Binding of a Iodinated Substance P Analog to a NK-1 Receptor on Isolated Cell Membranes from Rat Anterior Pituitary*

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Abstract
The characteristics of binding sites for substance-P (SP) on rat anterior pituitary membranes were studied, using 125I-labeled Bolton-Hunter SP as a ligand. The binding of [125I]Bolton-Hunter SP was saturable and reversible, and reached a plateau of maximal binding after approximately 12 min of incubation. Scatchard and Hill analyses of specific binding revealed a single class of noninteracting binding sites with a high affinity (Kd = 0.72 nM) and a moderate density (binding capacity = 32.16 fmol/mg protein). The biologically active tachykinins, which, in addition to SP, consist of physalaemin, eledoisin, kassinin, neurokinin-A, and neurokinin-B, could inhibit the binding in a concentration-dependent manner. Based on titration curves, the IC50 values of the tachykinins were measured, and the receptor was classified as a NK-1 receptor. These results demonstrate that a population of specific SP-binding sites is present in rat anterior pituitary and further support evidence that this peptide has an influence on pituitary function.