Localization of mRNA coding for the three subtypes of atrial natriuretic factor (ANF) receptors in rat anterior pituitary gland cells

Atrial Natriuretic Factor (ANF) action is mediated by highly selective and specific receptors. Three subtypes have been characterized and cloned: ANF receptor-A, -B and -C. These subtypes are all expressed in the anterior pituitary of the rat. In the present study, the mRNA for each subtype was detected by in situ hybridization. The amounts of ANFR-A and -B mRNA were found to be similar, and to be twice that of ANFR-C mRNA. At the ultrastructural level, the three types of ANFR mRNA were expressed in three anterior pituitary cell types, namely lactotrophs, corticotrophs, and gonadotrophs, identified by their hormonal content. No signal was revealed in somatotrophs or thyrotrophs. The different forms of mRNA were similar in terms of subcellular localization: in the cytoplasmic matrix and the nuclear euchromatin. These data indicate that the anterior pituitary is an important target tissue for ANF action.

An attempt to explain interindividual variability in 24-h urinary excretion of inorganic arsenic metabolites by C57 BL/6J mice

Forty C57 BL/6J mice, injected subcutaneously with 0.5 mg/kg arsenic as sodium arsenite, were examined for 24-h urinary excretion of total arsenic metabolites, creatinine and S-adenosylmethionine (SAM) and for 24-h faecal excretion of arsenic and levels of arsenic in the blood, liver, kidneys, lung, skin, spleen and bone at 24-h post-dose. Total urinary arsenic metabolites were calculated by summing up the inorganic (Asi), monomethylated (MMA) and dimethylated (DMA) derivatives directly measured by selective arsine generation-atomic absorption spectrometry (AG-AAS) or were measured by AG-AAS following complete mineralization. Both sets of results showed interindividual differences varying by as much as 7-fold and correlated with the 24-h urinary excretion of both SAM (r = 0.84 and r = 0.86, respectively) and creatinine (r = 0.82 and r = 0.87, respectively). There was interindividual variability of about a 30-fold range in 24-h faecal excretion of arsenic which correlated inversely with 24-h urinary excretion of arsenic metabolites (r = -0.69) and 24-h urinary excretion of both creatinine (r = -0.70) and SAM (r = -0.67). Body tissue levels of arsenic were low and not related to 24-h urinary excretion of arsenic metabolites, SAM and creatinine. Taken together, the results indicate that differences in the profile of urinary arsenic excretion and in the retention of arsenic in a particular organ do not contribute to interindividual variability in 24-h urinary excretion of arsenic metabolites by C57 BL/6J mice, but that variability in faecal excretion does, at least in part. It is speculated that there is most likely a predominant contribution from a diffuse tissue retention of arsenic or from a third route of arsenic elimination, i.e. respiratory, to this phenomenon in view of the small faecal contribution.

Cellular localization of the growth hormone receptor/binding protein in the human anterior pituitary gland

The increasing use of GH therapy has led to the description of its target cells in human tissues, but no data are yet available on the localization of the GH receptor in the human pituitary. In the present study, we used immunocytochemistry to detect the presence of GH receptor/binding protein (GHR/BP), and we examined its distribution among the different types of human anterior pituitary cells. Human pituitaries were taken from autopsies and were processed for embedding in paraffin wax. Immunocytochemistry was performed by using monoclonal antibody 263 raised against purified rat and rabbit GHR/BP, which cross-reacts with the human GH receptor. In order to determine the types of cells that display immunoreactivity for GHR/BP, adjacent pituitary sections were used to detect immunoreactivity for GH, PRL, ACTH, TSH, LH, and FSH. Several controls were carried out to verify the specificity of the immunostaining. Receptor immunoreactivity was found in the cytoplasm and nuclei of the somatotrophs, lactotrophs, and gonadotrophs but not in the thyrotrophs or corticotrophs. In order to demonstrate that the detected GHR/BP immunoreactivity was not caused solely by a cellular capture, we also investigated the cellular distribution of GHR gene expression. This was performed by in situ hybridization with use of complementary oligonucleotide radioactive probes encoding distinct domains of the GHR. Several tests were carried out to validate the detection of gene expression. In situ hybridization demonstrated the presence of GHR messenger RNAs in the anterior lobe of human pituitary, and examination of the signal strengthened the cell-specificity of GHR gene expression. These results demonstrate the presence of GHR/BP in discrete human pituitary cells and indicate a paracrine, autocrine, or intracrine role for GH in the pituitary.

