Ca2+ signal and the consequent secretory response.

Expression of gonadotropin-releasing hormone receptors and autocrine regulation of neuropeptide release in immortalized hypothalamic neurons

The hypothalamic control of gonadotropin secretion is mediated by episodic basal secretion and midcycle ovulatory surges of gonadotropin-releasing hormone (GnRH), which interacts with specific plasma membrane receptors in pituitary gonadotrophs. Similar GnRH receptors and their mRNA transcripts were found to be expressed in immortalized hypothalamic neurons, which release GnRH in a pulsatile manner in vitro. Activation of these neuronal GnRH receptors elicited dose-related intracellular Ca2+ concentration responses that were dependent on calcium mobilization and entry and were inhibited by GnRH antagonists. Exposure of perifused neurons to a GnRH agonist analog caused a transient elevation of GnRH release and subsequent suppression of the basal pulsatile secretion. This was followed by dose-dependent induction of less frequent but larger GnRH pulses and ultimately by single massive episodes of GnRH release. The ability of GnRH to exert autocrine actions on its secretory neurons, and to promote episodic release and synchronized discharge of the neuropeptide, could reflect the operation of the endogenous pulse generator and the genesis of the preovulatory GnRH surge in vivo.

Mechanism of agonist-induced [Ca2+]i oscillations in pituitary gonadotrophs

Gonadotropin-releasing hormone (GnRH) activates oscillatory Ca2+ signaling in pituitary gonadotrophs at a frequency (up to 25 min-1) that is dose-dependent and is determined by the degree of receptor-mediated inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) formation. Similar dose-dependent and frequency-modulated Ca2+ oscillations were elicited by intracellular administration of Ins(1,4,5)P3 and its nonhydrolyzable analogs, consistent with models in which Ins(1,4,5)P3 levels determine the frequency of Ca2+ oscillations but do not fluctuate in synchrony with [Ca2+]i. At constant agonist concentrations, Ca2+ spiking varied in amplitude, with a number of progressively larger transients before the onset of maximal oscillations, followed by a gradual decrease in spike amplitude that was accompanied by an increase in spiking frequency. The decline in the amplitude and increase in frequency of Ca2+ transients during stimulation by GnRH were not related to a decrease in the propagation of the Ca2+ signal within the cell but were associated with gradual depletion of the agonist-sensitive Ca2+ pool. Once initiated, the pattern of Ca2+ spiking was not altered by blockade of receptor occupancy, by inhibition of phospholipase C, or by reduction of extracellular [Ca2+]. Also, the endoplasmic reticulum (Ca2+)-ATPase blocker, thapsigargin, could substitute for Ins(1,4,5)P3 in initiating the oscillatory Ca2+ response. These findings indicate that although the Ins(1,4,5)P3 concentration determines the pattern of transients at the initiation of the oscillatory Ca2+ signal, maintenance of the signal does not require a sustained rise in Ins(1,4,5)P3. Since the frequency of Ca2+ oscillations is also influenced by depletion of luminal [Ca2+], it is possible that the Ins(1,4,5)P3-sensitive channels in the endoplasmic reticulum are tonically inhibited by high intraluminal Ca2+ levels and that Ins(1,4,5)P3 surmounts such inhibition by promoting Ca2+ discharge. When a critical level of Ca2+ discharge is attained, repetitive Ca2+ transients are generated by an autocatalytic mechanism in which a sustained rise in Ins(1,4,5)P3 is not an essential requirement.

Glucocorticoid status affects the response of rat striatal dopamine D2 receptors to hyperthermia and turpentine treatment

The influence of glucocorticoid status of the rats (absence of glucocorticoid hormones achieved by adrenalectomy and substitution by dexamethasone 5 mg/kg b.w.) on the response of striatal dopamine-D2 receptors to environmentally induced hyperthermia and treatment with a local inflammatory agent turpentine (1 ml/kg b.w.) was studied. Both stress situations affected the density of D2 receptors in opposite directions. While hyperthermia led to an increase, turpentine treatment reduced Bmax value. The changes in the D2 receptor binding affinity were expressed as a certain decrement, which was statistically significant in sham-adrenalectomized hyperthermic animals and in both turpentine treated groups (sham-operated and adrenalectomized) administered dexamethasone. The absence of glucocorticoids in the circulation caused an elevation of Kd values in the control and both stressed groups and dexamethasone attenuated these changes. Dexamethasone also attenuated stress-related alterations of Bmax, as well as Kd increase upon adrenalectomy in control and hyperthermic animals. These results corroborate the evidence on the role of D2 receptors in thermoregulation and stress and demonstrate the significance of glucocorticoid hormones in the control of these processes.

Effect of soman intoxication on the organization of rat brain ribosomes and the translational activity of mRNA in a cell-free system

The effect of soman on rat brain ribosomes organization and translational activity of mRNA in cell-free system was studied in rats exposed to 1.3 LD50 soman (120 micrograms/kg body weight) and in rats repeatedly injected with 0.4 LD50 soman (35 micrograms/kg). Fifteen minutes after the injection of 1.3 LD50 soman the heavy polyribosomal fraction from rat brain was found to be enriched and translational activity of mRNA was enhanced. In rats administered five injections of 0.4 LD50 soman at 24-h intervals, the low density ribosomes appeared as the predominant fraction whereas the activity of mRNA in all cell-free system was significantly impaired. It is concluded that soman intoxication expresses a stimulatory or inhibitory effect on the processes of protein synthesis in the rat brain, depending on the dose schedule of soman administration.

[Abdominal pregnancy terminating with a liveborn child]

A case is presented of abdominal pregnancy in a pregnant woman with two previous deliveries and four spontaneous abortions. She was cachectic, had spider nevi, and palmar erythema. Hepatic insufficiency was suspected. In the 35th week of pregnancy, severe pain appeared in the epigastrium and a detailed examination indicated abdominal pregnancy. Following laparatomy, a liveborn was extracted, weight 1800 g, height 45 cm, without any malformations. Owing to an unfavourable insertion of the placenta and the patient's very bad condition, the placenta was left in situ, with the drainage of Douglas' space. Fourteen days after operation, the placenta was easily removed by relaparotomy. It was partly hyalinized and partly necrotic.