Expression of mRNA coding for pituitary hormones and pituitary-specific transcription factor in the pituitary gland of the rdw rat with hereditary dwarfism.

The rdw rat (gene symbol: rdw) with hereditary dwarfism has been shown immunohistochemically to have subnormal numbers not only of 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 less GH and prolactin mRNAs than normal controls, whereas mRNAs for pro-opiomelanocortin and the alpha subunit of rat glycoprotein hormone revealed a significant increase. There was a non-significant difference in rat LH-beta subunit and FSH-beta 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 the rdw rat. In this study, however, no difference in mRNA expression for Pit-1 was found between rdw rats and controls. This work indicates that the rdw rat may not have the same genotype as the phenotypically similar dwarf mice, Snell, Jackson and Ames.