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Cysteamine and propionitrile are members of a family of compounds which induce the formation of acute duodenal ulcers in fasted and fed rats. Gastric acid secretion is increased by both agents, and acid hypersecretion appears to be required for ulcer formation. To determine the role of gastrin in the ulcerogenic mechanism, cysteamine and propionitrile were administered to fasted rats and their effect on fasting and food-stimulated serum gastrin levels was studied. Intragastric administration of cysteamine caused a 3- to 4-fold increase in fasting serum gastrin levels over the values of controls. Propionitrile was a less effective stimulant of gastrin release, causing a 1.5- to 2-fold increase in gastrin levels over matched control rats. The food-stimulated rise in serum gastrin levels after either a chow meal or intragastric instillation of a peptone solution was markedly enhanced by cysteamine pretreatment. Three hours after feeding the serum gastrin levels of cysteamine pretreated rats were 6 times higher than those of fed controls. The high serum gastrin levels of cysteamine-pretreated fed rats could not be explained solely by the additive effects of cysteamine and food, indicating that a potentiating interaction may exist between the two stimulants of gastrin release. The importance of this drug-induced stimulation of gastrin release, under both fasted and fed conditions, in the ulcerogenic process has yet to be ascertained.

Acute duodenal ulcer produced by subcutaneous injection of propionitrile in rats was studied by stereo, light, and electron microscopy in order to gain insight into the localization and mechanism of initial cell injury. Stereomicroscopy revealed an initial fissuring and splitting of the tips of the villus folds within 4 hours after two injections of propionitrile. This was followed by sloughing of the epithelium, shortening and effacement of the villus folds, and within 24 hours the appearance of discrete ulcers in the mucosa of the proximal duodenum. In most of the rats, two ulcers developed: the first and larger ulcer was on the antimesenteric side of the duodenum, and the other, a small and more superficial one, was on the opposite wall. Ultrastructural lesions appeared in the absorptive epithelial cells of the proximal duodenum within 5 hours following a single dose of propionitrile. The cytoplasmic changes of cellular injury were preceded and/or accompanied by beading and loss of microvilli. The initiation of propionitrile-induced alterations at the tip of the villi in the proximal duodenum suggests that the ulcerogenic agent acts from the luminal side of the duodenum and probably originates from the stomach.

Cysteamine and propionitrile cause severe duodenal ulcers with perforation within 24-48 h after a single injection in rats. These animal models were used to gain insight into the early, preulcerogenic biochemical changes in the duodenal mucosa. The results indicate that a single sc injection of cysteamine and propionitrile induced dose- and time-dependent decreases in the activity of phosphoprotein phosphatase (PPPase) in homogenate and particulate fractions of rat duodenal mucosa. The decrease in enzyme activity was detectable 4 h after the injection of the ulcerogens, it was maximal at 12 h, and hardly detectable at 24 h. No effect on the enzyme activity was found under in vitro conditions. PPPase activity in the liver was not influenced by either cysteamine or propionitrile. Furthermore, the toxic but nonulcerogenic derivative of cysteamine ethanolamine had no effect on PPPase in the duodenum. Thus, the effect of the duodenal ulcerogens on PPPase activity was indirect and organ specific, related only to the target organ (i.e., duodenal mucosa). The effect of the drugs was also selective at the level of mucosal cells: both duodenal ulcerogens depleted protein and alkaline phosphatase but not lysosomal acid phosphatase. The decrease of PPPase activity could be a general property of the duodenal ulcerogens since it is independent of their effect on endogenous somatostatin.

Neutralization of acid was evaluated in rat proximal duodenal segments isolated from biliary and pancreatic secretions. Duodenal ulcerogenic doses of cysteamine produced a significant decrease in acid disposal 0.5-2 hr after treatment. Oral or subcutaneous administration of the duodenal ulcerogen was effective. The potent ulcerogen cysteamine produced a more pronounced decrease than propionitrile (a weak duodenal ulcerogen). The failure of ethanolamine, a nonulcerogenic structural analog of cysteamine to significantly alter acid disposal suggests that the effect is not due to the toxic properties of the duodenal ulcerogen. The results reinforce the concept that the duodenum is able to dispose of significant quantities of acid. The decrease in acid-handling may contribute to duodenal susceptibility to acid after treatment with ulcerogens and possibly reflects pathophysiologic changes early in duodenal ulceration.

