Intravenous maternal L-arginine administration to twin-bearing ewes, during late pregnancy, is associated with increased fetal muscle mTOR abundance and post-natal growth in twin female lambs

The aims of this study were to determine whether well-fed twin-bearing ewes administered parenteral arginine (Arg), from 100 to 140 days of pregnancy, improves fetal skeletal muscle growth, influences the abundance and activation of mechanistic target of rapamycin (mTOR) protein, and postnatal muscle growth of the offspring. Ewes fed 100% of NRC-recommended nutrient requirements for twin-bearing ewes were administered an intravenous bolus of either 345 µmol Arg-HCl/kg body weight or saline solution (Control) 3 times a day. At 140 days of pregnancy (P140), a group of 11 control and 9 Arg-treated ewes were euthanized and hind leg muscles and M. longissimus dorsi (LD) were excised and weighed. A sample from LD was snap frozen in liquid nitrogen for later analysis of free AA (FAA) concentration, mTOR abundance and phosphorylation and biochemical indices (DNA, RNA and protein content). For the remaining 25 ewes (Arg n = 13; Control n = 12), Arg administration was continued until the initiation of parturition and ewes were allowed to lamb. Lambs were weaned at postnatal day 82 (PN82) and grazed on pasture until PN153, when a subset of 20 lambs (n = 10 per group) were euthanized. At P140 only the Psoas major was heavier in the Arg administered group compared to the control group. Females from Arg-treated ewes (Arg-F) had increased abundance of total mTOR, RNA concentration and RNA: DNA ratio in LD compared to females from Control group (Con-F) while males did not differ. At PN153, Arg-F lambs were heavier than Con-F and had heavier LD, plantaris and a trend for heavier psoas major muscles compared to Con-F. In contrast, live weight and individual muscle weights did not differ in male lambs. Lambs from Arg-treated ewes had heavier semimembranosus and tended to have heavier biceps femoris compared to control lambs. The RNA concentration in LD was greater in Arg-F compared to Con-F and DNA concentration was greater in Arg compared to control group. In conclusion Arg administration of the ewe during gestation increases female lamb weight and muscle weight after birth, these changes are associated with altered mTOR protein abundance, and have potential implications for sheep production.