Kisspeptin induces ovulation in heifers under low plasma progesterone concentrations
Introduction
The hypothalamo-pituitary-gonadal axis controls follicular development primarily by changes in pulsatile release of GnRH from the hypothalamus that induces downstream LH and FSH secretion from the pituitary gland. In turn, gonadotropins influence the pattern of steroid synthesis from ovarian cells [[1], [2], [3]] which provides positive and negative feedback on GnRH release and gonadotropin hormone synthesis and release. Because of a negative feedback effect, circulating concentrations of progesterone are inversely related to LH release [4,5]; hence, low concentrations of progesterone (less negative feedback) are associated with increased GnRH neuron activity and an increase in frequency of gonadotropin hormone pulses [[6], [7], [8], [9]]. However, there appears to be no direct link between sex steroid hormones and GnRH neurons in the hypothalamus since there is an absence of estradiol receptors alpha and progesterone receptors on GnRH neurons [10,11]. In 2003, the discovery that alterations of the kisspeptin/GPR54 system were associated with reproductive disturbances and idiopathic hypothalamic hypogonadism created a new understanding of steroidal control of GnRH release and its fundamental effect on reproductive physiology [12,13].
In rats, kisspeptin cells were closely associated with GnRH neurons that expressed the kisspeptin receptor GPR-54 [14,15]. In search of the bioactive portion of the 145-amino acid peptide, kisspeptin has been proteolytically cleaved into shorter peptides of 54-amino acids (kisspeptin-54) and 14-, 13- and 10-amino acids (kisspeptin-14, kisspeptin-13, kisspeptin-10) [16]. Bioactivity appears to be confined primarily to kisspeptin-10 since, in rats and sheep, administration of this short segment induced GnRH neuron activation, release of GnRH in the portal circulation, and a rise in plasma gonadotropin concentrations [15,17]. Administration (intraperitoneal, intravenous and subcutaneous) of kisspeptin 10 induced a marked increase in plasma concentrations of LH and FSH in several species including goats, sheep, mice and primates [[18], [19], [20], [21], [22]]. Continuous intravenous administration of kisspeptin over a period of 30 or 48 h induced ovulation in sheep during the anovulatory season [19]. The effectiveness of prolonged treatment, or the lack of effectiveness of short treatments, has been attributed to the short half-life of kisspeptin in circulation [23,24]. Predicted bovine kisspeptin-10 amino acid sequence is identical to murine C-terminal decapeptide and differs from human sequence by one amino acid [16]. While there is only slight variation among mammalian species in the sequence of the final 10 amino acids (i.e., the biologically-active fragment) at the C-terminal part of kisspeptin [16], the biological effect of heterospecific kisspeptin-10 sequences has not been critically examined in cattle [25,26].
The objective of this study was to compare the effect of a single iv bolus versus multiple doses of a 10-amino acid fragment of human or murine kisspeptin on LH secretion and the fate of the dominant follicle (ovulation, growth rate, regression and time to next wave emergence) during development in a low-progesterone environment. We predicted that 45 mg of kisspeptin-10 (administered as a single iv dose or given by multiple doses over a 2 h period) would elicit a surge in plasma LH leading to ovulation of the dominant follicle. We tested the hypotheses that (1) a single dose of murine kisspeptin-10 (homolog to the predicted bovine kisspeptin-10 sequence) will induce a greater response than human kisspeptin-10, (2) multiple-dose treatment with kisspeptin-10 (total dose of 45 mg) will induce a greater rise in plasma LH concentration and more ovulations than a single dose, and (3) multiple-dose murine kisspeptin-10 will induce ovulations at a rate comparable to that of GnRH treatment.
Section snippets
Animals
Three experiments were conducted on sexually mature Hereford cross-bred heifers. Experiment 1 was done on 30 heifers (455 ± 12 Kg body weight, 14–16 months of age) during the Spring (May–June). Experiment 2 was done on 24 heifers (426 ± 8 Kg body weight, 17–18 months of age) in the Summer (July–August). Experiment 3 was done on 18 heifers (426 ± 10 Kg body weight, 19–20 months of age) in the Fall (September–October). The animals were maintained in outdoors pens at the University of Saskatchewan
Experimental model
To validate the experimental protocol of dominant follicle development, data from the control groups in Experiment 1 (n = 10) and Experiment 2 (n = 6) were combined. The mean dominant follicle profile from wave emergence to ovulation after CIDR removal is shown in Fig. 2. The dominant follicle continued to grow from the day of wave emergence (Day 0) to Day 14. Ovulation did not occur in any of the heifers until after removal of the CIDR. The maximum diameter of the dominant follicle was
Discussion
Estrus synchronization, fixed-time artificial insemination, and management of embryo donors and recipients require exogenous control of ovarian follicular wave emergence and ovulation. Both single and multiple iv doses of human and murine kisspeptin-10 increased plasma LH concentrations, but the ovulation rates differed depending on the frequency of treatment. We found that: 1) a single dose of human kisspeptin-10 increased plasma LH concentration more than the bovine predictor sequence (i.e.,
Conflicts of interest
The authors declare that they have no competing interests.
Authors’ contributions
Carlos E.P. Leonardi participated in designed of study, collection, analysis and interpretation of data, and in writing and revising the manuscript. Fernanda C.F. Dias participated in design of study, interpretation of data and revising the manuscript. Estela R. Araujo participated analysis and interpretation of data, as well as, in writing and revising the manuscript. Gregg P. Adams participated in designing the study, interpretation of data and revising the manuscript. As Principal
Acknowledgements
The research was supported by grant from the Natural Sciences and Engineering Research Council of Canada. Carlos Leonardi was financially supported by CAPES scholarship from the Ministry of Education of Brazil. We thank Taryn Roberts, Dr. Rodrigo Carrasco and Eric Zwiefehofer for assistance with data collection, and Dr. OJ Ginther for all support to analyse LH and Progesterone concentrations.
References (42)
- et al.
New evidence for estrogen receptors in gonadotropin-releasing hormone neurons
Front Neuroendocrinol
(2001) - et al.
Peripheral administration of metastin induces marked gonadotropin release and ovulation in the rat
Biochem Biophys Res Commun
(2004) - et al.
Characteristics of stimulation of gonadotropin secretion by kisspeptin-10 in female goats
Anim Reprod Sci
(2010) - et al.
Trypsin resistance of a decapeptide KISS1R agonist containing an Nomega-methylarginine substitution
Bioorg Med Chem Lett
(2012) - et al.
Ultrasonography of the bovine ovary
Theriogenology
(1984) - et al.
Surges of FSH during the follicular and early luteal phases of the estrous cycle in heifers
Theriogenology
(1997) - et al.
Plasma-lh and Fsh after estradiol, norgestomet and gn-Rh treatment in ovariectomized beef heifers
Anim Reprod Sci
(1990) - et al.
Selection of the dominant follicle in cattle: establishment of follicle deviation in less than 8 hours through depression of FSH concentrations
Theriogenology
(1999) - et al.
The metastasis suppressor gene KiSS-1 encodes kisspeptins, the natural ligands of the orphan G protein-coupled receptor GPR54
J Biol Chem
(2001) - et al.
KiSS-1 system and reproduction: comparative aspects and roles in the control of female gonadotropic axis in mammals
Gen Comp Endocrinol
(2007)