Abstract
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
Highlights
Gonadotropin releasing hormone (GnRH) is a decapeptide hormone essential to reproduction through its actions on the release and synthesis of gonadotropins [1] [2] [3]
Kisspeptin may elicit the direct release of GnRH because it has been found that kisspeptin neuronal axons are associated with the dendrites of GnRH neurons [2]
It has been shown that the kisspeptin receptor, GPR54, is expressed by GnRH neurons and is directly stimulated by kisspeptin to cause the release of GnRH [4]
Summary
Gonadotropin releasing hormone (GnRH) is a decapeptide hormone essential to reproduction through its actions on the release and synthesis of gonadotropins [1] [2] [3]. Circulating concentrations of gonadotropins fluctuate throughout the estrous cycle and stimulate ovarian follicular development, while lutenizing hormone (LH) in particular is luteotrophic in many species and is responsible for causing ovulation. It is widely accepted that progesterone and estradiol −17 b control the release of gonadotropins through positive and negative feedback, the exact mechanisms by which this occurs are not clear. The release of GnRH may be controlled by other hormones, one of which is kisspeptin. Kisspeptin may elicit the direct release of GnRH because it has been found that kisspeptin neuronal axons are associated with the dendrites of GnRH neurons [2]. It has been shown that the kisspeptin receptor, GPR54, is expressed by GnRH neurons and is directly stimulated by kisspeptin to cause the release of GnRH [4]
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