Human urotensin II (UII) acts on the urotensin (UT) receptor and is the most potent mammalian vasoconstrictor identified to date. The role of UII in human cardiovascular regulation remains unclear, and the results of plasma measurements have been conflicting, perhaps because different measurement techniques have been used. The effects of cigarette smoking on plasma UII concentrations are unknown. The primary aim of our study was to demonstrate whether cigarette smoking had any effect on plasma UII concentrations in otherwise healthy volunteers. Our secondary aim was to compare the results obtained from assaying simultaneously using both radioimmunoassay (RIA) and immunoluminometric assay (ILMA).

Blood was taken from 20 healthy male non-smokers and 20 healthy male cigarette smokers. Plasma was separated and stored at −70°C. Samples were batch analysed simultaneously for UII using RIA and ILMA.

Median (range) plasma UII concentrations were lower in non-smokers [1.67 (1.0–2.27) pg ml⁻¹] compared to smokers [2.62 (1.87–3.46) pg ml⁻¹] (P = 0.03) measured using RIA. Those who had smoked a cigarette in the 10 min before sampling had greater concentrations of UII [3.10 (1.87–4.60) pg ml⁻¹] compared to controls (P = 0.01). Plasma UII concentrations determined by ILMA were consistently low with no differences between groups.

The data obtained by RIA show that smoking may increase plasma concentrations of UII with a more pronounced increase when a cigarette has been smoked recently. There was a complete lack of correlation between RIA and ILMA for the whole data set, which suggests that some of the variability in plasma UII reported in the literature may result from differences between assays.