Related Experiment Video
Updated: Aug 8, 2026

Parallel Measurement of Circadian Clock Gene Expression and Hormone Secretion in Human Primary Cell Cultures
Published on: November 11, 2016
MHPG circadian rhythmicity in blood of healthy subjects
M Marler1, A Halaris, J E Piletz
1Department of Psychiatry, Case Western Reserve University, Cleveland, Ohio.
Abstract:
An earlier study showed that plasma concentrations of total 3-methoxy-4-hydroxyphenylglycol (MHPG), the major metabolite of norepinephrine, display a circadian rhythm in 6 male healthy subjects. In the previous study, the period of the rhythm was not fixed to 24 h thereby undermining the reliability of the cosinor parameter estimates. The present study extends the findings to a larger group of 12 clinically healthy male volunteers. Plasma total MHPG concentrations were determined every 3h for one full day. The data were fitted to a cosinor model fixing the period of the putative MHPG rhythm at 24 h. Several estimation techniques were utilized including Fourier analysis and time domain analysis with 4 variations. It is concluded that a circadian rhythm indeed characterizes MHPG blood concentrations. The concordance among the various parameter estimates is discussed.
Related Concept Videos
Circadian Rhythms and Gene Regulation
Pulse rhythm
Conversely, an irregular pulse pattern is termed dysrhythmia, stemming from disruptions in cardiac muscle...
Sleep-Wake Cycles
NREM Sleep
NREM sleep comprises four progressive stages that seamlessly merge:
Management of Insomnia
Chronopharmacokinetics: Circadian Rhythms and Influence on Drug Response
The time of drug administration is an important factor to consider, as it can influence the toxic dose of a drug. For example, a study conducted by Prins et al. in 1997 examined the effects of the timing of...

