Comparative localization of prolactin-binding sites in different rat tissues by immunohistochemistry, radioautography...

Prolactin was localized in various rat tissues, using two different histological approaches: immunohistochemistry and autoradiography. Following injection of ovine prolactin (oPRL) to intact rats, oPRL was localized in the proximal convoluted tubules (PCT) of the kidney using an immunoperoxidase technique. Diffuse and weak staining was observed in the liver while no staining was observed on sections of adrenal, testis and brain. Incubation of [125I]oPRL on frozen cryostat tissue sections followed by radioautographic processing revealed specific radioautographic grains on cells of convoluted tubules of the kidney. Specific grains were also seen on hepatocytes of the liver, cells of the adrenal cortex, interstitial cells of the testis and epithelial cells of the choroid plexus of the brain. The amount of specific radioautographic grains seen per tissue agreed well with in vitro binding values of [125I]oPRL to crude membrane preparations in the same tissues. Our observations clearly show that in the rat specific binding sites for prolactin are present on cells of the proximal convoluted tubules of the kidney, hepatocytes of the liver, glandular cells of the zona reticularis, zona fasiculata and zona glomerulosa of the adrenal, interstitial cells of the testis and epithelial cells of the choroid plexus. These studies demonstrate the necessity of using more than one morphological approach in the identification of prolactin-binding sites in different tissues at the cellular level.