Effect of immunosuppressive therapy in inflammatory cardiomyopathy: data from The Czech Inflammatory Cardiomyopathy Immunosuppressive Trial.

INTRODUCTION: The indications for specific treatment in the cases of inflammatory cardiomyopathy are based on limited data from several small clinical trials. AIM: A comparison of the effect of two dose regimens of combined immunosuppressive therapy by adding them to conventional heart failure therapy and comparing them with conventional heart failure therapy alone in patients with inflammatory cardiomyopathy. METHODS AND STUDY POPULATION: We enrolled 20 patients; mean age 46.10±7.33 years, duration of symptoms <6 months, LVEF ≤40 %, NYHA class II-IV, with biopsy­proven myocarditis. Patients were randomly separated into groups treated with immunosuppressive therapy in addition to conventional heart failure therapy or to a group treated with conventional heart failure therapy alone. Clinical and echocardiographic parameters were evaluated. RESULTS: The baseline values of LVEF in the group of immunosuppressive therapy (LVEF 22.3±4.7 %) were similar to those in the group treated with conventional heart failure therapy (LVEF 21.7±4.7 %; p=0.757). After twelve months there was no statistically significant difference in LVEF between the two studied groups (LVEF 33.7±9.5 % for the immunosuppressive therapy group and 41.3±13.0 % for the conventional therapy group; p=0.175). CONCLUSION: In our study population, we proved no positive effect of combined immunosuppressive therapy on the left ventricular function over 12 months. The main limitation of the study is the small number of enrolled patients (Tab. 4, Fig. 1, Ref. 35).

Experimental model of occluded biliary metal stent recanalization using irreversible electroporation via a tubular catheter.

PURPOSE: To demonstrate the feasibility of irreversible electroporation (IRE) for treating biliary metal stent occlusion in an experimental liver model. METHODS AND MATERIALS: IRE was performed using an expandable tubular IRE-catheter placed in nitinol stents in the porcine liver. A 3-electrode IRE-catheter was connected to an IRE-generator and one hundred 100µs pulses of constant voltage (300, 650, 1000, and 1300 V) were applied. Stent occlusion was simulated by insertion of liver tissue both ex vivo (n = 94) and in vivo in 3 pigs (n = 14). Three scenarios of the relationship between the stent, electrodes, and inserted tissue (double contact, single contact, and stent mesh contact) were studied. Electric current was measured and resistance and power calculated. Pigs were sacrificed 72 h post-procedure. Harvested samples (14 experimental, 13 controls) underwent histopathological analysis. RESULTS: IRE application was feasible at 300 and 650 V for the single and double contact setup in both ex vivo and in vivo studies. Significant differences in calculated resistance between double contact and single contact settings were observed (ex-vivo p ˂ 0.0001, in-vivo p = 0.02; Mann-Whitney). A mild temperature increase of the surrounding liver parenchyma was noted with increasing voltage (0.9-5.9 °C for 300-1000 V). The extent of necrotic changes in experimental samples in vivo correlated with the measured electric current (r2 = 0.39, p = 0.01). No complications were observed during or after the in-vivo procedure. CONCLUSION: Endoluminal IRE using an expandable tubular catheter in simulated metal stent occlusion is feasible. The relationship of active catheter electrodes to stent ingrowth tissue can be estimated based on resistance values.

Salivary cortisol as a marker of acute stress in dogs: a review.

