Isabel Valverde - Academia.edu (original) (raw)
Papers by Isabel Valverde
Hormone and Metabolic Research, 1980
Tetrahedron Lett, 1996
A rapid and simple method for the resolution of Z-γ,γ′-di-tert-butyl-D,L-carboxyglutamic acid met... more A rapid and simple method for the resolution of Z-γ,γ′-di-tert-butyl-D,L-carboxyglutamic acid methyl ester is described. The new procedure is based on the enzymatic enantioselective saponification of the methyl ester by the endoprotease papain. Using a simple HPLC protocol the enantiomeric excess of Z-di-tert-butyl-L-Gla-OH has been shown to be higher than 99.5%. The procedures described in this communication allow the resolution, analysis, and downstream process of multi-gram amounts of the Gla derivative in 48 h.Papain catalyzed enantioselective hydrolysis of Z--γγ′-di-tert-butyl-Gla-OMe
Endocrine, Apr 1, 2005
The present study aims mainly at measuring, in normal rats, the GLP-1 response to oral intake of ... more The present study aims mainly at measuring, in normal rats, the GLP-1 response to oral intake of an olive oilenriched diet (OO), and at assessing the long-term effects of such a diet on the GLP-1 content of the intestinal tract, as well as the plasma D-glucose, insulin, and GLP-1 pattern during an oral glucose tolerance test. In meal-trained rats, the mean increment in plasma GLP-1 concentration at min 10 and 20 was 1.39 ± 0.23 ng/mL higher (p < 0.001) in the rats given access to the OO diet rather than control diet. Relative to the initial value (d 0), the gain in body weight at d 50 was also higher in the animals fed the OO rather than control diet. At d 50, the GLP-1 content of the jejunum, ileum, colon, and cecum were not significantly different in the two groups of rats. At d 19 and 36, the increment in both plasma insulin concentration and paired ratio between plasma insulin and D-glucose concentrations were again higher, during an oral glucose tolerance test conducted in overnight fasted animals, in the rats otherwise fed the OO, as distinct from control, diet. The intake of an olive oil-enriched diet thus increases, in normal rats, GLP-1 release, this coinciding during long-term exposure to the OO diet with higher body weight gain, increased secretory response of insulin-producing cells to oral glucose administration, and, after 36 d, improved glucose tolerance.
Diabetologia, 1985
Biogel P-30 filtration of plasma from Type 1 (insulin-dependent) diabetic patients and normal sub... more Biogel P-30 filtration of plasma from Type 1 (insulin-dependent) diabetic patients and normal subjects in basal state and after an oral glucose load was assayed with a C-terminal (30 K) and a glucagon-like immunoreactivity-cross-reacting antiserum (R8). Up to four immunoreactive peaks of approximate molecular sizes of greater than 20,000 (fraction I), 9000 (fraction II), 3500 (fraction III) and 2000 (fraction IV) were detected with the two antisera in both groups. In the basal state, the only significant difference observed between both groups was a higher R8-reactivity in fraction II in the group of diabetic patients, although the R8 minus 30 K values for this fraction did not show a significant difference between both groups. After glucose the only significant differences were an increase of R8-reactivity in fraction II in both groups (p less than 0.01) and a decrease of 30 K-reactivity in fraction III (IRG3500) in normal subjects (p less than 0.05). In seven out of 12 diabetic pa...
