Characterizatin of rdw Rat as a New Animal Model for Hereditary Dwarfism

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The rdw rat (gene symbol; rdw) with hereditary dwarfism has been shown immunohistochemically to have subnormal numbers not only of growth hormone (GH) but also of prolactin and thyrotrophin-positive cells. To characterize the dwarfism of this strain, the expression of pituitary hormone mRNAs was examined by Northern hybridization. The pituitary gland in the rdw rat expressed 30-100 times fewer GH and prolactin mRNAs than that of the normal controls, whereas mRNAs for proopiomelanocortin and the alpha subunit of rat glycoprotein hormone revealed a significant increase. There was a slight difference in rat luteinizing hormone-beta subunit and follicle-stimulating hormone-b subunit between normal and rdw rats. The suppressed expression of a pituitary-specific transcription factor, pit-1, is considered to cause hereditary dwarfism in mouse strains, Snell and Jackson, whose phenotypes resemble those of rdw rat. In this study, however, no difference in mRNA expression for pit-l was found between rdw rats and controls. This work indicates that rdw rat may not have the same genotype as the phenotypically similar dwarf mice, the snell, Jackson and Ames.