Intrathecal orexin A increases sympathetic outflow and respiratory drive, enhances baroreflex sensitivity and blocks the somato-sympathetic reflex

BACKGROUND

Intrathecal (i.t.) injection of orexin A (OX-A) increases blood pressure and heart rate (HR), but the effects of OX-A on sympathetic and phrenic, nerve activity, and the baroreflex(es), somato-sympathetic and hypoxic chemoreflex(es) are unknown.

EXPERIMENTAL APPROACH

Urethane-anaesthetized, vagotomized and artificially ventilated male Sprague-Dawley rats were examined in this study. The effects of i.t. OX-A (20 nmol 10 µL⁻¹) on cardiorespiratory parameters, and responses to stimulation of the sciatic nerve (electrical), arterial baroreceptors (phenylephrine hydrochloride, 0.01 mg kg⁻¹ i.v.) and peripheral (hypoxia) chemoreceptors were also investigated.

KEY RESULTS

i.t. OX-A caused a prolonged dose-dependent sympathoexcitation, pressor response and tachycardia. The peak effect was observed at 20 nmol with increases in mean arterial pressure, HR and splanchnic sympathetic nerve activity (sSNA) of 32 mmHg, 52 beats per minute and 100% from baseline respectively. OX-A also dose-dependently increased respiratory drive, as indicated by a rise in phrenic nerve amplitude and a fall in phrenic nerve frequency, an increase in neural minute ventilation, a lengthening of the expiratory period, and a shortening of the inspiratory period. All effects of OX-A (20 nmol) were attenuated by the orexin receptor 1 antagonist SB 334867. OX-A significantly reduced both sympathoexcitatory peaks of somato-sympathetic reflex while increasing baroreflex sensitivity. OX-A increased the amplitude of the pressor response and markedly amplified the effect of hypoxia on sSNA.

CONCLUSIONS

Thus, activation of OX receptors in rat spinal cord alters cardiorespiratory function and differentially modulates sympathetic reflexes.     

High concentrations of dexmedetomidine inhibit compound action potentials in frog sciatic nerves without ��2 adrenoceptor activation

BACKGROUND AND PURPOSE

Dexmedetomidine, an α₂-adrenoceptor agonist, exhibits anti-nociceptive actions at the spinal cord and enhances the effect of local anaesthetics in the peripheral nervous system. Although the latter action may be attributed in part to inhibition of nerve conduction produced by dexmedetomidine, this has not been fully examined yet.

EXPERIMENTAL APPROACH

We examined the effects of various adrenoceptor agonists including dexmedetomidine, and tetracaine, a local anaesthetic, on compound action potentials (CAPs) recorded from the frog sciatic nerve, using the air-gap method.

KEY RESULTS

Dexmedetomidine reversibly and concentration-dependently reduced the peak amplitude of CAPs (IC₅₀ = 0.40 mmol·L⁻¹). This action was not antagonized by two α₂-adrenoceptor antagonists, yohimbine and atipamezole; the latter antagonist itself reduced CAP peak amplitude. Clonidine and oxymetazoline, two other α₂-adrenoceptor agonists, also inhibited CAPs; the maximum effect of clonidine was only 20%, while oxymetazoline was less potent (IC₅₀ = 1.5 mmol·L⁻¹) than dexmedetomidine. On the other hand, (±)-adrenaline, (±)-noradrenaline, α₁-adrenoceptor agonist (-)-phenylephrine and β-adrenoceptor agonist (-)-isoprenaline (each 1 mmol·L⁻¹) had no effect on CAPs. Tetracaine reversibly reduced CAP peak amplitude (IC₅₀ of 0.014 mmol·L⁻¹).

CONCLUSIONS AND IMPLICATIONS

Dexmedetomidine reduced CAP peak amplitude without α₂-adrenoceptor activation (at concentrations >1000-fold higher than those used as α₂ adrenoceptor agonist), with a lower potency than tetracaine. CAPs were inhibited by other α₂ adrenoceptor agonists, oxymetazoline and clonidine, and also an α₂ adrenoceptor antagonist atipamezole. Thus, some drugs acting on α₂ adrenoceptors are able to block nerve conduction.     

Eprosartan modulates the reflex activation of the sympathetic nervous system in sodium restricted healthy humans

AIMS

To test the hypothesis that eprosartan inhibits both nonbaroreflex and arterial baroreflex mediated activation of the sympathetic nervous system, assessed by renal tubular function, systemic haemodynamics and vasoactive hormones, in sodium restricted healthy humans.

