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B I Posner

Publications and source records attributed to B I Posner.

At least 127 records · Page 7Linked to original sources
PubMed1984

Receptor-mediated endocytosis of [125I]insulin into pancreatic acinar cells in vivo.

One of the highest concentrations of insulin receptors is found in the cell membrane of the pancreatic acinar cell. A radioautographic study has been carried out to monitor the fate of in vivo injected 125I-labeled insulin after binding to the acinar cell membrane. [125I]Insulin remained for long periods of time (greater than 45 min) within the exocrine cell. Quantitative radioautography at the electron microscopic level revealed endocytosis of hormone and localization to zymogen granules and, to a lesser extent, multivesicular bodies, lysosomes, structures that were receptosome like, and small undefined structures of about 50-100 nm in diameter found dispersed among endoplasmic reticulum saccules. Treatment with the lysosomotropic agent chloroquine produced large secondary lysosomes which were seldom labeled. Rather, there was an increase in the proportion of label over zymogen granules and receptosome-like structures without increased retention of label by acinar cells. Thus, in pancreatic exocrine cells, nonlysosomal structures are of major quantitative importance in insulin internalization. The high concentration of grains about the bounding membrane of zymogen granules points to a merging of the endocytic and exocytic pathways in pancreatic acinar cells.

Animals↗
PubMed1984

Immunoassay of a somatomedin-binding protein from human amniotic fluid: levels in fetal, neonatal, and adult sera.

We developed a specific RIA for a somatomedin (Sm)-binding protein, with an approximate mol wt of 35-40,000, purified from midgestational human amniotic fluid (AF) and termed AF-binding protein (AFBP). After Sephadex G-200 chromatography AFBP-RIA activity was found in fractions of fetal and cord serum only at a kav corresponding to a mol wt of +/- 40,000. Whole serum or plasma dilutions in a range of 1:20 to 1:600 showed parallelism with the standard curve. Sm-binding activity in fetal serum was found solely at a mol wt of 30-40,000; in cord serum additionally at a mol wt range of 150-200,000. AFBP serum or plasma concentrations determined by RIA were influenced by several factors: AFBP values in eight adults were highest in the morning (mean +/- SEM, 0.7 +/- 0.1 mu geq/ml) and lowest at night (0.3 +/- 0.1). AFBP values in pre- and postnatal serum showed a gradual decline with increasing age: fetal serum: mean +/- SEM, 36.7 +/- 15.7 (n = 17); adults: 0.6 +/- 0.07 mu geq/ml (n = 19). In serum from GH-deficient children AFBP concentrations were significantly higher than in an age-matched control group (P less than 0.05). Elevated values also were found in serum of children with end-stage renal failure and in serum of pregnant women at 36 weeks of gestation. AFBP was found in urine of preterm infants (mean +/- SEM, 0.04 +/- 0.005 mu geq/ml; n = 31). AFBP immunoreactivity was demonstrable in serum of three orangoutan mothers and their three children and in medium of a hepatoma cell line (PLC/PRF/5) but not in bovine, porcine, rabbit, or rat serum or in medium of cell cultures of (pre-)term placentae. We conclude that AFBP immunoreactivity is present in pre- and postnatal serum and has striking similarity to an unsaturated serum Sm-binding protein with a mol wt of +/- 40,000.

Adolescent↗
PubMed1984

Hormone receptors in the epiphysial cartilage.

In order to assess which hormones may exert direct effects on skeletal growth at the epiphysial growth plate, the specific binding of hormones to the epiphysial cartilage of growing dogs and rabbits was studied. Membrane fractions obtained by centrifugation of homogenates prepared from dog and rabbit growth plate cartilage at 600, 15 000 and 105 000 g showed significant specific binding of serum insulin-like activity and insulin. Binding of growth hormone and prolactin by the three membrane fractions was negligible. Saturable binding sites for triiodothyronine could be demonstrated in nuclei from the dog growth plate. Nuclear binding showed an apparent Kd of 11 +/- 3.6 nmol/l and a maximum binding capacity of 4.1 +/- 1.6 pmol/mg DNA, a level comparable to dog liver. Using a viable chondrocyte suspension prepared from dog epiphysial cartilage, specific steroid binding in the cells could be demonstrated for [3H]dexamethasone but not 17 alpha-methyltrienolone, oestradiol-17 beta or 1 alpha, 25-dihydroxycholecalciferol. Scatchard analysis of dexamethasone binding showed high affinity binding sites having a Kd of 1.2 +/- 0.35 nmol/l and a capacity of 1700 sites/cell, and a low affinity binding with a Kd of 109 +/- 57 nmol/l and a capacity of 24 000 sites/cell. Steroid competition for the specific binding showed the following sequence of affinity: dexamethasone greater than corticosterone greater than 11-deoxycortisol greater than testosterone greater than oestradiol-17 beta.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Insulin-like growth factors: a role in growth hormone negative feedback and body weight regulation via brain.

