Cardioprotective effect of pindolol in ischemic-reperfused isolated rat hearts

The effects of pindolol and timolol on ischemia reperfusion damage were studied in isolated working rat hearts. Ischemia (15 min) decreased the mechanical function and the energy state, and increased the tissue levels of free fatty acids (FFA). During reperfusion (20 min), the mechanical function did not recover, but the energy state recovered incompletely, whereas FFA increased further. Pindolol (50 microM) accelerated recovery of the mechanical function and the energy state that had been decreased by ischemia during reperfusion, and inhibited the accumulation of FFA during ischemia and reperfusion, especially when it was applied during the whole period of reperfusion. Timolol (50 microM), however, did not accelerate recovery of the mechanical function and the energy state during reperfusion, although it attenuated FFA accumulation during reperfusion. The pindolol-induced recovery of the mechanical function during reperfusion was reduced by timolol. The results suggest that the intrinsic sympathomimetic activity of pindolol may play an important role, at least in part, in producing the cardioprotective effect, especially during reperfusion.

Positive inotropic and negative chronotropic effects of (-)-cis-diltiazem in rat isolated atria

1. The cardiovascular effects of (-)-cis-diltiazem, an optical isomer of diltiazem, were studied in the isolated atrium and aortic strip. (-)-cis-Diltiazem (30 microM or more) increased the developed tension of the rat left atrium, while (+)-cis-diltiazem (1 microM or more) decreased it. 2. (-)-cis-Diltiazem (1 to 100 microM) decreased the rate of spontaneous beating in the right atrium as did (+)-cis-diltiazem. 3. The potency of the positive inotropic action of (-)-cis-diltiazem was almost the same as that of ouabain in the rat left atrium, but in the guinea-pig left atrium it was considerably weaker than that of ouabain. 4. In both endothelium-intact and endothelium-denuded aortic strips, (-)-cis-diltiazem relaxed the Ca(2+)-induced contraction. In the endothelium-intact rat aortic strip depolarized by 15 mM KCl, Bay K 8644, a calcium channel agonist, increased the contractile force, whereas (-)-cis-diltiazem did not. 5. These results indicate that (-)-cis-diltiazem has a positive inotropic action in isolated atria in rats and guinea-pigs, but the mode of positive inotropic action of (-)-cis-diltiazem is different from that of ouabain or Bay K 8644.

Effects of dopamine receptor agonists on passive avoidance learning in mice: interaction of dopamine D1 and D2 receptors

The present study examined the effects of dopamine D1 and D2 receptor agonists on the acquisition stage of passive avoidance learning and on locomotor activity in mice. The D2 agonist, RU 24213 (1-10 mg/kg s.c.), and the non-selective agonist, apomorphine (0.3-3 mg/kg s.c.), but not the D1 agonist, SKF 38393 (1-10 mg/kg s.c.), impaired learning and activated locomotion. RU 24213 (1 mg/kg s.c.) was more effective in impairing learning than in activating locomotion. The concurrent administration of SKF 38393 (10 mg/kg i.p.) and RU 24213 (1 and 3 mg/kg s.c.) produced a synergistic effect in both behavioral situations. The D1 antagonist, SCH 23390 (0.025 mg/kg i.p.), slightly inhibited the effects of apomorphine and of the combination of SKF 38393 and RU 24213 on learning but not on locomotion. The D2 antagonist, (-)-sulpiride (40 mg/kg i.p.), completely blocked these effects in both situations. These results suggest that dopamine receptor agonists impair passive avoidance learning through the D2 receptor, and that D1 and D2 receptors act synergistically in this impairment, as they do in their effects on locomotion. The involvement of D1 and D2 receptors is qualitatively similar in each of these behaviors, although some small differences may exist.

