Lactotroph hyperplasia in the pituitaries of female mice expressing high levels of bovine growth hormone

PEPCK/bGH transgenic mice have very high blood levels of foreign GH, and pr ominent reproductive disturbances, especially in females. To obtain a deepe r insight into the causes of these abnormalities, pituitaries of PEPCK/bGH transgenics were studied by immunocytochemistry, electron microscopy and in situ hybridization (ISH) techniques. Pituitary weights were significantly reduced (P < 0.05) in transgenic males, while in transgenic females they we re increased without reaching significance compared to nontransgenic contro ls. In both sexes, GH cells were inhibited, as previously described in othe r lines of GH transgenic mice. In females, PRL cells were increased by 37% compared to controls. Ultrastructurally, the lactotrophs had characteristic s of stimulation and PRL mRNA was increased by 35%. In males the increase i n the number of PRL immunoreactive cells was not significant, the PRL mRNA signal did not differ from controls, and there were no changes in their ult rastructure. Only in females ACTH cells were significantly reduced (P < 0.0 5) in number and unchanged in males; however, POMC mRNA signal was increase d in both genders and reached significance (P < 0.05) in males. In females, but not in males, the percentage of LH cells was lower than in control mic e. In conclusion, the high blood bGH levels induced sex related changes in transgenic mice from the present line. The infertility of PEPCK/bGH transge nic females may be attributed to lactotroph hyperplasia and marked reductio n in number of gonadotrophs.