Inhibition of canine gastric acid secretion by an H-1 receptor antagonist to histamine

Histamine H-2 receptors are thought to mediate gastric acid secretory responses, where-as H-1 receptors supposedly regulate mucosal vascular responses to histamine. In an in vivo chambered canine stomach flap preparation, the H-1 receptor antagonist, tripelennamine, injected intraarterially (22.1 mol/kg) into the stomach flap reduced histamine-stimulated (1.25 /kg/min intravenously) acid secretion by approximately two thirds with a secondary reduction in gastric mucosal blood flow. This antisecretory action does not appear to be due to nonspecific mucosal damage. The H-2 receptor antagonist, metiamide, injected intraarterially (2.5 mol/kg) also inhibited gastric acid secretion by about two thirds as did intravenously injected metiamide (4.5 mol/kg), whereas intravenously administered tripelennamine (40.8 mol/kg) was ineffective as an acid secretory inhibitor. Intraarterial tripelennamine reduced the secretory actions of the H-2 agonist, 4-methyl-histamine (2.2 g/kg/min intravenously), while intravenous metiamide depressed the gastric mucosal dilator responses to the H-1 agonist, 2-methylhistamine (5 g/kg/min intravenously). Both histamine-receptor antagonists also reversed the systemic circulatory depressor effects of histamine and its analogs. These results suggest the need for reevaluation of inferences based upon the assumed specificity of H-2 and H-1 agonists and antagonists.     

Deleterious effects of digitalis on reperfusion-induced arrhythmias and myocardial injury in ischemic rat hearts: possible involvements of myocardial Na+ and Ca2+ imbalance

Summary Isolated rat hearts were made ischemic for 25 min after an initial recirculating perfusion, followed by 30 min of reperfusion. In some hearts, interventions including administration of ouabain and/or high [K⁺] in the buffer were performed during the first 10 min of reperfusion.During ischemia, intracellular Na⁺ (Na_i) increased from 15 to 64 [mol/g dry weight (dwt). During reperfusion, Na_i declined rapidly (at 10 min of reperfusion: 48 nol/g dwt, at 30 min: 25 mol/g dwt) and regular rhythm was recovered within 10 min in hearts without any intervention during reperfusion.⁴⁵Ca²⁺ uptake increased from 0.8 to 7.5 mol/g dwt after 30 min of reperfusion. Ventricular function recovered by 45 %.A 10-min perfusion with 10 or 50 M of ouabain increased Na_i (17 to 21 or 27 mol/g dwt) with increased left-ventricular (LV) contractile function, but these effects were reversed by combination of high perfusate [K⁺] (20 mM) in non-ischemic hearts.A 10-min reperfusion with ouabain retarded or stopped the decline in Na_i (at 10 min of reperfusion: 54 or 63 mol/g dwt, at 30 min: 32 or 40 mol/g dwt). These amounts of ouabain also increased the incidence of ventricular tachyarrhythmias during reperfusion to 30 % or 50 %, and increased the duration of ventricular fibrillation from 6.5 to 11.5 or 18.0 min.⁴⁵Ca²⁺ uptake reached to 8.8 or 10.0 mol/g dwt, and function recovered only 35 % or 28 %. When high perfusate [K⁺] was combined with ouabain during reperfusion, the retarded decline in Nai, augmented⁴⁵Ca²⁺ uptake, and reduced recovery of function caused by ouabain alone were attenuated. These results suggest that digitalis has toxic effects on reperfused ischemic hearts by inhibition of rapid active outward transport of previously elevated Na_i and potentiation of Ca²⁺ overload.The work was supported in part by grant HL 37936 from the National Heart, Lung and Blood Institute. J. R. Neely was deceased on November 29, 1988     

