PubMed Health⌕ Search

Biomedical subjects

E J Verspohl

Publications and source records attributed to E J Verspohl.

At least 55 records · Page 3Linked to original sources
PubMed1989

Atrial natriuretic peptide (ANP) acts via specific binding sites on cGMP system of rat pancreatic islets without affecting insulin release.

Atrial natriuretic peptide (ANP) has been shown to increase plasma insulin levels in vivo and to act on various target cells as a potent stimulator of the cGMP system. It has, therefore, been investigated whether ANP has a direct insulinotropic effect mediated by specific binding sites and by affecting the cGMP system in isolated rat pancreatic islets. Unlabelled ANP inhibited 125I-ANP binding in a concentration-related manner (Kd1 and Kd2 = 0.02 and 11.2 nM, Bmax1 and Bmax2 = 0.0147 and 0.0328 pmoles per 1 mg protein). ANP was able to augment cGMP levels in islets, but was not able to enhance insulin secretion at various glucose concentrations. Since the role of cGMP for the glucose-mediated insulin release is controversial, in addition to ANP M&B 22,948 (a cGMP phosphodiesterase inhibitor) was investigated to evaluate the possible role of cGMP for insulin release more precisely. Like ANP M&B 22,948 increased cGMP levels but did not affect insulin release. The data indicate no direct insulinotropic effect of ANP, although ANP binding sites are present on rat pancreatic islets and question the claimed role of cGMP for insulin secretion in general. Therefore, the recently observed in vivo elevation of plasma insulin levels in response to ANP is rather an indirect than a direct effect.

Animals↗
PubMed1989

A possible role of plasma glutathione in glucose-mediated insulin secretion: in vitro and in vivo studies in rats.

In isolated rat pancreatic islets exogenous glutathione which is not able to penetrate into cells, augmented glucose (11.1 mmol/l)-mediated insulin release. In the presence of a non-stimulatory glucose concentration (2.8 mmol/l) glutathione had no effect. The half-maximal synergistic action of glutathione on insulin secretion was observed at approximately 8.0 mumol/l. This concentration of glutathione is similar to that found in the plasma of non-fasted anaesthetised rats (6.5 mumol/l). Oral ingestion of glucose increased the arterial plasma glutathione in rats. Our data provide for the first time indirect evidence for a modulating effect of plasma glutathione in postprandial glucose-mediated insulin secretion which appears to be located at the extracellular site of islet cells.

Animals↗
PubMed1989

Effect of CCK-8 on pentose phosphate shunt activity, pyridine nucleotides, and glucokinase of rat islets.

In rat pancreatic islets the effects of cholecystokinin octapeptide (CCK-8) on pentose phosphate shunt (PPS) activity, glucokinase and hexokinase activity, and NADPH, NADP+, NADH, and NAD+ were studied. By elevating the glucose concentration from 3.0 to 8.3 and 16.7 mM the oxidation of [1-14C]- and [6-14C]glucose and the calculated PPS activity were increased in a concentration-dependent manner; 10 nM CCK-8 enhanced selectively the effect on [1-14C]glucose oxidation thereby increasing the PPS activity but only at an intermediate glucose concentration (8.3 mM). CCK-8 had no effect on glucokinase or hexokinase activity and CCK-8 did not influence glucose utilization. By elevating the glucose concentration, total NADPH and NADH were increased and total NADP+ and NAD+ were decreased. CCK-8 (10 nM) increased selectively NADPH and decreased NADP+ but did not change NADH or NAD+; the effect of CCK-8 on NADPH and NADH was only observed in the presence of an intermediate stimulatory glucose concentration (8.3 mM) but not at either a substimulatory glucose concentration or a maximally stimulatory glucose concentration for insulin release (3.0 or 16.7 mM). The data indicate first that CCK-8 does not act on glucose phosphorylation or glucose utilization and second that CCK-8 increases PPS activity and NADPH levels in rat pancreatic islets. Since the concentrations of glucose necessary for these CCK-8 effects are in the range of 8.3 mM and parallel with those necessary for insulin release as shown in earlier observations, glucose oxidation via pentose phosphate shunt and NADPH are suggested to be related to the CCK-8-modulated insulin release.