Biochemical and Molecular Medicine, 1996
Formycin A augments insulin release evoked by glucose (5.6 mM or more), this effect not being rap... more Formycin A augments insulin release evoked by glucose (5.6 mM or more), this effect not being rapidly reversible. The mechanism responsible for the insulinotropic action of formycin A was investigated in isolated pancreatic islets. It could not be ascribed to facilitation of glucose metabolism. On the contrary, formycin A inhibited glucose oxidation, lowered ATP content, and impaired glucosestimulated protein biosynthesis. The insulinotropic action of formycin A was apparently attributable to its conversion to formycin A 5-triphosphate, both this process and the secretory response to formycin A being abolished by the inhibitor of adenosine kinase 5-iodotubercidin. In agreement with the latter view, adenosine receptor antagonists such as 8-cyclopentyl-1,3-dipropylxanthine and 3,7-dimethyl-1propargylxanthine failed to suppress and, instead, augmented the insulinotropic action of formycin A. Unexpectedly, however, formycin A failed to decrease 86 Rb efflux, this coinciding with a low efficiency of formycin A 5-triphosphate to inhibit K ATP -channel activity in excised membranes and with the fact that formycin A increased glibenclamide-stimulated insulin release. The secretory response to formycin A represented a Ca 2+ -dependent process suppressed in the absence of extracellular Ca 2+ or presence of verapamil and associated with an increased net uptake of 45 Ca. Nevertheless, the view that formycin A exerts any major effect upon intracellular Ca 2+ redistribution, protein kinase C activity, or cyclic AMP net production also met with objections such as the minor secretory effect of formycin A in islets exposed to a high concentration of K + in the presence of a diazoxide analog, the resistance of formycin A insulinotropic action to bisindolylmaleimide, the poor increase of cyclic AMP content in formycin A-stimulated islets, and the pronounced enhancement by forskolin or theophylline of insulin release from islets exposed to formycin A. It is concluded, therefore, that the mechanism of action of formycin A in the pancreatic -cell remains to be elucidated.
Endocrine, 1995
A higher specific binding of GLP-1(7-36)amide is found in skeletal muscle plasma membranes from a... more A higher specific binding of GLP-1(7-36)amide is found in skeletal muscle plasma membranes from adult streptozotocin (STZ)-treated rats (insulin-dependent diabetes mellitus model) and from neonatal STZ-treated rats (non insulin-dependent diabetes mellitus model), as compared to that in normal controls; no apparent change in the affinity was observed, that indicating the presence in both diabetic models of an increased number of high affinity binding sites for the peptide. The maximal specific GLP-1(7-16)amide binding in the non insulin-dependent diabetes mellitus model was found to be significantly higher than that in the insulin-dependent diabetes mellitus model. As GLP-1(7-36)amide exerts a glycogenic effect in the rat skeletal muscle, the present data suggest that the action of the peptide in the muscle glucose metabolism may be increased in states of insulin deficiency accompanied or not by insulin resistance.
Tetrahedron Letters, 1996
ABSTRACT
Glucagon-like peptide 1(7-36)amide (GLP-1) is currently under investigation as a possible tool in... more Glucagon-like peptide 1(7-36)amide (GLP-1) is currently under investigation as a possible tool in the treatment of non-insulin-dependent diabetes mellitus. In addition to enhancing nutrient-stimulated insulin release, the peptide also favors glycogen synthesis and glucose use in liver, muscle, and adipose tissue. GLP-1 also activates glycogen synthase a in hepatocytes from both normal and diabetic rats. In the present study, the kinetic aspects of such an activation were investigated in hepatocytes from normal rats and from animals rendered diabetic induced by injection of streptozotocin, either in the adult age (insulin-dependent diabetes mellitus model) or in days 1 or 5 after birth (non-insulin-dependent diabetes mellitus models). GLP-1 increased, in a dose-dependent manner, glycogen synthase a activity in the hepatocytes from all groups studied. The activation of the enzyme reached a steady state within 1 min exposure to GLP-1, which, at 10(-12) M, caused a half-maximal activation. When comparing fed vs. overnight-starved normal rats, a somewhat lower basal activity of glycogen synthase a in fasted animals (P < 0.05) coincided with a greater relative increment in reaction velocity in response to GLP-1. The basal activity of glycogen synthase a and the relative extent of its inhibition by glucagon or activation by insulin and GLP-1 were modulated by the extracellular concentration of D-glucose. The activation of glycogen synthase a by either insulin or GLP-1 resulted not solely in an increase in maximal velocity but also in a decrease in affinity of the enzyme for uridine diphosphate-glucose; in diabetic animals, the capacity of insulin or GLP-1 to increase the maximal velocity and Michaelis-Menten constant were less marked than in normal rats. In conclusion, this study indicates that the GLP-1-induced activation of glycogen synthase a displays attributes of rapidity, sensitivity, and nutritional dependency that are well suited for both participation in the physiological regulation of enzyme activity and therapeutic purpose.
