António Albino-Teixeira

Assessment of renal dopaminergic system activity in the nitric oxide‐deprived hypertensive rat model

1 The present paper reports changes in the urinary excretion of dopamine, 5‐hydroxytryptamine and amine metabolites in nitric oxide deprived hypertensive rats during long‐term administration of NGnitro‐L‐arginine methyl ester (l‐NAME). Aromatic L‐amino acid decarboxylase (AAAD) activity in renal tissues and the ability of newly‐formed dopamine to leave the cellular compartment where the synthesis of the amine has occurred were also determined.

Role of superoxide and hydrogen peroxide in hypertension induced by an antagonist of adenosine receptors.

Treatment of Wistar rats for 7 days with 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), an antagonist of adenosine receptors, induces long-lasting hypertension associated with marked changes in vascular structure and reactivity and renin-angiotensin system activation. This study aimed at evaluating the role of oxidative stress in the development of DPSPX-induced hypertension and also at identifying the relative contribution of superoxide radical (O2.-) vs hydrogen peroxide (H2O2). Vascular and systemic prooxidant/antioxidant status was evaluated in sham (saline, i.p., 7 days) and DPSPX (90 microg/kg/h, i.p., 7 days)-treated rats. Systolic blood pressure was determined by invasive and non-invasive methods. The activity of vascular NADPH oxidase, superoxide dismutase (SOD), catalase and glutathione peroxidase was assayed by fluorometric/spectrophotometric methods. H2O2 levels were measured using an Amplex Red Hydrogen Peroxide kit. Plasma thiobarbituric acid reactive substances and plasma antioxidant capacity were also measured. In addition we tested the effects of antioxidants or inhibitors of reactive oxygen species generation on blood pressure, vascular hyperplasia and oxidative stress parameters. DPSPX-hypertensive rats showed increased activity of vascular NADPH oxidase, SOD, catalase and glutathione peroxidase, as well as increased H2O2 generation. DPSPX-hypertensive rats also had increased plasma lipid peroxidation and decreased plasma antioxidant capacity. Treatment with apocynin (1.5 mmol/l, per os, 14 days), or with polyethylene glycol (PEG)-catalase (10,000 U/kg/day, i.p., 8 days), prevented the DPSPX-induced effects on blood pressure, vascular structure and H2O2 levels. Tempol (3 mmol/l, per os, 14 days) failed to inhibit these changes, unless PEG-catalase was co-administered. It is concluded that O2.- generation with subsequent formation of H2O2 plays a major role in the development of DPSPX-induced hypertension.

The Caudal Medullary Ventrolateral Reticular Formation in Nociceptive‐Cardiovascular Integration. An Experimental Study in the Rat

The endogenous pain control system is composed of multiple functionally distinct brain regions, which are thought to integrate nociceptive information with various brain functions. The clear involvement of some pain control centres in cardiovascular modulation has been claimed as a strong indication of their role in nociceptive‐cardiovascular integration. Particular emphasis has been given to their putative function in triggering cardiovascular reactions to pain. However, the possibility of their participation in the less‐studied influence of cardiovascular conditions in pain perception has been largely ignored. We have recently addressed this issue by investigating the involvement of the caudal ventrolateral medullary reticular formation (cVLM) in hypertension‐induced hypoalgesia. Circuits capable of conveying cVLM‐elicited antinociception include a direct reciprocal cVLM‐spinal loop, and two disynaptic spinal pathways relaying in rostroventromedial medullary (RVM) neurones and A5 noradrenergic neurones. In the three pathways, the cVLM neurones involved are circumscribed to a small area of reticular formation located laterally to the lateral reticular nucleus, the VLMlat. The VLMlat has a vasodepressor effect similar to that obtained from the cVLM. In the spinal cord dorsal horn, c‐fos expression evoked by noxious stimuli is decreased in hypertensive animals, as compared to normotensive animals. In hypertensive animals following lesion of the VLMlat, spinal c‐fos expression is identical to that observed in normotensive animals. The collected data point to a role for the VLMlat in the depression of spinal nociceptive processing in response to rises in blood pressure. Since hypertension‐induced hypoalgesia is mediated by spinal α2‐adrenoreceptors, this effect could be conveyed by the cVLM‐A5‐spinal pathway.

