Effects of diethyl ether, halothane, ketamine and urethane on sympathetic activity in the rat

The Induction of Long-Term Potentiation by Medial Septum Activation under Urethane Anesthesia Can Alter Gene Expression in the Hippocampus

We studied changes in the expression of early genes in hippocampal cells in response to stimulation of the dorsal medial septal area (dMSA), leading to long-term potentiation in the hippocampus. Rats under urethane anesthesia were implanted with stimulating electrodes in the ventral hippocampal commissure and dMSA and a recording electrode in the CA1 area of the hippocampus. We found that high-frequency stimulation (HFS) of the dMSA led to the induction of long-term potentiation in the synapses formed by the ventral hippocampal commissure on the hippocampal CA1 neurons. One hour after dMSA HFS, we collected the dorsal and ventral hippocampi on both the ipsilateral (damaged by the implanted electrode) and contralateral (intact) sides and analyzed the expression of genes by qPCR. The dMSA HFS led to an increase in the expression of bdnf and cyr61 in the ipsilateral hippocampi and egr1 in the ventral contralateral hippocampus. Thus, dMSA HFS under the conditions of degeneration of the cholinergic neurons in the medial septal area prevented the described increase in gene expression. The changes in cyr61 expression appeared to be dependent on the muscarinic M1 receptors. Our data suggest that the induction of long-term potentiation by dMSA activation enhances the expression of select early genes in the hippocampus.

Chronic recording of the vagus nerve to analyze modulations by the light-dark cycle

OBJECTIVE

The vagus nerve is considered to play a key role in the circadian rhythm. Chronic continuous analysis of the vagus nerve activity could contribute to a better understanding of the role of the vagus nerve in light-dark modulations. This paper presents a continuous analysis of spontaneous vagus nerve activity performed in four rats.

APPROACH

We analyzed the vagus electroneurogram (VENG) and electroencephalogram (EEG) over a recording period of 28 days. Spike activity and heart rate estimation were derived from the VENG, and slow-wave activity was derived from the EEG. The presence of repetitive patterns was investigated with periodograms, cosinor fitting, autocorrelation, and statistical tests. The light-dark variations derived from the VENG spikes were compared with EEG slow waves, an established metric in circadian studies.

RESULTS

Our results demonstrate that light-dark variations can be detected in long-term vagus nerve activity monitoring. A recording period of about seven days is required to characterize accurately the VENG light-dark variations.

SIGNIFICANCE

As a major outcome of this study, vagus nerve recordings hold the promise to help understand circadian regulation.

Antihypertensive Mechanism of Orally Administered Acetylcholine in Spontaneously Hypertensive Rats

Acetylcholine (ACh) acts as a neurotransmitter and neuromodulator. A small dose of eggplant powder rich in ACh (equivalent to 22 g fresh eggplant/d) has been shown to reduce blood pressure (BP) in individuals with higher BP. Here, we investigated the mechanisms underlying the antihypertensive effects of low-dose orally administered ACh in spontaneously hypertensive rats (SHRs). The effects of ACh on BP and sympathetic nervous activity (SNA), including lumbar SNA (LSNA) and renal SNA (RSNA), were evaluated by subjecting conscious SHRs to a telemetry method. Single oral administration of ACh decreased LSNA and lowered BP. Repeated oral administration of ACh for 30 d decreased RSNA and suppressed the elevated BP. Noradrenaline levels in the urine also decreased. However, vagotomy and co-administration of M3 muscarinic ACh receptor antagonist reversed the BP-lowering effect; the dynamics of non-absorbable orally administered ACh was revealed using stable isotope-labeled ACh. In conclusion, ACh acts on the gastrointestinal M3 muscarinic ACh receptor to increase afferent vagal nerve activity, which decreases SNA by autonomic reflex, suppressing noradrenaline release and lowering BP. This study suggests the use of exogenous ACh as an antihypertensive food supplement for controlling the autonomic nervous system, without absorption into the blood.

Reduced genioglossus muscle activity caused by fluid overload in anesthetized rats

INTRODUCTION

Although the precise cause of obstructive sleep apnea (OSA) remains unknown, various anatomical or structural factors are thought to influence upper airway patency. Recent clinical studies show that OSA is frequently observed among patients with fluid-retaining states, such as heart/renal failure and postsurgery. It is important to note that a cause-effect relationship is not yet established, and our understanding of the effects of fluid overload is limited. The goal of this study was to investigate an animal model that can characterize the physiological changes that occur in response to fluid overload.

METHOD

Acute nonsurvival experiments were conducted in 16 Sprague-Dawley rats. Rats were initially anesthetized by inhaled isoflurane, while the femoral vein was cannulated and urethane (1.2-1.5 g/Kg body weight) was gradually delivered intravenously to induce anesthesia. Additional doses of urethane were delivered as necessary to maintain a surgical plane of anesthesia. A surgical incision was made on the cervical area to catheterize carotid artery to measure blood pressure. A pair of stainless-steel wires was injected into the tongue to measure genioglossus muscle activity (GGEMG). All physiological measurements were recorded as intravenous infusion of saline was provided to the rat (infusion rate = 22 ml/kg over 30 min).

RESULTS

Acute saline overloading resulted in a 33% decrease in GGEMG, when compared to baseline. There was also a gradual drop in the respiratory rate (13% decrease) that reached statistical significance at 10 min after infusion was stopped. The blood pressure exhibited a 14% increase which subsequently returned to baseline within 40 min stopping infusion. There were no significant changes in the heart rate.

CONCLUSION

The results of this study indicate that systemic fluid overload can affect significant changes in different physiological systems including reduction in genioglossus muscle activity, increase in blood pressure, and change autonomic nervous system function.

Renal effects of general anesthesia from old to recent studies

Various types of anesthesia are being utilized to maintain physiologically secured surgical conditions. Nearly all categories of general anesthesia are characterized by various perioperative and postoperative complications. These shortcomings are important aspects that need to be considered by the anesthesiologist and surgeon before administration of these compounds. The renal effects of anesthesia play an important role in understanding possible systemic changes due to the fact that the kidney has a direct or indirect impact on nearly all the systems of the body. Various studies have been conducted to find out changes in renal parameters and its systemic effects upon administration of the anesthesia and its postoperative repercussions. Besides that, the impaired renal function might have an impact on the excretion of anesthetic metabolites, which can lead to long-term dysfunction. Patients with a previous history of disease ought to be brought under consideration because these chemicals can ameliorate pre-existent symptoms. This review is intended to discuss the early and latest studies based on the effects of general anesthesia on the renal system.

Novel Approach for Simultaneous Recording of Renal Sympathetic Nerve Activity and Blood Pressure with Intravenous Infusion in Conscious, Unrestrained Mice

Renal sympathetic nerves contribute significantly to both physiological and pathophysiological phenomena. Evaluating renal sympathetic nerve activity (RSNA) is of great interest in many areas of research such as chronic kidney disease, hypertension, heart failure, diabetes and obesity. Unequivocal assessment of the role of the sympathetic nervous system is thus imperative for proper interpretation of experimental results and understanding of disease processes. RSNA has been traditionally measured in anesthetized rodents, including mice. However, mice usually exhibit very low systemic blood pressure and hemodynamic instability for several hours during anesthesia and surgery. Meaningful interpretation of RSNA is confounded by this non-physiological state, given the intimate relationship between sympathetic nervous tone and cardiovascular status. To address this limitation of traditional approaches, we developed a new method for measuring RSNA in conscious, freely-moving mice. Mice were chronically instrumented with radio-telemeters for continuous monitoring of blood pressure as well as a jugular venous infusion catheter and custom-designed bipolar electrode for direct recording of RSNA. Following a 48-72 hour recovery period, survival rate was 100% and all mice behaved normally. At this time-point, RSNA was successfully recorded in 80% of mice, with viable signals acquired up to 4 and 5 days post-surgery in 70% and 50% of mice, respectively. Physiological blood pressures were recorded in all mice (116±2 mmHg; n=10). Recorded RSNA increased with eating and grooming, as well-established in the literature. Furthermore, RSNA was validated by ganglionic blockade and modulation of blood pressure with pharmacological agents. Herein, an effective and manageable method for clear recording of RSNA in conscious, freely-moving mice is described.

