PITUITARY MORPHOLOGY IN MICE TRANSGENIC FOR PHOSPHOENOLPYRUVATE CARBOXYKINASE PROMOTER REGION-HUMAN GROWTH-HORMONE FUSION GENE

The adenohypophyses of female and male mice transgenic for the phospho enolpyruvate carboxykinase promoter region-human growth hormone (PEPCK /hGH) fusion gene were investigated by immunohistochemistry, electron microscopy, and in situ hybridization. Marked increase in body weight and decrease in pituitary weight were noted. Immunohistochemical and u ltrastructural investigation revealed that in both sexes somatotrophs and lactotrophs had the features of inhibited cells and the hybridizat ion signals for GH and PRL mRNA were diminished. Other adenohypophysia l cell types showed sex-related changes. In female mice, the numbers o f LH and TSH immunoreactive cells were decreased; ACTH cells showed no changes in number, and the intensity of POMC mRNA signal did not diff er from controls. In male mice, the numbers of ACTH, and LH immunoreac tive cells were increased without reaching significance and POMC mRNA displayed a stronger signal in comparison with controls. The present r esults demonstrate that in this line of transgenic mice with very high plasma hGH levels, somatotrophs and lactotrophs are inhibited in both sexes. The changes in non-GH producing cells may be attributed to hig h plasma levels of hGH and to its lactogenic activity in mice.