An orally active non-selective endothelin receptor antagonist, bosentan, markedly reduces injury in a rat model of colitis

Activation of endothelial cells by vasoactive mediators, such as endothelins, may be an early, strategically important step in the initiation of inflammation in the intestine. In view of recent evidence that inflammatory bowel disease is associated with elevated intestinal concentrations of endothelins and upregulated expression of endothelin receptors on vascular endothelium in intestine, endothelins may become therapeutic targets in inflammatory bowel disease. The recent availability of an orally active, mixed endothelin receptor antagonist, bosentan, allowed us to examine the role of endothelins in a rat model of colitis. Colitis was induced by intra-rectal administration of trinitrobenzene sulphonic acid. In each treatment group, rats were treated with bosentan (10-60 mg/kg p.o.) 24 and 2 h prior to (pre-dose) or 1 h after the induction (post-induction) of colitis and all animals were treated every 24 h thereafter for 5 days. On day 6, stool consistency and the presence of adhesions in the peritoneal cavity were accessed. Colonic tissue samples were removed for determination of macroscopic and microscopic tissue injury, and myeloperoxidase activity. Colitis was typified by tissue ulceration in the distal colon and a corresponding 35-fold increase in myeloperoxidase activity compared to non-inflamed controls. Daily treatment with bosentan dose-dependently reduced colonic damage and myeloperoxidase activity when bosentan was given prior to induction of colitis. In the pre-dose group, the greatest beneficial effect of bosentan was observed at 60 mg/kg; colonic damage and granulocyte infiltration were attenuated by > 80%. A partial therapeutic effect of bosentan was also observed at 60 mg/kg when the pre-treatment regimen was excluded. These findings demonstrate that an orally active, mixed endothelin receptor antagonist has marked protective and therapeutic effects in an animal model of colitis.

The polymerase chain reaction method as a tool for identifying members of the Anopheles gambiae complex (Diptera:Culicidae) in northeastern Tanzania

Polymerase chain reaction (PCR) primers developed at the Centers for Disease Control in Atlanta for the identification of members of the Anopheles (Cellia) gambiae Giles complex were tested on material collected in the Bagamoyo and Muheza districts of northeastern Tanzania. Part of the sample from Bagamoyo was chromosomally identified and correlated with the PCR identifications. This sample contained 170 Anopheles arabiensis, 328 An. gambiae, and 58 Anopheles merus, of which 121, 237, and 54 specimens, respectively, were identified with both PCR and chromosomes. Three specimens identified chromosomally as An. merus gave only the PCR fragment characteristic for Anopheles quadriannulatus, but on retesting gave the correct result. The Muheza sample consisted of 771 An. arabiensis, 852 An. gambiae, 43 An. merus, and 4 specimens producing the fragment characteristic for An. quadriannulatus. Because An. quadriannulatus has never been recorded from mainland Tanzania and due to the high number of specimens that produced no result (193), it is probable that DNA degradation led to misidentification of An. merus specimens as An. quadriannulatus. The overall probability of correct identification by PCR was 99.685% at first testing, which compares favorably with other genetic methods currently in use.

Eradication of Helicobacter pylori infection

Helicobacter pylori is probably the most common bacterial infection worldwide and the accepted cause of chronic active gastritis. It has a critical role in duodenal ulcer, where the prevalence of infection is 90-95%. There is a dramatic reduction in the rate of ulcer recurrence after successful eradication of the organism to about 4% per annum compared with up to 80% when the infection persists. What is true for duodenal ulcers is also true for patients with gastric ulcer who are infected with H. pylori. The risk of recurrent ulcer complications with bleeding is virtually abolished following successful eradication of H. pylori; in contrast, the risk of rebleeding is about 33% in patients still harboring the organism. The treatment of H. pylori infection in patients with confirmed peptic ulcer on first presentation or recurrence has been advocated by a Consensus Conference of the National Institutes of Health. The most evaluated regimens include dual therapy with a proton pump inhibitor and either amoxicillin or clarithromycin, and bismuth-based triple therapy with metronidazole and tetracycline. The use of a proton pump inhibitor-containing regimen offers the advantage of rapid symptom relief and the highest rates of duodenal ulcer healing. Moreover, combinations of a proton pump inhibitor and clarithromycin show more predictable and higher eradication rates than amoxicillin combinations. Newer triple therapies with a proton pump inhibitor plus two antibacterial agents given for 7-1O days are being increasingly described and may become the treatment of choice if initial results are confirmed. However, the optimum dosage regimen needs to be established. A new combination of ranitidine bismuth citrate and clarithromycin has also recently been shown to be effective. At this time it is reasonable to consider all patients with confirmed duodenal or gastric ulcer for eradication of H. pylori, and no patient should be considered for elective surgery without first being offered eradication therapy.

