Karla N. Sampaio

Differential chronotropic and dromotropic responses to focal stimulation of cardiac vagal ganglia in the rat

Vagal cardioinhibition is exerted through a reduction not only in the heart rate but also in the rate of propagation of the cardiac action potential and in myocardial contractility. In several species, such effects can be produced independently by selective activation of ganglia in identified ‘fat pads’. In this study we investigate differential control of heart rate and atrioventricular conduction by two ganglionic clusters in the rat, a species increasingly important in studies of cardiovascular control. Epicardial sites producing low‐threshold changes in P‐P and P‐R interval of the ECG in an arterially perfused preparation were explored with concentric bipolar stimulating electrodes. Stimulation sites centred on two principal ganglia, the sinoatrial (SA) ganglion at the junction of the right superior vena cava and right atrium, and the atrioventricular (AV) ganglion at the junction of the inferior pulmonary veins and left atrium. Stimulation of the SA ganglion decreased heart rate in all preparations, with little or no effect on AV conduction in one‐third. Stimulation of the AV ganglion consistently slowed conduction without eliciting a comparable bradycardia. Responses survived blockade of ganglionic transmission by trimetaphan, with an enhanced chronotropic selectivity to SA ganglion stimulation, suggesting that co‐excitation of preganglionic elements en passant may have contributed to the earlier mixed responses. Effective stimulation sites were precisely circumscribed and corresponded to principal ganglionic clusters confirmed histologically. We conclude that cardiac vagal ganglia in the rat show a topographical functional organisation and are amenable to investigation using the arterially perfused preparation.

Cardiovascular effects of scorpionfish (Scorpaena plumieri) venom

The aim of the present study was to investigate the cardiovascular activity of Scorpaena plumieri venom in both in vivo and in vitro models. In anesthetized rats, doses of the venom (14-216 microg protein/kg) induced a transient increase in the mean arterial pressure. However at higher dose (338 microg protein/kg) this effect was followed by a sudden hypotension and the animal evolved to death. The heart rate was temporarily increased and followed by bradycardia using doses > or =108 microg/kg. In isolated rat hearts the crude venom (5-80 microg protein) produced dose-dependent positive ventricular chronotropic, inotropic, lusitropic and coronary vasoconstriction responses. Partial purification of an active fraction (CF, cardiovascular fraction) which reproduced the cardiovascular effects induced by crude venom on isolated hearts was achieved by conventional gel filtration chromatography. Adrenergic blockades, prazosin and propranolol, significantly attenuated these responses. The coronary vasoconstriction response to CF was also attenuated by chemical endothelium denudation. In conclusion, the data showed that S. plumieri fish venom induces disorders in the cardiovascular system. It also suggests that alpha(1) and beta-adrenergic receptors, and the vascular endothelium, are involved at least partially, in these cardiac effects.

Cardiovascular changes following acute and chronic chemical lesions of the dorsal periaqueductal gray in conscious rats.

This study was carried out to investigate the effects of chemical lesions of dorsal periaqueductal gray (DPAG) on resting arterial pressure (AP) and heart rate (HR) as well as on cardiac baroreflex of conscious normotensive rats. Lesions were performed by bilateral microinjections of 150 mM NMDA into the DPAG (DPAG-lesion group). Controls were similarly injected with 165 mM NaCl (DPAG-sham group). Animals with chronic lesions confined only to the superior colliculus (SC-lesion group) were also used as controls of DPAG-lesion. Cardiovascular parameters were recorded 1 or 7 days after the microinjections of NMDA in acute and chronic groups, respectively. Cardiac baroreflex was assessed by measuring the HR responses to the intravenous injection of phenylephrine or sodium nitroprusside. Baroreflex was estimated by sigmoidal curve fitting of HR responses. An increased baroreflex gain was observed in chronic DPAG-lesion rats compared to both DPAG-sham (p < 0.01) and SC-lesion (p < 0.05) chronic groups. The chronic DPAG-lesion group showed also an elevation of both the tachycardia (p < 0.05) and bradycardia (p < 0.01) plateaus compared to chronic DPAG-sham rats, while the SC-lesion group showed an elevation of the bradycardia plateau only (p < 0.01). Similar results on baroreflex function were observed following acute lesion of the DPAG, i.e. an increase in baroreflex gain (p < 0.01) and the elevation of both tachycardia (p < 0.05) and bradycardia plateaus (p < 0.01) compared to the acute DPAG-sham group. Resting AP and HR did not differ among the chronic groups. In contrast, the acute lesion of the DPAG produced a reduction in AP (p < 0.01) accompanied by an increase in HR (p < 0.01). The present data suggest that the DPAG is involved in the tonic and reflex control of AP and HR in conscious rats. In addition, the SC seems to contribute to the baroreflex cardioinhibition.

