Perifusion system: its use in the study of the neuroendocrine control of human pituitary tumoral cells

Abstract

Regulation of hormone release involves both long term and short term controls, which depends upon which receptor is activated (nuclear or membrane) and upon which stimulating agent is used. When long term regulation is involved, protein synthesis is the major event determining the observed changes in hormone release. When short term regulation is involved, membrane transducing mechanisms are implicated and variations in ion fluxes, adenylate cyclase, phospholipase C, D or A2 activities are immediately followed by changes in hormone release. One same agent may have both long term and short term effects on hormone release as rapid changes in secretory rate, if they last, will end up in changes in synthesis rate.However, in vitro, short and long term regulations need different approaches. Primary culture is well adapted to long term secretory regulation whereas short term regulations need a dynamic approach and the perifusion technique is particularly useful in this case. Indeed, it bathes the tissues in continually fresh medium, thereby eliminating feedback or waste product effects. The tissues can be exposed to various conditions without the artifacts arising from physical manipulations and finally, the time course of any effects produced may be observed.In particular, small changes in release rates which would be blunted in standard culture by the relatively large amount of basal release, will be easily detected.We have used the perifusion system to study the neuroendocrine control of human pituitary tumoral cells, in order to further understand the dysregulation leading to the hypersecretory state of these tumors. Human pituitary tumors are of different types, secreting one or several hormones and nonsecreting. Among the secreting adenomas, we have focused our attention on the prolactinomas, secreting prolactin (PRL), and on the somatotropic adenomas secreting growth hormone (GH). Not only the perifusion system allowed us to study what could be called the "conventional" PRL anf GH release regulation by hypothalamic neuropeptides, it also allowed us to observe differences in the regulation between adenomas of the same cell type and to establish a relationship between the cell response and the number of receptors for a given neuropeptide. Furthermore, we could demonstrate that normal and tumoral pituitary cells produce and release neuropeptides which may interfere with the secretions of pituitary hormones.

Stimulatory effect of gonadotropin-releasing hormone (GnRH) on in vitro prolactin secretion and presence of GnRH specific receptors in a subset of human prolactinomas

“…Although unresponsiveness to TRH has been reported in cultured prolactinomas (27), TRH stimulated in vitro PRL secretion of all the adenomas that we studied in perifusion in the present study, as shown already (28). This result is consistent with the presence of specific TRH receptors in the large majority of prolactinomas (29) and demonstrates the functional activity of the perifused cells.…”