Co-treatment with low doses of buspirone prevents rewarding effects of methylphenidate and upregulates expression of 5-HT1A receptor mRNA in the nucleus accumbens

Accumulating studies consistently show that methylphenidate (MPD), the first line drug for treating Attention-Deficit Hyperactivity Disorder (ADHD), is abused by patients to whom the drug is prescribed. Like other psychostimulants, only low doses of MPD improve cognitive performance while higher doses impair it. Preventing the use of high doses of MPD is important for retaining its therapeutic efficacy. Previously, it has been shown that performance in Morris water maze test is improved in rats treated, orally, with MPD in doses of 2.5 mg/kg; but higher doses (5 mg/kg) impair it. The present study is designed to monitor rewarding effects of 2.5 mg/kg MPD in conditioned place preference (CPP) paradigm and its potential inhibition in buspirone co-treated animals. Our results show that rewarding effects of MPD in CPP paradigm are prevented in rats co-treated with buspirone in doses of 0.1 and 0.3 mg/kg. Animals treated with MPD exhibit a downregulation of 5-HT1A receptor mRNA in the nucleus accumbens which is also prevented in rats co-treated with 0.1 and 0.3 mg/kg but not 1.0 and 2.0 mg/kg buspirone. Administration of buspirone in these doses is not rewarding in CPP test and upregulates 5-HT1A receptor mRNA in the nucleus accumbens. The findings suggest that co-use of low doses of buspirone can prevent rewarding effects of MPD to help retain its therapeutic efficacy.

Neurochemical and behavioral effects of fluoxetine on midazolam induce dependence in an animal model of addiction

In the present study we have monitored effects of repeated coadministration of fluoxetine with midazolam; a benzodiazepine (CNS depressant). It is the primary drug of choice for procedural sedation, preoperative sedation, and in emergency departments. Repeated administration of this drug is reported to have abuse potential and may cause this by increasing dopaminergic neurotransmission. Since an important role of serotonin is there in the pathophysiology of anxiety and addiction, administration of midazolam may involve altered 5-HT metabolism as well. Present study was designed to monitor effects of repeated administration of fluoxetine with midazolam. Effects of fluoxetine and midazolam coadministration were monitored on motor activities in familiar and novel environments, hot plate test, forced swim test, conditioned place preference test and levels of dopamine, 5-HT and their metabolites. Both midazolam (2.5mg/kg) and fluoxetine (1mg/kg) were administered orally for 12 days. Conditioned place preference test was performed on day 13. Rats were decapitated and whole brain samples were collected and stored at -70°C until neurochemical analysis by HPLC-EC. Findings from the present study show attenuation of midazolam-induced reinforcement upon repeated co-administration of fluoxetine. These could be implicated to increased therapeutic utility of midazolam and related benzodiazepines.

810 Ischaemic Gallbladder Volvulus Within a Parastomal Hernia: Case Report and Literature Review

Case presentation

An 87-year-old female presented with 24 hours of severe central abdominal pain, preceded by five months of intermittent pain, and weight loss. Surgical history subtotal: colectomy and end ileostomy for ischaemia. Examination demonstrated generalised tenderness and longstanding parastomal hernia.

Abdominal CT demonstrated an oedematous gallbladder contained within the parastomal hernia and emergency laparotomy was performed. The gallbladder was twisted 360 degrees within the hernia and cholecystectomy and suture repair of parastomal hernia were performed.

Literature review: A 2013 review found most cases were diagnosed intra-operatively. Subsequent case reports were reviewed to identify contemporary practice.

Method

A pubmed search for “gallbladder volvulus”, 2012-2019 was performed. Articles meeting the inclusion criteria (gallbladder volvulus, english language, >18 years old, documented preoperative assessment and management) were analysed. Non-human and duplicate cases were excluded.

Results

24/43 screened cases met the criteria, including one within a parastomal hernia. 79% (19/24) were female, 50% (12/24) age >80. Although 96% (23/24) underwent imaging, only 38% (9/24) were diagnosed pre-operatively. One death was reported after non-operative management. 21 cases reported an operative approach with 48% (10/21) completed laparoscopically.

Conclusions

Gallbladder volvulus remains rare and difficult to identify on imaging.

Dose related acute behavioral and neurochemical profile of pioglitazone

Diabetics are twice as likely to have depression. It's normal to have long periods of sadness and anxiety. Pioglitazone has important role in the inflammatory response, which suggests that it might have the associated anti-depressant effects being manifested by its anti-depressant profile which needs further exploration. Monitoring changes in behavioral and neurochemical profile of pioglitazone in a dose-dependent manner was the purpose of this study. Pioglitazone was injected to rats at the doses of 0mg/kg, 2.5mg/kg, 5mg/kg and 10mg/kg. Behavioral activities in open field, Skinner's box and elevated plus maze were monitored 20, 35 and 45 minutes respectively after pioglitazone injection. whole brain samples were collected following decapitation of rats one-hour after injection. Samples were kept at -70ºC till HPLC-EC analysis for neurochemical profile. Results show anxiogenic and sedative effects of pioglitazone at all three doses as indicated by Skinner's box, elevated plus maze activity and open field. Also there was an overall decreased dopamine metabolism and increased serotonin turnover. This suggests that diabetic patients using pioglitazone as a therapeutic option, may experience more potent effects of CNS depressants. Findings may help in extending therapeutics in diabetic patients suffering from anxiety and/or depression.

Neurochemical and behavioral effects of lorazepam: A dose related study

Present study was designed to monitor the dose dependent effects of lorazepam; a benzodiazepine (CNS depressant). It is the primary drug of choice for treatment of anxiety and to produce calming effects. However, repeated administration of this lorazepam causes dependence and this might be caused by increased dopaminergic neurotransmission. Besides dopamine, 5-hydroxy tryptamine (5-HT) has also been reported to have pivotal role in the pathophysiology as well as treatment of anxiety and addiction. Repeated administration of lorazepam might involve altered 5-HT metabolism as well. Present study was therefore designed to monitor dose-dependent effects of lorazepam and to select its optimum dose for further experiments and pharmacological interventions. Effects of lorazepam were monitored on food intake, growth rate, activities in familiar and novel environments, light dark box activity, forced swim test and metabolism of dopamine and 5-HT. oral administration of lorazepam was done at the doses of 0mg/kg, 2mg/kg, 4mg/kg and 6mg/kg. Behaviors parameters were monitored following single administration of lorazepam. Rats were decapitated and whole brain samples were collected and stored at -70°C until neurochemical analysis by HPLC-EC. Findings from the present study could be implicated to increased therapeutic utility of lorazepam and related benzodiazepines.

Apomorphine-induced sensitization in rats exposed to restraint stress: Relationship with adaptation to stress

Drug abuse and impaired adaptation to stress are inter-related. Drug abuse is more potentiated upon exposure to stress and an impairment to cope with stress may lead to depression. On the other hand, use of addictive compounds increase the vulnerability to depression by inhibiting the adaptation to stress. Present study investigates relationship between behavioral tolerance to repeated restraint stress and apomorphine-induced sensitization. Apomorphine was injected either before or after the restraint stress episode, to monitor drug-induced behavioral sensitization and place preference. Apomorphine-induced sensitization and place preference were enhanced if the drug is experiencing during restraint stress. Conversely, apomorphine-induced sensitization and place preference were attenuated if the drug is experiencing after restraint stress. It shows that apomorphine, if experienced during restraint stress, produces greater sensitization Conversely, sensitization effects of apomorphine are blocked in animals receiving apomorphine after the termination of restraint stress. The results tend to show that drug of abuse may be effective for the treatment but not prevention of stress-induced depression.

