| Research Abstract |
Two strains of human growth hormone (GH)-releasing hormone (hGHRH) transgenic rats (2#and#3) were first established by microinjection of a 2.2 kbp-gene constract which consisted of mouse metallothionein I-promoter and human GHRH minigene (exon 1, intron 1, and fusion gene of exon 2-5) into male pronucleus of the oocytes from SD female rats by the standard method. HGHRH-Tg SD male rats were, next, mated with female dwarf rats (dr+/+). Two strains of hGHRH-Tg dr (+/+) were finally obtained by crossing male hGHRH-Tg dwarf rats (+/-) with female dr (+/+). One strain of hGHRH-Tg dr (#2) were analyzed for expression of pituitary hormones, GHRH receptor and c-fos. All hGHRH-Tg dr with high plasma hGHRH levels (>5,000 pg/ml) showed dwarf, but had pituitary adenomas which showed positive immunostaining for hGHRH with some staining for PRL and little staining for ACTH.They showed no immunostaing for GH,TSH-beta, LH-beta or FSH-beta. In contrast to decreased GH gene expression (1/20 of controls), mRNA for rat GHRH receptor and c-fos were markedly increased by 10 and 4 folds, respectively. Expression of hGRF gene was found in the pituitary, liver, spleen, kidney and ovary, while GRF Rc gene transcripts and adenoma formation were exclusively found in the pituitary by northern blot analysis and HE staining, respectively. These results suggest that 1) GH-independent adenoma formation can occur and 2) GRF could act on its Rc and stimulate adenoma formation of the somatotroph by the autocrine mechanism.
Although the numer of hGHRH-Tg dr was small due to GH deficiency and not enough to allow extensive survey for gene expression for cytokines, there was an increase in PTHrP gene expresion in adenomatous pituitary glands.
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