Neural influences on human esophageal and salivary alkali secretion

Esophageal secretion of HCO ₃ ^– ions occurs in opossum and man and may contribute to mucosal defense. Using a perfusion technique, neuroregulatory influences on esophageal and salivary HCO ₃ ^– secretion were investigated in 24 healthy human subjects. The sight and smell of food increased median salivary HCO ₃ ^– output from 424 to 573 mol/15 min (P=0.014), without significantly altering esophageal HCO ₃ ^– secretion (74–105 mol/15 min,P=0.24). Atropine reduced both salivary (610 to 68, 17, 10, and 3 mol/15 min in successive periods;P<0.028) and esophageal HCO ₃ ^– output (108 to 78, 35, 18, and 7 mol/10 cm/15 min;P<0.028), respectively. Following atropinization, cholinergic stimulation failed to increase salivary secretion but did unmask a small rise in esophageal alkali output (7 to 27 mol/10 cm/15 min,P=0.036), implicating a noncholinergic mechanism. Cold-induced pain activated sympathetic reflexes and reduced esophageal HCO ₃ ^– output (91 to 64 mol/10 cm/15 min,P=0.041) without influencing salivary secretion. These observations support a role for the autonomic nervous system in modulating human esophageal and salivary HCO ₃ ^– secretion.     

Influence of phorbol esters on contractile force,action potential and calcium current of isolated guinea-pig heart tissues

Phorbol-12,13-dibutyrate (PDB) reduced concentration-dependently the contractile force of guineapig papillary muscles (EC₅₀ 1.07 mol/l) while phorbol-12-myristate-13-acetate (PMA) was ineffective. The protein kinase C inhibitors staurosporine (0.1 mol/l) and polymyxin B (70 mol/l) did not antagonize the negative inotropic effect of PDB. Neither PMA nor PDB, in concentrations up to 30 mol/l caused significant changes of the membrane resting potential, the maximum depolarization velocity, the action potential duration or the functional refractory period in intact papillary muscles. In isolated ventricular cardiomyocytes the inward calcium current was halved by either 1 mol/l PDB or 10 mol/l PMA. PKC inhibitors attenuated, but could not completely abolish this effect of the phorboles. It is concluded that the negative inotropic effect of PDB is caused by a reduction of the slow inward calcium current and that this inhibition is, for the greater part, not mediated by an activation of protein kinase C.     

Modulation of pacemaker activity in sheep cardiac Purkinje fibers by stimulation of β-adrenoceptor subtypes

The electrophysiological effects mediated by ₁- and ₂- in spontaneously active sheep cardiac Purkinje fibers were investigated using the non-selective agonist (–)-isoproterenol (IPN) and the selective agonists (–)-noradrenaline (₁) and procaterol (₂) in the absence and presence of the selective antagonists bisoprolol (₁) and ICI 118,551 (₂).IPN (0.01 mol/l) increased the spontaneous rate by 54% and the slope of diastolic depolarization by 68% of the respective control values. Further, IPN increased the action potential duration at –20 mV (APD –20 mV) from 96 to 154 ms, reduced the APD –70 mV by 17% and the duration of the diastole by 39% and slightly hyperpolarized the maximum diastolic potential. These effects were partially inhibited by ICI 118,551 (0.03 mol/l), diminished by bisoprolol (0.1 mol/l) and almost completely blocked by the combination of both antagonists. Concentration response curves of IPN were influenced by the selective antagonists as follows: ICI 118,551 (0.03 mol/l) shifted the curves to the right by 0.2–0.4 log units and increased the slope factor. Bisoprolol (0.1 mol/l) induced a greater shift to the right by 1.1–1.5 log units. Combination of bisoprolol with ICI 118,551 shifted the curves to the right by 1.5–1.7 log units.Noradrenaline (0.3 mol/l) elicited similar actions as IPN. Bisoprolol (0.1 mol/l) shifted the concentration response curves of noradrenaline to the right by 1.1–1.9 log units. Actions of procaterol (0.1 mol/l) were weak, attained only 15–35% of the maximal effects of IPN and could be blocked by ICI 118,551 (0.03 mol/l).These results show that the increase of pacemaker activity induced by catecholamines in sheep cardiac Purkinje fibers is predominantly mediated by stimulation of ₁. However, contribution of ₂ mediated effects could be demonstrated.Supported by Ministerium für Wissenschaft und Forschung, Nordrhein-Westfalen, Projekt-Nr, 40008786.     