Restraint-induced behavioral deficits are attenuated or impaired by pre- or post-injection of apomorphine: A context-based study

Apomorphine, a psycho stimulant, has neuroprotective effects due to its ability to decrease oxidative stress. Stress-induced dopaminergic dysfunction might lead to posttraumatic stress disorder, depression and related disorders. This dopaminergic dysfunction is more pre-dominant in basal ganglia and prefrontal cortex. Targeting of this dysfunction by psychostimulants, involves elevating dopamine in these brain regions and reduction of stress. On the other hand, stress itself can aggravate addictive effects to psycho stimulants. Present study was therefore designed to monitor the role of apomorphine in the attenuation of stress-induced behavioral deficits. Rats were exposed to 2hr restraint stress either before or after the apomorphine administration, to monitor effects of apomorphine administration on stress-induced behavioral deficits. Stress-induced decreases in food intake, growth rate and elevated plus maze activity were exacerbated if apomorphine was experienced during restraint stress. Conversely, these behavioral deficits were attenuated if apomorphine was experienced after restraint stress. It shows that apomorphine, if experienced during restraint stress, produces greater behavioral deficits, while the same were attenuated in rats receiving apomorphine after the termination of restraint stress. Results suggest that apomorphine and possibly the other CNS stimulants may help to cope stress by attenuating stress-induced behavioral deficits, if experienced after stress.

Neurochemical and behavioral effects of midazolam: A dose related study

In the present study we have monitored dose dependent effects of midazolam; a benzodiazepine (CNS depressant). It is the primary drug of choice for procedural sedation, preoperative sedation, and in emergency departments. Repeated administration of this drug is reported to have abuse potential and may cause this by increasing dopaminergic neurotransmission. Since an important role of 5-hydroxy tryptamine (5-HT) is there in the pathophysiology of anxiety and addiction, administration of midazolam may involve altered 5-HT metabolism as well. Present study was designed to monitor dose-dependent effects of midazolam and select the optimum dose for further experiments. Effects of midazolam were monitored on food intake, growth rate, activities in familiar and novel environments, light dark box activity, hot plate test, forced swim test and levels of dopamine, 5-HT and their metabolites. Midazolam was administered orally (0mg/kg, 2.5mg/kg, 5.0mg/kg and 10mg/kg) and behaviors were monitored post single midazolam administrations. Rats were decapitated and whole brain samples were collected and stored at -70°C until neurochemical analysis by HPLC-EC. Findings from the present study could be implicated to increased therapeutic utility of midazolam and related benzodiazepines.

Enhancement and impairment of cognitive behaviour in Morris water maze test by methylphenidate to rats

Methylphenidate (MPD), a psycho-stimulant is a prescription medicine for the treatment of Attention deficit hyperactivity disorder (ADHD). The drug is also being increasingly used by general population for enhancing cognition. Only few preclinical studies have been carried out on the effects of MPD on cognition and these studies show either an enhancement or impairment of memory following the administration of MPD. The present study was designed to evaluate the effects of different doses of methylphenidate on acquisition and retention of memory in Morris water-maze test. Twenty four male Albino Wistar rats (weighing 180-220gm) were randomly assigned to four groups: (1) Control (2) 0.5mg/kg (3) 2.5mg/kg (4) 5 mg/kg methylphenidate. Animals received drug or water orally before training phase. Memory acquisition was monitored 2hrs post drug administration while memory retention was determined next day. It was found that the clinically relevant doses of methylphenidate (0.5mg/kg and 2.5mg/kg) improved memory acquisition and its retention but higher dose (5mg/kg) impaired both. We suggest that MPD-induced increase of catecholamine neurotransmission may have a role in the improvement of water maze performance while agonist activity of the drug for 5HT-1A receptor in the impaired performance at high doses. Food intake and body weight changes were not affected by MPD administration due to short-term administration of the drug. Results may help in improving pharmaco-therapeutic use of MPD for ADHD.

Repeated treatment with a low dose of reserpine as a progressive model of Parkinson's dementia

Present study was designed to monitor the cognitive profile of the animals upon repeated administration of reserpine, so as to determine that whether these animals should be used as animal models of Parkinson's dementia. In the present study, reserpine was injected daily (once a day for three weeks) at the dose of 0.1mg/kg. Short- and long term memories were assessed using a Morris water maze, on weekly basis. Novel object recognition test was performed after completion of the treatment (day 21). Animals were decapitated on day 21 and brain samples were stored at -70ºC until neurochemical analysis by HPLC-EC. Impairment of short- and long term activities (as monitored in Morris water maze) were not observed until after first week. Long term memory was found to be impaired earlier than the short term memory. Novel object recognition test also exhibited reserpine-induced impairment of working memory. Neurochemical analysis of the whole brain samples by HPLC-EC method showed that repeated administration of reserpine significantly increased DOPAC/ DA ratio (p<0.01). While 5-HIAA/ 5-HT ratio was found to be decreased (p<0.05) in reserpine injected animals. This further confirmed that these neurochemical deficits to be the underlying reason in memory impairment. In conclusion, present study provides evidence that repeated administration of reserpine can be used as a 'progressive' animal model of Parkinson's dementia. Results could be beneficial for face validity and screening of the drugs for the treatment of dementia secondary to Parkinson's and related disorders.

Effect of glycine: Studying memory and behavioral changes in mice

Glycine is an important chemical mediator of nervous system that plays a vital role in memory and other neurological functions. Therefore, the effect of glycine on these traits must be studied to understand biological mechanisms of intricate neurological system. We investigated the effect of different doses of glycine on memory and behavior using 30 albino mice models (treated and control). After two weeks of glycine dosing, we performed light and dark activity and novel-object recognition (NOR) tests to assess the cognitive traits. Brain and blood samples were taken and kept at -70°C using ultra-low temperature freezer. Neurochemical estimation of blood glycine level was estimated by high-performance liquid chromatography with electrochemical detectors (HPLC-ECD). Concentration of glycine (100, 300 and 500 mg/kg) is significantly observed (p<0.01) and it changes due to physiological variations in N-methyl-Daspartate (NMDA) an important neurotransmitter for memory. We observed significant increase in serotonin metabolites including 5-hydroxy tryptophan (5-HT, p<0.05) and 5-hydroxy indole acetic acid (5-HIAA, p<0.001) levels. Similarly,effects were found in case of dopamine (DA, p<0.05) and its metabolites: 3, 4-Dihydroxyphenylacetic acid (DOPAC,p<0.001) and homovanillic acid (HVA, p<0.001). Histopathological investigation of brain tissues showed cellular clumps at cortical junctions at higher doses of glycine as compared to control. These findings revealed that dose dependent concentration of glycine can be useful for memory loss and behavior deficits.

