Binding sites for lactogenic hormone in the rat uterus

Particulate fractions from both bilateral trauma-induced deciduoma and the remainder of the uterine wall contain ovine prolactin (o-PRL) binding activity which 1) is time and pH dependent, 2) is displaceable by excess unlabeled o-PRL but not by hormones without lactogenic activity, 3) binds an amount of ¹²⁵I-iodo-o-PRL comparable to that bound by rabbit mammary gland particles and 4) is more concentrated in the decidual tissue than in the remaining uterine wall. Two thirds of the binding activity sedimented between 1000 and 40,000g after Polytron homogenization in buffer containing 0.25 M KCl. The presence of NaN₃ during the prolonged incubation required to reach equilibrium resulted in lower nonspecific binding of PRL. Unilateral trauma was associated with markedly lower PRL binding by the deciduoma; the reduction was less in the case of the uterine wall. Both tissues of the unilaterally traumatized horn bound more PRL than did the untraumatized horn. In vitro binding by corresponding tissues from the pregnant uterus was comparable to that of the untraumatized pseudopregnant uterus. This may be attributable to endogenously bound placental lactogenic hormone.