Neuropeptide Y mediates orexin A-mediated suppression of pulsatile gonadotropin-releasing hormone secretion in ovariectomized rats

Objectives : Reproductive functions are influenced by various feeding regulators. Orexin, which is one of orexinergic peptides, suppresses the pulsatile secretion of luteinizing hormone (LH) in bilaterally ovariectomized (OVX) rats. However, the mechanism of this effect is still not clear. To investigate whether neuropeptide Y (NPY) is involved in the orexin A-mediated suppression of pulsatile LH secretion, we evaluated the effects of NPY antibody on the suppressive effect of orexin A. Methods : Orexin A was administered intracerebroventricularly (icv) and NPY antibody (NPY-Ab) was injected before icv administration of orexin A in OVX rats. Pulsatile LH secretion was analyzed by measuring serum LH concentrations in the next 2 h in blood samples drawn at 6-min intervals by radioimmunoassay. Results : Administration of orexin A significantly reduced the mean LH concentration and LH pulse frequency. Co-administration of NPY antibody with orexin A significantly restored the suppressive effect of orexin A on the mean LH concentration and LH pulse frequency. Conclusion : NPY mediated the suppressive effect of intracerebroventricularly injected orexin A on pulsatile LH secretion, suggesting that hypothalamic orexin suppressed pulsatile gonadotropin-releasing hormone (GnRH) secretion via NPY in the hypothalamus of female rats