Role of pulmonary stretch receptors and sympathetic system in the inhibition of reflex bradycardia produced by chemical stimulation of the periaqueductal gray matter of the rat.

The present study examined the role of the sympathetic system and pulmonary afferent feedback in the baroreflex inhibition by chemical stimulation of the dorsal periaqueductal gray matter (DPAG) of the anesthetized rat. The baroreflex bradycardia was induced by phenylephrine infusions (PHE, 50 μg/ml/min, i.v.) given either alone or combined with glutamate microinjections (GLU, 10 nmol/100 nl) into the DPAG. GLU microinjections alone produced marked increases in respiratory amplitude (67±19%), but barely changed the respiratory frequency (15±3 cpm) and blood pressure (14±2 mm Hg), and did not affect the heart rate. In contrast, the same injections produced a 92% inhibition of PHE-induced bradycardia (from -62 to -5 bpm). Because GLU microinjections per se had little effects on blood pressure, the baroreflex inhibition should be credited to the deactivation of both the vagal and sympathetic reflex pathways at the medulla. Indeed, the baroreflex was inhibited in only 47% following the DPAG stimulation of atenolol-treated rats. The GLU-evoked inhibition of baroreflex was also correlated with concomitant increases in respiratory amplitude. The role of pulmonary feedback in baroreflex inhibition was thus examined before and after the neuromuscular blockade of atenolol-treated rats. In spontaneously breathing rats, GLU microinjections reversed PHE-induced bradycardia to tachycardia, thereby producing a 153% inhibition of reflex bradycardia (from -38 bpm to +20 bpm). In contrast, the baroreflex inhibition was attenuated in only 53% after neuromuscular blockade (from -34 to -16 bpm). Data are the first evidence of the contribution of pulmonary stretch receptor feedback in DPAG-evoked inhibition of reflex bradycardia.

Involvement of the purinergic system in central cardiovascular modulation at the level of the nucleus ambiguus of anaesthetized rats.

Anatomical studies have demonstrated the existence of purinergic P2 receptors in the nucleus ambiguus (NA), a site containing cardiac vagal motoneurons. However, very little is known about the functional role of these receptors in central cardiac vagal regulation. The aims of our study were to evaluate the following: (1) the blood pressure and heart rate responses following purinoceptor activation within the NA; (2) the role of purinoceptors and excitatory amino acid (EAA) receptors in mediating the cardiovascular responses evoked by ATP and l‐glutamate stimulation of NA; and (3) the role of NA purinoceptors in mediating the cardiovascular responses of the Bezold–Jarisch reflex. In anaesthetized rats, microinjection of l‐glutamate (5.0 nmol/50 nl) into the NA induced a marked and immediate onset bradycardia with minimal change in arterial pressure. Microinjection of ATP into the NA induced a dose‐dependent (0.31–6.0 nmol/50 nl) bradycardia and pressor responses. It is noteworthy that the bradycardia occurred either before or simultaneously with a pressor response (when present), indicating that it was not a baroreceptor reflex mediated response due to the rise in arterial pressure. The pressor response was prevented by α1‐adrenergic blockade with prazosin, whereas muscarinic blockade with methyl‐atropine abolished the evoked bradycardia. Ipsilateral microinjection of PPADS (a P2 receptor antagonist; 500 pmol/100 nl) into the NA significantly attenuated the ATP‐induced bradycardia but spared the pressor response. In contrast, PPADS in the NA had no effect on the l‐glutamate‐evoked bradycardic response. Ipsilateral injection of kynurenic acid (a non‐selective EAA receptor antagonist; 10 nmol/50 nl) into the NA totally blocked the bradycardia induced by l‐glutamate and partly attenuated the ATP induced bradycardia. Finally, both the depressor and the bradycardic responses of the Bezold–Jarisch reflex were attenuated significantly (P < 0.01 and P < 0.05, respectively) following bilateral microinjection of PPADS into the NA. These results identify ATP and purinergic P2 receptors within the ventrolateral medulla as excitatory to cardiovagal neurons. Additionally, our data show that P2 receptors within the ventrolateral medulla are integral to the cardiovascular responses of the Bezold–Jarisch reflex.

