Kisspeptin Antagonists - Kisspeptin Signaling in Reproductive Biology - page 174

evident in the female rat after peptide 234 administration into the ARC (see below).
The effect on LH appears to be specifi c, as prolactin and cortisol secretion were
unaffected in the ovariectomised ewes [ 26 ].
In the rat, the KP neurons critical for gonadotropin secretion are located in the
hypothalamic ARC and AVPV nuclei. As the ARC is known to be the site of the
GnRH pulse generator [ 29 ], we explored the effects of KP-10 or peptide 234 admin-
istered intra-ARC or intra-medial preoptic area, which includes the AVPV, on pulsatile
LH secretion [ 30 ]. Intra-ARC administration of peptide 234 profoundly suppressed
LH pulse frequency (Fig. 8.12b ), but intra-mPOA administration of peptide 234 had
no effect [ 30 ] (data not shown). These data are the fi rst to identify the ARC as a key site
for KP modulation of LH pulse frequency, supporting the notion that KP/KISS1R
signalling in this region of the mediobasal hypothalamus is a component of the
hypothalamic GnRH pulse generator.
Testing KP's Role in Puberty
Hypogonadotropic hypogonadism and a failure to progress through puberty in mice
and humans with inactivating mutations of KISS1R is the phenotype which led to the
discovery of the importance of the KP/KISS1R system in regulating reproduction.
These fi ndings indicated an essential role for the KP system in translating neuroendo-
crine regulators of puberty into increased GnRH output. Puberty was thus a relevant
model to examine the effects of a KP antagonist. To study KP's role in prolonged
physiological processes such as puberty, protracted blockade of KP action was
required. Central infusion of KP antagonist, peptide 234 (10 nmol/24 h), by osmotic
minipump attached to an i.c.v. catheter for 7 days to pubertal (d30) female rats delayed
vaginal opening and decreased uterine and ovarian weights (data not shown) at the
expected time of puberty, without affecting body weight (data not shown) (Fig. 8.13a )
[ 31 ]. Eighty percent of animals infused with vehicle displayed complete canalisation
of the vagina by d36, while only 13% of the females treated with the antagonist
showed complete vaginal opening (Fig. 8.13a ). In the study on pubertal female rhesus
monkeys described earlier, peptide 234 inhibited GnRH pulses [ 26 ]. These fi ndings
provided direct evidence for a role of KP in initiating puberty, in support of indirect
data showing that exogenous KP administration advances puberty [ 32 ], Kiss1 gene
expression increases at puberty in rats, and the puberty is absent in KiSS1 and KISS1R
gene inactivation in humans. Thus, we are able to conclude that KP secretion is essen-
tial for increasing GnRH secretion and progression through puberty.
Testing if KP Mediates Gonadal Steroid Negative Feedback
The mechanism by which gonadal steroids mediate feedback has been a lively area
of research and debate over many years. The discovery of the KP/KISS1R system
suggested that it may play a part in negative steroid feedback. Gonadectomy of mice