The role of the sympathetic nervous system in cysteamine-induced gastric lesions in rats

Protective role of adrenal glucocorticoids for gastric mucosa in spontaneously hypertensive rats

BACKGROUND

Spontaneously hypertensive rats (SHR) are a representative animal model for disturbance of the pituitary-adrenal axis, as well as disturbance of the autonomic nervous system.

METHODS AND RESULTS

In this study, we showed that adrenalectomy in SHR-induced spontaneous gastric ulcer formation. We further investigated how abnormal adrenal secretion is related to the attenuation of gastric ulcerogenesis, in terms of leucocyte infiltration and nitric oxide (NO) formation. Bilateral adrenalectomy, as well as a sham-operation, were carried out at 12 weeks in hypertensive SHR and Wistar-Kyoto rats (WKY) and observations were made three weeks later. The number of myeloperoxidase (MPO) positive cells, NADPH diaphorase histochemistry and NO synthase (NOS) activity were determined in gastric specimens. Only in adrenalectomized, but not sham-operated SHR, WKY and adrenalectomized WKY, could gastric ulcers be observed. Although the number of cells positive for MPO was significantly lower in hypertensive SHR than those in WKY, such cells were increased after adrenalectomy in SHR. In contrast, adrenalectomized WKY developed no increase in MPO-positive numbers. The number of NADPH diaphorase-positive cells increased after adrenalectomy in both strains, the extent of which was much greater in SHR than in WKY. Although NOS activity in SHR was lower than that in WKY, it was significantly increased after adrenalectomy.

CONCLUSIONS

Our data show that the development of a significant gastric ulceration may be associated with entrapment of activated leucocytes in the gastric mucosa, as well as with an excessive production of NO in adrenalectomized SHR. An enhanced adrenal glucocorticoid may be a key factor for protecting the gastric mucosa in SHR.

Impairment of selectin-mediated leukocyte adhesion to venular endothelium in spontaneously hypertensive rats

The present study was designed to elucidate whether molecular mechanisms for leukocyte adhesion to microvascular endothelium may differ between spontaneously hypertensive rats and Wistar Kyoto rats. Leukocyte rolling and adhesion were investigated while monitoring venular wall shear rates in the mesenteric microcirculation stimulated with histamine or tert-butyl hydroperoxide in the two strains. In Wistar Kyoto rats, 10 microM histamine as well as 500 microM tertbutyl hydroperoxide promoted a significant reduction of venular leukocyte rolling velocity and subsequent adhesion. These changes in leukocyte behavior were blocked by monoclonal antibodies against P-selectin (PB 1.3) and against sialyl Lewis X-like carbohydrates (2H5). However, spontaneously hypertensive rats exhibited a blunted response of the stimulus-elicited leukocyte rolling, which was associated with impairment of venular P-selectin expression as well as a decrease in the expression of sialyl Lewis X-like carbohydrates on circulating neutrophils. No significant differences were detected between the two strains not only in the surface CD11b/CD18 expression but also in the CD18-mediated adhesivity of neutrophils to intracellular adhesion molecule-1 transfectants in vitro. These results suggest that impairment of selectin-mediated leukocyte adhesion is an event responsible for disorders of inflammatory responses in spontaneously hypertensive rats.

Sex differences and stress response of WKY rats

Wistar Kyoto (WKY), Fischer-344 (F-344), and Wistar male and female rats during either proestrus-estrus or diestrus phases of the estrus cycle were exposed to the ulcerogenic procedure of water restraint. Both male and female WKY rats revealed significantly more stomach ulcers as compared to Wistar and F-344 rats of the same sex. No persistent sex difference was observed, but ulcer severity was more pronounced during the proestrus-estrus phase as compared to the diestrus phase of the estrus cycle particularly in WKY female rats. In the second study, WKY females were observed as more active in the open-field test (OFT), but more immobile in the forced swim test (FST), as compared to WKY male rats. In addition, proestrus-estrus WKY females were less active in the OFT and significantly more immobile in the FST as compared to diestrus females. Thus, proestrus-estrus WKY females were judged as more emotional in the OFT and as exhibiting more signs of behavioral depression according to the FST. These studies suggest that the steroid hormone milieu in WKY rats may be responsible for these behavioral changes as well as the stress responsiveness in this stress-susceptible rat strain.

The neurobiology of stress ulcers

We have reviewed the neurobiology of stress ulcers from animal models to potential pharmacotherapeutic mechanisms. The evidence strongly supports the hypothesis that certain stress-related gastric lesions are 'brain-driven' events which may be more effectively managed through central manipulations than by altering local, gastric factors. Recent advances in the use of anxiolytic and antidepressant drugs in the management of stress-related gastric mucosal injury further supports the contention that a brain-gut axis, which may have nervous, peptidergic and classic monoaminergic components, modulates the intricate and complicated pattern of communication between the brain and the stomach. Delineation of the precise pathways which make up this communication as well as their manipulation by various pharmacological agents will be the focus of future research endeavour.