Beyond Conventional Therapies: Molecular Dynamics of Alzheimer's Treatment through CLOCK/BMAL1 Interactions.

BACKGROUND: Alzheimer's Disease (AD) represents a neurodegenerative disorder characterized by cognitive and behavioral impairments significantly hindering social and occupational functioning. Melatonin, a hormone pivotal in regulating the body's intrinsic circadian rhythm, also acts as a catalyst in the breakdown of beta-amyloid deposits, offering a promising therapeutic approach for AD. The upregulation of Brain and Muscle ARNT-Like 1 (Bmal1) gene expression, stimulated by melatonin, emerges as a potential contributor to AD intervention. Current pharmacological interventions, such as FDA-approved cholinesterase inhibitors and the recently authorized monoclonal antibody, Lecanemab, are utilized in AD management. However, the connection between these medications and Bmal1 remains insufficiently explored.

Objective: This study aims to investigate the molecular effects of FDA-endorsed drugs on the CLOCK: Bmal1 dimer. Furthermore, considering the interactions between melatonin and Bmal1, this research explores the potential synergistic efficacy of combining these pharmaceutical agents with melatonin for AD treatment.

Methods: Using molecular docking and MM/PBSA methodologies, this research determines the binding affinities of drugs within the Bmal1 binding site, constructing interaction profiles.

Results: The findings reveal that, among FDA-approved drugs, galanthamine and donepezil demonstrate notably similar binding energy values to melatonin, interacting within the Bmal1 binding site through analogous amino acid residues and functional groups.

Conclusion: A novel therapeutic approach emerges, suggesting the combination of melatonin with Lecanemab as a monoclonal antibody therapy. Importantly, prior research has not explored the effects of FDA-approved drugs on Bmal1 expression or their potential for synergistic effects.

An in silico investigation: Can melatonin serve as an adjuvant in NR1D1-linked chronotherapy for amyotrophic lateral sclerosis?

Chronobiology, which studies biological rhythms and their impacts on health, presents a potential avenue for treating amyotrophic lateral sclerosis. Clock gene-related therapies, focusing on genes responsible for regulating biological rhythms, may hold promise in the treatment. Among these clock genes, nuclear receptor subfamily 1 Group D member 1 (NR1D1) plays a vital role in neurodegenerative diseases. In this particular study, it was aimed to investigate the potential of FDA-approved drugs commonly used in amyotrophic lateral sclerosis treatment and melatonin, a hormone known for its role in regulating sleep-wake cycles, as ligands for clock gene-related therapy. The ligands were subjected to molecular docking and molecular dynamics simulation methods against the NR1D1 clock gene. These results suggested that combining melatonin with FDA-approved medications commonly used in the treatment might yield positive outcomes. This study provides preliminary data and lays the groundwork for future investigations involving in vitro (laboratory-based) and in vivo (animal or human-based) research on chronotherapy. In summary, this research highlights the potential of clock gene-related therapy utilizing melatonin in conjunction with FDA-approved drugs for amyotrophic lateral sclerosis treatment, offering insights into novel treatment strategies. The findings underscore the need for further studies to explore the effectiveness of this hypothetical approach in experimental and clinical settings.

A Systematic Review of Healthcare Professionals' Knowledge, Attitudes, and Practices Regarding Adverse Drug Reaction Reporting in Ethiopia.

Adverse drug reactions (ADRs) are a prominent cause of morbidity and mortality and higher healthcare expenditures. Healthcare professionals (HCPs) play a crucial role in ADR reporting through spontaneous reporting systems, but under-reporting is their major limitation. The goal of this study is to evaluate HCPs' knowledge, attitude, and practice regarding ADR reporting as well as the factors that influence reporting using research papers that are currently available. A literature search was conducted using sources such as PubMed, Scopus, and Google Scholar to find studies that evaluated HCPs' knowledge, attitudes, and practices regarding ADRs reporting in Ethiopia. A standard procedure of systematic review protocol was used to conduct this review. Demographic factors, sample size, response rate, survey delivery, HCP working setting, and encouraging and discouraging factors of ADR reporting were extracted from articles. A total of 17 articles were included in the systematic review out of 384. The number of HCPs in the included studies ranged from 62 to 708. Response rate ranges from 76.1% to 100%. Most of the research included in this evaluation looked at HCPs, who worked in hospitals. When pharmacists were compared to other HCPs, they were more likely to report ADRs; because they had higher knowledge, attitude, and practice. Lack of understanding, unavailability of reporting forms, uncertainty about the causal relationship between the drug and ADR, and failure to report because the ADR was well known were among the common hurdles to ADR reporting identified in research. To improve reporting, educational initiatives and continued training in pharmacovigilance and ADRs are frequently recommended considerations. In Ethiopia, there is a pressing need to close the gap in HCP knowledge, attitudes, and practice regarding PV and ADR reporting. To address this point, specific educational interventions based on existing gaps in ADR reporting should be developed and integrated into the health education curriculum or provided as in-service training after graduation.