Animals↗
PubMed1988

Proglumide antagonizes cholecystokinin effects on plasma glucose and insulin in rats in vivo.

Proglumide was shown to possess a low affinity for cholecystokinin (CCK) receptors and to inhibit the synergistic action of CCK8 on glucose-mediated insulin release in vitro. Proglumide (400 mg/kg i.p., given 15 min before an i.v. combination of CCK8 and glucose) reversed the CCK8 (0.5 nmol/kg)-induced increase of plasma insulin levels and decrease of glucose levels. It had no effect on plasma insulin and glucose levels when the glucose bolus was administered alone. Camostate (400 mg/kg p.o.; Foy-305; a trypsin inhibitor acting via endogenously released CCK) increased plasma insulin levels by 10 microU/ml during an oral glucose (500 mg/kg) tolerance test. Pretreatment with proglumide (400 mg/kg i.p.) antagonized this effect. The data indicate that proglumide has an antagonistic effect on either exogenously added or endogenously released CCK with respect to plasma insulin and glucose levels and that it has no effect on plasma insulin and glucose levels when glucose is given alone. Therefore, proglumide and the newly developed, more potent CCK receptor antagonists are able to disturb insulin and glucose homoeostasis.

Animals↗
PubMed1988

Significance of gamma-glutamyl transpeptidase and thiols in amino acid uptake by rat pancreatic islets: studies with glutamine and leucine.

The importance of gamma-glutamyl transpeptidase, the key enzyme of the gamma-glutamyl cycle and of thiols for the uptake of amino acids into rat pancreatic islets was investigated. Both serine-borate, an inhibitor of gamma-glutamy transpeptidase, and serine which does not inhibit this enzyme, but probably is a competitive inhibitor of amino acid uptake, inhibited the uptake of glutamine. The inhibitory effect of serine-borate was not greater than that of serine alone. The uptake of glutamine was not affected by either GSH (reduced glutathione) or diamide (a thiol oxidant). Neither substances affected the uptake of leucine. The results indicate that the uptake of glutamine by rat pancreatic islets is not dependent on the functioning of gamma-glutamyl transpeptidase and that thiols are not important for the uptake of the amino acids glutamine and leucine.

Amino Acids↗
PubMed1988

Decreased insulin secretory response of pancreatic islets during culture in the presence of low glucose is associated with diminished 45Ca2+ net uptake, NADPH/NADP+ and GSH/GSSG ratios.

In isolated rat pancreatic islets maintained at a physiologic glucose concentration (5.6 mM) the effect of glucose on parameters which are known to be involved in the insulin secretion coupling such as NADPH, reduced glutathione (GSH), 86Rb+ efflux, and 45Ca++ net uptake were investigated. The insulinotropic effect of 16.7 mM glucose was decreased with the period of culturing during the first 14 days being significant after 2 days though in control experiments both protein content and ATP levels per islet were not affected and insulin content was only slightly decreased. Both NADPH and GSH decreased with time of culture. 86Rb+ efflux which is decreased by enhancing the glucose concentration from 3 to 5.6 mM in freshly isolated islets was not affected by culturing whatsoever, even not after 14 days of culture when there was no longer any insulin responsiveness to glucose. The 45Ca++ net uptake was decreased during culturing. The data indicate (1) that the diminished glucose-stimulated release of insulin during culturing is not due to cell loss or simple energy disturbances, (2) that more likely it is the result of a diminished 45Ca++ net uptake as a consequence of the inability of islet cells to maintain proper NADPH and GSH levels, and (3) that potassium (86Rb+) efflux may not be related to changes of NADPH and GSH.

Adenosine Triphosphate↗
PubMed1988

Interaction of memantine with cholecystokinin receptors in mouse brain.

