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E J Verspohl

Publications and source records attributed to E J Verspohl.

71 records · Page 4Linked to original sources
PubMed1984

The role of old age in the effects of glucose on insulin secretion, pentosephosphate shunt activity, pyridine nucleotides and glutathione of rat pancreatic islets.

In pancreatic islets of adult (three month) and old (24 month) rats the effect of glucose on glucose oxidation, pyridine nucleotides, glutathione and insulin secretion was studied. DNA content was similar in both groups of animals; however, islets of old rats exhibited 30% less insulin content. While glucose-induced (16.7 mM) insulin secretion in islets of old rats was approximately 50% less than in islets of adults, no significant difference was observed in the insulin releasing effect of theophylline (1 mM). Although islet production of 14CO2 in the presence of 16.7 mM glucose increased equally in both groups, elevation of glucose failed to increase the percentage of total glucose oxidation via the pentose phosphate shunt in islets of old rats. Elevation of glucose increased the NADPH/NADP and the NADH/NAD ratio in both groups of islets in a similar manner. The effect of glucose on the GSH/GSSG ratio revealed a dose-related increase in the islets of adult rats, whereas islets of old rats did not respond to elevation of glucose. Our data seem to indicate that the lower secretory response of islets of old rats is related to the failure of glucose to increase the GSH/GSSG ratio. In contrast the insulin release induced by theophylline does not appear to depend on islet thiols.

Aging↗
PubMed1984

Dual regulation of glycogen metabolism by insulin and insulin-like growth factors in human hepatoma cells (HEP-G2). Analysis with an anti-receptor monoclonal antibody.

Insulin and the insulinlike growth factors (IGF-I and IGF-II) are members of a family of hormones that regulate the metabolism and growth of many tissues. Cultured HEP-G2 cells (a minimal deviation human hepatoma) have insulin receptors and respond to insulin by increasing their glycogen metabolism. In the present study with HEP-G2 cells, we used 125I-labeled insulin, IGF-I, and IGF-II to identify distinct receptors for each hormone by competition-inhibition studies. Unlabeled insulin was able to inhibit 125I-IGF-I binding but not 125I-IGF-II binding. A mouse monoclonal antibody to the human insulin receptor that inhibits insulin binding and blocks insulin action inhibited 75% of 125I-insulin binding, but inhibited neither 125I-IGF-I nor 125I-IGF-II binding. When glycogen metabolism was studied, insulin stimulated [3H]glucose incorporation into glycogen in a biphasic manner; one phase that was 20-30% of the maximal response occurred over 1-100 pM, and the other phase occurred over 100 pM-100 nM. The anti-receptor monoclonal antibody inhibited the first phase of insulin stimulation but not the second. Both IGF-I and IGF-II stimulated [3H]glucose incorporation over the range of 10 pM-10 nM; IGF-I was three to fivefold more potent. The monoclonal antibody, however, was without effect on IGF regulation of glycogen metabolism. Therefore, these studies indicate that insulin as well as the IGFs at physiological concentrations regulate glycogen metabolism in HEP-G2 cells. Moreover, this regulation of glycogen metabolism is mediated by both the insulin receptor and the IGF receptors.

Animals↗
PubMed1983

Adaptation of blood pressure to continuous heavy coffee drinking in young volunteers. A double-blind crossover study.

In a double-blind crossover trial, the effect of 4 week daily ingestion of eight cups of regular coffee (corresponding to 504 mg caffeine) vs eight cups of decaffeinated coffee was studied. Blood pressure, heart rate and urinary catecholamines were measured in eight healthy, young volunteers. In both groups, regular coffee immediately led to a significant increase in mean blood pressure (+ 3 and + 5 mm Hg respectively). The difference between both groups, however, existed only in the first 3 to 5 days of ingestion of regular coffee. On day 5 after ingestion of regular coffee, and thereafter in weekly intervals, no significant increase in catecholamine excretion was observed. The data suggest that long-term consumption of large amounts of coffee leads to only a small and transient rise in mean blood pressure. This may be due to an adaptation phenomenon. Therefore, continuous heavy coffee ingestion (eight cups/day for 4 weeks) by young persons does not appear to involve a risk of the development of hypertension.