Chronobiological Efficacy of Combined Therapy of Pelargonium Sidoides and Melatonin in Acute and Persistent Cases of COVID-19: A Hypothetical Approach.

Since the outbreak of the first SARS-CoV-2 epidemic in China, pharmacists have rapidly engaged and developed strategies for pharmaceutical care and supply. According to the guidelines of the International Pharmaceutical Federation (FIP), clinical pharmacists/hospital pharmacists, as members of care teams, play one of the most important roles in the pharmaceutical care of patients with COVID-19. During this pandemic, many immuno-enhancing adjuvant agents have become critical in addition to antivirals and vaccines in order to overcome the disease more easily. The liquid extract obtained from the Pelargonium sidoides plant is used for many indications such as colds, coughs, upper respiratory tract infections, sore throat, and acute bronchitis. The extract obtained from the roots of the plant has been observed to have antiviral and immunomodulatory activity. In addition to its anti-inflammatory and antioxidant effects, melatonin plays a role in suppressing the cytokine storm that can develop during COVID-19 infection. Knowing that the severity and duration of COVID-19 symptoms vary within 24 hours and/or in different time periods indicates that COVID-19 requires a chronotherapeutic approach. Our goal in the management of acute and long COVID is to synchronize the medication regimen with the patient's biological rhythm. This chapter provides a comprehensive review of the existing and emerging literature on the chronobiological use of Pelargonium sidoides and melatonin during acute and prolonged COVID-19 episodes.

Possible cytoprotective mechanisms of oxytocin against 5-fluorouracil-induced gastrointestinal mucositis.

Gastrointestinal mucositis is a common and dose-limiting side effect characterized by ulcerative lesions in the mucosa of the digestive tract in patients receiving anticancer drugs such as 5-fluorouracil (5-FU), a potent antineoplastic drug. Several protocols have reported the efficacy of therapeutic interventions to prevent this side effect, although complete success has not yet been achieved and mucositis remains one of the most serious complications associated with 5-FU therapy. Oxytocin, a well-known antistress agent, has been reported to have comparable effects to ranitidine. Previous studies have shown that oxytocin inhibits gastric acid secretion and the expression of proinflammatory cytokines in rats. If oxytocin can reduce stress-induced ulcers via antioxidant, antiapoptotic, and anti-inflammatory pathways, then it may have a dose-dependent effect on gastrointestinal mucositis caused by 5-FU.

Melatonin and REGN-CoV2 combination as a vaccine adjuvant for Omicron variant of SARS-CoV-2.

The omicron variant (B.529) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which emerged in late 2021, caused panic worldwide due to its contagiousness and multiple mutations in the spike protein compared to the Delta variant (B.617.2). There is currently no specific antiviral available to treat Coronavirus disease 2019 (COVID-19). However, studies on neutralizing monoclonal antibodies (mAb) developed to fight COVID-19 are growing and gaining traction. REGN-COV2 (Regeneron or imdevimab-casirivimab combination), which has been shown in recent studies to be less affected by Omicron's RBD (receptor binding domain) mutations among other mAb cocktails, plays an important role in adjuvant therapy against COVID-19. On the other hand, it is known that melatonin, which has antioxidant and immunomodulatory effects, can prevent a possible cytokine storm, and other severe symptoms that may develop in the event of viral invasion. Along with all these findings, we believe it is crucial to evaluate the use of melatonin with REGN-COV2, a cocktail of mAbs, as an adjuvant in the treatment and prevention of COVID-19, particularly in immunocompromised and elderly patients.

Novel Hybridized Computational Paradigms Integrated with Five Stand-Alone Algorithms for Clinical Prediction of HCV Status among Patients: A Data-Driven Technique.