Intracerebroventricular administration of ILA's, a preparation enriched in insulin-like growth factors, caused a marked decrease in growth hormone secretory episodes and in body weight associated with reduced food intake over 24 hours. Central injection of insulin and bovine serum albumin had no such effects. These findings suggest that insulin-like growth factors play a role in growth hormone negative feedback and body weight regulation at the level of the central nervous system.

Animals↗
PubMed1983

Characterization of lactogen binding sites in choroid plexus.

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 125I-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 degrees 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 non-inhibitory.

Animals↗
PubMed1983

Circumventricular organs: receptors and mediators of direct peptide hormone action on brain.

The concept of the brain as an endocrine target organ is not new, nor is it novel to consider the circumventricular organs as receptive regions of the brain for circulating substances. However, in this review we have emphasized the relatively novel concept that CVOs mediate exclusively the direct feedback actions of circulating peptide hormones on brain function. In addition we have presented speculations concerning the neural mechanisms by which signals arising from peptide hormone-receptor interaction might be relayed into the CNS, and indicated the possible involvement of CVO receptors in endocrine disorders. We hope that this analysis provides a conceptual framework for evaluating the functional relationship of circulating peptides to brain and inspires interest in this fascinating area of neuroendocrinology.

Animals↗
PubMed1983

Effect of colchicine on internalization of prolactin in female rat liver: an in vivo radioautographic study.

Binding and internalization of 125I-ovine prolactin into hepatocytes of female rats was visualized by the in vivo radioautographic method (Bergeron, J. J. M., G. Levine, R. Sikstrom, D. O'Shaughnessey, B. Kopriwa, N. J. Nadler, and B. I. Posner, 1977, Proc. Natl. Acad. Sci. USA, 745:051-5055). Receptor-mediated internalization of label was observed into lipoprotein-filled vesicles in the Golgi/bile canalicular region of the hepatocyte. Colchicine treatment had no effect on the internalization of label into the lipoprotein-filled vesicles. However, the location of the radio-labeled lipoprotein-filled vesicles was altered from the Golgi/bile canalicular region to subsinusoidal. Radioactive content of hepatocytes decreased as a function of time after injection of 125I-prolactin; however, colchicine treatment markedly retarded this loss of label. Subcellular fractionation experiments indicated that colchicine treatment led to decreased levels of 125I-prolactin accumulation in microsomes but augmented the accumulation of label in the L fraction. It is concluded that in normal female rats prolactin is internalized into lipoprotein-filled vesicles in the Golgi region before degradation of the hormone. Colchicine treatment accumulates labeled lipoprotein-containing vesicles in a subsinusoidal region and retards hormone catabolism. The labeled vesicles observed after colchicine treatment may correspond to the unique vesicles previously observed in the L fraction and found to be enriched in prolactin receptors (Khan, M. N., B. I. Posner, A. K. Verma, R. J. Khan, and J. J. M. Bergeron, 1981, Proc. Natl. Acad. Sci. USA, 78:4980-4981).

Animals↗
PubMed1983

Immunologic similarity of insulin receptors in Golgi and plasma membranes from rat liver.

Insulin receptor antibodies (IRA) have been shown to inhibit 125I-labeled insulin binding to plasmalemma and whole cells. An earlier study claimed that IRA was less able to inhibit 125I-labeled insulin binding to intracellular receptors than plasmalemma of rat liver. We have examined the effect of IRA serum from a patient with insulin-resistant diabetes mellitus on 125I-labeled insulin binding to plasmalemma and Golgi fractions prepared from female rat liver. Maximum inhibitions of 125I-labeled insulin binding were 44, 48, 55, and 51% for plasmalemma, Golgi light, Golgi intermediate, and Golgi heavy, respectively, and these were maintained at a serum dilution of up to 1:100. Half-maximal inhibition occurred at a serum dilution of 1:900. The IRA serum had no inhibitory effect on 125I-labeled ILAs and ovine prolactin (oPRL) binding to either plasma membrane or Golgi fractions. Analysis of the effect of the IRA serum showed that its inhibition of 125I-labeled insulin binding linearized the Scatchard plot, with abolition of the high affinity portion of the curve, and reduced the number of low affinity sites. The affinity of binding to Golgi but not plasmalemma insulin receptors was decreased. We conclude that there is immunologic similarity between intracellular and cell surface insulin receptors of rat liver. This is compatible with a fairly rapid equilibration between these two receptor populations, as expected with an active membrane recycling process.

