Arginine enhances embryo implantation in rats through PI3K/PKB/mTOR/NO signaling pathway during early pregnancy.

Our previous study has demonstrated that dietary arginine supplementation during early pregnancy enhanced embryo implantation in rats. However, the mechanism was not clear. The objective of this study was to determine the mechanism that arginine enhanced embryo implantation during early pregnancy. Rats were fed the basal diets supplemented with 1.3% (wt:wt) L-arginine-HCl or 2.2% (wt:wt) L-alanine (isonitrogenous control) once pregnancy. On d4 of pregnancy, rats were given intrauterine injection of L-NG-nitro arginine methyl ester (L-NAME, nitric oxide synthase inhibitor), α-difluoromethylornithine (DFMO, polyamine synthesis inhibitor), wortmannin (PI3K inhibitor), or rapamycin (mTOR inhibitor). On d7 of pregnancy, rats were killed. Intrauterine injection of L-NAME decreased the implantation sites, while dietary arginine supplementation increased the implantation sites. Intrauterine injection of DFMO decreased the pregnancy rate, which was reversed by dietary arginine supplementation. Intrauterine injection of rapamycin or wortmannin inhibited embryo implantation. However, dietary arginine supplementation did not reverse this inhibition. Western blot analysis revealed that the expression of uterine p-PKB and p-S6K1 was greater in rats fed the arginine-supplemented diet in the presence of L-NAME treatment compared with rats fed the control diet. In the presence of DFMO treatment, the expression of uterine iNOS and eNOS was significantly enhanced in the arginine group compared with the control group. Similarly, intrauterine injection of wortmannin or rapamycin decreased the expression of uterine iNOS and eNOS, which was enhanced by dietary arginine supplementation. These data indicated that dietary arginine supplementation during early pregnancy could enhance embryo implantation through stimulation of PI3K/PKB/mTOR/NO signaling pathway.