Oxytocin receptor messenger ribonucleic acid: characterization, regulation, and cellular localization in the rat pituitary gland

The hypothalamic neuropeptide oxytocin (OT) stimulates the release of several pituitary hormones, including ACTH, LH, and PRL. Although specific OT receptors have been identified in anterior pituitary membranes, the structure and cellular localization of these binding sites have not been elucidated. We previously cloned a rat OT receptor (OTR) gene and showed that its expression in rat uterus results in several transcripts ranging in size from 2.9-6.7 kilobases. In this study we show, by using Northern blot analysis, reverse transcriptase-polymerase chain reaction, and ultrastructural in situ hybridization that the same OTR gene is also expressed in the pituitary, where it gives rise to a 6.7- and a 4.8-kilobase messenger RNA. Ultrastructural in situ hybridization combined with immunogold labeling indicated that pituitary OTR gene expression is highly cell-specific and restricted to lactotrophs. In accordance with this finding, only the lactotroph-derived cell line MMQ expressed the OTR gene among several pituitary cell lines tested. Northern blot analysis, reverse transcriptase-polymerase chain reaction, and in situ hybridization analysis indicated a dramatic increase in pituitary OTR gene expression at the end of gestation and after estrogen treatment. Our results suggest that the OT effect on lactotrophs is direct, whereas OT actions on gonadotrophs and corticotrophs are either indirect or mediated via different receptors. Moreover, our findings imply that OT exerts its full potential as a physiological PRL-releasing factor only towards the end of gestation, and that therefore the role of OT as a hypothalamic PRL-releasing factor may so far have been underestimated.

Interindividual variability in the urinary excretion of inorganic arsenic metabolites by C57 BL/6J mice: possible involvement of a thiol/disulfide exchange mechanism

The 24-h urine of 75 C57 BL/6J mice injected s.c. with 0.5 mg/kg arsenic as sodium arsenite were examined for creatinine, S-adenosylmethionine (SAM), urea and inorganic arsenic metabolites including inorganic arsenic (ASi), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). There was interindividual variability of about a 10-fold range in the 24-h urinary excretion of creatinine (80-642 micrograms/24 h, variability (cv) of 33%), SAM (7.5-67.2 micrograms/24 h, cv of 38%), urea (9.5-89.7 mg/24 h, cv of 36%), ASi (0.1-1.6 microgram/24 h, cv of 48%), MMA (0.17-2.1 micrograms/24 h, cv of 50%), DMA (0.73-8.13 micrograms/24 h, cv of 32%) and total arsenic metabolites (1.0-10.4 micrograms/24 h, cv of 31%). Interindividual differences, varying by as much as 5-7-fold, were also found in the urinary proportion of ASi (3-23%, cv of 41%) and MMA (5-22%, cv of 37%), but not in the urinary proportion of DMA (64-90%, cv of 7%). The 24-h urinary excretion of all arsenic metabolites correlated with the 24-h urinary excretion of urea (r = 0.81), creatinine (r = 0.88) and SAM (r = 0.83) as did the 24-h urinary excretion of urea with creatinine (r = 0.94) and SAM (r = 0.86), and the 24-h urinary excretion of creatinine with SAM (r = 0.94). Taken together, these results suggest that the overall intracellular glutathione (GSH)-dependent redox state, as reflected by the 24-h urinary excretion of SAM and creatinine, is involved in the interindividual variability in total arsenic metabolite excretion by C57 BL/6J mice. These preliminary results were also discussed with regard to the involvement of intracellular GSH-dependent redox state in the regulation of the reduction and of the methylation steps of arsenic, and to interindividual variability in the urinary excretion of total arsenic metabolites as a possible complicating factor in the biological monitoring of occupational exposure to arsenic.

