Cortisol metabolites in dog plasma.

[1,2-³H]-Cortisol was administered i.v. to two male dogs, blood was obtained 2.5h later, and the plasma metabolites were characterized and quantified. The unconjugated fraction contained 20–30% of the plasma radioactivity, while 60 to 70% was found in the glucuronide fraction and 8–9% in the sulfate fraction. Cortols and cortolones were the most abundant metabolites in all fractions. 20-Di-hydrocortisol and 20-dihydrocortisone were predominant over cortisol and cortisone in the “free” as well as in the sulfate fractions. All fractions contained substantial amounts of 6β-hydroxy, C-20-reduced metabolites. The major one was assumed to be 6β-hydroxycortol or 6ν-hydroxycortolone. Others were identified as 6β-hydroxy-20β-dihydrocortisol and 6β-hydroxy-20β-dihydrocortisone. No 6β-hydroxycortisol or 6β-hydroxycortisone was detected. When compared with our analogous study on human plasma, the present results indicate that more extensive C-20 ketone reduction and 6β-hydroxylation occur in the dog.