Acute exposure to the insecticide O,S-dimethyl phosphoramidothioate (methamidophos) leads to impairment of cardiovascular reflexes in rats

Poisoning by organophosphorus insecticides is often accompanied by cardiac complications which may be serious and even fatal. However, the effects of these compounds on the cardiovascular mechanisms involved in blood pressure regulation are not known. The aim of this study was to evaluate the effects of a sublethal dose (8 mg/kg, i.p.) of the organophosphorus methamidophos on chemoreceptor (CR) and Bezold-Jarisch (BJR) cardiovascular reflexes. Male Wistar rats were treated with single intraperitoneal injections of methamidophos in saline (n=23) or saline (0.9 percent, n=20) and underwent catheterization of femoral artery and vein one day after the injections. Cardiovascular recordings were performed 24h after the catheterization procedure. Plasma cholinesterase (ChE) activity was measured 24h after similar treatments in separate groups (n=10/group). The bradycardic component of CR and BJR was significantly attenuated in animals treated with methamidophos. The ChE activity was 80 percent reduced in the methamidophos-treated animals. Methamidophos impairment of the bradycardic component of two important cardiovascular reflexes may contribute to the cardiovascular toxicity associated with acute organophosphorus insecticides exposure.

Temporal profile and mechanisms of the prompt sympathoexcitation following coronary ligation in Wistar rats.

Our aim was to assess the timing and mechanisms of the sympathoexcitation that occurs immediately after coronary ligation. We recorded thoracic sympathetic (tSNA) and phrenic activities, heart rate (HR) and perfusion pressure in Wistar rats subjected to either ligation of the left anterior descending coronary artery (LAD) or Sham operated in the working heart-brainstem preparation. Thirty minutes after LAD ligation, tSNA had increased (basal: 2.5±0.2 µV, 30 min: 3.5±0.3 µV), being even higher at 60 min (5.2±0.5 µV, P<0.01); while no change was observed in Sham animals. HR increased significantly 45 min after LAD (P<0.01). Sixty minutes after LAD ligation, there was: (i) an augmented peripheral chemoreflex – greater sympathoexcitatory response (50, 45 and 27% of increase to 25, 50 and 75 µL injections of NaCN 0.03%, respectively, when compared to Sham, P<0.01); (ii) an elevated pressor response (32±1 versus 23±1 mmHg in Sham, P<0.01) and a reduced baroreflex sympathetic gain (1.3±0.1 versus Sham 2.0±0.1%.mmHg−1, P<0.01) to phenylephrine injection; (iii) an elevated cardiac sympathetic tone (ΔHR after atenolol: −108±8 versus −82±7 bpm in Sham, P<0.05). In contrast, no changes were observed in cardiac vagal tone and bradycardic response to both baroreflex and chemoreflex between LAD and Sham groups. The immediate sympathoexcitatory response in LAD rats was dependent on an excitatory spinal sympathetic cardiocardiac reflex, whereas at 3 h an angiotensin II type 1 receptor mechanism was essential since Losartan curbed the response by 34% relative to LAD rats administered saline (P<0.05). A spinal reflex appears key to the immediate sympathoexcitatory response after coronary ligation. Therefore, the sympathoexcitatory response seems to be maintained by an angiotensinergic mechanism and concomitant augmentation of sympathoexcitatory reflexes.

