Effect Of Tolbutamide Research Articles

Comparative effects of linogliride fumarate and tolbutamide sodium on insulin secretion and glucose utilization in rat pancreatic islets

AbstractThe effects of linogliride fumarate (0.1 mmol/liter) and tolbutamide sodium (0.5 mmol/liter) on insulin secretion and glucose utilzation were directly compared in isolated perifused rat islets. Both compounds potentiated glucose‐primed (5.5 mmol/liter) insulin release. The insulin secretory response at the concentration chosen was qualitatively different for the two agents. In the presence of glucose, the insulin secretory effect of tolbutamide was biphasic, whereas linoglirde predominantly increased second‐phase insulin secretion. In the absence of exogenous glucos, tolbutamide stimulated first‐phase insulin release wherease linogliride was ineffective without glucose in the perifusion medium. Neither linogliride (0.1 mmol/liter) nor tolbutamide (0.5 mmol/liter) stimulated islet cell glucose usage as measured by conversion of [5−3H]‐glucose to 3H2O. The insulin secretagogue effect of linogliride was completely abolished when islet cell glucose usage was partially blocked (22% reduction) by mannoheptulose (MH) (10 mmol/liter). When glucose usage was significantly inhibited (55%) by 2‐deoxyglucose (2DG) (10 mmol/liter), linogliride‐stimulated insulin secretion was not significantly reduced. In contrast, tolbutamide‐stimulated first‐phase insulin release was not inhibited when glucose usage was reduced by either MH or 2‐DG, wherease secondphase insulin release was significantly inhibited. In summary, linogliride potentiates insulin secretion in isolated islets by a glucose‐dependent process, but with a kinetic profile and response to metabolic inhibitors different from that of tolbutamide.

Possible mechanism of proteolysis for the extrapancreatic action of tolbutamide

In order to assess the mode of the extrapancreatic action of the sulfonylureas, we evaluated the contribution of a proteolytic mechanism for sulfonylurea action by analyzing the effects of a protease inhibitor on insulin- or tolbutamide-stimulated liver fructose-2,6-bisphosphate (F-2,6-P 2) formation using isolated rat hepatocytes. The F-2,6-P 2 level in hepatocytes was significantly increased by the addition of insulin or tolbutamide. The stimulatory effect of insulin on the F-2,6-P 2 formation was most significant when its level was reduced by the addition of 2 μM of forskolin. Insulin action on F-2,6-P 2 formation was inhibited by the addition of a protease inhibitor, p-tosyl- l-arginine methyl ester hydrochloride (TAME). Tolbutamide (2 mM) significantly increased hepatocyte F-2,6-P 2 level ( P < 0.01 vs the control level). In the presence of TAME, the stimulatory effect of tolbutamide was also suppressed. The present data suggest that a proteolytic mechanism is important in both insulin and tolbutamide action on the F-2,6-P 2 formation, and it may be hypothesized that, like insulin, the chemical mediator of tolbutamide action is formed proteolytically.

Kinetic studies on drug disposition in rabbits. III. Effect of tolbutamide on renal excretion of sulfamethizole.

The effect of tolbutamide (TB) on the urinary excretion of sulfamethizole (SMZ) under constant infusion of SMZ at 100 mg/h was studied. Intravenous administration of TB (50 mg/kg) caused a decrease in the urinary excretion rate of SMZ but an increase in the unbound concentration of SMZ in plasma. The total concentration of SMZ in plasma decreased rapidly after TB injection and then increased gradually to a level higher than the control. The slope of the terminal phase of the unbound concentration of TB in plasma in the presence of SMZ was significantly smaller than that of TB alone. The analysis using the perfusion limited model showed that the elimination kinetics of SMZ in the presence of TB could be described by the mutual displacement of plasma protein binding of both drugs and the competitive inhibition of the tubular secretion of SMZ by the unbound concentration of TB in renal vein. Further the inhibitor constant was in good agreement with that for the in vitro uptake by renal cortex slices.