Role of histamine H3 receptors in control of mouse intestinal motility in vivo and in vitro: comparison with alpha2-adrenoceptors

We tested drugs acting at histamine H₃ receptors in mice on the gastrointestinal transit of a charcoal meal in vivo and on neurogenic contractions of isolated ileal preparations. The agonist (R)--methylhistamine (100 mol/kg) caused a maximum 25% reduction of gastrointestinal transit, an effect mimicked by immepip (100 mol/kg) and antagonized by thioperamide (20 mol/kg) or clobenpropit (20 mol/kg). In the isolated ileum, (R)--methylhistamine (10–100 M) caused a slight, thioperamide-insensitive, reduction (maximum 15%) of electrically evoked cholinergic contractions. In comparison, the ₂-adrenoceptor agonist clonidine (0.1 mol/kg) caused a 35.2% inhibition of the gastrointestinal transit and almost completely reduced (maximum 82% at 1 M) the cholinergic contraction of the isolated ileum, both effects being antagonized by idazoxan (0.4 mol/kg and 1 M, respectively). These results suggest that histamine H₃ receptors, located outside the myenteric plexus, mediate an inhibition of the gastrointestinal transit in vivo. Conversely, the presence of ₂-adrenoceptors in the cholinergic nerve endings and their inhibitory role in the control of gastrointestinal propulsion is confirmed.     

B cell adrenoceptors and sulphonylurea-induced insulin release in mouse islets

Summary Interactions of tolbutamide and glibenclamide with B cell adrenoceptors have been reported. This study evaluated the possible role of such interactions in the stimulation of insulin release. Mouse islets were incubated in the presence of 10 mmol/l glucose alone or with tolbutamide (10 mol/l) or glibenclamide (0.02 mol/l). At 0.01–10 mol/l, blockers of ₂-adrenoceptors (yohimbine, idazoxan) or ₁-adrenoceptors (prazosin) had practically no effect on glucose-induced insulin release and did not affect its potentiation by sulphonylureas, except for a slight increase by 10 mol/l prazosin and idazoxan. Nonspecific -blockers (phentolamine, dihydroergotamine) increased control release at 10 mol/l, but only the latter amplified the response to tolbutamide. Blockers of -adrenoceptors were tested at 0.1–100 mol/l: propranolol (₁, ₂), metoprolol (₁) and compound ICI 118-551 (₂). They increased glucose-induced insulin release at 100 mol/l but variably altered the effect of sulphonylureas. Blockers of adrenoceptors have, thus, no effect on insulin release in vitro at therapeutic concentrations. At high concentrations, they non-specifically affect the action of sulphonylureas. We conclude that an interaction with B cell adrenoceptors is not involved in the insulinotropic action of sulphonylureas.     

Somatostatin and Octreotide Stimulate Short-Circuit Current in Human Colonic Epithelium

