Microsomal enzyme activity, glutathione S-transferase-placental form expression, cell proliferation, and vitamin A stores in livers of rats consuming Great Lakes salmon.

Male and female Sprague-Dawley rats were fed diets incorporating lyophilized chinook salmon obtained from Lake Ontario and Lake Huron. After 70 days, females were bred and the progeny (F1) were reared on the same fish-based diets as the adults (F0). After 78-133 days on the diets, males and females of both generations were sacrificed and hepatic microsomal enzyme activities determined, along with glutathione S-transferase-placental form (GSTP) expression and hepatic cellular proliferation. Hepatic P450 enzyme activities (MROD, EROD, PROD, BROD, and aminopyrine) were increased significantly by fish diets from both sources. Increases in hepatic enzyme activity were greatest for fish caught from Lake Ontario and reflected the total levels of organochlorine contaminants in the fish. GSTP and cell proliferation rates did not show any diet-related or dose-related changes. Vitamin A stores were analyzed as the concentration of liver retinyl palmitate. In rats receiving the highest TEQ dose (i.e., 20% Lake Ontario fish diet), vitamin A stores were significantly lower in F0 adults, F1 weanlings, and F1 adult females.

Toxicity of fumonisin B1 administered intraperitoneally to male Sprague-Dawley rats.

The toxicity of purified fumonisin B1 (FB1) administered ip was examined in male Sprague-Dawley rats. FB1 was injected at 7.5 or 10 mg/kg body weight/day for 4 consecutive days. This resulted in significant reductions in body weight, food consumption and faeces production. Polyuria without a compensatory increase in water consumption was observed in treated rats. Erythrocytosis, elevated haematocrits and haemoglobin levels were attributed to dehydration. Nephrotoxicity in treated rats was evident by clinical changes including elevated blood urea nitrogen and by subtle changes in kidney morphology. Histopathology and serum biochemistry also indicated that the liver was an important target organ in FB1-treated rats. A small increase in liver glutathione concentration was also evident in rats receiving 10 mg FB1/kg body weight. Effects on the immune system included reduced thymus weight, disseminated thymic necrosis and consistently elevated serum immunoglobulin M levels. Circulating phagocytic cell numbers were elevated in treated rats, probably owning to tissue damage associated with ip dosing. The liver and kidneys appear to be target organs of FB1 in Sprague-Dawley rats.

The effects of fumonisin B1 on several markers of nephrotoxicity in rats.

Rats were injected intraperitoneally with saline or fumonisin B1 (FB1) at doses of 7.5 and 10.0 mg FB1/kg for 4 days. For each day of dosing, 24-hr urine samples were collected and analyzed for creatinine and protein content and the enzymes gamma-glutamyl-transpeptidase, lactate dehydrogenase, and N-acetyl-beta-D-glucosaminidase. Twenty-four hours after the last dose, animals were killed and kidneys removed for ion transport measurement and histopathology. Significant increases in urine volume and decreases in urine osmolality were observed in both FB1 dose groups. Creatinine excretion was decreased only in the 10 mg FB1/kg group on the final day of the study. Urine protein excretion was elevated in both treated groups and found to be due primarily to high-molecular-weight proteins indicative of increased glomerular permeability. Enzymuria, a marker of tubular cell damage, was also observed with increases in the urinary excretion of all three enzymes measured. In renal cortical slices tubular transport of the anion p-aminohippuric acid was reduced by 75-80% and cationic transport of tetraethylammonium was reduced by 40% in the FB1-treated animals. While these results suggest significant alterations in renal function, only minor histopathologic changes were observed in the kidneys of both dose groups. Results of the present study indicate that urine volume, proteinuria, enzymuria, and ion transport are sensitive indicators of early FB1-induced nephrotoxicity.

Autonomic pathways in development of neural stimulation-induced gastric mucosal damage.

Gastric mucosal erosions can be induced by electrical stimulation of either vagus nerves (5 Hz, 5 V, 1 ms) or the paraventricular nucleus (PVN) of the hypothalamus (200 microA, 60 Hz, 100-microseconds pulse width). We have utilized various pharmacological and surgical interventions to determine the contributions of different components of the autonomic nervous system to the development of this neurally induced gastric damage in urethan-anesthetized Sprague-Dawley rats. In all experiments damage was assessed macroscopically and scored blindly on a 0 (normal) to 3 (severe) scale with samples sectioned for subsequent histological assessment of damage at the light microscopic level. Animals pretreated with either hexamethonium (30 mg/kg iv) or atropine (2 mg/kg iv) demonstrated reduced gastric damage scores after vagal stimulation compared with untreated control animals (P < 0.05). In contrast animals that underwent cervical cord transection exhibited gastric damage after both vagal and PVN stimulation that was not significantly different compared with animals with an intact cord undergoing similar stimulation (P > 0.05). Such cord transection itself did not cause any significant change to the gastric mucosa in the time period studied. These data emphasize the importance of the autonomic nervous system, in particular the parasympathetic component in the development of vagal stimulation-induced gastric damage. In addition, the present studies suggest that neither vagal nor PVN stimulation-induced gastric damage is dependent on neural projections to sympathetic preganglionic neurons of the intermediolateral cell column of the spinal cord.

