Kisspeptin stimulates LH secretion but not ovulation in mares during vernal transition

Kisspeptin and the regulation of the reproductive axis in domestic animals

“…The second largest population of kisspeptin cells, albeit much smaller in number, is found in the medial preoptic area, in sheep, goats and cattle (Estrada et al 2006, Franceschini et al 2006, Goodman et al 2007, Matsuda et al 2015, Hassaneen et al 2016, Tanco et al 2016. Horses (Decourt et al 2008, McGrath 2015, by contrast, do not appear to contain kisspeptin neurons in the preoptic area at all. In pigs, the rostral population of kisspeptin neurons is in the periventricular nucleus rather than the preoptic area (Tomikawa et al 2010).…”

“…A single IV injection of a large dose of kisspeptin (10 mg) did advance ovulation in mares with large ovarian follicles (Briant et al 2006). Lower doses of kisspeptin, however, whether as bolus injections or continuous infusions, up to 9 days in length and across a range of doses, all increased circulating LH concentrations, but failed to induce an LH surge (Magee et al 2009, Decourt et al 2014, McGrath et al 2016, whether in cycling mares, anoestrous mares or those in vernal transition. Thus, the role that kisspeptin plays in the generation of the LH surge in horses is not clear.…”

“…Longer IV infusions have also stimulated LH secretion in ewes (Caraty et al 2007) and mares (Decourt et al 2014, McGrath et al 2016. IV kisspeptin also increased plasma LH in male goats (Saito et al 2012) and bull calves (Ezzat et al 2009), as well as testosterone in stallions (Akhtar et al 2017).…”

“…Anterior pituitary secretion of the gonadotrophin, luteinising hormone (LH), then acts as an amplifier to the GnRH signal (Clarke & Cummins 1982). In sheep, at least, the neurons that produce GnRH receive relatively little synaptic input compared to other neurons within the hypothalamus (Lehman et al 1988, Magee et al 2009, Decourt et al 2014, McGrath et al 2016. Thus, it would seem likely that much of the integration of the various factors that influence GnRH secretion occurs upstream of the GnRH neuron.…”

Effect of Kisspeptin on in vitro Maturation of Buffalo Oocytes

“…Administration of Kp induces secretion of gonadotropin hormones in many species such as bovines (Naniwa et al, 2013 andW hitlock et al, 2008), pre-pubertal heifers (Kadokawa et al, 2008), ewes (Redmond et al, 2011 andWang et al, 2012), acyclic mares (Wilborn., 2008), swine (Lents et al, 2008), dogs (Cheng et al, 2011 andElderen., 2014) and women (Jayasena et al, 2014). The ability of Kp to induce ovulation following intravenous administration has been demonstrated in bovine (Naniwa et al, 2013), prepubertal ewe lambs (Redmond et al, 2011), anestrous ewes (Caraty et al, 2007) and mare (McGrath et al, 2016). Moreover, supplementation of Kp to maturation media has been reported to improve the efficiency of pig (Saadeldin et al, 2012), bovine (Ming et al, 2015 andOliveira et al, 2016) and sheep (Byri et al, 2017) oocyte maturation in vitro.…”