METHODS

The effect of eprosartan on urinary sodium, lithium and water excretion, heart rate (HR), blood pressure and vasoactive hormones was measured before, during and after a cold pressor test (CPT) and sodium nitroprusside (SNP) infusion in a randomized, placebo controlled, double-blind, crossover study in 17 healthy subjects. Glomerular filtration rate and renal tubular function were determined by a continuous infusion clearance technique and vasoactive hormones by radioimmunoassays.

RESULTS

Eprosartan attenuated the impact of the CPT on HR (mean difference from placebo (95% confidence interval) (3.9 (0.7, 7.0) min⁻¹) and mean arterial pressure (MAP) (4.7 (0.3, 9.2) mmHg), but no effect of eprosartan was observed on the impact of the CPT on renal tubular function. During a SNP induced reduction in MAP of 10 mmHg eprosartan decreased fractional excretions of sodium (0.46 (0.14, 0.76)%) and lithium (5.1 (2.5, 7.6)%) and tended to increase HR (4.1 (−0.26, 8.4) min⁻¹) and plasma concentrations of norepinephrine (33.8 (−5.8, 72.1) pg ml⁻¹).

CONCLUSIONS

These findings suggest that during mild sodium restriction eprosartan has a small inhibitory effect on nonbaroreflex mediated activation of the sympathetic nervous system. During arterial baroreflex mediated activation of the sympathetic nervous system this effect is, however, completely overruled by an increased sensitivity of the arterial baroreflex.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• A sympatho-inhibitory effect of ACE-inhibitors and AT₁ receptor antagonists has been widely demonstrated in animal models, but in humans this effect tends only to be present during chronic treatment in conditions with pre-existing high levels of sympathetic activity.
• Sodium restriction increases renal sympathetic nerve activity and the activity of the renin-angiotensin system and may be a favourable condition to demonstrate sympatho-inhibition as a short-term effect of the AT₁ receptor antagonist eprosartan in healthy humans.

WHAT THIS STUDY ADDS

• Results from our study indicate that during sodium restriction eprosartan has a small inhibitory effect on nonbaroreflex mediated activation of the sympathetic nervous system.
• During arterial baroreflex mediated activation of the sympathetic nervous system this effect is, however, completely overruled by an increased sensitivity of the arterial baroreflex.

     

Effects of direct cedrol inhalation into the lower airway on autonomic nervous activity in totally laryngectomized subjects

Aims

Previous studies reported that Cedrol (odorant) inhalation (CI) induced changes in autonomic balance and baroreceptor sensitivity (BRS) in both healthy subjects and anosmic patients. This suggests that Cedrol may act on the lower airway, and that the pulmonary system may exert an inhibitory influence on the cardiovascular system.

Method

To test the above possibility, vaporized Cedrol (64.0 ± 7.7 10⁻⁹m) or blank air was directly inhaled through the lower airway from a hole in the trachea, but not through the upper airway, using totally laryngectomized subjects. During the experiment, ECG, systolic (SBP) and diastolic (DBP) blood pressures were measured. Sympathetic and parasympathetic nervous activity was estimated by spectral analyses of variability in these parameters (heart rate variability (HRV), SBP variability (SBPV) and DBP variability (DBPV)). BRS was computed from transfer gain between SBP and the R-R interval of the ECG.

Results

SBP and DBP significantly decreased during CI, although there were no significant differences in HR and respiratory rate. BRS significantly increased during CI. The low frequency components of SBPV and DBPV (indices for sympathetic activity) significantly decreased during CI, while high frequency components of HRV (an index for parasympathetic activity) significantly increased.

Conclusions

The present experiment using totally laryngectomized patients replicated the similar results in healthy subjects who inhaled Cedrol through the nose, suppression of sympathetic outflow and increase in parasympathetic outflow. These results demonstrated that Cedrol acts on the lower airway and pulmonary system, and suggest a new target for drug therapy of hypertension.

What is already known about this subject

• Relationships between smell sensation and autonomic changes have been studied extensively.
• However, the possibility that odorants may also act on the lung and lower airway remains unknown.

What this study adds

• The present results provide the first evidence that the lung and lower airway exert an inhibitory influence on the cardiovascular system in response to Cedrol (odorant) in the air under physiological conditions.

     

The pharmacokinetics and pharmacodynamics of cisatracurium in critically ill patients with severe sepsis

AIM

To characterize the pharmacokinetics (PK) and pharmacodynamics (PD) of cisatracurium in critically ill patients with severe sepsis.

METHODS

Blood samples were collected before and over 8 h after a single bolus dose of cisatracurium 0.1 mg kg⁻¹. Neuromuscular block was assessed by accelerometric peripheral nerve stimulation (TOF Watch). Plasma concentration and neuromuscular block data were fitted using population analysis.