Adaptation, Physiological↗
PubMed1983

Pentose phosphate shunt, pyridine nucleotides, glutathione, and insulin secretion of fetal islets.

In rat fetal islets it was tested whether their failure to respond to glucose with insulin secretion might be due to inadequate changes of the redox state of pyridine nucleotides and of glutathione. In islets of newborn (5 days) and adult (3 mo) rats elevation of glucose produced an increase in insulin secretion, pentose phosphate shunt (PPS) activity, and NADPH/NADP, NADH/NAD, and GSH/GSSG ratios. An increase in the NADH/NAD ratio was also observed in islets of fetal rats, but in contrast to islets of newborns and adults no increase in insulin release, PPS activity, and the GSH/GSSG ratio was observed. However, at all glucose concentrations tested islets of fetal rats exhibited a high NADPH/NADP ratio similar to the ratio of adult rats in the presence of 16.7 mM glucose. It is suggested that in fetal islets there exists a lack of hydrogen transfer from NADPH to GSSG. The high NADPH/NADP ratio may in turn suppress PPS activity. It is possible that the missing insulin release of fetal islets in response to glucose is at least in part due to the fact that the oxidation-reduction state of the GSH/GSSG system also does not respond to the elevation of the glucose concentration.

Animals↗
PubMed1983

Increased insulin binding to pancreatic islets of aged rats.

In rat pancreatic islets, the effect of old age (24-month-old) on [125I]insulin binding, glucose-induced insulin release and inhibition of insulin secretion by exogenous insulin were studied. The results were compared with corresponding data obtained from young (3-month-old) rats. Specifically bound [125I]insulin in islets of old rats was increased by 40% (P less than 0.02) compared to that in young rats. Scatchard plots of displacement studies indicated an increase in receptor number rather than receptor affinity. The insulin-releasing capacity of 16.7 mM glucose did not differ between islets of old and young rats when medium insulin was bound to added antiinsulin serum. In the presence of 16.7 mM glucose (without the addition of antiinsulin serum), insulin secretion was less in islets of old rats compared to that in young rats (283 +/- 38 vs. 528 +/- 29 microU/ml; P less than 0.001). Exogenous insulin inhibited glucose (16.7 mM)-induced insulin release more in islets of old rats than in those of young rats. In conclusion, the present in vitro results may be interpreted to reflect increased insulin binding to islets of aged rats and, consequently, increased inhibition of glucose-mediated insulin secretion due to increased feedback of insulin.

Aging↗
PubMed1982

Properties of the insulin receptor of rat pancreatic islet.

Rat pancreatic islets have been shown to possess specific binding sites for 125I-labeled insulin. Enzymatic and chemical modification of islets are used to reveal important structures and chemical groups for insulin binding. pretreatment with trypsin, neuraminidase, 1-ethyl-3-(3-dimethylamino)carbodiimide (a carboxyl reagent), tetranitromethane (a tyrosyl and thiol reagent), and 1,3-difluoro-4,6-dinitrobenzene (modification of protein functional groups) decreased binding of insulin. This was due to the diminuation of the receptor number; in the case of trypsin-pretreatment also the receptor affinity was decreased. Inhibition of insulin binding was in each case associated with a decrease of the inhibitory effect of exogenous insulin on glucose-induced insulin secretion (not measured in the case of difluorodinitrobenzene and tetranitromethane). Phospholipase A2, (cleavage of phospholipids) did not affect these parameters. 5,5'-dithiobis(2-nitrobenzoic acid) (Ellman's reagent) and possibly p-chloromercuribenzoate (both thiol reagents) increased the number of receptors and decreased receptor affinity, but did not influence the inhibitory effect of insulin on insulin release. It is concluded that protein functional groups, sialic acid, carboxyl and tyrosyl groups, but no phospholipids and probably not sulfhydryl groups are important for the interaction of insulin with insulin receptors of rat pancreatic islets.

Animals↗
PubMed1982

Insulin receptors on rat pancreatic islets: specificity of 125 I-insulin binding.

