Effect of central infusions of neuropeptide Y on GnRH/LH axis in ewes during the early anoestrous period

Neuropeptide Y (NPY) is a putative mediator of many physiological pro-cesses in the central nervous system including reproductive functions. In this study we examined the effect of NPY on the GnRH/LH secretory activity in early anoestrous ewes. Crossbreed ewes one week (group 1w, n=7) and six weeks (group 6w, n=7) after the last oestrous cycle were infused with Ringer solution (control) or 50 µg of NPY to the third ventricle for 5 min. Blood samples were collected during the days of infusion over 6 h at 10 min intervals and then the ewes were slaughtered and their brains fi xed in situ. Immunoreactive (ir) GnRH in the median eminence and LH cells in the adenohypophysis were localised by immunohistochemistry technique. Data were generated using computer analysis to determine the optical density for immuno-staining and the proportion of ir LH cells. Plasma LH was determined by radioimmunoassay. It was found that investigated anoestral groups differed only in the optical densities of ir GnRH and ir LH, which were lower in group 6w compared to group 1w (p<0.001). L