Detection and immunohistochemical localization of α1-pregnancy-associated protein (α1-PAP) in rats.

A protein exhibiting immunochemical cross-reactivity with the murine α1-pregnancy-associated protein (α1-PAP) has been detected in the sera of female rats. The protein has an α1-electrophoretic mobility, an estimated molecular weight of 150,000 and is readily detectable in the sera of non-pregnant 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 α1-PAP in the mouse. Immunohistochemical studies revealed a staining pattern for the rat protein similar to that seen for α1-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 α1-PAP, and that the rat strains examined more closely resemble high endogenous α1-PAP-producer mouse strains. It is proposed that α1-PAP, and a number of other rodent pregnancy proteins recently described, may be used in functional studies of human α2-PAG. [ABSTRACT FROM AUTHOR]