Samuel H.H. Chan

NADPH Oxidase–Derived Superoxide Anion Mediates Angiotensin II–Induced Pressor Effect via Activation of p38 Mitogen–Activated Protein Kinase in the Rostral Ventrolateral Medulla

The rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons are located, is a central site via which angiotensin II (Ang II) elicits its pressor effect. We tested the hypothesis that NADPH oxidase-derived superoxide anion (O2·−) in the RVLM mediates Ang II–induced pressor response via activation of mitogen-activated protein kinase (MAPK) signaling pathways. Bilateral microinjection of Ang II into the RVLM resulted in an angiotensin subtype 1 (AT1) receptor-dependent phosphorylation of p38 MAPK and extracellular signal-regulated protein kinase (ERK)1/2, but not stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK), in the ventrolateral medulla. The Ang II–induced p38 MAPK or ERK1/2 phosphorylation was attenuated by application into the RVLM of a NADPH oxidase inhibitor, diphenyleneiodonium chloride (DPI), an antisense oligonucleotide that targets against p22phox or p47phox subunit of NADPH oxidase mRNA, or the superoxide dismutase mimetic tempol. DPI or antisense p22phox or p47phox oligonucleotide treatment also attenuated the AT1 receptor-dependent increase in O2·− production in the ventrolateral medulla elicited by Ang II at the RVLM. Functionally, Ang II–elicited pressor response in the RVLM was attenuated by DPI, tempol, or a p38 MAPK inhibitor, SB203580. The AT1 receptor-mediated enhancement of the frequency of glutamate-sensitive spontaneous excitatory postsynaptic currents induced by Ang II in RVLM neurons was also abolished by SB203580. These results suggest that NADPH oxidase-derived O2·− underlies the activation of p38 MAPK or ERK1/2 by Ang II in the ventrolateral medulla. Furthermore, the p38 MAPK signaling pathway may mediate Ang II–induced pressor response via enhancement of presynaptic release of glutamate to RVLM neurons.

Spectral analysis of systemic arterial pressure and heart rate signals as a prognostic tool for the prediction of patient outcome in the intensive care unit

OBJECTIVES To evaluate the applicability of changes in spectra of systemic arterial pressure and heart rate signals in the prediction of patient outcome in an adult intensive care unit (ICU). To compare the prognostic predictability of this method with the Acute Physiology and Chronic Health Evaluation II (APACHE II) scoring system. DESIGN Prospective data collection from 52 ICU patients. SETTING Adult ICU at a large, university-affiliated, medical center. PATIENTS Consecutive patients who were admitted to the adult ICU due to noncardiac emergencies, and who remained for at least 2 days. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS The demographic data, diagnosis, and survival data were recorded for each patient enrolled in this study. For the period between admission and 24 hrs before discharge, the APACHE II score was tabulated daily. Likewise, continuous, on-line, and real-time spectral analysis of systemic arterial pressure and heart rate signals was carried out every day for at least 30 mins at 2200 to 2400 hrs. The averaged power density values during this 30-min recording period of the high-frequency (0.15 to 0.4 Hz), low-frequency (0.08 to 0.15 Hz), and very low-frequency (0.016 to 0.08 Hz) components of systemic arterial pressure and heart rate signals were subsequently computed. Systemic vascular resistance index and cardiac index were also determined daily. We observed a trend of changes in the spectral components of systemic arterial pressure and heart rate signals in patients who eventually survived (n = 25) or died (n = 27). Progressive increases in the power density values of both the low-frequency and very low-frequency components of systemic arterial pressure and heart rate signals appeared to be related to recovery. Conversely, progressive decreases in the power density values of these spectral components was indicative of deterioration and fatality. The predicted outcome based on the trend of changes in the low-frequency and very low-frequency components of systemic arterial pressure and heart rate signals correlated positively with daily APACHE II scores. No direct correlation, however, was indicated by mean systemic arterial pressure, heart rate, systemic vascular resistance index, and cardiac index. We also confirmed that the differential trend of spectral changes in patients who survived or died was not due to circadian rhythm, nor alterations in the responsiveness of the blood vessels to intravenous infusion of dopamine. CONCLUSION Power spectral analysis of systemic arterial pressure and heart rate signals offers a reasonable means of monitoring acute, critically ill patients, and may be used as an alternative prognostic tool for the prediction of patient outcome in the ICU.

