Role of vascular factors, including angiogenesis, in the mechanisms of action of sucralfate

This brief overview of our recent results implicates vascular factors in the mechanisms of acute and chronic actions of sucralfate. Pretreatment of rats with sucralfate and its components, such as SOS and sodium sulfate, prevented the ethanol-induced microvascular injury and maintained blood flow in the gastric mucosa. Thus, preservation of microvascular integrity seems to be one of the mechanisms of acute gastroprotection by sucralfate. Chronic experiments with subcutaneously implanted sponges containing sucralfate or SOS revealed that both compounds stimulated angiogenesis, whereas only sucralfate enhanced the area of granulation tissue. These processes may have a role in the ulcer-healing action of sucralfate.

Predicting chemically induced duodenal ulcer and adrenal necrosis with classification trees

Binary tree-structured statistical classification algorithms and properties of 56 model alkyl nucleophiles were brought to bear on two problems of experimental pharmacology and toxicology. Each rat of a learning sample of 745 was administered one compound and autopsied to determine the presence of duodenal ulcer or adrenal hemorrhagic necrosis. The cited statistical classification schemes were then applied to these outcomes and 67 features of the compounds to ascertain those characteristics that are associated with biologic activity. For predicting duodenal ulceration, dipole moment, melting point, and solubility in octanol are particularly important, while for predicting adrenal necrosis, important features include the number of sulfhydryl groups and double bonds. These methods may constitute inexpensive but powerful ways to screen untested compounds for possible organ-specific toxicity. Mechanisms for the etiology and pathogenesis of the duodenal and adrenal lesions are suggested, as are additional avenues for drug design.

Time course of recovery from gustatory adaptation to NaCl

Recovery from adaptation to NaCl was tested by comparing some relevant parameters of response to the adapting and test stimuli separated by different recovery intervals. The time course of response was determined using magnitude estimations and using the flow chamber for stimulus delivery. The course of recovery for all parameters used was a negatively accelerated function of the rest time, but the recovery rate of different parameters did not prove to be equal. Recovery was fastest for the initial maximum taste magnitude, followed by the time needed for the taste to disappear. The taste effect summed over time and the time required for the taste magnitude to decrease to 30% of its preadapted maximum were the slowest to recover. Although the recovery processes proceeded at a rapid rate during the initial period, all parameters remained depressed over a rather long period.

Magnitude estimation of adaptation to salt using a flow chamber for stimulus delivery

Adaptation course to NaCl was estimated using a flow chamber for stimulus delivery and changes in the perceived taste magnitude as the criterion. The adapting stimulus of different durations was applied to one side of the tongue. Magnitude estimates were made by comparing the intensity of taste at the end of each adaptation time with the perceived intensity of the same stimulus applied briefly to the unadapted side of the tongue. The course of adaptation followed a negatively accelerated decreasing function. The relationship between taste magnitude and the duration of the adapting stimulus can be approximated by a logarithmic equation and, somewhat less accurately, also by an exponential equation, which can be related to the Beidler theory of taste stimulation. Some advantages of the closed flow technique and comparison of taste magnitudes on the adapted and unadapted sides of the tongue are discussed.

Extremely long protection by pyrazole derivatives against chemically induced gastric mucosal injury

We tested the hypothesis that the gastrotoxicity of ethanol and other damaging agents is influenced through the modulation of alcohol dehydrogenase (ADH) by using either the ADH-inhibitor pyrazole or the noninhibitor derivatives of pyrazole. In time course experiments, the protection by both compounds was evident up to 48 hr before ethanol administration. Both drugs were also protected, from about 24 hr, from gastric mucosal damage induced by aspirin and hydrochloric acid. In order to examine the role of endogenous prostaglandins and sulfhydryls in this protection, indomethacin and N-ethylmaleimide were used, of which only the sulfhydryl alkylator antagonized (by about 50%) the protection by pyrazole and 3-methylpyrazole. Studies with monastral blue B revealed the protective role of both pyrazole and 3-methylpyrazole against early vascular injury in the gastric mucosa. We conclude that because both the ADH-inhibitor pyrazole and the noninhibitor derivatives of pyrazole exert gastro-protection, and because both compounds protect against aspirin and HCI, ADH inhibition is not involved in this protection. We also suggest that although prostaglandins appear to have minimal involvement in the mechanism of protection, endogenous sulfhydryls may be important mediators. Furthermore, the functional and structural mechanism of this protection seems to be the prevention of acute vascular injury.

