Sulphate conjugation catalyzed by phenol sulphotransferase (PST) is an important pathway in the metabolism of many drugs including triamterene. Variations in PST activity in an easily obtained tissue such as the platelet might reflect individual differences in the sulphate conjugation in other organs and tissues. Human platelets contain at least two forms of PST, a thermolabile (TL) form for which dopamine is a substrate and a thermostable (TS) form for which low concentrations of p-nitrophenol serve as a substrate. p-OH-triamterene, the major metabolite of triamterine, is conjugated with sulphate in vivo, p-OH-triamterene was a substrate for platelet PST with an apparent Michaelis-Menten value of 26 μM. Thermal stability studies indicated that p-OH-triamterene was a substrate for only the TS form of platelet PST. When platelet homogenates from 29 individual subjects were tested, there was a significant correlation between PST activities measured with 4 μM p-nitrophenol and with p-OH-triamterene (r = 0.985, P <0.0001) but not between activities measured with dopamine and with p-OH-triamterene (r = 0.023, P >0.2). These results confirmed that p-OH-triamterene was a substrate for only the TS form of human platelet PST. The same 29 subjects were treated with 1 mg/kg of triamterene orally. 24-h urinary excretions of triamterene, p-OH-triamterene and p-OH-triamterene sulphate averaged 15.3%, 6.3% and 78.4%, respecively, of the total of triamterene plus measured metabolites excreted. The excretion of triamterene plus the two metabolites averaged 43.1 ± 2.6% (mean ± s.e. mean) of the ingested dose. There was not a significant correlation between the proportion of p-OH-triamterene excreted as sulphate conjugated and the activities of either the TS or TL forms of platelet PST activity.
|Original language||English (US)|
|Number of pages||9|
|Journal||British Journal of Clinical Pharmacology|
|State||Published - 1983|
ASJC Scopus subject areas
- Pharmacology (medical)
- Pharmacology, Toxicology and Pharmaceutics(all)