Differential cardiovascular responses to blockade of nNOS or iNOS in rostral ventrolateral medulla of the rat

We investigated the contribution of neuronal or inducible nitric oxide synthase (nNOS or iNOS) at the rostral ventrolateral medulla (RVLM) to central cardiovascular regulation by endogenous nitric oxide (NO), using Sprague‐Dawley rats anaesthetized and maintained with propofol. Microinjection bilaterally into the RVLM of a NO trapping agent, carboxy‐2‐phenyl‐4,4,5,5‐tetramethylimidazoline‐l‐oxy‐l‐3‐oxide (10, 50 or 100 nmoles) resulted in significant hypotension and bradycardia. Similar application of a selective antagonist of nNOS, 7‐nitroindazole (1, 2.5 or 5 pmoles), or selective antagonists of iNOS, aminoguanidine (125, 250 or 500 pmoles), N6‐(l‐iminoethyl)‐L‐lysine (250 pmoles) or S‐methylisothiourea (250 pmoles), induced respectively a reduction or an enhancement in systemic arterial pressure, heart rate and power density of the vasomotor components in the spectrum of arterial blood pressure signals, the experimental index for sympathetic neurogenic vasomotor tone. Both hypotension and bradycardia induced by the NO precursor, L‐arginine (100 nmoles), were significantly blunted when aminoguanidine (250 pmoles) was co‐microinjected bilaterally into the RVLM. On the other hand, co‐administered 7‐nitroindazole (2.5 pmoles) was ineffective. Whereas low doses of S‐nitro‐N‐acetylpenicillamine (0.25 or 0.5 nmoles) elicited hypertension and tachycardia, high doses of this non‐nitrate NO donor (5 nmoles) induced hypotension and bradycardia. Reverse transcription – polymerase chain reaction analysis revealed that both iNOS and nNOS mRNA were expressed in the ventrolateral medulla. We conclude that the prevalence of nNOS over iNOS activity at the RVLM and the associated dominance of sympathoexcitation over sympathoinhibition may underlie the maintenance of sympathetic vasomotor outflow and stable systemic arterial pressure by the endogenous NO.

PARTICIPATION OF PARAVENTRICULAR NUCLEUS OF HYPOTHALAMUS IN CENTRAL REGULATION OF PENILE ERECTION IN THE RAT

PURPOSE To investigate the possible participation of the paraventricular nucleus of hypothalamus in central regulation of penile erection. MATERIALS AND METHODS Male adult Sprague-Dawley rats were anesthetized and maintained with pentobarbital sodium. The intracavernous pressure (ICP) was used as an experimental index for penile erection, and was recorded alongside systemic arterial pressure and heart rate. The effect on ICP of electrical (30-s train of 30-120 microA, 40-160 Hz, 1-ms rectangular pulses) or chemical (L-glutamate, 0.5 nmol/50 nl.) activation of the paraventricular nucleus of hypothalamus (PVN) or hippocampal formation was evaluated. RESULTS Electrical activation of the PVN elicited both multiple and single episodes of elevation in ICP, along with visible erection and ejaculation. The former pattern exhibited an increase in ICP that was more sustained, with higher peak amplitude and longer latency. Chemical stimulation of neuronal perikarya in the PVN also resulted in similar patterns of rise in ICP and visible erection. These effects were, nonetheless, not accompanied by significant alterations in systemic arterial pressure and heart rate. Activation of the hippocampal formation, as we reported previously, similarly elicited multiple and single episodes of increase in ICP. These erectile responses, however, were substantially reduced or eliminated upon electrolytic lesion of the ipsilateral PVN. CONCLUSION These observations suggest that the PVN may be an important nucleus that participates in central neural regulation of penile erection in the rat. Furthermore, an efferent pathway(s) from the hippocampal formation to PVN may constitute part of the neural circuitry in the forebrain in the regulation of erectile functions.

Effects of Long-Term Antiepileptic Drug Monotherapy on Vascular Risk Factors and Atherosclerosis.

Purpose:  Long‐term therapy with antiepileptic drugs (AEDs) has been associated with metabolic consequences that lead to an increase in risk of atherosclerosis in patients with epilepsy. We compared the long‐term effects of monotherapy using different categories of AEDs on markers of vascular risk and the atherosclerotic process.

Oxidative Impairment of Mitochondrial Electron Transport Chain Complexes in Rostral Ventrolateral Medulla Contributes to Neurogenic Hypertension

The role for mitochondrial electron transport chain (ETC) in neurogenic hypertension is unidentified. We evaluated the hypothesis that feedforward depression of mitochondrial ETC functions by superoxide anion (O2·−) and hydrogen peroxide (H2O2) in rostral ventrolateral medulla (RVLM), a brain stem site that maintains sympathetic vasomotor tone and contributes to oxidative stress and neural mechanism of hypertension. Compared with normotensive Wistar-Kyoto rats, spontaneously hypertensive rats exhibited mitochondrial ETC dysfunctions in RVLM in the forms of depressed complex I or III activity and reduced electron coupling capacity between complexes I and III or II and III. Microinjection of coenzyme Q10 into RVLM of spontaneously hypertensive rats reversed the depressed ETC activity and augmented O2·− production and hypertensive phenotypes. This mobile electron carrier also antagonized the elevated H2O2 in RVLM and vasopressor responses to complex I (rotenone) or III (antimycin A) inhibitor in Wistar-Kyoto or prehypertensive rats. Intracerebroventricular infusion of angiotensin II promoted mitochondrial ETC dysfunctions in Wistar-Kyoto rats, and coenzyme Q10 or gene knockdown of the p22phox subunit of NADPH oxidase antagonized the resultant elevation of H2O2 in RVLM. Overexpression of superoxide dismutase or catalase in RVLM of spontaneously hypertensive rats by gene transfer reversed mitochondrial dysfunctions and blunted the augmented O2·− and H2O2 in RVLM. We conclude that O2·−- and H2O2-dependent feedforward impairment of mitochondrial ETC complexes because of predisposed downregulation of superoxide dismutase or catalase and a cross-talk between NADPH oxidase-derived O2·− and ETC enzymes contribute to chronic oxidative stress in the RVLM of spontaneously hypertensive rats, leading to augmented sympathetic vasomotor tone and hypertension.