In situ gene expression of growth hormone (GH) receptor and GH binding protein in adult male rat tissues

Pituitary growth hormone (GH) acts as a growth promoter in a wide range of tissues after binding to its specific GH receptor (GHR) or to a cytosolic circulating GH binding protein (GHBP). To further characterize GH target cells in the rat, in situ hybridization was used to investigate the tissue and cell distribution of mRNAs encoding GHR and GHBP, and their hepatic developmental expression was examined. Cryostat sections of adult male rat tissue were hybridized with [35S]dATP-labeled oligonucleotide antisense probes, one directed against a specific sequence of the intracellular domain of rat GHR mRNA, the other against the hydrophilic tail of rat GHBP mRNA. Several tests were carried out to validate the in situ detection of mRNA. Co-expression of the two transcripts in liver, spleen, thymus, kidney, adrenal, skin, muscle, heart, and pituitary was autoradiographically detected. However, relative expression levels, as demonstrated by computer-assisted microdensitometry, appeared to be variable. Both transcripts showed higher levels of expression in the liver, anterior and intermediate pituitary lobes, outer kidney medulla, adrenal cortex, skin epidermis, heart and muscle, but lower levels in spleen, thymus, hypodermis, adrenal medulla and posterior pituitary lobe. As a physiological control, hepatic levels of expression were examined during development, and the two forms of mRNA were found to be present at low levels in fetal liver, increasing considerably after birth. These results permit the identification in the adult male rat of cells that might be directly responsive to GH, and demonstrate the differential expression of rGHR and rGHBP transcripts.

Localization of growth hormone receptor messenger RNA in human tissues

In order to identify GH target cells in human tissues, we investigated the celiuiar distribution of human GH receptor (GHR) messenger RNA. This was performed byin situ hybridization and Northern blot hybridization using complementary radioactive DNA probe encoding part of the extracellular domain of the GHR. Several tests were carried out to validate the detection of gene expression. Our results demonstrate that the GHR gene is expressed in all human tissues studied, including liver, muscle, kidney, heart, skin, thymus, adipose tissue, placenta, testis, ovary and mammary gland. The quantification of thein situ hybridization signal by densitometric analysis showed a greater expression of GHR transcript in liver, muscle, kidney, heart, and skin epidermis, and a reduced expression in thymus, mammary gland, testis, ovary, and dermis/ hypodermis. These results confirm the widespread distribution of the GHR gene expression in human tissues and identify the cells that might be responsive to GH.

Ultrastructural study of intestinal lactase gene expression

The distribution of the mRNA encoding rat intestinal lactase-phlorizin hydrolase (LPH) was analyzed by ultrastructural in situ hybridization, and compared to the distribution of the cognate protein. Different pictures were obtained depending on the epithelial cell position along the crypt-villus axis: i) cells localized at the crypt base were devoid of LPH mRNA and protein; ii) cells of the crypt-villus junction and of the villus base showed a high level of mRNA but a low amount of enzyme; and iii) enterocytes of the middle and upper part of the villi exhibited an intense protein immunolabeling, but a low content of LPH mRNA. The analysis of the intracellular distribution of the LPH mRNA revealed a gradient of concentration along the cellular axis, as the transcripts were the most abundant in the apical and subapical domains of the enterocytes. In addition, LPH mRNA labeling was often paired or arranged in a circular shape, suggesting that the transcripts may be located in closed vicinity to rounded structures within the cytoplasm. The results indicate that distinct patterns of mRNA and protein occur along the villus height during the continuous process of cell differentiation of the intestinal epithelium. In addition, the emergence of the functional polarity of the enterocytes comes together with the establishment of an intracellular gradient of concentration of the mRNA encoding a brush border enzyme. A link between the intracellular distribution of LPH mRNA molecules and the membranous flow is proposed.

Receptor-mediated nuclear translocation of growth hormone

We have previously shown that the growth hormone (GH) receptor-binding protein is associated with the nucleus. We show here both by electron microscopy and nuclear isolation that GH is subject to rapid nuclear translocation. The intracellular fate of intravenously injected 125I-bovine growth hormone (bGH) was examined in the rat hepatocyte by electron microscopic autoradiography. The hormone appeared rapidly at the plasma membrane, then sequentially in lysosomal and multivesicular bodies and/or the nuclear membrane before final translocation to the nuclear matrix. Maximal translocation to the nuclear matrix occurred within 30 min of injection. Nuclear translocation of 125I-hGH was also studied by isolation of nuclei from cells stably transfected with cDNAs encoding the GH receptor, GH-binding protein, and a membrane bound but cytoplasmic domain-deficient receptor. Specific internalization and nuclear translocation of hormone only occurred in cells transfected with the full-length receptor. The translocation was rapid and became saturated within 1 h after addition of hormone to the culture media. SDS-polyacrylamide gel electrophoresis of isolated nuclei showed that GH is transported to the nucleus as the intact molecule. Pretreatment of cells with lysosomotropic agents (chloroquine, ammonium chloride, and bacitracin) decreased hormone degradation and increased nuclear translocation of GH. The nuclear translocation of GH was achieved independent of the cytoskeletal system (microtubular, microfilament, and intermediate filament networks). Thus, GH is subject to rapid receptor-dependent nuclear translocation via the endosomal pathway.

