High plasma growth hormone (GH) levels inhibit expression of GH secretagogue receptor messenger ribonucleic acid levels in the rat pituitary.
Synthetic GH secretagogues (GHSs) act via a receptor (GHS-R) distinct from that of GH-releasing hormone. The GHS-R has been cloned from the pituitary and is expressed not only in the pituitary but also in specific areas of the brain, including the hypothalamus. Recent studies suggest that hypothalamic GHS-R expression is regulated by GH. This study was designed to investigate whether pituitary GHS-R expression is modulated by GH. Female Wistar-Furth rats were injected sc with either saline (control) or GC tumor cells (GC) that secrete rat GH. The tumors were allowed to develop for 1-4 weeks. At weeks 1-4, control (n = 4-8) and GC rats (n = 3-8) were killed. Pituitary GHS-R messenger RNA (mRNA) was measured by a quantitative competitive PCR assay. The endogenous GHS-R mRNA levels were measured by determining the amount of competitive template RNA required to produce equimolar amounts of native and competitive template PCR products. The mean log plasma GH levels were significantly greater in the GC rat group than in the control group at weeks 2, 3, and 4. At these times, the mean log pituitary GHS-R mRNA contents were significantly lower in the GC rat group than in the control group. No relationship could be established between log estradiol levels and GHS-R levels. These data indicate that pituitary GHS-R expression is modulated by GH.
Nass
R
R
Department of Medicine, University of Virginia, Charlottesville 22908, USA.
Gilrain
J
J
Anderson
S
S
Gaylinn
B
B
Dalkin
A
A
Day
R
R
Peruggia
M
M
Thorner
M O
MO
D000818:Animals; D004958:Estradiol / Q000097:blood; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D013006:Growth Hormone / Q000097:blood* / Q000378:metabolism; D009368:Neoplasm Transplantation; D010902:Pituitary Gland / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism*; D051381:Rats; D011920:Rats, Inbred WF; D011956:Receptors, Cell Surface / Q000235:genetics*; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D004958:Estradiol; D013006:Growth Hormone