Search for functional significance of peptidylarginine deiminase in rat pituitaries: variation during pregnancy and ultrastructural localization in prolactin cells.

We have studied the expression of peptidylarginine deiminase in rat pituitaries during pregnancy. Both the enzyme protein and its mRNA decreased to low levels after the onset of gestation. Both started to increase markedly during mid pregnancy reaching their maxima on day 18 and declined thereafter. The early phase of variations were accompanied with a progressive decrease in the pituitary prolactin content, an abrupt decrease in the prolactin mRNA content, and a small but significant increase in the serum estrogen. We also performed an immunoelectron microscopic study of the enzyme, and showed its scattered localization in the cytoplasm of prolactin cells.