Stereoselective excretion of (3-methoxy-4-sulphooxyphenyl)ethylene glycol (MHPG sulphate) in the dog.

3-Methoxy-4-hydroxyphenylethylene glycol (MHPG) labelled with six deuterium atoms ([2H6]MHPG) was infused into two female greyhound dogs. Plasma and urine were analyzed for endogenous MHPG and [2H6]MHPG and their conjugates by the technique of selected ion monitoring gas chromatography-mass spectrometry. This analysis showed that the major forms of MHPG and [2H6]MHPG in the plasma and urine of the greyhounds were the sulphate conjugates. However, the plasma concentration of [2H6]MHPG sulphate increased continuously during the infusion period and the renal clearance of this compound was found to be much less than that of the endogenous sulphate. The explanation that his was due either to saturation of a renal transport mechanism or to a deuterium isotope effect was eliminated. Stereochemical analysis showed that, while the [2H6]MHPG used for infusion was a racemic mixture of two stereoisomers, much more of the nature(-)stereoisomer of [2H6]MHPG sulphate was excreted in the dog urine. It was also shown that both the (+) and (-)stereoisomers of [2H6]MHPG sulphate were sulphoconjugated at the 4-position of the aromatic ring.