Pituitary growth hormone-releasing factor receptor expression in normal and dwarf rats.
Growth hormone-releasing factor (GRF) regulates GH release and somatotrope proliferation via a specific G-protein-coupled receptor. Little is known about the endocrine factors that regulate the expression of the GRF receptor (GRF-R) in the pituitary gland. We have developed a sensitive solution hybridization/RNAse protection assay for GRF-R mRNA in rat pituitary extracts. GRF-R transcripts were readily detectable in similar amounts in normal male and female rats, but were markedly reduced in extracts from age-matched growth hormone (GH)-deficient dwarf (dw) rats of either sex. The reduced GRF-R expression would appear to reflect somatotrope hypoplasia rather than GH deficiency per se since a similar reduction in GRF-R expression was seen in a transgenic model of dominant dwarfism, whereas GRF-R expression was significantly elevated in rats with GH deficiency induced by hypothyroidism. We were unable to demonstrate significant effects on GRF-R expression with infusions of human GH (hGH) or insulin-like growth factor 1, which stimulate growth in dw rats, but dexamethasone treatment induced a significant, time-related increase in GRF-R mRNA levels. We conclude that this assay can usefully quantify pituitary GRF-R expression in normal rats, and its reduction in two different strains of mutant dwarf rats with somatotrope hypoplasia.
Carmignac
D F
DF
Division of Neurophysiology, National Institute for Medical Research, London, UK.
Flavell
D M
DM
Robinson
I C
IC
D000704:Analysis of Variance; D000818:Animals; D030801:Animals, Genetically Modified; D013956:Antithyroid Agents; D003907:Dexamethasone / Q000494:pharmacology; D004393:Dwarfism, Pituitary / Q000378:metabolism*; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism*; D007037:Hypothyroidism / Q000139:chemically induced*; D008297:Male; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D018013:Receptors, Neuropeptide / Q000096:biosynthesis* / Q000235:genetics; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000096:biosynthesis* / Q000235:genetics; D012016:Reference Values; D012260:Ribonucleases
D013956:Antithyroid Agents; D005938:Glucocorticoids; D012333:RNA, Messenger; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D003907:Dexamethasone; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D012260:Ribonucleases; C048250:somatotropin releasing hormone receptor