The effect of memantine on CCK receptors in mouse brain has been investigated using particles of dissected cortex and striatum. Total binding of radio-labelled CCK33 was one-half maximal within 10 min of incubation and reached a maximum after 30 to 60 min when either cortex or striatum was used. Non-specific binding (presence of 100 microM unlabelled CCK8) was 50 to 80% of total binding at steady state conditions. CCK8 inhibited specific binding of radiolabelled CCK33 in a dose-dependent manner; the IC50 (half-maximal inhibitory concentration) was in the range 3 to 4 nM. Memantine increased CCK binding in a concentration-dependent manner, though at high concentrations. The EC50 (half-maximal effective concentration) of this effect was less than 100 microM. The memantine effect is not due to an inhibition of labelled CCK degradation in the medium. The effect of memantine on CCK binding is unique for brain since it was not observed in pancreatic acinar membranes. These data, therefore, suggest a modulatory effect of memantine on CCK receptors in mouse brain (cortex and striatum) particles.

Amantadine↗
PubMed1988

Insulin and insulin-like growth factor I regulate the same biological functions in HEP-G2 cells via their own specific receptors.

The receptors for insulin and insulin-like growth factor I (IGF-I) are closely related molecules, with an extracellular binding domain and an intracellular tyrosine kinase domain. The interaction of insulin and IGF-I with their respective receptors activates the receptor kinase domain, leading to the biological actions of the hormones. Since insulin generally regulates metabolic events and IGF-I generally regulates growth events, it is believed that structural differences in the tyrosine kinase domains of the two respective receptors may elicit different biological responses via different transmembrane signaling mechanisms. We studied the regulation of glycogen metabolism and amino acid uptake in human cultured HEP-G2 hepatoma cells, which have distinct receptors for both insulin and IGF-I. The receptor specificity of these responses was probed with specific monoclonal antibodies to both the insulin and IGF-I receptors. Stimulation of both [3H]glucose incorporation into glycogen and alpha-[3H]aminoisobutyric acid uptake by insulin was half-maximal at concentrations of 1-5 nmol/L. These effects were blocked by the insulin receptor monoclonal antibody MA-10, but not by the IGF-I receptor antibody alpha IR-3. Stimulation of both functions by IGF-I was half-maximal at concentrations of 1-5 nmol/L, and these effects were inhibited by alpha IR-3, but not by MA-10. These studies indicate that in HEP-G2 cells both insulin and IGF-I, via their own receptors, stimulate the same biological responses.

Amino Acids↗
PubMed1987

Cholecystokinin (CCK8) regulates glucagon, insulin, and somatostatin secretion from isolated rat pancreatic islets: interaction with glucose.

The effect of CCK8 on glucagon, insulin and somatostatin release and its interaction with glucose was studied in freshly isolated rat pancreatic islets. While glucose alone inhibited glucagon secretion [half-maximal effect (EC50) = 4.6 mM], glucose in the presence of 10 nM CCK8 increased glucagon release (EC50 = 6.9 mM). This effect of CCK8 was dose-dependent at 11.1 mM glucose (EC50 = 1.0 nM). The dose-response curve for glucose on insulin secretion was shifted to the left by 10 nM CCK8; the EC50 of glucose was 11.6 and 9.3 mM in the absence and presence of CCK8, respectively. Glucose alone enhanced somatostatin release; this glucose-induced release was further increased by 10 nM CCK8. Our data indicate that first, CCK8 is able to reverse the inhibitory effect of glucose on glucagon secretion, second, CCK8 sensitizes the beta cell to the insulinotropic effect of glucose, and third, CCK8 enhances the effect of glucose on somatostatin release.

Animals↗
PubMed1987

Significance of Ca2+, Rb+ fluxes, of cAMP and cGMP for the CCK8-modulated insulin release.

