Abstract

We analyzed tachykinin NK₃ receptor (NK₃R) gene expression by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) in uteri from young (3-month-old) and old (30-month-old) rats. In addition, we characterized the expression of the preprotachykinin-B (TAC-3) gene, which encodes neurokinin B (NKB), the preferred endogenous agonist of NK₃R. Compared with young rats, NK₃R messenger RNA (mRNA) levels were about 45-fold higher in uteri from old animals. TAC-3 mRNA was expressed in the rat uterus, and its levels were about 2.5-fold higher in old than in young rats. The contractile effect of the selective tachykinin NK₃R agonist [MePhe⁷]-NKB in uteri from young and old animals was investigated by using conventional organ bath technique. A marked correlation was observed between the magnitude of the contraction elicited by [MePhe⁷]-NKB and the level of expression determined by RT-PCR for the NK₃R. These observations are consistent with a role for the NKB/NK₃R ligand-receptor pair in regulating uterine functions and support the existence of a link between estrogen and the NK₃R/NKB activation pathway.