The pathogenesis of experimental adrenal hemorrhagic necrosis produced by acrylonitrile in the rat was investigated by various morphologic, biochemical, and pharmacologic methods. One dose of this chemical injected intravenously caused 100 per cent incidence of adrenal hemorrhage and necrosis in 90 to 120 minutes. Electron microscopy, histochemistry, and light microscopy combined with colloidal carbon labeling suggested an early damage (30 minutes after administration of acrylonitrile) to the vascular endothelium in the adrenal cortex, prominent at 60 minutes, when lesion to the parenchymal cells was not visible. The use of extracellular diffusion tracer horseradish peroxidase further indicated that parenchymal cell injury was a late event. Damage to the vascular endothelium in the adrenal cortex was associated with retrograde embolization of medullary cells and cell fragments into the cortical capillaries. The ultrastructurally demonstrated platelet aggregation and fibrin precipitation at the sites of discontinuous vascular endothelium were accompanied by a decrease in circulating platelets and fibrinogen as well as prolongation of prothrombin, partial thromboplastin, and thrombin time. The concentration of dopamine, unlike that of noradrenaline, in the adrenals but not in the brain of rats injected with acrylonitrile showed a time-dependent elevation. Pretreatment with phenoxybenzamine (alpha-adrenergic antagonist) or labetalol (alpha- and beta-adrenergic blocker) or metyrapone (11-beta-hydroxylase inhibitor) and the depletion of catecholamines by reserpine or prior medullectomy prevented the chemically induced adrenal necrosis. These results indicate that the presence of a functional adrenal cortex is necessary for the development of cortical damage which is associated with early vascular lesion caused and/or modulated by vasoactive amines from the medulla and/or (metabolites of) acrylonitrile.

Acrylonitrile-induced adrenal necrosis is associated with the early depletion of adrenal glutathione and elevation of adrenal dopamine. These biochemical events could result in increased susceptibility to free radical-mediated lipid peroxidation which may play a role in the pathogenesis of adrenal injury caused by acrylonitrile. In the studies reported here we found no elevation in malonaldehyde or conjugated diene concentrations of adrenal glands (or of glandular stomach and duodenal mucosa which may be other targets of acrylonitrile action) from rats given acrylonitrile. Conjugated diene concentrations in liver microsomes were significantly elevated (132%) 60 min after administration of carbon tetrachloride or 15 (38%), 30 (58%), and 60 (46%) min after injection of acrylonitrile whereas mitochondrial conjugated diene concentrations were not significantly altered by acrylonitrile. Our results suggest that while lipid peroxidation may not be involved in the pathogenesis of acrylonitrile adrenal injury it may occur in other tissues after acrylonitrile administration.

In rats, a single administration of acrylonitrile (vinyl cyanide) produces a rapidly occurring bilateral adrenal apoplexy. Structure-activity studies have shown that a close derivative, propionitrile (ethyl cyanide), causes duodenal ulcer without markedly affecting the adrenal glands. Prolonging the two-carbon chain of propionitrile by a methyl group (n-butyronitrile) enhances, replacing the methyl by bromide or nitrile decreases, while substitution by an amino group abolistes the ulcerogenic potency and variably affects the adrenocorticolytic action. On assaying a large number of nonnitrile compounds as well for ulcerogenic effect, such as thiols and amines, this effect was found to be related to a two-carbon structure bearing electronegative radicals on one or both ends of the chain.