In rat pancreatic islets the effects of cholecystokinin-8 (CCK8) on glucose-mediated insulin release, 45Ca2+ net uptake, 45Ca2+ efflux, 86Rb+ efflux, cAMP- and cGMP levels were studied. In the presence of a substimulatory glucose concentration (3 mM) CCK8 concentrations of up to 1 microM had no effect on insulin release, but CCK8 at 10 nM potentiated the stimulatory effect of glucose (11.1 mM). 10 nM CCK8 enhanced glucose-stimulated 45Ca2+ net uptake but was ineffective at substimulatory glucose levels. CCK8 had no effect on cAMP and cGMP levels in the presence of 11.1 mM glucose, CCK8 increased 86Rb+ (a measure of K+) in the presence of both 3 and 11.1 mM glucose. This effect was abolished when Ca2+ was omitted from the perifusion medium. CCK8 did not alter glucose (11.1 mM)-stimulated 45Ca2+ efflux rate. These data indicate that (1) CCK8 potentiates glucose-stimulated insulin secretion possibly via an effect on Ca2+ uptake, 2) by affecting Ca2+ uptake, CCK8 enhances K+ efflux, and 3) CCK8 does not mediate its effect via cAMP or cGMP. With respect to 86Rb+ efflux the mechanism of CCK8 action appears to be different from that of glucose. When the mechanism of CCK action on islets is compared with that on exocrine pancreas (data from others) there are similarities (importance of Ca2+ uptake and non-importance of cAMP and cGMP).

Animals↗
PubMed1986

The significance of mu- and delta-receptors in rat pancreatic islets for the opioid-mediated insulin release.

The binding and the insulinotropic effects of enkephalin analogs and of morphine were investigated in rat pancreatic islets. Binding of [3H]Met-enkephalin was saturable, specific and reversible; the rank order for inhibition competition of [3H]Met-enkephalin binding by various compounds was Met-enkephalin = D-Ala2-MePhe4, Met(0)ol enkephalin) greater than Leu-enkephalin greater than morphine with half-maximal inhibitory constants (IC50) of approx. 0.3, 0.3, 100 and greater than 100 nM, respectively. Both the natural enkephalins exerted their insulinotropic effect only at stimulatory glucose concentrations. They had a dual action; whereas insulin secretion was increased at low enkephalin concentration, this effect was reversed at higher concentrations. However, the various enkephalins exerted this effect at different concentrations; only the EC50 values (half-maximal effective concentrations) of their insulinotropic effect were in the same range as the IC50 values of inhibition of [3H]met-enkephalin binding. Cysteamine pretreatment of rats (depletion of somatostatin containing D-cells and decrease in somatostatin secretion) did not change the Met-enkephalin effect on insulin secretion. In contrast to Met-enkephalin, binding of [3H]morphine to islets was not saturable, and morphine had no effect on insulin secretion unless at unphysiologically high concentrations. The data, therefore, indicate that: mu-receptors (affinity for morphine) do not play a role in rat pancreatic islets; delta-receptors (binding site for Met-enkephalin when mu-receptors are not present) mediate the insulinotropic effect of low Met-enkephalin concentrations; and the insulinotropic action of Met-enkephalin is not mediated indirectly via the paracrine effect of an inhibition of somatostatin secretion.

Animals↗
PubMed1986

Proglumide (gastrin and cholecystokinin receptor antagonist) inhibits insulin secretion in vitro.

CCK-8 and its desulfated analog (des-CCK-8) increase insulin secretion from isolated rat pancreatic islets in the presence of 8.3 mM glucose in a concentration-dependent manner. Proglumide (DL-4-benzamido-N,N-dipropylglutaramic acid), a gastrin and cholecystokinin (CCK) receptor antagonist, inhibits the synergistic effect of CCK on insulin release in the presence of 8.3 mM glucose; its EC50 (half-maximal effective concentration) was 1.2 +/- 0.4 mM. Its effect is specific in that it does not inhibit the glucose- or GIP (glucose dependent insulinotropic peptide) induced insulin secretion to a major degree. CCK-8, des-CCK-8 and proglumide compete for binding of 125I-CCK-33 to rat pancreatic islets; the IC50 of proglumide was 0.8 mM. The affinity of proglumide is in the range of both its EC50 for inhibition of insulin secretion and its IC50 in other in vitro systems tested so far (exocrine pancreas, gall bladder, cortex). Its inhibitory effect presumably is not a gastrin antagonizing effect since gastrin does not stimulate insulin secretion. The data therefore indicate that proglumide should be monitored for diabetic effects in vivo.

