DIFFERENTIAL GLUCOCORTICOID EFFECTS ON CATECHOLAMINE RESPONSES TO STRESS

There have been relatively few studies of the relationships between glucocorticoid and catecholamine responses to stress. We have therefore determined plasma levels of adrenocorticotropic hormone (ACTH), cortisol (F), norepinephrine (NE), and epinephrine (Epi) in four intact sheep treated with cortisol, dexamethasone (DM), or saline (S) and subjected to both audiovisual (barking dog) and insulin-induced hypoglycemic stress. In control sheep, exposure to both stressors resulted in acute rises in ACTH, F, Epi, and NE, with the rises after insulin being greater than those after dog stress. Pretreatment with DM blocked the ACTH and F responses to stress. Both DM and F markedly attenuated the Epi response to hypoglycemia, whereas the rises in NE after each stress and those of Epi after dog stress were unaffected by steroid treatment. In a second experiment with six sheep treated with S or DM only and subjected to the same stressors in reverse order, the same results were obtained, excluding a confounding effect of prior stress. We conclude that 1) the poststress release of NE, presumably primarily from extra-adrenal sources, is largely steroid independent; 2) the mechanism of release of Epi from the adrenal medulla in response to audiovisual stress is different from that after hypoglycemia; and 3) this may reflect different inputs from central glucocorticoid receptors to splanchnic outflow in the two situations.