Comparative localization of prolactin-binding sites in different rat tissues by immunohistochemistry, radioautography and radioreceptor assay

Introduction

The major advancements in biomedical research over the past 30 years have been based in the broad field of molecular biology. DNA, RNA, and proteins are now routinely sequenced, altered, and their functions analyzed in great detail. The in situ-based methodologies (immunohistochemistry and in situ hybridization) were in their infancy 30 years ago. Today, they are mainstream, as evidenced by the tens of thousands of peer review articles published each year that have used either methodology. Still, much remains to be learned about how to maximize the power of immunohistochemistry and in situ hybridization. This book starts by building a foundation, assuming little or no prior knowledge in the area of molecular biology. I hope that, at the end of the book, you will have a fount of knowledge that allows you to be very knowledgeable and capable in the in situ-based molecular pathology methods.

Prolactin receptor messenger ribonucleic acid in normal and neoplastic human pituitary tissues

We examined the specific cell types in normal human pituitaries that expressed PRL receptor (PRL-R) messenger ribonucleic acid (mRNA) by combined in situ hybridization and immunohistochemistry. The distribution of PRL-R mRNA in 28 pituitary adenomas was examined by in situ hybridization and reverse transcription-PCR in 12 cases of adenomas. In another set of experiments, 34 PRL adenomas from men, women, and bromocriptine-treated patients were analyzed for PRL-R by in situ hybridization. In the normal pituitary, PRL- and LH-producing cells had significantly more mean grain counts per cell and higher percentages of cells positive for PRL-R than GH and TSH cells. PRL-R mRNA was present in all groups of adenomas by in situ hybridization and reverse transcription-PCR. PRL adenomas had a significantly higher density of labeling compared to other adenoma types. Although there was no difference in the levels of PRL-R mRNA in PRL adenomas from men and premenopausal and postmenopausal women, patients treated with bromocriptine before pituitary surgery had significantly lower levels of PRL-R compared to all other groups. These results indicate that in the normal pituitary, PRL and LH cells have the highest level of PRL-R mRNA, whereas PRL adenomas have significantly higher levels of PRL-R mRNA than other types of adenomas, and bromocriptine treatment decreases the levels of PRL-R mRNA in PRL adenomas.

Prolactin binding sites in the adrenal glands of mink (Mustela vison)

1. The purpose of this study was to determine if the mink adrenal gland might be a target organ for prolactin by establishing whether or not binding sites for the hormone exist in adrenal cell membranes. 2. Adrenal glands were collected from adult female mink in November, 1991, homogenized and subjected to differential centrifugation into three particulate fractions; 1500, 15,000 and 50,000 g. All binding determinations were made using 125I-oPRL and 200-300 micrograms protein from the 50,000 g particulate fraction. Optimal binding occurred within 8 hr at 25 degrees C. 3. Scatchard analysis of saturation data revealed a single set of high affinity (Kd = 9.27 x 10(-11) +/- 1.63 M), low capacity (Bmax = 34.22 +/- 5.37 fmol/mg) binding sites. 4. Binding sites appeared to be hormone specific as only oPRL (73% displacement) and oLH (8% displacement) inhibited binding of 125I-oPRL to adrenal membranes. No inhibition of 125I-oPRL binding to adrenal membranes occurred in the presence of a 500-fold excess of bTSH, oGH or oFSH. 5. Prolactin binding sites were readily detected in adrenal and kidney tissue, but were low in liver and almost non-detectable in spleen or lung tissue. 6. Our data suggest that the mink adrenal gland is a target organ for prolactin and that an interaction between the pituitary and adrenal glands may exist that is important for the regulation of such physiological processes as fur growth cycles.

Presence of immunoreactive growth hormone and prolactin in the ovine pineal gland

