Reproduction25 Na+ /K + ATPase as a signaling molecule during bovine spermcapacitationCorresponding AuthorBuhr, M.M.University of GuelphCollaboratorsThundathil, J.C.University of GuelphAnzar, M.University of GuelphBiology of Reproduction (2006) Vol. <strong>75</strong> p. 308-317.After entering the female reproductive tract, spermatozoa undergo a shortperiod of ‘capacitation’ in preparation for inseminating an ovum. The contributionsto this process of the various enzymes found in sperm are notwell understood. The objective of this study was to elucidate the role incapacitation of an enzyme commonly found in the plasma membranes ofmany body cells. Of the 4 forms of the enzyme Na + /K + ATPase that havebeen identified, two (ATP1A1 and ATP1A4) have been found in spermatozoaand inhibition of ATP1A4 has been shown to eliminate sperm motility.In other tissues, Na + /K + ATPase is involved in the maintenance of ionicgradients across cell membranes. In heart muscle, the enzyme is importantfor the restoration of calcium ion concentrations after contraction. It has recentlybeen shown that Na + /K + ATPase acts in cell signalling, independentof its action on ionic gradients. When cardiac muscle cells are treated withouabain, a drug that blocks the activity of Na + /K + ATPase, cellular responsesare similar to those associated with sperm capacitation. In the presentstudy, ouabain inhibited motility and induced sperm capacitation throughthe actions of Na + /K + ATPase on depolarization of the cell membrane andcell signalling without provoking an appreciable increase in intracellularcalcium.26Pregnancy, bovine somatotropin, and dietary n-3 fatty acids inlactating dairy cowsCorresponding AuthorThatcher, W.W.University of FloridaCollaboratorsBilby, T.R.University of FloridaGuzeloglu, A.University of FloridaMacLaren, L.A.Nova Scotia Agricultural CollegeStaples, C.R.University of FloridaJournal of Dairy Science (2006) Vol. 89 p. 33<strong>75</strong>-3385.At about 17-18 days after the cow ovulates, either another estrous cyclewill be set into motion by luteolysis (regression of the corpus luteum, CL) orthe CL will survive to support a latent pregnancy. Although the agent thatultimately provokes luteolysis is prostaglandin F2-alpha (PGF 2α ), a cascadeof signals and enzyme activity changes is required to increase the PGF 2αconcentration adequately. If pregnancy has been initiated, the conceptuswill secrete a level of interferon-tau (IFN-τ) sufficient to block PGF 2α synthesis.IFN-τ achieves this by inhibiting the synthesis of both estrogen andoxytocin receptors (OTR) in the uterine endometrium. Lowered OTR activityreduces oxytocin induced PGF 2α synthesis by reducing the activities ofkey synthetic enzymes. The objective of this study was to characterize theeffects of recombinant bovine somatotropin (rbST), pregnancy and dietaryomega-3 polyunsaturated long chain fatty acids (ω3 PUFA) on the eventscontrolling PGF 2α synthesis at the time when luteolysis would normally occurin non-pregnant cows. Both rbST and pregnancy changed expressionpatterns of the genes controlling the cascade of events influencing PGF 2αsynthesis compared with patterns observed in cyclic cows. Supplementationof diets with ω3 PUFA also reduced factors regulating PGF 2α synthesisin cyclic cows that would favour the establishment and maintenance ofpregnancy.120 Highlights in Canadian Dairy Cattle Research - 2007
Reproduction27Impact of a progesterone-releasing intravaginal device on plasmaprogesterone levels in lactating dairy cowsCorresponding AuthorKeefe, G.P.Atlantic Veterinary CollegeCollaboratorsSquires, E.J.University of GuelphWalsh, R.University of GuelphWilson, J.B.University of GuelphLeslie, K.E.University of GuelphBovine Practitioner (2006) Vol. 40 p. 108-112.The administration of progesterone (P4) to cows experiencing normalheat cycles suppresses estrous activity. When the P4 level falls, the cycleresumes and many studies have demonstrated higher fertility levels afterP4 treatment. The progesterone-releasing intravaginal device (PRID) is particularlyeffective in this regard as its withdrawal results in a rapid drop in P4activity. Although it has been assumed that the effectiveness of the PRIDis mediated by changes in circulating P4, actual measurement of peripheralblood P4 concentrations have not been reported. In this study, PRIDswere administered to lactating cows on day 25 or 31 after first observedestrus and withdrawn 14 days later. Peripheral blood was collected dailyfrom first estrus until 56 hours after PRID withdrawal. Blood of untreatedcontrol cows was sampled every second day from first observed estrusuntil a second estrus was observed. P4 response was assessed as the areaunder the curve (AUC) of plasma P4 concentration plotted against time.AUC was similar in control and treated cows before PRID insertion but wassignificantly greater for treated cows after insertion. In cows receiving aPRID 31 days post-estrus, maximum plasma P4 concentration was higherafter than before insertion.Reproduction 121
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