Role of oxygen radicals in canine myocardial metabolic derangement during regional ischemia

To clarify the role of oxygen radicals in the development of myocardial injury during ischemia, production of lipid peroxides mediated by oxygen radicals was determined in in vivo dogs subjected to regional ischemia and reperfusion. Myocardial injury was assessed by derangement in energy and carbohydrate metabolism caused by ischemia and reperfusion. The production of lipid peroxides mediated by oxygen radicals considerably increased not only during reperfusion after ischemia but also during ischemia. Removal of oxygen radicals by administration of radical scavengers [recombinant human superoxide dismutase + catalase or N-(2-mercaptopropionyl)glycine] completely prevented the increase in production of lipid peroxides during ischemia. However, the radical scavengers did not attenuate the myocardial energy and carbohydrate metabolic derangements caused by ischemia and reperfusion after ischemia. These results suggest that significant amounts of oxygen radicals are generated during ischemia as well as during reperfusion and that the oxygen radicals and subsequent lipid peroxidation are not major factors in development of myocardial injury during either ischemia or reperfusion after ischemia.

Involvement of serotonergic neuronal systems in the anti-amnesic action of naftidrofuryl oxalate

The effects of naftidrofuryl oxalate on cycloheximide- and 5-hydroxytryptophan (5-HTP)-induced amnesia were investigated using a passive avoidance task in mice. Naftidrofuryl oxalate significantly improved the cycloheximide-induced amnesia. This effect of naftidrofuryl oxalate was antagonized by 5-HTP, a serotonin (5-HT) precursor, and by p-chloroamphetamine (PCA), a 5-HT releaser. Single administration of 5-HTP in combination with pargyline, a monoamine oxidase inhibitor, induced amnesia (5-HTP-induced amnesia). This amnesia was attenuated by ritanserin, a 5-HT2-selective antagonist, but not by pindolol, a 5-HT1-selective antagonist. Naftidrofuryl oxalate also attenuated the 5-HTP-induced amnesia. A binding study revealed that naftidrofuryl oxalate inhibited the binding of [3H]ketanserin to 5-HT2 receptors in mouse brain synaptic membrane in a dose-dependent fashion (IC50 = 1.42 x 10(-7) M), but did not inhibit that of [3H]serotonin to 5-HT1 receptors. These results suggest that naftidrofuryl oxalate may attenuate cycloheximide- and 5-HTP-induced amnesia by blocking 5-HT2 receptor subtypes.

Attenuation of ischemia-induced regional myocardial acidosis by LP-805, a newly developed vasodilator, in dogs

The effect of 8-tert-butyl-6,7-dihydropyrrolo[3,2-e]-5-methyl- pyrazolo[1,5-a]pyrimidine-3-carbonitrile (LP-805), a newly developed vasodilator, on myocardial acidosis induced by ischemia was studied in anesthetized open-chest dogs. Ischemia was induced by partially occluding the left anterior descending coronary artery. The coronary flow was artificially reduced to about 1/3 of the original flow. Myocardial pH was measured with a glass micro pH electrode inserted into the left ventricular wall perfused by the occluded artery. Myocardial pH decreased from about 7.5 to about 6.9 after the onset of ischemia and remained at this low level until the occluded coronary artery was released. After 30 min of ischemia, either saline containing 0.1 N HCl or 10, 30 or 100 micrograms/kg of LP-805 was injected intravenously. LP-805 attenuated the decrease in myocardial pH induced by ischemia in a dose-dependent manner. In conclusion, LP-805 may reduce the influence of ischemia on the myocardium.

An enzyme-coupled assay for acyl-CoA synthetase

An enzyme-coupled, colorimetric method for the assay of acyl-CoA synthetase is described. Acyl-CoA formed from fatty acid and CoA by acyl-CoA synthetase was dehydrogenated by acyl-CoA oxidase. Hydrogen peroxide produced was then converted into formaldehyde in the presence of methanol by catalase. The formaldehyde reacted with a triazole compound, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, in an alkaline condition to form a purple dye, and the absorbance was measured spectrophotometrically.

