Nerve growth factor and its receptor in the anterior pituitary

beta-Nerve Growth Factor (NGF) is a 26-kilodalton protein that has, in recent years, been discovered to have functions beyond that of its classical neurotrophic actions. It has been linked to both the neuroendocrine and the immune systems, and NGF-like bio- and immunoreactivities have been found in the anterior pituitary (AP) gland. The purpose of this study was to assay for NGF immunoreactivity in the AP and to identify the cell type(s) by their hormone content. We also wanted to determine if the AP was a target for NGF action, by looking for the p75 (low affinity) and gp140trkA (high affinity) NGF receptors. Immunoreactivity was detected by immunolabeling with the avidin-biotin-peroxidase complex protocol. Immunolabelling showed NGF immunoreactivity in 31 +/- 5% of AP cells. For the NGF receptors, we found that AP cells were p75 negative, but gp140trkA positive (23 +/- 2%). We found NGF immunoreactivity in 10% of cells containing ACTH, 64% of cells with TSH, 75% of cells with LH, 51% of cells containing GH, and 42% of cells with PRL antigens. Expression of gp140trkA immunoreactivity was also found in 33% of ACTH-containing cells, 45% of TSH-containing cells, 44% of LH-containing cells, 23% of cells with GH, and 41% of cells containing PRL. This evidence demonstrates the presence of NGF immunoreactivity in specific hormone-containing AP cells that contain hormones. The presence of gp140trkA receptors suggests that some of these cells could be targets for NGF action, possibly through autocrine or paracrine pathways.