An endogenous antipyresis has been observed around parturition in several species, including rats. It has been proposed that the neuropeptide vasopressin is responsible for this antipyresis via an action on the V(1a) receptor subtype, but this concept is controversial. We therefore addressed the question of the regulation of V(1a) receptor expression within the rat hypothalamus around parturition, to assess its possible involvement in the antipyresis phenomenon observed at term. We analyzed V(1a) receptor mRNA and protein levels in the hypothalamus/preoptic area of female rats at Days 15 and 22 (parturition) of gestation, and at Day 5 of lactation. We used quantitative RT-PCR to assess the mRNA levels and designed a semiquantitative Western blot assay to analyze changes in protein levels between the three stages studied. No significant changes either in V(1a) receptor mRNA or protein levels were observed between the three stages, suggesting that variations in the hypothalamic V(1a) receptor expression levels alone cannot account for the endogenous antipyresis observed at term.