Fatty acids suppress recovery of heart function after hypothermic perfusion

Working rat hearts were perfused for 15 minutes at 37 degrees C before switching to a Langendorff perfusion (60 mm Hg aortic pressure) at 10 degrees C for 40 minutes of hypothermic arrest. Ventricular function was allowed to recover for 15 minutes at 37 degrees C by reestablishing the prehypothermic conditions. The perfusate was Krebs-Henseleit bicarbonate buffer containing 3% bovine serum albumin and either glucose (11 mmol/L) or glucose (11 mmol/L) plus palmitate (1.2 mmol/L) and gassed with 95% O2 and 5% CO2. In hearts receiving glucose alone as substrate, coronary flow was maintained constant during the 40 minutes of hypothermic arrest and returned to prehypothermic rates with rewarming. Ventricular function, as estimated by peak systolic pressure and heart rate, recovered to the prehypothermic level. When palmitate was added, coronary flow decreased continuously throughout the hypothermic perfusion (22% decrease by 40 minutes), and ventricular pressure development was lower throughout the rewarming perfusion. Tissue levels of adenosine triphosphate and creatine phosphate were well maintained and long-chain acyl coenzyme A and acyl carnitine decreased during hypothermia regardless of the substrate provided. With rewarming, tissue levels of adenosine triphosphate and creatine phosphate decreased in those hearts receiving palmitate. Omission of fatty acid either during hypothermia or during the first 5 minutes of rewarming improved recovery of function. Addition of oxfenicine to inhibit fatty acid oxidation, or inhibition of Ca2+ overload by verapamil and low perfusate Ca2+, prevented the effects of palmitate on ventricular function.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel species of cytochrome P-450 (P-450ib) specific for the small intestine of rabbits. cDNA cloning and its expression in COS cells

We have isolated a cDNA clone for a P-450, designated P-450ib (Ichihara, K., Kusunose, E., Kaku, M., Yamamoto, S., and Kusunose, M. (1985) Biochim. Biophys. Acta 831, 99-105), from a cDNA library of rabbit small intestine mucosa by using synthetic DNA fragment by the polymerase chain reaction, as a hybridization probe. The cDNA with a 1,829-base pair insert encodes a polypeptide of 501 amino acids. The deduced amino acid sequence contains all of the sequences of the NH2-terminal and 14 tryptic fragments from purified P-450ib. As the NH2-terminal methionine was not found in the sequence from the purified protein, the apoprotein of P-450ib is composed of 500 amino acids with a molecular weight of 57,193. P-450ib shows 35-41% sequence similarity with several members of 8 subfamilies in the P-450 II family, whereas it has a less than 30% sequence similarity with other P-450 families, suggesting that this P-450 is the first member of a novel subfamily within the P-450 II family. RNA blot analysis shows that mRNA hybridized to the cDNA is expressed in the small intestine, but not significantly in other tissues including liver, colon, kidney, lung, spleen, brain, stomach, and cecum, indicating that P-450ib is a P-450 specific to the small intestine. The protein expressed in COS-7 cells using the cDNA in an expression vector, pKCRH2, shows benzphetamine N-demethylase activity and gives a band identical with that of P-450ib in its mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Immunological and biological characteristics of recombinant human thyrotropin

Analyses of epitopes and biological activity were made on two preparations of recombinant human thyrotropin produced in Chinese hamster ovary cells. Seven monoclonal antibodies recognizing four epitopes on alpha subunit of hTSH (hTSH alpha) and three on beta subunit (hTSH beta) were used for the analysis. Binding activities of the two rhTSH with each antibody were almost identical with that of a pituitary-derived reference hTSH, except at one epitope on hTSH alpha. Their immunoreactivity measured by four commercial immunoassay kits and their bioactivity by thyrotropin dependent FRTL-5 cell system, however, agreed closely with those of the reference hTSH. From these results and its constant availability, rhTSH will be a good candidate for a future standard material in assays for hTSH.

The stability of immunological and biological activity of human thyrotropin in buffer: its temperature-dependent dissociation into subunits during freezing

The stability of thyroid-stimulating hormone (TSH) in buffer under various storage conditions was studied with regard to its immunoreactivity measured by an immunoradiometric assay and its bioactivity by a sensitive FRTL-5 cell bioassay. The immunoreactivity was well retained at 4 degrees C or 24 degrees C throughout the study period of 90 days. At -20 degrees C, however, it decreased proportionately with the storage time. The mean reduction was 42.1% at 90 days compared with that when stored at -80 degrees C. The bioactivity showed a similar course of change with its reduction of 44.3% at -20 degrees C in 90 days. The loss of both activities was attributed to the dissociation of human (h) TSH molecule into its subunits. The concentration of the alpha subunit of hTSH in those samples stored at -20 degrees C gradually increased from the initial undetectable level to that almost equivalent on a molar basis to the loss of immunoreactivity. The enrichment of albumin in the buffer to a level of more than 1.0% was effective in preventing the occurrence of such a phenomenon. These data indicate that hTSH, when frozen at -20 degrees C in buffer is gradually dissociated into its subunits, despite its outstanding stability for 90 days at both 4 degrees C and 24 degrees C. However, no apparent inconsistency between immunological and biological activities, was observed at any temperature between -20 degrees C and 24 degrees C.

