Study of the Role of Kisspeptin-GPR54 Signaling in . Metabolic Regulation of Hypothalainic-PituitaryGonadal (HPG) Axis in the Adult Male Rhesus Monkey (Macaca mulatta)

Abstract

In primates, changes in metabolic status affect the hypothalamic-pituitarygonadal (HPG) axis by still poorly understood mechanisms. Recently, hypothalamic kisspeptin-GPR54 (KP-Kiss lr) signaling has emerged as a significant regulator of this neuroendocrine axis. The role of this signaling pathway in conveying metabolic status related information to centers controlling reproductive axis is less understood. The present study was designed to examine involvement of KP-Kisslr signaling pathway in the metabolic regulation of the HPG axis in the adult male rhesLls monkey by three different approaches: firstly, we administered KP in metabolic paradigms of energy imbalance (fasting and insulin-induced hypoglycemia, or IIH), which are known to cause inhibition of the reproductive function, to evaluate effect of KP on the HPG axis. Secondly, we quantified and compared the expression of hypothalamic Kiss 1, Kiss 1 r, and GnRHl mRNA in normal feeding and short-term fasting conditions. Thirdly, we investigated the effect of exogenous Kp · challenge on the metabolic hormones that directly or indirectly modulate performance of the HPG axis. Materials and Methods: In KP administration studies, blood samples were taken before and after human-KPI0/vehicle/hCGIGnRH administration to the intact adult male rhesus monkey (n=3-5) under normal fed, short-term fasting, and IIH conditions. Plasma concentrations of cortisol and testosterone (T) were measured by using specific RIAs. In addition glucose levels were also determined either by enzyme assay or blood glucometer. In the expression study, total hypothalamic mRNA was extracted from normal fed (n=3) and 48-h fasted (n=3) monkeys. Kissl, Kisslr, and GnRHl mRNAs were quantified by reverse transcription followed by real-time polymerase chain reaction . In addition, blood samples were collected for measurement of plasma concentrations of glucose, cortisol, leptin, and T. In KP effect on metabolic hormones secretion studies, plasma concentration of adiponectin, insulin, leptin, and resistin were measured before and after KPI0 administration. KPIO effect was also checked on glucose-induced insulin , secretion in normal fed and short-term fasted monkey.