We have previously shown that central vasopressin receptors contribute to cardiovascular (CV) short-term variability in normotensive freely moving rats(1). In this study we investigate the effect of central vasopressin receptor blockade on blood pressure (BP) and heart rate (HR) short-term variability of conscious rats and its relationship to changes in body temperature (Tb) using transfer function. All procedures are in accordance with ECC Directive 86/609. Adult male Wistar outbred rats were anesthetized with xylazine/ketamine anesthesia (0.4ml 10% ketamine IP, 0.1ml 2%xylazine IP per animal) for insertion of TL11M2-PA-C50-PXT DSI implant for concomitant measurement of BP in aorta and Tb subcutaneously. After full recovery under the same anesthesia, rats were chronically instrumented with intracerebroventricular (icv) cannula (1). The role of central vasopressin receptors was assessed using selective nonpeptide V1a, V1b and V2 antagonists injected icv, as described previously (1). At the end of experimentation rats were euthanized with bolus overdose of thiopentone sodium. Arterial BP and Tb were digitalized at 1000Hz. Systolic BP (SBP), diastolic BP (DBP) and HR were derived from the arterial BP as maximum, minimum and inverse of interbeat interval, respectively. Time spectra and transfer function (gain, phase and coherence) were calculated on 15 overlapping 2048 point time series involving 410-s registration period. Spectra were analyzed in very-low-frequency (VLF: 0.0195 – 0.195Hz), low-frequency (LF: 0.195 – 0.8Hz) and high-frequency (HF: 0.8 – 3Hz) range. At neutral ambient temperature (22°C ± 2) 100ng of V1a antagonist increased coherence between Tb and SBP in LF spectral band (0.56 ± 0.03, p < 0.05). Moreover SBP and HR coherence in LF spectral band was increased by 100ng (0.76 ± 0.02, p < 0.05) and 500ng of V1a antagonist (0.8 ± 0.03, p < 0.05). 100ng of V2 antagonist increased coherence between SBP and HR (0.83 ± 0.04, p < 0.05), Tb and SBP (0.74 ± 0.1, p < 0.05) and Tb and HR (0.58 ± 0.03, p < 0.05). 100ng and 500ng of V2 antagonist increased coherence between Tb and SBP in VLF band (0.66 ± 0.15, p < 0.05; 0.59 ± 0.1, p < 0.05). Phase analysis in LF band under V2 receptor blockade indicate that changes in temperature precede those of SBP and HR. In rats exposed to 34°C ± 2 ambient temperature we noted increase of coherence between SBP and HR in LF spectral band under V2 receptor blockade (0.83 ± 0.02, p < 0.05). Results suggest that central V1a and V2 receptors contribute to CV short-term variability in LF and VLF spectral band involving baroreceptor reflex – dependent and – independent thermoregulation, respectively.