pH, healing rate and symptom relief in acid-related diseases

Suppression of gastric acid secretion is widely used and logical for the treatment of acid-related diseases. Healing of duodenal ulcer, gastric ulcer and gastroesophageal reflux disease is correlated significantly with the degree and the duration of suppression of intragastric acidity over 24 hours and with the length of the treatment. To date, proton pump inhibitors are the most effective agents among the currently available antisecretory drugs in offering the highest healing rate and fastest resolution of symptoms. Combinations of an antisecretory drug with one or more antimicrobial agents accelerate healing of peptic ulcers.

The role of Helicobacter pylori in pathogenesis: the spectrum of clinical outcomes

Helicobacter pylori is probably the commonest bacterial infection worldwide and is now accepted as the cause of chronic active type B gastritis. Most patients continue through life with a chronic superficial gastritis while some develop either duodenal or gastric ulcer. In a very small proportion the lymphoid reaction to H. pylori infection appears to progress to become a mucosal associated lymphoid tissue (MALT) lymphoma, while in others the evidence suggests that chronic superficial gastritis progresses to atrophy, the loss of gastric acid secretory capacity and the development of gastric cancer. The mechanisms involving H. pylori infection in peptic ulceration are increasingly well understood and H. pylori is now accepted as having a critical role in duodenal ulcer, where the prevalence of infection is 90 to 95%. More important is the dramatic reduction in duodenal ulcer recurrence after successful eradication of the organism to about 4% in a year compared to recurrences of up to 80% in those who ulcers have been healed but in whom the infection persists. There is also increasing evidence for the involvement of H. pylori in gastric ulcer, where infection is seen in between 60 and 80%, and there is a similar dramatic reduction in recurrence following cure of H. pylori infection. The progression of H. pylori gastritis from the acute infection to chronic superficial gastritis, predominantly antral gastritis or a pangastritis with increasing atrophy appears to be associated with the differing outcomes seen in this disease. Moreover, there is increasing data on the roles played by bacterial heterogeneity and the virulence of the organism, host factors such as the HLA genotype and immune response, environmental factors and the age of acquisition of infection play in determining these clinical outcomes of the disease.

Habit, prejudice, power and politics: issues in the conversion of H2-receptor antagonists to over-the-counter use

H2-receptor antagonists have been widely prescribed in the last 20 years and are considered to rank among the safest drugs known. In several countries they have been switched to over-the-counter (OTC) status, and a similar move is under consideration in Canada. Some concerns have been raised as to the effectiveness of these drugs in the treatment of dyspepsia and heartburn, their safety when taken for self-diagnosed symptoms, and the potential for their use to delay diagnosis or mask serious disease. The author presents evidence to support the use of OTC H2-receptor antagonists in the treatment of dyspepsia. He argues that the safety record of these drugs is reassuring and that they are unlikely to mask gastric cancer. Finally, he describes the appropriate place of OTC H2-receptor antagonists in the overall management of acid-related disorders.

The effect of indomethacin-induced gastric mucosal injury on 24-h intragastric acidity and plasma gastrin concentration in healthy volunteers

AIMS

To determine the influences of prostaglandin inhibition by indomethacin on 24-h intragastric acidity and plasma gastrin concentration, related to gastric mucosal injury.