[Factor VIII epitopes recognized by inhibitors in hemophiliacs]

A 44-year-old male hemophiliac with high titer anti-factor VIII antibody (66 bethesda units/ml) was admitted on November 11, 1989 because of epigastralgia and melena. A gastric ulcer with a spurting artery was revealed by an upper gastrointestinal endoscopy. Infusion of activated prothrombin complex concentrates and endoscopical ethanol injection to the bleeding vessel were ineffective. After clipping of the vessel, the bleeding was completely ceased. The inhibitor antibody was purified by Sephacryl S 200 and Protein A cellulofine column chromatography. Purified IgG showed factor VIII inhibitor activity. Factor VIII epitopes recognized by the inhibitors was examined by western blotting. Factor VIII concentrate purified by the antigen. This factor VIII preparation was composed of a doublet of light chains (M.W. 80 kD) and 3 heavy chains (M.W. 160-200 kD) when examined by SDS-PAGE followed by immunoblotting using monoclonal antibodies against factor VIII light and heavy chains. The inhibitor in this case reacted to the heavy chains of factor VIII, whereas antifactor VIII antibody in the other case reacted to the light chain of factor VIII.

Effects of thoracic epidural anesthesia on myocardial pH and metabolism during ischemia

The effect of thoracic epidural anesthesia (TEA) on the ischemic myocardium was examined in open-chest dogs anesthetized intravenously. Ischemia induced by brief coronary artery occlusion caused an elevation of the ST segment in epicardial ECG and a reduction in myocardial pH and contractile force. TEA with 0.15 ml/kg of 0.4% bupivacaine solution attenuated an ischemia-induced decrease in myocardial pH and an increase of the ST segment in epicardial ECG. This attenuation was maintained even after the restoration of blood pressure and heart rate, which had been decreased significantly after TEA, to pre-TEA levels, suggesting that a beneficial effect of TEA should not be confined to its hemodynamic changes such as decreased blood pressure and heart rate. In contrast, the subendocardial contents of ATP, creatine phosphate (CP) and lactate were not affected by TEA, either in the presence or the absence of 5 min LAD occlusion. These results suggest that neither hemodynamic nor metabolic changes are responsible for the reduced myocardial ischemic acidosis induced by TEA after brief coronary artery occlusion. The acidosis-saving property of TEA is favorable for the ischemic heart.

The effect of pimobendan on myocardial mechanical function and metabolism in dogs: comparison with dobutamine

The effect of pimobendan, a newly developed cardiotonic agent, on myocardial mechanical function and energy metabolism has been examined in the dog heart, and compared with that of dobutamine. Either saline, vehicle for pimobendan, dobutamine (0.3 and 1 microgram kg-1), or pimobendan (0.3 and 1 mg kg-1) was injected intravenously. Dobutamine and pimobendan both increased the first derivative of left ventricular pressure and percent segment shortening, indicating their positive inotropic action. After 2 min of dobutamine injection, or after 20 min of pimobendan injection, the myocardium was removed, and used for determination of the tissue levels of metabolites of energy and carbohydrate metabolism. In general, all metabolic parameters measured were not changed by either dobutamine or pimobendan injection. In animals with aortic constriction for 10 months, dobutamine and pimobendan injections did not alter the myocardial energy and carbohydrate metabolism. Although dobutamine and pimobendan increased the cardiac mechanical function, they did not disturb the myocardial energy and carbohydrate metabolism.

