Technical note: A radioimmunoassay for porcine intrauterine folate bindingprotein

A RIA was developed for porcine intrauterine folate binding protein (FBP). Displacement of [I-125]FBP caused by increasing dilutions of uterine flushi ngs collected from either d-15 pregnant or nonpregnant gilts or media from culture of endometrial tissue from d-15 pregnant or nonpregnant gilts was p arallel to the displacement caused by the standard curve. Addition of known amounts of purified allantoic fluid FBP to dilutions of either intrauterin e flushings or endometrial culture medium were measured accurately with the RIA. To test specificity, 2-mL samples of uterine flushings collected from d-15 pregnant and nonpregnant gilts were preincubated with 10 mu Ci of [H- 3]folic acid and then chromatographed using Sephadex G-100 (Sigma Chemical Co., St. Louis, MO). The fractions were subsequently assayed for radioactiv ity by Liquid scintillation spectrophotometry and for FBP by RIA. The [H-3] folic acid and FBP peaks coincided, indicating that the RIA is specific for FBP. Uterine flushings were collected on d 10, 11, 12, 13, 14, and 15 of t he cycle or pregnancy from 1) White crossbred, 2) progesterone-treated Whit e crossbred (200 mg of progesterone at 48 and 72 h after estrus), and 3) Me ishan gilts and assayed for FBP. Total FBP increased 140-fold from d 10 to 15, and the pattern of change across day did not differ between pregnant an d nonpregnant gilts. Progesterone treatment increased intrauterine FBP cont ent on d 10 and II. No difference in FBP concentrations was detected betwee n White crossbred and Meishan gilts. These results indicate that; the RIA f or FBP is valid, allowing measurement of this protein in uterine flushings and endometrial culture medium. The onset of FBP secretion by the uterus be tween d 10 and 15 of the cycle or pregnancy is influenced by the timing of onset of progesterone influence in a manner similar to the endometrial prot eins uteroferrin and retinol binding protein. In contrast to these endometr ial proteins, FBP concentrations are similar in Meishan and White crossbred gilts.