Obesity Surgery, 2005
Methods: The present study aimed to gain information on the time course for changes in glucose to... more Methods: The present study aimed to gain information on the time course for changes in glucose tolerance, as well as insulin, glucagon and GLP-1 secretion, during an oral glucose tolerance test (OGTT), in 31 obese patients examined 1, 3 and 6 months after Larrad's biliopancreatic diversion (BPD) or 6 months after vertical banded gastroplasty (VBG).
Hormone and metabolic research. Supplement series
In the mechanism of glucose-stimulated insulin release, the coupling between glucose metabolism a... more In the mechanism of glucose-stimulated insulin release, the coupling between glucose metabolism and the remodelling of cationic fluxes in the B-cell apparently represents a multifactorial process involving changes in the generation rate of H+, reducing equivalents and ATP. This process is susceptible to feedback regulatory mechanisms through which primary changes in cationic movements affect glucose metabolism. The interplay between metabolic and ionic events may participate in the rhythmogenesis of bioelectrical and secretory phenomena.
New England Journal of Medicine, 1973
To elucidate further the nature of glucocorticoid-induced alteration of carbohydrate metabolism, ... more To elucidate further the nature of glucocorticoid-induced alteration of carbohydrate metabolism, plasma glucagon levels, both basal and after an arginine stimulus, were studied in normal volunteers before and after glucocorticoid treatment. In one group of 13, after ...
New England Journal of Medicine, 1973
The mean basal glucagon levels were 455 ± 63 (SEM) pg per milliliter in eight patients with porta... more The mean basal glucagon levels were 455 ± 63 (SEM) pg per milliliter in eight patients with portacaval shunts, 217 ± 23 pg per milliliter in 28 patients without shunts, and 146 ± 10 pg per milliliter in 15 controls. After arginine stimulation, glucagon rose to 828 ± 122 pg per milliliter in 25 ...
The American journal of physiology
The methyl esters of succinic acid were introduced a few years ago as new potent insulin secretag... more The methyl esters of succinic acid were introduced a few years ago as new potent insulin secretagogues. In the present study, they were found to increase O2 uptake by rat islets incubated in the absence or presence of D-glucose; to decrease 86Rb outflow from prelabeled islets; to stimulate biosynthetic activity in the islets, with a preferential effect on the synthesis of proinsulin; to inhibit 45Ca efflux from prelabeled islets perifused in the absence of extracellular Ca2+ but to augment 45Ca net uptake and to cause a biphasic stimulation of 45Ca outflow in islets incubated or perifused in the presence of extracellular Ca2+; and to evoke a biphasic stimulation of insulin release. The insulinotropic action of these methyl esters coincided with a shift to the left of the sigmoidal relationship between insulin output and D-glucose concentration, was concentration related in the 2-10 mM range, failed to be duplicated by succinic acid, displayed both Ca2+ dependency and resistance to a lowering of extracellular pH, and was operative in the absence of D-glucose whether or not the islets were stimulated by non-nutrient secretagogues. It is concluded that the respiratory, cationic, biosynthetic, and secretory responses of the islets to succinate methyl esters display the characteristic features usually encountered in the process of nutrient-stimulated insulin release.