The emergence of health informatics opens new opportunities and doors for different disease diagnoses. The current work proposed the implementation of five different stand-alone techniques coupled with four different novel hybridized paradigms for the clinical prediction of hepatitis C status among patients, using both sociodemographic and clinical input variables. Both the visualized and quantitative performances of the stand-alone algorithms present the capability of the Gaussian process regression (GPR), Generalized neural network (GRNN), and Interactive linear regression (ILR) over the Support Vector Regression (SVR) and Adaptive neuro-fuzzy inference system (ANFIS) models. Hence, due to the lower performance of the stand-alone algorithms at a certain point, four different novel hybrid data intelligent algorithms were proposed, including: interactive linear regression-Gaussian process regression (ILR-GPR), interactive linear regression-generalized neural network (ILR-GRNN), interactive linear regression-Support Vector Regression (ILR-SVR), and interactive linear regression-adaptive neuro-fuzzy inference system (ILR-ANFIS), to boost the prediction accuracy of the stand-alone techniques in the clinical prediction of hepatitis C among patients. Based on the quantitative prediction skills presented by the novel hybridized paradigms, the proposed techniques were able to enhance the performance efficiency of the single paradigms up to 44% and 45% in the calibration and validation phases, respectively.

The circadian clock gene Bmal1: Role in COVID-19 and periodontitis.

The physiological processes of most living organisms follow a rhythmic pattern, which is controlled by the interaction between environmental cues and the internal circadian timing system. Different regulatory circadian genes are expressed in most cells and tissues, and disruptions in the sleep-wake cycle affect these genes, which may result in metabolic disorders and cause alterations of the immune system. The manifestations of these disrupted genes are evident in inflammatory conditions such as periodontitis and some viral diseases, including COVID-19. The brain and muscle ARNT-like protein-1 (Bmal1), an important circadian regulatory gene, decreases when the sleep-wake cycle is disrupted. Circadian genes have been linked to different events, including cytokine storm in inflammatory conditions and virus invasion. The evaluation of the effects of these regulatory circadian genes, especially Bmal1, in periodontitis and viral infection suggests that both diseases may have a common pathogenesis via the NF-κB pathway. This brief review highlights the role and importance of the circadian clock gene Bmal1 in the disease process of periodontitis and suggests its role and importance in viral infections, including COVID-19.

COVID-19-related arrhythmias and the possible effects of ranolazine.

The COVID-19 pandemic has become a burden to the global healthcare community. Despite the severity of the complications associated with COVID-19, no antiviral agent is yet available for the treatment of this disease. Several studies have reported arrhythmias as one of the numerous manifestations associated with COVID-19 infection. Clinicians use different therapeutic agents in the management of COVID-19 patients with arrhythmias, apart from ranolazine; however, some of these drugs are administered with caution because of their significant side effects. In this study, we reviewed the potential antiarrhythmic effects of ranolazine in the management of cardiac arrhythmias associated with COVID-19. Ranolazine is a second-line drug approved for the treatment of chronic stable angina pectoris. Previous studies have shown that ranolazine produces its beneficial cardiac effects without any significant impact on the body's hemodynamics; hence, blood pressure is not altered. Due to its reduced side effects, ranolazine may be more effective than other drugs in producing the desired relief from COVID-19 related arrhythmias, since it produces its antiarrhythmic effect by modulating sodium, potassium and calcium channels, and suppressing cytokine expression.

Acute kidney injury due to COVID-19 and the circadian rhythm.

The COVID-19 pandemic caused by the novel coronavirus (SARS-CoV-2) affects several organs including the kidneys. When examining patients with acute kidney injury (AKI) due to COVID-19, it is important to consider the circadian rhythm because in addition to its biological clock function, disruption of the circadian rhythm has been reported to be associated with the pathogenesis of several disorders, including AKI. Angiotensin-converting enzyme 2 (ACE2), an important component of the renin-angiotensin-aldosterone system (RAAS), displays circadian rhythmicity. Studies have shown that over-expression of human ACE2 increases the replication of SARS-CoV-2, which may lead to disruptions and tissue damage due to the suppression of the brain and muscle ARNT-like protein-1(Bmal1) gene and high pro-inflammatory cytokines expressions in the tissues. Therefore, understanding and regulating the circadian rhythm and expression pattern of the key components of RAAS can prevent or reduce the severity of acute kidney injury that may occur with COVID-19 infection.

Antidepressant effect of Gentiana olivieri Griseb. in male rats exposed to chronic mild stress.