Role of gastric acid secretion and blood flow in the development of vagal stimulation induced gastric mucosal damage.

Vagal stimulation has been shown to result in the development of gastric mucosal erosions in the rat, although the mechanisms underlying the development of such erosions are not known. The effects of vagal stimulation on gastric acid secretion and mucosal blood flow were examined in urethane-anesthetized male Sprague-Dawley rats to determine whether changes in these factors correlate with the mucosal damage in response to vagal stimulation. Electrical stimulation (5 Hz, 5 V, 1 ms for 60 min) of afferent or efferent components of the vagi was not found to induce any significant increase in the mean acid secretory rate compared with control animals (p > 0.05). In contrast, stimulation of intact vagus nerves induced a significant increase in the mean acid secretory rate compared with control and efferent- and afferent-stimulated groups (p < 0.01). Measurement of gastric blood flow with laser-Doppler flowmetry demonstrated intact vagal stimulation to have no significant effect on gastric blood flow. These data suggest that such vagal stimulation induced increases in acid secretion in urethane-anesthetized animals may represent a part of the integrated physiological response to such stimulation which leads to the development of gastric mucosal erosions within 60 min. Pretreatment with antisecretory agents such as cimetidine and interleukin-1 beta significantly reduce the gastric mucosal injury compared with untreated animals (p < 0.05), emphasizing the important role of acid secretion in the development of vagal-induced gastric damage.

Neurally mediated gastric mucosal damage in hypophysectomized rats.

The role of the pituitary hormones in the development of neurally mediated gastric mucosal damage was examined in both normal and hypophysectomized urethane-anaesthetized male Sprague-Dawley rats. Gastric mucosal damage was elicited either by electrical stimulation of intact vagal nerves or by electrical stimulation in the paraventricular nucleus. Macroscopic damage was scored following the stimulation period and samples of the stomach were fixed for histological assessment. Damage scores were assigned based on a 0 (normal) to 3 (severe) scale. Control experiments in which the vagi were not stimulated did not result in any significant gastric damage in either normal (0.56) or sham surgery (0.14) animals, whereas hypophysectomized animals were observed to have significant damage (1.44, p < 0.05). Stimulation of the vagi in hypophysectomized animals resulted in damage that was not significantly different compared with the hypophysectomized control animals (1.25, p > 0.05). In normal animals, stimulation of vagal nerves resulted in mean damage scores of 2.00, values that were not significantly different from those observed in hypophysectomized animals (1.25, p > 0.05). Similarly, stimulation in the paraventricular nucleus of hypophysectomized animals resulted in gastric lesions (2.00) that were not significantly different from those observed in normal animals (1.91, p > 0.05). These data suggest that such neurally mediated gastric damage does not depend upon neurosecretory projections to the pituitary gland, but that the maintenance of an intact gastric mucosa under normal conditions requires the presence of pituitary hormones.

Vagal stimulation-induced gastric damage in rats.

The role of the vagus nerve in the development of gastric mucosal damage was examined in urethan-anesthetized male Sprague-Dawley rats. Electrical stimulation was applied to the vagus nerves for a period of 60 min, after which macroscopic gastric damage was scored and samples of the stomach were fixed for later histological assessment. Damage scores were assigned blindly based on a 0 (normal) to 3 (severe) scale. Stimulation of vagal afferents or efferents in isolation did not result in significant damage to the gastric mucosa (P greater than 0.1). In contrast, stimulation of both intact vagus nerves resulted in significant gastric mucosal damage (mean damage score, 2.0 +/- 0.33, P less than 0.01). A second series of experiments demonstrated this gastric damage to be induced within 30-60 min; extending the stimulation period to 120 min did not worsen the gastric damage scores significantly (P greater than 0.1). In a third study, stimulation of both intact vagus nerves after paraventricular nucleus (PVN) lesion resulted in damage scores (0.33 +/- 0.17) that were significantly reduced compared with intact PVN and non-PVN-lesioned animals (P less than 0.01). These results indicate that the development of vagal stimulation-induced gastric damage requires the activation of both afferent and efferent vagal components and suggest further that such damage is dependent upon an intact PVN.

Induction of rat hepatic monooxygenase activity by polychlorinated diphenyl ethers.

Polychlorinated diphenyl ethers are recognized environmental contaminants. Twelve of these compounds were tested for their ability to induce liver cytochrome P-450 and monooxygenase activities in Sprague-Dawley rats. All the compounds increased P-450 levels or increased monooxygenase activities in a manner resembling 3-methylcholanthrene, phenobarbital or a combination of both (mixed). The responses obtained resembled those of the polychlorinated biphenyls, some of which are known to be toxic.