The aim of this study was to generate hemorrhage-triggered fluctuations in blood pressure (BP) at low-frequency (LF, below 0.2 Hz) in conscious rats, and to investigate with spectral analysis the relative roles of hemorrhage-activated catecholamines, the renin-angiotensin system (RAS) and arginine-vasopressin (AVP) on the generation of these fluctuations. After severe hemorrhage (20 ml/kg), the spontaneous BP recovery was characterised by the occurrence of slow fluctuations of systolic and diastolic BP centered around 0.065 Hz. The occurrence of these LF fluctuations was prevented when α₁-adrenergic activity was blocked by Prazosin. These oscillations were always present in spite of inhibition of angiotensin II and were increased after inhibition of the AVP activity. In conclusion, the present results show an association between the secretion of catecholamines resulting from a severe hemorrhage and the occurrence of slow fluctuations of BP. The buffering role of AVP suggest the establishment of a hierarchy between humoral Systems in the genesis of the LF oscillations of BP, with the slow oscillations being generated by the main catecholaminergic pressor system and being dampened by the other systems.