HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Heitzman, R. J. Search for Related Content PubMed PubMed Citation Articles by Heitzman, R. J.

The Absorption, Distribution and Excretion of Anabolic Agents¹

ARC Institute for Research on Animal Diseases, Compton, Newbury, Berkshire, RG16 ONN, United Kingdom

Abstract

The metabolic fate of the anabolic agents, diethylstilbestrol, hexestrol, trenbolone acetate, zeranol and the endogenous steroids are discussed under the headings absorption, distribution and excretion. There is an optimum concentration of anabolic agent in the systemic circulation that results in a maximum increase in growth rate of farm animals. This optimum blood concentration should be maintained over a long period. However, there is rapid metabolism and excretion of anabolic agents with short half-lives in blood, and metabolic clearance rate equals entry rate. The rate of absorption of the agent, which is determined by formulation and site of administration, is most important and is best achieved by the use of slow release implants. The pattern of exponential absorption from compressed pellets of single anabolic agents is not ideal, and a more constant payout of drug, in particular estradiol-17β, is best achieved in combined preparations of agents or from silicone rubber implants impregnated with the agent. The high metabolic clearance rate and rapid excretion of anabolic substances influences the distribution of residues. Outside the site of administration, less than 1% of the administered dose is present in the animal. The lowest concentrations of residues are found in muscle and fat, higher concentrations are present in liver and kidney and the highest concentrations are in the bile, urine and feces.

¹ Paper presented at the Symposium on "Metabolic Fate of Anabolic Substances in Food Animals" at the meeting of the Amer. Soc. of Anim. Sci., Raleigh, NC, USA, on July 29, 1981.