Animals↗
PubMed1983

Origin of insulin-receptive nerve terminals in rat median eminence.

The origin of insulin-receptive axon terminals in the rat median eminence was determined by combining surgical and chemical ablation techniques and the in vivo radioautographic approach, in which labeling of the median eminence with blood-borne [125I]insulin served as a quantifiable marker for the presence of receptive axonal elements. Whereas unilateral deafferentation of the median eminence from the ipsilateral brain produced as much as a 50% ipsilateral loss of insulin-binding sites, transection of axonal projections to median eminence from neurons located lateral to the ventromedial hypothalamic nucleus produced no detectable loss in insulin-binding capacity. Unilateral electrocoagulation of various regions of the medial basal hypothalamus indicated that insulin-receptive axon terminals arise primarily from neurons in and about the hypothalamic arcuate nucleus and from the posterior ventrolateral subdivision of the hypothalamic ventromedial nucleus. A primary site of origin from the arcuate nucleus was confirmed in rats treated neonatally with monosodium L-glutamate, which, in addition to a selective destruction of arcuate neurons, produced a profound reduction in the insulin-specific binding capacity of the median eminence. The results of this study indicate that insulin-binding axon terminals arise from a unique class of tuberoinfundibular neuron with hormone-receptive capacity. These neurons may function to mediate direct interaction of circulating insulin with central autonomical, behavioral, and neuroendocrine systems.

Animals↗
PubMed1983

Immunocytochemical detection of insulin in rat hypothalamus and its possible uptake from cerebrospinal fluid.

Insulin-like immunoreactivity (IRI) was detected in the rat hypothalamus, particularly in the paraventricular, periventricular, supraoptic, suprachiasmatic, arcuate, and lateral hypothalamic nuclei. The immunostainable IRI was diffusely distributed in comparison to the neuronal concentrations of immunostainable vasopressin in the periventricular nucleus, or of IRI in islet B cells, suggesting that immunostainable IRI in the hypothalamus is not concentrated in neuronal perikarya. To determine if insulin in cerebrospinal fluid (CSF) may be a source of some insulin in brain tissue, [125I]iodoinsulin was stereotaxically injected into a lateral cerebral ventricle, and the uptake of radioactivity into periventricular hypothalamus was localized by both quantitative autoradiography of paraffin-embedded brain sections and by measuring the radioactivity present in microdissected brain regions. In brains that received lateral ventricular injections of labeled insulin, the concentration of radioactivity in the periventricular region of the hypothalamus, as revealed by autoradiographic grains, was significantly greater than that in the periventricular region of brains that received lateral ventricular injections of labeled insulin mixed with an equimolar excess of an unlabeled peptide (insulin, ribonuclease, or both together). The highest levels of radioactivity detected in both autoradiographic and microdissection procedures were in regions nearest to the third ventricle, suggesting that insulin in the lateral ventricles has access to the periventricular neuropile in the hypothalamus. The staining pattern of immunostainable insulin in the hypothalamus along with the distribution of radioactivity after CSF injection of labeled insulin are consistent with the hypothesis that insulin is taken up into brain from the CSF.

Animals↗
PubMed1983

Receptors for the insulin-like growth factors on human erythrocytes.

We have examined the presence and properties of specific receptors for the insulin-like growth factors (IGFs) on human erythrocytes (RBC). HPLC purified IGF-I and II peptides were used as ligands. RBCs were separated in density fractions representing cell groups of different ages. Binding to all cell fractions was found for both IGF tracers. Porcine insulin displaced this binding only partially, with a potency that was at least 10 times lower. IGF-II was equipotent with IGF-I in displacing [125I] IGF-I binding, but was somewhat more potent than IGF-I in displacing its homologous tracer. In the youngest cell fraction from 7 normal adults, the level of specific binding per 3 X 10(9) cells was 5.2 +/- 0.4% (mean +/- SE) and 6.3 +/- 0.5% of added radioactivity for IGF-I and IGF-II respectively. It declined rapidly as a function of cell age. Binding for unfractionated cell samples was 2.2 +/- 0.1% and 3.1 +/- 0.1% respectively. We conclude that: a) Specific receptors for the IGFs exist on human erythrocytes. b) Binding to these receptors is dependent on cell age. c) The binding in isolated young RBCs is of sufficient magnitude to permit their use for the clinical measurement of these receptors.

