Chronobiologic quantification of nocturnal low-dose dopamine effect on circadian rhythms of thyroid-related hormones and prolactin (PRL).

Six clinically-healthy young men provided plasma samples every 30 min for 24 h (from 09:00-09:00 on 2 occasions. TSH, free T3 and free T4 were determined in the 30-min samples, while prolactin was determined in samples 1-3h apart. During the first test span, each man received an infusion of physiologic saline between 21(00)-01(00). Upon re-sampling several weeks later, 3 men received a low dose of dopamine (0.1 microgram/kg/min) and 3 men received a high dose (1.0 microgram) over the same hours (21:00-01:00). The least-squares fit of a 24-h cosine to each data series described a statistically-significant circadian rhythm (p less than 0.01) for each subject on each day of study. While overall group comparisons revealed no significant difference in mesor for any hormone studied, some intra-individual differences in rhythm parameters between saline and dopamine infusion were found. Dopamine Rx produced a statistically-significant increase in amplitude for PRL and T4 and an advance in acrophase for TSH, T3 and T4, but a delay for PRL. Studies measuring hormones of interest for the 24th immediately preceding and the 24th immediately following dopamine infusion at varying circadian stages (rather than only between 21:00-01:00) are warranted and have to be individualized--one of the points of this paper. The other main point is that data reduction to a mean and a standard deviation entails loss of information that can be recovered by chronobiologic methods, here used only as a model, in view of the limitations of the sampling design on hand.