Inhibitory effect of phospholipase A2 isolated from Crotalus durissus terrificus venom on macrophage function

Recent work demonstrated that crotoxin, the main toxin of Crotalus durissus terrificus venom, inhibits macrophage spreading and phagocytic activities. The crotoxin molecule is composed of two subunits, an acidic non-toxic and non-enzymatic polypeptide named crotapotin and a weakly toxic basic phospholipase A₂ (PLA₂). In the present work, the active subunit responsible for the inhibitory effect of crotoxin on macrophage function was investigated. Peritoneal macrophages harvested from naive rats were used. Crotapotin (2.12, 3.75, or 8.37 nM/ml), added for 2 h to the medium of peritoneal cell incubation, did not modify the spreading and phagocytic activities of these cells. On the other hand, the PLA₂ (1.43, 2.86, or 6.43 nM/ml) subunit caused a significant reduction (30, 33, and 35%, respectively) of the spreading activity. The PLA₂ also inhibited the phagocytosis of opsonised zymosan, opsonised sheep erythrocytes, and Candida albicans, indicating that this inhibitory effect is not dependent on the type of receptor involved in the phagocytosis process. The inhibitory effect of PLA₂ was not due to loss of cell membrane integrity, since macrophage viability was higher than 95%. These findings indicate that the inhibitory effect of crotoxin on macrophage spreading and phagocytic activities is caused by the phospholipase A₂ subunit.     

Magnetic resonance imaging and Cogan's syndrome

We report the case of a 25-year old man with vestibulocochlear and ocular impairment compatible with Cogan's syndrome. Later on, severe headache developed. CT scan showed an ischaemic lesion in the right frontal lobe. Magnetic resonance imaging demonstrated multiple bilateral nodular lesions on T2-weighted sequences. These were unmodified at a second MRI examination performed six months later. Under corticosteroids, the neurological and ophthalmic symptoms disappeared, but the patient remained deaf. We believe that this patient had vasculitis involving the brain, with infarcts. To our knowledge, no case of Cogan's syndrome with cerebral magnetic resonance imaging has yet been reported.     

Cardiac receptors affect regional flow during acute infarction in conscious rats

This study was conducted to determine if cardiac receptors have a role in the control of the regional circulations during small acute myocardial infarction in the conscious rat. Cardiocirculatory dynamics and cardiac output distribution (microspheres) were measured in conscious rats 24 and 48 h after surgery for left main coronary artery ligation or the sham procedure. Data from animals without treatment were compared to data from animals treated to induce chemical cardiac denervation (85% phenol applied to the supraventricular surface of the heart and the root of the great vessels). The results suggest that neurogenic vasopressor stimuli originating from the heart contribute to changes in peripheral resistance secondary to small, acute, experimentally induced myocardial infarction in the conscious rat.     

Niflumic acid-induced increase in potassium currents in frog motor nerve terminals: effects on transmitter release

The actions of the nonsteroidal antiinflammatory drug niflumic acid were studied on frog neuromuscular preparations by conventional electrophysiological techniques. Niflumic acid reduced the amplitude and increased the latency of endplate potentials in a concentration-dependent manner. Neuromuscular junctions pretreated with niflumic acid (0.05–0.5 mM) showed much less depression than control when they were stimulated with trains of impulses. Inhibition of acetylcholine release was reverted by raising the extracellular Ca²⁺ concentration but not by simply washing out the preparations with niflumic acid-free solutions. Pretreatment with indomethacin (0.1 mM), another nonsteroidal antiinflamatory drug, did not affect the niflumic acid-induced inhibition of evoked responses. Niflumic acid (0.1 mM) did not change the amplitude of miniature endplate potentials and had a dual action on the frequency of miniatures: it decreased their frequency at 0.1 mM whereas it produced an enormous increase in the rate of spontaneous discharge at 0.5 mM. Niflumic acid (0.1–1 mM) reversibly increased the amplitude and affected the kinetics of presynaptic voltage-activated K⁺ current and Ca²⁺-activated K⁺ current in a concentration-dependent manner. Niflumic acid (0.1–1 mM) irreversibly decreased the amplitude and reversibly affected the kinetics of the nodal Na⁺ current. Indomethacin (0.1 mM) had no effect on presynaptic currents. In conclusion, niflumic acid reduces acetylcholine release by increasing presynaptic K⁺ currents. This may shorten the depolarizing phase of the presynaptic action potential and may reduce the entry of Ca²⁺ with each impulse.     