In vitro somatostatin is a potent inhibitor of intestinal ion secretion in animal models and cultured human cell lines, providing a rationale for its use in secretory diarrheas. However, the effects of somatostatin on ion transport in native human colonic epithelium have not been reported. In this study the effects of somatostatin and octreotide on the basal short-circuit current and the cAMP- and Ca²⁺-stimulated short-circuit current were studied in isolated human colonic mucosa mounted in Ussing chambers. Under basal conditions somatostatin and octreotide (1 mol/liter) stimulated a small, bumetanide-sensitive increase in short-circuit current. Following stimulation of secretion with prostaglandin E₂, somatostatin and octreotide further increased the short-circuit current in a dose dependent fashion (ED₅₀ 10 nmol/liter for both). This stimulation of short-circuit current was not affected by pretreatment of the tissue with basolateral tetrodotoxin (1 mol/liter) or mucosal amiloride (10 mol/liter). In contrast, somatostatin and octreotide had no effect when secretion was stimulated with 8-bromo-cAMP, and pretreatment of the tissue with somatostatin and octreotide (0.1 mol/liter) did not alter the secretory response to carbachol. The absence of any inhibitory effect of somatostatin and octreotide on electrogenic secretion in the human colon may explain the variable results obtained when somatostatin or octreotide are used for the treatment of secretory diarrheas.     

Influence of vanadate on electrophysiological and contractile parameters of atrial myocardium

Summary Whereas vanadate increases isometric force of contraction in stimulated rat left atria (EC₅₀ 36.6 mol/l), it decreases force of contraction in guinea-pigs (EC₅₀ 4.7 mol/l). Action potential duration at 90 and 30% repolarisation is decreased in guinea-pig atria by 70 and 60%, but in rat atria by only 40 and 7% respectively.Whereas the time course of the negative inotropic action is rapid and correlates with that of the shortening of the action potential, there is no relationship between action potential changes and the slowly developing positive inotropic effect. Negative and positive inotropic actions seem to be the result of two superimposed processes, whose kinetics suggest an extra- and intracellular site of action.Na⁺, K⁺-ATPase prepared from rat and guinea-pig atria and ventricle is inhibited by vanadate to a similar extent: IC₅₀ (mol/l) rat: atria 1.05, ventricle 0.49; guineapig: atria 0.75, ventricle 0.62. This indicates that the discrepancy in inotropy cannot be explained by the different sensitivity of the Na⁺, K⁺-ATPase to vanadate.

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Wirkung von Vanadat auf elektrophysiologische und kontraktionsdynamische Parameter des Vorhofs

Zusammenfassung Vanadat erhöht die isometrische Kontraktionskraft elektrisch gereizter linker Rattenvorhöfe (EC₅₀ 36.6 mol/l), senkt sie jedoch beim Meerschweinchen (EC₅₀ 4,7 mol/l). Am Meerschweinchen nimmt die Aktionspotentialdauer bei 90 bzw. 30% Repolarisation um 70 bzw. 60% ab, dagegen am Rattenvorhof nur um 40 bzw. 7%.Während die negativ inotrope Wirkung rasch eintritt und im Zeitverlauf mit der Verkürzung des Aktionspotentials korreliert, besteht keine solche Beziehung zur sich langsam entwickelnden positiv inotropen Wirkung. Negativ bzw. positiv inotrope Vanadat-Wirkungen beruhen wahrscheinlich auf zwei sich überlagernden Prozessen, die aufgrund ihrer Kinetik einem extra- bzw. intrazellulären Angriffspunkt entsprechen könnten.Die Na⁺, K⁺-ATPase von Vorhöfen und Ventrikeln der Ratte und des Meerschweinchens wird durch Vanadat etwa gleich stark gehemmt: IC₅₀ (mol/l) Ratte: Vorhöfe 1,05, Ventrike 0,45; Meerschweinchen: Vorhöfe 0,75, Ventrikel 0,62. Dies zeigt, daß die unterschiedliche inotrope Wirkung nicht auf eine verschiedene Empfindlichkeit der Na⁺, K⁺-ATPase gegenüber Vanadat zurückzuführen ist.

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The data have been presented at the Symposium Cardiac Effects of Vanadate, Munich, October 26–27, 1979.     