Signal transduction by the growth hormone receptor

It has been proposed that dimerization of identical receptor subunits by growth hormone (GH) is the mechanism of signal transduction across the cell membrane. We present here data with analogs of porcine GH (pGH), with GH receptors (GHR) mutated in the dimerization domain and with monoclonal antibodies to the GHR which indicate that dimerization is necessary but not sufficient for transduction. We also report nuclear uptake of GH both in vivo and in vitro, along with nuclear localization of the receptor and GH-binding protein (GHBP). This suggests that GH acts directly at the nucleus, and one possible target for this action is a rapid increase in transcription of C/EBP delta seen in 3T3-F442A cells in response to GH. This tyrosine kinase-dependent event may be an archetype for induction of other immediate early gene transcription factors which then interact to determine the programming of the subsequent transcriptional response to GH.

Expression of the growth hormone receptor gene in human digestive tissue

We have examined the forms and the distribution of the messenger ribonucleic acids (mRNAs) encoding the GH receptor (GHR) in human digestive tissues. GHR mRNAs were identified and characterized by Northern blot, dot blot, and in situ hybridization analyses, using complementary DNAs coding for the extracellular part of the human liver GHR. Amplification using the polymerase chain reaction was also used, as tissues express low levels of GHR mRNAs. Our results demonstrate that the GHR gene is expressed in human liver, pancreas, esophagus, stomach, small intestine, and colon. A single 4.5-kilobase mRNA form, which probably encodes the full-length membrane receptor, was detected. GHR mRNA was visualized by in situ hybridization in hepatocytes, exocrine pancreas, and some islet cells; signal was also present in the mucosa of the digestive tract. No specific GH-binding-protein mRNA was found, suggesting that in man, the soluble form of the receptor is generated through proteolytic cleavage of the membrane receptor.

Role of extracellular glutathione and gamma-glutamyltranspeptidase in the disposition and kidney toxicity of inorganic mercury in rats

The role of extracellular glutathione (GSH) and membrane-bound gamma-glutamyltranspeptidase (gamma-GT) as contributory factors in the disposition and toxicity of inorganic mercury (HgCl2, 1 mg kg-1, i.p.) was investigated in rats pretreated with acivicin (AT-125, 10 mg kg-1), a gamma-GT inhibitor. A high degree of gamma-GT inhibition (75%) and of protection (90%) against HgCl2-induced nephrotoxicity was obtained in gamma-GT-inhibited rats 24 h post-treatment. Pretreatment with acivicin affected the fractional distribution profile of 203 Hg, resulting in a twofold decrease in the renal incorporation of mercury 4 h post-treatment and a threefold increase in the 24-h urinary excretion of mercury. Plasma radioactivity remained constant over 24 h in rats dosed with 203Hg alone, whereas it decreased by 60% between 4 h and 24 h in gamma-GT-inhibited rats. In gamma-GT-inhibited rats treated with HgCl2 the renal and plasma reduced glutathione (GSH) content increased by 68% and 330% respectively, as compared to controls. The gamma-GT inhibition affected the distribution profile of mercury within urinary proteins, shifting the binding of mercury from the high-molecular-weight fraction (3% against 80%) to the low-molecular-weight fraction (72% against 10%). A significant but less impressive shift of mercury from the high- to the low-molecular-weight fraction also arose in the plasma. These results taken together support the pivotal role of extracellular GSH and membrane-bound gamma-GT in the renal incorporation, toxicity and excretion of inorganic mercury in rats.

