DETERMINATION OF GUANINE-NUCLEOTIDE SENSITIVITY OF [I-125] NEUROPEPTIDE-Y BINDING IN THE RAT PITUITARY-GLAND BY QUANTITATIVE AUTORADIOGRAPHY

[125I]-neuropeptide Y receptors were characterized in the rat pituitary gland using quantitative autoradiography. Scatchard analysis of saturation isotherms showed high affinity (K(d) 8.5 x 10-11 M) and single class of binding sites (B(max) 0.22 pmol/mg of protein) in the posterior lobe of the pituitary gland, with no specific binding in the intermediate or anterior lobe. Increasing concentrations of guanine nucleotide analogues and peptide YY inhibited neuropeptide Y binding. In addition, neuropeptide Y binding was pertussis-toxin-sensitive. These results add additional information about a possible neuronal (through neuropeptide Y) and hormonal (through peptide YY) regulation of posterior pituitary function, which is most probably GTP-dependent.