The use of antisera raised against bovine growth hormone (GH) and ovine prolactin (PRL) enabled the detection of related immunoreactive (ir) sequences of proteins in ovine pineal tissue. The isolation of PRL-like ir-material was accomplished using a 0.25 M ammonium sulphate (pH 5.5) extraction followed by ethanol precipitation, whereas the resulting 2.0 M ammonium sulphate (pH 7.0) precipitate contained a GH-like immunoreactivity. Gel chromatography of the GH-like immunoreactivity (Sephadex G-100) indicated the presence of several GH-like fragments ranging in the M(r) range of 7,000 to 55,000. Analyses of the PRL-like ir-material found in pineal tissue on HPLC using a TSK 545-DEAE column led to the resolution into a single peak of immunoreactivity. A single peak of activity was also observed following chromatofocusing and hydrophobic interaction chromatography of the ir-peak from the TSK 545-DEAE column. The PRL-like ir-material inhibited the binding of [125I]ovine PRL-S14 to anti-ovine PRL antibodies without showing an affinity for binding to anti-rat PRL or anti-bovine GH antibodies. Scatchard analysis of the binding of pineal PRL-like ir-material and pituitary ovine PRL-S14 to liver membranes from day-20 pregnant rats revealed similar affinity constants (Ka of 4.7 +/- 0.2 x 10(9) M-1). In addition, the replication of Nb 2 Node rat lymphoma cells was stimulated by pineal PRL-like ir-material, an effect known to be specific for lactogenic hormones. The pineal PRL-like immunoreactivity appeared on sodium dodecyl sulfate polyacrylamide gels as a single major band of M(r) 24,000. The functional status of PRL- and GH-like ir-material in the ovine pineal remains to be determined, but evidence is presented that the overall protein synthesis rate of the rat pineal responded to circulating concentrations of PRL.

Prolactin receptor messenger RNA is synthesized by the epithelial cells of the choroid plexus

To identify cellular sites of prolactin receptor messenger RNA synthesis in the rat brain, we used a combined reverse transcriptase-polymerase chain reaction protocol to generate single stranded DNA probes for in situ hybridization. The results of these experiments identify the epithelial cells of the choroid plexus as a major site of prolactin receptor gene expression in the rat central nervous system.

Modulation of IgA synthesis by neuroendocrine peptides

Prolactin, estrogen, and progesterone together induce proliferation of the mammary glands with a coincident increase in the IgA-secreting plasma cells in the tissue. Of these three hormones, Prolactin is the most effective single peptide in stimulating IgA production. Vasoactive intestinal peptide (VIP) and somatostatin have also been shown to modulate IgA production. Although more extensive investigation is required, delineation of an immune axis involving prolactin, VIP, and somatostatin in mucosal immune tissue such as mammary gland is a promising area of research with clinical relevance to neonatal resistance to infection.

The distribution of lactogen receptors in the mammalian hypothalamus: an in vitro autoradiographic analysis of the rabbit and rat

The hypothalamus contains a high concentration of lactogen receptors as detected with in vitro radioreceptor assay techniques. In an effort to define the location of the lactogen receptors relative to specific hypothalamic nuclei, an in vitro autoradiography technique was applied to frozen sections of rat and rabbit brains. Three lactogenic hormones, i.e. human growth hormone (hGH), ovine prolactin (oPRL), and rat prolactin (rPRL), were radiolabeled with iodine-125. Competition for observed binding sites was assessed with unlabeled hGH, oPRL, and bovine growth hormone (bGH). Analysis of the autoradiographs with a microcomputer-based densitometry system revealed that the rabbit hypothalamus contains specific lactogen binding sites within the supraoptic, paraventricular, suprachiasmatic, ventromedial, arcuate, and dorsomedial nuclei and the medial preoptic area. Unlabeled bGH was effective in competing for binding sites in all areas when hGH but not oPRL was used as the radiolabeled ligand, suggesting the presence of growth hormone receptors in the rabbit hypothalamus with a distribution similar to that of the lactogen binding sites. In contrast to the rabbit, no lactogen binding sites were detected in the rat hypothalamus regardless of the ligand used in the assay. All of the ligands were successful, however, in detecting lactogen receptors within the rat choroid plexus and liver. The results from the rabbits indicate that the influences of prolactin on hypothalamic activity are mediated via lactogen receptors that are widely distributed throughout the various pertinent hypothalamic nuclei. The broad distribution of lactogen receptors in the rabbit hypothalamus attests to the extensive influence of prolactin on hypothalamic regulatory systems. The results from the rat raise questions as to the nature of rat brain prolactin receptors in comparison to prolactin receptors in rat peripheral tissues.

Net production of cerebrospinal fluid is decreased by SCH-23390

A high density of binding sites for the ligands 3H-SCH-23390 and 3H-SKF-83566 has been found in the choroid plexus. Although these sites have similar pharmacology to D1 dopamine receptors, the high-affinity component of 3H-SCH-23390 binding in the choroid plexus has been identified as the 5-HT1c subtype of serotonin receptor. We investigated the possible role of these receptors in modulating the production of cerebrospinal fluid (CSF) in rats. (R) SCH-23390 produced up to a 50% decrease in net CSF production, compared to saline. This compound is a partial agonist at 5-HT1c serotonin receptors, and an antagonist at D1 dopamine receptors. The (S) enantiomer of SCH-23390 (SCH-23388) was ineffective. Drugs interacting with receptors for neurotransmitters in the choroid plexus may hold promise for the treatment of patients with increased intracranial pressure, including those with mass lesions, head trauma, acute or chronic hydrocephalus, or pseudotumor cerebri.