Public interest in the welfare of domestic dogs has increased in recent years. Dogs under human care should experience as little stress as possible, and as such it is necessary to measure and quantify their levels of stress. Stress parameters that can be measured noninvasively may help to identify the poor welfare of animals. This review aimed to determine whether and under what conditions the hormone cortisol in dog saliva can be used as a noninvasive acute stress marker. The use of salivary cortisol as a stress marker has some disadvantages, which can lead to data misinterpretations. A key factor is the standardized method of sampling and subsequent processing before analysis. In addition, possible circadian alternation and individual variability of cortisol hormone levels should be consistently considered during the preparation of the experimental scheme, statistical data processing and final interpretation of the results. Because of the complex nature of the stress response, the observation of salivary cortisol should be supplemented with behavioral observations, but it should be noted that behavioral stress symptoms may not always be positively correlated with stress hormone production. Besides behavioral observations, it is advisable to supplement the measurement of cortisol by other salivary stress markers of sympathetic-adrenal-medullary and hypothalamic-pituitary-adrenal pathways. This comprehensive assessment of the stress impact on the individual will enable one to characterize the level and type of stress.

Epidemiological Trends for Childhood and Adolescent Cancers in the Period 1994-2016 in the Czech Republic.

BACKGROUND: Our study aimed to evaluate incidence and mortality trends for childhood and adolescent cancers in the period 1994-2016 in the Czech Republic. MATERIAL AND METHODS: Data on childhood cancers, which are recorded in the Czech National Cancer Registry, were validated using a clinical database of childhood cancer patients and combined with data from the National Register of Hospitalised Patients and with data from death certificates. These validated data were used to establish cancer incidence. Data from death certificates were used to evaluate long-term trends in mortality. Incidence and mortality trends were assessed by the average annual percentage change. RESULTS: The age-standardised incidence trend for childhood cancers (i.e. those diagnosed in patients aged 0-19 years) showed a statistically significant slight long-term increase in the number of new cases, +0.5% annually on average (p < 0.01), more specifically an increase of +0.6% in girls and a statistically insignificant decrease of 0.1% in boys. In children aged 0-14 years, other malignant epithelial neoplasms and malignant melanomas showed the largest statistically significant average annual increase in incidence (+4.9%; p < 0.01), followed by central nervous system neoplasms (+1.3%; p < 0.05). Lymphomas, by contrast, showed a statistically significant average annual decrease in incidence in children aged 0-14 years (2.1%; p < 0.01). In adolescents aged 15-19 years, other malignant epithelial neoplasms and malignant melanomas also showed a statistically significant average annual increase in incidence (+5.2%; p < 0.01), followed by central nervous system neoplasms (+1.5%; p < 0.05). Mortality trends showed a statistically significant long-term decrease: on average, 5.1% annually in children aged 0-14 years (p < 0.01), and 3.7% annually in adolescents aged 15-19 years (p < 0.01). CONCLUSION: Available data make it possible to analyse long-term trends in childhood cancer incidence and mortality.

Prevalence and evolution of spasticity in patients suffering from first-ever stroke with carotid origin: a prospective, longitudinal study.

BACKGROUND AND PURPOSE: The main aim of the study was to document the occurrence and evolution of post-stroke spasticity (PSS). The secondary goal was to identify predictors for increases and decreases in PSS rates during 12 months of subsequent follow-up. METHODS: In a longitudinal, multicenter, prospective cohort study, assessments were done at 7 days (V1), 6 months (V2), and 12 months (V3) after stroke onset. A total of 307 consecutive patients from four comprehensive stroke centers with the first-ever stroke of carotid origin and the presence of motor deficit at day 7 were included. The demographic data, baseline characteristics, Barthel index, degree and pattern of paresis and muscle tone were evaluated and recorded. Spasticity was assessed using the modified Ashworth scale. RESULTS: Spasticity was present in 45.0% of patients at V1, in 49.5% at V2, and in 43.2% at V3. A significant number of patients experienced changes in spasticity between visits: increased/new occurrence of spasticity in 32.5% (V1 and V2) and in 13.6% (V2 and V3) of patients; decreased occurrence/disappearance of spasticity in 18.5% (V1 and V2) and in 18.3% (V2 and V3) of patients. The number of patients with severe spasticity increased throughout the year, from 2.6% to 13.0% (V2) and 12.5% (V3). CONCLUSIONS: Spasticity developed in almost half of the included patients. The degree of spasticity often changed over time, in both directions. The rate of severe spasticity increased during the first year, with the maximum at 6 months following stroke onset.