RESULTS

Steady-state volume of distribution was determined to be 111 ± 71 ml kg⁻¹ and plasma clearance was 5.2 ± 1.8 ml min⁻¹ kg⁻¹ in these patients with greater inter-patient variability compared with other populations. The time to maximum block (8.3 ± 2.9 min) and delay time of transferring from central to effect compartment (17.2 min) was much longer, while the maximum block (95.0 ± 6.3%) was less compared with those in other patient populations. The effect compartment concentration resulting in 50% of maximum effect (128 ± 58 ng ml⁻¹) was larger than previously described.

CONCLUSIONS

This study suggests that standard dosing of cisatracurium in patients with severe sepsis results in a slower patient response with a reduced effect. Use of a larger dose may overcome this reduced delayed response.     

Ethyl pyruvate promotes spinal cord repair by ameliorating the glial microenvironment

BACKGROUND AND PURPOSE

Spinal cord injury (SCI) triggers a series of endogenous processes, including neuroinflammation and reactive astrogliosis, which may contribute to the failure of neural regeneration and functional recovery. In the present study, the effect of ethyl pyruvate on spinal cord repair was explored.

EXPERIMENTAL APPROACH

Functional assessment and histological analyses of astrogliosis, neuroinflammation, neuronal survival and axonal regeneration were performed to investigate the effects of ethyl pyruvate (0.086, 0.215, 0.431 or 0.646 mmol·kg⁻¹·day⁻¹) on spinal cord repair in a rat model of SCI. The effect of ethyl pyruvate (5, 10 or 15 mM) on astrocytic activation was also evaluated in an in vitro‘scratch-wound’ model.

KEY RESULTS

Functional assessment showed evident improvement of behavioural functions in the ethyl pyruvate-treated rats. Reactive astrogliosis was significantly inhibited in vivo, after injection of ethyl pyruvate (0.431 mmol·kg⁻¹day⁻¹), and in vitro‘scratch-wound’ model in the presence of 10 or 15 mM ethyl pyruvate. The difference between effective concentration in vitro and in vivo suggests that the inhibitory effect of ethyl pyruvate on astrogliosis in damaged spinal cord is indirect. In addition, ethyl pyruvate (0.431 mmol·kg⁻¹day⁻¹) attenuated SCI-induced neuroinflammation; it decreased the Iba-1-, ED-1- and CD11b-positive cells at the lesion site. Importantly, histological analyses showed a significantly greater number of surviving neurons and regenerative axons in the ethyl pyruvate-treated rats.

CONCLUSIONS AND IMPLICATIONS

Ethyl pyruvate was shown to inhibit astrogliosis and neuroinflammation, promote neuron survival and neural regeneration, and improve the functional recovery of spinal cord, indicating a potential neuroprotective effect of ethyl pyruvate against SCI.     

Effects of chronic sympatho-inhibition on reflex control of renal blood flow and plasma renin activity in renovascular hypertension

Background and purpose:

We determined if chronic sympatho-inhibition with rilmenidine has functional significance for the kidney by altering responses of renal blood flow (RBF) and plasma renin activity (PRA) to stress and acute hypotension in rabbits with renovascular hypertension.

Experimental approach:

RBF to each kidney and renal sympathetic nerve activity (RSNA) to the left kidney were measured in rabbits in which a renal artery clip induced hypertension (2K1C) and in sham-operated rabbits. After 2 weeks, a subcutaneous minipump was implanted to deliver rilmenidine (2.5 mg·kg⁻¹·day⁻¹) to 2K1C rabbits for 3 weeks.

Key results:

After 5 weeks of renal artery stenosis, mean arterial pressure (MAP) was 23% higher and PRA 3-fold greater than in sham-operated rabbits. Blood flow and renal vascular conductance in the stenosed kidney were lower (−75% and −80%) compared with sham, and higher in the non-clipped kidney (68% and 39%). Responses of RBF and PRA to hypotension were similar in 2K1C and sham rabbits. Airjet stress evoked a greater increase in MAP in 2K1C rabbits than sham controls. Chronic rilmenidine normalized MAP, reduced RSNA and PRA, and did not reduce RBF in the stenosed kidney. Responses of RBF (clipped and non-clipped kidney), RSNA and PRA to hypotension and airjet were little affected by rilmenidine.

Conclusions and implications:

Our observations suggest that chronic sympatho-inhibition is an effective antihypertensive therapy in renovascular hypertension. It normalizes MAP and reduces basal PRA without compromising blood flow in the stenosed kidney or altering responses of MAP, haemodynamics and PRA to acute hypotension and stress.     

Ketamine-induced ventricular structural, sympathetic and electrophysiological remodelling: pathological consequences and protective effects of metoprolol

BACKGROUND AND PURPOSE

Growing evidence suggests that long-term abuse of ketamine does harm the heart and increases the risk of sudden death. The present study was performed to explore the cardiotoxicity of ketamine and the protective effects of metoprolol.