Growth hormone receptor binding protein in rat anterior pituitary

GH is synthesized by the somatotrophs in the pituitary, where it may have paracrine actions. In order to identify the GH target cells in rat pituitary, the cellular distributions of rat GH receptor binding protein messenger ribonucleic acid (rGH-RBP mRNA) and protein were investigated at the electronmicroscopic level, using in situ hybridization and immunocytology, respectively, on ultrathin frozen sections of rat pituitary. Ultrastructural distribution of 125I-bGH, 30 min after intracardiac administration was also performed in order to determine the pituitary cell types that bind the labeled hormone. In situ hybridization was performed using digoxigenin-labeled oligonucleotide probe revealed by indirect immunogold reaction. rGH-RBP mRNA was readily identified in the cytoplasmic matrix, associated with the endoplasmic reticulum and the nucleus of the somatotrophs, the lactotrophs and the gonadotrophs. No significant signal was detected in the corticotrophs or thyrotrophs. The number of gold particles in each pituitary cell type was estimated by direct counting, and was compared to the results of hybridization performed on rat liver sections as a control. The results showed that the level of rGH-RBP mRNA was higher in hepatocytes than in the pituitary cells, and was higher in the somatotrophs and lactotrophs than in the gonadotrophs. Immunocytological detection of rGH-RBP was performed using two monoclonal antibodies (mAbs 43 and 263) directed against independent epitopes of the extracellular domain of the rGH-R. Indirect immunocytological detection showed regionalization of rGH-RBP; it was present in the cytoplasmic matrix and the nucleus of the hepatocytes and in discrete pituitary cells: somatotrophs, lactotrophs and gonadotrophs, but not in thyrotrophs or corticotrophs. Gold particle number was also higher in somatotrophs and lactotrophs than in gonadotrophs and higher in the nucleus compared to the cytoplasmic matrix. Radioiodinated GH was uptaken 30 min after injection by the same three pituitary cell types, showing evidence for the functional role of the GH receptor. In conclusion, we find that the cellular localization of rGH-RBP mRNA and protein is similar in discrete cell subpopulations of the pituitary, suggesting a direct effect of GH on somatotrophs, lactotrophs and gonadotrophs, through paracrine, autocrine or intracrine mechanisms.

Visualization of gene expression of short and long forms of prolactin receptor in rat digestive tissues

Several effects of prolactin have been characterized in various tissues of the gastrointestinal tract. In the present study, the expression of short and long forms of prolactin receptor was explored and quantified in the digestive tract and correlated to the prolactin specific functions. Sections of all digestive tissues were analyzed by in situ hybridization, using 35S-labeled oligoprobes unique to each form of receptor. Macroautoradiogram signals were quantified and expressed in arbitrary units. In rat liver, prolactin receptor mRNAs are expressed to a much greater degree in females than in males. The short-form transcript is significantly expressed to a greater degree in liver, whereas the long form predominates in the pancreas and esophagus. In the remainder of the gastrointestinal tract, there is an equivalent distribution of short- and long-form transcripts. Relatively high signal intensities are seen in the stomach, duodenum, jejunum, ileum, and colon, whereas the rectum is essentially negative. The identification of prolactin receptor gene expression to limited regions should help establish specific functions associated with this hormone in the digestive tissues.

Internalization and nuclear localization of peptide hormones

The presence of neuropeptide receptors on the plasma membrane is well accepted, as is its internalization and down-regulation. The analysis of the fate of these peptides within their target-cells is difficult. Endogenous peptides or administered native peptides are visualized in these cells using immunocytology after cryoultramicrotomy. Labelled peptides can be injected and their internalization kinetics studied using ultrastructural autoradiography. The pituitary gland is a suitable model for the study of the neuropeptide mechanism, with the lactotroph function being taken as an example in the present case. Prolactin (PRL) release depends on two main neuropeptides: thyrotropin-releasing hormone (TRH) and somatostatin (SS). The TRH immunoreactivity obtained from endogenous as well as injected material was restricted to the plasma membrane, secretory granules, cytoplasmic matrix and nucleus. The internalization kinetics of exogenous native TRH showed an increase of immunoreactive material in all compartments including the nucleus. The endogenous SSs (SS14 and SS28) were detected in the same subcellular lactotroph compartments. Injection of 125I-SS showed a rapid binding of SS at the plasma membrane level before internalization. For 60 min of in vivo uptake, 125I-SS28, the large SS molecule, was detected in the cytoplasm only, while 125I-SS14 was found in the nuclear matrix. In vitro 125I-SS28 was restricted to the nuclear membrane. Under physiological conditions the endogenous neuropeptides were visualized in the nucleus, but after injection of labelled peptides only small molecules were found in the nucleus. The significance of the presence of these neuropeptides is discussed.