Epidemiology of Multiple Myeloma in the Czech Republic.

BACKGROUND: Multiple myeloma (MM) is a cancer of plasma cells with an incidence of 4.8 cases per 100,000 population in the Czech Republic in 2014; the burden of MM in the Czech Republic is moderate when compared to other European countries. This work brings the latest information on MM epidemiology in the Czech population. MATERIAL AND METHODS: The Czech National Cancer Registry is the basic source of data for the population-based evaluation of MM epidemiology. This database also makes it possible to assess patient survival and to predict probable short-term as well as long-term trends in the treatment burden of the entire population. RESULTS: According to the latest Czech National Cancer Registry data, there were 504 new cases of MM and 376 deaths from MM in 2014. Since 2004, there has been a 26.9% increase in MM incidence and an 8.3% increase in MM mortality. In 2014, there were 1,982 persons living with MM or a history of MM, corresponding to a 74.4% increase when compared to MM prevalence in 2004. The 5-year survival of patients treated in the period 2010-2014 was nearly 40%. CONCLUSION: The available data make it possible to analyse long-term trends in MM epidemiology and to predict the future treatment burden as well as treatment results.Key words: multiple myeloma - epidemiology - Czech National Cancer Registry - Registry of Monoclonal Gammopathies - Czech Republic.

Effects of heme degradation products on reactivation of latent HIV-1.

Human immunodeficiency virus (HIV-1) infection can be currently controlled by combined antiretroviral therapy, but a sterilizing cure is not achievable as this therapy does not target persistent HIV-1 in latent reservoirs. Therefore, different latency reversal agents are intensively explored in various models. We have previously observed that heme arginate, a drug approved for human use, reveals a strong synergism with PKC inducers in reactivation of the latent provirus. Heme is physiologically decomposed by heme oxygenases into 3 degradation products: iron (Fe2+), carbon monoxide (CO) and biliverdin which is further converted to bilirubin by biliverdin reductase. In this paper, we have studied the effects of individual heme-degradation products on latent HIV-1 reactivation in ACH-2 cells harboring integrated HIV-1 provirus and in H12 clone of Jurkat cells harboring HIV-minivirus expressing EGFP. We employed addition of ascorbate to generate Fe2+, resulting in increased expression of both HIV-1 p24 Ag and EGFP in PMA-stimulated ACH-2 and H12 cells, respectively, as characterized on RNA and protein levels. On the other hand, addition of a CO-donor or bilirubin decreased the p24 expression. The reactivation of latent HIV-1 by iron or heme arginate was inhibited by antioxidant N-acetyl cysteine, or by an iron chelator desferrioxamine, suggesting that the effects were mediated by iron- or heme-induced redox stress. Finally, we demonstrated the stimulatory effects of heme arginate and PMA on HIV-1 expression in peripheral blood mononuclear cells of HIV-infected patients cultured ex vivo. These results may constitute a new direction in the latent HIV-1 reactivation and therapy.

MicroRNAs in urine supernatant as potential non-invasive markers for bladder cancer detection.

