Luteal protein secretion during preimplantation in the ferret

Ferret CL were collected on Days 5-11 of pregnancy or pseudopregnancy and incubated in McCoy's medium with radiolabeled amino acids to determine the ability of ferret CL to synthesize and secrete proteins during the preimplantation period. Products recovered from the medium were separated by one- and two-dimensional SDS-PAGE followed by fluorography and were quantified by densitometry. Selected secretory proteins were tentatively identified with specific antibodies on Western blots. Ferret CL synthesized and secreted a relatively large number of radiolabeled products. The predominant secretory proteins had molecular masses of 16, 22, 28, 32, 47, 68, and 185 kDa and were secreted at all stages of the preimplantation period. There were no qualitative changes in ferret luteal protein synthesis and secretion between Days 5-11 of pregnancy, and neither ovine prolactin (oPRL) nor dibutyryl cAMP (dcAMP) affected the pattern of protein secretion. However, oPRL (100 and 1000 ng/ml) increased incorporation of radiolabeled amino acids into luteal proteins during a 36-h incubation. The relative mobility of a 185-kDa radiolabeled product was identical to that of alpha 2-macroglobulin (alpha 2M) subunits. Antibody to human alpha 2M cross-reacted with a product (185 kDa) in ferret luteal extracts and culture medium, and the partially purified protein (185 kDa) inhibited trypsin activity. The major radiolabeled secretory protein (32 kDa) exhibited weak cross-reaction with antibody to a human tissue inhibitor of metalloproteinase (TIMP). This study demonstrates the wide range of proteinaceous secretory products of the ferret CL, two of which have been tentatively identified as protease inhibitors.