Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2010
Publication Date: 10/12/2010
Citation: Barb, C.R., Hausman, G.J., Kraeling, R.R. 2010. Luteinizing hormone secretion as influenced by age and estradiol in the prepubertal gilt. Animal Reproduction Sciences. 122:324-327. Interpretive Summary: The occurrence of puberty in the female pig is the culmination of a serious of events that results in estrus, ovulation and normal luteal function. In pigs, infertility is a major cause of decreased numbers of animals marketed per year, which leads to reduced income and increased economic instability for producers. One of the primary reasons for infertility is that animals fail to exhibit estrous cycles (anestrous) and ovulate. In the prepubertal pig there is negative feedback by ovarian estrogen that prevents the release of gonadotropin-releasing hormone (GnRH), brain hormone that release luteinizing harmone (LH) from the pituitary gland necessary for ovulation. It was demonstrate an age related reduction in the sensitivity to the negative feedback action of ovarian estrogen on LH secretion occurs prior to onset of puberty in the female pig. Thus, understanding these interactions is necessary in order to develop new methods to enhance onset of puberty and reproductive function in the pig.
Technical Abstract: The aim of this study was to determine if there is an age related reduction in the sensitivity of the negative feedback action of estradiol on luteinizing hormone (LH) secretion in the prepubertal gilt. Ovariectomized gilts at 90 (n = 12), 150 (n = 11) or 210 (n = 12) days of age received estradiol benzoate (EB) osmotic pump implants 6/group and the remaining animals received vehicle control (C) implants except for 150-d C (n = 5). Blood samples were collected every 15 min for 8 h and LH and estradiol were measured. Serum estradiol averaged 5' 1, 5' 1 and 7' 2 pg/ml for the 90, 150 and 210 day old gilts implanted with estradiol, respectively, whereas, serum estradiol was undetectable in C gilts. Mean serum LH, basal LH concentrations and LH pulse amplitude were lower at in E treated gilts at all ages compared to control animals. While LH pulse frequency increased (P < 0.05) from 0.8 ± 0.2 to 5.2 ± 0.2 /8 h between 90 and 210 days of age in ED gilts, respectively, whereas LH pulse frequency was similar between 210 day old ED and C gilts. These results demonstrate an age related reduction in the sensitivity to the negative feedback action of estradiol on LH secretion and support the idea that the gilt conforms to the gonadostat hypothesis.