ENDOTOXIN STIMULATES SECRETION OF CORTISOL, BUT NOT ACTH IN HEIFERS PRETREATED WITH SUPPRESSIVE DOSES OF A GLUCOCORTICOID

The ability of triamcinolone acetonide (TA) to suppress actions of lip opolysaccharide (LPS) in the pituitary-adrenal axis was examined in Ho lstein heifers. The study was carried our. using repeated measure/spli t plot factorial design involving four heifers which were repeatedly u sed in four experimental groups thus yielding eight experimental units (EU). Each EU received two treatments, the first at zero hour and the second at 28 h. Heifers in Groups I (n = 2) and II (n = 2) were given sterile saline as treatment (TRT) 1. For TRT 2, group I was given ste rile saline, and group II received Escherichia coli lipopolysaccharide (LPS). In group III (n = 2) and group IV (n = 2) triamcinolone aceton ide was given as TRT 1. Sterile saline (SAL) was TRT 2 for Gr III, and group IV heifers received LPS. Administration of LPS elicited increas es in concentrations of the stress hormones ACTH (P < 0.05) and cortis ol (P < 0.001) in SAL-pretreated heifers. However, in TA-pretreated an imals, the endotoxin could only cause increase (P < 0.001) in concentr ations of cortisol, but not ACTH. Therefore, the significant response of cortisol to LPS stimulation suggest that, at doses used in this stu dy, triamcinolone acetonide did not suppress LPS-triggered cortisol se cretion from adrenal zonae fasciculata and reticularis cells. The LPS- induced ACTH response appears to have been blunted by prior administra tion of triamcinolone acetonide.