Animals↗
PubMed1986

Decreased insulin binding to pancreatic islets of genetically obese (fa/fa) rats.

Binding of insulin and insulin secretion were studied in isolated pancreatic islets of homozygous obese fa/fa rats, their lean littermates (Fa/?) and Wistar rats. Despite normoglycemia fa/fa rats exhibit hyperinsulinemia. Glucose-induced insulin secretion from pancreatic islets in vitro was increased by more than 50% in fa/fa rats compared with islets of lean littermates and normal Wistar rats when calculated per microgram islet protein. Exogenous insulin inhibited glucose (16.7 mM)-induced insulin secretion in islets of either of these rats, and maximum inhibition was rather the same (secretion was reduced by 62.3-65.6%). However, the EC50 (half-maximal effective concentration) for inhibition was increased in fa/fa rats being 1.4 +/- 0.1 nM compared with 0.6 +/- 0.2 and 0.5 +/- 0.2 nM in lean littermates and Wistar rats, respectively (P less than 0.05 vs. fa/fa rats). Islets of fa/fa rats found 24% less [125I]insulin (P less than 0.01) than islets of lean littermates and of Wistar rats. Scatchard analysis of data of displacement of [125I]insulin binding by native insulin showed 2 binding sites; a decrease in the number of high affinity insulin binding sites (Bmax) from 4.2 +/- 1.3 and 4.7 +/- 1.6 fmol/mg protein to 2.6 +/- 0.7 fmol/mg protein was calculated when islets of lean littermates and normal Wistar rats were compared to islets of fa/fa rats. The Kd of the high affinity binding site was not changed (0.77 +/- 0.06, 0.78 +/- 0.11 and 0.61 +/- 0.14 nM, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Pharmacokinetics of intravenously administered glutathione in the rat.

By means of an open two compartment model with a distribution and elimination phase, the pharmacokinetic properties of intravenously administered GSH (reduced glutathione) have been investigated in the rat. After a bolus injection of four various GSH doses (50 to 300 mumol kg-1), arterial plasma concentrations of GSH, GSSG (= oxidized glutathione), total thiols and soluble thiols minus GSH were elevated and then rapidly decreased nonexponentially. With increasing dose, the rate constant for drug elimination and plasma clearance increased from 0.84 to 2.44 ml min-1 and the half-life of the elimination phase decreased from 52.4 to 11.4 min. Both the apparent volume of distribution and the degree of penetration of GSH into the tissues were diminished with increasing dose (from 3.78 to 1.33 litres kg-1 and from 6.00 to 0.51 as k12/k21, respectively). The data indicate that GSH is rapidly eliminated. This is mainly due to rapid oxidation in plasma rather than by increased tissue extraction or volume distribution. Thus plasma GSH levels appear to be quickly regulated by which the body may maintain concentrations within narrow physiological limits.

Animals↗
PubMed1986

Evidence that cholecystokinin interacts with specific receptors and regulates insulin release in isolated rat islets of Langerhans.

