Steen Gammeltoft - Academia.edu (original) (raw)

Papers by Steen Gammeltoft

International Journal of Pediatric Obesity, 2007

To investigate whether changes in leptin concentrations during weight loss can be explained by ge... more To investigate whether changes in leptin concentrations during weight loss can be explained by gender, puberty, baseline adiposity and changes in adiposity, body composition, rate of weight loss, physical activity and insulin concentrations. A longitudinal study with 9 repeated measures during a 12-week weight loss programme. Fifty-three boys and 62 girls (7.9-15.2 years) with body mass index (BMI) standard deviation scores (SDS) of median 2.78 and 2.70, respectively. Height, weight, fat mass percentage assessed by bioimpedance, Tanner stages, testicular size, physical activity scores, blood leptin (ng/ml) and insulin concentrations (pmol/l) were measured at baseline, and except for Tanner stage and testicular size, repeated regularly during the programme. The weight loss was accompanied by a steep decline in leptin concentrations during the first 10-11 days, followed by a less steep decline until day 82. Leptin declined to 39% in boys and 51% in girls of the level that was expected given the relationship at baseline between leptin and BMI SDS, and the BMI SDS changes during weight loss. The biphasic leptin decline was independent of gender, puberty, baseline adiposity or concomitant changes in BMI SDS, fat mass percentage, rate of weight loss, physical activity scores or insulin concentrations. The biphasic leptin decline, which exceeded the level expected, was independent of puberty, baseline adiposity and changes in adiposity, body composition, rate of weight loss, physical activity scores and insulin concentrations. The dissociation of the leptin-weight relationship during weight loss may contribute to the general leptin variability in obese subjects.

Cellular and Molecular Methods in Neuroscience Research

The development of polymerase chain reaction (PCR) produced a technological breakthrough in nucle... more The development of polymerase chain reaction (PCR) produced a technological breakthrough in nucleic acid detection by increasing molecular sensitivity capabilities. In situ PCR is a marriage of two established technologies: PCR and in situ hybridization based on the amplification within intact cells or tissue sections of specific DNA sequences, or mRNA species, to levels detectable by in situ hybridization and/or immunohistochemistry. Thus, PCR results can be correlated spatially with cell morphology.

Regulatory Peptides, 1999

The histamine-producing ECL cells are numerous in the acid-producing (oxyntic) mucosa. They respo... more The histamine-producing ECL cells are numerous in the acid-producing (oxyntic) mucosa. They respond to gastrin by secretion of histamine that acts on parietal cells to produce acid. In addition, gastrin has a trophic effect on the oxyntic mucosa which is exerted on stem cells and ECL cells. To elucidate the molecular actions of gastrin on the stomach we attempted to identify genes that are regulated by gastrin in oxyntic mucosa and in isolated ECL cells. Differential display polymerase chain reaction was used to identify mRNAs that are differentially expressed in rats that are hypergastrinemic after treatment with the proton pump inhibitor omeprazole for 48 h compared with rats that are hypogastrinemic after 24 h fasting. Differences in mRNA levels were confirmed by Northern blot analysis (comparing mRNA from fasted rats, omeprazole-treated rats and rats treated with omeprazole 1 the CCK (cholecystokinin) receptor antagonist 2 YF476). The cDNAs were identified by sequencing followed by data base search. Hypergastrinemia induced by omeprazole treatment resulted in overexpression of mRNA for histidine decarboxylase, fetuin, pepsinogen and cytochrome P450 in the oxyntic mucosa. This was prevented by CCK receptor blockade. In isolated ECL cells gastrin upregulated mRNAs for histidine decarboxylase and 2 synaptotagmin V as well as one mRNA transcript without known homology.

Peptides, 1984

Binding charactert~tic.~ and role m degradathm. PEPTIDES 5(2) 367-370, 1984.~The physiological ro... more Binding charactert~tic.~ and role m degradathm. PEPTIDES 5(2) 367-370, 1984.~The physiological role of VIP in the liver is controversial. VIP receptors are present, hut their function in the metabolic regulation is uncertain. The interaction of porcine VIP with isolated cells from pig liver was studied with respect to receptor-binding, degradation and giycogenolytic action. In this model, VIP and hver showed homology of animal species. I. Receptor-binding was heterogenous with Ka values of 10-s mol/I and 4-10-s mold, and a total amount of binding sites of 7.10-H tool per liP cells. The peptide specificity showed that porcine and chicken VIP were equally potent in inhibiting receptor-bound ~aI-VIP; secretin was about 30 times less potent; giucagon and somatostatin were ineffective. 2. Receptor-bound ~nI-VIP was degraded since about 70% was released as radioactivity not reacting with VIP-antiserum. 3. Glucose-release was not stimulated by VIP (10-e mold) whereas the rate was increased twofold by glueagon (10-6 tool/i). In conclusion, VIP receptors in pig liver cells are different from other tissues regarding peptide specificity. It is suggested that receptor-binding mediates degradation of VIP by pig liver rather than metabolic effects. Neuropeptlde Binding sites Liver Receptor-mediated degradation Giycogenolysis

Neuroscience, 1995

The chromaffin cells of the adult rat adrenal medulla are essentially growth arrested in situ, bu... more The chromaffin cells of the adult rat adrenal medulla are essentially growth arrested in situ, but can proliferate in vitro, suggesting the existence of growth inhibitory factors in the adrenal gland. We have investigated whether pituitary adenylate cyclase-activating polypeptide 38 (PACAP38) could be involved in the growth arrest of adrenal chromaffin cells. In adult rat adrenal gland, PACAP38 was detected by radioimmunoassay and high-performance liquid chromatography and its concentration in the medulla was estimated as 24 nmol/kg wet tissue. Immunohistochemistry of the neonatal and adult rat adrenal medulla showed PACAP38 immunoreactivity in a widely distributed network of delicate nerve fibers surrounding the chromaffin cells. In a primary culture system, PACAP38 inhibited growth factor-stimulated DNA synthesis by 90% in neonatal and adult rat chromaffin cells with half-maximal inhibition at 4 and 0.5 nM, respectively, as demonstrated by bromodeoxyuridine pulse-labeling and immunocytochemical staining of cell nuclei. In comparison, corticosterone inhibited neonatal and adult chromaffin cell proliferation by 70% and 95%, respectively, with half-maximal effect at 100 nM. In neonatal chromaffin cells, 100 nM PACAP38 and 1 microM corticosterone added together abolished proliferation completely (99.8% inhibition). Finally, PACAP38 increased cell survival but showed little neurite-promoting activity in the chromaffin cells. Our data suggest that neurally derived PACAP38, in conjunction with glucocorticoids, may override growth factor mitogenic signals, leading to the postmitotic state of chromaffin cells in the adult adrenal medulla.

Neuroscience, 1999

Transforming growth factor-βs are members of a superfamily of multifunctional cytokines regulatin... more Transforming growth factor-βs are members of a superfamily of multifunctional cytokines regulating cell growth and differentiation. Their functions in neural and endocrine cells are not well understood. We show here that transforming growth factor-βs are synthesized, stored and released by the neuroendocrine chromaffin cells, which also express the transforming growth factor-β receptor type II. In contrast to the developmentally related

Molecular and Cellular Endocrinology, 1999

Leptin regulates energy homeostasis via binding to receptors in the hypothalamus and peripheral t... more Leptin regulates energy homeostasis via binding to receptors in the hypothalamus and peripheral tissues. We have investigated the signaling pathways and effects of leptin on glucose transport in C 2 C 12 muscle cells. Long and short forms of leptin receptor are expressed in differentiated C 2 C 12 myotubes. Leptin enhanced the DNA-binding activity of the transcription factor STAT3 and extracellular signal-regulated kinase 2 (ERK2) activity was stimulated by leptin after 15 min. Leptin increased glucose uptake and GLUT4 recruitment to the cell surface after 30 min, whereas no changes in GLUT1 was observed. PD98059, an ERK2 kinase-1 inhibitor, and wortmannin, an inhibitor of phosphatidylinositol 3-kinase blocked the leptin-induced increase in glucose uptake and GLUT4 recruitment to the cell surface. In contrast, insulin-stimulated glucose transport and GLUT4 translocation was inhibited by wortmannin, but not by PD98059. Our results suggest that leptin may regulate glucose metabolism by acting directly on skeletal muscle and that the signaling pathways involved may be different from that activated by insulin.

The Journal of Pediatrics, 1986

Journal of Neuroscience Research, 1992

Receptor‐mediated internalization and degradation of insulin‐like growth factors, IGF‐I and IGF‐I... more Receptor‐mediated internalization and degradation of insulin‐like growth factors, IGF‐I and IGF‐II, were studied in primary cultures of neonatal rat astrocytes. Surface‐bound IGF‐II was rapidly internalized and 80% of cell‐associated radioactivity was located intracellularly after 30 min. IGF‐I was internalized at a slower rate, and only 40% of cell‐associated radioactivity was inside the cell utter 30 min. A pulse‐chase experiment demonstrated that 55% and 70% of internalized IGF‐I and IGF‐II, respectively, was degraded to free amino acids after a 3‐hr chase. Lysosomal and protease inhibitors had different effects on the binding, internalization, and processing of IGF‐I and IGF‐II. Inhibition of lysosomal acidification by chloroquine increased the amounts of surface‐bound IGF‐II and intracellular IGF‐I and reduced the degradation of IGF‐I. The chelating agent phenanthroline increased the surface binding of IGF‐I and IGF‐II and internalization of IGF‐II and reduced the degradation o...

Journal of Neurochemistry, 2002

Neurotrophic factors yield neuroprotection by mechanisms that may be related to their effects as ... more Neurotrophic factors yield neuroprotection by mechanisms that may be related to their effects as inhibitors of apoptosis as well as their effects on ion channels. The effect of ciliary neurotrophic factor (CNTF) on high‐threshold voltage‐activated Ca channels in cultured fetal mouse brain cortical neurones was investigated. Addition of CNTF into serum‐free growth medium resulted in delayed reduction of the Ca2+ currents. The currents decreased to 50% after 4 h and stabilized at this level during incubation with CNTF for 48 h. Following removal of CNTF the inhibition was completely reversed after 18 h. CNTF reduced the current of all pharmacological subtypes of Ca channels as shown by use of selective blockers of L, N, and P/Q type Ca channels (nifedipine, ω‐conotoxin MVIIA, ω‐agatoxin IVA). The Ca channel depression was mediated via the CNTF receptor, because enzymatic cleavage of the α‐subunit glycerophosphatidylinositol anchor of the receptor eliminated the response. The CNTF effe...

Journal of Neurochemistry, 1992

To elucidate the function of insulin-like growth factor-I1 (IGF-11) in the choroid plexus, the ge... more To elucidate the function of insulin-like growth factor-I1 (IGF-11) in the choroid plexus, the gene expression and receptor binding of IGF-I1 were studied in isolated epithelial cells from the porcine choroid plexus. The choroid plexus expressed multiple IGF-I1 transcripts of 1.2, 1.6, 2.4, and 4.4 kb, at levels higher than those found in porcine liver and kidney. These data suggest that IGF-I1 is synthesized by the choroid plexus. Choroid plexus epithelial cells contained high levels of IGF-I receptors on the cell surface whereas very low levels of receptor binding were found for 1251-IGF-II and '251-insulin. Solubilization of epithelial cells showed that a large proportion of the IGF-I receptors were present in the detergent-insoluble fraction whereas IGF-I1 receptors and insulin receptors were concentrated in the detergent-soluble fraction. These results suggest that IGF-I receptors are located in clathrin-coated pits of the plasma membrane whereas IGF-I1 receptors and insulin receptors are present in endosomal vesicles. The tyrosine kinase activity of the IGF-I receptor @subunit was stimulated by IGF-I, IGF-11, and insulin, in order

Experimental and Clinical Endocrinology & Diabetes, 2009

Diabetes, 1998

To identify molecules that contribute to insulin resistance, we compared the patterns of gene exp... more To identify molecules that contribute to insulin resistance, we compared the patterns of gene expression in skeletal muscle of the obese ob/ob mouse, a genetic model of obesity and severe insulin resistance, with that of its thin littermate (ob/+) using the mRNA differential display method. From about 9,000 cDNAs displayed, we found 12 differentially expressed in ob/ob mice skeletal muscle that could be recovered from the differential display gels and confirmed by Northern blot analysis and sequenced. Eight mRNAs were overexpressed in ob/ob muscle: Id2 (a negative regulator of the basic helix-loop-helix family of transcription factors), fast skeletal muscle troponin T, ribosomal protein L3, the integral protein of the peroxisomal membrane 22PMP, the mammalian homolog of geranylgeranyl pyrophosphate synthase, an mRNA related to phosphatidylinositol-glycan-specific phospholipase D, and two unknown mRNAs. The level of overexpression of these mRNAs in skeletal muscle varied from a 500% ...

