Friedman, S. B., Ader, R. 1967. Adrenocortical response to novelty and noxious stimulation. Neuroendocrinology 2, 209-212.

It was found in rats that the magnitude of the stress response to being transferred into an experimental cage is virtually the same as that produced by electrical shock. ... Exposure to a new environment, or novelty, may contribute significantly to the adrenocortical response often attributed to the effects of noxious or painful stimulation.