Circadian rhythm of gene expression of myocardial contractile protein, left ventricular pressure and contractility.

Objective. A number of cardiovascular variables exhibit a circadian rhythm. Whether myocardial contractile response and gene expression of the contractile protein also show changes with a similar period was here investigated. Method. Circadian variabilities in the left ventricular developed pressure (LVP) and contractility (LV dp/dt max) were measured in 24 Sprague-Dawley rats by directly left ventricular catheterizing and compared with changes in the gene expression of alpha-myosin heavy chain (alpha-MHC) in myocytes obtained from the same animals by dot blotting analysis. Results. A circadian rhythm was seen in the variability of LVP (P<0.001), LV dp/dt max (P<0.001) and the biochemically measured expression of the alpha-MHC gene (P<0.01). As compared to the amplitude of the rhythm in alpha-MHC gene expression, the amplitude of the contractility rhythm was large (P<0.01) and the circadian amplitude of the LVP (P<0.001) was the largest, representing perhaps a composite of intracardiac plus any extracardiac contributions. Conclusion. One of factors determining the circadian rhythm of myocardial contractile function is alpha-MHC gene expression level.