Diabetes, 1991

The insulin-receptor affinity of five human insulin analogues with one to four amino acid substit... more The insulin-receptor affinity of five human insulin analogues with one to four amino acid substitutions was measured with human hepatoma cells (HepG2). The binding affinities ranged from 0.05% for Asp 825 insulin, 18% for Asp B9 ,Glu B27 insulin, 80% for Asp B28 insulin, and 327% for Asp B1° insulin to 687% for His A8 ,His B4 ,Glu B10 ,His B27 insulin relative to human insulin. Binding constants obtained by competition experiments at steady state with [ 125 l]Tyr A14-labeled insulin and unlabeled analogues and by kinetic studies with [ 125 l]Tyr A14-labeled analogues and insulin gave essentially the same values. The kinetic studies showed that differences in affinity between analogues were due to differences in both dissociation and association rate constants. The affinity for insulinlike growth factor I receptor was low, ranging from <0.005% for Asp 825 insulin to 0.6% for His A8 ,His B4 ,Glu B10 ,His B27 insulin. The potencies of insulin analogues in activation of the tyrosine kinase of solubilized and partially purified insulin receptors from HepG2 cells, measured with the exogenous substrate poly(Glu 80-Tyr 20), ranked in the same order as the binding affinities, the actual values being somewhat elevated for the high-affinity analogues, however. We conclude that these human insulin analogues are active in insulin-receptor binding and tyrosine kinase stimulation but show wide variation in affinity.

Cephalalgia, 1997

Serotonergic neurons play a major role in the regulation of pain and may therefore also be involv... more Serotonergic neurons play a major role in the regulation of pain and may therefore also be involved in the pathophysiology of tension-type headache. Platelets are important in the regulation of the free serotonin level in plasma and may be a model of serotonergic neurons. The aim of the present study was to investigate the peripheral serotonin (5HT) metabolism in patients with chronic tension-type headache. The 5HT levels in platelets and in plasma, the beta-thromboglobulin (ß-TG) levels in plasma, and the urinary excretion of 5-hydroxyindoleacetic acid (5HIAA) were measured in 40 patients with chronic tension-type headache and in 40 healthy controls. The platelet uptake index was calculated as the ratio between platelet 5HT and plasma 5HT levels. There were, no significant differences in platelet 5HT, plasma 5HT ß-TG, or 5HIAA between patients and controls. The platelet uptake index was significantly lower in patients 243 (136-367) than in controls 352 (202-508), p=0.03. Our result...

Brain Research, 1985

The regional distribution of receptors for vasoactive intestinal polypeptide (VIP) was studied in... more The regional distribution of receptors for vasoactive intestinal polypeptide (VIP) was studied in the rat central nervous system (CNS). The specific binding was highest in cerebral cortex, limbic forebrain and cerebellum, whereas moderate to low binding was found in hypothalamus, thalamus, brainstem and pituitary. The lowest binding was observed in pons and spinal cord. Scatchard analysis showed curvilinear plots with upward concavity, which was interpreted as two classes of binding sites. The K d values were similar in all regions and calculated as 2.4 and 62 nmol/liter, respectively. The variations of specific [12sI]VIP binding were due to differences in the total amount of receptors and were in the range of 1.7-8.6 pmol per mg protein. The regional distribution of VIP receptors was parallel with the occurrence of VIP-containing nerve terminals with exceptions of cerebellum, olfactory areas and nucleus caudatus, where a greater number of receptors than expected from the VIP content was found. In these regions, VIP may interact with receptors for a different, but homologous neuropeptide. In conclusion, the regional distribution of VIP receptors in CNS gives further evidence for the role of VIP as a central neurotransmitter.