Mechanisms of the inhibitory effect of cyclic adenosine monophosphate on calcium current in intact mollusk neurons

Inhibitory effects of cyclic adenosine monophosphate (cAMP) on calcium current (ICa) were investigated in experiments on unidentified neurons isolated fromHelix pomatia by means of voltage clamping techniques using two microelectrodes. Intracellular level of cAMP was raised by intracellular injection of this substance or by extracellular application of dibutyryl-cAMP or isobutylmethyl-xanthine. A set of neurons showing inhibitory effects of cAMP on ICa was used. Effects on barium current (IBa) of an equal extent were also revealed. Injection of cGMP through a double-barreled microelectrode into these neurons produced an increase in amplitude of ICa. Intracellular application of phorbol ester had no effect on this current, however. Intracellular injection of EGTA led to enhancement of ICa amplitude, but the inhibitory effect of cAMP persisted following the action of EGTA. Tolbutamide and H-8 (but to a lesser extent) inhibited ICa. The inhibitory effects of tolbutamide and dibutyryl cAMP were not found to be cumulative in six out of twelve instances. These findings would imply that the inhibitory action of cAMP on ICa is unassociated with activation of cAMP-dependent protein kinase, cGMP-dependent protein kinase or protein kinase C; nor does it depend on level of intracellular Ca2+. The possibility of direct interaction between cAMP and channel-forming protein is considered.

Tolbutamide reverses hypoxic pulmonary vasoconstriction in isolated rat lungs.

We have investigated the effects of tolbutamide on the hypoxic vasoconstriction of isolated, perfused rat lungs. We did this because lowered ATP may link hypoxia and constriction, and tolbutamide mimics the effects of ATP in other tissues by blocking ATP-sensitive potassium (ATP-K) channels. Pulmonary vasoconstriction, induced by lowering the oxygen of the gas ventilating the lungs from 95 to 2%, was always reduced or abolished by tolbutamide (1.7 x 10(-4)-8.5 x 10(-3) M). High concentrations (greater than or equal to 10(-3) M) of diazoxide, a drug that opens ATP-K channels, dramatically constricted the pulmonary vasculature and this effect was also reversed by tolbutamide. The opening of ATP-K channels may therefore underlie hypoxic pulmonary vasoconstriction.

How do sulfonylureas approach their receptor in the B-cell plasma membrane?

Since it was unknown whether the uncharged or the anionic form of hypoglycemic sulfonylureas and meglitinide is the effective modulator of ATP-dependent K+ channels and insulin secretion, we studied the inhibitory effects of tolbutamide and meglitinide on the ATP-dependent K+ current at different external pH. The whole-cell configuration of the patch-clamp technique was used in mouse pancreatic B-cells. When the concentrations of the undissociated forms of these drugs were kept constant at increasing pH of the bath solution (6.4 to 8.4), the rate of development and the degree of K+ channel block varied only slightly. Raising the pH-value in the bath solution at constant total concentration of tolbutamide diminished both the rate of development and the degree of K+ channel block. It is concluded that the undissociated forms of tolbutamide and related compounds are the effective forms. Examination of the K+ current records during the application and removal of different concentrations of tolbutamide, meglitinide, glipizide and glibenclamide at pH 7.4 indicated that the kinetics of the current records reflected not only association and dissociation of the drug-receptor complex but perhaps also the kinetic of drug distribution between bath and the lipid phase of the plasma membrane. As there is evidence against an interaction between sulfonylureas and their receptor via a binding site freely accessible from the cytoplasm, the drugs probably get access to their binding site on the receptor from the lipid phase of the B-cell plasma membrane.

Effects of tolbutamide, glibenclamide and diazoxide upon action potentials recorded from rat ventricular muscle