METHODS

A pre- and post-treatment study design was employed in 10 Helicobacter pylori negative healthy male subjects. All subjects underwent upper gastrointestinal endoscopy at least 3 days before and after 7 days dosing with indomethacin 50 mg t.d.s. Mucosal damage was scored according to the Lanza method, and biopsies were taken for H. pylori status and assay of mucosal concentrations of prostaglandin (PG)E2 and leukotriene (LT)B4. Before and on the last day of dosing, intragastric acidity was measured by continuous 24-h pH monitoring, and plasma gastrin levels determined by radioimmunoassay in blood samples collected over the same period.

RESULTS

All subjects completed the study and no serious adverse events were reported. The mucosal injury score increased significantly from 0 (0-2) to 3.4 (0-8) (mean and range of values, P < 0.05) after dosing with indomethacin. No differences were observed in 24-h mean pH or meal stimulated plasma gastrin concentrations. Mucosal PGE2 and LTB4 were unchanged 8-10 h after the last indomethacin dose.

CONCLUSIONS

Endogenous prostaglandins do not appear to alter intragastric acidity or gastrin secretion, in contrast to the PGE analogues, whose effects must be more pharmacological than physiological.

Helicobacter pylori and gastric neoplasia: evolving concepts

There is evidence that Helicobacter pylori infection is associated with gastric cancer and mucosa-associated lymphoid tissue (MALT) lymphoma and possibly with non-ulcer dyspepsia. Eradication therapy for confirmed H. pylori infection may therefore become mandatory in patients with non-ulcer dyspepsia severe enough to warrant endoscopy and in first-degree relatives of patients with gastric cancer. However, routine treatment of asymptomatic carriers awaits confirmation of the association with cancer.

Critical issues in the pathophysiology and management of peptic ulcer disease

OBJECTIVE

To discuss some of the critical issues in the pathophysiology and management of peptic ulcer disease.

OPINION

Peptic ulcer disease has multiple causes, although gastric acid has traditionally been considered the primary aggressive factor. Helicobacter pylori infection is established as a major causative factor, but some aspects of the mechanisms by which H. pylori causes peptic ulceration remain unclear. Treatment with proton pump inhibitors (PPIs) is the most effective means of healing peptic ulcers. In addition to healing a higher proportion of ulcers than H2-receptor antagonists, PPIs provide faster healing and relief of symptoms. The ability of PPIs to produce effective and sustained inhibition of gastric acid secretion suggests that they may also become the treatment of choice for gastric ulcers caused by non-steroidal anti-inflammatory drugs. However, eradication of H. pylori infection is more effective than maintenance therapy with antisecretory agents in reducing the rate of recurrence of peptic ulcers initially healed using antisecretory therapy. H. pylori eradication is therefore the optimal, and almost certainly the most cost-effective, approach to the long-term management of patients with peptic ulcer disease. Despite the fact that 90-95% of patients with demonstrable duodenal ulceration are probably infected with H. pylori, it is recommended that, in routine clinical practice, infection is diagnosed before eradication therapy is instituted. H. pylori testing 4-6 weeks after the completion of eradication therapy is also recommended to check that the infection has been successfully cured. For routine clinical practice, the highly sensitive and specific rapid urease test is probably the most useful diagnostic approach. The most appropriate H. pylori eradication regimen remains to be defined. However, 1-2 weeks of treatment with a combination of a PPI and two antimicrobial agents achieves eradication rates in excess of 90%, which are similar to those attained using standard triple therapy, but with the advantage of better patient compliance and greater tolerability. Preliminary evidence also suggests that H. pylori eradication prevents the recurrence of peptic ulcer bleeding, although further studies are required.

CONCLUSION

H. pylori eradication by 1-2 weeks' treatment with a combination of a PPI and two antimicrobial agents appears to be the optimal (and probably the most cost-effective) approach to the long-term management of patients with peptic ulcer disease, and represents a major advance in the management of such patients.