Biochemical study of prolactin binding sites in Xenopus laevis brain and choroid plexus

The occurrence of prolactin binding sites in some brain structures (telencephalon, ventral hypothalamus, myelencephalon, hypophysis, and choroid plexus) from Xenopus laevis (anuran amphibian) was studied by the in vitro biochemical technique. The higher binding values were obtained at the level of the choroid plexus and above all of the hypothalamus. On the bases of hormonal specificity and high affinity, these binding sites are very similar to those of prolactin receptors of classical target tissues as well as of those described by us in other structures from Xenopus. To our knowledge, the present results provide the first demonstration of the occurrence of prolactin specific binding sites in Xenopus laevis choroid plexus cells.

Regional distribution and species variation of prolactin binding sites in the brain

The binding of 125I-labeled ovine prolactin (125I-oPRL) to membranes from different brain regions of pigeon, rabbit, rat, pig, calf, horse, and ewe was studied. The hypothalamus from rabbit, pig, horse, and pigeon showed a low but specific binding for 125I-oPRL clearly different from the other brain regions examined (cortex and cerebellum), whereas in the brain from rat, calf, and ewe the binding was very small and quite uniform in the various regions. Also the membranes from choroid plexus of rabbit, pig, calf, and horse showed an evident specific binding for prolactin. The binding of 125I-oPRL to hypothalamus and choroid plexus membranes from rabbit and horse was inhibited in a dose-dependent manner by unlabeled oPRL and hGH but not by many other polypeptide hormones. Scatchard analysis of the binding revealed the presence of binding sites with low capacity and high affinity for ovine ligand.

Use of slide-mounted frozen sections to study the autoradiographic localization, characterization and quantification of luteinizing hormone-releasing hormone receptors in the rat pituitary

Slide-mounted frozen sections were used for the autoradiographic localization, characterization and quantification of LHRH receptors. The radioligand was the iodinated LHRH agonist [D-Ser(TBU)6, des-Gly-NH2(10)]LHRH ethylamide (LHRH-A). Specificity studies demonstrated that specific labeling was concentrated in the anterior pituitary lobe and that the tracer could be displaced with either LHRH or LHRH-A. Scatchard analysis of saturation curves gave one-site interactions with a high affinity (Kd = 0.48 +/- 0.1 nM) for the iodinated LHRH-A. In order to evaluate the effects of different treatments on the LHRH receptor concentration, the effects of sex steroids on the density of radioautographic reaction were evaluated using an image analyzer. The results obtained were similar to those previously reported with classical binding assays. Thus, this simple technique appears suitable for the study of localization and characterization of LHRH receptors in different experimental conditions.

In vivo autoradiographic analysis of prolactin binding in brain and choroid plexus of the domestic ring dove

The binding of intravenously administered prolactin to choroid plexus and brain tissue was determined radioautographically in the ring dove, a species that exhibits prolactin-induced alterations in brain function. An intense autoradiographic reaction was detected over the epithelial cells of the choroid plexus 5 min after the intravenous injection of 125I-ovine prolactin. A significant reaction was also observed over the infundibulum but no significant uptake of prolactin occurred in other brain areas. The binding of radiolabelled prolactin to infundibulum appeared to be non-specific, since excess unlabelled hormone did not reduce silver grain density. In contrast, 125I-ovine prolactin binding in choroid plexus was significantly reduced by excess unlabelled ovine prolactin or human growth hormone, but not by ovine luteinizing hormone. Specific binding to choroid plexus was also detected in vitro. The lack of significant brain uptake of prolactin in vivo is discussed in relation to recent in vitro evidence for specific binding sites for prolactin in several dove brain regions. Similarities between the binding results obtained in this avian species and those reported previously in mammals suggest that the two vertebrate groups exhibit similar patterns of prolactin interaction with neural target tissues.

Extrahypothalamic brain prolactin: characterization and evidence for independence from pituitary prolactin

