BINDING OF AN IODINATED SUBSTANCE-P ANALOG TO CULTURED ANTERIOR-PITUITARY PROLACTIN-CONTAINING AND LUTEINIZING HORMONE-CONTAINING CELLS

Several lines of anatomic, biochemical, and pharmacological evidence suggest that the neuropeptide substance P has a direct action on cells of the anterior pituitary lobe via a specific neurokinin-1 receptor. In the present study we confirmed this association by combining Bolton-Hunter iodinated substance P-receptor autoradiography with immunocytochemistry on cultured anterior pituitary cells. Radiolabeled substance P was bound to living cell cultures at 0-degrees-C, and after a brief wash the cultures were fixed and processed immunocytochemically for prolactin and luteinizing hormone. A large proportion of cultured anterior pituitary cells possessed substance P binding sites. When receptor autoradiography was combined with immunocytochemistry, it was evident that both prolactin- and luteinizing hormone-immunoreactive cells were labeled with radiolabeled substance P. However, a small proportion of the radioligand-labeled cells were not stained by the immunocytochemical procedure, suggesting that additional cell types possess substance P receptors. The present study presents morphological evidence that substance P binds to prolactin- and luteinizing hormone-containing cells of the anterior pituitary lobe. Therefore, it is likely that substance P has a direct action on mammotrophs and gonadotrophs.