Malaria infection potential of anopheline mosquitoes sampled by light trapping indoors in coastal Tanzanian villages

Anopheline mosquito populations were studied during 1992 in seven villages south of Bagamoyo, coastal Tanzania, prior to malaria control intervention using insecticide treated bednets. To collect mosquitoes, CDC light traps were used in ten houses per village fortnightly for 12 months. Anopheles females were identified and checked by ELISA for the presence of malaria sporozoite antigen and source of bloodmeal. An.funestus peaked in June-July after the long rains. Three members of the An.gambiae complex had different seasonality: An.arabiensis, An.gambiae and small numbers of An.merus were collected. In most villages transmission was extremely high and perennial with the entomological inoculation rate reaching three to eleven infective bites per person per night in July and persisting at around 0.1 and 1 for most of the remainder of the year. Sporozoite infection rates within the An.gambiae complex ranged from 2% to 25%, with the peaks in January and July following the two rainy periods. An.funestus showed a similar pattern. The light traps were reliable, simple to operate, and proved to be satisfactory to study the mosquito vector population.

Optimizing acid suppression for treatment of acid-related diseases

Gastric acid is of central importance in the pathogenesis of duodenal ulcer, gastric ulcer, and gastroesophageal reflux disease. Pharmacological reduction of acid secretion is, therefore, the mainstay of current treatment, but the optimal degree of acid suppression remains incompletely understood. This paper considers the ideal ways of assessing and reporting the pharmacological effectiveness of acid-inhibiting drugs and relating such data to clinical efficacy. Twenty-four-hour intragastric pH measurements are widely used for this purpose, although this technique cannot measure secretion quantitatively. Data on suppression of 24-hr intragastric acidity for groups of subjects have been successfully correlated with healing rates for duodenal ulcer, gastric ulcer, and gastroesophageal reflux disease. Three primary determinants of healing have been derived from antisecretory data. These are the degree of suppression of acidity, the duration of suppression of acidity, and the duration of treatment. The order of importance of these determinants varies depending on the disease. Data on 24-hr intragastric acidity should be accompanied whenever possible by data on 24-hr plasma gastrin levels, as the relationship between suppression of acidity and a rise in gastrin varies widely between individuals. It is not possible to predict the plasma gastrin level from the intragastric pH or any other measurement of intragastric acidity. Comparative data sets in groups of subjects may provide useful information. Proton pump inhibitors produce a greater and longer-lasting degree of suppression of acidity than conventional doses of H2-receptor antagonists. For this reason, they are more effective in healing duodenal ulcer and gastric ulcer. However, in view of the importance of duration of treatment, healing rates with the H2-receptor antagonists approach those obtained with proton pump inhibitors if treatment is continued for a longer time. In gastroesophageal reflux disease in particular, although the optimal degree of acid suppression is not yet defined, the consistently superior performance of proton pump inhibitors demonstrates that increased suppression of acidity is clinically beneficial.

Critical reappraisal of mucosal repair mechanisms

The repair of the mucosal surface of the stomach is a complex process involving a number of different cell systems. These include mucosal enterocytes, matrix proteins, and cells responsible for angiogenesis. The regulation of each of these systems is as yet poorly defined and the interaction between the different components remains to be characterized. The signal system involved in recognition of damage initiates a cascade of events which broadly comprise cell migration, cell proliferation, lineage determination, matrix reconfiguration, and angiogenesis. Critical regulators of this process include the trefoil peptides, specific adhesion molecules, and the modulators of cell lineage. The utility of specific pharmacotherapeutic probes, whether responsible for surface protection, growth factor delivery, acid inhibition, or growth factor amplification, remains to be rigorously defined. The repair of the mucosal defect is critical in establishing the functional integrity of the gastric luminal surface. In order to facilitate rapid and long-lasting repair of mucosal injury, a precise understanding of the specific biological events participant in the repair process is required. At this time, there is only a paucity of such information available.

