Effect of alternate-day prednisolone administration on hypophyseal-adrenocortical activity in dogs

Charles W. Brockus From the Departments of Small Animal Surgery and Medicine (Brockus, Dillon) and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine, Auburn University, AL 36849.

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Allen R. Dillon From the Departments of Small Animal Surgery and Medicine (Brockus, Dillon) and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine, Auburn University, AL 36849.

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Robert J. Kemppainen From the Departments of Small Animal Surgery and Medicine (Brockus, Dillon) and Physiology and Pharmacology (Kemppainen), College of Veterinary Medicine, Auburn University, AL 36849.

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Abstract

Objective

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

Animals

12 Beagles.

Procedure

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 and Clinical Relevance

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. (Am J Vet Res 1999;60:698–702)

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