Prolactin binding sites in the uterus of the mink

The present study was conducted to determine if specific binding sites for prolactin (PRL) are present in the uterus of the mink. Uteri of anestrous mink were homogenized and subjected to differential centrifugation into three particulate fractions, 1500, 15 000 and 50 000 X g. Binding of [125I]oPRL to membranes in an aliquot (200-400 micrograms protein) of the 50 000 X g particulate fraction was quantified. Time and temperature for optimal binding were 18 h at 25 degrees C. Scatchard plot analysis revealed a single set of binding sites for PRL with a Kd of 8.25 X 10(-11) +/- 0.68 M. The maximum amount of [125I]oPRL bound was 28 fmoles/mg protein. Prolactin binding sites were detected in both the uterus and kidney of mink, but not in skeletal muscle, spleen, diaphragm or lung. These data indicate that uterine cell membranes of the mink contain sites that bind prolactin with high affinity.