Urinary bladder carcinoma contributes to 4% of newly diagnosed oncological diseases in the Czech Republic. Biomarkers for its early non-invasive detection are therefore highly desirable. Urine seems to be an ideal source of such biomarkers due to the content of cell-free nucleic acids, especially microRNAs (miRNAs).To find potential biomarkers among miRNAs in urine supernatant, we examined in total 109 individuals (36 controls and 73 bladder cancer patients) in three phases. In the first - discovery - phase, microarray cards with 381 miRNAs were used for miRNA analysis of 13 controls and 46 bladder cancer patients. In the second - verification - phase, the results of this first phase were verified on the same groups of subjects by single-target qPCR assays for the selected miRNAs. For the third - validation - phase, new independent samples of urine supernatant (23 controls and 27 bladder cancer patients) were analyzed using single-target qPCR assays for 13 verified in the previous phase. The results of all phases were normalized to miR-191, miR-28-3p, and miR-200b, which were selected as suitable for our study by the qBase+®.We found that miR-125b, miR-30b, miR-204, miR-99a, and miR-532-3p are significantly down-regulated in patients' urine supernatant. In our experiments, the analysis of miR-125 levels provided the highest AUC (0.801) with 95.65% specificity and 59.26% sensitivity, the analysis of miR-99a lead to AUC (0.738) with 82.61% specificity and 74.07% sensitivity. We demonstrate that levels of these miRNAs could potentially serve as promising diagnostic markers for the non-invasive diagnostics of bladder cancer.

[Localized Amyloidosis Involving the Nasal Cavity]. / Lozisková amyloidóza v dutine nosní.

BACKGROUND: Amyloidosis is a disease characterized by deposits of abnormal protein known as amyloid in various organs and tissues. It can be classified into systemic or localized forms, the latter of which is less frequent. Deposition of amyloidogenic monoclonal light chains leads to the most common type of this disease called light-chain (AL) amyloidosis. (18)F-FDG positron emission tomography/ computed tomography hybrid imaging (FDG-PET/ CT) demonstrates tracer uptake usually in all patients with localized amyloidosis as opposed to the systemic form. CASE: Herein, we present a case of an otherwise healthy 56-year-old women diagnosed with a nasal polyp on the right side. The biopsy results were consistent with amyloidosis. FDG-PET/ CT imaging revealed a pathological, metabolically active lesion measuring 11 × 9 mm with a maximum standardized uptake value (SUV(max)) of 3.47. No other distant pathological changes were identified. After a radical resection, the patient has been regularly followed-up with clinical and imaging methods (MRI, FDG-PET/ CT), both of which repeatedly showed normal findings with disease-free survival of 27 months. Thus, FDG-PET/ CT imaging plays an important role not only for obtaining the right diagnosis but also in the follow-up of patients after surgical resection. In accordance with the literature, this case report confirms that FDG-PET/ CT imaging holds promise as an auxiliary method for distinguishing between localized and systemic forms of amyloidosis.

The effect of storage conditions on the hygiene and sensory status of wild boar meat.

The aim of this study was to compare hygiene status of wild boar meat (shoulder and leg) stored up to 21days at 0°C, 7°C or 15°C. The microbial counts increased gradually in the expected sequence of increasing storage temperatures, with TVC at the end of storage ranging from approx. 2logCFU/g (0°C) to 5logCFU/g (15°C). The lactic acid bacteria and psychrotrophic microflora didn't exceed 2logCFU/g and 2.5logCFU/g, respectively. Whereas odor of the meat stored at 0°C and 7°C was still acceptable at the end of storage, the odor of the meat stored at 15°C was barely acceptable after only 7d of storage and also the content of ammonia was significantly higher. Game meat obtained from animals hunted in the correct way and stored at low temperatures had good microbiological and hygiene status which could be maintained for more than 15days of storage.

[Radiofrequency ablation of pancreatic neuroendocrine tumor]. / Radiofrekvencní ablace neuroendokrinního nádoru pankreatu.

