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Biomedical subjects

B I Posner

Publications and source records attributed to B I Posner.

At least 145 records · Page 8Linked to original sources
PubMed1982

Ontogeny of growth factor receptors in the human placenta.

The present study was undertaken to further elucidate the role during gestation of insulin, epidermal growth factor-urogastrone (EGF-URO), and a slightly acidic insulin-like growth factor we have referred to as insulin-like activity (ILAs). We examined the ontogeny of the placental receptors for these peptides utilizing membrane fractions (600 x g, 15,000 x g, 100,000 x g) and cytosol (200,000 x g supernatant) prepared by differential centrifugation of early gestation (11-19 wk) and term gestation (38-42 week) human placentae. Aliquots of each membrane fraction were also assayed for 5' nucleotidase activity. The ontogeny of the insulin and EGF receptors closely resembled the pattern of 5' nucleotidase activity, with greater levels seen in term tissue for all membrane fractions assayed. Highest levels of specific binding per mg protein and enzyme specific activity were seen in the 100,000 x g fraction within either gestational age group. The pattern of [125I]-ILAs specific binding was quite different: binding per mg protein was higher in membranes from early gestation placentae regardless of the fraction, with the biggest differential occurring in the 600 X g pellet. As observed with [125I]-insulin and [125I]-EGF, the 100,000 x g pellets from either age group were also enriched in [125I]-ILAs binding. Although neither early gestation nor term cytosol bound [125I]-insulin or [125I]-EGF, binding of [125I]-ILAs to both gestational age groups was clearly demonstrable with significantly higher levels observed in cytosol from early gestation placentae. A knowledge of the mechanisms involved in placental growth may well be a prerequisite to a full understanding of fetal growth control. The demonstration of specific human placental receptors for insulin, EGF-URO, and ILAs as early as 11-19 wk of gestation suggests that these peptides should continue to receive attention as possible modulators of placental growth and function. Furthermore, the high levels of [125I]-ILAs specific binding to membrane and cytosols from early gestation placentae may indicate a more important role for the insulin-like growth factors compared to insulin or EGF-URO during early placental development.

ErbB Receptors↗
PubMed1982

Brain receptors for blood-borne calcitonin in rats: circumventricular localization and vasopressin-resistant deficiency in hereditary diabetes insipidus.

Specific binding sites for blood-borne calcitonin were localized by means of quantitative radioautography to the circumventricular organs of the rat brain. By this method, using normal Long-Evans rats as controls, specific binding of blood-borne calcitonin in the median eminence region of the hypothalamus was reduced by one-third in homozygous Brattleboro rats, which are genetically deficient in vasopressin. Competitive binding analysis in vitro of the hypothalami from these animals confirmed the binding deficit in homozygous rats, and Scatchard analysis suggested a reduction in the number of binding sites. In homozygous rats daily vasopressin replacement therapy restored normal water balance but did not normalize the hypothalamic calcitonin binding deficit. These studies delineate for the first time specific sites within the central nervous system which could serve to mediate direct actions of blood-borne calcitonin on brain function. The deficit in the Brattleboro rat may provide a model for further investigation of the role of calcitonin within selective regions of the central nervous system.

Animals↗
PubMed1982

The role of cell age in the difference in insulin binding between adult and cord erythrocytes.

Erythrocytes (RBCs) from cord blood are known to bind more insulin than those of adults. We have investigated the possibility that this difference is due to the younger cell age of the neonatal cells. Samples from 13 normal full term neonates and 12 adults were fractionated into 5 fractions of defined density by dextran gradient centrifugation. Fractions of comparable density, a variable known to correlate well with age, were then compared for insulin binding. Plasma insulin and glucose levels were the same in the two study groups. The density distribution curve was shifted to the left for the cord samples, indicating a younger cell age. The difference was most marked in the lightest fraction, which contained 4.66 + 0.46% (mean +/- SE) adult cells vs. 15.26 +/- 1.27% cord cells (P less than 0.01). Insulin binding was identical when fractions of equal density were compared in the two groups. The only exception was the lightest (youngest) fraction (density, less than 1.092), in which the cord cells displayed a considerably higher percentage of specific binding; (19.98 +/- 1.57 vs. 13.32 +/- 0.92 P less than 0.005). This difference was shown to be due to a high percentage of very light cells in cord samples, compared to adult samples, in this fraction which, unlike the others, did not have a lower limit of density. When a lower density cutoff was introduced (1.089 g/ml), the remaining cells of this fraction (density, 1.089-1.092) displayed quite similar percentages of specific binding (13.07 +/- 1.63 vs. 11.86 +/- 1.27). Cells below this density were virtually absent in the adult, comprising less than 0.3% of all adult cells compared to 7.2% of the cord cells. These results indicate that the difference in insulin binding between adult and cord cells is due to a younger RBC age distribution in cord blood. This difference is most marked in the youngest cell fractions. Age fractionation of RBCs by density gradient centrifugation appears to be a promising method of assessing RBC insulin receptors in situations in which substantial changes in cell age are seen.

