GONADOTROPIN-RELEASING-HORMONE (GNRH)-RECEPTOR COUPLING TO INOSITOL PHOSPHATE AND PROLACTIN PRODUCTION IN GH(3) CELLS STABLY TRANSFECTED WITH RAT GNRH RECEPTOR COMPLEMENTARY DEOXYRIBONUCLEIC-ACID

This study examines the relation between inositol phosphate (IP) produ ction and PRL release in four GGH(3) cell lines (GGH(3)1', GGH(3)2', G GH(3)6', and GGH(3)12'; lactotropic GH(3) cells that have been stably transfected with rat GnRH receptor complementary DNA). Production of I Ps is an early response of GGH(3) cells to a GnRH agonist, measurable at 15-30 min and maximal at 60 min after treatment with Buserelin in [ H-3]inositol preloaded cells. In contrast, PRL release, which requires protein synthesis, is not measurable until 1-3 h and total cAMP produ ction is not measurable until about 24 h (3). In one of the lines stud ied (GGH(3)2'), PRL was also released in response to TRH. Measurable e xpression of the PRL gene requires 1-2 days (2). All four lines produc e IPs robustly after treatment with Buserelin, although the IP respons e 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 (PT S) 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 au gment Buserelin-stimulated IP production in GGH(3)1' and G6H(3)6' cell s, but have no action in the other two lines. Both CTX and PTX inhibit Buserelin-stimulated PRL production. This study suggests that IP prod uction is the earliest measurable response of GGH(3) cells to a GnRH a gonist, 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 60 regulate IP production by different mecha nisms.