Journal of Endocrinology, 1995
We have found [125I]glucagon-like peptide (GLP)-1(7-36)amide specific binding activity in rat liv... more We have found [125I]glucagon-like peptide (GLP)-1(7-36)amide specific binding activity in rat liver and isolated hepatocyte plasma membranes, with an M(r) of approximately 63,000, estimated by cross-linking and SDS-PAGE. The specific binding was time- and membrane protein concentration-dependent, and equally displaced by unlabelled GLP-1(7-36)amide and by GLP-1(1-36)amide, achieving its ID50 at 3 x 10(-9) M of the peptides. GLP-1(7-36)amide did not modify the basal or the glucagon (10(-8) M)-stimulated adenylate cyclase in the hepatocyte plasma membranes. These data, together with our previous findings of a potent glycogenic effect of GLP-1(7-36)amide in isolated rat hepatocytes, led us to postulate that the insulin-like effects of this peptide on glucose liver metabolism could be mediated by a type of receptor probably different from that described for GLP-1 in pancreatic B-cells or, alternatively, by the same receptor which, in this tissue as well as in muscle, uses a different transduction system.
Journal of Clinical Investigation, 1968
The effects of ingested and infused glucose upon circulating glucagon-like immunoreactivity (GLI)... more The effects of ingested and infused glucose upon circulating glucagon-like immunoreactivity (GLI) were compared in 14 triply catheterized conscious dogs. Within 60 min after the intraduodenal administration of 2 g/kg of glucose, the mean level of glucagon-like immunoreactivity in the vena caval plasma more than doubled, whereas after intravenous infusion of the same dose over a 90 min period no change in the mean vena caval level was observed; during glucose infusion mean glucagon-like immunoreactivity in the pancreatic venous effluent declined, suggesting that hyperglycemia suppresses rather than stimulates pancreatic glucagon secretion. To determine if the rise in glucagon-like immunoreactivity that occurs during glucose absorption was of pancreatic origin, the effect of pancreatectomy performed 1 hr after the intraduodenal administration of glucose was determined. Although circulating insulin disappeared after resection of the pancreas, the level of glucagon-like immunoreactivity continued to rise, establishing its extrapancreatic origin. In other experiments, measurements of Glucagon-like immunoreactivity in plasma obtained simultaneously from pancreaticoduodenal and mesenteric veins and from the vena cava revealed the increment after intraduodenal glucose loading to be greatest in the mesenteric vein in 8 of 12 experiments, favoring the gut as the likely source of the rise. To characterize gut glucagon-like immunoreactivity, acid-alcohol extracts of canine jejunum were compared with similar glucagon-containing extracts of canine pancreas with respect to certain physical and biological properties. On a G-25 Sephadex column the elution volume of the jejunal immunoreactivity was found to be smaller than that of glucagon, which suggested a molecular size at least twice that of pancreatic glucagon. Furthermore, the in vivo and in vitro biological activities of the eluates containing jejunal glucagon-like immunoreactivity appeared to differ from those of eluates containing pancreatic glucagon. The jejunal material lacked hyperglycemic activity when injected endoportally into dogs, was devoid of glycogenolytic activity in the isolated perfused rat liver, and did not increase hepatic 3',5' cyclic adenylate in the perfused liver; however, like glucagon it appeared to stimulate insulin release. It seems quite clear the material in intestinal extracts either is a different substance or a different form from that of true pancreatic glucagon, although it crossreacts in the radioimmunoassay with antibodies to glucagon. It is concluded, (a) that hyperglycemia does not stimulate and probably suppresses the secretion of pancreatic glucagon; (b) that during intestinal absorption of glucose, a rise in glucagon-like immunoreactivity occurs; (c) this immunoreactivity is derived from an extrapancreatic site, probably the gut; (d) that the glucagon-like immunoreactivity extractable from jejunum is not the same as pancreatic glucagon but is a larger molecule devoid of hyperglycemic and glycogenolytic activity, a cross-reactant in radioimmunoassay for glucagon; and (e) that the eluate in which jejunal immunoreactivity is contained can stimulate insulin release in conscious dogs.