Ultrastructural localization of endogenous hormones and receptors in bone tissue: an immunocytological approach in frozen samples

In addition to their well-known mechanical role, bones are essential for the regulation of calcium phosphate metabolism. Most of the peptide and steroid hormones acting on bone tissue exert their cellular effects directly on bone cells after binding to cell receptors. A combined method using immunocytology on ultrathin frozen sections has been applied to bone tissue and made possible the ultrastructural localization of endogenous hormones and hormone receptors. There is immunocytological evidence, at the osteoblast level, for: (1) the presence of calcitonin, parathyroid hormone, growth hormone, 1,25 dihydroxyvitamin D3, aldosterone, corticosterone and progesterone; (2) the existence of 1,25 dihydroxyvitamin D3 and progesterone receptors; (3) the absence of estradiol and receptors, testosterone and gonadoliberin. Ultimate goals of future studies are to extend the ultrastructural localization of hormones at the osteoclast level, to assess the distribution of adhesive proteins and of their receptors in bone cells and matrix, and to use well-calcified human bone samples in order to evaluate better the role of therapeutic agents.

Prolactin receptor immunoreactivity in rat anterior pituitary

Prolactin (PRL) receptors have been identified in both classical and nonclassical target organs. Actions of PRL on the secretion of anterior pituitary hormones have been reported. In order to confirm the presence of PRL receptors on specific cell types of the anterior pituitary, immunocytology on ultrathin frozen sections was carried out using monoclonal antibodies specific to the rat PRL receptor. Anterior pituitary glands were removed and fixed in 4% paraformaldehyde or 2.5% glutaraldehyde and postfixed in 1% osmium tetroxide. Tissues were frozen and ultrathin sections were made by cryoultramicrotomy. In anterior pituitary cells, all endocrine cell populations showed PRL-R-like immunoreactivity. The relative labeling frequency based on immunolabeling studies was somatotrophs > lactotrophs > thyrotrophs approximately corticotrophs > gonadotrophs. Within all endocrine cell types, no apparent differences could be observed in the subcellular localization of PRL-R-like immunoreactivity. At the subcellular level, gold particles, either isolated or in groups of two, were seen at the level of the plasma membrane, in the cytoplasmic matrix, in the vicinity of the endoplasmic reticulum and in the nucleus. The identification of receptors specific to PRL within different cells of the anterior pituitary raises the interesting possibility that PRL may act via an autocrine or paracrine network in regulating anterior pituitary function.

Intracellular gonadotropin-releasing hormone immunoreactivity in gonadotrophs of intact or castrated male rats: semiquantitative estimation of testosterone and GnRH antagonist treatment

Changes in intracellular gonadotropin-releasing hormone (GnRH) immunoreactivity (GnRH-IR) in pituitary gonadotrophs were assessed by the use of a semiquantitative immunocytochemical method in male rats undergoing various manipulations known to greatly modify gonadotropin secretion. In basal conditions, immunoreactive GnRH was localized in the cytoplasmic matrix, the secretory granules and the nucleus of these cells. Following intravenous stimulation with GnRH (100 ng i.v.), the GnRH-IR increased rapidly in all these three subcellular compartments, peaking at 15 min. In untreated, long-term castrated rats, GnRH-IR increased both in the basal state and after administration of GnRH. Injection of the castrated rats with testosterone propionate reduced the observed GnRH-IR to the level observed in intact rats. Acute or chronic treatment of castrated rats with a potent GnRH antagonist rendered GnRH-IR completely undetectable in all the three previously positive subcellular compartments of gonadotrophs, and GnRH-IR did not reappear after stimulation with GnRH. In sum, the fact that modifications of GnRH immunoreactivity are observed in rat gonadotrophs: (1) confirms the GnRH internalization process; (2) suggests different sites of action for GnRH within the cell, and (3) demonstrates rapid clearance of intracellular GnRH after stimulation.

