Summary
Prolactin binding sites have been demonstrated previously in rat choroid plexus using in vivo radioautography (Walsh et al. 1978). In the present study we have employed this procedure to characterize further the binding specificity of these sites. Following the injection of 125 I-hGH or 125I-oPRL an intense radioautographic reaction was observed over the choroid plexus. The reaction was significantly reduced by coinjecting excess unlabeled hGH or oPRL but not bGH. The specific binding of 125I-oPRL to choroid plexus from rat, rabbit, sheep and pig was demonstrated by in vitro assays. Subsequently a survey of 125I-oPRL specific binding in a number of regions of pig brain indicated that the highest binding was in choroid plexus. A detailed study of the characteristics of 125I-oPRL binding to pig choroid plexus was undertaken. Specific binding increased with choroid plexus homogenate protein to a maximum of 30% (3.0 mg protein/tube). Binding was maximum at 4 ° C by 30–40 h of incubation. During the incubation the integrity of 125I-oPRL in the incubation medium declined steadily to 50% after 20 h and 35–40% after 48 h. Radioactivity eluted from binding sites was fully intact as judged by rebinding to lactogen receptor-enriched membranes. Binding showed a broad pH optimum of 5.5–7.5. On cell fractionation of choroid plexus binding sites were enriched in microsomes. The binding of 125I-oPRL and 125I-hGH was inhibited in a dose-dependent manner by unlabeled lactogens and was of high affinity. hGH and oPRL were equipotent inhibitors of the binding of both radioligands whereas bGH and a variety of structurally unrelated peptides were noninhibitory.
These studies indicate rat choroid plexus binds lactogens other than prolactin as do other wellcharacterized lactogen receptors. Furthermore, the in vitro binding studies on pig brain have demonstrated notable enrichment of lactogen binding sites in choroid plexus and have indicated that they have characteristics of lactogen receptors. The physiologic significance of our findings is unknown but the presence of lactogen receptors in choroid plexus raises the possibility of its being a target organ for prolactin. It is also possible that the receptors play a role in transporting prolactin from the blood to the CSF.
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Bergeron JJM, Levine G, Sikstrom R, O'Shaughnessy D, Kopriwa B, Nadler NJ, Posner BI (1977) Polypeptide hormone binding sites in vivo: Initial localization of 125I-labeled insulin to hepatocyte plasmalemma as visualized by electron microscope radioautography. Proc Natl Acad Sci USA 74: 5051
Bergeron JJM, Posner BI (1979) In vivo studies on the initial localization and fate of polypeptide hormone receptors by the technique of quantitative radioautography. J Histochem Cytochem 27: 1512
Brightman MW (1967) The intracerebral movement of proteins injected into blood and cerebrospinal fluid of mice. Prog Brain Res 29: 19
Clemens JA, Sawyer BD (1974) Identifiction of prolactin in cerebrospinal fluid. Exp Brain Res 21: 399
DiCarlo R, Muccioli G (1981) Presence of specific prolactin binding sites in the rabbit hypothalamus. Life Sci 28: 2299
Fuxe K, Hokfelt T, Eneroth P, Gustafsson J-A, Skett P (1977) Prolactin-like immunoreactivity: Localization in nerve terminals of rat hypothalamus. Science 196: 899
Josefsberg Z, Posner BI, Patel B, Bergeron JJM (1979) The uptake of prolactin into female rat liver: Concentration of intact hormone in the Golgi apparatus. J Biol Chem 254: 209
Kopriwa BM, Leblond CP (1962) Improvements in the coating technique of radioautography. J Histochem Cytochem 10: 269
Login IS, MacLeod RM (1977) Prolactin in human and rat serum and cerebrospinal fluid. Brain Res 132: 477
Lowry OH, Rosebrough NJ, Farr AL, Randall RJ (1951) Protein measurement with the Folin phenol reagent. J Biol Chem 193: 265
McMurty JP, Malvern PV (1974) Radioimmunoassay of endogenous and exogenous prolactin in milk of rats. J Endocrinol 61: 211
Nolin JM, Witorsch RJ (1976) Detection of endogenous immunoreactive prolactin in rat mammary epithelial cells during lactation. Endocrinology 99: 949
Pollay M (1974) Transport mechanisms in the choroid plexus. Fed Proc 33: 2064
Posner BI, Kelly PA, Shiu RPC, Friesen HG (1974) Studies of insulin, growth hormone and prolactin binding: Tissue distribution, species variation and characterization. Endocrinology 95: 521
Posner BI, Kelly PA, Friesen HG (1974) Induction of a lactogenic receptor in rat liver: Influence of estrogen and the pituitary. Proc Natl Acad Sci USA 71: 2407
Posner BI, Josefsberg Z, Bergeron JJM (1979) Intracellular polypeptide hormone receptors: Characterization and induction of lactogen receptors in the Golgi apparatus of rat liver. J Biol Chem 254: 12494
Tolis G, Wilson G, Kleissl P, Naftolin F, Posner B (1979) Seminal fluid prolactin: Studies in normal subjects and in hypergonadotropic oligospermia. Fertil Steril 32: 96
Toubeau G, Desclin J, Parmentier M, Pasteels JL (1979) Compared localizations of prolactin-like and adrenocorticotropin immunoreactivities within the brain of the rat. Neuroendocrinology 29: 374
Van Deurs B (1978) Microperoxidase uptake into the rat choroid plexus epithelium. J Ultrastruct Res 62: 168
Van Deurs B, Von Bulow F, Moller M (1981) Vesicular transport of cationized ferritin by the epithelium of the rat choroid plexus. J Cell Biol 89: 131
van Houten M, Posner BI, Kopriwa BM, Brawer JR (1979) Insulin binding sites in the rat brain: In vivo localization to the circumventricular organs by quantitative radioautography. Endocrinology 105: 666
van Houten M, Posner BI (1981) Cellular basis of direct insulin action in the central nervous system. Diabetologia 20: 255
Walsh RJ, Posner BI, Gulati AN, Weingold AB (1982) Comparison of cerebrospinal fluid electrolyte concentrations between normal and hyperprolactinemic patients. Horm Metab Res 14: 557
Walsh RJ, Posner BI, Kopriwa BM, Brawer JR (1978) Prolactin binding sites in the rat brain. Science 201: 1041
Witorsch RJ, Smith JP (1977) Evidence for androgen dependent intracellular binding of prolactin in rat ventral prostate gland. Endocrinology 101: 929
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Supported by NIH grants 1R01AM 19573-01 (B.I.P.) and NS15609 (R.J.W.) and MRC grant MA-7749. During this work Dr. Van Houten was supported by a grant from the Canadian Diabetes Association
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Posner, B.I., van Houten, M., Patel, B. et al. Characterization of lactogen binding sites in choroid plexus. Exp Brain Res 49, 300–306 (1983). https://doi.org/10.1007/BF00238589
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DOI: https://doi.org/10.1007/BF00238589