EXPERIMENTAL APPROACH

Rats and rabbits were divided into control, ketamine, metoprolol alone and ketamine plus metoprolol groups. Ketamine (40 mg·kg⁻¹·day⁻¹, i.p.) and metoprolol (20 mg·kg⁻¹·day⁻¹, p.o.) were administered continuously for 12 weeks in rats and 8 weeks in rabbits. Cardiac function, electrophysiological disturbances, cardiac collagen, cardiomyocte apoptosis and the remodelling-related proteins were evaluated.

KEY RESULTS

Rabbits treated with ketamine showed decreased left ventricular ejection fraction, slowed ventricular conduction velocity and increased susceptibility to ventricular arrhythmia. Metoprolol prevented these pathophysiological alterations. In ketamine-treated rats, cardiac collagen volume fraction and apoptotic cell number were higher than those of control animals; these effects were prevented by co-administration of metoprolol. Consistently, the expressions of poly (ADP-ribose) polymerases-1, apoptosis-inducing factor and NF-κB-light-chain-enhancer of activated B cells were all increased after ketamine treatment and sharply reduced after metoprolol administration. Moreover, ketamine enhanced sympathetic sprouting, manifested as increased growth-associated protein 43 and tyrosine TH expression. These effects of ketamine were prevented by metoprolol.

CONCLUSIONS AND IMPLICATIONS

Chronic treatment with ketamine caused significant ventricular myocardial apoptosis, fibrosis and sympathetic sprouting, which altered the electrophysiological properties of the heart and increased its susceptibility to malignant arrhythmia that may lead to sudden cardiac death. Metoprolol prevented the cardiotoxicity of ketamine, indicating a promising new therapeutic strategy.     

Metformin attenuates pressure overload-induced cardiac hypertrophy via AMPK activation

Aim:

To identify the role of metformin in cardiac hypertrophy and investigate the possible mechanism underlying this effect.

Methods:

Wild type and AMPKα2 knockout (AMPKα2^−/−) littermates were subjected to left ventricular pressure overload caused by transverse aortic constriction. After administration of metformin (200 mg·kg⁻¹·d⁻¹) for 6 weeks, the degree of cardiac hypertrophy was evaluated using echocardiography and anatomic and histological methods. The antihypertrophic mechanism of metformin was analyzed using Western blotting.

Results:

Metformin significantly attenuated cardiac hypertrophy induced by pressure overload in wild type mice, but the antihypertrophic actions of metformin were ablated in AMPKα2^−/− mice. Furthermore, metformin suppressed the phosphorylation of Akt/protein kinase B (AKT) and mammalian target of rapamycin (mTOR) in response to pressure overload in wild type mice, but not in AMPKα2^−/− mice.

Conclusion:

Long-term administration of metformin may attenuate cardiac hypertrophy induced by pressure overload in nondiabetic mice, and this attenuation is highly dependent on AMPK activation. These findings may provide a potential therapy for patients at risk of developing pathological cardiac hypertrophy.     

Safety, tolerability and pharmacokinetics of an intravenous bolus of sildenafil in patients with pulmonary arterial hypertension

AIMS

To assess pharmacokinetics and pharmacodynamics of a 10 mg intravenous sildenafil bolus in pulmonary arterial hypertension (PAH) patients stabilized on 20 mg sildenafil orally three times daily.

METHODS

Pharmacokinetic parameters were calculated using noncompartmental analysis.

RESULTS

After an acute increase, plasma concentrations stabilized within the range reported previously for a 20 mg oral tablet. At 0.5 h, mean ± SD changes from baseline were −8.4 ± 11.7 mmHg (systolic pressure), −2.6 ± 7.3 mmHg (diastolic pressure) and −3.5 ± 10.4 beats min⁻¹ (heart rate). There was no symptomatic hypotension.

CONCLUSIONS

Although further research is warranted, a 10 mg sildenafil intravenous bolus appears to provide similar exposure, tolerability and safety to the 20 mg tablet.     

Enhanced salt sensitivity following shRNA silencing of neuronal TRPV1 in rat spinal cord

Aim:

To investigate the effects of selective knockdown of TRPV1 channels in the lower thoracic and upper lumbar segments of spinal cord, dorsal root ganglia (DRG) and mesenteric arteries on rat blood pressure responses to high salt intake.

Methods:

TRPV1 short-hairpin RNA (shRNA) was delivered using intrathecal injection (6 μg·kg⁻¹·d⁻¹, for 3 d). Levels of TRPV1 and tyrosine hydroxylase expression were determined by Western blot analysis. Systolic blood pressure and mean arterial pressure (MAP) were examined using tail-cuff and direct arterial measurement, respectively.

