Changes in the expression of tachykinin receptors in the rat uterus duringthe course of pregnancy

In the mammalian female reproductive tract, tachykinin neuropeptides, such as substance P (SP), are localized to a population of sensory fibers and th eir precise physiological role is still unknown. The aim of the present stu dy was to characterize the population of tachykinin receptors in the pregna nt rat uterus and to assess their regulation during the course of pregnancy and after delivery. The expression of the tachykinin NK1 receptor (NK1R), the tachykinin NK2 receptor (NK2R), and the tachykinin NK3 receptor (NK3R) in uteri from rats at different stages of pregnancy and on Day 1 postpartum was investigated by using a semiquantitative reverse transcription-polymer ase chain reaction. The contractile effect of tachykinin receptor agonists acting selectively on the NK1R, the NK2R, or the NK3R was investigated by c onventional organ bath techniques, Serum levels of estrogen and progesteron e were measured by RIA. Our data show that the expression and function of N K1R and NK3R varied along the course of pregnancy and at postpartum. Uterin e NK2R mRNA levels remain stable during the course of pregnancy and at Day 1 postpartum; and the contractions elicited by activating selectively the N K2 receptor in the presence of the neutral endopeptidase inhibitor phosphor amidon (1 muM) were similar in early, mid, or late pregnancy. These results show that the expression and function of tachykinin receptors within the u terus vary with reproductive state and length of gestation, supporting a ro le for tachykinins in pregnancy and/or parturition in the rat.