The Choice of Euthanasia Method Affects Metabolic Serum Biomarkers

The impact of euthanasia methods on endocrine and metabolic parameters in rodent tissues and biological fluids is highly relevant for the accuracy and reliability of the data collected. However, few studies concerning this issue are found in the literature. We compared the effects of three euthanasia methods currently used in animal experimentation (i.e. decapitation, CO₂ inhalation and pentobarbital injection) on the serum levels of corticosterone, insulin, glucose, triglycerides, cholesterol and a range of free fatty acids in rats. The corticosterone and insulin levels were not significantly affected by the euthanasia protocol used. However, euthanasia by an overdose of pentobarbital (120 mg/kg intraperitoneal injection) increased the serum levels of glucose, and decreased cholesterol, stearic and arachidonic acids levels compared with euthanasia by CO₂ inhalation and decapitation. CO₂ inhalation appears to increase the serum levels of triglycerides, while euthanasia by decapitation induced no individual discrepant biomarker level. We conclude that choice of the euthanasia methods is critical for the reliability of serum biomarkers and indicate the importance of selecting adequate euthanasia methods for metabolic analysis in rodents. Decapitation without anaesthesia may be the most adequate method of euthanasia when taking both animal welfare and data quality in consideration.

Cannabinoid signaling in health and disease

Cannabis sativa has long been used for medicinal purposes. To improve safety and efficacy, compounds from C. sativa were purified or synthesized and named under an umbrella group as cannabinoids. Currently, several cannabinoids may be prescribed in Canada for a variety of indications such as nausea and pain. More recently, an increasing number of reports suggest other salutary effects associated with endogenous cannabinoid signaling including cardioprotection. The therapeutic potential of cannabinoids is therefore extended; however, evidence is limited and mechanisms remain unclear. In addition, the use of cannabinoids clinically has been hindered due to pronounced psychoactive side effects. This review provides an overview on the endocannabinoid system, including known physiological roles, and conditions in which cannabinoid receptor signaling has been implicated.

Cardiac remodelling in a baboon model of intrauterine growth restriction mimics accelerated ageing

KEY POINTS

Rodent models of intrauterine growth restriction (IUGR) successfully identify mechanisms that can lead to short-term and long-term detrimental cardiomyopathies but differences between rodent and human cardiac physiology and placental-fetal development indicate a need for models in precocial species for translation to human development. We developed a baboon model for IUGR studies using a moderate 30% global calorie restriction of pregnant mothers and used cardiac magnetic resonance imaging to evaluate offspring heart function in early adulthood. Impaired diastolic and systolic cardiac function was observed in IUGR offspring with differences between male and female subjects, compared to their respective controls. Aspects of cardiac impairment found in the IUGR offspring were similar to those found in normal controls in a geriatric cohort. Understanding early cardiac biomarkers of IUGR using non-invasive imaging in this susceptible population, especially taking into account sexual dimorphisms, will aid recognition of the clinical presentation, development of biomarkers suitable for use in humans and management of treatment strategies.

ABSTRACT

Extensive rodent studies have shown that reduced perinatal nutrition programmes chronic cardiovascular disease. To enable translation to humans, we developed baboon offspring cohorts from mothers fed ad libitum (control) or 70% of the control ad libitum diet in pregnancy and lactation, which were growth restricted at birth. We hypothesized that intrauterine growth restriction (IUGR) offspring hearts would show impaired function and a premature ageing phenotype. We studied IUGR baboons (8 male, 8 female, 5.7 years), control offspring (8 male, 8 female, 5.6 years - human equivalent approximately 25 years), and normal elderly (OLD) baboons (6 male, 6 female, mean 15.9 years). Left ventricular (LV) morphology and systolic and diastolic function were evaluated with cardiac MRI and normalized to body surface area. Two-way ANOVA by group and sex (with P < 0.05) indicated ejection fraction, 3D sphericity indices, cardiac index, normalized systolic volume, normalized LV wall thickness, and average filling rate differed by group. Group and sex differences were found for normalized LV wall thickening and normalized myocardial mass, without interactions. Normalized peak LV filling rate and diastolic sphericity index were not correlated in control but strongly correlated in OLD and IUGR baboons. IUGR programming in baboons produces myocardial remodelling, reduces systolic and diastolic function, and results in the emergence of a premature ageing phenotype in the heart. To our knowledge, this is the first demonstration of the specific characteristics of cardiac programming and early life functional decline with ageing in an IUGR non-human primate model. Further studies across the life span will determine progression of cardiac dysfunction.

Effects of various types of anesthesia on hemodynamics, cardiac function, and glucose and lipid metabolism in rats

Anesthesia can affect respiratory, circulatory, and endocrine systems but is necessary for certain experimental procedures such as echocardiography and blood sampling in small animals. We have now investigated the effects of four types of anesthesia [pentobarbital sodium (PENT), ketamine-xylazine (K/X), and low- or high-dose isoflurane (ISO)] on hemodynamics, cardiac function, and glucose and lipid metabolism in Sprague-Dawley rats. Aortic pressure, heart rate, and echocardiographic parameters were measured at various time points up to 45 min after the induction of anesthesia, and blood was then collected for measurement of parameters of glucose and lipid metabolism. Systolic aortic pressure remained constant in the PENT group, whereas it showed a biphasic pattern in the K/X group and a gradual decline in the ISO groups. Marked bradycardia was observed in the K/X group. The serum glucose concentration was increased and the plasma insulin level was reduced in the K/X and ISO groups compared with the PENT group. The concentrations of free fatty acids and norepinephrine in plasma were increased in the K/X group. Despite the metabolic effects of K/X and ISO, our results suggest that the marked bradycardic effect of K-X renders this combination appropriate for measurement of Doppler-derived indexes of left ventricular diastolic function, whereas the relative ease with which the depth of anesthesia can be controlled with ISO makes it suitable for manipulations or data collection over long time periods. On the other hand, PENT may be best suited for experiments that focus on measurement of cardiac function by M-mode echocardiography and metabolic parameters.

CB1 receptor activation in the rat paraventricular nucleus induces bi-directional cardiovascular effects via modification of glutamatergic and GABAergic neurotransmission

We have shown previously that the cannabinoid receptor agonist CP55940 microinjected into the paraventricular nucleus of the hypothalamus (PVN) of urethane-anaesthetized rats induces depressor and pressor cardiovascular effects in the absence and presence of the CB₁ antagonist AM251, respectively. The aim of our study was to examine whether the hypotension and/or hypertension induced by CP55940 given into the PVN results from its influence on glutamatergic and GABAergic neurotransmission. CP55940 was microinjected into the PVN of urethane-anaesthetized rats twice (S₁ and S₂, 20 min apart). Antagonists of the following receptors, NMDA (MK801), β₂-adrenergic (ICI118551), thromboxane A₂–TP (SQ29548), angiotensin II–AT₁ (losartan) or GABA_A (bicuculline), or the NO synthase inhibitor L-NAME were administered intravenously 5 min before S₂ alone or together with AM251. The CP55940-induced hypotension was reversed into a pressor response by AM251, bicuculline and L-NAME, but not by the other antagonists. The CP55940-induced pressor effect examined in the presence of AM251 was completely reversed by losartan, reduced by about 50–60 % by MK801, ICI118551 and SQ29548, prevented by bilateral adrenalectomy but not modified by bicuculline and L-NAME. Parallel, but smaller, changes in heart rate accompanied the changes in blood pressure. The bi-directional CB₁ receptor-mediated cardiovascular effects of cannabinoids microinjected into the PVN of anaesthetized rats depend on stimulatory glutamatergic and inhibitory GABAergic inputs to the sympathetic tone; the glutamatergic input is related to AT₁, TP and β₂-adrenergic receptors and catecholamine release from the adrenal medulla whereas the GABAergic input is reinforced by NO.

