The influence of repeated prestressors on single stress response in rats.

The effect of various stressors of different intensity applied in random order before the final single immersion restraint stress was tested in two inbred rat strains, isoprenaline-sensitive and isoprenaline-resistant. The isoprenaline-sensitive strain revealed higher incidence of heart lesions after this single acute stress and low incidence of gastric lesions. The isoprenaline-resistant strain had the opposite characteristics. These differences were constantly reproducible when this strong stressor was used. After prestress by different stressors (tail-flick, ether anaesthesia, Porsolt swimming stress) at different time schedules, the incidence of gastric ulcer lesions, the weight of organs (heart, adrenals, spleen) changed substantially in isoprenaline-sensitive rats only. The most important result was reversal of the extent of gastric lesions. The isoprenaline-sensitive strain revealed more lesions than the isoprenaline-resistant one. The repeated different prestressors mainly changed the reactivity of animals, isoprenaline-sensitive rats becoming more similar to isoprenaline-resistant rats. These findings urged us to interpret carefully the results obtained in stress research with different and multiple stressors both in animals and humans.