Hormone and Metabolic Research, 1980
Tetrahedron Lett, 1996
A rapid and simple method for the resolution of Z-γ,γ′-di-tert-butyl-D,L-carboxyglutamic acid met... more A rapid and simple method for the resolution of Z-γ,γ′-di-tert-butyl-D,L-carboxyglutamic acid methyl ester is described. The new procedure is based on the enzymatic enantioselective saponification of the methyl ester by the endoprotease papain. Using a simple HPLC protocol the enantiomeric excess of Z-di-tert-butyl-L-Gla-OH has been shown to be higher than 99.5%. The procedures described in this communication allow the resolution, analysis, and downstream process of multi-gram amounts of the Gla derivative in 48 h.Papain catalyzed enantioselective hydrolysis of Z--γγ′-di-tert-butyl-Gla-OMe
Endocrine, Apr 1, 2005
The present study aims mainly at measuring, in normal rats, the GLP-1 response to oral intake of ... more The present study aims mainly at measuring, in normal rats, the GLP-1 response to oral intake of an olive oilenriched diet (OO), and at assessing the long-term effects of such a diet on the GLP-1 content of the intestinal tract, as well as the plasma D-glucose, insulin, and GLP-1 pattern during an oral glucose tolerance test. In meal-trained rats, the mean increment in plasma GLP-1 concentration at min 10 and 20 was 1.39 ± 0.23 ng/mL higher (p < 0.001) in the rats given access to the OO diet rather than control diet. Relative to the initial value (d 0), the gain in body weight at d 50 was also higher in the animals fed the OO rather than control diet. At d 50, the GLP-1 content of the jejunum, ileum, colon, and cecum were not significantly different in the two groups of rats. At d 19 and 36, the increment in both plasma insulin concentration and paired ratio between plasma insulin and D-glucose concentrations were again higher, during an oral glucose tolerance test conducted in overnight fasted animals, in the rats otherwise fed the OO, as distinct from control, diet. The intake of an olive oil-enriched diet thus increases, in normal rats, GLP-1 release, this coinciding during long-term exposure to the OO diet with higher body weight gain, increased secretory response of insulin-producing cells to oral glucose administration, and, after 36 d, improved glucose tolerance.
Diabetologia, 1985
Biogel P-30 filtration of plasma from Type 1 (insulin-dependent) diabetic patients and normal sub... more Biogel P-30 filtration of plasma from Type 1 (insulin-dependent) diabetic patients and normal subjects in basal state and after an oral glucose load was assayed with a C-terminal (30 K) and a glucagon-like immunoreactivity-cross-reacting antiserum (R8). Up to four immunoreactive peaks of approximate molecular sizes of greater than 20,000 (fraction I), 9000 (fraction II), 3500 (fraction III) and 2000 (fraction IV) were detected with the two antisera in both groups. In the basal state, the only significant difference observed between both groups was a higher R8-reactivity in fraction II in the group of diabetic patients, although the R8 minus 30 K values for this fraction did not show a significant difference between both groups. After glucose the only significant differences were an increase of R8-reactivity in fraction II in both groups (p less than 0.01) and a decrease of 30 K-reactivity in fraction III (IRG3500) in normal subjects (p less than 0.05). In seven out of 12 diabetic pa...