The electrocardiogram signal of Seba's short-tailed bat, Carollia perspicillata

A number of studies have successfully used electrocardiogram (ECG) signals to characterize complex physiological phenomena such as associative learning in bats. However, at present, no thorough characterization of the structure of ECG signals is available for these animals. The aim of the present study was to quantitatively characterize features of the ECG signals in the bat species Carollia perspicillata, a species that is commonly used in neuroethology studies. Our results show that the ECG signals of C. perspicillata follow the typical mammalian pattern, in that they are composed by a P wave, QRS complex and a T wave. Peak-to-peak amplitudes in the bats' ECG signals were larger in measuring configurations in which one of the electrodes was attached to the right thumb. In addition, large differences in the instantaneous heart rate (HR) distributions were observed between ketamine/xylazine anesthetized and awake bats. Ketamine/xylazine might target the neural circuits that control HR, therefore, instantaneous HR measurements should only be used as physiological marker in awake animals.

Rg3-enriched Korean Red Ginseng enhances blood pressure stability in spontaneously hypertensive rats

Background

Korean Red Ginseng (Panax ginseng) has been shown to exert antihypertensive effects. In particular, ginsenoside Rg3 is thought to be a potent modulator of vascular function. The present study was performed to examine the antihypertensive efficacy of Korean Red Ginseng (KRG) extract and Rg3-enriched KRG (REKRG) extract.

Methods

Spontaneously hypertensive rats (SHRs) and Wistar–Kyoto rats (WKYs) were divided into six groups (WKY control, WKY-KRG, WKY-REKRG, SHR control, SHR-KRG, and SHR-REKRG), and systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured at the carotid artery, followed by injection of 3 mg/kg KRG or 3 mg/kg REKRG.

Results

REKRG treatment significantly decreased SBP and DBP 3 hours post-treatment in the SHR group compared with SHR control group. However, SBP and DBP were not significantly different in KRG-treated SHRs compared with control SHRs. REKRG treatment did not significantly alter SBP or DBP 3 hours post-treatment in the WKY group compared with WKY control group. Similarly, there were no differences in SBP or DBP with KRG treatment in the WKY group and WKY control group. Both KRG and REKRG increased endothelial nitric oxide synthase phosphorylation levels in the aorta, and the increases in endothelial nitric oxide synthase phosphorylation levels by REKRG treatment were higher than those with KRG treatment. Similarly, nitric oxide production in plasma from WKYs and SHRs was also increased by both KRG and REKRG.

Conclusion

These results suggest that REKRG has a more beneficial effect on blood pressure control than KRG in SHRs.

Endocannabinoids in cerebrovascular regulation

The cerebral blood flow is tightly regulated by myogenic, endothelial, metabolic, and neural mechanisms under physiological conditions, and a large body of recent evidence indicates that inflammatory pathways have a major influence on the cerebral blood perfusion in certain central nervous system disorders, like hemorrhagic and ischemic stroke, traumatic brain injury, and vascular dementia. All major cell types involved in cerebrovascular control pathways (i.e., smooth muscle, endothelium, neurons, astrocytes, pericytes, microglia, and leukocytes) are capable of synthesizing endocannabinoids and/or express some or several of their target proteins [i.e., the cannabinoid 1 and 2 (CB1 and CB2) receptors and the transient receptor potential vanilloid type 1 ion channel]. Therefore, the endocannabinoid system may importantly modulate the regulation of cerebral circulation under physiological and pathophysiological conditions in a very complex manner. Experimental data accumulated since the late 1990s indicate that the direct effect of cannabinoids on cerebral vessels is vasodilation mediated, at least in part, by CB1 receptors. Cannabinoid-induced cerebrovascular relaxation involves both a direct inhibition of smooth muscle contractility and a release of vasodilator mediator(s) from the endothelium. However, under stress conditions (e.g., in conscious restrained animals or during hypoxia and hypercapnia), cannabinoid receptor activation was shown to induce a reduction of the cerebral blood flow, probably via inhibition of the electrical and/or metabolic activity of neurons. Finally, in certain cerebrovascular pathologies (e.g., subarachnoid hemorrhage, as well as traumatic and ischemic brain injury), activation of CB2 (and probably yet unidentified non-CB1/non-CB2) receptors appear to improve the blood perfusion of the brain via attenuating vascular inflammation.

Optimizing anesthetic regimen for surgery in mice through minimization of hemodynamic, metabolic, and inflammatory perturbations

The role of anesthetics in animal research models is crucial, yet often ignored, and is almost never the primary focus of examination. Here, we investigated the impact of anesthetic regimens on different parameters of hemodynamics (blood pressure (BP) and heart rate (HR)), metabolism (glucose, insulin, and free fatty acids (FFA)), and inflammation (IL-6 and TNF-α) in two frequently used mouse strains (C57BL/6 and FVB). All animals were at a similar surgical plane of anesthesia, mechanically ventilated, and monitored for 60 min. The following anesthetic regimens were studied: (1) fentanyl-ketamine-midazolam (FKM), (2) fentanyl-midazolam-haldol (FMH), (3) pentobarbital (P), (4) fentanyl-fluanisone-midazolam (FFM), (5) fentanyl-midazolam-acepromazine (FMA), (6) ketamine-medetomidine-atropine (KMA), (7) isoflurane (ISO), and (8) propofol-fentanyl-midazolam (PFM). Metabolic and inflammatory parameters were compared with those obtained from non-anesthetized animals. Hemodynamics: BP >80 mm Hg were only obtained with KMA, whereas hypotension (BP <60 mm Hg) was observed with FKM and P. HR >500 beats/min was observed with ISO and PFM, whereas HR <400 beats/min was induced with KMA, FMH (BL/6), P (BL/6), and FKM (FVB). Metabolism: Glucose and insulin were most disturbed by KMA and ISO and mildly disturbed by FMA, whereas FFM, PFM, and P did not have any effect. FFA increased largely by FMA, with ISO and FKM having no effects. Inflammation: Cytokines were increased least with ISO/FFM/FMA, whereas FKM and KMA induced the largest increases in cytokines. When aiming at achieving surgical anesthesia without large disturbances in hemodynamic, metabolic, and inflammatory profiles, FFM, ISO, or PFM may be the most neutral anesthetic regimens in mice.

The depressor response to intracerebroventricular hypotonic saline is sensitive to TRPV4 antagonist RN1734

Several reports have shown that the periventricular region of the brain, including the paraventricular nucleus (PVN), is critical to sensing and responding to changes in plasma osmolality. Further studies also implicate the transient receptor potential ion channel, type V4 (TRPV4) channel in this homeostatic behavior. In previous work we have shown that TRPV4 ion channels couple to calcium-activated potassium channels in the PVN to decrease action potential firing frequency in response to hypotonicity. In the present study we investigated whether, similarly, intracerebroventricular (ICV) application of hypotonic solutions modulated cardiovascular parameters, and if so whether this was sensitive to a TRPV4 channel inhibitor. We found that ICV injection of 270 mOsmol artificial cerebrospinal fluid (ACSF) decreased mean blood pressure, but not heart rate, compared to naïve mice or mice injected with 300 mOsmol ACSF. This effect was abolished by treatment with the TRPV4 inhibitor RN1734. These data suggest that periventricular targets within the brain are capable of generating depressor action in response to TRPV4 ion channel activation. Potentially, in the future, the TRPV4 channel, or the TRPV4–K_Ca coupling mechanism, may serve as a therapeutic target for treatment of cardiovascular disease.

Pharmacological approaches that slow lymphatic flow as a snakebite first aid

Background

This study examines the use of topical pharmacological agents as a snakebite first aid where slowing venom reaching the circulation prevents systemic toxicity. It is based on the fact that toxin molecules in most snake venoms are large molecules and generally first enter and traverse the lymphatic system before accessing the circulation. It follows on from a previous study where it was shown that topical application of a nitric oxide donor slowed lymph flow to a similar extent in humans and rats as well as increased the time to respiratory arrest for subcutaneous injection of an elapid venom (Pseudonaja textilis, Ptx; Eastern brown snake) into the hind feet of anaesthetized rats.

Methodology/Principal Findings

The effects of topical application of the L-type Ca²⁺ channel antagonist nifedipine and the local anesthetic lignocaine in inhibiting lymph flow and protecting against envenomation was examined in an anaesthetized rat model. The agents significantly increased dye-measured lymph transit times by 500% and 390% compared to controls and increased the time to respiratory arrest to foot injection of a lethal dose of Ptx venom by 60% and 40% respectively. The study also examined the effect of Ptx venom dose over the lethal range of 0.4 to 1.5 mg/kg finding a negative linear relationship between increase in venom dose and time to respiratory arrest.