Who volunteers for phase I clinical trials? Influences of anxiety, social anxiety and depressive symptoms on self-selection and the reporting of adverse events

ObjectiveTo investigate the influence of anxiety, social anxiety and depressive symptoms on the willingness of healthy subjects to volunteer for phase I studies and to report adverse events.Materials and methodsA group of healthy subjects who had never participated in a clinical trial (“Naïve Subjects”) were invited to participate in a phase I study. All subjects were assessed for trait anxiety (State-Trait Anxiety Inventory, STAI-T), social anxiety (Social Avoidance and Distress, SAD, and Fear of Negative Evaluation, FNE) and depressive symptomatology (Beck Depression Inventory, BDI-II). Subjects who accepted the invitation to participate were compared with those who refused. The personality traits of a group of “Actual Participants” were examined, and the relation of these traits to adverse events reported during participation was evaluated.ResultsA significant inverse correlation was found between the STAI-T (R = −0.203, p < 0.05) and SAD (R = −0.204, p < 0.05) scores and the willingness to participate. Naïve Subjects who refused the invitation to participate showed higher scores on STAI-T (Z = −2.600, p < 0.01) and SAD (Z =−2.524, p < 0.05) inventories. Logistic regression using BDI-II, STAI-T, SAD and FNE as covariates also showed that the only unique predictors of participation were the STAI-T (p < 0.05) and SAD (p < 0.01) scores. Significant positive correlations were found between trait anxiety and reporting of adverse events.ConclusionParticipants in phase I studies are a self-selected sample defined by low trait-anxiety and social avoidance behaviors. This self-selection bias may affect the study results because less anxious subjects tend to report fewer adverse events. The characterization of a participant’s personality traits may be important in phase I studies.

Long-term administration of 1,3-dipropyl-8-sulfophenylxanthine causes arterial hypertension.

Adenosine has been shown recently to be the main factor responsible for the trophic effects of sympathetic innervation. As sympathetic denervation causes hypertrophic and hyperplastic changes reminiscent of those occurring in blood vessels of spontaneously hypertensive rats, we decided to study the effect of a continuous blockade of adenosine receptors on both blood vessel structure and blood pressure. A continuous infusion of 1,3-dipropyl-8-sulfophenylxanthine (DPSPX; 30 micrograms/kg per h for 7 days) to Wistar rats caused hyperplastic changes in peritoneal fibroblasts and mesenteric arterioles, hypertrophic changes in the smooth muscle of the tail artery and significant increase in the size of left ventricle myocardial cell nuclei. Both diastolic and systolic blood pressure increased significantly above control values. The results confirmed the trophic effects of adenosine and showed that chronic blockade of adenosine receptors causes arterial hypertension.

MICROINJECTION OF ANGIOTENSIN II IN THE CAUDAL VENTROLATERAL MEDULLA INDUCES HYPERALGESIA

Nociceptive transmission from the spinal cord is controlled by supraspinal pain modulating systems that include the caudal ventrolateral medulla (CVLM). The neuropeptide angiotensin II (Ang II) has multiple effects in the CNS and at the medulla oblongata. Here we evaluated the expression of angiotensin type 1 (AT(1)) receptors in spinally-projecting CVLM neurons, and tested the effect of direct application of exogenous Ang II in the CVLM on nociceptive behaviors. Although AT(1)-immunoreactive neurons occurred in the CVLM, only 3% of AT(1)-positive neurons were found to project to the dorsal horn, using double-immunodetection of the retrograde tracer cholera toxin subunit B. In behavioral studies, administration of Ang II (100 pmol) in the CVLM gave rise to hyperalgesia in both the tail-flick and formalin tests. This hyperalgesia was significantly attenuated by local administration of the AT(1) antagonist losartan. The present study demonstrates that Ang II can act on AT(1) receptors in the CVLM to modulate nociception. The effect on spinal nociceptive processing is likely indirect, since few AT(1)-expressing CVLM neurons were found to project to the spinal cord. The renin-angiotensin system may also play a role in other supraspinal areas implicated in pain modulation.