Binding sites of isolated rat pancreatic islets have been shown to interact with insulin. Employing various species-insulins, insulin analogues and substances not being structurally related to insulin, structure-specificity as well as pH- and temperature-dependence of insulin binding to rat pancreatic islets have been studied. Rat insulin displaced 125 I-insulin from its binding sites in the same concentration-dependent manner as pork insulin did, whereas the insulin analogue des-(phe-val-asp)B1-3-p-glu B4-insulin was less effective. Pork C-peptide hardly competed for binding and pork proinsulin did not compete at all. Both the species' insulins inhibited glucose (16.7 mM)-induced insulin secretion. The inhibitory effect was less when des-(phe-val-asp)B1-3-p-glu B4-insulin was employed and no inhibition of insulin secretion was observed by the use of pork C-peptide or proinsulin. Glucagon and somatostatin did not affect insulin binding. pH optimum of insulin binding appears to be in the range between 7.0 and 8.0. Binding was augmented with increasing temperature up to 37 degrees C. It is concluded that rat pancreatic islets possess insulin because binding and biological potency of substances related to insulin were in harmony. Moreover pH- and temperature-optimum of insulin binding are in a physiological range.

Animals↗
PubMed1980

Evidence for presence of insulin receptors in rat islets of Langerhans.

Binding of insulin to islets of Langerhans was studied. It was found that "specific" binding of [125I]insulin ("specific" binding equals total binding minus nonspecific binding) was saturable with respect to time and insulin concentration and depended on the number of incubated islets. Furthermore, bound insulin was displaced by native insulin in a dose-dependent manner. Bound [125I]insulin was easily dissociated and there was little [125I]insulin degradation both in the incubation medium and during the processes of binding and dissociation. Scatchard analysis of experiments with increasing [125I]insulin concentration and with displacement of insulin binding by native insulin revealed "high affinity" binding sites with a dissociation constant of 0.461 +/- 0.08 n M and 3.5 X 10(6) high affinity binding sites per islet. There also existed "low affinity" binding sites with dissociation constant (Kd) of 43.9 +/- 11.6 nM and 5.9 X 10(7) low affinity binding sites. High affinity binding sites of islets from rats pretreated with alloxan decreased by about one half, whereas Kd was unaffected. Because the Kd of specific high affinity binding and mean effective dose (ED50) of the biological effects of insulin on normal pancreatic islets are in the same range (between 0.46 and 1.19 nM), the insulin-receptor interaction may be biologically significant.

Alloxan↗
PubMed1979

Effect of Methylene Blue on pyridine nucleotides and insulin secretion of rat pancreatic islets.

Methylene Blue, which is known to oxidise NADPH in red blood cells, was used to assess a possible role of NADPH in the glucose-stimulated secretion of insulin. When islets from rats were incubated with 3 mg/ml of glucose, Methylene Blue (0.5), 1.0, 2.0 or 5.0 micrograms/ml) significantly decreased the concentration of NADPH, increased that of NADP+ and decreased the NADPH/NADP+ ratio in a dose-dependent manner. This effect was associated with inhibition of the glucose-induced insulin release. No significant change of NADH, NAD+ and ATP could be observed. It is suggested that the secretory response of the pancreatic islet to glucose stimulation depends on the NADPH/NADP+ ratio.

Animals↗
PubMed1979

Pentosephosphate shunt activity of rat pancreatic islets: its dependence on glucose concentration.

Although several attempts have been made to establish a relationship between glucose concentration and pentosephosphate shunt (PPS) activity of pancreatic islets in vitro, no such relationship has been found. Recently it has been shown that exogenous insulin, when added in vitro, inhibited islet PPS activity. Since it was possible that the failure to detect such a relationship was due to insulin released into the incubation medium, we reinvestigated the subject, introducing GPAIS (guinea pig antiinsulin serum) to bind insulin in the medium. When five islets were incubated with 16.7 mM glucose for 90 min, the absolute rate as well as the percentage of islet PPS activity were found to be significantly higher (P less than 0.05) in the presence of GPAIS than in its absence. In the presence of GPAIS, the absolute rate and the percentage of islet PPS activity increased in a dose-related manner (18, 43, and 124 pmol/five islets.90 min and 2.3%, 3.2%, 9.4%, respectively) when the glucose concentration was raised from 5.6 to 11.1 and 16.7 mM. Our data, therefore, indicate that the activity of islet PPS activity in vitro depends on the concentration of glucose, provided that insulin does not accumulate in the incubation medium. This suggests that PPS activity might play a role in glucose-induced insulin secretion. However, whether the PPS contributes to the secretory mechanism by producing a signal for insulin secretion or by forming cofactors required by the secretory mechanism remains to be established.

