title: Gonadotropin-releasing hormone desensitization preferentially inhibits expression of the luteinizing hormone beta-subunit gene in vivo.
abstract: In this study we investigated changes in steady state cytoplasmic mRNA levels for LH subunits in pituitaries of male rats desensitized by continuous infusion of GnRH in vivo. Seven days of GnRH infusion (340 micrograms/day) reduced (P less than 0.01) LH beta mRNA levels in intact adult male rats and prevented the LH beta mRNA rise observed after castration. In contrast, common alpha mRNA doubled (P less than 0.05) in intact rats, and the elevated alpha mRNA after 7 days castration was unchanged. Serum and pituitary LH levels were suppressed below values of intact controls. Fourteen days of GnRH infusion (290 micrograms/day) further reduced LH beta mRNA levels in both intact and castrated male rat pituitaries. alpha mRNA levels in intact rat pituitaries were unchanged by 14 days of GnRH infusion, while in castrated rats there was a 23% (P less than 0.05) decrease, though values were still twice those of intact controls. As at 7 days, serum and pituitary LH were suppressed. Infusion of a superagonist analog (Buserelin) at a dose of 14 micrograms/day for 28 days reduced LH beta mRNA to 15% of intact control values in both castrated and intact rats. Common alpha mRNA was significantly (P less than 0.05) increased in intact rats and reduced by 13% (P less than 0.05) in castrates by superagonist infusion. These results were similar to those produced by 20- to 30-fold higher doses of native GnRH. GnRH and agonist analog effects were specific since no changes were observed in other mRNA species (GH, PRL, actin). These results indicate that in GnRH-desensitized gonadotropes LH beta gene expression is inhibited, and this may largely explain the reduced LH biosynthesis. However, there is a differential effect of continuous GnRH or agonist analog treatment on LH subunit gene expression, with a time-dependent stimulation of common alpha gene expression in intact rats. This may be caused by a stimulatory interaction between GnRH and progestagens at the level of the gonadotrope. Thus, common alpha gene expression is less tightly coupled than that of LH beta to GnRH action.
authors.affiliation: Endocrinology Research Group, Clinical Research Centre, Harrow, Middlesex, United Kingdom.
authors.forename: M R
authors.initials: MR
authors.lastname: Lalloz
authors.forename: A
authors.initials: A
authors.lastname: Detta
authors.forename: R N
authors.initials: RN
authors.lastname: Clayton
mesh_terms: D000818:Animals; D005786:Gene Expression Regulation / Q000187:drug effects*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood / Q000235:genetics*; D008297:Male; D010902:Pituitary Gland / Q000032:analysis; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone