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Induction of Prolactin (PRL) Receptors by PRL in the Rat Lung and Liver. Demonstration and Characterization of a Soluble Receptor^*

T. AMIT, R. J. BARKEY, M. GAVISH and M. B. H. YOUDIM

Rappaport Family Institute for Research in the Medical Sciences Haifa 31096, Israel
Department of Pharmacology, Faculty of Medicine, Technion-Israel Institute of Technology Haifa 31096, Israel

Abstract

A soluble PRL receptor has been identified in the 100,000 x g supernatant from homogenates of lungs and livers of male and female rats treated with either estradiol (E₂; 2 mg kg^–1 day^–1 for 7 days, sc) or ovine PRL (oPRL; 0.1 mg kg^–1 day^–1 for 14 days, sc). Fifty percent of the total PRL-binding activity in the liver homogenate of E₂-treated male rats was found in the supernatant fraction, and only 12% in intact female rats. The soluble PRL receptor has the same specificity, protein dependence, and binding affinity (K_a = 2.8 x 10⁹ M^–1) characteristics as the membrane-bound receptor. A sheep anti-PRLreceptor antiserum specifically inhibited the binding of [¹²⁵I] iodo-oPRL to the soluble PRL receptor. Column chromatography on Sepharose 6B revealed a single peak of [¹²⁵I]iodo-oPRLreceptor complex from liver of E₂-treated rats, having a mol wt of 340,000, whereas the 100,000 x g supernatant from lungs and livers of oPRL-treated rats revealed two specific peaks of [¹²⁵I] iodo-oPRL complex with mol wts of 340,000 (A) and 165,000 (B), respectively. Peak A represented 25% and 27% and peak B, 35% and 49% of the total column radioactivity for liver and lung 100,000 x g supernatant fraction, respectively. Peak B coeluted with a rabbit anti-oPRL antiserum, suggesting that it is a PRL antibody. Anti-PRL-receptor antibody reduced the radioactivity associated with peak A but not peak B. Heat inactivation at 60 C (30 min) resulted in a complete loss of binding in peak A without affecting peak B. The results indicate that the soluble PRL-binding sites, increased in rat lung and liver after treatment with oPRL or E₂, may represent an intermediate step in new receptor synthesis before incorporation into the membrane. (Endocrinology 114: 545, 1984)

Footnotes

^* This work was supported by grants from the Chief Scientist’s Office of the Israel Ministry of Health and from the Wellcome Trust, England (to M.B.H.Y. and R.J.B.) and is in partial fulfillment of the requirements for a D.Sc. thesis (by T.A.) at the Technion-Israel Institute of Technology.

To whom requests for reprints should be addressed.

To whom correspondence should be addressed.

Received January 31, 1983.

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