Phospholipid requirement of progesterone 5 alpha-reductase from gastric mucosa microsomes of guinea pig

Progesterone 5 alpha-reductase partially purified from gastric mucosa microsomes was stimulated by short-chain synthetic phosphatidylcholines (PC), such as dilauroyl PC, but not by various PC from biological sources. Phosphatidylserine (PS) activated the gastric 5 alpha-reductase to a limited extent compared to the liver 5 alpha-reductase described previously [Ichihara, K., and Tanaka, C. (1987) Biochem. Biophys. Res. Commun. 149, 482-487]. In search of more effective phospholipid activators, we tested the effects of various lysophospholipids on 5 alpha-reductase activity. Strongly stimulatory effects were observed when lysophosphatidylcholine (lysoPC) and lysophosphatidylethanolamine (lysoPE) were used instead of PC and phosphatidylethanolamine. Examination of synthetic lysoPC and lysoPE differing in acyl chain lengths showed that fatty chains of 12 to 16 carbons were effective in stimulating the 5 alpha-reductase. By contrast, other lysophospholipids such as lysophosphatidic acid, lysophosphatidylglycerol or lysophosphatidylserine (lysoPS) greatly inhibited 5 alpha-reductase activity. These findings suggest that gastric 5 alpha-reductase may be under dual regulation; lysoPC and lysoPE may play important roles as positive effectors, whereas lysophosphatidic acid, lysophosphatidylglycerol and lysoPS act as negative effectors in progesterone 5 alpha-reductase regulation.

The inhibitory effect of bevantolol on the accumulation of non-esterified fatty acids during ischaemia in the dog heart in situ

1. The left anterior descending coronary artery (LAD) was completely ligated for 90 min (i.e. myocardial ischaemia was produced) in the dog anaesthetized with pentobarbital. 2. Bevantolol, a beta 1-adrenoceptor antagonist, was injected (1 mg/kg, intravenously) 5 min before LAD occlusion. The bevantolol injection decreased heart rate without affecting blood pressure. 3. The myocardial samples were taken from the LAD area immediately after the end of LAD occlusion, and were subjected to analysis of the myocardial levels of non-esterified fatty acids (NEFA). 4. In dogs in which saline was injected, ischaemia produced accumulation of NEFA, especially arachidonic and palmitoleic acids, in the myocardium. 5. In dogs in which bevantolol was injected, the accumulation of NEFA induced by ischaemia was almost completely inhibited. 6. It is concluded that bevantolol inhibits ischaemia-induced accumulation of NEFA in the myocardium, and that stimulation of the beta 1-adrenoceptors is probably responsible for NEFA accumulation induced by ischaemia.

Effect of NCO-700, an inhibitor of protease, on lysosomal rupture in the ischemic myocardium

The effect of NCO-700 (1), a protease inhibitor, on subcellular distribution of lysosomal enzymes was studied in the ischemic perfused rat heart. Ischemia was induced by lowering the afterload pressure of the working heart preparation. The subcellular distribution of lysosomal enzymes was estimated by the ratio of the activities of cathepsin D, beta,N-acetylglucosaminidase, and acid phosphatase in the cytoplasm to the total enzyme activities. Ischemia caused subcellular redistribution of lysosomal enzymes from the lysosomes to the cytoplasm, indicating the rupture of lysosomes. Compound 1 (1.75 x 10(-4) M) was provided for the heart 5 min before the onset of ischemia. Compound 1 appeared to inhibit the rupture of lysosomes being caused by ischemia. The mechanism by which 1 protects the myocardium against ischemic injury may involve the inhibition of lysosomal rupture in the ischemic myocardium.

Effects of MCI-176, a new quinazolinone calcium antagonist, on myocardial energy and carbohydrate metabolism in ischemic dog hearts

The effect of 2-(2,5-dimethoxyphenylmethyl)-3-(2-dimethylaminoethyl)- 6-isopropoxy-4(3H)-quinazolinone hydrochloride (MCI-176), a calcium antagonist, on ischemic myocardial metabolism was studied in dog hearts subjected to an occlusion of the left anterior descending coronary artery (LAD) for 3 or 30 min. MCI-176 (0.03 or 0.1 mg/kg), when injected i.v. 5 min before occlusion, increased coronary blood flow and decreased systemic aortic pressure. When the LAD was ligated, the levels of creatine phosphate, ATP, total adenine nucleotides and energy change potential decreased in the ischemic myocardium. Three minutes after ischemia, MCI-176 (0.1 mg/kg) significantly (P less than 0.05) diminished these impairments of energy metabolism. Even 30 min after ischemia, pretreatment with MCI-176 tended to lessen the depletion of ATP and total adenine nucleotides, although these effects were not statistically significant. Myocardial ischemia produced a breakdown of glycogen, an accumulation of lactate, and an inhibition of glycolytic flux through phosphofructokinase reaction. MCI-176 (0.1 mg/kg) significantly (P less than 0.05) reduced these alterations of carbohydrate metabolism after 3 min of ischemia. These results suggest that pretreatment with MCI-176 reduces the impairments of myocardial energy and carbohydrate metabolism in ischemic dog hearts, suggesting that the drug is capable of improving the imbalance between oxygen supply and oxygen demand in the ischemic myocardium.

