Effects of l-arginine on endometrial microvessel density in nutrient-restricted Hu sheep

Nutrient deficiency in ruminants can lead to estrus cycle disorders, a decreased pregnancy rate, and reduce birth weight. l-arginine (L-Arg), an important amino acid, can improve uterine homeostasis in pregnant sheep and prevent intrauterine growth restriction (IUGR). However, most studies of L-Arg have been conducted on pregnant sheep and few have reported the effects of L-Arg on microvessel density (MVD) in the non-pregnant ovine endometrium. The processes of normal uterine cyclical development and implantation are dependent on a balanced of endometrial MVD. In this study, female Hu sheep were randomly assigned to either a control group (n = 6), a nutrient-restricted group (n = 6), or an L-Arg supplemented nutrient-restricted group (n = 6). The effects of L-Arg on MVD in ovine endometrium were then studied. Our results showed that ovine endometrial MVD was significantly increased by nutrient restriction, but L-Arg counteracted the effect of nutrient restriction on MVD (P < 0.05). Levels of angiogenic growth factors (including VEGFA, VEGFR2, and FGF2) had significant increases (P < 0.05) in endometrium of nutrient restriction on sheep, but that L-Arg supplementation substantially decreased (P < 0.05) their expressions in nutrient restriction sheep. Furthermore, oxidative stress caused by nutrient restriction was also alleviated by L-Arg supplementation in the ovine endometrium. Overall, the results suggested that L-Arg has crucial roles in maintaining the balance of endometrial MVD and angiogenic growth factors, and increasing anti-oxidation capability in the endometrium of nutrient-restricted sheep. This study will provide a theoretical basis and technical means for the normal development of endometrial microvessels in low nutrition level.