Effects of single administration of apomorphine on memory and monoamine metabolism: A dose related study

In the present study, we have monitored dose dependent effects of apomorphine on learning and memory. Behavioral sensitization and craving, which develop upon repeated treatment with dopamine receptor agonist apomorphine, are major limitations of the therapeutic use of apomorphine in Parkinson's patients. Effects of single (intraperitoneal) injection of apomorphine at different doses (i.e., 0.5, 1.0, & 2.0 mg/ml/kg) on locomotion in a familiar environment (Skinner's box) and memory in Morris water maze were investigated. Results show significantly enhanced activity in Skinner's box in a dose dependant manner. Low dose (0.5 mg/ml/kg) of apomorphine impaired both short- as well as long-term memory while both high and moderate doses of the drug (1.0, & 2.0 mg/ml/kg) enhanced the cognitive profile in rats. However, the memory-enhancing effects of apomorphine at moderate (1.0 mg/ml/kg) dose were more pronounced as compared to high (2.0 mg/ml/kg) dose of the drug. Rats were decapitated on day 2. Whole brains of rats were collected and stored at -70°C. Biogenic amines (i.e., 5-Hydroxytryptamine; 5-HT and dopamine) and metabolites (i.e., Dihydroxyphenylacetic acid; DOPAC, Homovanillic acid; HVA & 5-Hydroxyindoleacetic acid; 5HIAA) were estimated by reverse phase High Performance Liquid Chromatography with electrochemical detector (HPLC-EC). Both low (0.5mg/ml/kg) as well as moderate (1.0mg/ml/kg) dose of apomorphine increased levels of dopamine, DOPAC, HVA, 5-HT and 5-HIAA. Whereas, high (4.0 mg/kg) dose of apomorphine increased levels of dopamine, DOPAC and HVA, while decreased 5-HT and 5-HIAA levels. Results would be helpful in elucidating memory enhancing effects of apomorphine at different doses and its implication for extending therapeutics in cognitive disorders.

Repeated treatment with reserpine as a progressive animal model of depression

Treatment-resistant depression is a major health problem worldwide. Restricted validity of the existing animal models of depression along with the need for the study of progressive development of resistance to antidepressants, demands the modeling of a progressive animal model of depression. Present study was designed to test the hypothesis that the repeated administration of reserpine could serve as a progressive animal model of depression. Animals were injected with reserpine (1.0mg/kg; once a day) for three weeks. Results from the present study showed impaired locomotive effects of reserpine in Skinner's box following second as well as third week. These hypolocomotive effects were more pronounced after third week than the second week. Reserpine-induced behavioral depression was evident in the animals after 2 weeks, as assessed by using forced swim test. Depletion of 5-HT, dopamine and metabolites was also observed in the brain samples. Results from the present study suggest that repeated administration of reserpine could be serve as a progressive model of depression and could be used as a convenient and economic animal model for the face validity of anxiolytic compounds. Findings have potential implications with reference to the understanding and the management of treatment-resistant depression.

Effects of sugar rich diet on brain serotonin, hyperphagia and anxiety in animal model of both genders

Lower levels of 5-hydroxytryptamine (5-HT; serotonin) in the brain elicit sugar craving, while ingestion of sugar rich diet improves mood and alleviates anxiety. Gender differences occur not only in brain serotonin metabolism but also in a serotonin mediated functional responses. The present study was therefore designed to investigate gender related differences on the effects of long term consumption of sugar rich diet on the metabolism of serotonin in the hypothalamus and whole brain which may be relevant with the hyperphagic and anxiety reducing effects of sugar rich diet. Male and female rats were fed freely on a sugar rich diet for five weeks. Hyperphagic effects were monitored by measuring total food intake and body weights changes during the intervention. Anxiolytic effects of sugar rich diet was monitored in light-dark transition test. The results show that ingestion of sugar rich diet decreased serotonin metabolism more in female than male rats. Anxiolytic effects were elicited only in male rats. Hyperphagia was comparable in both male and female rats. Finings would help in understanding the role of sugar rich diet-induced greater decreases of serotonin in sweet craving in women during stress.

Behavioral, hormonal and central serotonin modulating effects of injected leptin

Leptin is viewed as an important target for developing novel therapeutics for obesity, depression/anxiety and cognitive dysfunctions. The present study therefore concerns behavioral, hormonal and central serotonin modulating effects of systemically injected leptin. Pharmacological doses (100 and 500 μg/kg) of leptin injected systemically decreased 24h cumulative food intake and body weight in freely feeding rats and improved acquisition and retention of memory in Morris water maze test. Potential anxiety reducing, hormonal and serotonin modulating effects of the peptide hormone were determined in a separate experiment. Animals injected with 100 or 500 μg/kg leptin were tested for anxiety in an elevated plus maze test 1h later. A significant increase in the number of entries and time passed in open arm of the elevated plus maze in leptin injected animals suggested pronounced anxiety reducing effect. Moreover, circulating levels of leptin correlated significantly with anxiety reducing effects of the peptide hormone. Serum serotonin increased and ghrelin decreased in leptin injected animals and correlated, positively and negatively respectively, with circulating leptin. Corticosterone increased at low dose and levels were normal at higher dose. Serotonin metabolism in the hypothalamus and hippocampus decreased only at higher dose of leptin. The results support a role of leptin in the treatment of obesity, anxiety and cognitive dysfunctions. It is suggested that hormonal and serotonin modulating effects of leptin can alter treatment efficacy in particularly comorbid conditions.

Apomorphine induced conditioned place preference and sensitization is greater in rats exposed to unpredictable chronic mild stress

CNS stimulants are the class of the drugs that may be used to get relief from depression. Apomorphine is a D1 and D2 receptor agonist with a CNS stimulatory effect used for the treatment of Parkinson's disease is also abused. Although many drugs of abuse produce tolerance and dependence. Long term use of pshycostimulants produce reverse tolerance described as sensitization. These drugs also have a number of other beneficial effects but their therapeutic use is limited because of abuse potential. Conditioned place preference (CPP) test is used to monitor the reinforcing effect of drugs of abuse. Stress is an important factor that precipitates and potentiates addictive effects of different drugs of abuse. The present study was designed to investigate the addictive effect of apomorphine (1mg/kg) in rats previously exposed to repeated unpredictable chronic mild stress for 10 days (animal model of depression). Results from present study illustrate that unpredictable chronic mild stress potentiates the reinforcing effects of apomorphine as the number of entries and the time spent in the CPP compartment associated with drug administration is increased. Motor activity was taken as a parameter for behavioral sensitization which is induced by repeated administration of apomorphine, monitored as the number of cage crossings in light compartment of the CPP apparatus, also increased.

Conformational analysis and geometry optimization of apomorphine as an Anti-parkinsonian agen

Apomorphine, a dopamine D₁/D₂agonist, is an important drug of choice for the treatment of Parkinson's and related disorders. The present study was designed to perform the conformational analysis and geometry optimization of apomorphine. Resultant optimized structure corresponds to a substance as it is found in nature. This could be used for a variety of experimental and theoretical investigations especially in the field of pharmacokinetics. The results indicate that the best conformation of the molecule is present at minimum potential energy -88702.9595 kcal/mol. At this point molecule will be more active as histamine H1 receptor agonist.