Drugs which influence the electrical activity of insulin-secreting B cells of mammalian islets of Langerhans by closing (tolbutamide and glibenclamide) or opening (diazoxide) ATP-sensitive potassium channels were applied to the ventricular muscle of the rat. Action potentials were recorded from ventricular epicardium of perfused intact rat hearts. Tolbutamide (0.5-2.0 mM), glibenclamide (0.01-0.1 mM) and diazoxide (0.5 mM) each evoked a dose-dependent increase (7-33%) in the duration of the ventricular action potential measured at 50% of repolarization. These drugs were without effect upon the resting membrane potential or the peak of the action potential. Single-channel recordings of ATP-sensitive K+ channels were obtained from excised membrane patches of enzymatically isolated rat ventricular myocytes. Tolbutamide and diazoxide inhibited openings of ATP-sensitive K+ channels. Diazoxide inhibited ATP-sensitive K+ channel openings in the presence of ATP. Diazoxide did not evoke opening of ATP-sensitive K+ channels. It is concluded that these drugs could act to increase the duration of the cardiac action potential by inhibiting openings of ATP-sensitive K+ channels.

Phosphoinositide Hydrolysis and Insulin Secretion in Response to Glucose Stimulation Are Impaired in Isolated Rat Islets by Prolonged Exposure to the Sulfonylurea Tolbutamide*

Isolated rat islets of Langerhans were incubated for 2 h in a [3H]inositol-containing medium supplemented with 7 mM glucose and the sulfonylurea tolbutamide (50-200 microM). After labeling, the ability of these islets to respond during a subsequent perifusion to 20 mM glucose or 15 mM alpha-ketoisocaproate (KIC) was assessed. The following major observations were made. Prior exposure to tolbutamide inhibited [3H]inositol efflux, inositol phosphate accumulation, and the insulin secretory responses of subsequently perifused islets to 20 mM glucose stimulation. When present during the 2-h labeling period, the calcium channel blocker nitrendipine (500 nM), a compound that abolishes tolbutamide-induced increases in PI hydrolysis, blocked these inhibitory effects of tolbutamide. In addition, the diacylglycerol kinase inhibitor monooleoylglycerol (50 microM) restored the impaired second phase insulin secretory response noted after a 2-h tolbutamide exposure. Prior exposure to tolbutamide (200 microM) also desensitized the islet, in terms of [3H] inositol phosphate accumulation, [3H]inositol efflux, and insulin secretory responses, to 15 mM KIC. The inclusion of monooleoylglycerol during the stimulatory period with KIC restored second phase insulin secretion. The results support the conclusion that chronic tolbutamide-induced increases in PI hydrolysis render the beta-cell insensitive to a subsequent 20-mM glucose or 15-mM KIC stimulus. Blocking tolbutamide-induced increases in PI hydrolysis during the labeling period eliminates the adverse effects of the sulfonylurea. The ineffectiveness of glucose and KIC to maintain insulin secretory responses from prior tolbutamide-exposed islets appears to be the result of the inability of these agonists to appropriately activate PI hydrolysis.

O-214 - Effects of tolbutamide, a putative ATP-regulated K+ channel blocker, on the hypoxia-induced shortening of action potential duration in guinea-pig ventricular muscles

O-214 - Effects of tolbutamide, a putative ATP-regulated K+ channel blocker, on the hypoxia-induced shortening of action potential duration in guinea-pig ventricular muscles

Effect of tolbutamide and glyburide on cAMP-dependent protein kinase activity in rat liver cytosol

Effect of tolbutamide and glyburide on cAMP-dependent protein kinase activity in rat liver cytosol

An analysis of the haemodynamic effects of tolbutamide in conscious dogs.

1. In conscious chronically instrumented dogs, tolbutamide (5-45 mg/kg) induced significant dose-related increases in mean arterial pressure and left ventricular end-diastolic pressure. 2. Cardiac output was decreased while heart rate, d(LVP)/dt, and regional myocardial performance at the left ventricle were not significantly affected. Computed total peripheral resistance was increased. 3. Pretreatment with the alpha-antagonist phentolamine (1-1.5 mg/kg) abolished the pressor response. Furthermore, the pressor response to norepinephrine (0.1 microgram/kg) was enhanced by pretreatment with tolbutamide (45 mg/kg). 4. In an isolated tissue preparation using ring segments of canine femoral arteries, neither tolbutamide nor its major hepatic metabolites (carboxytolbutamide, p-toluene-sulfonamide and p-toluene-sulfonylurea) caused any smooth muscle contraction. However, pretreatment of these tissues with 10(-4), 10(-3), or 10(-2) mol/l tolbutamide potentiated the contractile response to norepinephrine by up to 19% and to phenylephrine by up to 8%. 5. It was concluded that the pressor effect of tolbutamide arises by potentiating the alpha-adrenoceptor mediated vasoconstrictor action of circulating endogenous catecholamines.

