STRESS-SUSCEPTIBLE pigs, unable to maintain homeostasis on exposure to stress, show a lack of response to exogenous ACTH injection when compared to stress-resistant pigs. Dexamethasone was used to block endogenous ACTH production before injection and adrenal production of corticosteroid remained high in stress-susceptible pigs even after the blocking. Endogenous ACTH levels also remained high in stress-susceptible pigs after dexamethasone blocking. However, once ACTH is injected into stress-susceptible animals, the adrenal response is significantly lower than stress-resistant animals and is apparently not sufficient to maintain homeostasis.
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Sebranek et al. (1973) studied this question.