Surrogate markers for survival in patients with AIDS and AIDS related complex treated with zidovudine

OBJECTIVE

To determine whether early effects of zidovudine treatment on CD4+ lymphocyte count and concentrations of beta 2 microglobulin, neopterin, or HIV p24 antigen or antibody are correlated with survival in patients with AIDS or AIDS related complex.

DESIGN

Retrospective study of changes in laboratory markers and survival.

SETTING

Multicentre trial at university hospital clinics.

SUBJECTS

90 Patients with AIDS or AIDS related complex.

INTERVENTION

Patients started zidovudine 200 mg orally every four hours. Fifty six of the patients died a median 17 months after starting zidovudine; the remaining 34 patients were followed up for a median 25.5 months.

MAIN OUTCOME MEASURES

Changes in CD4+ lymphocyte count and serum concentrations of p24 antigen and antibody, beta 2 microglobulin, and neopterin; survival of the patient.

RESULTS

The pretreatment characteristics that independently predicted poor survival were determined using a multivariate proportional hazards model: a diagnosis of AIDS (v AIDS related complex), age over 45 years, and the logarithm of serum neopterin concentration. When these baseline characteristics were controlled for the logarithm of CD4+ lymphocyte count at weeks 8-12 of treatment (p = 0.007) and an increase in serum beta 2 microglobulin concentration at weeks 8-12 (p = 0.05) also independently correlated with survival. In the 38 patients with a better pretreatment prognosis, 24 month survival estimated by the product-limit method was 88% for those with a good response on both surrogate markers during early treatment compared with only 50% for those with a poor response on either marker. In the 38 with a worse pretreatment prognosis, 24 month survival was estimated to be 49% for those with a good response on both surrogate markers compared with only 18% for those with a poor response on either.

CONCLUSION

These data suggest that CD4+ lymphocyte count at 8-12 weeks and, perhaps, change in serum beta 2 microglobulin concentration could be surrogate end points for clinical outcome in trials of antiretroviral drugs for patients with HIV disease.

The mode of action of sucralfate: the 1 x 1 x 1 mechanism of action

Of the multiple actions of sucralfate, not all are equally relevant. In fact, certain actions of the drug contribute to healing of acute ulcers or to ulcer prevention, whereas other actions are more important in accelerating the healing of gastric and duodenal ulcers. The action of sucralfate can now be defined by the '1 x 1 x 1' mechanism of action--that is, one action of sucralfate is important for acute prevention, one is relevant to both acute and chronic protection, and one is important for chronic ulcer healing. Maintenance of mucosal vascular integrity and of blood flow, which ensures rapid epithelial restitution to repair superficial defects, are the most important acute actions of sucralfate. On the other hand, increased bicarbonate and mucus secretion seem to be relevant in both acute and chronic protection of the gastroduodenal mucosa. Finally, the enhanced binding by sucralfate of fibroblast growth factor and epidermal growth factor stimulates angiogenesis, granulation tissue, and epithelization for ulcer healing. This 1 x 1 x 1 theory of the mechanism of action of sucralfate concentrates on the relevant effects of this drug (which has more than a dozen actions) and may help to elucidate the molecular mechanism of action.

Interaction between stimuli with different taste qualities evaluated by reaction time

The influence of adaptation to taste stimuli of 1 quality on tastants with other qualities was investigated by comparing the reaction time (RT) to a test solution after adapting-solution flow with the RT to the same test solution after water flow. Adapting solutions were strong concentrations of NaCl, HCl, QHCl, and sucrose; test solutions were the same compounds but in lower concentrations. Adaptation to sucrose significantly shortened RT to NaCl and HCl, and to a lesser degree to QHCl. A similar cross-enhancement was found in sucrose when other compounds served as adapting solutions, In all other taste combinations, only a cross-adaptation effect was observed. Results are discussed in relation to some adaptation phenomena, water taste data, and magnitude-estimation data.

Dopamine in gastrointestinal disease

Dopamine is an important enteric neuromodulator. Herein we review the data that support a role for dopaminergic involvement in experimental duodenal and gastric ulceration; gastric, pancreatic, and duodenal secretion; gastrointestinal motility; and gastric and intestinal submucosal blood flow regulation. There also is support for a role for dopamine and dopamimetic agents in the treatment of certain experimental gastrointestinal diseases because some highly selective dopamine agonists are gastroprotective when given either parenterally or centrally. Based upon these observations, we suggest that dopamine is a key element of the "brain-gut axis" and represents a potentially important target for pharmacotherapeutic exploitation.