To determine the nature of the pancreatic islet cell cholecystokinin (CCK) receptor, we studied CCK receptor binding and biologic activity in isolated rat pancreatic islets. Binding of 70 pM 125I-CCK to collagenase-prepared isolated rat pancreatic islets at 24 degrees C was one-half maximal after 5 min and maximal at 60 min. At 60 min, specific binding was 12% of total radioactivity per 100 micrograms islet protein; nonspecific binding (in the presence of 1 microM CCK 8) was less than 2% of total radioactivity. Unlabeled CCK 33 inhibited labeled hormone binding one-half maximally at 2 nM; Scatchard analysis showed one binding site (Kd, 2.3 +/- 0.4 nM; Bmax, 8.1 pmol/mg protein). The agonist selectivity of this binding site was: CCK 8 = CCK 33 greater than desulfated-CCK 8 greater than CCK 4. Two CCK antagonists were studied; N-carbobenzoxy-L-tryptophan was more potent than dibutyryl-cGMP. When the effect of CCK on insulin release from the islets was studied, the order of potency of CCK agonists and antagonists on insulin secretion was the same as the order of their ability to inhibit 125I-CCK binding. The effect of CCK on insulin secretion was dependent on the glucose concentration in the media. CCK had no effect at 5.6 mM glucose and was fully effective at 11.0 mM glucose. These data, therefore, indicate that: specific binding sites for CCK are present in rat pancreatic beta cells; and CCK acts in concert with glucose to stimulate insulin secretion.

Animals↗
PubMed1986

Cysteine analogues potentiate glucose-induced insulin release in vitro.

In rat pancreatic islets, cysteine analogues, including glutathione, acetylcysteine, cysteamine, D-penicillamine, L-cysteine ethyl ester, and cysteine-potentiated glucose (11.1 mM) induced insulin secretion in a concentration-dependent manner. Their maximal effects were similar and occurred at approximately 0.05, 0.05, 0.1, 0.5, 1.0, 1.0 mM, respectively. At substimulatory glucose levels (2.8 mM), insulin release was not affected by these compounds. In contrast, thiol compounds, structurally different from cysteine and its analogues, such as mesna, tiopronin, meso-2,3-dimercaptosuccinic acid (DMSA), dimercaprol (BAL), beta-thio-D-glucose, as well as those cysteine analogues that lack a free-thiol group, including L-cystine, cystamine, D-penicillamine disulfide, S-carbocysteine, and S-carbamoyl-L-cysteine, did not enhance insulin release at stimulatory glucose levels (11.1 mM); cystine (5 mM) was inhibitory. These in vitro data indicate that among the thiols tested here, only cysteine and its analogues potentiate glucose-induced insulin secretion, whereas thiols that are structurally not related to cysteine do not. This suggests that a cysteine moiety in the molecule is necessary for the insulinotropic effect. For their synergistic action to glucose, the availability of a sulfhydryl group is also a prerequisite. The maximal synergistic action is similar for all cysteine analogues tested, whereas the potency of action is different, suggesting similarity in the mechanism of action but differences in the affinity to the secretory system.

Acetylcysteine↗
PubMed1984

[Chronic analgesic-induced headache].

Fifty-two patients, most of whom had had daily headaches for years, were examined and treated. Among them there were 40 who originally had migraine, the others had vasomotor or post-contusional headaches. Average duration of the migraine was 21 years, of chronic headache 7.6 years. All patients had been taking analgesics of a mixed type regularly and for a long time, on average 35.6 tablets or suppositories weekly. All patients had taken more than three different drugs. After an observation period of 3-6 months for grading the headaches and registering the amount of drug intake, all patients were admitted to hospital when all analgesics were at once discontinued. Changing degrees of withdrawal symptoms were the rule: increased headaches, nausea, vomiting, tachycardia, sweating, sleep disorders, and in some also hallucinations and cerebral episodes. At the end of the hospital stay chronic headache had completely disappeared or markedly improved in 77% of patients. Even after an average of 16 months of subsequent observation, chronic headache continued to be significantly improved in 70% of patients. There was a significant reduction in frequency and intensity of attacks in the patients with originally typical migraine. Regular intake of analgesics of the mixed type induces chronic headaches. These are most commonly caused by ergotamine tartrate and aminophenol derivatives, while psychological and physical dependence on anti-migraine drugs is initiated and maintained by additional barbiturates, caffeine and codeine.

Adrenergic beta-Antagonists↗