Immobilization-induced increases of systolic blood pressure and dysregulation of electrolyte balance in ethanol-treated rats

Clinical and experimental studies revealed that alcohol drinking and life event stresses are predisposing factors to hypertension. Intra and extra cellular levels of electrolytes may play important role in the pathogenesis and treatment of hypertension. Dietary intake of sodium, potassium, calcium and magnesium is suggested to have a role in the regulation of blood pressure. The present study was designed to monitor the effects of acute exposure to 2h immobilization stress and ethanol administration at a dose of 2.5 g/kg body weight (i.p.) and combined effect of acute administration of ethanol and immobilization stress on systolic blood pressure (SBP), intraerythrocyte, serum and tissue electrolytes in rats. Results showed that acute exposure to 2h immobilization increased SBP, intraerythrocyte sodium and decreased intraerythrocyte potassium in water as well as in ethanol injected rats. The concentration of Na⁺ and Ca²⁺ increased while that of K⁺ and Mg²⁺ decreased in the heart and kidney tissue. Ethanol administration also increased Na⁺ and Ca²⁺ levels and decreased K⁺ and Mg²⁺ levels in the heart and kidney tissue. Restraint stress decreased serum levels of Na⁺, K⁺, Ca²⁺, P, and Cl⁻ and increased serum Mg²⁺, glucose and haematocrit. Ethanol administration also decreased serum levels of Na⁺, K⁺, Ca²⁺, P, and Cl⁻ and increased serum Mg²⁺, glucose and haematocrit. The effects of ethanol and stress on the changes of blood and tissues electrolytes were additive and may be involved in the greater occurrence of hypertension in alcoholics. Our results suggested an important role of intra and extra cellular electrolytes in both stress and ethanol-induced hypertension. The findings may help to develop strategies for the treatment of hypertension in alcoholics.

Behavioral deficits in rats following acute administration of glimepiride: Relationship with brain serotonin and dopamine

A considerable body of literature suggests that depression and diabetes mellitus are co-morbid. The present study was designed to test any possible behavioral deficits and/or neurochemical changes in the brain as induced by the anti-diabetic drugs. Twenty-four rats were divided into four groups: (i) saline (ii) glimepiride (2.5mg/kg)- (iii) glimepiride (5.0mg/kg)- and (iv) glimepiride (10 mg/kg) injected animals. Behavioral activities in Skinner's box, open field and elevated plus maze were monitored 20, 35 and 45 minutes post injection respectively. Animals were decapitated 60 minutes post injection to collect brain samples. Samples were kept at -70°C until neurochemical analysis by HPLC-EC. Results from the present study show decreased time spent in the open arm of the elevated plus maze (p<0.05) at all the three doses. A decrease in the HVA (Homovanillic acid) levels at all three doses (p<0.01) was also observed along with decreased 5-HT (5-Hydroxytryptamine) (p<0.05 at 5.0 and 10mg/kg) and 5-HIAA (5-Hydroxyindoleacetic acid) (p<0.05 at all three doses) levels. Since a decrease in 5-HT metabolism can induce depression-like effects, the present study therefore suggests that the occurrence of depression in diabetic patients is due to the use of glimipride. Effects of long-term administration of smaller doses of glimipride are to be explored further to monitor tolerance in glimipride-induced deficits of serotonin. The finding may help to explore the cause of depression in diabetics for improving pharmacotherapy in diabetes.

Dose-dependent effects of tryptophan on learning and memory

The concentration of 5-hydroxytryptamine (5-HT, Serotonin) varies as a result of physiological changes in the availability of its precursor tryptophan to the serotonergic neurons in the brain. Increase in brain tryptophan occurs following an increase in plasma tryptophan concentration. Tryptophan intake increases brain serotonin metabolism and enhances memory. The Present study was designed to investigate the effects of oral administration of tryptophan (TRP) at different doses (100, 300 and 500mg/kg) for two weeks on learning and memory functions and Neurochemical changes in rats. Control rats were given drinking water. Assessment of memory in rats was done by using the water Maze. on the 14th day trail training of water Maze was given to rats and after 1h of this 2nd trial of these rats were done. On the next day (After 24h of trail) long-term memories of these rats were monitored. After 1 hour of this all rats were killed by decapitation using guillotine. Brain and blood was collected and stored at -70°C. Neurochemical estimations of Plasma and brain tryptophan, 5-HT and 5-HIAA in brain were made by HPLC-EC. Result showed that administration of tryptophan enhanced performance on water Maze test. Tryptophan treated animals exhibited higher level of Plasma as well as brain tryptophan. 5-HT and 5-HIAA levels were also increased in tryptophan treated rats. Findings are discussed in context with the role of 5-HT metabolism in learning and memory process in rats. Results may help to understand the 5-HT changes following long term TRP administration in a dose dependent manner and will help to suggest the use of TRP in serotonin related illnesses.

Conformational analysis and geometry optimization of buspirone-A 5-HT1A receptor agonist

Buspirone, a partial 5-HT1A receptor agonist, is a clinically prescribed anxiolytic. In the present study, conformational analysis and geometry optimization of buspirone were done as per Hartree-Fock (HF) calculation method by Argus Lab 4.0.1 software. The minimum potential energy was calculated by geometry convergence function by Argus Lab software. The results indicate that the best conformation of molecule is present at minimum potential energy of-100679.5513 kcal/mol. At this point, buspirone will be more active.

Unpredictable chronic mild stress induced behavioral deficits: a comparative study in male and female rats

Stress is an important precipitant factor for depression. Changes in various body systems that occur in depression are similar to those observed in response to stress. Chronic stress may alter behavioral, neurochemical and physiological responses to drug challenges and novel stressors. Unpredictable chronic mild stress (UCMS) also produces alteration in the serotonergic (5-HT; 5-hydroxytryptamine) neurotransmission. Unpredictable chronic mild stress (UCMS) could be used as an animal model of depression. Neurochemical and behavioral effects of UCMS can be reversed by antidepressant agents, suggesting an important role of serotonin. In rodents, UCMS can elicit depression-like symptoms. The objective of the present study was to evaluate and compare the behavioral deficits induced by chronic mild stress in male and female rats and finding out the vulnerability of the two groups. Male and female rats exposed to UCMS exhibited a significant decrease in cumulative food intake as well as in growth rate. Loco motor activity in home cage and open field was also decreased. Results may contribute to our understanding of the interaction between stress and behavioral functions have to depressive disorders.

Neurochemical and behavioral effects of Cinnamomi cassiae (Lauraceae) bark aqueous extract in obese rats

Obesity is a risk factor leading to a number of chronic and metabolic disorders. Obesity is the fifth leading cause of global deaths. At least 2.8 million adults are dying each year as being overweight or obese. Cinnamomi cassiae is widely used traditional medicinal plant, used indigenously, to decrease glucose and cholesterol. 5-Hydroxy tryptamine (5-HT; Serotonin) is an important neurotransmitter reported to be involved in the pathophysiology of anorexia. Present study was designed to investigate the neurochemical and behavioral effects of cinnamon bark aqueous extract (CBAE) in obese rats and to find the possible involvement of 5-HT in reducing the body weight in these experimental animals. CBAE was repeatedly administered orally in the test animals for 5 weeks. A decrease in the food intake along with a concomitant increase in brain 5-HT level was observed in rats administered with CBAE. Findings may help in extending therapeutics in the pathophysiology of obesity and related eating disorders. Decrease activities in behavioral models were also monitored in CBAE treated animals.