A hyperpolarization-activated chloride current in xenopus laevis oocytes under voltage-clamp

Voltage-clamp experiments have been performed on ovulated Xenopus laevis oocytes. Two kinds of oocytes were studied: mature oocytes presenting the white spot due to germinal vesicle breakdown (GVBD) were found to be essentially unexcitable; oocytes without the white spot appeared to possess ionic channels which open transiently on hyperpolarization. The current is carried by chloride ions and, in Holtfreter's solution, has a reversal potential at approximately - 15 mV.     

<Emphasis Type="Italic">Helicobacter pylori</Emphasis> and <Emphasis Type="Italic">cagA</Emphasis> and <Emphasis Type="Italic">vacA</Emphasis> gene status in children from Brazil with chronic gastritis

Helicobacter pylori has been shown to be strongly associated with chronic gastritis, gastric and duodenal ulceration, and is a risk factor for gastric carcinoma. Histology, urease, culture, and polymerase chain reaction have been employed as for H. pylori diagnostic methods, pre and post treatment or during follow-up of dyspeptic adult individuals referred for endoscopy. In order to obtain a more-sensitive and specific method for H. pylori detection, we evaluated gastric body and antrum biopsies of 134 consecutive Brazilian consecutive dyspeptic children aged 1-16 years by rapid urease test, histology and polymerase chain reaction using two pairs of oligonucleotides. Our results indicated that polymerase chain reaction with Southern blotting and hybridization with specific chemiluminescent probes increased the number of positive H. pylori patients by 35%. The genotyping of H. pylori strains directly from gastric biopsy using the same nucleic acid methodology revealed that there is no association of chronic gastritis in our infant patients with vacA s1 and the presence of the cagA gene. These data suggest an initial infection of children with normal mucosa and probably others factors than vacA s1 genotype or the presence of the cagA gene are associated with the onset of gastric disease. Altogether, our results reinforce the need for using more sensitive diagnostic methods in order to understand the role of H. pylori in the genesis of gastric disease in children and its progression in adults.     

Stunning and myocardial contractile autoregulation studied on the isolated isovolumic blood-perfused dog heart

AIM: To study, for the first time, the effects of stunning on homeometric and heterometric autoregulation. METHODS AND RESULTS: Ischaemia (15 min)/reperfusion (30 min) was induced in the isovolumic blood-perfused dog heart preparation. Heart rate elevations (n = 9) from 60 to 200 beats min-1, in steps of 20 beats min-1, promoted the same inotropic stimulation in control (C) and stunning (S), indicating that ischaemia/reperfusion does not affect the changes in calcium kinetics elicited by the Bowditch effect. Sudden ventricular dilation (VD) (n = 10) evoked an instantaneous increase in developed pressure (Delta1DP) followed by a continuous slow performance increase (Delta2DP) in C and S. Delta1DP (C: 35 +/- 2.2 mmHg; S: 27 +/- 2.1 mmHg; P = 0.002) and Delta2DP (C: 20 +/- 1.6 mmHg; S: 14 +/- 1.3 mmHg; P = 0.002) decreased proportionally, while Delta2/Delta1DP (C: 0.57 +/- 0.13; S: 0.58 +/- 0.14) and slow response time course (T/2) were unchanged (C: 55 +/- 6.6 s; S: 57 +/- 7.7 s) after ischaemia/reperfusion. The reduction of Delta1DP can be understood as a decline of the myofilaments calcium responsiveness, the main pathophysiological effect of stunning. The reason for the weakening of Delta2DP, due to intracellular calcium gain, was not determined but it was supposed that its complete manifestation could be restricted by cyclic adenosine monophosphate (cAMP) myocardial content reduction. As reported by others, Delta2DP depends on myocardial cAMP, and it has been shown that myocardial cAMP is decreased after ischaemia/reperfusion. CONCLUSIONS: Contractile depression due to stunning has no effect on the inotropic stimulation generated by the Bowditch phenomenon. Immediate and time-dependent enhancements of contraction evoked by sudden VD are proportionally reduced and the slow response time course is unaffected in the stunned myocardium.