Facilitation of lumbar monosynaptic reflexes by locus coeruleus in the rat.

The present study was initiated to delineate whether species difference exists between cats and rats in the descending influence of locus coeruleus (LC) on spinal motoneuronal activity. In male Sprague-Dawley rats anesthetized with chloral hydrate (400 mg/kg, i.p.), localized activation of LC promoted an exclusive facilitation of lumbar spinal extensor and flexor monosynaptic reflexes (MSRs). Such LC-evoked potentiations may vary in degree (37.5-147.4%), duration (70.6-72.9 ms) and latency (3.0-5.5 ms) among different animals. While minimally affecting the control MSRs, the alpha 1-adrenoceptor blocker prazosin (20 micrograms/kg, i.v.) significantly antagonized the enhancing effect of the LC on MSRs, suggesting the participation of noradrenergic neurotransmission in the process. Since these results are in general agreement with previous observations from our laboratory on the cat, we conclude that the LC exerts similar facilitatory actions on both extensor and flexor motoneuron activity of the hindlimb in at least two animal species, rat and cat.

Concentration and regional distribution of propofol in brain and spinal cord during propofol anesthesia in the rat

We evaluated the pharmacokinetics and regional distribution of propofol in the brain and spinal cord during propofol anesthesia in Sprague-Dawley rats, using high-performance liquid chromatographic determination of propofol concentration in brain, whole blood and plasma. We found that the concentration of propofol in the brain increased and decreased expeditiously during and after a 15-min and 30-min period of i.v. infusion of an anesthetic dose (60 mg/kg per h) of propofol. Furthermore, propofol was evenly distributed in the brain and spinal cord during infusion, with a significant inter-individual variation. Upon the establishment of anesthesia 15 and 30 min following intravenous infusion of propofol, the concentration of propofol in the brain, whole blood and plasma was respectively 15.7 +/- 1.9 and 39.4 +/- 2.7 micrograms/g, 4.5 +/- 1.2 and 13.6 +/- 1.3 micrograms/ml and 1.8 +/- 0.5 and 5.1 +/- 0.9 micrograms/ml (mean +/- SEM, n = 6 or 7). These high brain/blood and brain/plasma ratios during anesthesia suggest that propofol manifests a pharmacokinetic profile that is different from at least thiopental.

Mitochondrial dysfunction and ultrastructural damage in the hippocampus during kainic acid-induced status epilepticus in the rat.

Summary:  Purpose: Prolonged and continuous epileptic seizure (status epilepticus) results in cellular changes that lead to neuronal damage. We investigated whether these cellular changes entail mitochondrial dysfunction and ultrastructural damage in the hippocampus, by using a kainic acid (KA)‐induced experimental status epilepticus model.

Potentiation of Baroreceptor Reflex Response by Heat Shock Protein 70 in Nucleus Tractus Solitarii Confers Cardiovascular Protection During Heatstroke

BackgroundWhereas hypotension and bradycardia seen during the onset of heatstroke may be protected by prior induction of heat shock protein 70 (HSP70) in the brain, the underlying mechanism is not fully understood. We evaluated the hypothesis that HSP70 may confer cardiovascular protection during heatstroke by potentiating the baroreceptor reflex (BRR) control of peripheral hemodynamic performance. Methods and ResultsAdult male Sprague-Dawley rats subjected to a brief hyperthermic heat shock (HS; 42°C for 15 minutes) induced discernible expression of HSP70 in the bilateral nucleus tractus solitarii (NTS), the terminal site in the brain stem for primary baroreceptor afferents. This HSP70 expression was detected at 8 hours, peaked at 24 hours, and returned to baseline by 48 hours after HS. Brief hyperthermia also significantly potentiated the BRR response in a temporal profile that correlated positively with changes in HSP70 expression at the NTS. Prior HS also appreciably alleviated hyperthermia, severe hypotension, and bradycardia manifested during the onset of heatstroke (45°C for 60 minutes) elicited 24 hours later. Microinjection bilaterally of anti-HSP70 antiserum (1:20) into the NTS or denervation of the sinoaortic baroreceptor afferents significantly reversed the enhancement of BRR response and cardiovascular protection during heatstroke induced by prior HS. ConclusionsThese results suggest that HS-induced expression of HSP70 in the NTS may alleviate severe hypotension and bradycardia exhibited during the onset of heatstroke by potentiating both the sensitivity and capacity of BRR response.