Concentration-dependent effects of tolbutamide, meglitinide, glipizide, glibenclamide and diazoxide on ATP-regulated K+ currents in pancreatic B-cells

The influence of the hypoglycemic drugs tolbutamide, meglitinide, glipizide and glibenclamide on ATP-dependent K+ currents of mouse pancreatic B-cells was studied using the whole-cell configuration of the patch-clamp technique. In the absence of albumin, tolbutamide blocked the currents half maximally at 4.1 mumol/l. In the presence of 2 mg/ml albumin half maximal inhibition of the currents was observed at 2.1 mumol/l meglitinide, 6.4 nmol/l glipizide and 4.0 nmol/l glibenclamide. The hyperglycemic sulfonamide diazoxide opened ATP-dependent K+ channels. Half maximally effective concentrations of diazoxide were 20 mumol/l with 0.3 mmol/l ATP and 102 mumol/l with 1 mmol/l ATP in the recording pipette. Thus, the action of diazoxide was dependent on the presence of ATP in the recording pipette. The free concentrations of the drugs which influenced ATP-dependent K+ currents were comparable with the free plasma concentrations in humans and the free concentrations which affected insulin secretion in vitro. The results support the view that the target for the actions of sulfonylureas and of diazoxide is the ATP-dependent K+ channel of the pancreatic B-cell or a structure closely related to this channel.

Distinct mechanisms for two amplification systems of insulin release.

The mechanisms whereby activation of the cyclic AMP-dependent protein kinase A or the Ca2+-phospholipid-dependent protein kinase C amplifies insulin release were studied with mouse islets. Forskolin and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) were used to stimulate adenylate cyclase and protein kinase C respectively. The sulphonylurea tolbutamide was used to initiate insulin release in the presence of 3 mM-glucose. Tolbutamide alone inhibited 86Rb+ efflux, depolarized beta-cell membrane, triggered electrical activity, accelerated 45Ca2+ influx and efflux and stimulated insulin release. Forskolin alone only slightly inhibited 86Rb+ efflux, but markedly increased the effects of tolbutamide on electrical activity, 45Ca2+ influx and efflux, and insulin release. In the absence of Ca2+, only the inhibition of 86Rb+ efflux persisted. TPA (100 nM) alone slightly accelerated 45Ca2+ efflux and insulin release without affecting 45Ca2+ influx or beta-cell membrane potential. It increased the effects of tolbutamide on 45Ca2+ efflux and insulin release without changing 86Rb+ efflux, 45Ca2+ influx or electrical activity. Omission of extracellular Ca2+ suppressed all effects due to the combination of TPA and tolbutamide, but not those of TPA alone. Though ineffective alone, 10 nM-TPA amplified the releasing action of tolbutamide without affecting its ionic and electrical effects. In conclusion, the two amplification systems of insulin release involve at least partially distinct mechanisms. The cyclic AMP but not the protein kinase C system initiating signal (Ca2+ influx) triggered by the primary secretagogue.

Adverse cardiovascular effects of sulphonylurea drugs. Clinical significance.