Pharmacological evidence for beta3 adrenoceptors in the control of rat gastric acid secretion

The effect of the ₃-adrenoceptor agonist BRL37344 on gastric acid secretion evoked by different secretory stimuli was investigated in anaesthetized rats with lumen-perfused stomachs in comparison with the ₂-adrenoceptor agonist clenbuterol. Intravenous injections of BRL37344 (1–10 mol/kg) and clenbuterol (0.01–1 mol/kg) dose-dependently reduced 2-deoxy-D-glucose-induced acid secretion, with BRL37344 about forty times less potent than clenbuterol. BRL37344 (0.1–3 mol/kg) inhibited pentagastrin-induced acid output, whereas clenbuterol was effective only at high doses (10–100 mol/kg). The inhibitory effect of BRL37344 on pentagastrin-induced acid secretion was not modified by the nonselective –adrenoceptor antagonist propranolol, but it was prevented by bupranolol, a ₃-adrenoceptor antagonist. Furthermore, neither BRL37344 (10 mol/kg) nor clenbuterol (100 mol/kg) modified the acid secretion induced by histamine. These data suggest that ₃ adrenoceptors have an inhibitory role in the control of rat gastric acid secretion induced by indirect stimuli.     

Mechanisms in rabbit aorta for hyperglycaemia-induced alterations in angiotensin II and norepinephrine effects

Summary The (Na⁺, K⁺)-ATPase activity operative in rabbit aortic intima-media incubated with normal plasma levels of glucose and myo-inositol (70 mol/l) is decreased when the glucose content of the medium is raised from 5 to 10 mmol/l or higher; this effect is prevented by aldose reductase inhibitors and by raising the myo-inositol content of the medium to 500 mol/l. The decrease in (Na⁺, K⁺)-ATPase activity results from the loss of a component normally regulated (stimulated) by endogenously released adenosine through a receptor that stimulates phosphatidylinositol turnover in a discrete pool. The replenishment of this phosphatidylinositol pool selectively requires myo-inositol transport and is inhibited when increased polyol pathway activity impairs myo-inositol transport at a normal plasma level. Adenosine is a vasodilator, some endothelium-released vasodilators modulate the responses to vasoconstrictors by stimulating an increase in (Na⁺, K⁺)-ATPase activity in vascular smooth muscle. Whether adenosine mediates this effect in angiotensin II or norepinephrine-stimulated aorta was examined. Angiotensin II (100 nmol/l) and norepinephrine (1 mol/l) evoked marked increases in (Na⁺, K⁺)-ATPase activity in aortic intima-media incubated with 5 mmol/l glucose and 70 mol/l myo-inositol, which were inhibited when adenosine deaminase was added or the medium myo-inositol omitted to inhibit myo-inositol transport. Raising the medium glucose to 30 mmol/l inhibited the angiotensin II and norepinephrine evoked increases in (Na⁺, K⁺)-ATPase activity, and this was prevented when tolrestat (10 mol/l) was added or the myo-inositol content of the medium was raised from 70 to 500 mol/l. Hyperglycaemia causes decreased (Na⁺, K⁺)-ATPase activity prevented by aldose reductase inhibitors and by raising plasma myo-inositol by a mechanism which inhibits an adenosine-(Na⁺, K⁺)-ATPase regulatory system, which modulates the responses to angiotensin II and norepinephrine in some blood vessels.     