Conclusions/Significance

The findings suggest that a range of agents that inhibit lymphatic flow could potentially be used as an adjunct treatment to pressure bandaging with immobilization (PBI) in snakebite first aid. This is important given that PBI (a snakebite first aid recommended by the Australian National Health and Medical research Council) is often incorrectly applied. The use of a local anesthetic would have the added advantage of reducing pain.

Snakebite remains a major problem worldwide causing death or serious illness in many tens of thousands of victims annually. An approach to reduce the burden of envenoming is to provide optimum first aid procedures. We have previously shown that topical application of a nitric oxide (NO) donor slowed lymph flow to similar extent in humans and rats as well as increased the time to respiratory arrest by ∼50% for subcutaneous injection of eastern brown snake venom into the hind feet of anaesthetized rats. The present study examines the use of several other topical pharmacological agents that aim to slow venom toxins reaching the circulation through the lymphatic system. The study found that the agents examined were similarly effective to that previously found for the NO donor. The fact that one of these is a commonly used topical local anesthetic may be an ideal adjunct first aid, as it provides first aid while reducing pain.

Pathology influences blood pressure change following vagal stimulation in an animal intubation model

Purpose

The haemodynamic response to critical care intubation is influenced by the use of sedation and relaxant drugs and the activation of the vagal reflex. It has been hypothesized that different disease states may have a contrasting effect on the cardiovascular response to vagal stimulation. Our objective was to determine whether the blood pressure response to vagal stimulation was modified by endotoxaemia or hypovolaemia.

Methods

New Zealand White rabbits were anaesthetised with urethane before tracheotomy. The exposed left Vagus nerve of randomised groups of control (n = 11), endotoxin (n = 11, 1 mg/kg), hypovolaemia 40% (n = 8) and hypovolaemia 20% (n = 8) rabbits were subjected to 10 Hz pulsed electrical stimulations of 25 s duration every 15 min. Haemodynamic parameters were recorded from a catheter in the right carotid artery connected to an iWorx monitor. Serum catecholamines were measured every 30 min using reverse-phase ion-pairing liquid chromatography. The change in blood pressure after vagal stimulation was compared to controls for one hour after the first death in the experimental groups.

Results

29% of the rabbits died in the hypovolaemia 40% group and 27% in the endotoxin group. One rabbit died in the hypovolaemia 40% group before vagal stimulation and was excluded. Following electrical stimulation of the Vagus nerve there was a fall in blood pressure in control rabbits. Blood pressure was conserved in the hypovolaemic rabbits compared to controls (p<0.01). For the endotoxaemic rabbits, there was a non-significant trend for the mean blood pressure to decrease more than the controls. Serum catecholamines were significantly raised in both the hypovolaemic and endotoxaemic rabbits.

Conclusions

Pathology may contribute to modifications in blood pressure when vagal activation occurs. Patients who are either already vasoconstricted, or not vasoplegic, may be less at risk from intubation-related vagally mediated reductions in blood pressure than those with vasodilatory pathologies.

Elevated blood pressure, heart rate and body temperature in mice lacking the XLαs protein of the Gnas locus is due to increased sympathetic tone

Imbalances of energy homeostasis are often associated with cardiovascular complications. Previous work has shown that Gnasxl-deficient mice have a lean and hypermetabolic phenotype, with increased sympathetic stimulation of adipose tissue. The Gnasxl transcript from the imprinted Gnas locus encodes the trimeric G-protein subunit XLαs, which is expressed in brain regions that regulate energy homeostasis and sympathetic nervous system (SNS) activity. To determine whether Gnasxl knock-out (KO) mice display additional SNS-related phenotypes, we have now investigated the cardiovascular system. The Gnasxl KO mice were ∼20 mmHg hypertensive in comparison to wild-type (WT) littermates (P ≤ 0.05) and hypersensitive to the sympatholytic drug reserpine. Using telemetry, we detected an increased waking heart rate in conscious KOs (630 ± 10 versus 584 ± 12 beats min(-1), KO versus WT, P ≤ 0.05). Body temperature was also elevated (38.1 ± 0.3 versus 36.9 ± 0.4°C, KO versus WT, P ≤ 0.05). To investigate autonomic nervous system influences, we used heart rate variability analyses. We empirically defined frequency power bands using atropine and reserpine and verified high-frequency (HF) power and low-frequency (LF) LF/HF power ratio to be indicators of parasympathetic and sympathetic activity, respectively. The LF/HF power ratio was greater in KOs and more sensitive to reserpine than in WTs, consistent with elevated SNS activity. In contrast, atropine and exendin-4, a centrally acting agonist of the glucagon-like peptide-1 receptor, which influences cardiovascular physiology and metabolism, reduced HF power equally in both genotypes. This was associated with a greater increase in heart rate in KOs. Mild stress had a blunted effect on the LF/HF ratio in KOs consistent with elevated basal sympathetic activity. We conclude that XLαs is required for the inhibition of sympathetic outflow towards cardiovascular and metabolically relevant tissues.

Triphasic blood pressure responses to cannabinoids: do we understand the mechanism?

The cannabinoids comprise three major classes of substances, including compounds derived from the cannabis plant (e.g. Δ(9) -tetrahydrocannabinol and the chemically related substances CP55940 and HU210), endogenously formed (e.g. anandamide) and synthetic compounds (e.g. WIN55212-2). Beyond their psychotropic effects, cannabinoids have complex effects on blood pressure, including biphasic changes of Δ(9) -tetrahydrocannabinol and WIN55212-2 and an even triphasic effect of anandamide. The differing pattern of blood pressure changes displayed by the three types of compounds is not really surprising since, although they share an agonistic effect at cannabinoid CB(1) and CB(2) receptors, some compounds have additional effects. In particular, anandamide is known for its pleiotropic effects, and there is overwhelming evidence that anandamide influences blood pressure via (i) CB(1) receptors, (ii) TRPV1 receptors, (iii) endothelial cannabinoid receptors and (iv) degradation products. This review is dedicated to the description of the effects of externally added cannabinoids on cardiovascular parameters in vivo. First, the cardiovascular effects of cannabinoids in anaesthetized animals will be highlighted since most data have been generated in experiments of that type. The text will follow the three phases of anandamide on blood pressure, and we will check to which extent cardiovascular changes elicited by other cannabinoids show overlap with those effects or differ. The second part will be dedicated to the cardiovascular effects of the cannabinoids in conscious animals. In the third part, cardiovascular effects in humans will be discussed, and similarities and differences with respect to the data from animals will be examined.

Endocannabinoid system in cardiovascular disorders - new pharmacotherapeutic opportunities

The long history of Cannabis sativa had its development stimulated and oriented for medicine after the discovery and chemical characterization of its main active ingredient, the 9-tetrahydrocannabinol (9-THC). Consequently, a binding site for 9-THC was identified in rat brains and the first cannabinoid receptor (CB1) was cloned, followed by the CB2 and by the discover of two endogenous agonists: anandamide and 2-arachidonoyl glycerol. Cannabinoid receptors, endocannabinoids and the enzymes that catalyze its synthesis and degradation constitute the endocannabinoid system (ECS), which plays an important role in the cardiovascular system. In vivo experiments with rats have demonstrated the action of anandamide and 2-AG on the development of atherosclerotic plaque, as well as an effect on heart rate, blood pressure, vasoactivity and energy metabolism (action in dyslipidemia and obesity). Recent studies with an antagonist of CB1 receptors showed that the modulation of ECS can play an important role in reducing cardiovascular risk in obese and dyslipidemic patients. Similarly, studies in rats have demonstrated the action of CB2 receptors in adhesion, migration, proliferation and function of immune cells involved in the atherosclerotic plaque formation process. The evidence so far gathered shows that the modulation of ECS (as agonism or antagonism of its receptors) is an enormous potential field for research and intervention in multiple areas of human pathophysiology. The development of selective drugs for the CB1 and CB2 receptors may open a door to new therapeutic regimens.This review article aims to address the key findings and evidences on the modulation of ECS, in order to prospect future forms of therapeutic intervention at the cardiovascular level. A recent, emerging, controversial and of undoubted scientific interest subject, which states as a potential therapeutic target to reach in the 21^st century.

