02846naa a2200265 a 450000100080000000500110000800800410001910000190006024501080007926000090018752021040019665000170230065000190231765000100233665000140234665000240236065300110238470000180239570000190241370000200243270000160245270000160246870000210248477300750250515288682002-11-22       1998    bl uuuu     u00u1 u    #d1 aJUENGEL, J. L.  aSteady-state concentrations of mRNA encoding two inhibitors of protein kinase C in ovine luteal tissue.  c1998  aProstaglandin F 2alpha (PGF 2alpha) decreases secretion of progesterone from the corpus luteum in domestic ruminants. However, it is less effective during the early part of the oestrous cycle (Louis et al., 1973) and at the time of maternal recognition of pregnancy (Silvia and Niswender, 1984; Lacroix and Kann, 1986). Decreased luteal responsiveness mar be due to failure of PGF 2alpha to activate fully its normal second messenger system, protein kinase C (PKC). Alternatively, increased resistance of the corpus luteum to PGF2alpha might be attributable to greater concentrations of recently identified biological inhibitors of PKC. These possibilities were addressed by measuring steady-state concentrations of mRNA encoding PGF2alpha receptor and two inhibitors of PKC, protein kinase C inhibitor-l (PKCI-l) and kinase C inhibitor protein-l (KCIP-l, brain 14~3-3 protein), in corpora lutea collected from ewes on days 4, 10 and 15 of the oestrous cycle (n = 5 per day) and day 15 of pregnancy (n = 7). There were no differences in mean concentrations of mRNA encoding PGF2alpha receptor among the groups. However, concentrations of mRNA encoding both inhibitors of PKC were higher (P &lt 0.01) on day 4 of the oestrous cycle compared with the other groups. Treatment of ewes with a luteolytic dose of PGF2", which activates PKC, did not change concentrations of mRNA encoding either PKCI-l or KCIP-I up to 24 h later. Luteal expression of mRNA encoding the PKC inhibitors and PGF2alpha receptor was also examined in ewes treated with oestradiol in vivo for 16 h in the midluteal phase. High concentrations of oestradiol in serum (20 and 70 pg ml-1 did not influence quantities of any of the mRNAs examined. Therefore, an increase in PKC inhibitors mar be involved in resistance of the corpus luteum to PGF2alpha during the early part of the oestrous cycle but does not appear to mediate the increased resistance of the corpus luteum to PGF2alpha during maternal recognition of pregnancy. Neither PGF2alpha nor oestradiol affected steady-state concentrations of mRNAs encoding PKCI-l or KCIP-I.  aCorpo Lúteo  aEndocrinologia  aOvino  aProteína  aReprodução Animal  aKinase1 aMELNER, M. H.1 aCLAPPER, J. A.1 aTURZILLO, A. M.1 aMOSS, G. E.1 aNETT, T. M.1 aNISWENDER, G. D.  tJournal of Reproduction and Fertilitygv. 113, n. 2, p. 299-305, 1998.