Effect of transplantation of embryonic anterior hypothalamic tissue from spontaneously hypertensive rats to normotensive Wistar rats on circadian rhythms of systolic arterial pressure and heart rate.

The anterior hypothalamus (AH) participates in the regulation of arterial pressure. The suprachiasmatic nuclei (SCN) of the AH are a major circadian oscillator necessary for the generation and/or the entrainment of circadian rhythms. Circadian rhythms of systolic arterial pressure (SAP) and heart rate (HR) were investigated in spontaneously hypertensive rats (SHR) and in normotensive Wistar rats (NWI) with intact SCN, grafted with SHR embryonic AH tissue containing the SCN. Prominent circadian rhythms for SAP and HR in both NWI and SHR with acrophases during dark were found. The elevation of the MESOR (midline-estimated statistic of rhythm) of the SAP in normotensive rats grafted with AH embryonic tissue obtained from SHR was accompanied by disappearance of the circadian rhythm of SAP. This result suggests an interaction between the grafted tissue containing the SCN on the one hand, and the host SCN on the other hand. Our data ascribe a role for the SCN in the entrainment of the circadian rhythm of arterial pressure. The circadian rhythm of HR was not eliminated by the SCN graft in spite of the amplitude decrease and the phase delay observed. It seems that the entrainment of the circadian rhythm of HR is probably not crucially dependent on the SCN in rats. The circadian rhythms of SAP and HR in rats were differently affected by the grafts, thus suggesting a multioscillatory system for circadian regulation in rats.