Background: The flowering parts of Gentiana olivieri, known as 'Afat' in the southeastern Anatolia region of Turkey, are used as a tonic, an appetizer, and for the treatment of several mental disorders, including depression. The purpose of this study is to investigate the antidepressant effect of G. olivieri ethanol extract (GOEE) in a chronic mild stress-induced rat model, which was used to mimic a depressive state in humans, and to compare the effect with that of imipramine.Methods: Male Sprague-Dawley rats were randomly divided into six groups: control, stress, treated with imipramine (positive control) and treated with GOEE at three different (200, 500, 1000 mg/kg) doses groups. The rats in all groups, except the control group, were exposed to chronic mild stress. At the end of the 3-week experimental period, biochemical and behavioral parameters were examined.Results: The results showed that treatment with GOEE or imipramine significantly improved rats' sucrose consumption which was diminished by chronic mild stress, restored serum levels of corticosterone and proinflammatory cytokines (interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α)), prevented the increase of liver index of rats. Moreover, in the hippocampus tissue, decreased serotonin and noradrenaline levels were significantly increased by treatment with GOEE or imipramine, and antioxidant parameters (thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), and glutathione (GSH)) were significantly improved by treatment with GOEE though not with imipramine.Conclusion: The data demonstrate that G. olivieri may exert its antidepressant activity by improving monoaminergic system disorders, and by favorably affecting the antioxidant, inflammatory and the endocrine mechanisms.

The vasorelaxant effect of hydrogen sulfide is enhanced in streptozotocin-induced diabetic rats.

Hydrogen sulfide (H2S) is an endogenous gas which has potent relaxant effect in vascular and nonvascular smooth muscles. In the present study, we have investigated how streptozotocin (STZ)-induced diabetes affected the relaxant effect of H2S in rat isolated thoracic aorta and mesenteric and pulmonary arteries. Diabetes was induced by IV injection of STZ (35 mg/kg). Insulin treatment was applied by using insulin implants. At the end of 4 and 12 weeks, the thoracic aorta and mesenteric and pulmonary arteries were isolated, and the relaxation responses to sodium hydrogen sulfide (NaHS), diazoxide, and acetylcholine were evaluated. The mRNA and protein levels of H2S-synthesizing enzymes were also examined by RT-PCR and Western Blot. The relaxation response to NaHS in the arteries isolated from both 4 and 12 week-diabetic rats was increased when compared with that obtained from the control group. Glibenclamide inhibited the relaxation response to NaHS in the arteries isolated from either diabetic or non-diabetic group of rats. Concurrent treatment of insulin to STZ-injected rats prevented the potentiation of the relaxant effect of NaHS in the arteries. However, acetylcholine and diazoxide-induced relaxation responses were not altered in diabetic group of rats. The mRNA and protein levels of H2S-synthesizing enzymes were also not altered in diabetic rats. STZ-induced experimental diabetes in rats resulted in the potentiation of the relaxation response to H2S in vascular tissues. The potentiated relaxation to H2S in diabetic arteries may play a role in vascular complications frequently seen in severe diabetes.

Estimation of anti-inflammatory, antinociceptive and antioxidant activities of Arctium minus (Hill) Bernh. ssp. minus.

ETHNOPHARMACOLOGICAL RELEVANCE: Arctium minus (Hill) Bernh. ssp. minus (Asteraceae) leaves are used to alleviate rheumatic pain, against fever and sunstroke with externally application in Turkish folk medicine. AIM OF THE STUDY: To evaluate the anti-inflammatory, antinociceptive and antioxidant activities of aqueous and ethanol extracts prepared from the leaves of Arctium minus ssp. minus. MATERIALS AND METHODS: The ethanolic and aqueous extracts from the leaves of Arctium minus ssp. minus were evaluated in mice for anti-inflammatory activity using carrageenan-induced hind paw edema model and for antinociceptive activity using p-benzoquinone-induced abdominal contractions test. Moreover, the antioxidant power of the extracts has been determined by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and flow injection analysis-luminol chemiluminescence (FIA-CL). In addition, the total phenolic content in both extracts was determined with spectrophotometric method. RESULTS: Our results showed that only the ethanol extract exhibited a dose-dependent anti-inflammatory activity ranging between 11.1 and 23.6% at 200mg/kg dose as well as displayed a significant antinociceptive activity without inducing any gastric damage. Although, both extracts were shown to possess significant DPPH radical-scavenging activity, that of aqueous extract was found to have more pronounced activity. In FIA-CL system, the ethanol extract was shown to possess a significant scavenger activity against H(2)O(2) while the aqueous extract was much more potent antioxidant activity against HOCl-luminol CL than ethanol extract. CONCLUSION: According to our results, it was concluded that Arctium minus ssp. minus contains potent natural antioxidants. In this study, in vivo experimental results have also supported the folk medicinal utilization of Arctium minus ssp. minus.