Bound inorganic phosphate and early contractile failure in global ischaemia

Inorganic phosphate (P_i) accumulates extremely rapidly in ischaemic heart muscle and intracellular binding of this metabolite may account for the precipitous loss of function seen at the onset of severe ischaemia. We have used³¹P-NMR spectroscopy to measure the free cytosolic [P_i] and chemical assay techniques to measure total tissue P_i at 0, 1, 2, 3, 5, and 12 min of complete global ischaemia in the isolated isovolumic rat heart. At zero time, the P_i assayed chemically was 30.77±5.52 mol/g dry wt (mean±SD, n=7) whilst P_i assayed by NMR was 3.39±1.21 mol/g dry wt (n=15). Thus, 27.38 mol/g dry wt of P_i was bound at a cytosolic [P_i] of 0.82 mM. After 12 min of ischaemia, 49.88 mol/g dry wt of P_i was bound at a cytosolic [P_i] of 4.11 mM. When all data were fitted, using a non-linear, least squares fit (p<0.05), to the binding isotherm: Bound P_i=B_max. [P_i]/(K_d+[P_i]), the apparent binding parameters K_d and B_max were estimated to be 1.1±0.6 mM and 64.0±10.2 mol/g dry wt respectively. During the first minute of global ischaemia when the rate-pressure product had decreased by 79% of its pre-ischaemic value, bound P_i had increased by 58% and free cytosolic [P_i] by 162%. When functional and metabolite changes were expressed as a fraction of the total change which occurred during the 12-min ischaemic period, bound P_i had the profile most similar to the rate-pressure product. Both the amount of bound P_i and free cytosolic [P_i] correlated with loss of contractile function as the ischaemic period progressed. The results snow that during ischaemia, P_i is bound progressively as free cytosolic [P_i] is increased as the result of high energy phosphate hydrolysis. While these results are consistent with the possibility that P_i binding may contribute to ischaemic contractile failure, no molecular explanation for the possible effect of bound P_i on contraction has been propsed.     

High plasma leucine concentrations without neurological symptoms in a patient with classical maple syrup urine disease

It has been found that the amino acid analyser used in this study systematically overestimated plasma leucine at high concentrations. The concentration reported as 2249 mol/L had a true value of 1430 mol/L and leucine values reported as >2000 mol/L were approximately 1500 mol/L.     

Loss of glycogen during preconditioning is not a prerequisite for protection of the rabbit heart

Depletion of gycogen has been proposed as the mechanism of protection from ischemic preconditioning. The hypothesis was tested by seeing whether pharmacological manipublation of preconditioning causes parallel changes in cardiac glycogen content. Five groups of isolated rabbit hearts were studied. Group 1 experienced 30 min of ischemia only. Group 2 (PC) was preconditioned with 5 min of global ischemia followed by 10 min of reperfusion. Group 3 was preconditioned with 5 min exposure to 400 nM bradykinin followed by a 10 min washout period. Group 4 experienced exposure to 10 M adenosine followed by a 10 min washout period, and the fifth group was also preconditioned with 5 min ischemia and 10 min reperfusion but 100 M8-(p-sulfophenyl) theophylline (SPT), which blocks adenosine receptors, was included in the buffer to block preconditioning's protection. Transmural biopsies were taken before treatment, just prior to the 30 min period of global ischemia, and after 30 min of global ischemia. Glycogen in the samples was digested with amyloglucosidase and the resulting glucose was assayed. Baseline glycogen averaged 17.3±0.6 mol glucose/g wet weight. After preconditioning glycogen decreased to 13.3±1.3 mol glucose/g wet weight (p<0.005 vs. baseline). Glycogen was similarly depleted after pharmacological preconditioning with adenosine (14.0±1.0 mol glucose/g wet weight, p<0.05 vs. baseline) suggesting a correlation. However, when proconditioning was performed in the pressence of SPT, which blocks protection, glycogen was also depleted by the same amount (13.3±0.7 mol glucose/g wet weight, p=ns vs. PC). Bradykinin, which also mimics preconditioning, caused no depletion of glycogen (16.3±0.8 mol glucoseig wet weight, p=ns vs. baseline). Because preconditioning with bradykinin did not deplete glycogen and because glycogen continued to be low when protection from preconditioning was blocked with SPT, we conclude that loss of glycogen per se does not cause the protection of preconditioning.     