Prompted by reports of immunohistochemical localization of a prolactin-like immunoreactivity (PLI) within the rat brain, a study was undertaken to define the immunologic and biologic characteristics of this material in extrahypothalamic regions of the rat brain. Ninety-seven percent recovery of rat prolactin standard, added to homogenates of brain parts, insured that neuronal tissue did not interfere with the radioimmunoassay for rat prolactin. PLI was consistently found in the cerebellum, thalamus, brainstem (pons-medulla), hippocampus, cerebral cortex and caudate. Examination of the elution profile of each of the extrahypothalamic brain parts from Sephadex G-75 columns showed that, although a small amount of brain PLI elutes in the vicinity of the anterior pituitary prolactin marker, the bulk of brain-based PLI migrates with the void volume and as late eluting, low molecular weight material. While increasing amounts of brain extracts progressively displaced more 125I-prolactin from antibody binding, the displacement curve was not parallel to that produced by the addition of increasing amounts of anterior pituitary prolactin standards of rat origin. Extracts of various brain parts from hypophysectomized animals, analyzed for biologic activity in the Nb2 lymphoma cell assay, revealed prolactin-like bioactivity, but the bioactivity/immunoreactivity ratio for some of the brain parts was significantly lower than that for pituitary prolactin. Hypophysectomy, which led to the expected fall in serum prolactin to undetectable levels, and restraint stress, which resulted in a statistically significant 4-fold rise in serum prolactin, caused no change in prolactin concentrations in extrahypothalamic brain parts, indicating that brain PLI is regulated independently of pituitary prolactin and of circulating serum prolactin levels.

Characteristics of prolactin binding sites in the brain of the ring dove (Streptopelia risoria)

Radiolabeled ovine prolactin ([125I]oPRL) was found to bind specifically to crude membrane fractions prepared from ring dove brain homogenates. Specific binding changed with incubation time and temperature but did not fluctuate systematically with pH. Specific binding levels were highest in hypothalamus and forebrain and were lowest in cerebellum and brain stem. A linear increase in specific binding was observed in pooled midbrain and forebrain membrane fractions as membrane protein concentrations increased from 0.2 to 6.0 mg/ml. Scatchard analysis of binding saturation and competitive binding data revealed that dove midbrain/forebrain membranes bound oPRL with high affinity (Kd = 2.1-2.6 X 10(-10) M) but had low binding capacity (Bmax = 2.9-4.8 fmol/mg protein). Unlabeled oPRL and human growth hormone competed most effectively with radiolabeled oPRL for occupation of midbrain/forebrain binding sites. Turkey PRL and human placental lactogen were less effective as competitors but were 8-15 times more effective than ovine or turkey growth hormone, porcine insulin, or ovine luteinizing hormone. Subcutaneous injection of unlabeled oPRL lowered specific binding in liver and midbrain/forebrain by 76 and 39%, respectively, over that observed after saline injection. Prior MgCl2-induced desaturation of membrane binding sites greatly reduced or eliminated these treatment differences. These results suggest the existence of specific, saturable binding sites for PRL in dove brain which conceivably could mediate the reported effects of PRL on behavior and gonadal function in this species.

Autoradiographic localization of beta-adrenergic receptors in the rabbit pituitary

The localization and characterization of beta-adrenergic receptors in the rabbit pituitary have been studied using [125I]cyanopindolol as a specific ligand. Slide-mounted frozen sections were used for the autoradiographic localization and characterization of beta-adrenergic receptors. The displacement curves obtained from optical density of radioautograms or counting of scraped off sections demonstrated that beta-adrenergic receptors were mostly of the beta 2-subtype and highly concentrated in the intermediate lobe. Low concentrations of beta 2-adrenergic receptors were also found to be uniformly distributed in the anterior and posterior lobes. These results suggest that epinephrine and/or norepinephrine might play a physiological role in the regulation of the secretion of not only the intermediate lobe but also the anterior and posterior lobes of the rabbit pituitary.

Hypercalciuria in hyperprolactinemic rats: effects of benzthiazide

There is evidence that prolactin (PRL) excess plays a role in the etiology of osteoporosis associated with human prolactinoma. Calcium balance in human hyperprolactinemia has not been thoroughly investigated. In the present study, rats with excess circulating PRL levels (male anterior pituitary-grafted Fischer 344 rats) had urinary calcium excretion twice that of control rats (4.16 +/- 0.43 v 2.25 +/- 0.30 mg/24h X 100 g BW). Calcium excretion expressed per mg of calcium intake was also high in pituitary-grafted rats. The excess calcium excretion in hyperprolactinemic rats was not accompanied by a concomitant rise in sodium excretion. This dissociation suggests that PRL has an effect on the renal handling of calcium. Since thiazide diuretics have a well-described hypocalciuric action, their effect was tested in these rats. In normal rats, benzthiazide, a long-acting agent, significantly reduced urinary calcium excretion in a dose-dependent fashion. Hyperprolactinemic rats responded to benzthiazide in a manner similar to control rats. In pituitary-grafted rats, benzthiazide also decreased the calcium excretion to intake ratio and normalized the calcium to sodium excretion ratio. Since the hypercalciuria of experimental hyperprolactinemia can be corrected by thiazide diuretics, these agents may have therapeutic potential in human PRL excess.

