The prolactin, or lactogenic hormone, receptor has been purified (approximately 80%) from lactating mouse liver and human term placenta by the nondenaturing zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate and a prolactin affinity column. The isolated "core-binding unit" has a molecular weight of 37,000 +/- 2,000 daltons. It retains the specificity for lactogenic hormones and binds prolactin with an affinity (Ka = 2 to 6 X 10(9) M-1) similar to that of the receptor as it occurs in its membranous environment (Ka = 3 to 5 X 10(9) M-1). Whether this "core-binding unit" exists on the cell surface in a cryptic or active form is influenced greatly by its association with other membrane proteins and the concentration of phosphatidylcholine within its local membranous environment.

No 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.