Unusual pathogens in narcotic-associated endocarditis

We report the cases of three adults with a history of intravenous drug abuse who developed endocarditis caused by Corynebacterium xerosis, Neisseria subflava, and Neisseria flavescens, respectively. No cases of endocarditis caused by C. xerosis or N. flavescens and only one case caused by N. subflava have previously been reported in association with narcotic addiction. The prominent clinical features in all patients included poor response to antibiotic therapy, persistent fever, and major embolic events. Stigmata of infection with human immunodeficiency virus, as manifested by oral candidiasis, cervical lymphadenopathy, and serologic evidence, were present in two of the three patients. At our institution, where Staphylococcus aureus remains the most frequent etiologic agent of narcotic-associated endocarditis, the occurrence of these three cases in a 9-month period is striking. We speculate that infection with human immunodeficiency virus may play a role in the pathogenesis of endocarditis caused by these unusual organisms.

Experimental gastric and duodenal ulcers. Advances in pathogenesis

New developments in the study of the pathogenesis of experimental gastric and duodenal ulcers indicate a complex multifactorial process leading to ulceration. The concept of gastric cytoprotection with prevention of hemorrhagic mucosal lesions by PG, SH, or other compounds without inhibiting acid secretion was discovered while investigating animal models of gastric erosions and ulcers. Subsequent research into the pathophysiology of gastric ulcer has been revitalized. New studies have demonstrated that the development or prevention of vascular injury in the gastric mucosa plays a crucial role in gastric mucosal injury and protection. The pathophysiology of experimental duodenal ulcer disease has shown that controlling gastric acid secretion is not the only approach to the prevention or treatment of this disorder. Data from human and animal experiments suggest that duodenal dysmotility contributes to the decreased neutralization of acid whether secreted at a normal or subnormal rate, in the duodenal bulb. Dopamine infusion corrected experimentally induced duodenal hypermotility, but other neurotransmitters may also be involved. Multidisciplinary investigations using experimental models of gastric and duodenal ulcers lead not only to the discovery of new concepts and pathogenetic mechanisms but also to the recognition of new chemicals that may exert gastroprotective and antiulcerogenic effects.

Experimental pathogenesis: drugs and chemical lesions in the gastric mucosa

The goals of this article are to review the similarities and differences in the pathogenesis of acute gastric mucosal injury induced by alcohol, exemplified mostly by ethanol, and aspirin, as a representative of nonsteroidal anti-inflammatory drugs, and to deduce implications from pathogenetic studies for a better understanding of the concept of gastric cytoprotection. The main similarity between the hemorrhagic erosions caused by ethanol and aspirin is their localization in the acid-producing glandular stomach, the rate-limiting step in their pathogenesis being the extent of microvascular injury in the gastric mucosa. The major differences include the fast healing and low probability of transition into chronic gastritis after a single exposure to aspirin. On the other hand, perforated ulcer may develop, especially in the elderly, after chronic aspirin but not ethanol consumption. The main implications of pathogenetic investigations include the relative nature of gastroprotection: that is, initially, the superficial epithelial layer is not protected against concentrated luminal solutions, but it is rapidly replaced by migrating, adjacent, surviving cells if blood flow is maintained and the basement membrane is relatively intact. Vascular changes thus seem to be the rate-limiting step both in the pathogenesis and prevention of chemically induced acute gastric mucosal injury. The ultimate biochemical mechanisms of gastroprotection seem to include an effect on structural and enzymic proteins, and vascular mediators which influence vascular permeability and, indirectly, the extent of tissue injury.

Protection of gastric mucosa against hypertonic sodium chloride by 16,16-dimethyl prostaglandin E2 or sodium thiosulfate in the rat: evidence for decreased mucosal penetration of damaging agent

Protection of the gastric mucosa may be the result of either increased cellular resistance to injury (cytoprotection) or, alternatively, decreased exposure of mucosal cells to the damaging agent. To determine whether decreased exposure of mucosal cells to damaging agents plays a role in mucosal protection by 16,16-dm PGE2 or sodium thiosulfate, we estimated the intramucosal concentration of 22NaCl and measured its absorption from the gastric lumen into the systemic circulation 1 and 5 min after intragastric administration of hypertonic (25% w/v) 22NaCl. In an attempt to explain the differences observed, we also measured the net transmucosal water flux in control animals and rats pretreated with the protective agents. Administration of hypertonic NaCl rapidly (within 1 min) induced extensive hemorrhagic mucosal lesions that were significantly reduced by pretreatment with 16,16-dm PGE2 or sodium thiosulfate. Ultra-low temperature autoradiography indicated that luminal hypertonic 22NaCl penetrates the upper layers of the mucosa in relatively high concentrations (12.5% w/v) within 1 min but its concentration decreases rapidly and reached low levels (3.12% w/v) by 5 min. Absorption of NaCl from the gastric lumen into the systemic circulation 1 and 5 min after hypertonic NaCl was lower in both pretreatment groups than in the control. Net gastric transmucosal water flux (from serosa to mucosa) increased (P less than 0.05) from 100 +/- 2 in controls, to 1470 +/- 8 and 715 +/- 9 microliters in rats pretreated with 16,16-dm PGE2 and sodium thiosulfate, respectively. We conclude that 16,16-dm PGE2 and sodium thiosulfate protect the gastric mucosa against hypertonic NaCl, diminish mucosal penetration of NaCl, decrease mucosal absorption of NaCl, and significantly increase serosal to mucosal transmucosal water flux.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of shift work on gastrointestinal (GI) function: a review