BACKGROUNDS: Pancreatic neuroendocrine tumors (PNETs) include a broad range of neoplasms spanning from relatively benign to malignant. Radical resection has been advocated as the only curative method. Debulking (R2) resection can be indicated for locally unresectable PNETs. Debulking surgery improves the quality of life and prolongs overall survival. The disadvantages of this approach include bleeding, pancreatic fistula and tumor spread. No alternative method that would eliminate these complications has been published yet. Considering the encouraging results of the studies describing radiofrequency ablation (RFA) of locally advanced pancreatic cancer, a question arises, whether it might be possible to use RFA as a R2 resection alternative in PNETs. CASE: A 73-year-old gentleman had been admitted due to abdominal pain and hyperglycaemic syndrome. Contrast-enhanced CT showed a tumor of pancreatic head invading portal vein (PV) and superior mesenteric vein (VMS). A surgery was indicated on the basis of EUS-guided FNAB that verified a PNET of uncertain biological behaviour. The surgery confirmed a locally advanced tumor of pancreatic head invading the PV and SMV. Due to the polymorbidity, radical pancreatoduodenectomy with SMV resection was not indicated. Because of the presence of symptoms, RFA of the PNET using ValleyLab generator with cooltip cluster electrode, was performed. Postoperative course was uneventful. Final immunohistochemical examination verified a well-differentiated grade 1 PNET. The patient was regularly monitored during a three-year follow-up. The quality of life was evaluated using standardized EORT QLQ-30 questionnaire. Pain was assessed by a ten-point visual analogue scale (VAS). Ablated area was evaluated annually by contrast-enhanced CT. Postoperatively, abdominal pain ceased (pain decrease from 2 to 0 on VAS). Insulin dose was reduced from 46 IU (international units) to 20 IU of Humulin-R per day. CT verified tumor regression according to RECIST (response evaluation criteria in solid tumors). During the three-year follow-up, no local progression or tumor dissemination was observed. CONCLUSION: We present the first case report of a patient with locally advanced symptomatic pancreatic neuroendocrine tumor successfully treated by intraoperative radiofrequency ablation. More clinical studies are needed to evaluate the clinical relevance of this cytoreductive method in the PNET indication.

[Treatment of AL-amyloidosis--results from one clinic and review of published experience with new agents (bortezomib, thalidomide and lenalidomide) in AL-amyloidosis]. / Lécba AL-amyloidózvy--výsledky jednoho pracoviste a prehled publikovanych zkuseností s novými léky (bortezomibem, thalidomidem a lenalidomidem) u AL-amyloidózy.

PATIENTS: Fifteen patients with light chain deposits in the form of AL-amyloidosis and 2 patients with light chain deposition as amorphous matter (light chain deposition disease) were treated at our clinic as of 1999. Median age at the diagnosis was 63 (34-77) years. The light chain deposition caused: nephrotic syndrome in 12 (70%) patients, renal insufficiency with reduced filtration in 4 (23%) patients, cardiomyopathy in 4 (23%) patients, hepatosplenomegaly in 2 (12%) patients, manifest coagulopathy in 2 (12%) patients, periorbital hematoma in 2 (12%) patients, visceral and somatic neuropathy in 2 (12%) patients. Treatment with high-dose dexamethasone in combination with adriamycin and vincristine (VAD) or cyclophosphamide (CAD orjust CD) was used in 11 patients. In 4 patients, therapy was completed with high-dose chemotherapy and autologous transplantation; complete haematological and organ treatment response was achieved in all 4 patients with remission lasting 113+, 87+, 50, 45+ months. Of the remaining 7 patients in whom high-dose dexamethasone therapy was not completed with high-dose chemotherapy, 3 achieved complete haematological remission (CR) and very good partial remission (VGPR), with 2 patients achieving complete organ treatment response. Organ response in the third patient cannot be assessed due to the short evaluation period. PR with no organ treatment response was achieved in other 2 patients and 2 patients died during the treatment. Therapy with prednisone and alkylating cytostatics was used in 2 patients with serious organ damage, both patients died after a short period of time due to the disease and thus treatment response cannot be evaluated. Combination of thalidomide, dexamethasone and cyclophosphamide (CTD) was used in 4 patients. Two of these patients did not complete full 2 cycles, one for unmanageable thalidomide-associated constipation, the other died. Two patients underwent a total of 5 and 6 cycles of this treatment with PR effect and plateau after the previous decline of monoclonal immunoglobulin concentrations. Treatment combination of bortezomib (Velcade), cyclophosphamide and dexamethasone (VCD) was used in three patients. In one patient (6 completed CTD cycles with the PR result) this combination led to complete haematological remission, complete remission was also achieved in the second patient and the application of 2 CVD cycles led to CR in the third (5 CTD cycles with PR result). Just one of the 3 female patients has been followed up for more than 12 months and so it is possible to evaluate organ treatment response in this patient; nephrotic syndrome ceased, meaning that organ CR has been achieved. CONCLUSION: Early diagnosis (before severe organ damage occurs) enables administration of aggressive treatment (high-dose chemotherapy and autologous transplantation) with the outlook of complete haematological and organ treatment response. New drugs thalidomide and bortezomib further expand treatment armamentarium; according to our limited experience and published information, bortezomib may be considered as very effective and well tolerated agent suitable, in combination, for patients with the diagnosis of AL-amyloidosis.

