PORCINE CONCEPTUS AND ENDOMETRIAL RETINOID-BINDING PROTEINS

Porcine conceptus secretory proteins were obtained from medium in whic h pig conceptuses, collected on Day 15 of pregnancy, were cultured for 30 h. Culture medium was pooled, dialysed and concentrated by Amicon ultrafiltration for retinol and retinoic acid (RA) binding studies. Pr oteins in the 20-kDa range, conceptus-secreted retinol-binding protein (RBP), bound both [H-3]retinol and [H-3]RA specifically. Cross-compet ition experiments indicate that [H-3]RA was completely displaced with excess cold retinol; however, excess cold RA did not completely displa ce [H-3]retinol, suggesting that conceptus RBP has greater affinity fo r retinol than RA. Cellular RBP and retinoic acid receptor (RAR)-alpha and RAR-gamma mRNA transcripts (0.7 kb; 3.8 and 2.8 kb; 3.4 kb respec tively) were detected in poly (A)(+) RNA isolated from Day-15 conceptu s, Day-15 pregnant endometrium, late pregnant myometrium and late preg nant fetal tissues of pigs by Northern blot analysis. RAR-alpha and RA R-gamma immunoreactive proteins were detected in extracts of Day-15 co nceptus, Day-15 pregnant endometrium and late pregnant fetal tissues b y Western blot analysis. Collectively, results indicate that biochemic al molecules required for retinoid transport, metabolism and regulator y effects are present in porcine conceptus and endometrial tissues dur ing early pregnancy in swine.