Peroxisome proliferator-activated receptor γ is involved in weaning to estrus of primiparous sows by regulating the expression of hormone genes in hypothalamus-pituitary-ovary axis

Abstract

The objective of this study was to determine whether peroxisome proliferator-activated receptor γ (PPARγ) is involved in the regulation of weaning to estrus of primiparous sows. Twelve sows composed of 6 groups of 2 full-sibs in a similar age (325.2 d), body weight (BW; 152.4 kg) and backfat thickness (BFT; 27.0 mm) at start of lactation, were allocated to accept 31 MJ (restricted group, R-group) or 53 MJ (control group, C-group) DE/d treatment, respectively. The experimental results indicated that the low energy intake resulted in excessive losses of BW and BFT during lactation in R-group sows, which may be related to decrease of serum 15-deoxy-Δ 12,14-prostaglandin J2 (15d-PGJ2), a ligand of PPARγ. The obvious peak and the frequency of LH, FSH and estradiol (E 2) were only observed in C-group sows. Except for E2 at d 1 and 2, serum FSH, LH and E2 concentrations in R-group were lower than those in C-group sows after weaning. However, the serum progesterone (P4) level in R-group sows was always more than that in C-group. The expression abundances of PPARγ and GnRH receptor (GnRH-R) in pituitary, FSH receptor (FSH-R), LH receptor (LH-R), estrogen receptor (ES-R) and aromatase in ovary of anestrous sows were lower than those of estrous sows. Neither the BFT nor the BW was associated with the mRNA abundance of PPARγ in hypothalamus during lactation. Expressions of PPARγ in pituitary and ovary were affected evidently by the BFT changes and only by the loss of BW of sows during and after lactation. Furthermore, PPARγ mRNA level in ovary was significantly related to the expression abundances of GnRH-R, FSH-R, ES-R and aromatase, and GnRH-R was obviously associated with PPARγ expression in pituitary. However, PPARγ expression in hypothalamus likely has no effects on these genes expression and no obvious difference for all sows. Not serum E2 or P4 alone but the ratios of E2 to P 4 and 15d-PGJ2 to P4, and serum FSH and LH were evidently related to PPARγ expression in pituitary and ovary. It is concluded that PPARγ is associated with body conditions, reproduction hormones and their receptor expression, which affected the functions of pituitary and ovary and ultimately the estrus after weaning of primiparous sows.