Effects of phenylbutazone and anabolic steroids on adrenal and thyroid gland function tests in healthy horses

Abstract

SUMMARY Adrenal and/or thyroid gland function tests were evaluated in horses at various times during short-term therapy with phenylbutazone, stanozolol, and boldenone undecylenate. There were no significant treatment or time effects on mean basal plasma cortisol concentrations in horses during treatment with the following: phenylbutazone, given twice daily (4 to 5 mg/kg, iv ) for 5 days; stanozolol, given twice weekly (0.55 mg/kg, im ) for 12 days; boldenone undecylenate, given twice weekly (l.1 mg/kg, im ) for 12 days; or nothing. There was no significant effect of phenylbutazone treatment on the changes in plasma cortisol concentration during the combined dexamethasone-suppression adrenocorticotropic hormone ( acth )-stimulation test. Plasma cortisol concentration was significantly decreased from base line at 3 hours after dexamethasone administration and was significantly increased from base line at 2 hours after acth in all horses ( P < 0.05). Likewise, the stimulation of basal plasma cortisol concentrations at 2 hours after administration of acth ( P < 0.05) was not affected by treatment with stanozolol or boldenone undecylenate. There were no significant treatment effects on mean basal plasma concentrations of thyroxine (T 4 ) or triiodothyronine (T 3 ) among horses during the following treatments; stanozolol, given twice weekly (0.55 mg/kg, im ) for 12 days; boldenone undecylenate, given twice weekly (1.1 mg/kg, im ) for 12 days; or nothing. There was a significant time effect on overall mean basal plasma T 4 and T 3 concentrations ( P < 0.05): plasma T 4 was lower on day 8 than on days 1, 10, and 12; plasma T 3 was higher on day 8 than on days 4 and 12. Treatment with neither anabolic steroid significantly affected the increases in plasma concentrations of T 4 and T 3 in horses after thyroid-stimulating hormone ( tsh ) was administered. Plasma concentrations of T 4 and T 3 were significantly elevated above base line at 3 and 6 hours after tsh was given in all horses ( P < 0.05). Under the conditions of the study, it can be concluded that (i) short-term treatment of horses with phenylbutazone does not significantly affect basal plasma cortisol concentration, nor response of the pituitary-adrenal axis to dexamethasone or acth ; (ii) short-term treatment of horses with 2 different anabolic steroids (stanozolol and boldenone undecylenate) does not significantly affect basal concentrations of plasma cortisol, T 4 , and T 3 , nor response of the pituitary-adrenal axis to acth or response of the pituitary-thyroid axis to tsh ; and (iii) basal plasma concentrations of T 4 and T 3 in horses vary over time.