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

We investigated endocrine circadian rhythm (CR) during pulsatile and nonpul satile 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 activit y were measured every 2 hours for 24 hours on the last day of the second PL HB week and the second and fourth NLHB weeks. Acquired data were compared w ith those of the normal control goats (Cont) to determine the presence or a bsence of CR, as well as the timing, acrophase, amplitude, and mesor of CR. Variations in melatonin, CR were consistently detected at all sampling poi nts. In contrast, CR of cortisol during PLHB and NLHB was observed in a few cases, although considerable CR was noted in most of the Cent cases. The v ariations in renin activity indicated CR in most of the Cent cases and in a ll cases at all sampling points during PLHB and NLHB, whereas their acropha ses were diversified. In conclusion, the CR of melatonin, reflecting the fu ndamental circadian clock, was maintained during both PLHB and NLHB, while it could be modified for stress sensitive cortisol and hemodynamic responsi ve renin during these bypass modalities.