Gonadotropin-releasing hormone (GnRH)-receptor coupling to inositol phosphate and prolactin production in GH3 cells stably transfected with rat GnRH receptor complementary deoxyribonucleic acid.

Abstract

This study examines the relation between inositol phosphate (IP) production and PRL release in four GGH3 cell lines (GGH(3)1', GGH(3)2', GGH(3)6', and GGH(3)12'; lactotropic GH3 cells that have been stably transfected with rat GnRH receptor complementary DNA). Production of IPs is an early response of GGH3 cells to a GnRH agonist, measurable at 15-30 min and maximal at 60 min after treatment with Buserelin in [3H]inositol preloaded cells. In contrast, PRL release, which requires protein synthesis, is not measurable until 1-3 h and total cAMP production is not measurable until about 24 h (3). In one of the lines studied (GGH(3)2'), PRL was also released in response to TRH. Measurable expression of the PRL gene requires 1-2 days (2). All four lines produced IPs robustly after treatment with Buserelin, although the IP response to TRH is minimal in all lines, being the best in the GGH(3)2' line. Pretreatment of cells with cholera toxin (CTX) or pertussis toxin (PTX) attenuated TRH-induced IP production in GGH(3)1', GGH(3)2', or GGH(3)12' cells. No effect of CTX or PTX is measurable in GGH(3)6' cells in terms of TRH stimulation of IP production. In contrast, both toxins augment Buserelin-stimulated IP production in GGH(3)1' and GGH(3)6' cells, but have no action in the other two lines. Both CTX and PTX inhibit Buserelin-stimulated PRL production. This study suggests that IP production is the earliest measurable response of GGH3 cells to a GnRH agonist, although this event does not appear to be coupled to Buserelin-stimulated PRL release. Further, the studies with toxins suggest that Buserelin and TRH appear to regulate IP production by different mechanisms.