Induction of Cryptic Lactogenic Hormone Binding in Livers of Adult Female Mice Treated Neonatally with Estradiol or Nafoxidine

Abstract

Female mice were treated with 25 micrograms of either estradiol-17 beta or the antiestrogen Nafoxidine (U11100A) or sesame oil carrier within 36 h of birth. The former treatments result in persistently elevated serum PRL levels in the adult animals. Therefore, when the mice reached maturity (3-6 months of age), their livers were examined for the level of lactogenic binding. When microsomal preparations were examined for their ability to bind either lactogenic hormone, PRL, or hGH, no differences in the control or treated groups were observed. The presence of masked or cryptic binding sites were observed. The presence of masked or cryptic binding sites was examined by either solubilization of the membrane preparations or by treatment with the methyl donor S-adenosyl-L-methionine. In all cases cryptic sites were present. In control animals unmasking of cryptic binding sites produced an increment in binding of 20-60%, but in the estradiol-17 beta- and Nafoxidine-treated animals, a 120-170% increase in binding sites was observed with no significant changes in Ka. These increases observed in the latter groups are similar to the 94-175% increase seen in livers of late pregnant and lactating mice. Thus, the persistently high serum PRL levels in neonatally treated mice result in the induction of hepatic lactogenic receptors, primarily in a masked or cryptic form.

Purification of a prolactin receptor.

“…The high-affinity PRL-binding proteins were eluted next with 5 M MgCl2/0.5% Chaps. High MgCl2 previously had been used to elute receptors from hGH affinity columns (4) and as an agent for exchange binding assays in some species (7,20,22,23 NaDodSO4/polyacrylamide gel electrophoresis profiles of the solubilized membranes and affinity-purified receptor eluted with 5 M MgCl2 are shown in Fig. 2.…”