Previous structure-activity and pharmacologic studies with duodenal ulcerogens cysteamine and propionitrile implicating catecholamines in the pathogenesis of duodenal ulceration have now been followed up by dose- and time-response biochemical investigations to assess the importance of monoamines in the development of duodenal ulcers. The concentrations of norepinephrine (noradrenaline), dopamine, serotonin and their metabolites were measured in total brain, brain regions, stomach, duodenum, pancreas and adrenals in the rat. Turnover of catecholamines was determined in rats pretreated with the inhibitor of tyrosine hydroxylase alpha-methyl-p-tyrosine. The duodenal ulcerogens caused a dose- and time-dependent depletion of norepinephrine in virtually all the tissues examined. The effect was maximal 4 or 7 hr after cysteamine or propionitrile, and norepinephrine levels returned to normal in 24 hr. Dopamine changes were selective and often biphasic, e.g., elevation in adrenals, biphasic in brain cortex, hippocampus and midbrain, but uniformly decreasing in glandular stomach and duodenum. In the median eminence dopamine levels decreased by 181 and 324% at 15 and 30 min, respectively, after cysteamine, but neither dopamine nor 3,4-dihydroxyphenylacetic acid was modified in the periventricular nucleus. Serotonin levels were relatively stable, revealing slight elevations or no changes in most of the tissues. The turnover of norepinephrine was accelerated by both chemicals in virtually all brain regions, but dopamine turnover was affected only in a few areas, e.g., in the corpus striatum and medulla oblongata cysteamine decreased dopamine turnover, whereas propionitrile first (at 1 hr) accelerated then (at 8 hr) significantly suppressed it.(ABSTRACT TRUNCATED AT 250 WORDS)

Cysteamine and propionitrile, experimental duodenal ulcerogens, stimulated gastric acid secretion in the rat. Gastric acid secretion was measured by two separate methods, the conventional pylorus ligation technique and a non-invasive technique based on the pH dependent liberation of azure A from azuresin in the stomach with subsequent excretion of the liberated dye in the urine. Volume, acid concentration and acid content of gastric fluids aspirated immediately before the pylrous ligation were markedly increased 1,4 and 7 hours after a single dose of either cysteamine or propionitrile. Both acid concentration and acid output of gastric contents collected 30 minutes after pylorus ligation were also significantly elevated 1.5 hours after propionitrile and 4.5 hours after cysteamine. Significant increases in gastric acid secretion after these chemicals were also measured by the non-invasive technique which demonstrated a 4 to 6 fold increase in 24 hour urinary azure A output in rats injected with either propionitrile or cysteamine. Enhanced gastric acid output may play an important role in the pathogenesis of duodenal ulcer produced by propionitrile and cysteamine.

Since it has been shown that acrylonitrile prevents the appearance of spontaneous pituitary adenomas, we have investigated its effect in acute experiments on rat pituitaries by histology, immunocytochemistry, electron microscopy and morphometry; in addition, serum prolactin and growth hormone levels were measured by radioimmunoassay. Electron microscopy of prolactin cells revealed hypertrophy of the Golgi region without significant change in volume densities and diameters of forming and storage granules. In the 24 h group, crinophagy was observed in prolactin cells and growth hormone cells. Corticotrophs, thyrotrophs and gonadotrophs were unaltered. Dilation, congestion and rupture of capillaries, as well as pericapillary and intercellular oedema were evident in the 24 h group. One hour after intravenous acrylonitrile injection, serum prolactin levels were within the normal range, whereas at 24 h, hyperprolactinemia was noted. Serum growth hormone concentrations were unchanged. It can be concluded that acrylonitrile has a complex effect on prolactin cells. Hypertrophy of Golgi complex and hyperprolactinemia may reflect increased prolactin synthesis and release. Since volume densities and diameters of secretory granules in prolactin cells remained unchanged, it appears that newly synthesized prolactin was preferentially released and not the prolactin stored in secretory granules. Crinophagy may be the morphological manifestation of a discrepancy between hormone synthesis and release suggesting increased degradation of unused hormone by lysosomes.

