Influence of pulsatile and nonpulsatile left heart bypass on the hormonal circadian rhythm

We investigated endocrine circadian rhythm (CR) during pulsatile and nonpulsatile left heart bypass (PLHB and NLHB). A ventricular assist device (VAD) was installed in five goats. After 2 weeks of PLHB, NLHB was subsequently conducted for 4 weeks. The levels of melatonin, cortisol, and renin activity were measured every 2 hours for 24 hours on the last day of the second PLHB week and the second and fourth NLHB weeks. Acquired data were compared with those of the normal control goats (Cont) to determine the presence or absence of CR, as well as the timing, acrophase, amplitude, and mesor of CR. Variations in melatonin, CR were consistently detected at all sampling points. In contrast, CR of cortisol during PLHB and NLHB was observed in a few cases, although considerable CR was noted in most of the Cont cases. The variations in renin activity indicated CR in most of the Cont cases and in all cases at all sampling points during PLHB and NLHB, whereas their acrophases were diversified. In conclusion, the CR of melatonin, reflecting the fundamental circadian clock, was maintained during both PLHB and NLHB, while it could be modified for stress sensitive cortisol and hemodynamic responsive renin during these bypass modalities.