Results:

In rats injected with control shRNA, high-salt diet (HS) caused higher systolic blood pressure compared with normal-salt diet (NS) (HS:149±4 mmHg; NS:126±2 mmHg, P<0.05). Intrathecal injection of TRPV1 shRNA significantly increased the systolic blood pressure in both HS rats and NS rats (HS:169±3 mmHg; NS:139±2 mmHg). The increases was greater in HS rats than in NS rats (HS: 13.9%±1.8%; NS: 9.8±0.7, P<0.05). After TRPV1 shRNA treatment, TRPV1 expression in the dorsal horn and DRG of T8-L3 segments and in mesenteric arteries was knocked down to a greater extent in HS rats compared with NS rats. Blockade of α1-adrenoceptors abolished the TRPV1 shRNA-induced pressor effects. In rats injected with TRPV1 shRNA, level of tyrosine hydroxylase in mesenteric arteries was increased to a greater extent in HS rats compared with NS rats.

Conclusion:

Selective knockdown of TRPV1 expression in the lower thoracic and upper lumbar segments of spinal cord, DRG, and mesenteric arteries enhanced the prohypertensive effects of high salt intake, suggesting that TRPV1 channels in these sites protect against increased salt sensitivity, possibly via suppression of sympatho-excitatory responses.     

Absence of tolerance and toxicity to high-dose continuous intravenous furosemide in haemodynamically unstable infants after cardiac surgery

What is already known about this subject

• Continous i.v. infusion of furosemide is superior to intermittent administrations, especially in haemodynamically unstable infants, because it results in a more controlled diuresis (although doses are generally chosen rather low).

What this study adds

• High-dose continuous furosemide infusion is an effective treatment for volume overload in haemodynamically unstable infants.
• Development of tolerance to furosemide was not observed despite high doses and prolonged exposure.
• Maximum serum furosemide concentrations remained well below the presumed toxic concentration.

Aim

To evaluate a high-dose continuous furosemide regimen in infants after cardiac surgery.

Methods

Fifteen haemodynamically unstable infants with volume overload admitted to a paediatric intensive care unit were treated with an aggressive furosemide regimen consisting of a loading bolus (1–2 mg kg⁻¹) followed by a continuous infusion at 0.2 mg kg⁻¹ h⁻¹ which was adjusted according to a target urine output of 4 ml kg⁻¹ h⁻¹. Frequent sampling for furosemide concentrations in blood and urine was done for 3 days with simultaneous assessment of sodium excretion and urine output.

Results

The mean furosemide dose was 0.22 (± 0.06), 0.25 (± 0.10) and 0.22 (± 0.11) mg kg⁻¹ h⁻¹ on the first, second and third day, respectively. Median urine production was 3.0 (0.6–5.3), 4.2 (1.7–6.6) and 3.9 (2.0–8.5) ml kg⁻¹ h⁻¹, respectively, on the first, second and third day of the study. The target urine production was reached at a median time of 24 (6–60) h and this was maintained during the study period. The regimen did not result in toxic serum concentrations and was haemodynamically well tolerated.

Conclusion

High-dose continuous furosemide infusion for 72 h in haemodynamically unstable infants after cardiac surgery appears to be a safe and effective treatment for volume overload. Development of tolerance against the effects of furosemide and ototoxic furosemide concentrations were not observed.     

Sex-dependent control of murine emotional-affective behaviour in health and colitis by peptide YY and neuropeptide Y

BACKGROUND AND PURPOSE

Peptide YY (PYY) and neuropeptide Y (NPY) are involved in regulating gut and brain function. Because gastrointestinal inflammation is known to enhance anxiety, we explored whether experimental colitis interacts with genetic deletion (knockout) of PYY and NPY to alter emotional-affective behaviour.

EXPERIMENTAL APPROACH

Male and female wild-type, NPY (NPY^−/−), PYY (PYY^−/−) and NPY^−/−; PYY^−/− double knockout mice were studied in the absence and presence of mild colitis induced by ingestion of dextran sulphate sodium (2%) in drinking water. Anxiety-like behaviour was tested on the elevated plus maze and open field, and depression-like behaviour assessed by the forced swim test.

KEY RESULTS

In the absence of colitis, anxiety-like behaviour was increased by deletion of NPY but not PYY in a test- and sex-dependent manner, while depression-like behaviour was enhanced in NPY^−/− and PYY^−/− mice of either sex. The severity of DSS-induced colitis, assessed by colonic myeloperoxidase content, was attenuated in NPY^−/− but not PYY^−/− mice. Colitis modified anxiety- and depression-related behaviour in a sex-, genotype- and test-related manner, and knockout experiments indicated that NPY and PYY were involved in some of these behavioural effects of colitis.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate sex-dependent roles of NPY and PYY in regulation of anxiety- and depression-like behaviour in the absence and presence of colitis. Like NPY, the gut hormone PYY has the potential to attenuate depression-like behaviour but does not share the ability of NPY to reduce anxiety-like behaviour.     