Adult↗
PubMed1982

The effect of growth hormone treatment on somatomedin levels in growth hormone-deficient children.

Serum levels of immunoreactive somatomedin (IRSM) and insulin-like activity (ILAs) by receptor assay have been measured in 177 GH-deficient (GHD) children treated with 2 U GH three times weekly for 6-10 months. The overall mean (+/- SD) pretreatment IRSM and ILAs levels were 0.21 +/- 0.30 and 0.39 +/- 0.25 U/ml, respectively. Pretreatment IRSM and ILAs levels were in the normal range for chronological age and sex in 15.8% and 33% of these GHD children. Mean IRSM and ILAs levels increased after 1 month of therapy to 0.36 +/- 0.51 and 0.62 +/- 0.33 U/ml, respectively (P less than .0001). The increase in serum IRSM levels (from 0.2 to 2.0 U/ml) that normally occurs from 1-16 yr of age is also evident in untreated GHD children, albeit to a lesser extent. In addition, the mean increase in IRSM after GH was greater in older patients. However, individual responses varied greatly. An increase in IRSM or ILAs with an increase in height velocity (HV) was observed in the majority of children, but all other combinations occurred, including increased SM with decreased HV, decreased SM with increased HV, and decreased SM with decreased HV. In summary 1) age-dependent factors in GHD children importantly influence basal and treatment SM leels; 2) a basal SM level is not a very sensitive diagnostic test, since a significant proportion of GHD children have SM levels in the normal range; and, 3) SM levels in individual patients may not increase with GH therapy and, thus, cannot be used to predict a clinical response to GH therapy.

Adolescent↗
PubMed1981

Intracellular hormone receptors: evidence for insulin and lactogen receptors in a unique vesicle sedimenting in lysosome fractions of rat liver.

Previous studies have established the presence of polypeptide hormone receptors in Golgi fractions from rodent liver. In this study we attempted to identify peptide hormone receptors in other intracellular elements, particularly lysosomes. Tritosomes were prepared by a standard procedure, and highly purified secondary lysosomes were prepared by fractionating the L fraction of rat liver in a discontinuous metrizamide gradient into subfractions L1 to L4. Binding of 125I-labeled insulin and 125I-labeled somatotropin was studied with membranes prepared from osmotically shocked fractions. The L2 and L3 fractions, virtually devoid of galactosyltransferase (UDP galactose:2-acetamido-2-deoxy-D-glucosylglycopeptide galactosyltransferase, EC 2.4.1.38) but highly enriched in acid phosphatase [orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2], appeared as classical secondary lysosomes by electron microscopy. When compared with Golgi fractions, the level of specific binding per 50 micrograms of protein of 125I-labeled somatotropin in L2 and L3 was 1/3, whereas that of 125I-labeled insulin was comparable. L1, which was reduced in acid phosphatase and increased in galactosyltransferase activities, showed higher hormone binding than did L2 and L3. This was not attributable to Golgi fraction contamination, as evident by specific binding/galactosyltransferase ratios. Binding to tritosome membranes could be largely accounted for by variable contamination with Golgi fractions as judged by specific binding/galactosyltransferase ratios. To clarify the distribution of receptor sites in lysosomal preparations, we fractionated the entire L fraction on a continuous Percoll gradient. Acid phosphatase and galactosyltransferase activities were segregated to the high and low density ranges of the gradient, respectively; however, the fractions enriched in hormone binding were of intermediate density, distinct from Golgi and lysosomal biochemical markers. We conclude that intracellular receptors are found not only in galactosyltransferase-containing very low density lipoprotein-marked Golgi vesicles but also in a unique vesicle of intermediate density between classical Golgi and lysosomal structures.