Sulphonylureas are widely used in the treatment of diabetes mellitus. Since the publication of the University Groups Diabetes Program (UGDP) results the discussion on their possible cardiovascular side effects has been lively and sometimes even passionate. The initial UGDP findings about the adverse effects of tolbutamide on the cardiovascular system have been criticised, particularly for shortcomings in the study design. The results of other epidemiological studies of the sulphonylurea effects on cardiovascular morbidity and mortality published this far have been contradictory. This is understandable because the factors involved are very complex. Most of these studies have used tolbutamide only, and the findings cannot necessarily be directly extrapolated to other sulphonylureas. Only properly performed prospective studies may provide further information on this issue. High concentrations of several sulphonylureas may have inotropic effects on heart muscle in in vitro animal models, but human studies performed in vivo do not support the view of clinically significant inotropy for sulphonylureas. High concentrations of tolbutamide or glibenclamide (glyburide) may affect the myocardial metabolism in isolated organs, but the possible clinical significance of these findings remains unknown. Some epidemiological and experimental studies have associated oral antidiabetic treatment with the occurrence of cardiac arrhythmias or increased digitalis toxicity. Only a few results are available, and there may be differences between the sulphonylureas in this respect. Antiaggregatory properties have been postulated for some sulphonylureas. Gliclazide, in particular, has been studied, but some other compounds of this class have also been effective in short term studies. If confirmed, these effects on haemostasis would be noteworthy. The sulphonylurea effects on serum lipids, especially on HDL-cholesterol, have been discussed widely during the last few years. Decreases in HDL-cholesterol concentrations were suggested to be associated with sulphonylurea therapy. However, these findings were not confirmed in recent cross-sectional and longitudinal studies performed with different sulphonylureas. Chlorpropamide, and to a lesser extent tolbutamide, may cause dilutional hyponatraemia and aggravate existing heart failure. Glibenclamide may increase the clearance of water in the kidney.

Blood Sugar Lowering Activity ofSwertia chirata(Buch-Ham) Extract

AbstractNinety five percent ethanol extract of Swertia chirata (Buch-Ham) was fed to healthy albino rats consisting of fed, fasted and glucose loaded models. Significant blood sugar lowering effect was observed in these models. Swertia chirata fed orally caused enhancement of the blood sugar lowering effect of tolbutamide in healthy albino rats.

Opposite effects of tolbutamide and diazoxide on the ATP-dependent K+ channel in mouse pancreatic ?-cells

The influence of the antidiabetic sulphonylurea tolbutamide on K+ channels of mouse pancreatic beta-cells was investigated using different configurations of the patch clamp technique. The dominant channel in resting cells is a K+ channel with a single-channel conductance of 60 pS that is inhibited by intracellular ATP or, in intact cells, by stimulation with glucose. In isolated patches of beta-cells membrane, this channel was blocked by tolbutamide (0.1 mM) when applied to either the intracellular or extracellular side of the membrane. The dose-dependence of the tolbutamide-induced block was obtained from whole-cell experiments and revealed that 50% inhibition was attained at approximately 7 microM. In cell-attached patches low concentrations of glucose augmented the action of tolbutamide. Thus, the simultaneous presence of 5 mM glucose and 0.1 mM tolbutamide abolished channel activity and induced action potentials. These were not produced when either of these substances was added alone at these concentrations. The inhibitory action of tolbutamide or glucose on the K+ channel was counteracted by the hyperglycaemic sulphonamide diazoxide (0.4 mM). Tolbutamide (1 mM) did not affect Ca2+-dependent K+ channels. It is concluded that the hypo- and hyperglycaemic properties of tolbutamide and diazoxide reflect their ability to induce the closure or opening, respectively, of ATP-regulated K+ channels.

Evidence for direct effect of tolbutamide on hepatic glycogenolysis induced by Ca 2+-dependent hormones

The effects of tolbutamide and glibenclamide on hepatic glycogenolysis in perfused rat liver were investigated. Tolbutamide per se did not influence glucose output from the liver, but at therapeutic concentrations (about 350 μM) it significantly inhibited the glycogenolysis induced by phenylephrine, vasopressin and angiotensin II, while glibenclamide did not. Neither tolbutamide nor glibenclamide inhibited the glycogenolysis induced by glucagon. Tolbutamide potentiated the inhibitory effect of submaximal concentrations of insulin on glycogenolysis induced by phenylephrine. This effect of tolbutamide was elicitable even in the absence of calcium in the perfusate, and was additive to that of trifluoperazine. However, tolbutamide did not potentiate the inhibitory effect of insulin on glucagon-induced glycogenolysis. Tolbutamide inhibited the glycogenolysis induced by A23187, a calcium ionophore. These results indicate that, in addition to its known effect on insulin secretion, tolbutamide has a direct effect on the liver to inhibit glycogenolysis induced by Ca 2+-dependent hormones (cat-echolamines, vasopressin and angiotensin II) and A23187. Thus, it is likely that tolbutamide inhibits the effect of Ca 2+ mobilized by Ca 2+-dependent hormones to stimulate glycogenolysis.

