Evaluation of the Hypothalamic Kisspeptin System throughout the Estrous Cycle in Gilts

Kisspeptin has been demonstrated to affect reproductive cyclicity and the attainment of puberty in multiple species, presumably through its actions on gonadotropin releasing hormone and luteinizing hormone. Kisspeptin administration causes increased plasma concentrations of LH in pigs, sheep, and rats. The objective of this experiment was to evaluate changes in the hypothalamic kisspeptin system throughout the estrous cycle in gilts. Estrus was synchronized in forty crossbred gilts (191 d, 121 kg) and estrus detection was performed by exposing gilts to a mature boar. 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, 9, 14, 16, and 19 of the estrous cycle. Ten animals were slaughtered on d 1, 9, 14, and 21 of the estrous cycle when medial basal hypothalami, anterior pituitary glands, and blood were collected. Relative expression of hypothalamic kisspeptin (KISS1), kisspeptin receptor (KISS1R), estrogen receptors-a, anterior pituitary gland GnRH receptor, β-actin, and GAPDH was determined using real-time reverse transcriptase PCR. Fold changes in relative expression were determined using the Relative Expression Software Tool. Relative expression of KISS1 was increased (P = 0.006) 3.2 fold on d 1 versus d 21 and 2.3 fold (P = 0.003) on d 9 versus d 21 of the estrous cycle, but was not different (P > 0.05) among the remaining days of the estrous cycle. Relative expression of estrogen receptor-b was decreased (P = 0.05) 0.8 fold on d 9 versus d 21 and (P = 0.005) 0.7 fold on d 14 versus d 21, but was not different (P > 0.05) among the remaining days. Relative expression of anterior pituitary gland GnRH receptor was increased (P