Effect of alternate-day prednisolone administration on hypophyseal-adrenocortical activity in dogs.
OBJECTIVE
To evaluate effect of alternate-day oral administration of prednisolone on endogenous plasma ACTH concentration and adrenocortical response to exogenous ACTH in dogs.


METHODS
12 Beagles.


METHODS
Dogs were allotted to 2 groups (group 1, 8 dogs treated with 1 mg of prednisolone/kg of body weight; group 2, 4 dogs given excipient only). During a 30-day period, blood samples were collected for determination of plasma ACTH and cortisol concentrations before, during, and after treatment with prednisolone. From day 7 to 23, prednisolone or excipient was given on alternate days. Sample collection (48-hour period with 6-hour intervals) was performed on days 1, 7, 15, 21, and 28; on other days, sample collection was performed at 24-hour intervals. Pre- and post-ACTH plasma cortisol concentrations were determined on days 3, 9, 17, 23, and 30.


RESULTS
A significant difference was detected between treatment and time for group 1. Plasma ACTH concentrations significantly decreased for 18 to 24 hours after prednisolone treatment in group-1 dogs. At 24 to 48 hours, ACTH concentrations were numerically higher but not significantly different in group-1 dogs. Post-ACTH plasma cortisol concentration significantly decreased after 1 dose of prednisolone and became more profound during the treatment period. However, post-ACTH cortisol concentration returned to the reference range 1 week after prednisolone administration was discontinued.


CONCLUSIONS
Single oral administration of 1 mg of prednisolone/kg significantly suppressed plasma ACTH concentration in dogs for 18 to 24 hours after treatment. Alternate-day treatment did not prevent suppression, as documented by the response to ACTH.
Brockus
C W
CW
Department of Small Animal Surgery and Medicine, College of Veterinary Medicine, Auburn University, AL 36849, USA.
Dillon
A R
AR
Kemppainen
R J
RJ
D000302:Adrenal Cortex / Q000187:drug effects / Q000502:physiology; D000324:Adrenocorticotropic Hormone / Q000097:blood / Q000378:metabolism*; D000818:Animals; D004285:Dogs / Q000502:physiology*; D004334:Drug Administration Schedule; D005260:Female; D006854:Hydrocortisone / Q000097:blood / Q000378:metabolism*; D008297:Male; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000502:physiology*; D011239:Prednisolone / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors
D000324:Adrenocorticotropic Hormone; D011239:Prednisolone; D006854:Hydrocortisone