[Studies on specific receptors for prolactin (PRL) in the rat ovary]

The characteristics of specific receptors for prolactin (PRL) in the ovary were examined. The binding of 125I-ovine PRL to the receptor was dependent upon time, temperature, and tissue concentration. Equilibrium was reached by 16 h at 23 degrees C in the 12.5 mg tissue/tube. Scatchard analysis revealed a high affinity, low capacity and single class of binding site. Ovine PRL bound to rat liver membranes with a Kd (dissociation constant) of 3.51 X 10(-10) M and to rat ovarian membranes with a Kd of 2.21 X 10(-10) M, respectively. The number of binding sites in rat liver and ovary were 205.2 fmoles/mg of protein and 226.1 fmoles/mg of protein, respectively. Bound 125I-ovine PRL was displaceable by unlabelled human, ovine and rat PRL but not by rat LH, FSH, TSH or GH. However, on the immunological aspects, 125I-ovine PRL bound only to anti-ovine PRL serum but did not bind to anti-human PRL serum or anti-rat PRL serum. Unlabelled human and rat PRL could not inhibit the binding of labelled ovine PRL to the anti-ovine PRL serum. These data indicate the existence of specific PRL receptors in the rat ovary, the characteristics of which are similar to those of receptors in the liver. The binding specificity for various mammalian species suggests a difference between biological and immunological binding sites of the PRL molecule.