Neuroreflex control of cardiovascular function is impaired after acute poisoning with chlorpyrifos, an organophosphorus insecticide: Possible short and long term clinical implications

Although it is well-established that severe poisoning by organophosphorus (OP) compounds strongly affects the cardiorespiratory system, the effects of sub-lethal exposure to these compounds on the neural control of cardiovascular function are poorly explored. The aim of this study was to evaluate the effects of acute sub-lethal exposure to chlorpyrifos (CPF), a commonly used OP insecticide, on three basic reflex mechanisms involved in blood pressure regulation, the peripheral chemoreflex, the baroreflex and the Bezold-Jarisch reflex. Adult male Wistar rats were injected intraperitoneally with a single dose of CPF (30 mg/kg) or saline (0.9%). 24 h after injections, cardiovascular reflexes were tested in awake rats. Potassium cyanide (KCN) and phenylbiguanide (PBG) were injected intravenously to activate the chemoreflex and the Bezold-Jarisch reflex, respectively. The baroreflex was activated by phenylephrine and sodium nitroprusside infusions. Blood samples were taken for measurements of butyrylcholinesterase (BChE) activity while acetylcholinesterase (AChE) activity was measured in brainstem samples. Animals treated with CPF presented signs of intoxication such as ataxia, tremor, lacrimation, salivation, tetany, urination and defecation. The hypertensive and the bradycardic responses of the chemoreflex as well as the hypotensive and bradycardic responses of the Bezold-Jarisch reflex were attenuated in CPF treated animals (P < 0.05). Concerning the baroreflex responses, CPF treatment reduced the bradycardia plateau, the range and the gain of the reflex (P < 0.05). Plasma BChE and brainstem AChE were both reduced significantly after CPF treatment (P < 0.05). Our results showed that acute sub-lethal exposure to CPF impairs the cardiovascular responses of homeostatic and defensive cardiovascular reflexes. These effects are associated with a marked inhibition of plasma BChE and brainstem AChE.

Scientific production in pharmaceutical care: comparison between Brazil, USA and Spain

The aim of this study was to estimate the evolution of the field of Pharmaceutical Care (PC) by measuring the quality and quantity of the scientific production on the topic of PC in Brazil compared to two pioneering countries in the field, the United States of America (USA) and Spain. The databases Web of Science, Scopus, Medline, Lilacs and SciELO were used as sources for the literature search. Pharmaceutical Care, or the appropriate translations, was used as the search term for the literature search, which was limited to articles published between 1990 and 2009. A score of quality (SQ) was calculated using variables such as impact factor and the frequency of the citations. We included 3265 articles published in 544 journals. We found that there was a steady increase in scientific production since 1990 and that the USA had a higher quality of scientific production than Spain, whereas the Spain produced the highest quantity of articles. In comparison, the Brazilian production of scientific publications on PC is low in terms of both quality and quantity but has increased steadily since 2002. Nevertheless, Brazil has not yet reached the level of the USA or Spain. In conclusion, Brazils scientific production has evolved over the second decade studied in this work, with particularly high levels of production in the last five years. However, an increase in the quantity and quality of the publications should be encouraged.

Refinement of anesthetic choice in procedures preceding psychopharmacological studies

Rationale Previous studies indicated that some general anesthetics induce long-term antidepressant and/or anxiolytic-like effects. This raises the concern about the use of anesthesia in surgeries that precede psycopharmacological tests, since it may be a potential bias on results depending on the experimental design used. Objectives To evaluate whether commonly used general anesthetics in surgeries preceding psychopharmacological tests would affect rat behavior in tests predictive of antidepressant or anxiolytic-like effects. We also evaluated whether prior anesthesia would interfere in the detection of the antidepressant-like effect of imipramine or the anxiolytic-like effect of diazepam. Methods We tested if a single exposure to subanesthetic or anesthetic doses of 2,2,2-tribromoethanol, chloral hydrate, thiopental or isoflurane would change rat’s behavior in the forced swimming test (FST) or in the elevated plus-maze (EPM) test, at 2 hours or 7 days after administration. Results Previous anesthesia with the aforementioned anesthetics did not change rat behavior in FST per se nor it changed the antidepressant-like effect induced by imipramine treatment. Rats previously anesthetized with tribromoethanol or chloral hydrate exhibited, respectively, anxiogenic-like or anxiolytic-like behavior in the EPM. Prior anesthesia with thiopental or isoflurane did not produce any per se effect in rat behavior in the EPM nor disturbed the anxiolytic-like effect of diazepam. Conclusion Our results suggest that, in our experimental conditions, tribromoethanol and chloral hydrate are improper anesthetics for surgeries that precede behavioral tests related to anxiety. Isoflurane or thiopental may be suitable for anesthesia before evaluation in animal models predictive of antidepressant or anxiolytic-like effect.