The action of phosphatidate phosphatase on the fatty-acid composition of safflower triacylglycerol and spinach glycerolipids

The microsomal phosphatidate phosphatase (EC 3.1.3.4) in maturing seeds of safflower (Carthamus tinctorius L.) was specific and selective for unsaturated phosphatidates. The relative order of specificity for phosphatidate molecular species was 1,2-dilinoleoyl = 1,2-dioleoyl > 1-palmitoyl-2-oleoyl > 1,2-dilauroyl = 1,2-dimyristoyl > 1,2-dipalmitoyl. The order of selectivity was similar to that of the specificity. The broad selectivity for unsaturated phosphatidate species (1,2-di-unsaturated-acyl and 1-saturated-acyl-2-unsaturatedacyl) led us to conclude that the phosphatidate-phosphatase reaction does not, or only very little, affect the fatty-acid composition of the diacylglycerol product and in turn the fatty-acid composition of triacylglycerol in safflower oil. As compared with the safflower microsomal enzyme, the chloroplast phosphatidate phosphatase of spinach (Spinacia oleracea L.) leaves showed a broader specificity. This agreed with the selectivity profile indicated by labelling patterns of phosphatidate and diacylglycerol synthesized from [(14)C]acetate in spinach chloroplasts (S.E. Gardiner et al. 1984, Biochem. J. 224, 637-643).

Effect of ubenimex on the immune system of patients with hematological malignancies

The effect of in vivo administration of ubenimex (Bestatin) on the immune status of patients with hematological malignancies in remission was studied. Natural killer (NK) cell activities, lymphokine activated killer (LAK) cell activities, production of interferon-gamma (gamma-IFN) and surface antigens of peripheral lymphocytes were examined before and after administration of ubenimex. Analysis of the T, B and NK cell compartment ax conducted by assessing expression of the following antigens: CD3+CD19- (T), CD3-CD19+ (B), CD8+CD11b- (Tc), CD8+CD11b+ (Ts), CD4+Leu8-(Th), CD4+Leu8+(Ti), CD16CD57 (NK) using a 2-color flow cytometric analysis. NK and LAK activity was significantly lower in patients with hematological malignancies as compared to normal subjects. The absolute numbers of lymphocytes and NK cells were also lower than those in healthy controls. The reduced NK and LAK activity, however, was elevated after ubenimex administration. The absolute numbers of helper T cells, cytotoxic T cells and NK cells were also increased after administration of the drug. These findings were not observed in patients treated without ubenimex. Serum levels of IFN-gamma were not markedly changed after ubenimex administration. But peripheral blood mononuclear cells cultured with rIL2 showed appreciable levels of IFN-gamma production, and production increased after ubenimex administration. These results shows that ubenimex is a powerful immunomodulator that augments or restores some immune functions in patients with hematological malignancies.

Involvement of GABAergic systems in benzodiazepine-induced impairment of passive avoidance learning in mice

The possible involvement of GABAergic neuronal systems in benzodiazepine (BZP)-induced impairment of a passive avoidance response was investigated. Chlordiazepoxide (CDP) impaired passive avoidance when administered prior to training. The CDP-induced impairment was antagonized by pretreatment with picrotoxin, but not by pretreatment with bicuculline or post-training administration of picrotoxin. On the contrary, when combined with muscimol, the dose at which CDP impaired the response was lower than the dose at which it did so alone. The synergy of muscimol and CDP was attenuated by pretreatment with flumazenil or bicuculline. From these results, we conclude that GABAergic systems play an important role in the BZP-induced impairment of passive avoidance.

