Dietary supplementation with 0.4% L-arginine between days 14 and 30 of gestation enhances NO and polyamine syntheses and water transport in porcine placentae.
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BACKGROUND: Most embryonic loss in pigs occurs before d 30 of gestation. Dietary supplementation with L-arginine (Arg) during early gestation can enhance the survival and development of conceptuses (embryo/fetus and its extra-embryonic membranes) in gilts. However, the underlying mechanisms remain largely unknown. METHODS: Between d 14 and 30 of gestation, each gilt was fed daily 2kg of a corn- and soybean-meal based diet (12% crude protein) supplemented with either 0.4% Arg (as Arg-HCl) or an isonitrogenous amount of L-alanine (Control). There were 10 gilts per treatment group. On d 30 of gestation, gilts were fed either Arg-HCl or L-alanine 30min before they were hysterectomized, followed by the collection of placentae, embryos, fetal membranes, and fetal fluids. Amniotic and allantoic fluids were analyzed for nitrite and nitrate [NOx; stable oxidation products of nitric oxide (NO)], polyamines, and amino acids. Placentae were analyzed for syntheses of NO and polyamines, water and amino acid transport, concentrations of amino acid-related metabolites, and the expression of angiogenic factors and aquaporins (AQPs). RESULTS: Compared to the control group, Arg supplementation increased (P<0.05) the number of viable fetuses by 1.9 per litter, the number and diameter of placental blood vessels (+25.9% and+17.0% respectively), embryonic survival (+18.5%), total placental weight (+36.5%), the total weight of viable fetuses (+33.5%), fetal crown-to-rump length (+4.7%), and total allantoic and amniotic fluid volumes (+44.6% and+75.5% respectively). Compared to control gilts, Arg supplementation increased (P<0.05) placental activities of GTP cyclohydrolase-1 (+33.1%) and ornithine decarboxylase (+29.3%); placental syntheses of NO (+26.2%) and polyamines (+28.9%); placental concentrations of NOx (+22.5%), tetrahydrobiopterin (+21.1%), polyamines (+20.4%), cAMP (+27.7%), and cGMP (+24.7%); total amounts of NOx (+61.7% to+96.8%), polyamines (+60.7% to+88.7%), amino acids (+39% to +118%), glucose (+60.5% to+62.6%), and fructose (+41.4% to+57.0%) in fetal fluids; and the placental transport of water (+33.9%), Arg (+78.4%), glutamine (+89.9%), and glycine (+89.6%). Furthermore, Arg supplementation increased (P<0.05) placental mRNA levels for angiogenic factors [VEGFA120 (+117%), VEGFR1 (+445%), VEGFR2 (+373%), PGF (+197%), and GCH1 (+126%)] and AQPs [AQP1 (+280%), AQP3 (+137%), AQP5 (+172%), AQP8 (+165%), and AQP9 (+127%)]. CONCLUSION: Supplementing 0.4% Arg to a conventional diet for gilts between d 14 and d 30 of gestation enhanced placental NO and polyamine syntheses, angiogenesis, and water and amino acid transport to improve conceptus development and survival.
