Effect of Dietary L-Arginine Supplementation on Fetoplacental Vegfr2 Gene Activity and Reproductive Performance in a Bioluminescent Murine Pregnancy Model.

Abstract

Arginine is a conditionally essential amino acid for mature mammals, yet it is considered to be essential for young, developing mammals. Regarded as one of the most versatile amino acids, arginine serves as a precursor for many molecules and has been reported to improve the reproductive performance of rats and pigs. While the mechanism is still unclear, arginine has been proposed to alter angiogenesis during pregnancy. To this end, the objective of this study was to determine whether the beneficial effect that dietary arginine supplementation has on reproductive performance is associated with an alteration of fetoplacental vascular endothelial growth factor receptor-2 (Vegfr2) transcription activity. Homozygous FVB/N-Tg(Vegfr2-luc)-Xen transgenic male mice (Vegf2-luc), genetically modified with a cloned murine Vegfr2 promoter upstream to firefly luciferase, were purchased from Caliper Life Sciences, Inc. (Hopkinton, MA, USA). Eighteen wild-type FVB/N females were bred to Vegfr2-luc males so that only the fetoplacental tissues would possess the Vegfr2-luc transgene. Once bred, females (n=6 per diet) received a control diet (Con) or the diet supplemented with either 2.0% (wt:wt) L-arginine (+Arg), or 4.1% (wt:wt) alanine (+Ala) which served as an isonitrogenous control for the +Arg diet. Body weight and total feed intake were recorded during gestation. Pregnant mice were imaged daily from day 12 to day 18 of gestation to detect luciferase activity as an indicator of Vegfr2 gene expression using the IVIS 100 imaging system (Caliper Life Sciences, Inc.). Number of pups and litter weight were recorded at birth, and the number of placental attachments was determined three weeks postpartum. All data were analyzed using ANOVA followed by Fisher's LSD test for pairwise comparison. The threshold of significance was fixed at P ≤ 0.05 and a tendency at P ≤ 0.10. Total feed intake did not differ significantly between groups; however, animals in the +Arg group consumed more arginine than others (P < 0.05). Arginine supplementation increased weight gain during the latter third of gestation (day 12 to day 18), total litter size, number of pups born alive, number of placental attachment sites, litter birth weight, and litter weight of pups born alive (P < 0.05). Conversely, individual birth weights of pups born alive was less (P < 0.05) in those born to arginine supplemented dams. There was a tendency (P = 0.07) for average total fetoplacental Vegfr2 gene activity to differ between groups, and this effect was significantly greater in the arginine supplemented animals when compared to the animals receiving the isonitrogenous alanine supplemented diet (P < 0.05). When corrected for fetoplacental mass, Vegfr2 gene activity did not significantly differ between groups; however, animals supplemented with arginine displayed an earlier rise in Vegfr2 gene activity. In conclusion, our results demonstrate that the beneficial effect of dietary arginine supplementation on mammalian reproduction is associated with an earlier increase in Vegfr2 transcription activity in fetoplacental tissues. This research was supported by the USDA-ARS Biophotonics Initiative #58-6402-3-0120. (platform)