Neurochemical and behavioral effects of green tea (Camellia sinensis): a model study

Being rich in polyphenolic compounds such as flavonoids, green tea is suggested to be a potential candidate for the treatment of obesity, stress, depression, Parkinson's and other disorders. Since serotonin has an important role in the pathophysiology of these disorders, present study was designed to monitor the effects of green tea in rats. Green tea extract was provided to the male Albino Wistar rats for 5 weeks, and effects on behaviors were monitored. Results show a decrease in food intake after 5th week but not before. An increase in locomotive activities of the animals was observed, as monitored in novel as well as in familiar environment. Anxiolytic effects were observed in elevated plus maze but not in light dark activity box. An increase in dopamine and serotonin turnover was observed. Our results suggest that beneficial effects of green tea drinking might be due to alteration of serotonin and/or dopamine metabolism. We thereby propose that in further experiments, green tea should be administered in animal model of learned helplessness and effects on the development of adaptation to stress should be monitored. Neurochemical estimations of catecholamine and indoleamine in these animal models of stress exposed to green tea would help in understanding the anxiolytic effects of green tea.

Regional neurochemical profile following development of apomorphine-induced reinforcement

Dopamine is primary neurotransmitter which mediates the reinforcing effects of abused drugs, serotonin (5-Hydroxytryptamine; 5-HT) also has a crucial role in the pathophysiology of addiction. The binding sites of various drugs of abuse are different from each other, their final rewarding effects are mediated by an increase in the dopamine level in the Nucleus Accumbens. The present study used conditioned place preference (CPP) test to monitor apomorphine's reinforcing effects. Associated alterations in 5-HT and dopamine metabolism were also monitored in various brain regions by HPLC-EC. Withdrawal from apomorphine administration (at a dose of 1.0 mg/kg on six alternate days) induced reinforcement as monitored in the conditioned place preference (CPP) paradigm. Serotonin and dopamine metabolism was also changed particularly in the ventral and dorsal striatum. Results therefore suggest desensitization of dopamine receptors in the presynaptic site is involved in apomorphine-induced reinforcement. Desensitization of somatodendritic 5-HT(1A) receptors resulting in increased availability of 5-HT at 5-HT(2C) receptors could attenuate apomorphine-induced reinforcement. Therefore, further investigations in this area should focus on attempts to attenuate apomorphine-induced reinforcement by desensitizing somatodendritic 5-HT(1A) receptors.

Effects of apomorphine on locomotive activity and monoamine metabolism: a dose related study

We have monitored dose dependent effects of apomorphine on motor activity and monoamine metabolism. Behavioral sensitization and craving, which develop upon repeated treatment with dopamine receptor agonist apomorphine, are major limitations of the therapeutic use of apomorphine in Parkinson's patients. Effects of single (intraperitoneal) injection of apomorphine at different doses (i.e., 1.0, 2.0 & 4.0 mg/kg) on exploration in a novel environment (open field) and locomotion in a familiar environment (home cage) were investigated. Results show significantly enhanced activity in home cage (monitored 5min post injection) in a dose dependent manner. However, no significant influence of apomorphine on exploration of open field was observed in the present study (monitored 15 min and 40 min post injection). Animals were decapitated 1 hr post apomorphine injection and whole brains of animals were collected and stored at -70°C. Biogenic amines (i.e., 5-Hydroxytryptamine and dopamine) and metabolites (i.e., Dihydroxyphenylacetic acid, Homovanillic acid & 5-Hydroxyindoleacetic acid) were estimated by reverse phase High Performance Liquid Chromatography with electrochemical detector (HPLC-EC). Effect of low (1.0mg/kg) dose of apomorphine was found to be non-significant on 5-Hydroxytryptamine (5-HT), 5-Hydroxyindoleacetic acid (5-HIAA) and dopamine (DA) levels. Moderate (2.0 mg/kg) dose of drug increased (p<0.05) levels of Homovanillic acid (HVA). Whereas, high (4.0 mg/kg) dose of apomorphine decreased Dihydroxyphenylacetic acid (DOPAC) levels. Results could be helpful in elucidating the effect of apomorphine at different doses and its implication for extending therapeutics in Parkinson's and related disorders.

Neurochemical and behavioral effects of m-CPP in a rat model of tardive dyskinesia

Present study was designed to monitor the responsiveness of 5HT (5-Hydroxytryptamine) -2C receptors following the long-term administration of haloperidol in rats. Effects of m-CPP (meta-Chlorophenyl piperazine) were monitored 48 h after withdrawal from repeated (twice a day for 5 week) administration of haloperidol (at the dose of 1 mg/kg). Vacuous chewing movements (VCMs) were monitored on weekly basis. Two days after withdrawal, animals were injected with saline (1 ml/kg of body weight) or m-CPP (3 mg/kg of body weight). Activities in open field and light dark activity box were monitored 15 and 30 min post injection respectively. Animals were then decapitated (4 h post injection) to collect dorsal striatum (DS) samples for the neurochemical analysis by HPLC-EC (High Performance Liquid Chromatography with Electrochemical detection) method. Results from the present study showed significant hypolocomotive effect of m-CPP (p<0.05) in both repeated haloperidol as well as repeated saline injected rats. Neurochemical analysis of DS by HPLC-EC method showed that administration of m-CPP significantly (p<0.05) decreased 5-HIAA (5-Hydroxyindol acetic acid) in repeated haloperidol injected rats. In conclusion, present study provides evidence that 5HT-2C receptors become hypersensitive in a rat model of Tardive Dyskinesia (TD). These findings have potential implication in the treatment of TD and attenuation of EPS induced by typical neuroleptics.

Decrease in cardiac output and muscle sympathetic activity during vasovagal syncope

The importance of cardiac output (CO) to blood pressure level during vasovagal syncope is unknown. We measured thermodilution CO, mean blood pressure (MBP), and leg muscle mean sympathetic nerve activity (MSNA) each minute during 60 degrees head-up tilt in 26 patients with recurrent syncope. Eight patients tolerated tilt (TT) for 45 min (mean age 60 +/- 5 yr) and 15 patients developed syncope during tilt (TS) (mean age 58 +/- 4 yr, mean tilt time 15.4 +/- 2 min). In TT patients, CO decreased during the first minute of tilt (from 3.2 +/- 0.2 to 2.5 +/- 0.3 l x min(-1) x m(-2), P = 0.001) and thereafter remained stable between 2.5 +/- 0.3 (P = 0.001) and 2.4 +/- 0.2 l x min(-1) x m(-2) (P = 0.004) at 5 and 45 min, respectively. In TS patients, CO decreased during the first minute (from 3.3 +/- 0.2 to 2.7 +/- 0.1 l x min(-1) x m(-2), P = 0.02) and was stable until 7 min before syncope, falling to 2.0 +/- 0.2 at syncope (P = 0.001). Regression slopes for CO versus time during tilt were -0.01 min(-1) in TT versus -0.1 l x min(-1) x m(-2) x min(-1) in TS (P = 0.001). However, MBP was more closely correlated to total peripheral resistance (R = 0.56, P = 0.001) and MSNA (R = 0.58, P = 0.001) than CO (R = 0.32, P = 0.001). In vasovagal reactions, a progressive decline in CO may contribute to hypotension some minutes before syncope occurs.

