Dosing time-dependent differences in efficacy of combination antihypertensive treatment have reported contradictory outcomes and circadian system could be responsible. The aim of our study was to study changes in expression of circadian regulatory genes affected by morning and evening dosing with combination treatment in short term and long term settings.
Design and method:
Spontaneously hypertensive rats aged between 8–10 weeks were treated with fixed combination of valsartan (10 mg/kg) and amlodipine (4 mg/kg), either in the morning (07:00) or in the evening (19:00) with treatment duration 1 and 6 weeks and with placebo group running in parallel for every treatment group. Body and cardiac characteristics were quantified by gravimetric and haemodynamic measurements, respectively. Relative expressions of selected genes were analyzed using qRT-PCR method in samples from left ventricles, right ventricles, aortas and kidneys.
After short term experiment, only morning treatment group demonstrated significantly better outcomes (p < 0.05) in terms of blood pressure control and heart rate decrease when compared to placebo, but after long term experiment this effect applied to both treatment groups, no significant difference was seen between morning and evening treatment. Effect of therapy was confirmed by significant >43% decrease in gene expression of atrial natriuretic peptide (Anp) in left ventricles, and >58% increase of renin (Ren) in kidneys of treatment groups except the evening groups in 1-week experiment (p < 0.05). Circadian regulatory genes expression (Per2, Bmal1) in left ventricles, right ventricles and aortas showed antiphase rhythmic pattern in both experiments and significant changes were observed in all treated evening groups by >63% increase of Per2 and >52% decrease of Bmal1 compared to placebo groups, while morning groups remained unchanged (p < 0.05).
In summary, circadian regulatory genes showed enhanced gene expression in evening groups compared to placebo groups in both short and long term settings with morning groups unaffected by combination therapy. Although in evening groups of short term settings therapeutical effect is not yet seen, circadian genes are changing the same way they do in long term settings.