Diclofenac readily penetrates the cerebrospinal fluid in children

AIMS

The primary aim was to study the cerebrospinal fluid (CSF) penetration of intravenous diclofenac in children. The secondary aim was to evaluate the plasma diclofenac concentration at the onset of wound pain after inguinal surgery in children.

METHODS

A total of 31 children (24 boys) aged 3 months to 12 years received a single intravenous injection of diclofenac 1 mg kg⁻¹. Paired CSF and blood samples were obtained 5 min to 22 h (median 69 min) later. In children having inguinal surgery a second blood sample was obtained at the time that the children felt wound pain for the first time after surgery. Diclofenac concentrations in CSF, plasma and protein free plasma were measured by gas chromatography with mass spectrometric detection.

RESULTS

In the 28 CSF samples obtained at 5 min to 3 h 43 min after injection, diclofenac concentrations ranged between 0.5 and 4.7 μg l⁻¹. At 5.5 h the CSF concentration was 0.1 μg l⁻¹, and no diclofenac was detected in the two CSF samples obtained at 22 h. The median of plasma diclofenac concentration at the time when pain returned after inguinal surgery was 104 μg l⁻¹ (range 70–272 μg l⁻¹). No serious or unexpected adverse effects were reported.

CONCLUSIONS

Diclofenac penetrates the CSF rapidly, and a sufficient concentration to inhibit cyclooxygenase enzymes is sustained for up to 4 h.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Diclofenac, a nonselective nonsteroidal anti-inflammatory drug,, exerts analgesic action both in the peripheral tissues and in the central nervous system by inhibiting cyclooxygenase enzymes COX-1/2, but central nervous system penetration of diclofenac has not been evaluated in humans.

WHAT THIS STUDY ADDS

• Diclofenac penetrates the cerebrospinal fluid rapidly, and after a single intravenous dose of 1 mg kg⁻¹, sufficient concentrations to inhibit COX-1/2 are sustained for up to 4 h.

     

Properties of submucosal venules in the rat distal colon

Background and Purpose

Venules within the gut wall may have intrinsic mechanisms for maintaining the circulation even upon the intestinal wall distension. We aimed to explore spontaneous and nerve-mediated contractile activity of colonic venules.

Experimental Approach

Changes in the diameter of submucosal venules of the rat distal colon were measured using video microscopy. The innervation of the microvasculature was investigated using fluorescence immunohistochemistry.

Key Results

Submucosal venules exhibited spontaneous constrictions that were abolished by blockers of L-type Ca²⁺ channels (1 μM nicardipine), Ca²⁺-ATPase (10 μM cyclopiazonic acid), IP₃ receptor (100 μM 2-APB), Ca²⁺-activated Cl⁻ channels (100 μM DIDS) or store-operated Ca²⁺ entry channels (10 μM {"type":"entrez-protein","attrs":{"text":"SKF96365","term_id":"1156357400","term_text":"SKF96365"}}SKF96365). Transmural nerve stimulation (TNS at 10 Hz) induced a phasic venular constriction that was blocked by phentolamine (1 μM, α-adrenoceptor antagonist) or sympathetic nerve depletion using guanethidine (10 μM). Stimulation of primary afferent nerves with TNS (at 20 Hz) or capsaicin (100 nM) evoked a sustained venular dilatation that was attenuated by calcitonin gene-related peptide (CGRP) 8-37 (2 μM), a CGRP receptor antagonist. Immunohistochemistry revealed sympathetic and primary afferent nerves running along submucosal venules.

Conclusions and Implications

Submucosal venules of the rat distal colon exhibit spontaneous constrictions that appear to primarily rely on Ca²⁺ release from sarcoplasmic reticulum and subsequent opening of Ca²⁺-activated Cl^– channels that trigger Ca²⁺ influx through L-type Ca²⁺ channels. Venular contractility is modulated by sympathetic as well as CGRP-containing primary afferent nerves, suggesting that submucosal venules may play an active role in regulating the microcirculation of the digestive tract.     

Neuroprotective effect of the glucagon-like peptide-1 receptor agonist, synthetic exendin-4, in streptozotocin-induced diabetic rats

BACKGROUND AND PURPOSE

Glucagon-like peptide-1 (GLP-1) receptors are widely expressed in neural tissues and diminish neuronal degeneration or induce neuronal differentiation. The aim of this study was to investigate the effect of the GLP-1 pathway on peripheral nerves in streptozotocin-induced diabetic rats.