Biochemical and Molecular Medicine, 1996
Formycin A augments insulin release evoked by glucose (5.6 mM or more), this effect not being rap... more Formycin A augments insulin release evoked by glucose (5.6 mM or more), this effect not being rapidly reversible. The mechanism responsible for the insulinotropic action of formycin A was investigated in isolated pancreatic islets. It could not be ascribed to facilitation of glucose metabolism. On the contrary, formycin A inhibited glucose oxidation, lowered ATP content, and impaired glucosestimulated protein biosynthesis. The insulinotropic action of formycin A was apparently attributable to its conversion to formycin A 5-triphosphate, both this process and the secretory response to formycin A being abolished by the inhibitor of adenosine kinase 5-iodotubercidin. In agreement with the latter view, adenosine receptor antagonists such as 8-cyclopentyl-1,3-dipropylxanthine and 3,7-dimethyl-1propargylxanthine failed to suppress and, instead, augmented the insulinotropic action of formycin A. Unexpectedly, however, formycin A failed to decrease 86 Rb efflux, this coinciding with a low efficiency of formycin A 5-triphosphate to inhibit K ATP -channel activity in excised membranes and with the fact that formycin A increased glibenclamide-stimulated insulin release. The secretory response to formycin A represented a Ca 2+ -dependent process suppressed in the absence of extracellular Ca 2+ or presence of verapamil and associated with an increased net uptake of 45 Ca. Nevertheless, the view that formycin A exerts any major effect upon intracellular Ca 2+ redistribution, protein kinase C activity, or cyclic AMP net production also met with objections such as the minor secretory effect of formycin A in islets exposed to a high concentration of K + in the presence of a diazoxide analog, the resistance of formycin A insulinotropic action to bisindolylmaleimide, the poor increase of cyclic AMP content in formycin A-stimulated islets, and the pronounced enhancement by forskolin or theophylline of insulin release from islets exposed to formycin A. It is concluded, therefore, that the mechanism of action of formycin A in the pancreatic -cell remains to be elucidated.
Endocrine, 1995
A higher specific binding of GLP-1(7-36)amide is found in skeletal muscle plasma membranes from a... more A higher specific binding of GLP-1(7-36)amide is found in skeletal muscle plasma membranes from adult streptozotocin (STZ)-treated rats (insulin-dependent diabetes mellitus model) and from neonatal STZ-treated rats (non insulin-dependent diabetes mellitus model), as compared to that in normal controls; no apparent change in the affinity was observed, that indicating the presence in both diabetic models of an increased number of high affinity binding sites for the peptide. The maximal specific GLP-1(7-16)amide binding in the non insulin-dependent diabetes mellitus model was found to be significantly higher than that in the insulin-dependent diabetes mellitus model. As GLP-1(7-36)amide exerts a glycogenic effect in the rat skeletal muscle, the present data suggest that the action of the peptide in the muscle glucose metabolism may be increased in states of insulin deficiency accompanied or not by insulin resistance.
Tetrahedron Letters, 1996
ABSTRACT
Glucagon-like peptide 1(7-36)amide (GLP-1) is currently under investigation as a possible tool in... more Glucagon-like peptide 1(7-36)amide (GLP-1) is currently under investigation as a possible tool in the treatment of non-insulin-dependent diabetes mellitus. In addition to enhancing nutrient-stimulated insulin release, the peptide also favors glycogen synthesis and glucose use in liver, muscle, and adipose tissue. GLP-1 also activates glycogen synthase a in hepatocytes from both normal and diabetic rats. In the present study, the kinetic aspects of such an activation were investigated in hepatocytes from normal rats and from animals rendered diabetic induced by injection of streptozotocin, either in the adult age (insulin-dependent diabetes mellitus model) or in days 1 or 5 after birth (non-insulin-dependent diabetes mellitus models). GLP-1 increased, in a dose-dependent manner, glycogen synthase a activity in the hepatocytes from all groups studied. The activation of the enzyme reached a steady state within 1 min exposure to GLP-1, which, at 10(-12) M, caused a half-maximal activation. When comparing fed vs. overnight-starved normal rats, a somewhat lower basal activity of glycogen synthase a in fasted animals (P < 0.05) coincided with a greater relative increment in reaction velocity in response to GLP-1. The basal activity of glycogen synthase a and the relative extent of its inhibition by glucagon or activation by insulin and GLP-1 were modulated by the extracellular concentration of D-glucose. The activation of glycogen synthase a by either insulin or GLP-1 resulted not solely in an increase in maximal velocity but also in a decrease in affinity of the enzyme for uridine diphosphate-glucose; in diabetic animals, the capacity of insulin or GLP-1 to increase the maximal velocity and Michaelis-Menten constant were less marked than in normal rats. In conclusion, this study indicates that the GLP-1-induced activation of glycogen synthase a displays attributes of rapidity, sensitivity, and nutritional dependency that are well suited for both participation in the physiological regulation of enzyme activity and therapeutic purpose.