Clostridium perfringens occurrence and ribotypes in healthy broilers reared in different European countries.

The main aim of this study was to investigate the occurrence and ribotypes of Clostridium perfringens in broiler flocks reared in 2 European countries that apply European Union Regulation 1831/2003. A total of 1,532 cecum contents were collected between June 2005 and November 2006 from birds belonging to 51 intensively reared flocks produced in the Czech Republic and 41 intensive production, organic, and free-range flocks reared in Italy. Clostridium perfringens was detected in 64.7 and 82.9% of the Czech Republic and Italian flocks, respectively, at mean loads ranging between 3.65 and 4.77 log10 cfu per gram of cecum content. More than 1 ribotype was identified among isolates belonging to the same flock in 57.1 and 76.5% of the Czech Republic and Italian flocks, respectively. Moreover, common ribotypes were identified between strains belonging to 2 up to 8 different flocks. In particular, 4 ribotypes were shared between strains isolated in the 2 European countries. The results of this study report on C. perfringens occurrence and mean populations in broilers reared on diets devoid of antibiotic growth promoters. Moreover, these findings show for the first time the presence of common ribotyping profiles among isolates collected from birds reared more than 1,000 km apart.

[Kidney damage in multiple myeloma and other monoclonal gammopathies]. / Poskození ledvin pri mnohocetném myelomu a dalsích monoklonálních gamapatliích.

Multiple myeloma typically damages the skeleton in the form of osteolytic lesions or diffuse osteoporosis and causes a decrease in blood production. Renal insufficiency is diagnosed immediately at the onset of illness when establishing diagnosis in up to 20% of patients. Where patients suffer from an advanced form of the illness, it occurs in up to 40%. The predominant cause of damage to the kidneys is the monoclonal light chains. Most frequently, nephropathy is caused by the precipitation of light chains with the Tamm-Horsfall protein in the distal part of the loop of Henle and subsequent tubular ruptures and the creation of fibrous changes in the interstitium. Less frequently, there is clinically serious damage to tubular functions without indication of renal insufficiency. In some patients monoclonal immunoglobulin induces changes in the glomeruli. A rare type of damage is deposits of light chains in the form of AL-amyloid and subsequent nephritic syndrome. A very rare form is the deposition of monoclonal immunoglobulin in the form of amorphous matter (light-chain deposition disease) or in the form of crystals within tissue histiocytes (crystal storing histiocytosis). Both of these disorders cause renal insufficiency and less frequently nephritic syndrome such as AL amyloidosis. With timely and intensive treatment of multiple myeloma, which quickly suppresses the creation of light chains, a significant proportion of patients experience reparative changes and improved kidney function. The benefit of plasmapheresis for patients with severe kidney damage has not been confirmed by randomised studies. At the present time the first positive results are becoming available from tests of the use of pre-emptive haemodialysis with special columns that are permeable for light chains. The aim of the text is to provide information on the various forms of nephropathy whose closer analysis can reveal multiple myeloma and contribute to the timely diagnosis of the cause of the nephropathy.