Stimulation of GTP hydrolysis in guinea pig bronchial membranes by mastoparan

Guanine nucleotide-binding proteins, or G proteins, play an important role in transmitting information from membrane receptors to intracellular effector systems. Activation of G proteins results in the hydrolysis of GTP, and the measurement of GTPase activity represents a means by which the role of G proteins in signal transduction can be investigated. GTPase activity of guinea pig bronchial membranes was measured as the liberation of ³²P_i from [-³²P]GTP. GTPase activity was divided into two components, one possessing a high affinity and the other a low affinity for GTP. The contribution of high- and low-affinity GTPase to total hydrolysis was dependent on Mg²⁺. In the presence of submicromolar Mg²⁺, high-affinity GTPase represented 65–80% of all activity, whereas in the presence of 26 µM Mg²⁺, all detectable hydrolysis was due to the low-affinity GTPase. High-affinity GTPase was stimulated by Mg²⁺ in the 0.15–1.1 M range (2.5-fold maximal stimulation, apparent Km for Mg²⁺ 0.31 M). Mastoparan (1–100 M) caused a concentration-dependent stimulation of high-affinity (but not low-affinity) GTPase (71 ± 13% maximal stimulation, EC₅₀ 0.38 M), suggesting that high-affinity GTPase may be due to a G protein. Carbachol (10 M) and fenoterol (10 M) had no effect on high-affinity GTP hydrolysis, suggesting that under the conditions described, GTPase activity of bronchial membranes is not activated by muscarinic or -adrenergic receptors, respectively. Offprint requests to: K. J. Rhoden     

Effect of a hypoglycaemic agent M&B 39890A on glucagon secretion in isolated rat islets of Langerhans

Summary Administration of the compound M&B 39890A lowered serum glucose levels significantly (p<0.001) in genetically obese mice, while no effect on serum insulin levels was observed. In in vitro experiments with isolated rat islets of Langerhans M&B 39890A inhibited arginine-stimulated glucagon release at all concentrations tested (0.5, 5.0 and 50 mol/l). Insulin secretion was not inhibited by M&B 39890A (0.5 and 5.0 mol/l), but was slightly decreased at 50 mol/l. M&B 39890A (5 mol/l) also inhibited glucagon secretion in vitro in the presence of 2 mmol/l, 6 mmol/l and 20 mmol/l glucose, while exerting no effect on insulin secretion. These results suggest that the hypoglycaemic action of M&B 39890A may be due to its direct and selective effect on glucagon secretion; this appears to operate by a mechanism different to that of glucose.     

Experimental streptozotocin-induced diabetes and intestinal glucose metabolism in the rat,in vivo and in vitro

The intestine has a high glycolytic activity, but its metabolic role could be altered in diabetes mellitus. The aim of the present work was to investigate in vivo the glucose retained and the lactate produced by the intestine of normal and diabetic rats and in vitro the effect of different arterial glucose concentrations on glucose utilization and lactate, alanine, and pyruvate production in normal and diabetic rats when the glucose is supplied to the intestine exclusively via the vascular route. In vivo, the normal and diabetic rats retained similar percentages of the arterially supplied glucose (14.7±3.2 and 12.6±2.4, respectively). In vitro, when the preparations were perfused under hyperglycemic conditions, the glucose consumed, as a fraction of the quantity infused, was significantly lower (P<0.05) in the diabetic (247.0±22.8 mol/mmol infused glucose) than in normal (315.0±16.3 mol/mmol infused glucose) rats. The lactate produced was significantly higher in diabetic than in normal rats whether the preparations were perfused under isoglycemic (P<0.01; 1916.4±124.0 vs 1284±67.7 mol/mmol consumed glucose) or hyperglycemic (P<0.05; 1356.4±199.7 vs 898.0±87.3 mol/mmol consumed glucose) conditions. There was significantly (P<0.05) greater alanine release from the diabetic (123.7±21.8 mol/mmol consumed glucose) than from the normal (40.7±10.3 mol/mmol consumed glucose) rat preparations perfused under isoglycemic conditions.     

