Role of ovarian steroids in development of uterine binding sites for prolactin in the ferret.

The objectives of this study were to investigate 1) the presence of specific prolactin (PRL) binding sites in the ferret uterus, 2) the uterine location of 125I-labeled ovine PRL (oPRL) binding sites, 3) changes in uterine PRL binding sites during pseudo-pregnancy, and 4) regulation of PRL binding sites by ovarian steroids. Binding was determined through use of 125I-oPRL and 300-800 micrograms of protein from the 50,000 x g particulate fraction. Optimal binding occurred within 6 h at 25 degrees C. Scatchard analysis of saturation data revealed a single set of high-affinity (Kd = 4.99 x 10(-11) +/- 0.88 M), low-capacity (22.76 +/- 1.62 fmol/mg) binding sites. Analysis of hormonal specificity revealed that ovine growth hormone (oGH) cross-reacted with oPRL for the uterine binding sites, displacing 38% of the bound ligand. However, no inhibition of 125I-oPRL binding occurred in the presence of a 500-fold excess of bovine thyroid-stimulating hormone (bTSH), ovine LH (oLH), or ovine FSH (oFSH), suggesting hormonal specificity of the binding sites that are located in the luminal and glandular epithelium. Prolactin binding to ferret uterine membranes increased during the first half of pseudopregnancy, plateaued between Days 21 and 28, and then declined. The concentration of PRL binding sites in uteri of ferrets on Day 1 of pseudopregnancy was 4.91 +/- 0.42 fmol/mg of protein.(ABSTRACT TRUNCATED AT 250 WORDS)