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 deter mine the ability of ferret CL to synthesize and secrete proteins durin g the preimplantation period. Products recovered from the medium were separated by one- and two-dimensional SDS-PAGE followed by fluorograph y and were quantified by densitometry. Selected secretory proteins wer e tentatively identified with specific antibodies on Western blots. Fe rret CL synthesized and secreted a relatively large number of radiolab eled products. The predominant secretory proteins had molecular masses of 16, 22, 28, 32, 47, 68, and 185 kDa and were secreted at all stage s of the preimplantation period. There were no qualitative changes in ferret luteal protein synthesis and secretion between Days 5-11 of pre gnancy, 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 lutea l proteins during a 36-h incubation. The relative mobility of a 185-kD a radiolabeled product was identical to that of alpha2-macroglobulin ( alpha2M) subunits. Antibody to human alpha2M cross-reacted with a prod uct (185 kDa) in ferret luteal extracts and culture medium, and the pa rtially purified protein (185 kDa) inhibited trypsin activity. The maj or radiolabeled secretory protein (32 kDa) exhibited weak cross-reacti on with antibody to a human tissue inhibitor of metalloproteinase (TIM P). This study demonstrates the wide range of proteinaceous secretory products of the ferret CL, two of which have been tentatively identifi ed as protease inhibitors.