Expression of interleukin 8 and CD54 by human gastric epithelium after Helicobacter pylori infection in vitro

BACKGROUND/AIMS

Helicobacter pylori is associated with neutrophil infiltrates, although the mechanism of their recruitment is only partially defined. The aim of the study was to determine if Kato III, a human gastric epithelial cell line, expressed cytokines and the intercellular adhesion molecule 1 (ICAM-1), which could contribute to the initiation of inflammation during infection with H. pylori.

METHODS

Kato III cells were stimulated with H. pylori and were examined for evidence of infection, cytokine production, and the expression of ICAM-1.

RESULTS

The expression of interleukin 8 messenger RNA and immunoreactive protein by Kato III cells was significantly increased over constitutive levels within 3 hours of infection with H. pylori. Infected Kato III supernatants activated neutrophils as evidenced by increased CD11b/CD18 and decreased L-selectin that could be blocked by anti-interleukin 8. In contrast, Campylobacter jejuni, lipopolysaccharide, killed H. pylori, and supernatants from cultures of H. pylori did not increase interleukin 8. Interleukins 2 and 6; interferons alfa, beta, and gamma; and tumor necrosis factor were not produced by resting or H. pylori-stimulated Kato III cells. In addition to producing interleukin 8, Kato III constitutively expressed surface ICAM-1, which acts as an intercellular adhesion molecule for neutrophils.

CONCLUSIONS

Our results indicate that H. pylori stimulates the gastric epithelium to initiate inflammation and neutrophil recruitment and activation.

NSAID--induced gastroduodenal ulcers: exploring the silent dilemma

Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective medications and are very commonly prescribed. They are used by a large proportion of elderly persons who are most prone to adverse events. NSAID gastropathy is the commonest side effect. The relative risk of adverse events is high, but the absolute risk for any individual patient is low. Individualizing the risk/benefit ratio would lead to cost effective care.

Sucralfate: the Bangkok review

Sucralfate is a site-protective ulcer healing drug with a remarkable range of mechanisms of action. Recent studies highlight the capacity of sucralfate to bind basic fibroblast growth factor (bFGF) and deliver it in high concentration to the ulcer. Basic fibroblast growth factor stimulates the production of granulation tissue, angiogenesis and re-epithelization, thus improving the quality of ulcer healing. The effect of sucralfate in reducing parietal cell sensitivity may be another factor important in the lower relapse rate demonstrated after duodenal ulcer healing. Sucralfate has been demonstrated to be efficacious in healing both duodenal and gastric ulcers together with mild oesophagitis, and it is safe for both short-term use and maintenance. In stress ulcer prophylaxis it is as effective as acid suppression or neutralization and has the advantage of lesser rates of nosocomial pneumonia than are demonstrated with antacids or H2 antagonists. The potential advantages of sucralfate lie in the better quality of ulcer healing associated with longer duration of remission.

Hp and pH--the relevance of gastric acid to the treatment of Helicobacter pylori infection

Helicobacter pylori infection causes inflammation of the gastric and duodenal mucosa, which results in a disturbance of the regulation of gastrin, gastric acid, and pepsin secretion. Acid secretion may be diminished, normal, or increased, depending on the stage of H. pylori infection, although the meal-stimulated gastrin response is invariably elevated. The exact mechanisms involved are not known, but probably involve the release of cytokines in response to bacterial products initiating mucosal inflammation. Helicobacter pylori is suppressed, although not eradicated, by proton pump inhibitors. In various dose combinations with amoxycillin, omeprazole in a twice daily dose of up to 40 mg b.i.d. eradicates the organism in up to 82% of patients. This synergistic effect may be due to the direct effects of omeprazole, the protection of amoxycillin from acid degradation, or the enhancement of host defense mechanisms accompanying acid suppression.

