GROWTH-HORMONE EXPRESSION IN MURINE BONE-MARROW CELLS IS INDEPENDENT OF THE PITUITARY TRANSCRIPTION FACTOR PIT-1

GH has been shown to promote the development and function of leukocyte s. The expression of both GH and GH-receptors in lymphoid cells has le d to the hypothesis that GH acts in an autocrine or paracrine fashion. The described effects of GH on hematopoiesis and B cell development, led us to investigate GH expression in bone marrow cells. By immunocyt ochemistry, we show that bone marrow-derived granulocytes and macropha ges contain immunoreactive GH. We found that 65 +/- 24% of the granulo cytes were stained with anti-GH, whereas 5.8 +/- 1.5% of the granulocy tes contained detectable amounts of GH mRNA as assessed by in situ hyb ridization. To address a possible alternative regulation mechanism in bone marrow and to establish whether locally derived GH might still pl ay a role in pituitary-deficient dwarf mice, we also addressed GH expr ession in bone marrow from hypopituitary Snell dwarf mice. These mice have a mutated gene for the pituitary transcription factor Pit-1 that is deficient in DNA binding. Our finding that GB expression (immunorea ctive protein and mRNA) in bone marrow cells from dwarf mice is simila r to that in normal mice points to a Pit-1 independent regulation of G H in mouse bone marrow.