A single dose of acrylonitrile can produce fatal adrenal apoplexy within approximately 2 h. Our previous studies also indicate that multiple injections of the chemical cause acute hemorrhagic and occasional nonperforating duodenal ulcers. Other authors have reported increase in gut and lung neoplasia after chronic exposure. The present study was designed to elucidate the subacute and chronic actions of acrylonitrile on the adrenals, stomach and duodenum by correlating biochemical, functional and morphologic investigations, as well as to gain insight into the mechanisms of action of acrylonitrile. Rats were exposed to 0, 0.0001% (1 ppm), 0.002%, 0.01%, 0.05% or 0.2% acrylonitrile in drinking water, or to the same amount of the chemical given through daily gavage, for 7, 21 or 60 days. Acrylonitrile caused a time- and dose-dependent decrease in plasma corticosterone levels; aldosterone was affected only by the 'high' dose and prolonged time of exposure. Young rats were more susceptible than adults to this action of acrylonitrile. The adrenal cortex, especially the zona fasciculata, was atrophic in rats that had ingested the nitrile through drinking water. At 0.05% and 0.2%, it also caused decreased food intake and body weight gain. The adrenals were enlarged with a hyperplastic zona fasciculata after daily doses of a bolus of acrylonitrile. Ingestion of the chemical did not interfere with compensatory enlargement of the adrenal gland following unilateral adrenalectomy. On the other hand, the ACTH-induced elevation of corticosterone plasma concentration was significantly attenuated by acrylonitrile in drinking water. Electron microscopy of the adrenal glands revealed no consistent changes in the steroid-producing cells. We thus postulate that accelerated turnover of circulating corticoids and/or interference with the secretion or action of ACTH may primarily be responsible for the decreased plasma levels of corticosterone and aldosterone in rats that ingest acrylonitrile. The mucosa in the stomach at the junction of the forestomach and glandular region of animals that had ingested acrylonitrile was hyperplastic. The corpus also showed regional mucosal hyperplasia with the appearance of 'cobble-stoning'. These changes were preceded and associated with an elevated concentration of non-protein sulfhydryls mostly in the mucosa of the glandular stomach. A similar, less prominent elevation also occurred in the proximal duodenum. These alterations may resemble the preneoplastic combination of elevated glutathione and focal hyperplasia described in the liver with hepatocarcinogens.(ABSTRACT TRUNCATED AT 400 WORDS)

Intravenous injection of acrylonitrile (ACN) causes adrenal hemorrhagic necrosis. ACN and its metabolites react with glutathione and bind covalently with macromolecules. Hence the purpose of this investigation was to measure the distribution and covalent binding of radiolabel derived from [1-14C]ACN in order to determine whether binding of ACN or its metabolites may be implicated in the pathogenesis of ACN-induced adrenal injury. Following intravenous injections of ACN, concentrations of total radiolabel were highest in the blood, liver, duodenum, kidneys, and adrenals. Except for blood, there was a time-dependent decrease in total radiolabel in these tissues. Compared with other major organ systems, the levels of covalently bound radiolabel were lower in the adrenal glands. These results do not support a role of covalent binding of ACN or its metabolites in the adrenal toxicity of ACN, but suggest that the initial high concentrations of total radiolabelled compounds derived from ACN could play a role in the action of ACN on the adrenal glands.

Pretreatment of rats with the polychlorinated biphenyl (PCB) Aroclor 1254 or phenobarbital markedly increased the duodenal ulcerogenic action of acrylonitrile. The extent of forestomach and hepatic lesions in these rats, on the other hand, was not modified. The duodenal ulcers produced by Aroclor 1254 and acrylonitrile morphologically resembled the ulcers induced in other animal models of the human duodenal ulcer disease. The possible mechanisms of this potentiation of acrylonitrile action are discussed.

The effects of the duodenal ulcerogens cysteamine and propionitrile on gastroduodenal myoelectric activity and intraluminal pressure in the fasted rat as well as on contractility of isolated gut muscle strips were investigated. Duodenal ulcerogens, unlike the nonulcerogen but toxic analogue ethanolamine, caused an early disruption of the myoelectric migrating complex, a marked increase in the spiking activity, and a decrease in the frequency of the slow waves in the duodenum. Both the increased spiking activity and the decreased slow wave frequency were dose dependent for cysteamine. Manometrically recorded contractions at the stomach corpus, midantrum, and antropyloric region as well as in the proximal duodenum of the conscious rat showed decreased contractions at the corpus and midantrum and an increase at the pyloric and duodenal sites during an intravenous infusion of cysteamine. In vitro studies demonstrated that circularly or longitudinally cut muscle strips taken from different regions of the stomach and duodenum responded to cysteamine with increased contractility. In summary, the duodenal ulcerogens cysteamine and propionitrile rapidly induce motor abnormalities in the stomach and duodenum of the rat. In vitro studies suggest that a cholinergic mechanism may be involved. It is possible that motor changes play a role in the pathogenesis of the experimentally induced duodenal ulcers.