Detection and immunohistochemical localization of alpha 1-pregnancy-associated protein (alpha 1-PAP) in rats

A protein exhibiting immunochemical cross-reactivity with the murine alpha 1-pregnancy-associated protein (alpha 1-PAP) has been detected in the sera of female rats. The protein has an alpha 1-electrophoretic mobility, an estimated molecular weight of 150,000 and is readily detectable in the sera of nonpregnant female rats of each strain examined. During pregnancy, the serum concentration increases up to five-fold, reaching maximal levels at the same gestational stage as alpha 1-PAP in the mouse. Immunohistochemical studies revealed a staining pattern for the rat protein similar to that seen for alpha 1-PAP in the mouse, with positive cells being observed in lumbar lymph nodes, the lamina propria of gut mucosa, Peyer's patches, intracellularly in some hepatocytes and, during pregnancy, also in the placenta and metrial gland. On the basis of these immunochemical, physicochemical and immunohistochemical findings, it is proposed that the protein detected in rat sera represents the analogue of the murine alpha 1-PAP, and that the rat strains examined more closely resemble high endogenous alpha 1-PAP-producer mouse strains. It is proposed that alpha 1-PAP, and a number of other rodent pregnancy proteins recently described, may be used in functional studies of human alpha 2-PAG.