Diurnal variation of plasma cortisol and homovanillic acid in healthy subjects.

We investigated the relationship between plasma levels of cortisol, the dopamine metabolite homovanillic acid (HVA) and norepinephrine in healthy human subjects. Plasma cortisol and HVA levels were measured at 0800h, and in an integrated sampling procedure involving samples every 15 min between 1300 and 1600h. Plasma norepinephrine was measured at 0800 and 1300h. Cortisol, HVA and norepinephrine indices did not show significant correlations with each other. Both cortisol and HVA showed significant decreases over time. Longitudinal Random Effects (LRE) models were used to test whether individual cortisol and HVA curves over time were correlated; significant correlations were not found with this procedure. While significant correlations between cortisol and catecholamine indices have been reported in depressed patients, our results do not suggest such correlations in healthy subjects.