EXPERIMENTAL APPROACH

Diabetic and nondiabetic rats were treated with the GLP-1 receptor agonist, synthetic exendin-4 (i.p., 1 nmol·kg⁻¹·day⁻¹) or placebo for 24 weeks, and current perception threshold values, cAMP levels and nerve fibre size in the sciatic nerve were measured. We also investigated GLP-1 receptor expression, quantitative changes in PGP9.5-positive intraepidermal nerve fibres and cleaved caspase 3–stained Schwann cells by immunohistochemistry.

KEY RESULTS

GLP-1 receptor expression was detected in the sciatic nerve and skin. After exendin-4 treatment, the increase seen in current perception threshold values at 2000 and 250 Hz in diabetic rats was reduced. Also, the decrease in myelinated fibre size or axon/fibre area ratio in the sciatic nerve and the loss of intraepidermal nerve fibre in the skin of diabetic rats were ameliorated. These responses were closely associated with the attenuation of Schwann cell apoptosis and improvement in the cAMP level in exendin-4-treated diabetic rats, compared with placebo-treated animals.

CONCLUSION AND IMPLICATIONS

Synthetic exendin-4 may prevent peripheral nerve degeneration induced by diabetes in an animal model, supporting the hypothesis that GLP-1 may be useful in peripheral neuropathy. The neuroprotection is probably attributable to GLP-1 receptor activation, antiapoptotic effects and restoration of cAMP content.     

Formulation of long-acting nifedipine tablets influences the heart rate and sympathetic nervous system response in hypertensive patients

AIMS

The haemodynamic responses to nifedipine vary between short- and long-acting formulations. However, the latter have not been compared despite marked differences in their constitution. Our 1-month randomized, crossover study was designed to compare the 30-mg osmotic, constant-release nifedipine gastrointestinal therapeutic system (N-GITS) with an encapsulated mini-tablet Coracten XL.

METHODS

Forty-four hypertensive patients aged 63 ± 7 years were studied. The formulation was changed on day 15 and (for a single dose) day 30. At days 0, 14, 15, 29 and 30, patients were monitored for 6 h after dosing, during which blood pressure (BP), heart rate (HR) and plasma levels of norepinephrine (NE) and nifedipine were measured. The primary outcome was the difference in plasma NE between formulations at the time of peak nifedipine level.

RESULTS

Systolic BP decreased rapidly after the first dose of Coracten, achieving nadir at 5 h. HR rose by 1.2 ± 8.8 beats min⁻¹. After N-GITS HR fell by 2.4 ± 7.7 beats min⁻¹ (P = 0.159). Plasma NE was higher in the Coracten- (480 ± 38.3 pg ml⁻¹) than N-GITS-treated patients (343 ± 75.0 pg ml⁻¹) at the time of peak nifedipine concentrations (4 and 5 h, respectively) and their change from baseline was significantly (P = 0.0046) different. A similar difference between the drugs was seen again at days 15 and 30, at 5 h after switching formulations.

CONCLUSIONS

This study suggests that two different formulations of once-daily nifedipine result in different BP and plasma NE responses, and that switching between formulations causes opposite effects upon the sympathetic nervous response to falling BP.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Pharmacokinetic and pharmacodynamics studies are usually carried out separately with theoretical linking or interpretations.
• The pharmacokinetics of short- vs. long-acting formulations of nifedipine is well known, but the pharmacokinetics of different once-a-day formulations of nifedipine is generally not well known by the practising physician.

WHAT THIS STUDY ADDS

• This study provides practical patient-based information linking pharmacokinetics to pharmacodynamics in one of the target populations of patients, those with hypertension, who might receive the two different drugs.

     

Lopinavir/ritonavir population pharmacokinetics in neonates and infants

AIMS

Because of immature hepatic metabolism, lopinavir could present specific pharmacokinetics in the first weeks of life. We aimed at determining the optimal dosing regimen in neonates and infants weighing 1 to 10.5 kg.

METHODS

Lopinavir/ritonavir (LPV/r) pharmacokinetics were studied in 96 infants using a population approach.

RESULTS

A one-compartment model described LPV/r pharmacokinetics. Normalized to a 70 kg adult using allometry, clearance (CL/F) and distribution volume (V/F) estimates were 5.87 l h⁻¹ 70 kg⁻¹ and 91.7 l 70 kg⁻¹. The relative bioavailabilty, F, increased with post-menstrual age (PMA) and reached 50% of the adult value at 39.7 weeks.