Effect of tolbutamide on fructose-6-phosphate, 2-kinase and fructose-2, 6-bisphosphatase in rat liver

The effects of tolbutamide on the activities of fructose-6-phosphate,2-kinase and fructose-2,6-bisphosphatase were examined using rat hepatocytes. Tolbutamide stimulated fructose-6-phosphate,2-kinase activity and inhibited fructose-2,6-bisphosphatase activity, resulting in an increase of fructose-2,6-bisphosphate level. Changes in the activities of the enzyme by tolbutamide were due to variation in the Km value, but not dependent on alteration of Vmax. Glucagon inhibition of fructose-2,6-bisphosphate formation resulting from an inactivation of fructose-6-phosphate,2-kinase and an activation of fructose-2,6-bisphosphatase was released by tolbutamide. Tolbutamide stimulation of fructose-2,6-bisphosphate formation through regulation of fructose-6-phosphate,2-kinase/fructose-2,6-bisphosphatase may produce enhancement of glycolysis and inhibition of gluconeogenesis in the liver.

Characterization of the sulfonylurea-induced potentiation of the insulin response in cultured 3T3 adipocytes

Studies were carried out to determine the role of sulfonylureas in the regulation of insulin-sensitive hexose uptake in cultured 3T3 adipocytes. Exposure (0–72 hr) of cells to the sulfonylurea-derivative tolbutamide (0.05–0.3 mg/ml) induced a time- and concentration-dependent potentiation of the stimulatory effect of insulin on hexose uptake (500 vs 340%). The effect was maximal within 24 hr and completely reversible. It was strictly limited to the presence of insulin. Basal hexose uptake and insulin binding were not affected by the drug. High concentrations of the agent (>0.3 mg/ml) induced a decrease in insulin response, suggesting a concentration optimum. Lineweaver-Burk analysis of uptake data revealed that the potentiating effect of tolbutamide was due to enhancement of the insulin-induced increase in apparent V max, i.e. in the number or activity of hexose transporters. This enhancement was inhibited by cycloheximide (1 μg/ml), indicating involvement of protein synthesis in the induction of the effect. It is concluded that sulfonylureas act by influencing synthesis of protein(s) which potentiate the effect of insulin on hexose uptake.

Effects of tolbutamide on cultured heart cells of mice

To investigate the direct effects of tolbutamide on the myocardium, we studied the ultrastructure, direct effects of tolbutamide on the myocardium, we studied the ultrastructure, beating rhythm, cytotoxicity determining the 51Cr release from damaged cells and the 45Ca activity in the cultured heart cells of mice. After 48 h of cultivation, tolbutamide was added to give a final concentration of 0.37, 0.93, 1.85, and 3.7 nM. The addition of high dose of tolbutamide (greater than 1 mM) to the culture medium produced irregular beating after 1 min and cessation of beating after 20 h. The cultured heart cells incubated with control solution or low concentrations of tolbutamide (less than 1 mM) showed little change in the beating rhythm and frequency. Cytotoxicity of tolbutamide on the cultured heart cells was observed only in high concentrations (greater than 1 mM): the 51Cr release index was 23% at 1.85 mM and 40% at 3.7 mM. On electron microscopy, the heart cells cultured with high concentration of tolbutamide (greater than 1 mM) showed electron-dense bodies in the mitochondria and shortened Z-Z intervals. However, these ultrastructural alterations were not observed in the cultured heart cells incubated with low concentration of tolbutamide (less than 1 mM). The 45Ca activity of cultured heart cells, after the incubation for 24 h in medium containing 45Ca, was significantly increased only with high concentrations of tolbutamide (greater than 1 mM). We conclude that tolbutamide in dose of less than 1 mM had no cytotoxicity and had little effect on the beating rhythm, ultrastructure and intracellular calcium concentration of the cultured heart cells of mice.