Temporal variation in the recovery from impairment in adriamycin-induced wound healing in rats.

BACKGROUND: An adriamycin-induced impairment of wound healing has been demonstrated experimentally in rats. The purpose of this study is to investigate a possible temporal variation in recovery from the impairment of wound healing caused by adriamycin administration. METHODS: The subjects were 120 female Spraque-Dawley rats. They were divided into eight groups, undergoing adriamycin administration (8 mg/kg, i.v.) at 9 a.m. or 9 p.m. on day 0 and laparotomy on day 0, 7, 14 or 21. Blast pressures were recorded after the incision line had been opened, and tissue samples were kept at -30 degrees C for later measurement of hydroxyproline levels. RESULTS: Adriamycin treatment in rats at 9 p.m. resulted in significantly lower blast pressure levels than treatment at 9 a.m. between days 7 and 21, indicating a lag effect of healing time in wounded tissues. However the decreased hydroxyproline levels were not changed at these days and sessions. CONCLUSION: It is concluded that adriamycin-induced impairment of wound healing in adult female rats exhibits nycthemeral variation.

Twenty-four-hour variation of L-arginine/nitric oxide/cyclic guanosine monophosphate pathway demonstrated by the mouse visceral pain model.

The L-arginine/nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway is known to be involved in central and peripheral nociceptive processes. This study evaluated the rhythmic pattern of the L-arginine/NO/cGMP pathway using the mouse visceral pain model. Experiments were performed at six different times (1, 5, 9, 13, 17, and 21 h after light on) per day in male mice synchronized to a 12 h:12 h light-dark cycle. Animals were injected s.c. with saline, 2 mg/kg L-arginine (a NO precursor), 75 mg/kg L-N(G)-nitroarginine methyl ester (L-NAME, a NOS inhibitor), 40 mg/kg methylene blue (a soluble guanylyl cyclase and/or NOS inhibitor), or 0.1 mg/kg sodium nitroprusside (a nonenzymatic NO donor) 15 min before counting 2.5 mg/kg (i.p.) p-benzoquinone (PBQ)-induced abdominal constrictions for 15 min. Blood samples were collected after the test, and the nitrite concentration was determined in serum samples. L-arginine or L-NAME caused both antinociception and nociception, depending on the circadian time of their injection. The analgesic effect of methylene blue or sodium nitroprusside exhibited significant biological time-dependent differences in PBQ-induced abdominal constrictions. Serum nitrite levels also displayed a significant 24 h variation in mice injected with PBQ, L-NAME, methylene blue, or sodium nitroprusside, but not saline or L-arginine. These results suggest that components of L-arginine/NO/cGMP pathway exhibit biological time-dependent effects on visceral nociceptive process.

Biological time-dependent difference in effect of peroxynitrite demonstrated by the mouse hot plate pain model.

We previously demonstrated the rhythmic pattern of L-arginine/nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) cascade in nociceptive processes. The coupled production of excess NO and superoxide leads to the formation of an unstable intermediate peroxynitrite, which is primarily responsible for NO-mediated toxicity. In the present study, we evaluated the biological time-dependent effects of exogenously administered peroxynitrite on nociceptive processes and peroxynitrite-induced changes in the analgesic effect of morphine using the mouse hot-plate pain model. Experiments were performed at four different times of day (1, 7, 13, and 19 hours after lights on, i.e., HALO) in mice of both sexes synchronized to a 12 h:12 h light-dark cycle. Animals were injected intraperitoneally (i.p.) with saline or 10 mg/kg morphine 30 min before and 0.001 mg/kg peroxynitrite 30 sec before hot-plate testing, respectively. The analgesic effect of morphine exhibited significant biological time-dependent differences in the thermally-induced algesia; whereas, administration of peroxynitrite alone exhibited either significant algesic or analgesic effect, depending on the circadian time of its injection. Concomitant administration of peroxynitrite and morphine reduced morphine-induced analgesia at three of the four different study time points. In conclusion, peroxynitrite displayed nociceptive and antinociceptive when administered alone according to the circadian time of treatment, while it diminished analgesic activity when administered in combination with morphine at certain biological times.

Effects of cyclooxygenase inhibitors on nitric oxide production and survival in a mice model of sepsis.

