Plasma [³H]noradrenaline kinetics in man: is separation of alumina extracts by high performance liquid chromatography necessary?

1. After an 80 min intravenous infusion of 1-[³H]noradrenaline ([³H]NA) in 19 subjects, the proportion of alumina-extractable ³H due to [³H]NA was 86 ± 2% in arterial and 78 ± 2% in venous plasma. [³H]Dihydroxy-phenylethyleneglycol ([³H]DHPG) accounted for 8 ± 1% in arterial and 13 ± 1% in venous plasma. [³H]Dihydroxymandelic acid ([³H]DOMA) was not detected.

2. No time-dependent change in the proportion of alumina-extractable ³H due to [³H]NA was seen in either arterial or venous plasma over this period. In venous plasma the proportion of alumina-extractable ³H due to [³H]DHPG increased slightly between 30 and 80 min, from 10 ± 1% to 13 ± 1%.

3. The results were unchanged with chronic β-blockade and with either 1-[2,5,6-³H]NA or 1-[7,8-³H]NA.

4. After [³H]NA infusion in man the radioactivity recovered after alumina extraction is predominantly [³H]NA and thus can be used directly to determine [³H]NA kinetics without the need for metabolite separation.