Adult↗
PubMed1983

Binding of insulin by monkey and pig hypothalamus.

Membrane preparations from monkey and pig hypothalami bound [125I]insulin specifically. The binding appeared to be greater by preparations from anterior than posterior portions of the pig hypothalamus. Binding was time dependent, and its dissociation was first order with a half-time at 22 degrees C of 14 min. Desalanine insulin was as effective as native insulin in inhibiting the binding of [125I]insulin, while proinsulin was less effective and desoctapeptide insulin still less effective in accord with their biologic activities. Binding by membranes from cortex and thalamus appeared to be less than from hypothalamus. [125I]insulin was infused into an arterial split monkey brain preparation to determine if insulin that was blood borne bound specifically to the primate hypothalamus. Half the brain was perfused with [125I]insulin alone and the other half with [125I]insulin plus an excess of unlabeled insulin. Radioautography showed specific binding of insulin localized to the median eminence, infundibular nucleus, and microvessels. Thus, the monkey and pig hypothalami bind insulin with characteristics similar to those reported for known target tissues for insulin. Furthermore, insulin from the blood stream binds to specific anatomical structures in the hypothalamus of the monkey.

Animals↗
PubMed1982

Galactose transfer to endogenous acceptors within Golgi fractions of rat liver.

The distribution of galactosyl transferase was studied using trans and cis Golgi fractions isolated by a modification of the Ehrenreich et al. procedure (1973. J. Cell Biol. 59:45-72) as well as an intact Golgi fraction isolated by a new one-step procedure. Two methods of assay were used. The first method analyzed the ability of Golgi fractions to transfer galactose (from uridine diphosphogalactose [UDP-gal] substrate) to the defined exogenous acceptor ovomucoid. The second method assessed the transfer of galactose from UDP-gal substrate to endogenous acceptors (endogenous glycosylation). The trans Golgi fraction (Golgi light) was highly active by the first method but revealed only low activity by the second method. Golgi fractions enriched in central and cis elements (the Golgi intermediate, heavy and especially the intact Golgi fraction) were highly active in both methods of assay. The endogenous glycosylation approach was validated by gel fluorography of the endogenous acceptors. For all Golgi fractions, transfer of galactose was revealed to secretory glycopeptides. It is concluded that galactosyl transferase activity in vivo occurs primarily in central and cis Golgi elements but not trans Golgi vesicles.

Animals↗
PubMed1982

Effect of colchicine on the uptake of prolactin and insulin into Golgi fractions of rat liver.

In previous studies we have shown that 125I-labeled prolactin is taken up by a receptor-dependent process and concentrated in an intact form in Golgi elements from female rat liver (J. Biol. Chem., 1979, 254:209-214). In this study we have examined the effect of colchicine on this uptake process into Golgi elements. Colchicine [25 mumol (10 mg)/100 gm body wt] was injected intraperitoneally in adult female rats, and hepatic Golgi fractions were prepared at 1, 2, and 3 h postinjection. The enzyme recoveries and morphological appearance of fractions from colchicine-treated and control (alcohol alone) animals were similar. At times greater than 1 h after colchicine there was a marked (greater than 60%) inhibition of uptake of 125I-ovine prolactin (125I-oPRL) into Golgi light and intermediate fractions but no inhibition of uptake into Golgi heavy and plasmalemma elements. At times from 2 to 45 min postinjection, 125I-oPRL was extracted from Golgi elements and found to be largely intact as judged by rebinding to receptors. The inhibitory effect of colchicine was seen at doses ranging from 0.25 mumol to 25 mumol/100 g body wt. Vincristine also inhibited 125I-oPRL uptake into the Golgi light and intermediate fractions but lumicolchicine had no inhibitory effect. There was a smaller effect of colchicine both at early (1 h) and later (3 h) times on the extent and pattern of 125I-insulin uptake. Colchicine treatment did not produce a significant change in lactogen receptor levels in the Golgi fractions. These results demonstrate that colchicine treatment inhibited the transfer of prolactin into Golgi vesicular elements. The much smaller effect on insulin uptake suggests that there may be differences in the manner in which the two hormones are handled in the course of internalization.

Animals↗