Obesity Surgery, 2005
Methods: The present study aimed to gain information on the time course for changes in glucose to... more Methods: The present study aimed to gain information on the time course for changes in glucose tolerance, as well as insulin, glucagon and GLP-1 secretion, during an oral glucose tolerance test (OGTT), in 31 obese patients examined 1, 3 and 6 months after Larrad's biliopancreatic diversion (BPD) or 6 months after vertical banded gastroplasty (VBG).
Hormone and metabolic research. Supplement series
In the mechanism of glucose-stimulated insulin release, the coupling between glucose metabolism a... more In the mechanism of glucose-stimulated insulin release, the coupling between glucose metabolism and the remodelling of cationic fluxes in the B-cell apparently represents a multifactorial process involving changes in the generation rate of H+, reducing equivalents and ATP. This process is susceptible to feedback regulatory mechanisms through which primary changes in cationic movements affect glucose metabolism. The interplay between metabolic and ionic events may participate in the rhythmogenesis of bioelectrical and secretory phenomena.
New England Journal of Medicine, 1973
To elucidate further the nature of glucocorticoid-induced alteration of carbohydrate metabolism, ... more To elucidate further the nature of glucocorticoid-induced alteration of carbohydrate metabolism, plasma glucagon levels, both basal and after an arginine stimulus, were studied in normal volunteers before and after glucocorticoid treatment. In one group of 13, after ...
New England Journal of Medicine, 1973
The mean basal glucagon levels were 455 ± 63 (SEM) pg per milliliter in eight patients with porta... more The mean basal glucagon levels were 455 ± 63 (SEM) pg per milliliter in eight patients with portacaval shunts, 217 ± 23 pg per milliliter in 28 patients without shunts, and 146 ± 10 pg per milliliter in 15 controls. After arginine stimulation, glucagon rose to 828 ± 122 pg per milliliter in 25 ...
The American journal of physiology
The methyl esters of succinic acid were introduced a few years ago as new potent insulin secretag... more The methyl esters of succinic acid were introduced a few years ago as new potent insulin secretagogues. In the present study, they were found to increase O2 uptake by rat islets incubated in the absence or presence of D-glucose; to decrease 86Rb outflow from prelabeled islets; to stimulate biosynthetic activity in the islets, with a preferential effect on the synthesis of proinsulin; to inhibit 45Ca efflux from prelabeled islets perifused in the absence of extracellular Ca2+ but to augment 45Ca net uptake and to cause a biphasic stimulation of 45Ca outflow in islets incubated or perifused in the presence of extracellular Ca2+; and to evoke a biphasic stimulation of insulin release. The insulinotropic action of these methyl esters coincided with a shift to the left of the sigmoidal relationship between insulin output and D-glucose concentration, was concentration related in the 2-10 mM range, failed to be duplicated by succinic acid, displayed both Ca2+ dependency and resistance to a lowering of extracellular pH, and was operative in the absence of D-glucose whether or not the islets were stimulated by non-nutrient secretagogues. It is concluded that the respiratory, cationic, biosynthetic, and secretory responses of the islets to succinate methyl esters display the characteristic features usually encountered in the process of nutrient-stimulated insulin release.
