Evaluation of the hypothalamic kisspeptin system throughout the estrous cycle in gilts

Abstract Text: Kisspeptin has been demonstrated to increase peripheral concentrations of LH in pigs, presumably by its actions on GnRH, as has been demonstrated in other species. To determine if hypothalamic expression of kisspeptin (Kiss1), kisspeptin receptor (Kiss1R), estrogen receptor alpha (ER-α), and estrogen receptor beta (ER-β) varies throughout the estrous cycle, the following experiment was performed. Forty crossbred prepubertal gilts of similar age (191 d) and weight (121 kg) were administered an intramuscular injection of PG600 (200 IU human chorionic gonadotropin and 400 IU equine chorionic gonadotropin). Twelve days after the administration of PG600, gilts were fed 15 mg of altrenogest (Matrix) daily for 15 days to synchronize estrus. Estrus detection was performed by exposing gilts to a mature boar beginning 4 days after the cessation of altrenogest and continuing for 4 days. The first day gilts stood immobile was denoted d 1 of the estrous cycle. Blood samples were collected via jugular venipuncture on d 1, 4, 7, 10, 13, 16, 19, and 21 of the estrous cycle. Ten animals were slaughtered on d 1, 9, 14, and 21 of the estrous cycle, when hypothalami, anterior pituitary glands, and blood were collected. Relative expression of hypothalamic Kiss1, Kiss1R, ER-α, ER-β, and β-actin was determined using real-time reverse transcriptase PCR. Fold changes in relative expression were determined using the Relative Expression Software Tool. Relative expression is based on the expression ratio of a target gene versus a reference gene. The expression ratio results of the investigated transcripts were tested for significance by a Pair Wise Fixed Reallocation Randomized Test with day compared as independent time effects. Relative expression of Kiss1 was increased (P<0.05) 3.2 fold on d 1 versus d 21 and 2.3 fold on d 9 versus d 21 of the estrous cycle. Relative expression of Kiss1 was not different (P>0.05) among the remaining days. Relative expression of ER-β was decreased (P<0.05) 0.8 fold on d 9 versus d 21 and 0.7 fold on d 14 versus d 21. Relative expression of ER-β was not different (P>0.05) when comparing the remaining slaughter days. Relative expression of Kiss1R and ER-α were each not different (P>0.05) among days. These data provide preliminary evidence that hypothalamic expression of kisspeptin varies throughout the porcine estrous cycle, which may modulate the subsequent release of GnRH.

Keywords: kisspeptin; hypothalamus; pig