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

Objectives : Reproductive functions are influenced by various feeding regula- tors. Orexin, which is one of orexinergic peptides, suppresses the pulsatile secretion of luteinizing hormone (LH) in bilaterally ovariectomized (OVX) rats. However, the mecha- nism of this effect is still not clear. To investigate whether neuropeptide Y (NPY) is in- volved 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 ad- ministered intracerebroventricularly (icv) and NPY antibody (NPY-Ab) was injected be- fore 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 in- tervals 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) se- cretion via NPY in the hypothalamus of female rats. J. Med. Invest. 58 : 11-18, February, 2011