Cyclic GMP-Mediated Activation of a Glibenclamide-Sensitive Mechanism in the Rabbit Sphincter of Oddi

We investigated whether glibenclamide-sensitive potassium channels are involved in cyclic GMP (cGMP)-mediated relaxation of the rabbit Oddi's sphincter. Changes in isometric tension were measured in the presence of atropine (1 M) and guanethidine (4 M). Concentration–response curves for nitroglycerin, vasoactive intestinal polypeptide (VIP), and sodium nitroprusside (SNP) were shifted to the right in the presence of (p-chloro-d-Phe⁶, Leu¹⁷)-VIP (VIPa), a VIP receptor antagonist. Glibenclamide (1 M) attenuated the relaxations to VIP, nitroglycerin, or 8-bromo cGMP. In the presence of tetrodotoxin (TTX), glibenclamide attenuated relaxations to VIP without effect on those to nitroglycerin. Furthermore, nitroglycerin increased both cAMP and cGMP concentrations, however, it failed to increase the tissue cAMP concentration in the presence of TTX. VIPa also blocked the increase in content of either cyclic nucleotide. VIP increased cAMP with a TTX-sensitive increase in cGMP content. 8-Bromo cGMP (1 M) significantly increased the tissue cAMP content. This was blocked by either TTX or VIPa (both 1 M). We conclude that ATP-sensitive potassium channel (K_ATP) activation contributes to cGMP-mediated relaxation of the Oddi's sphincter of the rabbit. Activation of K_ATP results from a cyclic AMP-mediated process due to cGMP-dependent VIP release from neurons.     

Inhibition of biliary phospholipid and cholesterol secretion by cefoperazone

The effect of cefoperazone, a third-generation cephalosporin, on biliary lipid secretion in rats was examined. Rats were anesthetized with ether and the mid-lumbar vein and common bile duct cannulated. Bile acid secretion was maintained by intravenous taurocholic acid infusion (28 mol/hr). A 1-hr control period was followed by intravenous cefoperazone infusion at either submaximal (20 mol/hr), or supramaximal (60 mol/hr) concentrations. At the cefoperazone infusion rate of 20 mol/hr (biliary secretion of 7.1±1.6 mol/hr) phospholipid secretion fell 19% and cholesterol secretion fell 31%; at a cefoperazone infusion rate of 60 mol/hr (biliary secretion rate of 27.1±5.1 mol/hr) phospholipid and cholesterol secretion were further reduced 40% and 56%, respectively, of controls. All changes were significant (P<0.01). Inhibition of both cholesterol and phospholipid secretion paralleled each other, was dose-dependent, and reversible. Cefoperazone's inhibitory action was abolished at a bile acid infusion rate of 108 mol/hr. Cefoperazone was not found to be associated with bile acid micelles or mixed micelles as determined by ultracentrifugation and gel filtration. Thus, the effect of cefoperazone on biliary lipid secretion is not due to the impairment of mixed micelle formation in the canalicular lumen but rather its inhibitory effect appears to be due to a presecretory event.     

17β-Estradiol Attenuates Quinolinic Acid Insult in the Rat Hippocampus

A number of studies have shown that 17-estradiol has neuroprotective properties. In this study the neuroprotective effect of 17-estradiol against quinolinic-acid-induced neuronal damage was investigated. Ovariectomized rats were separated into three groups of five animals each. Rats received daily subcutaneous injections of either olive oil or 17-estradiol in olive oil for 7 days prior to and following a single intrahippocampal injection of 1 mol quinolinic acid in 2 L phosphate-buffered saline. The brains were removed and the hippocampi either sectioned and stained for microscopic examination or used in glutamate receptor saturation binding studies. Glutamate receptor displacement binding studies were also performed using concentrations of 0.05 nM–5 M 17-estradiol or quinolinic acid. The results show that 17-estradiol protects hippocampal neurons from quinolinic-acid-induced neurodegeneration by competing with quinolinic acid to bind to the N-methyl-D-aspartate (NMDA) receptor. This would result in a decrease in intracellular free-calcium influx and resultant neuronal swelling.