Adenosine elicits an eNOS-independent reduction in arterial blood pressure in conscious mice that involves adenosine A2A receptors

AIMS

Adenosine plays an important role in the regulation of heart rate (HR) and vascular reactivity. However, the mechanisms underlying the acute effect of adenosine on arterial blood pressure in conscious mice are unclear. Therefore, this study investigated the effect of the nucleoside on mean arterial blood pressure (MAP) and HR in conscious mice.

METHODS

Chronic indwelling catheters were placed in C57Bl/6J (WT) and endothelial nitric oxide synthase knockout (eNOS(-/-)) mice for continuous measurements of MAP and HR. Using PCR and myograph analysis, involvement of adenosine receptors was investigated in human and mouse renal blood vessels.

RESULTS

Bolus infusion of 0.5 mg kg(-1) adenosine elicited significant transient decreases in MAP (99.3 ± 2.3 to 70.4 ± 4.5 mmHg) and HR (603.2 ± 18.3 to 364.3 ± 49.2 min(-1)), which were inhibited by the A(2A) receptor antagonist ZM 241385. Activation of adenosine A(2A) receptors with CGS 21680 (0.02 mg kg(-1)) caused a significant reduction in MAP from 99.6 ± 1.2 to 73.1 ± 3.6 mmHg accompanied by tachycardia (610.5 ± 9.3 to 677.5 ± 9.5 min(-1)). The reduction in MAP observed after adenosine or CGS 21680 administrations was not significantly different in WT and eNOS(-/-) mice. In isolated human and mouse intrarenal arteries, adenosine caused a relaxation dependent on A(2A) adenosine receptor activation. A(2A) receptors were present in both human and mouse arteries whereas A(1) and A(2B) receptors were only present in mouse arteries.

CONCLUSION

In conclusion, acute adenosine administration and selective stimulation of adenosine A(2A) receptors results in an immediate, transient eNOS-independent reduction in MAP. A(2A) receptor activation causes relaxation of human and mouse arteries.

Modulation of gastric motility by brain-gut peptides using a novel non-invasive miniaturized pressure transducer method in anesthetized rodents

Acute in vivo measurements are often the initial, most practicable approach used to investigate the effects of novel compounds or genetic manipulations on the regulation of gastric motility. Such acute methods typically involve either surgical implantation of devices or require intragastric perfusion of solutions, which can substantially alter gastric activity and may require extended periods of time to allow stabilization or recovery of the preparation. We validated a simple, non-invasive novel method to measure acutely gastric contractility, using a solid-state catheter pressure transducer inserted orally into the gastric corpus, in fasted, anesthetized rats or mice. The area under the curve of the phasic component (pAUC) of intragastric pressure (IGP) was obtained from continuous manometric recordings of basal activity and in responses to central or peripheral activation of cholinergic pathways, or to abdominal surgery. In rats, intravenous ghrelin or intracisternal injection of the thyrotropin-releasing hormone agonist, RX-77368, significantly increased pAUC while coeliotomy and cacal palpation induced a rapid onset inhibition of phasic activity lasting for the 1-h recording period. In mice, RX-77368 injected into the lateral brain ventricle induced high-amplitude contractions, and carbachol injected intraperitoneally increased pAUC significantly, while coeliotomy and cecal palpation inhibited baseline contractile activity. In wild-type mice, cold exposure (15 min) increased gastric phasic activity and tone, while there was no gastric response in corticotropin releasing factor (CRF)-overexpressing mice, a model of chronic stress. Thus, the novel solid-state manometric approach provides a simple, reliable means for acute pharmacological studies of gastric motility effects in rodents. Using this method we established in mice that the gastric motility response to central vagal activation is impaired under chronic expression of CRF.

Measurement of gastric acid secretion in the anaesthetized rat

The protocols described in this unit are designed to assess the effects of substances on gastric acid secretion by the rat stomach, with the animal under general anesthesia. Both stimulatory and inhibitory effects of compounds can be evaluated and specific mechanisms of action can also be investigated. Acid secretion is induced by substances that directly activate parietal cell receptors (histamine and bethanechol), by indirect stimuli, like 2-deoxy-D-glucose, by electrical stimulation of vagal nerves, or by the peptide pentagastrin. Reference antisecretory drugs are represented by histamine H(2) receptor antagonists and proton pump inhibitors. This model allows the evaluation of complete dose-response curves together with a time-course of the secretory/antisecretory effects. Indirect effects involving activation or inhibition of vagal pathways are evaluated in intact animals by means of electrical vagal stimulation or in vagotomized animals.

An improved strategy for evaluating the extent of chronic arterial baroreceptor denervation in conscious rats

There is no index or criterion of aortic barodenervation, nor can we differentiate among rats that have suffered chronic sham, aortic or sino-aortic denervation. The objective of this study was to develop a procedure to generate at least one quantitative, reproducible and validated index that precisely evaluates the extent of chronic arterial barodenervation performed in conscious rats. Data from 79 conscious male Wistar rats of about 65-70 days of age with diverse extents of chronic arterial barodenervation and used in previous experiments were reanalyzed. The mean arterial pressure (MAP) and the heart rate (HR) of all rats were measured systematically before (over 1 h) and after three consecutive iv bolus injections of phenylephrine (PHE) and sodium nitroprusside (SNP). Four expressions of the effectiveness of barodenervation (MAP lability, PHE ratio, SNP ratio, and SNP-PHE slope) were assessed with linear fixed models, three-level average variance, average separation among levels, outlier box plot analysis, and overlapping graphic analysis. The analysis indicated that a) neither MAP lability nor SNP-PHE slope was affected by the level of chronic sodium intake; b) even though the Box-Cox transformations of both MAP lability [transformed lability index (TLI)] and SNP-PHE slope [transformed general sensitivity index (TGSI), {((3-(ΔHR(SNP)-ΔHR(PHE)/ΔMAP(SNP)-ΔMAP(PHE)))(-0.4)-1)/-0.04597}] could be two promising indexes, TGSI proved to be the best index; c) TLI and TGSI were not freely interchangeable indexes for this purpose. TGSI ranges that permit differentiation between sham (10.09 to 11.46), aortic (8.40 to 9.94) and sino-aortic (7.68 to 8.24) barodenervated conscious rats were defined.

Uridine adenosine tetraphosphate affects contractility of mouse aorta and decreases blood pressure in conscious rats and mice

AIM

in the anaesthetized rat, uridine adenosine tetraphosphate (Up(4) A) is a circulating, endothelium-derived vasoconstrictor presumably operating as such in un-anaesthetized animals. The present study investigated the in vivo effects of Up(4) A in conscious mice and rats, and its direct vascular effects in the mouse aorta in vitro.

METHODS

in vivo, Up(4) A was given as step-up infusion at rates of 8-512 nmol min(-1) kg(-1) for 30 min periods in chronically catheterized rodents. In vitro, the effect of Up(4) A on rings of mouse aortae mounted in a myograph was tested.

RESULTS

high doses of Up(4) A (mice: 512 nmol min(-1) kg(-1) ; rats: 128 nmol min(-1) kg(-1) ) caused hypotension (99 (+/-)4 to 64 7(+/-) mmHg and 114 (+/-) 3 to 108 (+/-) 3 mmHg, respectively, both P < 0.01). In rats, Up(4) A significantly decreased sodium excretion by >75% and potassium excretion by approximately 60% without significant changes in urine flow. Exposure of phenylephrine-contracted rings to increasing concentrations of Up(4) A elicited contraction at 10(-7) and 10(-6) molL(-1) (18 ± 2% and 76 (+/-) 16% respectively); unexpectedly, 10(-5) molL(-1) caused a biphasic response with a contraction (19 6(+/-)2%) followed by a relaxation (-46 (+/-) 6%). No relaxation was observed when the concentration was increased further. Bolus exposure to 10(-5) molL(-1) of Up(4) A caused contraction (+80 (+/-) 2%). Added successively to untreated vessels, increasing concentrations of Up(4) A (10(-7) -10(-5) molL(-1) ) induced a biphasic response of contraction followed by relaxation.