A comparison of post-prandial changes in flow-mediated dilatation in patients with type 2 diabetes with and without macroalbuminuria

During the post-prandial period there is a decrease in systemic vascular resistance. This study compared meal-induced changes in flow-mediated dilatation (FMD) in patients with Type 2 diabetes with and without evidence of diabetic nephropathy as defined by the presence of macroalbuminuria. The effects on FMD of other factors such as smoking history, antihypertensive treatment and insulin use were also examined. Twelve patients with macroalbuminuria (>300 mg albumin/day) and 12 age- and sex-matched patients with normoalbuminuria (<50 mg albumin/day) participated in the study. Following a 12-hr overnight fast, forearm basal and reactive hyperaemic blood flow was assessed by venous occlusion plethysmography before and 2-hr after ingestion of a meal (2750 kJ) consisting of 56% fat, 26% carbohydrate and 16% protein. Plasma lipid and glycaemic indices were measured at the same times. The combined and grouped data was analysed using paired t tests and correlation and regression analyses. The meal resulted in significant increases in plasma glucose and triglyceride concentrations. While the meal resulted in a similar increase in basal blood flow rate in both patient groups, post-meal reactive hyperaemic flow increased significantly (p=0.04) in normoalbuminuric patients (mean individual increase: 33%) but remained unchanged in patients with macroalbuminuria (mean individual increase: 4%). The use of antihypertensive agents and insulin was also associated with an attenuated post-prandial hyperaemic response. In summary, our study demonstrated that the degree of renal impairment in patients with Type 2 diabetes may influence vasoactivity following a meal. Patients with evidence of diabetic nephropathy had a decreased post-prandial hyperaemic response, a result that indicated a reduced vasodilator reserve. The mechanism of this reduction in vasodilatation of peripheral vessels during the post-prandial period is probably multifactorial. These changes in vasoactivity have the potential to combine with other cardiovascular risk factors to enhance the development of atheroma.

Effects of omapatrilat on systemic arterial function in patients with chronic heart failure

The mechanisms of action of omapatrilat, an agent that inhibits both neutral endopeptidase 24.11 and angiotensin-converting enzyme, on arterial function in patients with heart failure have not been previously reported. Forty-eight patients in New York Heart Association functional class II to III, left ventricular ejection fraction < or = 40%, and in sinus rhythm were randomized to a dose-ranging (2.5, 5, 10, 20, or 40 mg) study of omapatrilat for 12 weeks. Measurements were obtained at baseline and 12 weeks. Decreases in systolic (25.0 +/- 4.5 vs 2.8 +/- 5.0 mm Hg, p < 0.05) and mean arterial (13.9 +/- 3.0 vs 0.3 +/- 3.3 mm Hg, p < 0.05) pressure were seen after 12 weeks of therapy with higher doses. Ventricular-arterial coupling was improved with a dose-related decrease in augmentation index (-13.8 +/- 1.7% vs +6.1 +/- 2.1%, p < 0.01). There was no change in resting forearm blood flow between groups; however, maximum forearm vasodilator response during reactive hyperemia increased in the high-dose groups compared with the control group (+266 +/- 43% vs - 14 +/- 92%, p < 0.05). Omapatrilat induced an increase in postdose plasma atrial natriuretic peptide levels (30 +/- 11 vs -2 +/- 7 pmol/L, p < 0.01) in high-dose groups consistent with endopeptidase 24.11 inhibition. Omapatrilat shows beneficial changes in ventricular-vascular coupling and arterial function in heart failure.

The clinical, cardiac, renal, arterial and neurohormonal effects of omapatrilat, a vasopeptidase inhibitor, in patients with chronic heart failure

OBJECTIVES

We sought to examine the effects of long-term vasopeptidase inhibition in patients with heart failure.

BACKGROUND

The long-term effects of omapatrilat, an agent that inhibits both neutral endopeptidase and angiotensin-converting enzyme, on clinical status, neurohormonal indexes and left ventricular function in patients with chronic heart failure (CHF) have not been previously documented.

METHODS

Forty-eight patients in New York Heart Association functional class II or III, with left ventricular ejection fraction (LVEF)< or =40% and in sinus rhythm were randomized to a dose-ranging pilot study of omapatrilat for 12 weeks. Measurements were performed at baseline and 12 weeks.

RESULTS

There was an improvement in functional status, as reported by the patient (p<0.001) and physician (p<0.001) at 12 weeks. Dose-dependent improvements in LVEF (p<0.001) and LV end-systolic wall stress (sigma) (p<0.05) were seen, together with a reduction in systolic blood pressure (p<0.05). There was evidence of a natriuretic effect (p<0.001), and total blood volume decreased (p<0.05). Omapatrilat induced an increase in postdose plasma atrial natriuretic peptide levels (p<0.01) in the high dose groups, with a reduction in predose plasma brain natriuretic peptide (p<0.001) and epinephrine (p<0.01) levels after 12 weeks of therapy. Omapatrilat was well tolerated.

CONCLUSIONS

The sustained hemodynamic, neurohumoral and renal effects of omapatrilat, together with improved functional status, suggest that vasopeptidase inhibition has potential as a new therapeutic modality for the treatment of CHF.

Brain stem stroke causing baroreflex failure and paroxysmal hypertension

BACKGROUND

Paroxysmal neurogenic hypertension has been associated with a variety of diseases affecting the brain stem but has only rarely been reported after brain stem stroke. The mechanism is thought to involve increased sympathetic activity and baroreflex dysfunction. We undertook microneurographic recordings of muscle sympathetic nerve activity (MNSA) during beat-to-beat blood pressure (BP) monitoring to investigate this hypothesis.

CASE DESCRIPTION

We investigated a 75-year-old woman who developed paroxysmal hypertension (BP 220/110 mm Hg) after a large left-sided medullary infarct. The paroxysms were triggered by changes in posture and were accompanied by tachycardia, diaphoresis, and headache. Serum catecholamines were substantially increased (norepinephrine level, 23.9 nmol/L 9 days after stroke; normal level, <3.8 nmol/L), and heart rate variability, measured by spectral analysis, was decreased in both low- and high-frequency domains (0.04 and 0.06 ms(2), respectively; normal level, 0.14+/-0.02 ms(2)). MNSA was increased in frequency (61 bursts per minute; normal level, 34+/-18 bursts per minute), and the burst amplitude was not inversely related to diastolic BP. BP and MNSA responses to cold pressor and isometric handgrip stimuli were intact.

CONCLUSIONS

Extensive unilateral infarction of the brain stem in the region of the nucleus tractus solitarius may result in partial baroreflex dysfunction, increased sympathetic activity, and neurogenic paroxysmal hypertension.

Baroreceptor denervation presenting as part of a vagal mononeuropathy

A 48-year-old woman presented with a history of progressive cough, dysphonia, dysphagia, and postural symptoms. Subsequent neurological investigations were consistent with a bilateral vagal mononeuropathy, and neurosarcoidosis was diagnosed after scalene node biopsy. Autonomic investigations including microneurography, neurohormones, and heart rate variability demonstrated arterial and cardiopulmonary baroreflex failure. In addition, parasympathetic control of heart rate was absent and consistent with a bilateral, nonselective lesion in the proximal vagus.

Neurohumoral prediction of benefit from carvedilol in ischemic left ventricular dysfunction. Australia-New Zealand Heart Failure Group

BACKGROUND

Plasma neurohormones were analyzed for prediction of adverse outcomes and response to treatment in 415 patients with ischemic left ventricular dysfunction randomly assigned to receive carvedilol or placebo.