Animals↗
PubMed1981

Decreased sensitivity of old and progeric human fibroblasts to a preparation of factors with insulinlike activity.

To determine whether old cells have a reduced response to a preparation of factors from human plasma with insulinlike activity (ILA), we analyzed the response to ILA of early and late passage human fibroblasts from young, old, and progeric donors in the acute stimulation of [3H]2-deoxy-D-glucose (2dG) uptake and the delayed stimulation of [3H]thymidine (TdR) incorporation into DNA. The ILA concentration required to produce equivalent, relative stimulation of TdR incorporation was increased two- to three-fold in late passage cells and cells from old and progeric donors (P less than 0.01). 50 and 95% of maximal stimulation (ILA50, ILA95) was achieved by 0.26 +/- 0.07 and 1.38 +/- 0.13 ng insulin equivalents/ml (mean +/- SD) respectively, in cells from young adults at early passage. Corresponding values were 0.54 +/- 0.05 and 2.90 +/- 0.25 in cells from old donors; greater than 0.9 +/- 0.1 and greater than 3.1 +/- 0.1 in cells from a 9-yr-old progeric donor; and 0.4 +/- 0.05 and 1.1 +/- 0.04 in cells from normal children (9-13 yr). For two cell strains from young adults, ILA50 and ILA95 were 0.30 +/- 0.02 and 1.0 +/- 0.3 ng eq/ml at 30% of their in vitro lifespan completed (%LC) and these values increased at rates of 0.005 ng eq/ml per %LC and 0.04 ng eq/ml per %LC, respectively. The mean stimulation of 2dG uptake ratio (ILA/control) decreased from early to late passage from 2.1 +/- 0.6 to 1.3 +/- 0.1 in young adult donors (P less than 0.05), but there were no significant differences between young and old donors at either early or late passage. The mean stimulation ratio in progeric cells (1.2 +/- 0.2) did not change with in vitro passage, but was significantly lower than that of age-matched normal cells (2.1 +/- 0.8, P less than 0.001). In progeria cells, the reduced stimulation of 2dG uptake upon addition of ILA was due to an increased basal rate of uptake (0.19 +/- 0.01 pmol [3H]2dG/min per mg protein vs. 0.13 +/- 0.01 in age-matched normal cells), and not to a decline in the maximal rate of uptake (0.26 +/- 0.01 vs. 0.27 +/- 0.02, respectively). Similar results were found for in vitro aging in cells from an old donor.

Adolescent↗
PubMed1981

Receptors for insulin-like peptides (ILAs) in rat reticulocytes and erythrocytes.

Rat reticulocytes possess receptors for an insulin-like somatomedin peptide ILAs. At 20 C, pH 7.4 and 10(8) cells per ml, the binding of 125I-ILAs reached a steady-state at 120 min. Binding was partially reversible at 20 C and totally reversible at 37 C. Insulin did not compete with ILAs at concentrations as high as 10 microgram/ml. Insulin-like growth factor II (IGF II) competed with the same potency as ILAs itself, while insulin-like growth factor I (IGF I) was five times less potent. The optimum pH for 125I-ILAs binding was 8.5. Mature erythrocytes possessed seven times less binding sites than reticulocytes. These data suggest that the somatomedins might mediate the effect of growth hormone on erythropoiesis.

Animals↗
PubMed1981

Blood-borne adrenocorticotropin binds specifically to the median eminence-arcuate region of the rat hypothalamus.

The quantitative light microscope radioautographic approach was utilized to locate specific binding sites for blood-borne 125I-labeled ACTH1-24 in the rat brain. Specific binding occurred exclusively in the external zone of the median eminence, adjacent to the primary portal plexus, and to a lesser extent in the ventral arcuate nucleus. This localization may indicate that the hypophysiotropic median eminence is a new target site for circulating adrenocorticotropin. Alternatively, ACTH binding sites in the median eminence-arcuate region may provide the hypothalamus with a hormone-selective capacity to concentrate pituitary ACTH for possible retrograde transport and redistribution within the central nervous system.