CONCLUSION

up(4) A has direct biphasic effects on vascular smooth muscle of the mouse aorta but vasoconstriction dominates at low concentrations. In conscious rodents, step-up infusions of Up(4) A elicit hypotension and electrolyte retention.

Anesthesia for noncardiac procedures for children with a Berlin Heart EXCOR Pediatric Ventricular Assist Device: a case series

OBJECTIVES

To report our experience of providing anesthesia for noncardiac procedures in children with in situ Berlin Heart EXCOR Pediatric ventricular assist devices and to suggest principles of anesthetic management.

BACKGROUND

With the initiation of the first North American training and support center for Berlin Heart at our institution in 2006, we have been asked to provide anesthesia for noncardiac procedures to these children. No current anesthetic approach to these children has been reported.

METHODS/MATERIALS

Anesthetic records for all noncardiac procedures for children with Berlin Heart between August 2006 and February 2009 in a tertiary care pediatric hospital were retrospectively reviewed. Charts were reviewed for demographic and clinical data, perioperative management, and occurrence of hypotension.

RESULTS

Twenty-nine procedures were performed on 11 patients. Hypotension was a common occurrence with all anesthetic induction and maintenance agents even at low doses. Ketamine induction, however, was less likely to produce hypotension, odds ratio for hypotension 0.1333 (95% confidence range 0.021-0.856). Hypotension was responsive to fluid bolus (60%) and alpha-receptor agonists (100%). Preoperative stability and presence of biventricular ventricular assist device (BiVAD) did not predict intraoperative hemodynamic course.

CONCLUSIONS

Unlike patients with other ventricular assist devices, these children do not tolerate reductions in systemic vascular resistance (SVR) because of the relatively fixed cardiac output of this device. Agents that reduce SVR should be avoided where possible. Preoperative stability is not predictive. Fluids and alpha-agonists should be first-line response to hypotension in this population. Further study of this unusual population is warranted to further delineate best anesthetic practice.

Effects of anesthetics on cystometric parameters in female rats

AIM

The purpose of this study was to evaluate the effect of ketamine, propofol, midazolam and ether on cystometric parameters in rats.

METHODS

Thirty adult female Wistar rats were divided into four groups according to the agent used for the anesthesia; group 1: ether inhalation, group 2: midazolam, group 3: propofol and group 4: ketamine. After surgical implantation of catheter, cystometry was performed in awake rats followed by same procedure under anesthesia. Immediately following awake cystometry, six rats were anesthetized with midazolam (25 mg/kg) intraperitoneally (i.p.), seven rats were anesthetized with propofol (20 mg/kg) i.p., and 11 rats were anesthetized with ketamine (15 mg/kg) i.p. In other six rats, ether inhalation anesthesia was used after awake cystometry. Cystometric parameters such as resting bladder pressure, micturition pressure and the period between micturition were analyzed with Wilcoxon signed-rank test for statistical analysis.

RESULTS

There was no statistically significant effect of ether and midazolam on cystometric parameters, compared to awake rats. Propofol was found to change all measured cystometric parameters without statistically significant difference. The period between micturition was clearly prolonged by propofol but it was also not statistically significant. Ketamine was found to be very depressant on micturition.

CONCLUSION

The results suggest that ether and midazolam are preferable to ketamine for anesthetized cystometry studies. The results were questionable for propofol, and further studies are needed to make it clear.

Acute hypertension reveals depressor and vasodilator effects of cannabinoids in conscious rats

BACKGROUND AND PURPOSE

The cardiovascular effects of cannabinoids can be influenced by anaesthesia and can differ in chronic hypertension, but the extent to which they are influenced by acute hypertension in conscious animals has not been determined.

EXPERIMENTAL APPROACH

We examined cardiovascular responses to intravenous administration of anandamide and the synthetic cannabinoid, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN55212-2), in conscious male Wistar rats made acutely hypertensive by infusion of angiotensin II (AII) and arginine vasopressin (AVP). Rats were chronically instrumented for measurement of arterial blood pressure and vascular conductances in the renal, mesenteric and hindquarters beds.

KEY RESULTS

Anandamide dose-dependently decreased the mean arterial blood pressure of rats made hypertensive by AII-AVP infusion, but not normotensive rats. Interestingly, acute hypertension also revealed a hypotensive response to WIN55212-2, which caused hypertension in normotensive animals. The enhanced depressor effects of the cannabinoids in acute hypertension were associated with increased vasodilatation in hindquarters, renal and mesenteric vascular beds. Treatment with URB597, which inhibits anandamide degradation by fatty acid amide hydrolase, potentiated the depressor and mesenteric vasodilator responses to anandamide. Furthermore, haemodynamic responses to WIN55212-2, but not to anandamide, were attenuated by the CB(1) receptor antagonist, AM251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophen yl)-4-methyl-1H-pyrazole-3-carboxamide].

CONCLUSIONS AND IMPLICATIONS

These results broadly support the literature showing that the cardiovascular effects of cannabinoids can be exaggerated in hypertension, but highlight the involvement of non-CB(1) receptor-mediated mechanisms in the actions of anandamide.

Is urethane-chloralose anaesthesia appropriate for pharmacokinetic-pharmacodynamic assessment? Studies with carvedilol

INTRODUCTION

The aim of the work was to establish the impact of urethane-chloralose anaesthesia on pharmacokinetic-pharmacodynamic (PK-PD) properties of carvedilol in control rats and L-NAME hypertensive animals.

METHODS

Male Wistar Rats were randomly divided into: control (n=12) with tap water to drink and L-NAME rats (n=12) with L-NAME solution (40 mg/kg/day) to drink for 2 weeks. Effects of carvedilol (1 mg kg(-1), i.v.) on blood pressure and heart rate were recorded during 3 h in conscious and urethane (500 mg kg(-1), i.p.) - chloralose (50 mg kg(-1), i.p.) anaesthetized rats. Carvedilol plasma pharmacokinetics was studied by means of traditional blood sampling. PK-PD modeling of carvedilol was made by means of an effect compartment model.

RESULTS

Neither urethane-chloralose nor L-NAME modified estimation of pharmacokinetic parameters of carvedilol. Although urethane-chloralose did not modify potency of carvedilol comparing with awake animals in control and hypertensive group, maximal negative chronotropic response was significantly greater in anaesthetized L-NAME rats in comparison to awake animals. Conversely, anaesthesia did not modify maximal chronotropic response to carvedilol in control rats. Whilst no differences were found in the estimated potency of carvedilol hypotensive response comparing control and L-NAME rats in both awake and anaesthetized conditions, maximal hypotensive effect of carvedilol was significantly greater in anaesthetized control and L-NAME animals in comparison to conscious rats. L-NAME rats showed a greater maximal hypotensive response comparing to control group.

DISCUSSION

Urethane-chloralose anaesthesia is an acceptable experimental condition for the evaluation of PK-PD properties of carvedilol, considering that it does not affect the potency of carvedilol for its chronotropic and hypotensive effect. Conclusions obtained from urethane-chloralose anaesthetized animals, regarding the impact of l-NAME treatment on PK-PD properties of carvedilol, did not differ from those obtained from conscious animals. Anaesthesia did not modify pharmacokinetic behaviour of carvedilol in both normotensive and L-NAME hypertensive rats.

