High concentrations of neuropeptide Y in pituitary portal blood of rats

Pituitary portal blood was collected from urethane-anesthetized rats and examined for the presence of neuro-peptide Y (NPY) using high-performance liquid chromatography and radioimmunoassay. Other rats were perfused with fixative, and coronal sections through the hypothalamus and median eminence were processed for immunohisto chemicallocalization of NPY. Combined high-performance liquid chromatography and radioimmunoassay analysis of pituitaryportal plasma and systemic plasma revealed a single peak of NPY immunoreactivity which corresponded in retention timeto synthetic porcine NPY. Increasing amounts of portal or systemic plasma produced displacement curves which wereparallel to the NPY standard curve. The concentration of NPY immunoreactivity in portal plasma (52.0±4.0 ng/ml, mean±SEM) was three times greater (p < 0.005) than in systemic plasma (16 ± 4.5 ng/ml). NPY-labeled fibers were observed in the external zone of the median eminence in the vicinity of hypothalamo-hypophyseal portal vessels. The observation of significantly higher concentrations of NPY immunoreactivity in the portal plasma supports the hypothesis that NPY may be released from the hypothalamus to affect pituitary function.