CONCLUSIONS

Size and PMA explained some CL/F and V/F variability in neonates/infants. Based upon trough concentration limitations, suggested LPV/r dosing regimens were 40 mg 12 h⁻¹, 80 mg 12 h⁻¹ and 120 mg 12 h⁻¹ in the 1–2 kg, 2–6 kg and 6–10 kg group, respectively.     

Spontaneous release of acetylcholine from autonomic nerves in the bladder

Background and purpose:

Bladder contractility is regulated by intrinsic myogenic mechanisms interacting with autonomic nerves. In this study, we have investigated the physiological role of spontaneous release of acetylcholine in guinea pig and rat bladders.

Experimental approach:

Conventional isotonic or pressure transducers were used to record contractile activity of guinea pig and rat bladders.

Key results:

Hyoscine (3 µmol·L⁻¹), but not tetrodotoxin (TTX, 1 µmol·L⁻¹), reduced basal tension, distension-evoked contractile activity and physostigmine (1 µmol·L⁻¹)-evoked contractions of the whole guinea pig bladder and muscle strips in vitro. ω-Conotoxin GVIA (0.3 µmol·L⁻¹) did not affect physostigmine-induced contractions when given either alone or in combination with ω-agatoxin IVA (0.1 µmol·L⁻¹) and SNX 482 (0.3 µmol·L⁻¹). After 5 days in organotypic culture, when extrinsic nerves had significantly degenerated, the ability of physostigmine to induce contractions was reduced in the dorso-medial strips, but not in lateral strips (which have around 15 times more intramural neurones). Most muscle strips from adult rats lacked intramural neurones. After 5 days in culture, physostigmine-induced or electrical field stimulation-induced contractions of the rat bladder strips were greatly reduced. In anaesthetized rats, topical application of physostigmine (5–500 nmol) on the bladder produced a TTX-resistant tonic contraction that was abolished by atropine (4.4 µmol·kg⁻¹ i.v.).

Conclusions and implications:

The data indicate that there is spontaneous TTX-resistant release of acetylcholine from autonomic cholinergic extrinsic and intrinsic nerves, which significantly affects bladder contractility. This release is resistant to blockade of N, P/Q and R type Ca²⁺ channels.British Journal of Pharmacology (2009) 157, 607–619; doi:10.1111/j.1476-5381.2009.00166.x; published online 3 April 2009     

Pyrazinamide blood concentrations in children suffering from tuberculosis: a comparative study at two doses

Aims

To evaluate the pharmacokinetics and pharmacodynamic indices of pyrazinamide at doses of 15 and 25 mg kg⁻¹ in children suffering from tuberculosis.

Methods

Twenty children with tuberculosis received pyrazinamide at a single dose of 25 mg kg⁻¹ (group I) and 15 mg kg⁻¹ (group II). Serial blood samples were collected and the drug concentrations were analyzed spectrophotometrically. The pharmacokinetic parameters were calculated and the duration of time for which pyrazinamide concentrations in serum remained above the pyrazinamide inhibitory concentrations of 20 μg ml⁻¹ and 25 μg ml⁻¹ was studied.

Results

The mean peak serum concentration was 42.4 ± 3.3 μg ml⁻¹ (95% CI ± 6.5) and 38.6 ± 3.9 μg ml⁻¹ (95% CI ± 7.7) in groups I and II, respectively. The elimination half-life was 9.3 ± 1.3 h and 10.5 ± 2.3 h (P = 0.6) and clearance was 0.06 ± 0.01 l h⁻¹ kg⁻¹ and 0.04 ± 0.01 l h⁻¹ kg⁻¹ (P = 0.08) in groups I and II, respectively. Pharmacokinetic parameters and PKPD indices were comparable with both the doses.

Conclusions

The study indicates that comparable serum concentrations of pyrazinamide are attained with 25 mg kg⁻¹ and 15 mg kg⁻¹ doses in children. The elimination half-life was longer and volume of distribution greater in children than in the adult population.

What is already known about this subject

• Pyrazinamide is recommended in doses varying from 15 to 40 mg kg⁻¹. The most commonly used average daily dose is 25 mg kg⁻¹. Its use is associated with dose dependent hepatotoxicity.
• Lower doses are not used because of lack of pharmacokinetic data especially in children. There is only one detailed study of pyrazinamide in children at a dose of 35 mg kg⁻¹.

What this study adds

• This is the first study evaluating serum concentrations of pyrazinamide in children at a dose of 15 mg kg⁻¹ which is on the lower side of the recommended dose. The study also compared the serum concentrations and pharmacokinetics achieved with this dose with the widely used dose of 25 mg kg⁻¹ in children suffering from tuberculosis.
• The pharmacokinetics and pharmacodynamic indices of pyrazinamide were comparable with the 25 and 15 mg kg⁻¹ doses.