Role of endogenous sleep-wake and analgesic systems in anesthesia

Classical anesthetics of the gamma-aminobutyric acid type A receptor (GABA(A))-enhancing class (e.g., pentobarbital, chloral hydrate, muscimol, and ethanol) produce analgesia and unconsciousness (sedation). Dissociative anesthetics that antagonize the N-methyl-D-aspartate (NMDA) receptor (e.g., ketamine, MK-801, dextromethorphan, and phencyclidine) produce analgesia but do not induce complete loss of consciousness. To understand the mechanisms underlying loss of consciousness and analgesia induced by general anesthetics, we examined the patterns of expression of c-Fos protein in the brain and correlated these with physiological effects of systemically administering GABAergic agents and ketamine at dosages used clinically for anesthesia in rats. We found that GABAergic agents produced predominantly delta activity in the electroencephalogram (EEG) and sedation. In contrast, anesthetic doses of ketamine induced sedation, followed by active arousal behaviors, and produced a faster EEG in the theta range. Consistent with its behavioral effects, ketamine induced Fos expression in cholinergic, monoaminergic, and orexinergic arousal systems and completely suppressed Fos immunoreactivity in the sleep-promoting ventrolateral preoptic nucleus (VLPO). In contrast, GABAergic agents suppressed Fos in the same arousal-promoting systems but increased the number of Fos-immunoreactive neurons in the VLPO compared with waking control animals. All anesthetics tested induced Fos in the spinally projecting noradrenergic A5-7 groups. 6-hydroxydopamine lesions of the A5-7 groups or ibotenic acid lesions of the ventrolateral periaqueductal gray matter (vlPAG) attenuated antinociceptive responses to noxious thermal stimulation (tail-flick test) by both types of anesthetics. We hypothesize that neural substrates of sleep-wake behavior are engaged by low-dose sedative anesthetics and that the mesopontine descending noradrenergic cell groups contribute to the analgesic effects of both NMDA receptor antagonists and GABA(A) receptor-enhancing anesthetics.

Effects of Anesthesia on Plasma and Kidney ANG II Levels in Normotensive and ANG II-Dependent Hypertensive Rats

BACKGROUND

Previous studies have implicated that normotensive rats with normal renal renin activity respond to anesthesia and surgery with greater increases in plasma and kidney angiotensin II (ANG II) concentrations than ANG II-dependent hypertensive rats with intrarenal renin depletion. In the present study, we therefore compared plasma and kidney ANG II levels in anesthetized and conscious normotensive and ANG II-dependent hypertensive rats.

METHODS

Salt-replete Hannover-Sprague-Dawley rats (HanSD) served as controls. As models of ANG II-dependent hypertension we used: 1st, transgenic rats harboring the Ren-2 renin gene (TGR); 2nd, two-kidney, one-clip (2K1C) Goldblatt hypertensive rats, and, 3rd, ANG II-infused hypertensive rats. As additional model with enhanced renin-angiotensin system (RAS) activity, salt-depleted HanSD and TGR were employed.

RESULTS

In anesthetized salt-repleted HanSD, plasma and kidney ANG II levels were higher than in salt-repleted TGR, ANG II-infused and 2K1C rats. Salt depletion caused marked increases in ANG II levels in HanSD but did not alter them in TGR. In contrast, in conscious animals immediately after decapitation plasma and kidney ANG II levels were similar in salt-repleted and salt-depleted TGR, in ANG II-infused rats, in the clipped kidney of 2K1C rats and in salt-depleted HanSD and in all these groups they were significantly higher than in salt-repleted HanSD.

CONCLUSIONS

These findings indicate that anesthesia increases plasma and kidney ANG II levels in HanSD to a greater degree than in ANG II-dependent models of hypertension. Therefore, the results from studies employing anesthetized animals must be interpreted with caution.

Cardiovascular pharmacology of cannabinoids

Cannabinoids and their synthetic and endogenous analogs affect a broad range of physiological functions, including cardiovascular variables, the most important component of their effect being profound hypotension. The mechanisms of the cardiovascular effects of cannabinoids in vivo are complex and may involve modulation of autonomic outflow in both the central and peripheral nervous systems as well as direct effects on the myocardium and vasculature. Although several lines of evidence indicate that the cardiovascular depressive effects of cannabinoids are mediated by peripherally localized CB1 receptors, recent studies provide strong support for the existence of as-yet-undefined endothelial and cardiac receptor(s) that mediate certain endocannabinoid-induced cardiovascular effects. The endogenous cannabinoid system has been recently implicated in the mechanism of hypotension associated with hemorrhagic, endotoxic, and cardiogenic shock, and advanced liver cirrhosis. Furthermore, cannabinoids have been considered as novel antihypertensive agents. A protective role of endocannabinoids in myocardial ischemia has also been documented. In this chapter, we summarize current information on the cardiovascular effects of cannabinoids and highlight the importance of these effects in a variety of pathophysiological conditions.

Indirect sensing of insulin-induced hypoglycaemia by the carotid body in the rat

The most physiologically important sensors for systemic glucoregulation are located in extra-cranial sites. Recent evidence suggests that the carotid body may be one such site. We assessed rat carotid body afferent neural output in response to lowered glucose, indirectly by measurement of ventilation, and directly by recording single or few-fibre chemoafferent discharge, in vitro. Insulin (0.4 Ukg(-1)min(-1))-induced hypoglycaemia (blood glucose reduced by ca 50% to 3.4 +/- 0.1 mmoll(-1)) significantly increased spontaneous ventilation in sham-operated animals but not in bilateral carotid sinus nerve sectioned (CSNX) animals. In both groups, metabolic rate (measured as ) was almost doubled during hypoglycaemia. The ventilatory equivalent was unchanged in the sham group leading to a maintained control level of P(a, CO(2)), but was significantly reduced in the CSNX group, giving rise to an elevation of 6.0 +/- 1.3 mmHg in P(a, CO(2)). When pulmonary ventilation in sham animals was controlled and maintained, phrenic neural activity increased during hypoglycaemia and was associated with a significant increase in P(a, CO(2)) of 5.1 +/- 0.5 mmHg. Baseline chemoreceptor discharge frequency, recorded in vitro, was not affected, and did not increase when the superfusate [glucose] was lowered from 10 mm to 2 mm by substitution with sucrose: 0.40 +/- 0.20 Hz to 0.27 +/- 0.15 Hz, respectively (P > 0.20). We suggest therefore that any potential role of the carotid bodies in glucose homeostasis in vivo is mediated through its transduction of some other metabolically derived blood-borne factor rather than glucose per se and that this may also provide the link between exercise, metabolic rate and ventilation.

Blood sampling methodology is crucial for precise measurement of plasma catecholamines concentrations in mice

Epinephrine (E) and norepinephrine (NE) play a major role in regulating metabolism and cardiovascular physiology. Both are secreted in response to stress and their measurement in plasma allows the study of sympathoadrenal function. Several studies investigating sympathoadrenal physiology are conducted using mice. Review of the literature revealed that basal mouse NE and E plasma concentrations range within 4-140 nM depending on the blood sampling method. Such variability doesn't allow study comparison and may conceal catecholamine variations in response to stress. Therefore, our aim was to determine a reliable sampling method to measure mouse plasma catecholamine concentrations. Results showed that arterial catheterization is the most accurate sampling method: E and NE basal levels were similar to those found in humans (1.1+/-0.3 nM and 4.1+/-0.5 nM, respectively). Retro-orbital bleeding led to analogous results. On the contrary, decapitation was stressful for mice and consequently NE and E concentrations were high (24.6+/-2.7 nM and 27.3+/-3.8 nM, respectively). These different bleeding methods were compared in terms of their ability to detect sympathoadrenal system stimulation (cold-pressure test). With catheter and retro-orbital samplings the expected increase in NE and E levels was easily perceived. In contrast, with decapitation no significant change in E was detected. In conclusion, arterial-catheter and retro-orbital blood sampling methods appear to be the most accurate procedures for studying the sympathetic nervous system in mice in both unstressed and stressed conditions.

Endocrine effects of centrally injected nociceptin in the rat

In the present study we investigated the mechanisms involved in the endocrine effect of nociceptin/orphanin FQ (OFQ) in the rat and the possible interaction between OFQ and morphine in the control of growth hormone (GH) secretion. The intracerebroventricular administration of OFQ (2.3 or 23 microg/rat, i.c.v.) in freely moving male rats caused an increase in the secretion of both GH and prolactin (PRL). The possible involvement of the catecholaminergic (CA) system was studied by administering OFQ to CA-depleted rats (rats given 200 mg/kg of alpha-methyl-p-tyrosine subcutaneously 2 h before the i.c.v. dose of OFQ). In these CA-depleted rats, administration of OFQ (23 microg/rat, i.c.v.) did not stimulate GH secretion, whereas it significantly enhanced PRL secretion. In rats anesthetized with ketamine, which induces a significant increase of GH, PRL and corticosterone secretion by activating the sympathetic tone, OFQ (23 microg/rat, i.c.v.) did not modify GH and corticosterone levels, whereas again it significantly potentiated PRL secretion. Overall these results indicate that CA system is involved in the stimulatory action of OFQ on GH but not on PRL secretion. In fact the stimulation of PRL, but not that of GH, was still evident after impairment of the CA system. Pretreatment with OFQ (23 microg/rat, i.c.v.) attenuated the GH secretion induced by morphine (1 mg/kg, given by intra-arterial injection), thus showing a negative interaction between OFQ and morphine in the control of GH secretion.