Journal of Endocrinology, 1995
We have found [125I]glucagon-like peptide (GLP)-1(7-36)amide specific binding activity in rat liv... more We have found [125I]glucagon-like peptide (GLP)-1(7-36)amide specific binding activity in rat liver and isolated hepatocyte plasma membranes, with an M(r) of approximately 63,000, estimated by cross-linking and SDS-PAGE. The specific binding was time- and membrane protein concentration-dependent, and equally displaced by unlabelled GLP-1(7-36)amide and by GLP-1(1-36)amide, achieving its ID50 at 3 x 10(-9) M of the peptides. GLP-1(7-36)amide did not modify the basal or the glucagon (10(-8) M)-stimulated adenylate cyclase in the hepatocyte plasma membranes. These data, together with our previous findings of a potent glycogenic effect of GLP-1(7-36)amide in isolated rat hepatocytes, led us to postulate that the insulin-like effects of this peptide on glucose liver metabolism could be mediated by a type of receptor probably different from that described for GLP-1 in pancreatic B-cells or, alternatively, by the same receptor which, in this tissue as well as in muscle, uses a different transduction system.
Journal of Clinical Investigation, 1968
The effects of ingested and infused glucose upon circulating glucagon-like immunoreactivity (GLI)... more The effects of ingested and infused glucose upon circulating glucagon-like immunoreactivity (GLI) were compared in 14 triply catheterized conscious dogs. Within 60 min after the intraduodenal administration of 2 g/kg of glucose, the mean level of glucagon-like immunoreactivity in the vena caval plasma more than doubled, whereas after intravenous infusion of the same dose over a 90 min period no change in the mean vena caval level was observed; during glucose infusion mean glucagon-like immunoreactivity in the pancreatic venous effluent declined, suggesting that hyperglycemia suppresses rather than stimulates pancreatic glucagon secretion. To determine if the rise in glucagon-like immunoreactivity that occurs during glucose absorption was of pancreatic origin, the effect of pancreatectomy performed 1 hr after the intraduodenal administration of glucose was determined. Although circulating insulin disappeared after resection of the pancreas, the level of glucagon-like immunoreactivity continued to rise, establishing its extrapancreatic origin. In other experiments, measurements of Glucagon-like immunoreactivity in plasma obtained simultaneously from pancreaticoduodenal and mesenteric veins and from the vena cava revealed the increment after intraduodenal glucose loading to be greatest in the mesenteric vein in 8 of 12 experiments, favoring the gut as the likely source of the rise. To characterize gut glucagon-like immunoreactivity, acid-alcohol extracts of canine jejunum were compared with similar glucagon-containing extracts of canine pancreas with respect to certain physical and biological properties. On a G-25 Sephadex column the elution volume of the jejunal immunoreactivity was found to be smaller than that of glucagon, which suggested a molecular size at least twice that of pancreatic glucagon. Furthermore, the in vivo and in vitro biological activities of the eluates containing jejunal glucagon-like immunoreactivity appeared to differ from those of eluates containing pancreatic glucagon. The jejunal material lacked hyperglycemic activity when injected endoportally into dogs, was devoid of glycogenolytic activity in the isolated perfused rat liver, and did not increase hepatic 3',5' cyclic adenylate in the perfused liver; however, like glucagon it appeared to stimulate insulin release. It seems quite clear the material in intestinal extracts either is a different substance or a different form from that of true pancreatic glucagon, although it crossreacts in the radioimmunoassay with antibodies to glucagon. It is concluded, (a) that hyperglycemia does not stimulate and probably suppresses the secretion of pancreatic glucagon; (b) that during intestinal absorption of glucose, a rise in glucagon-like immunoreactivity occurs; (c) this immunoreactivity is derived from an extrapancreatic site, probably the gut; (d) that the glucagon-like immunoreactivity extractable from jejunum is not the same as pancreatic glucagon but is a larger molecule devoid of hyperglycemic and glycogenolytic activity, a cross-reactant in radioimmunoassay for glucagon; and (e) that the eluate in which jejunal immunoreactivity is contained can stimulate insulin release in conscious dogs.