ASAS Nonruminant Nutrition: Vitamins, Minerals, and Energy

Ovoinhibitor is a serine protease-inhibiting protein that specifically inhibits serine proteinases such as trypsin and chymotrypsin. During recent attempts to raise monoclonal antibodies (MABS) against chicken bursa of Fabricius proteins, one MAB was produced that specifically recognized chicken ovoinhibitor. This was the first demonstration of ovoinhibitor in an avian immune organ. Further immunocytochemical research revealed that in the pituitary and the brain of the chicken, some cells undeniably displayed immunoreactivity for ovoinhibitor. The present study was aimed at identifying the hypophysial hormoneproducing cells that express ovoinhibitor immunoreactivity. Therefore, pituitary glands from 4-week old birds were fixed in phosphate-buffered paraformaldehyde (4 % w/v) and 30-μm vibratome sections were stained as floating sections in 12-well tissue culture plates. The mouse MAB against ovoinhibitor was used in conjunction with polyclonal antibodies against Luteinizing Hormone (LH), Growth Hormone (GH), Proopiomelanocortin (POMC) and Prolactin (PRL) and S-100, respectively. The mouse MAB was visualized with a rhodamine-conjugated secondary antibody, whereas the polyclonal rabbit antisera were detected with a biotinylated secondary antibody combined with FITC-conjugated streptavidin. This procedure stained ovoinhibitor-positive cells in red, while the pituitary hormone-positive cells were stained green; overlapping antigens were clearly visible in yellow. The results of these dual-staining experiments revealed partial co-localization of ovoinhibitor with GH, LH, and POMC, each time in a subset of the respective hormone producing cells. By contrast, no co-localization with PRL and S-100 could be demonstrated. Serine protease inhibitors from another family (the serpins) have recently been identified in rat brain and pituitary. In the latter, they have been suggested to play a role in the regulation of cellextracellular matrix interactions .