Recent statistics suggest approximately 20 percent of the American work force is engaged in shift work. The evidence which is reviewed in this manuscript suggests that shiftworkers are at risk for the development of gastrointestinal diseases or disorders. The susceptibility to shiftwork related gastrointestinal complaints may be related to the disruption of the individual's time structure. Central nervous system and endocrine mechanisms which may contribute to the pathogenesis of digestive diseases/disorders in shift workers are discussed.

Pathways of gastrointestinal protection and repair: mechanisms of action of sucralfate

Protection, i.e., prevention of major lesions and the mechanisms of repair/healing of major tissue loss in the gastrointestinal mucosa, are multifactorial processes. Conceptually, it is useful to categorize the components and mechanisms of gastroprotection and distinguish between: (1) Preservation of existing cells either by enhanced resistance of cells or by decreased exposure to damaging agents that can be achieved by maintenance of proper blood flow, vascular permeability, motility, mucus and bicarbonate secretion. If these mechanisms fail and tissue necrosis ensues, (2) replacement of lost tissue is achievable by either the original cells (e.g., epithelia), by cell migration (restitution) and proliferation (regeneration), and/or by connective tissue repair (e.g., fibroblasts, collagen) through cell proliferation and production of extracellular matrix. For acute gastroprotection ("cytoprotection"), maintenance of blood flow in the upper mucosa and epithelial restitution are listed as key mechanisms. For the long-term safeguarding of the mucosa, proper mucus and bicarbonate secretion, as well as ability to respond by cell proliferation, are the proposed key mechanisms of mucosal defense. The mechanisms of action of sucralfate are also multifactorial. The acute gastroprotection by sucralfate is a prostaglandin- and sulfhydryl-sensitive process: after early protection of microvasculature and maintenance of blood flow, along with direct or indirect preservation of the proliferative zone, rapid restitution repairs the initial epithelial defect. The mechanisms of accelerated healing by sucralfate of chronic ulcers include enhanced mucus and bicarbonate secretion, increased ability of mucus to maintain pH gradient, stimulated binding of epidermal growth factor and other growth factors, and maintained or enhanced blood flow resulting in increased cell proliferation leading to granulation tissue formation and re-epithelialization. The slight direct antipeptic and bile-acid binding property of sucralfate might also contribute to its ability to accelerate ulcer healing.

Individual gustatory reaction times to various groups of chemicals that provoke basic taste qualities

Reaction times (RTs) to four groups of substances that provoke different taste qualities were measured. Measurements for all substances with the same taste, equalized in perceived intensity and provoking a very strong taste, were made concurrently for each subject. The comparisons were made on the individual level. No significant differences in RTs to substances with the same taste quality were found. When the factor of perceived intensity is kept constant, no effect of the stimulus chemical composition on RTs seems to be present. RTs to stimuli with different tastes differ significantly, the shortest being to salt and the longest to bitter. The difference in RTs for sour and sweet substances is small, and the subjects were not all alike in terms of the order of RTs with respect to these stimuli.

Effect of duodenal ulcerogens cysteamine, mepirizole, and MPTP on duodenal myoelectric activity in rats

Increased gastric acid secretion, enhanced acid delivery to the duodenum, and reduced alkaline secretion in the proximal duodenum are relatively well-established pathophysiologic abnormalities in duodenal ulcer. Impaired duodenal motility, however, may also contribute to duodenal ulceration by altering the distribution of acid and alkaline secretions along the upper digestive tract. We tested the hypothesis that the duodenal ulcerogens cysteamine, MPTP, and mepirizole modify duodenal motility in the rat and that motility changes might be a common and early alteration in experimental duodenal ulceration. All three duodenal ulcerogens rapidly produced extensive changes in duodenal myoelectric activity and reduced the frequency of myoelectric slow waves. Cysteamine induced marked hypermotility for at least 6 hr; MPTP rapidly decreased motility and fragmented the myoelectric migrating pattern. Mepirizole induced biphasic changes: an early hypermotility phase of about 30 min was followed by profound hypomotility. These results indicate that marked alterations of duodenal motility are common during experimental duodenal ulceration. In light of the differential effect of the ulcerogens on duodenal motility, it remains to be determined how these changes influence acid neutralization in the proximal duodenum. Nevertheless, our results suggest that all three duodenal ulcerogens, which are different in structure, alter duodenal motility.