Lesions of the caudal ventrolateral medulla block the hypertension-induced inhibition of noxious-evoked c-fos expression in the rat spinal cord

The effect of lesioning the lateral portion of the caudal ventrolateral medullary reticular formation (VLMIat) on the noxious‐evoked expression of the c‐fos proto‐oncogene in spinal neurons, was studied in short‐term hypertensive rats. Occlusion of the renal artery for 96 h in unlesioned animals induced a 52% increase in blood pressure (BP) and a 66% decrease in the number of Fos‐immunoreactive (Fos‐IR) spinal cells following noxious cutaneous stimulation, as compared to values in normotensive controls. Lesioning the VLMIat in hypertensive rats by unilateral quinolinic acid (QA) injection (0.3 μl of a 180 nmol/μl solution) 24 h before noxious stimulation, prevented the Fos‐IR cell decrease. In normotensive rats, lesioning the VLMIat produced no changes in c‐fos expression. To investigate the role played by the VLMIat in cardiovascular control, BP and heart rate (HR) were measured during local injections of QA or glutamate (0.5 μl of a 100 nmol/μl solution) to normotensive animals. Injections of QA produced an immediate rise in BP and HR which reached maximal values (18 and 14% increase, respectively) 5 min after the administration onset, then returning gradually to baseline levels. Glutamate injections resulted in an immediate decrease of the same values, which reached 29 and 39%, respectively, 4 min after the beginning of injection, after which they decreased to baseline levels.

Purine agonists prevent trophic changes caused by sympathetic denervation

Surgical denervation of the lateral saphenous vein of the dog causes marked extraneuronal changes, both of a morphological and functional type. In an attempt to investigate the factor(s) responsible for the trophic effects exerted by the sympathetic innervation on the dog saphenous vein we studied the effects of noradrenaline, adenosine, inosine and N-ethylcarboxamidoadenosine (NECA) on vascular tissue after sympathetic denervation. The saphenous vein was denervated using either surgical or chemical (6-hydroxydopamine, 6-OHDA) methods. Noradrenaline (0.1 microgram/kg per h), adenosine (10 micrograms/kg per h), inosine (10 micrograms/kg per h) or NECA (0.1 microgram/kg per h) were delivered continuously for 5 days through Alzet minipumps connected to the vein. 6-OHDA-induced denervation resulted in morphological changes similar to those described for surgical denervation. Smooth muscle cells and fibroblasts showed ultrastructural signs of increased synthetic activity and their size was significantly increased. In confirmation of earlier studies, constant i.v. infusions of noradrenaline did not prevent the morphological changes induced by denervation. Adenosine prevented the morphological changes induced by chemical or surgical denervation. Similarly to adenosine, infused NECA prevented the structural consequences of denervation. In contrast, inosine did not prevent the changes caused by surgical denervation. The results are compatible with an involvement of purines in the trophic effects of sympathetic innervation. Moreover, the effects of adenosine do not appear to be mediated by inosine.

Adenosine A2A Receptors Modulate α-Synuclein Aggregation and Toxicity.

Abstract Abnormal accumulation of aggregated &agr;‐synuclein (aSyn) is a hallmark of sporadic and familial Parkinsons disease (PD) and related synucleinopathies. Recent studies suggest a neuroprotective role of adenosine A2A receptor (A2AR) antagonists in PD. Nevertheless, the precise molecular mechanisms underlying this neuroprotection remain unclear. We assessed the impact of A2AR blockade or genetic deletion (A2AR KO) on synaptic plasticity and neuronal cell death induced by aSyn oligomers. We found that impairment of LTP associated with aSyn exposure was rescued in A2AR KO mice or upon A2AR blockade, through an NMDA receptor‐dependent mechanism. The mechanisms underlying these effects were evaluated in SH‐SY5Y cells overexpressing aSyn and rat primary neuronal cultures exposed to aSyn. Cell death in both conditions was prevented by selective A2AR antagonists. Interestingly, blockade of these receptors did not interfere with aSyn oligomerization but, instead, reduced the percentage of cells displaying aSyn inclusions. Altogether, our data raise the possibility that the well‐documented effects of A2AR antagonists involve the control of the latter stages of aSyn aggregation, thereby preventing the associated neurotoxicity. These findings suggest that A2AR represent an important target for the development of effective drugs for the treatment of PD and related synucleinopathies.

Impaired resolution of inflammation in human chronic heart failure.

Lipoxins (LXs) are proresolving and anti‐inflammatory eicosanoids whose role in chronic heart failure (CHF) pathogenesis has never been investigated. This study evaluated levels of LXs in CHF patients, its relationship with disease severity and correlation with established CHF biomarkers. The effect of low‐dose aspirin [acetylsalicylic acid (ASA)] on the levels of LXs was also studied.