Biting pattern and host-seeking behavior of Anopheles arabiensis (Diptera: Culicidae) in northeastern South Africa

Biting rhythm as well as vertical and horizontal distribution of host-seeking Anopheles arabiensis Patton was studied at a remote warm-water spring in the Kruger National Park, South Africa, which usually is devoid of human presence. An. arabiensis seeking hosts were collected throughout the night with several peaks, often with greatest biting activity during the predawn period. Abundance did not decline linearly as a function of distance from the breeding area, but was related to vegetation patterns. Most bites occurred on the ankles or feet and decreased rapidly above that height. Wearing closed shoes or raising feet off the ground could reduce vector contact and therefore the risk of malaria infection.

Adenosine A1 receptors are not involved in contraction of canine gastric muscularis mucosae by adenosine analogues

In vitro contractility studies were conducted in canine gastric muscularis mucosae muscle strips with the adenosine analogues 2-chloroadenosine (CIAD), 5'-N-ethylcarboxamidoadenosine (NECA), 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA), R-N6-(2-phenylisopropyl)adenosine (R-PIA), S-PIA, N6-cyclohexyladenosine (CHA) and (2-p-carboxyethyl)phenylamino-5'-N-carboxamidoadenosine (CGS21680) as well as the A1-selective antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). Adenosine analogues contracted the muscle strips with the following rank order of potency: CPCA > NECA > CIAD > R-PIA > CHA > S-PIA > CGS21680. CPCA, R-PIA, and CHA were partial agonists. At a concentration selective for adenosine A1 receptors (50 nM), DPCPX did not alter the concentration-response curves to CIAD or CHA. However, at higher concentrations (1-10 microM), DPCPX antagonized CIAD-mediated contractions in a competitive manner (pA2 = 6.96; slope = 0.93). CIAD-mediated contraction was not altered by treatment of the muscle strips with tetrodotoxin (1 microgram/ml) or mepyramine (1 microM). Our results indicate that adenosine A1 receptors, nerves or mast cells are not involved in contraction of canine gastric muscularis mucosae by adenosine analogues.

Appropriate acid suppression for optimal healing of duodenal ulcer and gastro-oesophageal reflux disease

Comparisons of the effectiveness of treatments for healing duodenal ulcer are essential to determine optimal management strategies for both economic analysis and quality-of-life evaluation. Differences are usually made on the basis of the proportion of ulcers healed at varying time intervals. It has been shown by meta-analysis that healing of duodenal ulcers with antisecretory drugs is directly correlated to the degree of acid suppression. More recently, sophisticated meta-analysis of 24-hour intragastric acidity data and clinical trials of antisecretory drugs has demonstrated that the optimal degree and duration of gastric acid suppression for healing duodenal ulcer can be achieved by an aggregate time above pH 3 of 18-20 hours/day. These conditions predict 100% ulcer healing at 4 weeks. Antisecretory drug regimens that approach these criteria should achieve faster healing than other agents, with a concomitant acceleration of symptom resolution. Regression analysis was performed on the healing-time curves for each drug class to determine the rate of ulcer healing per week. The mean proportion of ulcers healed, irrespective of treatment duration, was highest for omeprazole, which also provided a significantly faster rate of duodenal ulcer healing than all other drug classes (p < 0.001). It has recently been shown that healing of erosive oesophagitis with antisecretory drugs is directly correlated with both the duration of acid suppression over the 24-hour period (p < 0.05) and the elevation of intra-oesophageal pH above 4. Furthermore, oesophageal acid exposure time can be normalized by maintaining the intra-oesophageal pH above 4 for at least 96% of the 24-hour period.(ABSTRACT TRUNCATED AT 250 WORDS)