Adrenal gland: chemically induced structural and functional changes in the cortex

The adrenal cortex is the target of a surprisingly large number of exogenous chemicals. Until recently, the toxic action of these chemicals was discovered serendipitously. Following our observations that acrylonitrile, cysteamine or pyrazole induces hemorrhagic adrenocortical necrosis in the rat, we recently recognized a structure-activity correlation which predicts the adrenocorticolytic property of alkyl chemicals, i.e., 2-3 carbons with double or triple bonds and with nucleophilic terminal radicals (e.g., -CN, -SH, -NH2). On the basis of our results obtained with electron microscopic, histochemical and biochemical studies as well as those of others, we propose the following sequence of events in the pathogenesis of chemically induced adrenocortical necrosis: 1) Depletion of glutathione and increased dopamine concentration in the adrenals; 2) Endothelial damage and rupture of capillary walls in the adrenal cortex due to either direct attack by the chemicals (metabolites) and/or released monoamines; 3) Retrograde embolization of medullary tissue fragments into the cortical capillaries; 4) Enhanced destruction of cortical vascular walls with subsequent platelet aggregation, fibrin deposition which is often associated with a systemic drop in platelet counts, and changes in blood coagulation; 5) Escape of plasma and cellular elements of blood into extravascular spaces and damage of adrenocortical parenchymal cells; and 6) Hemorrhage and necrosis in the adrenal cortex. This pathogenetic sequence was investigated in detail with acrylonitrile, and studied in various aspects with thioguanine, cysteamine and pyrazole.

Effects of thyrotropin-releasing hormone and its analogue L-6-ketopiperidine-2-carbonyl-leucyl-L-prolin-amide on behaviour and electroencephalogram

A comparative dose-response investigation of thyrotropin-releasing hormone (TRH) and L-6-ketopiperidine-2-carbonyl-leucyl-L-proline-amide (RGH-2202) was carried out on rats and cats. RGH-2202 reduced the occurrence of photically evoked after-discharge in rats more significantly than TRH. Neither of the two compounds influenced the parameters of visually evoked potentials. Both compounds desynchronized the background electrocortical activity in rats. The amplitude of the acoustic startle reflex in rats was decreased dose-dependently only by RGH-2202, and this effect was nearly 3 times more potent than that of TRH. Both compounds increased the time spent awake, the latency to light sleep and the proportion of light sleep in a dose-dependent manner. The higher doses of TRH equalled the effects of the lower doses of RGH-2202. In cats the latency increasing effect of TRH on paradoxical sleep was about 30% less than that of RGH-2202; furthermore, the relative increase in the proportion of light sleep coupled with a corresponding decrease of deep sleep and paradoxical sleep was significant only in the case of RGH-2202. In a complex conditioned reflex situation in cats, the dose-dependent motivation decreasing effect on food intake and, as a consequence, on spontaneous motor activity was more pronounced in the case of TRH. The effective doses of RGH-2202 and TRH in rats were nearly equal, while in cats RGH-2202 showed about 1/10 of the potency of TRH. This finding suggests a considerably lower species variability of the effects of RGH-2202.(ABSTRACT TRUNCATED AT 250 WORDS)

Biphasic effect of duodenal ulcerogens on gastric emptying in the rat

The effect of the duodenal ulcerogen cysteamine on gastric emptying of a liquid meal was compared to that of two newly identified duodenal ulcerogens, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and mepirizole. Emptying rates after acute and chronic treatment with duodenal ulcerogens were obtained. Acute administration of cysteamine, MPTP, or mepirizole significantly delayed gastric emptying of the meal. Chronically treated rats, however, showed either no change or accelerated gastric emptying after cysteamine, MPTP, or mepirizole. Gastric emptying in chronically treated animals was faster in rats that developed the most severe duodenal ulcers. These results indicate that delayed gastric emptying instead of accelerated emptying is a more common abnormality during duodenal ulceration. After the ulcer develops, however, unaltered or accelerated gastric emptying is observed experimentally, thus suggesting that accelerated gastric emptying in duodenal ulcers is an acquired alteration. The implications that these experimental findings may have in the pathogenesis of duodenal ulcer, in light of the clinical data available, are discussed.