Adrenal Cortex↗
PubMed1981

Specific binding and internalization of blood-borne [125I]-iodoinsulin by neurons of the rat area postrema.

The specificity and cellular location of binding sites for blood-borne [125I]iodoinsulin in the area postrema and adjacent paravagal region of the rat brain was determined by means of quantitative light and electron microscope radioautography. In both regions coinjected unlabeled insulin inhibited the binding of [125I]iodoinsulin in a dose-dependent manner, and insulin analogs blocked [125I]iodoinsulin binding in rank order of their known in vitro bioactivity. Electron microscope radioautography of this region showed that insulin specifically bound to neuronal dendrites and cell bodies and that some of the specifically bound radioactivity was internalized and concentrated in a variety of subcellular vacuoles. These observations demonstrate that certain neurons of the area postrema are endowed with the receptive capacity common to all known insulin-sensitive cells. Anatomic considerations suggest that insulin target neurons in the area postrema could mediate insulin feedback on parasympathetic function by relaying information regarding circulating insulin status to central autonomic circuits governing vagal activity. This study represents the first demonstration of a receptor-mediated uptake and concentration of a blood-borne polypeptide hormone by central neurons.

Animals↗
PubMed1981

Diurnal rhythm of plasma immunoreactive beta-endorphin and its relationship to sleep stages and plasma rhythms of cortisol and prolactin.

To determine the diurnal rhythm of plasma beta-endorphin (beta-End), 10 healthy male volunteers between the ages of 20 and 32 yr were studied in a sleep laboratory setting for a 24-h period. Blood samples were taken through an indwelling catheter at 0800, 1000, 1400, 1800, 2200, 2300, and 2400 h and then half-hourly until 0730 h, and they were then assayed for total beta-End-like immunoreactivity (ir beta-End), PRL, and cortisol. Subjects were habituated by spending the night before the study in the sleep laboratory with an indwelling catheter and electrodes for sleep recording in place. There was a clear diurnal variation of ir beta-End, with lowest levels between 2200 and 0330 h and highest levels between 0400 and 1000 h. There was no evidence for direct entrainment with sleep stage. There was a close correlation with cortisol levels, suggesting a similar secretory pattern for beta-End and PRL in only 5 of the subjects. Because the beta-End antiserum used has a cross-reactivity of 30% with beta-lipotropin gel permeation chromatography was done on extracts of plasma taken at 1400, 2400, 0400, and 0730 h for each subject. The peak in the beta-End elution position showed a clear diurnal variation similar to that of ir beta-End.

Adult↗
PubMed1981

Cellular basis of direct insulin action in the central nervous system.

The in vivo radioautographic method has been applied to elucidate the mechanism of direct peptide hormone "feedback" action in the CNS. Using this method we have identified the circumventricular organs of the brain as general endocrine target tissues for a variety of blood-borne polypeptide hormones, including insulin. In the arcuate-median eminence region of the hypothalamus blood-borne insulin directly interacts with receptive nerve terminals, suggesting that insulin acts to influence the electrical activity of select hypothalamic nerve circuits at the level of synaptic transmission. Recent results obtained from preliminary surgical and chemical lesion studies of brain indicate that insulin-receptive nerve terminals in the arcuate-median eminence region arise from neurons intrinsic to the medial basal hypothalamus. This has lead us to propose the concept of the hypothalamic tuberoinfundibular insulin-receptive neuron and its axon collaterals as a pathway for the centripetal flow of insulin "signals" in the form of electrical impulses. We envisage that the neuroanatomic pathway, provided by the hypothalamic tuberoinfundibular neuron, functions to link changes in the body metabolic activity, as reflected in changing levels of circulating insulin, to the neuronal process of elaborating specific central metabolic-regulatory programs. This pathway could be of key importance in understanding and combating metabolic disease.

Animals↗
PubMed1980

Insulin binding sites localized to nerve terminals in rat median eminence and arcuate nucleus.

Specific binding sites for blood-borne insulin were determined to be selectively localized on axons and axon terminals in the external median eminence and the hypothalamic arcuate nucleus by means of quantitative fine structural radioautography. This localization suggests that discrete populations of hypothalamic nerve terminals are potential targets for the direct effects of insulin and that insulin may act through synaptic mechanisms to influence hypothalamic circuits regulating energy balance and hypophyseal function.

Animals↗