[Indication to occlusion of patent foramen ovale in patient with pulmonary hypertension after a cardioembolic stroke]. / Indikace k uzáiveru perzistujícího foramen ovale u nemocné s plicní hypertenzí a probehlou paradoxní embolizací.

Patent foramen ovale (PFO), atrial septal aneurysm and Chiari's network are known risk factors for cardioembolic stroke. We report a case of young woman with pulmonary hypertension and PFO treated by implantation of Amplatzer occluder after paradoxical embolism.

Coagulation profile and liver function in 102 patients after total cavopulmonary connection at mid term follow up.

OBJECTIVE: To examine coagulation factors and liver function test abnormalities in patients after total cavopulmonary connection (TCPC). DESIGN: Cross sectional study comprising clinical and echocardiographic evaluation, and biochemical and coagulation profile screening. SETTING: Tertiary referral centre. METHODS: 102 patients aged 4-24 years (median 10 years) at one to eight years (median five years) after TCPC were examined. All patients were maintained on a low dose of aspirin. 96% of patients were in a good clinical condition (New York Heart Association class I or II). No intracardiac thrombi were detected on echocardiography and ventricular function was good in 91% of patients. RESULTS: Total bilirubin was increased in 27% and gamma glutamyltransferase in 54% of patients. Serum total protein, albumin, and prealbumin were normal in almost in all patients. Compared with the control group, patients after TCPC had significantly lower fibrinogen, factor V, factor VII, and protein C concentrations, prolonged international normalised ratio, and increased antithrombin III concentration. Factor V concentration was abnormally decreased in 35%, factor VII in 16%, and protein C in 28% of patients. Antithrombin III was increased in 23% of patients. Factor VII, factor V, protein C, and antithrombin III correlated significantly with serum prealbumin. There was also a significant correlation between procoagulant factor VII and both anticoagulant protein C and antithrombin III. CONCLUSIONS: Almost half of patients after TCPC had laboratory signs of mild cholestasis. Decreased liver synthesis of procoagulant and anticoagulant factors was observed but overall coagulation homeostasis appeared to be in balance in this selected group of patients with a good clinical outcome.

Melatonin action in neonatal gonadotrophs.

Neonatal pituitary cells express MT1 and MT2 subtype of melatonin receptors that are coupled to pertussis toxin-sensitive G proteins. Their activation by melatonin leads to a decrease in cAMP production and activity of protein kinase A, and attenuation of gonadotropin-releasing hormone (GnRH)-induced gonadotropin secretion. Single cell calcium and electrophysiological recordings have revealed that a reduction in gonadotropin release results from melatonin-induced inhibition of GnRH-stimulated calcium signaling. Melatonin inhibits both calcium influx through voltage-dependent calcium channels and calcium mobilization from intracellular stores. Inhibition of calcium influx, probably in a cAMP/protein kinase C-dependent manner, and the accompanying calcium-induced calcium release from ryanodine-sensitive intracellular pools by melatonin results in a delay of GnRH-induced calcium signaling. Melatonin-induced attenuation of GnRH-induced and inositol (1,4,5)-trisphosphate-mediated calcium release from intracellular pools attenuates the amplitude of calcium signal. The potent inhibition of GnRH-induced calcium signaling and gonadotropin secretion by melatonin provides an effective mechanism to protect premature initiation of pubertal changes that are dependent on plasma gonadotropin levels. During the development, such tonic inhibitory effects of melatonin on GnRH action gradually decline due to a decrease in expression of functional melatonin receptors. In adult animals, melatonin does not have obvious direct effects on pituitary functions, whereas the connections between melatonin release and hypothalamic functions, including GnRH release, are preserved, and are critically important in synchronizing the external photoperiods and reproductive functions through still not well characterized mechanisms.