Steroid metabolism in racing greyhounds
thesisposted on 13.06.2014, 14:50 by Simon Biddle
The metabolism of androgenic anabolic steroids has been studied in the racing greyhound. Various drug preparations have been investigated utilising different derivatisation techniques, coupled with gas chromatographic analysis, to enable the identification of key metabolites in canine post administration samples. This has led to an increased understanding of some of the generic routes of steroid metabolism that take place in the greyhound. This valuable information can help to support metabolism studies in the future. The identification of specific metabolites for each compound investigated, has provided a means for controlling the misuse of these compounds, and contributed valuable enhancements to screening protocols utilised in the canine sports drug testing industry. Utilisation of the techniques described, resulted in the identification of specific major metabolites of the anabolic steroid methyltestosterone, namely 17α-methyl-5β- androstan-3α-17β-diol and 17α-methyl-5β-androstan-3α,16α,17β-triol. 16α- hydroxylation was shown to be a major phase I metabolic pathway in the canine along with phase II conjugation with glucuronic acid. Similar results were obtained during the metabolism study of the progestatgenic steroid norethisterone. Several di- and trihydroxy metabolites were detected in the glucuronic acid fraction of the post administration urines from this study. The norethisterone metabolism study also provided some insight, into the area of trace contaminants of pharmaceutical preparations. Low levels of nandrolone metabolites were also detected in the norethisterone post administration urine samples, leading to the discovery that the administered pharmaceutical tablets contained small quantities of nandrolone and 19- norandrostenedione, albeit below FDA approved contaminant levels. Modern methods of drug screening employ such highly sensitive techniques, that they allow for the detection of metabolites of such trace contaminants, following administration of the drug preparation to the greyhound. It is therefore important to have a broad understanding of the metabolism of various drug preparations, both banned and permitted substances alike; as detection of a trace amount of a banned substance metabolite, arising from the administration of a permitted medication, whose iii metabolite profile is unknown, and therefore potentially not detected, could present an interesting case. In conjunction with research into controlling the use of banned substances for the purposes of suppressing oestrus in the greyhound bitch, an investigation into normal/reference levels of endogenous hormones has been carried out. The endogenous steroid levels in a population of 212 greyhound bitches have been studied with a view to establishing a method for the detection of the exogenous administration of the endogenous anabolic steroid testosterone. The major urinary metabolites investigated were epiandrosterone, 5β-androstane-3α,17β-diol and 5α-androstane-3β,17β-diol. Statistical evaluations have been carried out to support the implementation of a suitable threshold for the key testosterone metabolites, namely 5β-androstane-3α,17β-diol and epiandrosterone. The detection of 5β-androstane-3α,17β-diol was found to be a very good indicator of the exogenous administration of testosterone to the greyhound bitch, when compared with the reference population data for this metabolite. However, further statistical/analytical data evaluation was deemed necessary before an absolute threshold could be implemented for this analyte, for the purposes of controlling the misuse of testosterone in the racing greyhound bitch. To support the understanding of endogenous steroid levels in the female greyhound, yet further, the endogenous reproductive steroid profiles were measured throughout the entire oestrus cycle of a cohort of 33 racing bitches. The results of the study clearly indicate a surge in androgen metabolites during the first 7-10 days of the oestrus cycle, in particular epiandrosterone and 5α-androstane-3β,17β-diol. This unique set of data has provided detailed information regarding the fluctuating concentrations of androgen and progesterone metabolites (following ovulation), at key stages of the canine oestrus cycle. The information obtained from this research can be used to support regulatory decisions regarding the misuse of testosterone in the racing greyhound bitch.
HFL Sport Science, LGC