Radioautographic localization of beta-adrenergic receptors in the rat ventral prostate

Previous studies performed with crude homogenates have demonstrated the presence of beta-adrenergic receptors in the rat ventral prostate. The precise localization of these receptors in prostatic tissue, however, has not been determined. The present study describes the localization of beta-adrenergic receptors using in vitro radioautography. beta-adrenergic receptors are present exclusively in the epithelial cells, while no receptors could be detected in the stromal cells. The silver grains mostly are associated with the apical pole of the glandular cells and are much less concentrated in the basal nuclear region of the epithelium. Very low concentrations of grains are found in the lumen of the acini. Castration caused a dramatic fall in the receptor concentration, while treatment with dihydrotestosterone reversed these effects. The specific presence of beta-adrenergic receptors in prostatic epithelial cells and their control by androgens suggest that they could play a physiologic role in androgen action in prostatic tissue. Moreover, the level and activity of beta-adrenergic receptors could be used as parameters of prostatic activity.

Distribution of epidermal growth factor receptors in the rat ovary

The distribution of epidermal growth factor (EGF) was studied in the ovary using light microscope radioautography which was performed at different time intervals (2-60 min) after intravenous (i.v.) injection of [125I]EGF into adult rat at random stages of the estrous cycle and also after topical localization of iodinated EGF on slide-mounted frozen ovarian sections. After i.v. injection of label, the labeling was mostly observed in the theca interna cells of secondary, preovulatory and atretic follicles and luteal cells of corpus luteum. Primordial and primary follicles did not show any significant labeling. The time-course study performed on luteal cells showed that, 2 min after injection, most silver grains were found at the periphery of the cells. At the 10 min time interval, silver grains were found both at the periphery and over the cytoplasm of these cells. The number of grains was very reduced over the cytoplasm at the 60 min time interval. In the in vitro study, a positive radioautographic reaction was seen in the same cellular elements as found in vivo, with the additional labeling of the granulosa cells of growing and preovulatory follicles. Control experiments indicated that the radioautographic labeling was due to specific interaction of [125I]EGF with its receptor. These results clearly indicate that EGF binding sites are present in luteal, thecal and granulosa cells, and provide support for the inhibitory and stimulatory actions of EGF on different parameters of ovarian cells.

Radioautographic localization and regulation of the insulin receptors in rat testis

Luteinizing hormone (LH) is involved in maintenance of the insulin receptor in rat Leydig cells. In the cryptorchid model, spontaneous LH elevation increases insulin binding in Leydig cell membrane; this result is confirmed by the number of insulin receptors determined by radioautography. Administration of testosterone or LH-RH to control or cryptorchid rats lower insulin binding in testis membranes indicating the key role of LH. Isolated Leydig cells respond in vitro to LH by increasing their insulin binding. Localization and specificity of this binding has been studied by radioautography and we have demonstrated the preferential localization of insulin receptor in Leydig cells vs tubular cells. We conclude that insulin plays a synergistic role with LH on steroidogenesis via a specific membrane receptor which number appears modulated by pituitary LH.

Cyclosporine inhibits prolactin induction of ornithine decarboxylase in rat tissues

Cyclosporine (CyA), formerly cyclosporin A, significantly inhibited the ability of prolactin (PRL) to elevate ornithine decarboxylase (ODC) activity in a variety of rat tissues. Administration of PRL to hypophysectomized rats also resulted in an induction of ODC activity which was inhibited markedly in all tissues studied in the presence of CyA. Transglutaminase ( TGase ) activity was not affected in any significant manner by PRL or CyA in most tissues studied. However, it was elevated in the adrenal by 10(-8) M PRL. Bromocryptine, which selectively antagonizes pituitary PRL release, decreased the kidney ODC basal levels to 30% of vehicle control and serum PRL level to 4.3 +/- 1.4 compared to 28 +/- 10 in controls, suggestive of PRL maintenance of steady-state ODC activity in the kidney. CyA administration did not affect the action of glucagon, a known cyclic AMP-mediated hormone, or 8-bromo-cyclic AMP on kidney ODC activity. The elevation of rat kidney ODC activity by dexamethasone and triiodothyronine (T3), compounds which elevated serum prolactin levels in all cases, was also blocked by administration of CyA. Epidermal growth factor (EGF), which did not induce rat kidney ODC activity by itself, was capable of producing a small increment in ODC activity in the presence of CyA. The marked effect of CyA to selectively block ODC induction by PRL may be due to the ability of CyA to interact with receptor-required phospholipids in membranes and thus to antagonize hormone-receptor interaction.