The rationale of acid suppression in the treatment of acid-related disease

Acid-related disorders such as gastric and duodenal ulcers and gastro-oesophageal reflux disease have a high prevalence. Traditionally, acid suppression has proved to be the most effective means by which to heal these disorders, but relapse rates are high after cessation of treatment. Recently, Helicobacter pylori infection has been shown to modify several aspects of gastric function. Eradication of H. pylori infection virtually abolishes duodenal ulcer recurrence, implicating this organism in the pathogenesis of peptic ulcers and initiating a whole new strategy in the management of these acid-related disorders. More potent degrees of acid suppression result in faster healing. Moderate acid suppression, as occurs with H2-receptor antagonists, can heal just as many ulcers if treatment is continued for longer. The combination of proton pump inhibitors and antibiotics have successfully eradicated H. pylori in duodenal ulcer patients. Both H2-receptor antagonists and the proton pump inhibitors have satisfactory safety profiles. Due to their superiority in symptom relief, and in the healing of duodenal and gastric ulcers and erosive oesophagitis, and due to their ability to eradicate H. pylori infection in combination with antibiotics, the proton pump inhibitors will probably become accepted as first-line therapy for the treatment of acid-related diseases.

Inflammation, acid and ulcers

Chronic active type B gastritis is invariably the result of Helicobacter pylori infection and is an important factor in duodenal ulcer disease. The actions of mediators produced (a protein factor, a lipid soluble "pore-forming factor" and urease) or induced (immune/inflammatory cell mediators) by this bacterium on the control of gastric acid secretion are currently being investigated. These studies are reviewed in light of our current knowledge of the physiological control of gastric acid secretion.

Evaluation of the polymerase chain reaction method for identifying members of the Anopheles gambiae (Diptera: Culicidae) complex in southern Africa

Chromosomally and electrophoretically identified field samples of members of the Anopheles gambiae Giles complex from southern Africa and colony material were used to test the polymerase chain reaction (PCR) method of identification. The samples included An. arabiensis Patton, An. quadriannulatus Theobald, and An. merus Donitz. Only one of the 217 specimens examined was disputed. Twenty specimens (9%) were reamplified because of the presence of multiple bands or lack of amplification after the first assay. Specimens of An. merus from this region displayed both the diagnostic An. merus PCR band as well as the An. quadriannulatus band, possibly because of interspecific hybridization or random variation within the population. This work extends the geographical range over which the PCR technique has been verified to southern Africa.

Brain damage after profoundly hypothermic circulatory arrest: correlations between neurophysiologic and neuropathologic findings. An experimental study in vertebrates

Five groups of neonatal pigs were subjected to cardiopulmonary bypass with circulatory arrest periods that varied from 70 to 120 minutes for the investigation of brain changes in induced deep-core hypothermia (15 degrees C) with circulatory arrest. The parameters that were analyzed were (1) microscopy of the brain in animals at 6 hours after bypass procedures and (2) intraoperative monitoring of somatosensory evoked potentials. Microscopic cellular damage appeared in all animals with a circulatory arrest period of more than 70 minutes. These changes involved mainly Purkinje's cells of the cerebellum, and they affected particularly the inferior half of the cerebellum. The prolongation of latency in the cortical responses, which reflects a slowing of the neural transmission with hypothermia, occurred in all animals. The late evoked potentials remained absent in all piglets with circulatory arrest periods of 90, 105, and 120 minutes, but they were fully recovered in all piglets of the control group and those with 70-minute arrest times. We concluded that the cerebellar region is the most sensitive site in which ischemic lesions attain their maximal severity and extent, and the maximum time of circulatory arrest without histopathologic and neurophysiologic sequelae should not exceed 70 minutes.

Neuropathological features of profoundly hypothermic circulatory arrest: an experimental study in the pig

Twenty-four neonatal pigs were exposed to periods of circulatory arrest of between 70 and 120 min under profound hypothermia at 15 degrees C. Brain tissue taken 6h after cardiopulmonary bypass was examined histologically and by electron microscopy for evidence of hypoxic damage. Specimens from control pigs and animals subjected to 70 min arrest showed no morphological changes in the cerebral or cerebellar neurones. The earliest changes were seen after 90-min arrest; these were highly significant after 120 min. The changes involved mainly the Purkinje cells of the cerebellum with vacuolation in the cytoplasm; the inferior half of the cerebellum was particularly affected. The frequency and pattern of selective vulnerability of the cerebellum may be related primarily to the nature of its blood supply.