METHODS AND RESULTS

Atrial natriuretic peptide, brain natriuretic peptide (BNP), or norepinephrine (NE) levels above the group median were associated with increased mortality rates and heart failure. On multivariate analysis, both BNP and NE interacted with treatment to predict death or heart failure independent of age, New York Heart Association class, and left ventricular ejection fraction. For placebo, supramedian levels of BNP were associated with 3-fold the mortality rate of inframedian levels (20/104; 19% vs 6/99; 6%; P<0.01). For carvedilol, mortality rate was comparable in these 2 subgroups (12/109; 11% vs 8/94; 9%; NS). Corresponding rates for heart failure were 29/104 (28%) versus 3/99 (3%; P<0.001) for placebo and 16/109 (15%) versus 7/94 (7%; NS) for carvedilol. High NE levels did not predict additional benefit from carvedilol, which significantly reduced heart failure admissions only in those with NE levels below the median (13.1% to 4. 0%; P<0.01). In the 23% of the study population with supramedian BNP but inframedian levels of NE, carvedilol reduced hospital admission with heart failure by >90% (P<0.001).

CONCLUSIONS

Carvedilol reduced mortality rates and heart failure in those with higher pretreatment BNP levels but lesser activation of plasma NE. Neurohumoral profiling may guide introduction of beta-blockade in heart failure.

Neuroendocrine prediction of left ventricular function and heart failure after acute myocardial infarction. The Christchurch Cardioendocrine Research Group

OBJECTIVE

To determine the relations of plasma levels of brain natriuretic peptide (BNP), atrial natriuretic factor (ANF), N-terminal ANF (N-ANF), cyclic guanosine monophosphate (cGMP; the cardiac peptide second messenger), and plasma catecholamines to left ventricular function and to prognosis in patients admitted with acute myocardial infarction.

DESIGN

Plasma hormones and ventricular function (radionuclide ventriculography) were measured 1-4 days after myocardial infarction in 220 patients admitted to a single coronary care unit. Radionuclide scanning was repeated 3-5 months after infarction. Clinical events were recorded over a mean period of 14 months.

RESULTS

Both early and late left ventricular ejection fraction (LVEF) were most closely related to plasma BNP (r = -0.60, n = 220, p < 0.001; and r = -0.53, n = 192, p < 0.001, respectively), followed by ANF, N-ANF, cGMP, and the plasma catecholamines. Early plasma BNP concentrations less than twofold the upper limit of normal (20 pmol/l) had 100% negative predictive value for LVEF < 40% at 3-5 months after infarction. In multivariate analysis incorporating all the neurohormonal factors, only BNP remained independently predictive of LVEF < 40% (p < 0.005). Survival analysis by median levels of candidate predictors identified BNP as the most powerful discriminator for death (p < 0.0001). No early deaths (within 4 months) occurred in patients with plasma BNP concentrations below the group median (27 pmol/l), and over follow up only three of 26 deaths occurred in this subgroup. Of all episodes of left ventricular failure, 85% occurred in patients with plasma BNP above the median (p < 0.001). In multivariate analyses, BNP alone gave additional predictive information beyond sex, age, clinical history, LVEF, and plasma noradrenaline for both subsequent onset of LVF and death.

CONCLUSIONS

Plasma BNP measured within 1-4 days of acute myocardial infarction is a powerful independent predictor of left ventricular function, heart failure, or death over the subsequent 14 months, and superior to ANF, N-ANF, cGMP, and plasma catecholamines.

Regional plasma levels of cardiac peptides and their response to acute neutral endopeptidase inhibition in man

1. The cardiac natriuretic peptides, atrial natriuretic peptide and brain natriuretic peptide, are degraded via clearance receptors and the enzyme neutral endopeptidase (EC 3.4.24.11). We studied the regional plasma concentrations of these peptides and their response to acute neutral endopeptidase inhibition in a consecutive series of patients with a broad spectrum of severity of cardiac dysfunction who were undergoing diagnostic right and left heart catheterization (24 patients, mean age 62.6 years).2. Baseline blood samples were obtained for hormone analysis from femoral artery, femoral vein, renal vein, hepatic vein, superior vena cava, coronary sinus and pulmonary artery, and initial haemodynamic measurements were made. Twelve patients then received a neutral endopeptidase inhibitor (SCH 32615, 200 mg intravenously) and 12 received vehicle alone. The cardiac catheterization procedure was then completed and haemodynamic and hormone measurements were repeated.3.Haemodynamic status was similar at baseline in both groups, and at repeated measurement (post-procedure after placebo or active drugs) haemodynamic variables were not significantly different from baseline values. Plasma levels of atrial and brain natriuretic peptides exhibited an arteriovenous increment (344% and 124% respectively) across the heart (femoral artery to coronary sinus) and decrement (by 28-54% and 9-16% respectively) across all other tissue beds (P<0.05 for all) except the lung (no change). Final levels of atrial natriuretic peptide rose above initial levels at all sites in both groups (P<0.05) except coronary sinus levels in the vehicle group (no change). The increase was consistently greater in the inhibitor group at all sites (P<0.05 versus placebo). Levels of brain natriuretic peptide rose at all sites in the inhibitor group only (P<0.05). The transcardiac step-up in atrial natriuretic peptide was markedly augmented after the administration of neutral endopeptidase inhibitor. Other tissue gradients were not significantly altered by neutral endopeptidase inhibitor.4. Atrial and brain natriuretic peptides in plasma are degraded by a number of tissues, and respond differently to cardiac catheterization. Neutral endopeptidase has a significant role in determining plasma levels of natriuretic peptides, in part perhaps by influencing the amount of intact peptide reaching the circulation after secretion from the heart.

Arginine vasopressin V1-receptor antagonism in an ovine model of acute myocardial infarction

Arginine vasopressin (AVP) has an uncertain role in the pathogenesis of increased myocardial and other regional vascular resistance after cardiac injury. The extreme increase in plasma AVP levels observed in some individuals after myocardial infarction potentially exacerbates already compromised myocardial perfusion. We assessed whether blockade of AVP, by administration of the specific V1-receptor antagonist OPC-21268, can reduce the severity of myocardial injury after embolization in our ovine model of acute myocardial infarction. Embolizations resulted in a pattern of changes in ECG and cardiac enzymes consistent with moderate to severe acute myocardial infarction, resulting in left ventricular dysfunction [left ventricular ejection fraction (LVEF) reduced from 52-53% to 38%]. However, no statistically significant differences were observed between groups in hemodynamic or neurohumoral indices of myocardial damage. By contrast, the hypothalamus-pituitary-adrenal (HPA) response [including plasma AVP (p < 0.01), adrenocorticotropic hormone (ACTH; p < 0.01), and cortisol (p < 0.01)) to embolizations was significantly increased in the sheep infused with OPC-21268. In conclusion, whereas plasma HPA responses differed between the two groups, the similar responses in cardiac enzymes, LVEF, and hemodynamic and neurohumoral factors in both groups does not support a role of V1 receptor-mediated exacerbation of myocardial injury in this model of myocardial infarction. Assessment of different receptor antagonists or examination of other models of cardiac injury may further clarify the role of the markedly increased AVP levels that can occur in myocardial infarction.