Animals↗
PubMedDate not supplied

Influence of diadenosine tetraphosphate (Ap4A) on lipid metabolism.

Diadenosine polyphosphates (Ap(x)A) are physiologically released and may be partly involved in the pathogenesis of diabetes mellitus. Ap(4)A (diadenosine tetraphosphate) leads to an increase in blood glucose while it decreases insulin levels in plasma. A possible link between Ap(x)A and diabetes mellitus-associated diseases such as insulin resistance and hyperlipidemia (plasma free fatty acids, cholesterol and its biosynthesis, triacylglycerols) has not been investigated yet. Parameters such as free fatty acid and cholesterol content in blood were determined enzymically. The biosynthesis of cholesterol and triacylglycerols was determined in HepG2 cells using the radioactive precursor [(14)C]-acetate and by using gas chromatography. Plasma free fatty acids were significantly decreased 5 and 10 min after an Ap(4)A bolus (0.75 mg kg(-1) b.w.) given to rats. Plasma cholesterol was reduced 5 and 60 min after Ap(4)A administration. LPDS (lipoprotein-deficient serum)-stimulated cholesterol biosynthesis in HepG2 cells was significantly reduced after 1 h incubation with Ap(4)A. Triacylglycerol (TAG) biosynthesis in HepG2 cells was not significantly influenced by Ap(4)A; there was just a tendency for a concentration-dependent decrease in TAG levels. In conclusion Ap(4)A as a diabetogenetic compound is not likely to be responsible for the development of insulin resistance or of hyperlipidemia. Parameters such as free fatty acids, cholesterol and triacylglycerols are not elevated by Ap(4)A, but are even decreased. Ap(4)A seems to be involved in the development of diabetes mellitus by increasing blood glucose and decreasing plasma insulin as shown earlier, but not in diabetes mellitus-associated diseases such as insulin resistance or hyperlipidemia.

Acetates↗
PubMedDate not supplied

Heterologous desensitization of insulin secretion by GIP (glucose-dependent insulinotropic peptide) in INS-1 cells: the significance of Galphai2 and investigations on the mechanism involved.

Heterologous desensitization is a term that describes the observation that chronic exposure of a cell to an agonist attenuates its response to other agonists. To characterize the cellular mechanisms that might be responsible for heterologous desensitization in an insulin secretory cell system (INS-1), we investigated the link between G-protein alphai2 level and insulin secretion as the biological effect after prolonged incubation with glucose-dependent insulinotropic polypeptide (GIP). Persistent activation (8 h) of the GIP signalling pathway decreased the GLP (glucagon-like peptide)-1 dependent insulin secretion (specific radioimmunoassay) accompanied by an upregulation of G-protein alphai2 protein level to about 126% whereas G-protein alphai3 and alphas protein levels remained unchanged (assessed by Western blots using specific antibodies). This was accompanied by similar changes in Galphai2 mRNA. By using either the CaM kinase II inhibitor KN-62, the calcineurin inhibitor FK 506 or the protein kinase A (PKA) inhibitor Rp-8-Br-cAMPS, the GIP-mediated Galphai2 mRNA increase was fully reversed. Heterologous desensitization of GLP-1-dependent insulin secretion by pretreatment with GIP, however, was not inhibited by calcium/calmodulin-dependent enzymes (using KN-62 and FK 506), but only by suppressing the cAMP/PKA signalling pathway using Rp-8-Br-cAMPS. The outcome is not disturbed by effects initiated by these compounds per se since an 8-h preincubation of cells did not affect glucose-induced insulin secretion. We, therefore, suggest that heterologous desensitization in INS-1 cells may be mediated by Galphai2 changes but depend on the cAMP/PKA signalling pathway probably distant form the Galphai2 protein.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMedDate not supplied

In vitro effect of exogenous insulin on insulin secretion. Studies with glucose, leucine, arginine, aminophylline and tolbutamide.

