Dietary L-arginine supplementation enhance myofiber hyperplasia

Abstract Text: Supplementing the gestation diet with L-arginine positively affects primary myofiber hyperplasia in the semitendinosus muscles (STM) of 75-d old fetuses. Because primary fibers serve as a scaffold for secondary fiber formation we hypothesized that offspring from sows fed extra arginine bare the potential for greater secondary fiber hyperplasia. Impaired fiber hyperplasia is observed especially in piglets subjected to intra uterine growth retardation and/or intra uterine crowding. Thus, the goal of this experiment was to establish if arginine supplementation of the dams has a positive effect on muscle development of their low birth weight offspring. For the experiment 5 intact (I), 5 unilaterally hysterectomized-ovariectomized (HO) and 5 unilaterally ovariectomized (OL) sows were subjected to a crossover design in terms of diets (parities 5 and 6). From d 14 to 28 of gestation they were either offered 25 g/d of L-arginine (Arg) in addition to the standard gestation diet or they received the corresponding control diet (C). At farrowing, from each litter, 2 female and 2 male piglets with the lowest and medium birth weight were sacrificed. Internal organs and the STM were collected and weighed. Histological analyses of muscles were performed using mATPase staining after pre-incubation at pH 4.5 and 10.2. Compared to OL, progeny from OH and I sows had lower (P < 0.05) relative weights of liver (2.90 vs. 2.33; 2.30), kidney (0.84 vs. 0.73; 0.72) and STM (2.30 vs. 2.09; 1.95) and a greater (P < 0.05) brain-to-liver ratio (0.80 vs. 1.25; 1.46). The latter is also known as brain sparing and is indicative of intrauterine growth retardation. Independent of the sow group, brain-to-liver ratios (1.12 vs. 1.22) tended (P < 0.08) to be lower in offspring from Arg compared to C sows, which suggest that L-arginine supplementation alleviated the effect of intrauterine growth retardation. Supplying Arg to I and OL, but not OH, sows instead of C resulted in greater myofiber hyperplasia and larger muscle area. These differences resulted mainly from a greater myofiber number in the light portion (3.50 vs. 3.24 × 10⁵ P < 0.05) of the muscle. The current finding confirms previous assumptions that arginine supply during early gestation positively affects muscle formation.

Keywords: L-arginine, myofiber hyperplasia, pig