The effects of selective ((5,5-dimethyl-3-(3-florophenyl)-4-(4-methylsulphonyl-2(5H)-furanon); DFU) and (N-(2-cyclohexyloxy-4-nitrophenyl)-methansulphonamide; NS 398)) or non-selective (diclophenac and proquazon) inducible cyclooxygenase (COX-2) inhibitors on the survival, nitrite (stable product of nitric oxide (NO) as an index for inducible NO synthase (iNOS) activity) and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha), stable product of prostacyclin as an index for COX-2 activity) production in serum, lungs, brain and/or kidney were investigated in endotoxin-induced sepsis model in mice. Endotoxin (10 mg x kg(-1), i.p.)-induced mortality was prevented by DFU, NS 398 and proquazon (0.1, 10 and 1 mg x kg(-1), respectively) and enhanced 2.6-fold with 0.1mg x kg(-1) diclophenac. Endotoxin-induced increase in the serum levels of nitrite was only inhibited by 10 mg x kg(-1) diclophenac. Endotoxin caused a significant decrease only in the brain levels of nitrite without affecting 6-keto-PGF(1alpha) levels in all tissues. The decreased levels of nitrite induced by endotoxin is further reduced by 0.1mg x kg(-1) DFU and 1 and 10mg x kg(-1) diclophenac while 10 mg x kg(-1) DFU and 1mg x kg(-1) proquazon increased it. On the other hand, 1mg x kg(-1) diclophenac and proquazon, and 10 mg x kg(-1) NS 398 increased the endotoxin-induced lung levels of 6-keto-PGF(1alpha). The results suggest that the COX inhibitors may have different effects on the survival and NO production depending on tissue and dose.

The mechanisms of peroxynitrite-induced relaxations in isolated rat anococcygeus muscle.

We have previously reported that peroxynitrite (ONOO(-)) caused relaxations on isolated rat anococcygeus muscle and in the present study the possible mechanisms of the relaxant effect were investigated. ONOO(-) (0.03- 1.0 mmol/l)-induced relaxations were reduced significantly by the presence of an ATP-sensitive potassium channel (K(+)(ATP) channel) blocker, glibenclamide (0.3 micromol/l), or 1H-(1,2,4)oxadiazolo(4,3-alpha)quinoxalin-1-one (ODQ) (30.0 micromol/l), a guanylyl cyclase inhibitor. However, 3-aminobenzamide (3.0 mmol/l), an inhibitor of poly(ADP- ribose)synthase, did not influence the relaxant effect of ONOO(-) (1.0 mmol/l). Results of the present study implicate that activation of K(+)(ATP) channels and/or cGMP/K(+)(ATP) channel interaction might play a role in the relaxant responses to ONOO(-) in isolated rat anococcygeus muscle.

Circadian variation of nitric oxide synthase activity in mouse tissue.

Endogenous nitric oxide (NO) is an important mediator in the processes that control biological clocks and circadian rhythms. The present study was designed to elucidate if NO synthase (NOS) activity in the brain, kidney, testis, aorta, and lungs and plasma NOx levels in mice are controlled by an endogenous circadian pacemaker. Male BALB/c mice were exposed to two different lighting regimens of either light-dark 14:10 (LD) or continuous lighting (LL). At nine different equidistant time points (commencing at 09:00h) blood samples and tissues were taken from mice. The plasma and tissue homogenates were used to measure the levels of NO2 + NO3- (NOx) and total protein. The NOx concentrations were determined by a commercial nitric oxide synthase assay kit, and protein content was assessed in each homogenate tissue sample by the Lowry method. Nitric oxide synthase activity was calculated as pmol/mg protein/h. The resulting patterns were analyzed by the single cosinor method for pre-adjusted periods and by curve-fitting programs to elucidate compound rhythmicity. The NOS activity in kidneys of mice exposed to LD exhibited a circadian rhythm, but no rhythmicity was detected in mice exposed to LL. Aortic NOS activity displayed 24h rhythmicity only in LL. Brain, testis, and lung NOS activity and plasma NOx levels displayed 24h rhythms both in LD and LL. Acrophase values of NOS activity in brain, kidney, testis, and lungs were at midnight corresponding to their behavioral activities. Compound rhythms were also detected in many of the examined patterns. The findings suggest that NOS activity in mouse brain, aorta, lung, and testis are regulated by an endogenous clock, while in kidney the rhythm in NOS activity is synchronized by the exogenous signals.