Postnatal development of blood pressure and baroreflex in mice

Postnatal development of blood pressure, heart rate and their regulation by arterial baroreceptor reflex in mice was examined. We first confirmed that simultaneous recordings of pulsatile blood pressure by the "servo null" method and the conventional catheter method gave almost identical tracings in halothane-anesthetized adult mice. We then measured blood pressure by servo null method together with electrocardiograph in mice of various ages from newborn to adult. Mean blood pressure increased progressively with age from 19 + 2 mm Hg in P0 newborn to 74+/-1 in adult mice, while heart rate initially increased from 365+/-12 bpm in newborn to 441+/-15 in infant (7 days old), and then decreased to 337+/-15 in adult mice. Between 1 and 2 weeks of age, gain of arterial baroreceptor reflex abruptly increased from a newborn value of 0.3 to a near adult value of 1.1 ms/mm Hg. On the other hand, sensitivity to anesthesia did not differ except for P1 and P2 newborns. We conclude that pulsatile blood pressure can be accurately measured by the servo null method even in the newborn mice and that baroreflex heart rate control mature at around 2 weeks after birth in the mice.

Effects of induced hypothermia on renal sympathetic nerve activity and baroreceptor reflex in urethane-anesthetized rabbits

OBJECTIVE

To evaluate the role of the autonomic nervous system in hemodynamic changes during induced hypothermia.

DESIGN

Prospective, randomized animal study.

SETTING

An animal research laboratory in a medical university.

SUBJECTS

A total of 29 anesthetized rabbits.

INTERVENTIONS

Animals were anesthetized by intraperitoneal urethane. After tracheostomy and administration of gallamine, respiration was maintained by mechanical ventilatory support. The animals were divided into five groups (one control and the four experimental groups); animals were treated with an intact neuraxis and normothermia (control group), animals with an intact neuraxis (intact group), cervical vagotomized animals (vagotomy group), the carotid sinus and aortic nerves denervated animals (SAD group), and animals with SAD plus vagotomy (SADV group). The left renal sympathetic nerves were exposed by a retroperitoneal approach.

MEASUREMENTS AND MAIN RESULTS

We examined the effects of surface cooling on HR, mean arterial pressure, central venous pressure, and renal sympathetic nerve activity (RSNA) in the animals. Changes of baroreflex sensitivity and plasma catecholamines were also measured simultaneously. Surface cooling caused progressive and profound decreases in HR in all experimental groups. In all groups, RSNAs increased at the early phase, which were followed by return to the precooling level.

CONCLUSIONS

Hemodynamics and RSNA during induced hypothermia are regulated by mechanisms other than the baroreceptor reflex system, possibly the dermal cold receptors. Suppression of the baroreflex occurred on HR but not on RSNA during hypothermia, which may indicate direct effects of hypothermia on the heart. RSNA responses may be activated earlier than systemic catecholamine responses during induced hypothermia.

Endocannabinoids as cardiovascular modulators

Cannabinoids, the bioactive constituents of the marijuana plant and their synthetic and endogenous analogs cause not only neurobehavioral, but also cardiovascular effects. The most important component of these effects is a profound decrease in blood pressure and heart rate. Although multiple lines of evidence indicate that the hypotensive and bradycardic effects of anandamide and other cannabinoids are mediated by peripherally located CB1 cannabinoid receptors, anandamide can also elicit vasodilation in certain vascular beds, which is independent of CB1 or CB2 receptors. Possible cellular mechanisms underlying these effects and the cellular sources of vasoactive anandamide are discussed.

Effect of Korea red ginseng on the blood pressure in conscious hypertensive rats

The change of blood pressure and heart rate after intravenous injection of Korea red ginseng (KRG) were studied in the conscious normotensive and one-kidney, one-clip Goldblatt hypertensive (1K, 1C-GBH) rats. Crude saponin (CS) of KRG (50, 100 mg/kg i.v.) induced a hypotensive effect and bradycardia in a dose-dependent manner in the anesthetized rats. On the other hand, CS of KRG (100 mg/kg) induced a hypotensive effect and reflex tachycardia in the conscious rats. Saponin-free fraction (SFF) of KRG did not affect them in the anesthetized normotensive rats (P>.05). The maximal hypotensive effect by CS of KRG in the conscious 1K, 1C-GBH hypertensive rats and L-nitroarginine methyl ester (L-NAME, 40 mg/kg)-treated conscious hypertensive rats was not different from that of conscious normotensive rats (Delta 31.6+/-6.3, Delta 27.5+/-5.8 vs. Delta 26.7+/-4.3 mmHg, P>.05). However, pretreatment of L-NAME significantly inhibited the reflex tachycardia by CS of KRG (70.8+/-7.0 vs. 30.6+/-15.0 bpm, P<.05). Hemolysate-sensitive nitric oxide (NO) current by the CS of KRG was greater than that of the SFF of KRG (651.9+/-128.2 pA for CS and 164.9+/-92.5 pA for SFF, P<.001). These findings suggest that KRG has a hypotensive effect and its effect may be due to saponin fraction of KRG in the conscious rats. The releasing effect of NO of KRG, like NO donor, may be partly contributed to the hypotensive effect of KRG.

Sympathetic activity in the rat: effects of anaesthesia on noradrenaline kinetics

Noradrenaline (NA) kinetics represent an effective tool for evaluating the activity of the sympathetic system: thus plasma NA concentration, spillover rate (SOR) and metabolic clearance rate (MC) were measured in the rat. The dilution technique was adapted and validated: pithing that caused mechanical destruction of the spinal cord was shown to reduce drastically NA-SOR and plasma NA concentration with no effect on NA-MC. NA-SOR and plasma NA concentration were restored within their normal limits when 2.5 Hz electrical stimulation of the sympathetic roots was superimposed. Normal values of NA kinetics in non-anaesthetised normotensive 12-week-old rats are reported: NA-SOR=196.1+/-26.4 ng/kg/min, NA-MC=413.9+/-38.8 ml/kg/min and plasma NA=486+/-52 pg/ml. NA kinetic was investigated in response to anaesthesia, known to depress excitable tissues of the central nervous system and expected to depress the activity of the sympathetic system. When NA-SOR was significantly reduced during anaesthesia with either sodium pentobarbital or chloralose, plasma NA concentration was not changed because NA-MC was also reduced. Thus, plasma NA concentration can be a misleading marker of the sympathetic activity. The response of the sympathetic activity to four different anaesthetic agents is shown to be heterogeneous, ranging from inhibition to stimulation. Sodium pentobarbital anaesthesia was associated with a statistically significant reduction of both NA-SOR (105.6+/-14.1 ng/kg/min, P<0. 01) and NA-MC (239.3+/-18.7 ml/kg/min, P<0.001) while plasma NA was not changed (438+/-47 pg/ml). Chloralose reduced NA-SOR (101.6+/-20. 1 ng/kg/min, P<0.05) while ketamine did not (150.6+/-35.5 ng/kg/min, n.s.): both compounds reduced NA-MC (257.9+/-27.8 ml/kg/min, P<0.01 and 265.8+/-34.3 ml/kg/min, P<0.05, respectively). Diethyl ether was shown to increase both NA-SOR (472.2+/-111 ng/kg/min, P<0.05) and plasma NA concentration (1589+/-436 pg/ml, P<0.01), while NA-MC remained unchanged. Thus, any investigation of the activity of the sympathetic system in the anaesthetised rat has to take into account the specific effects related to the anaesthetic agent used.