Effects of benzodiazepines on passive avoidance response and latent learning in mice: relationship to benzodiazepine receptors and the cholinergic neuronal system

The effects of benzodiazepines on learning and memory were investigated, using passive avoidance and latent learning tasks, with particular attention being paid to the possible involvement of benzodiazepine receptors and the cholinergic neuronal system. Benzodiazepines such as diazepam, nitrazepam and chlordiazepoxide (CDP) impaired the passive avoidance response when administered before training, but not when administered immediately after training or before the retention test. CDP also impaired latent learning in the water finding task. State-dependent learning was not observed with CDP at the dose used. A benzodiazepine inverse agonist, Ro 15-4513, and a benzodiazepine antagonist, Ro 15-1788, completely and partially reversed, respectively, the disruptive effects of CDP on learning and memory at the doses which did not enhance learning and memory. The disruptive effects of CDP on learning and memory were partially antagonized by a choline esterase inhibitor, physostigmine, and by a blocker for muscarinic acetylcholine receptors, scopolamine, at the doses which increase acetylcholine release. These results suggest that benzodiazepines induce disruptive effects on learning and memory through benzodiazepine receptors, and that benzodiazepine-induced impairment of learning and memory is, at least in part, the result of the dysfunction of the cholinergic neuronal system.

Both d-cis- and l-cis-diltiazem have anti-ischemic action in the isolated, perfused working rat heart

The effect of diltiazem (d-cis-diltiazem) on the ischemic myocardium was compared with that of l-cis-diltiazem, an optical isomer having less potent calcium channel-blocking action, in the isolated, perfused working rat heart. Ischemia decreased mechanical function and tissue levels of ATP and creatine phosphate, and increased tissue levels of nonesterified fatty acids (NEFA), AMP and lactate. Reperfusion did not restore mechanical function, but restored incompletely the levels of metabolites (except NEFA) that had been altered by ischemia. The ischemia-induced changes in NEFA were prevented by d-cis-diltiazem completely and by l-cis-diltiazem incompletely. Other metabolic changes induced by ischemia were attenuated by d-cis-diltiazem but not by l-cis-diltiazem. In heart pretreated with d-cis- or l-cis-diltiazem, both the mechanical function and the levels of metabolites recovered during reperfusion, the degree of recovery with both drugs being similar. These results indicate that not only d-cis-diltiazem but also l-cis-diltiazem has an anti-ischemic action probably due to inhibition of the tissue NEFA accumulation. These results also suggest that the mechanism of the protective effect of d-cis-diltiazem on the ischemic myocardium is not entirely due to the calcium channel-blocking action. Treatment with low Ca2+ (1.0 mM CaCl2) also attenuated the ischemia-induced changes. The interval between reoxygenation and start of function in the reperfused heart that had been treated with low Ca2+ was significantly longer than that with d-cis- or l-cis-diltiazem. The effect of these isomers to shorten this interval may contribute to their common anti-ischemic action.

Dichloroacetate attenuates myocardial acidosis and metabolic changes induced by partial occlusion of the coronary artery in dogs

The present study was undertaken to examine whether dichloroacetate, which inhibits pyruvate dehydrogenase kinase and, therefore, increases the activity of pyruvate dehydrogenase, attenuates myocardial acidosis and metabolic changes induced by coronary occlusion. In dogs anesthetized with pentobarbital, the left anterior descending coronary artery was incompletely occluded to reduce the left anterior descending flow to a half to one third of the original flow (partial occlusion) to produce myocardial (regional) ischemia. Partial occlusion was continued for 90 min, and a bolus injection of saline or dichloroacetate was made intravenously 30 min after the onset of occlusion. Partial occlusion decreased myocardial pH significantly. An injection of dichloroacetate (150 mg/kg) increased myocardial pH that had been lowered by partial occlusion. Myocardial metabolites were measured in other dogs. Partial occlusion decreased the myocardial levels of adenosine triphosphate, creatine phosphate and energy charge potential, and increased that of lactate significantly, without affecting the myocardial levels of pyruvate and nonesterified fatty acids. Dichloroacetate attenuated the ischemia-induced changes in the myocardial levels of adenosine triphosphate, creatine phosphate, energy charge potential and lactate. These results indicate that dichloroacetate attenuates the myocardial acidosis and metabolic changes during coronary partial occlusion.