Ultrastructural expression of prolactin receptor in rat liver

Prolactin (PRL) is a trophic hormone which acts mainly at the plasma membrane level of hepatocyte. The mechanisms involved in the transduction of the signal after binding of PRL to its receptors are not yet well documented. In the present study we have examined the subcellular patterns of PRL receptor expression in rat liver by ultrastructural in situ hybridization and immunocytology. In situ hybridization was performed using digoxigenin-labeled oligonucleotide probes revealed by indirect immunogold reaction. The expression of both the long and short forms of PRL-receptor mRNA was readily identified in the cytoplasmic matrix, and in association with the endoplasmic reticulum, but a low expression of these forms was detected in the nucleus of hepatocyte. Moreover, this expression appeared clearly higher in female rather than in male hepatocytes. On the other hand, immunogold detection of PRL-receptor protein was performed using two monoclonal antibodies (U5 and T6), specific to the extracellular domain of the PRL-receptor. Indirect immunocytological detection confirmed the presence of PRL receptor-like immunoreactivity at the level of the plasma membrane, and in the cytoplasmic matrix associated or not with endocytotic vesicles, the endoplasmic reticulum, the peroxisomes, the Golgi complex, and the nuclei of both male and female hepatocytes. No clear difference was found between U5 and T6 mAbs, with regard to the subcellular localization. These results show the distribution of both PRL-receptor mRNA and PRL receptor protein in numerous subcellular compartments of hepatocyte, and evidence that these compartments are involved in the early stage of the PRL action.

Evidence for the presence of alpha and beta-related T3 receptors in rat liver mitochondria

Although the dependence of mitochondrial structure and function on thyroid hormone status is well established, several attempts to demonstrate a direct pathway of T3 action on mitochondria have been made during the last decade without being firmly conclusive. In this study, we present evidence firstly for the presence of specific binding sites for [125I]-T3 in rat liver mitochondria 5 min after injection, as assessed by ultrastructural autoradiography. In the same way, using immunocytological techniques and protein immunoblotting, T3 receptor-like immunoreactivity was revealed mainly in the nucleus and mitochondria of hepatocytes. Whereas the colloidal gold labeling over mitochondria was found to be specific at the ultrastructural level, these results were confirmed biochemically by Western blotting experiments which revealed the presence of two protein bands in mitochondria: a stronger one of 55 kDa and a weaker one of 48 kDa. At the opposite, receptor T3 mRNAs were not detected in mitochondria by ultrastructural in situ hybridization thus confirming that the synthesis of receptor T3 occurs in the cytoplasm and that nuclear-encoded T3 receptors may belong to the bulk of cytosolic precursor polypeptides which are targeted to and imported into mitochondria. These results confirm that a direct pathway of T3 action on mitochondria occurs in situ which could now explain how the rapid activation of several mitochondrial functions can take place within minutes after thyroid hormone injection.

Orthodontic treatment needs in Westmead Hospital Dental Clinical School

One hundred and fifty-four adolescents, 76 female and 78 male consented to take part in this survey. The two authors examined and assessed them for dental aesthetics, malocclusion related features and TMJ related signs. The patients were also questioned about their opinion of dental aesthetics, their interest in having orthodontic treatment and their TMJ symptoms. Only 63 per cent of the adolescents who were considered suitable for orthodontic treatment expressed an interest in wanting treatment. Twenty-seven per cent of patients had signs and/or symptoms of TMJ disturbance. No association was found between individual malocclusion problems and TMJ signs and symptoms. The authors considered 56.5 per cent of the total group for orthodontic treatment, the majority for aesthetic reasons, and placed them into high, medium and low priority groups. Fixed appliance therapy for both arches was the recommended type of treatment for most patients.

Visualization of gene expression of short and long forms of prolactin receptor in rat reproductive tissues

Prolactin receptor gene expression was visualized in various tissues by in situ hybridization. Probes specific to the intracellular domains of the short and long form of receptor were prepared. The specificity of these signals was controlled by competition with excess unlabeled homologous probes or heterologous probes; moreover, some tissues, such as penis and vagina, show no expression of either form of receptor mRNA. Macroautoradiogram signals (optical density) were quantified and expressed in arbitrary units. The long form of receptor mRNA was preferentially expressed in testis, epididymis, prostate, seminal vesicle, and mammary gland from lactating animals, whereas the expression of the two forms of mRNA was equivalent in ovary, uterus, and pregnant mammary gland. Signals were also localized at the light microscopic level to individual cells. This approach has permitted the precise localization of prolactin receptor mRNAs in reproductive tissues. Actions of prolactin have not been demonstrated in all tissues expressing receptor transcripts; thus it will be interesting to correlate the expression of long and short forms of receptor with specific functions.