Effects of diet and arginine treatment during the luteal phase on ovarian NO/PGC-1α signaling in ewes

The aim of this study was to determine whether arginine (Arg) supplementation of malnourished ewes affects the expression of key NO/PGC-1α signaling pathway genes in the ovary. On Day 6-15 of the estrous cycle, 24 multiparous Hu sheep (BW = 43.56 ± 1.53 kg) were randomly assigned to three groups: control group (CG; n = 6), restriction group (RG; n = 9) and l-arginine group (AG; n = 9), and administered Arg treatment (or vehicle) three times per day. The ewes were slaughtered at the end of treatment, and blood samples and ovaries were collected for analysis. The results of our analyses showed that both short-term feed-restriction and/or supplementation with L-Arg-HCl affected the number of different size follicles observed in the ovary, and the relative day of estrus behavior initiation of ewes. Specifically, the relative day of estrus behavior initiation was significantly advanced in AG compared with that in RG ewes (P 0.05). Both the number of ≤2 mm-ovarian follicles (P 0.05) and the total number of ovarian follicles (P 0.05) were significantly increased in the RG and AG compared with that in the CG ewes. RG ewes exhibited a higher proportion of ≤2 mm (P 0.05), but a lower proportion of5 mm follicles than did CG ewes (P 0.05). The mean number of corpus lutea ≥5 mm was significantly increased in AG as compared to that in either CG or RG ewes. Furthermore, the expression of eNOS, nNOS, iNOS, PDE5A, PDE9A, PRKG2, and PPARGC1A varied significantly among the treatment groups (P 0.05). GUCY1A3 mRNA levels were significantly increased in RG and AG as compared to those in CG ewes (P 0.05), whereas conversely, GUCY1B3 mRNA levels were significantly decreased in CG and RG as compared to those in AG ewes (P 0.05). P53 mRNA levels were found to vary significantly among the three experimental treatment groups (P 0.05), and similarly, the relative expression levels of P53 were greater in AG and RG than in CG ewes (P 0.05). The levels of eNOS protein were significantly higher in RG than in either CG or AG ewes (P 0.05). The relative expression levels of PGC-1α were significantly higher in RG (P 0.05) and significantly lower in AG ewes (P 0.05) than in CG ewes. In conclusion, the results of the present study indicate that feed-restriction negatively affects follicular development, and that Arg-supplementation may modulate the expression of key NO/PGC-1α signaling pathway genes in the ovary and thereby accelerate ovulatory processes and the estrous rate. Elucidation of mechanisms underlying these effects of Arg on gene expression in the ewe ovary requires further investigation.