Autonomic control of vasovagal syncope

In the pathophysiological study of vasovagal syncope, the nature of the interaction between baroreceptor sensitivity (BS), sympathetic withdrawal, and parasympathetic activity has yet to be ascertained. Altered BS may predispose toward abnormal sympathetic and parasympathetic responses to orthostasis, causing hypotension that may progress to syncope if there is sympathetic withdrawal. To examine this hypothesis, we monitored blood pressure (BP), heart rate (HR), BS, forearm blood flow, and muscle nerve sympathetic activity (MNSA) continuously in 18 vasovagal patients during 60 degrees head-up tilt, syncope, and recovery. Results were compared with those of 17 patients who were able to tolerate tilt for 45 min. During early tilt, BP was maintained in both groups by an increase in HR and MNSA from baseline (P < 0.01), but BS decreased more in the syncopal group (P < 0.05). At the start of presyncope (mean 2.7 +/- 0.2 min before syncope and 15.2 +/- 12 min after tilt), when BP fell, HR and sympathetic activity remained increased from baseline (P < 0.01). Thereafter, BP and HR correlated directly with sympathetic activity and regressed in linear fashion until syncope (P < 0.001), whereas BS increased to baseline. At syncope, BP, HR, and sympathetic activity fell below baseline (P < 0.01, P < 0.05, and P < 0.01, respectively), but BS did not increase. During recovery, sympathetic activity increased to baseline and BS increased (P < 0.05), whereas HR and BP remained low (P < 0.01 and P < 0.05, respectively). The mechanism for the initiation of hypotension during presyncope remains unknown, but BS may contribute. Vasodilatation and bradycardia during presyncope appear to be more closely related to withdrawal of sympathetic activity than to increased parasympathetic cardiac activity.

Plasma N-terminal pro-brain natriuretic peptide and adrenomedullin: new neurohormonal predictors of left ventricular function and prognosis after myocardial infarction

BACKGROUND

Newly discovered circulating peptides, N-terminal pro-brain natriuretic peptide (N-BNP) and adrenomedullin (ADM), were examined for prediction of cardiac function and prognosis and compared with previously reported markers in 121 patients with myocardial infarction.

METHODS AND RESULTS

The association between radionuclide left ventricular ejection fraction (LVEF) and N-BNP at 2 to 4 days (r=-.63, P<.0001) and 3 to 5 months (r=-.58, P<.0001) after infarction was comparable to that for C-terminal BNP and far stronger than for ADM (r=-.26, P<.01), N-terminal atrial natriuretic peptide (N-ANP), C-terminal ANP, cGMP, or plasma catecholamine concentrations. For prediction of death over 24 months of follow-up, an early postinfarction N-BNP level > or = 160 pmol/L had sensitivity, specificity, positive predictive value, and negative predictive values of 91%, 72%, 39%, and 97%, respectively, and was superior to any other neurohormone measured and to LVEF. Only 1 of 21 deaths occurred in a patient with an N-BNP level below the group median (Kaplan-Meier survival analysis, P<.00001). For prediction of heart failure (left ventricular failure), plasma N-BNP > or = 145 pmol/L had sensitivity (85%) and negative predictive value (91%) comparable to the other cardiac peptides and was superior to ADM, plasma catecholamines, and LVEF. By multivariate analysis, N-BNP but not ADM provided predictive information for death and left ventricular failure independent of patient age, sex, LVEF, levels of other hormones, and previous history of heart failure, myocardial infarction, hypertension, or diabetes.

CONCLUSIONS

Plasma N-BNP measured 2 to 4 days after myocardial infarction independently predicted left ventricular function and 2-year survival. Stratification of patients into low- and high-risk groups can be facilitated by plasma N-BNP or BNP measurements, and one of these could reasonably be included in the routine clinical workup of patients after myocardial infarction.

The effects of pathophysiological increments in brain natriuretic peptide in left ventricular systolic dysfunction

Plasma levels of brain natriuretic peptide (BNP) are raised in patients with left ventricular impairment and may play a role in the adaptation to left ventricular impairment. Manipulation of BNP levels may have therapeutic potential. The effects of BNP have not been well studied in patients with left ventricular impairment. We studied the effects of low-dose BNP infusion, reproducing the increment in plasma BNP seen with progression from mild to severe heart failure in patients with impaired left ventricular systolic function. BNP was infused in a placebo-controlled, single-blind, crossover design at a rate of 3.3 pmol x kg(-1) x min(-1) over 4 hours to 8 patients with a history of congestive heart failure and persistent impairment of left ventricular systolic function (left ventricular ejection fraction <35%). Endocrine, renal, and hemodynamic effects were measured. Compared with time-matched placebo-control, BNP infusion decreased mean systemic arterial pressure (peak decrease, 17.1 mm Hg; P=.04), mean pulmonary artery pressure (peak decrease, 6.1 mm Hg; P=.007), mean pulmonary capillary wedge pressure (peak decrease, 5.5 mm Hg; P=.04), and systemic vascular resistance (peak decrease, 1400 dyne s(-1) cm(-5); P=.015), but cardiac output and heart rate were unchanged. Urinary volume and urinary excretion of sodium and potassium were not altered. BNP infusion increased plasma cGMP (2.3-fold change, P=.002). Plasma atrial natriuretic peptide levels were increased for the first hour of BNP infusion (peak increase, 11.5 pmol/L; P=.005). Plasma aldosterone levels were unchanged during but increased over time-matched control levels after the end of the BNP infusion (peak increase, 90 pmol/L; P=.02). Plasma renin activity and cortisol and catecholamine levels were unchanged. Low-dose infusion of BNP causes favorable hemodynamic changes and relative neurohormonal suppression but has attenuated renal effects in patients with impaired left ventricular systolic function.

An ovine model of acute myocardial infarction and chronic left ventricular dysfunction

In order to develop and validate an ovine model of myocardial infarction with subsequent impairement of left ventricular function, 15 instrumented sheep underwent selective microembolization of the left coronary arteries with 0.5 mL 90 microns polystyrene beads. Hemodynamics and plasma hormones were measured preembolization (baseline) and then at hours 2, 4, 6, and 12 and days 1, 2, 3, 5 and 7 postembolization. Of the 15 sheep studied, 2 (13%) died on the day of embolization from arrhythmias. In the remaining sheep, left ventricular systolic pressure and stroke work (both P < 0.001) were reduced promptly and remained below basal levels. Mean arterial pressure (P < 0.001) increased initially, then decreased to below basal levels by hour 6. Heart rate (P < 0.001) and left atrial pressure (P < 0.05) were increased while cardiac output was decreased (P < 0.05). Left ventricular ejection fraction at day 7 was reduced (38.8 +/- 3.5 vs 46.0 +/- 3.9% preembolization; P < 0.05). The cardiac enzymes creatine kinase (P < 0.001) and troponin-T (P < 0.001) were increased following microembolization and returned to basal levels by days 2 and 5 respectively. Plasma atrial and brain natriuretic peptides (both P < 0.001) and plasma renin activity (P < 0.005) were all increased following embolization. This ovine model mimics the hemodynamic and neurohumoral features of acute myocardial infarction, resulting in left ventricular dysfunction, and should prove suitable for the study of interventions in a number of these conditions.

Neurohormonal response to head-up tilt and its role in vasovagal syncope

In a controlled study, 26 patients with a history of recurrent syncope were found to have increased arginine vasopressin, corticotrophin, and atrial natriuretic factor levels after 5 minutes of 60 degrees head-up tilt, long before they became hypotensive. The exaggerated neurohormonal response in these patients may indicate a greater sensitivity to central hypovolemia which may predispose to vasovagal syncope, mediated by the vasodilatory effects of atrial natriuretic factor or the sensitization of mechanoreceptors by arginine vasopressin.