Using rat pancreatic islets and the perfused rat pancreas, the effect of exogenous insulin on insulin secretion mediated by glucose, leucine, arginine, aminophylline and tolbutamide was studied. (1) In both systems the insulin releasing capacity of glucose was inhibited by exogenous insulin. In the perfused pancreas the inhibition concerned the first and the second phase of insulin release; (2) the EC50 (half-maximal inhibitory effect of insulin on glucose-induced insulin secretion) in islets was 1.2 nM (= 160 microU/ml) and 2.8 nM (390 microU/ml) in perfused pancreas; (3) exogenous insulin also inhibited insulin release in response to leucine and arginine in the isolated islet system and in the perfused pancreas; (4) using aminophylline and tolbutamide in combination with glucose, the extent of the inhibitory effect of insulin was in the range of the inhibitory effect when glucose was used alone as stimulator in islets. Data suggest that the insulinogenic action of physiological stimulators including glucose, leucine and arginine is inhibited by exogenous insulin whereas this seems not to be the case when insulin release was stimulated by aminophylline and tolbutamide. Comparing the EC50s, isolated islets seem to be more sensitive to inhibition than the perfused pancreas when glucose was used as stimulator. As far as glucose is concerned the inhibitory effect seems to depend on the extent of its concentration and/or the extent to which the mechanism of insulin release is sensitive to stimulation. The EC50 of the inhibitory effect of exogenous insulin was in the range of dissociation constant of binding of insulin to insulin receptors of islets.

Aminophylline↗
PubMedDate not supplied

The role of cholecystokinin (CCK8) on glucose production and elimination, and on plasma insulin and glucose in rats.

The effects of the gastrointestinal hormone and neurotransmitter cholecystokinin (CCK8) are complex, since it exhibits both an insulinotropic and a glucagonotropic effect. We investigated CCK8 in vivo with respect to glucose fluxes (production and elimination) at both low (6 mM) and high plasma glucose levels (9 mM) using the primed constant D-[3-3H]glucose infusion technique. In the presence of high glucose levels there was a dose-dependent increase in glucose elimination by CCK8. No effect of CCK8 on glucose production at a high glucose infusion rate (500 mg/kg per h) was observed in contrast to a low glucose infusion rate (100 mg/kg per h); plasma glucagon levels were elevated. All effects on glucose production and elimination were specific, since they were abolished by the CCK receptor antagonist L-364,718. In summary, glucose elimination was slightly increased by CCK8 at low glucose levels but increased to a greater extent at high glucose levels; glucose production was increased by CCK8 only at low glucose levels. Thus, CCK is a regulator of glucose homeostasis.

Animals↗
PubMedDate not supplied

Stimulation of insulin secretion from pancreatic islets by the cholecystokinin-tetrapeptide analogs Trp-Pro-Asp-Phe-NH2 and Trp-Pro-Asp-Phe(4'-NO2)-NH2.

The cholecystokinin-tetrapeptide (CCK4) analogs Trp-Pro-Asp-Phe-NH2 (3) and Trp-Pro-Asp-Phe-(4'-NO2)-NH2 (4) were found to be nearly equipotent to cholecystokinin-octapeptide (CCK8) in potentiating glucose-induced insulin secretion from islets of Langerhans isolated from rat pancreas. This stimulatory action was found to be dose-dependent and, in the case of 4, to exhibit a biphasic dose-response curve; i.e., at concentrations greater than 1.0 nM, the stimulating effect of 4 is reversed. These results suggest that conformational restriction of CCK4 and/or modification of the phenylalanine residue could produce more potent analogs capable of stimulating insulin release. Such compounds could have potential therapeutic utility in the treatment of non-insulin-dependent diabetes mellitus (NIDDM).

Amino Acid Sequence↗