Immunocytochemical and biochemical evidence of renin in human lactotrophic cell cultures

Primary cell cultures from human prolactin (PRL)-secreting adenomas were used to test the ability of human lactotrophs to synthesize renin in vitro. The renin content of the culture medium and of cellular extracts was measured by enzyme-linked immunosorbent assay. The level of PRL release in the culture medium and the amount of PRL in a cellular extract were determined by radioimmunoassay. Morphologic studies included indirect immunofluorescence, pre-embedding immunoelectron microscopy using a three-layer peroxidase-antiperoxidase method and postembedding immunoelectron microscopy using protein A-gold complexes. Renin was detected in cellular extracts and was found to be absent in the culture medium, whereas PRL was extracellularly secreted. PRL and renin immunoreactivity was observed in all the cultures studied by immunofluorescence. The subcellular localization of renin was found to be similar to that of PRL and was observed in the rough endoplasmic reticulum, the Golgi apparatus, and cytoplasmic secretory granules. The results suggest that, in vitro, renin may be synthesized and intracellularly metabolized in human adenomatous lactotrophic cells rather than secreted. Cell cultures may be a useful model to further the understanding of the role of a local renin-angiotensin system in PRL secretion.