Increase in neurokinin B expression and in tachykinin NK(3) receptor-mediated response and expression in the rat uterus with age.

We analyzed tachykinin NK(3) receptor (NK(3)R) 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 NK(3)R. Compared with young rats, NK(3)R 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 NK(3)R agonist [MePhe(7)]-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 [MePhe(7)]-NKB and the level of expression determined by RT-PCR for the NK(3)R. These observations are consistent with a role for the NKB/NK(3)R ligand-receptor pair in regulating uterine functions and support the existence of a link between estrogen and the NK(3)R/NKB activation pathway.

Expression of preprotachykinin-B, the gene that encodes neurokinin B, in the rat uterus.

Neurokinin B, a peptide belonging to the tachykinin family, is undetectable in peripheral tissues from nonpregnant animals. In the present study, we analysed the expression of the preprotachykinin-B (PPT-B) gene, which encodes neurokinin B, in the rat uterus. Preprotachykinin-B mRNA was expressed in the uterus and its levels varied greatly depending upon the hormonal conditions. This is consistent with a role of this tachykinin in the regulation of uterine functions.

Hormonal regulation of the contractile response induced by okadaic acid in the rat uterus.

The contractile effect of okadaic acid (OA), a highly selective inhibitor of protein serine/threonine phosphatases, was analyzed in the rat uterus during the estrous cycle and during the course of pregnancy. Contractile effects were related to circulating levels of estrogen and progesterone and to mRNA levels of myosin light chain kinase (MLCK) and of myosin light chain protein phosphatase catalytic (PP1-delta) and larger regulatory subunit (MYPT). Both in nonpregnant and pregnant uteri, OA (20 microM) induced a transient contraction, which after plateauing, slowly decreased. In the nonpregnant uterus, the amplitude of this contraction varied at different stages of the estrous cycle, being higher at proestrus and lower at diestrus. In the pregnant uterus, the contraction to OA increased significantly during the course of pregnancy, reaching a maximum in day 21 pregnant rats, and declined after delivery. Whatever the day of pregnancy, the amplitude of the contraction to OA was not significantly modified when obtained in Ca(2+)-free solution. The magnitude of the OA-induced contraction in spontaneously cycling and pregnant rats was positively correlated to the ratio of estrogen/progesterone serum levels. Reverse transcription-polymerase chain reaction assays on myometrial tissue demonstrated that mRNA expression of PP1-delta and MYPT was higher at early (day 3) than at late (day 21) pregnancy. MLCK mRNA levels were similar in day 3 and day 21 pregnant rats. These data suggest that changes in the expression and activity of myosin phosphatase may contribute to modulating the level of uterine contractile force during the estrous cycle, pregnancy, and labor.

Differential expression of amiloride-sensitive Na+ channel subunits messenger RNA in the rat uterus.

The expression of the amiloride-sensitive Na+ channel was investigated by reverse transcription-polymerase chain reaction (RT-PCR) in uteri from pregnant and non-pregnant rats. Three subunits (alpha,beta,gamma) of this epithelial Na+ channel have been characterized in the rat. All three subunit mRNAs were present in day 16 pregnant uteri while only alpha and beta subunit mRNAs were detected in uteri from non-pregnant or day 1 postpartum rats. The level of expression of the alpha subunit was similar in day 16 pregnant and non-pregnant animals while the level of expression of the beta subunit was higher in pregnant than in non-pregnant rats. These findings show that amiloride-sensitive Na+ channels are expressed in the rat uterus and that mRNA expression levels of the alpha, beta and gamma subunits are selectively and differentially regulated during pregnancy in the rat.