Effects of a new Na+/H+ antiporter inhibitor on postischemic reperfusion in pig heart.

We investigated the effects of a new compound (3-methylsulfonyl-4-piperidinobenzoyl) guanidine hydrochloride (HOE 694) known to inhibit the Na+/H+ exchanger in a porcine model of ischemia/reperfusion. Ischemia was induced by coronary occlusion (twice for 10 min, with a 30-min reperfusion interval) followed by a 4-h reperfusion period. Treated animals (n = 8) received HOE 694 as a bolus (7 mg/kg) 20 min before ischemia and subsequently as a continuous infusion (0.07 mg/kg) throughout the experiment. Control pigs (n = 11) received vehicle. Regional wall function (percentage of segment shortening, % SS) of the treated animals was significantly improved as compared with that of controls after the 4-h reperfusion period (74.1 +/- 2.5 vs. 50.9 +/- 5.4, p < 0.005). Ventricular fibrillation (VF) could be prevented completely in treated pigs but occurred in 9 of 11 control animals (p < 0.001). Ultrastructural changes after ischemia and reperfusion were moderate and slightly abnormal in controls but much milder and completely recovered in the treated group, respectively. The tissue content of high-energy phosphates did not show a significant difference between groups. Inhibition of the sarcolemmal Na+/H+ antiporter with HOC 694 is antiarrhythmic and diminishes myocardial ischemic cell injury by preventing Na+ overload.

Disturbed lipid metabolism in diabetic coronary vessels.

The aim of this study was to clarify whether or not arachidonic acid metabolic disorders are caused by a substrate inavailability and whether such disorders might contribute to circulatory disturbances in the diabetic myocardium. Norepinephrine induced a decrease in the conductivity of both coronary arterial bed and myocardial microcirculation in alloxan-diabetic dogs. It was markedly (p less than 0.05) attenuated both by indomethacin and acetylsalicylic acid pretreatments indicating an imbalance among the vasoactive prostanoids in diabetes. TXA2 release from the diabetic coronary rings was found to be elevated and could be normalized after the blockade of vascular adrenoceptors by phentolamine (p less than 0.05). PGI2 synthesis was also enhanced by adrenergic blockade in the diabetic arterial rings. After pretreatment with 14C arachidonic acid, in order to measure substrate availability, the arachidonic acid metabolic rate was less in the diabetic coronary arteries than in healty vessels (p less than 0.05). Ten mumol/l norepinephrine decreased arachidonic acid metabolism in the presence of prelabelled substrate in the diabetic animals, compared to an increase observed in metabolically healthy dogs. Therefore diabetes appears to diminish arachidonic acid metabolism and uptake independent of adrenoceptors and to induce an imbalance between vasoconstrictor and vasodilator cyclooxygenase products, resulting in elevated TXA2 release controlled by adrenergic mechanisms which may contribute to an impairment in myocardial microcirculation.

Effect of glimepiride on the electrical activity of isolated rabbit heart muscle.

The effect of glimepiride (CAS 93479-97-1) on the electrical threshold, conduction time, effective refractory period and automaticity of left atrium and right ventricle in the isolated rabbit heart was investigated and compared with those of chlorpropamide and glibenclamide. From the sulphonylureas investigated only glibenclamide diminished the electrical activity of rabbit heart muscle preparations. Chlorpropamide and glimepiride have a mild effect to change the basic parameters on the opposite direction. It seems that glimepiride does not have a significant effect on cardiac muscle in vitro.

The effect of sulphonylurea therapy on the outcome of coronary heart diseases in diabetic patients.

A retrospective study was performed on 1040 diabetic patients. The survival time of those treated with first generation sulphonylureas (n = 227) was considerably (P < 0.001) shorter after the first attack of angina pectoris (5 +/- 1 years, mean +/- S.E.) or acute myocardial infarction (6 +/- 1 years) than of those (9 +/- 1 years) on glibenclamide treatment (n = 144), with regime alone (n = 282) or treated with insulin (n = 387). The systolic blood pressure of patients with first generation sulphonylureas (166 +/- 1/91 +/- 1 mmHg) proved to be higher (P < 0.01) than those treated with glibenclamide (159 +/- 1/91 +/- 1 mmHg) or being on regime alone (155 +/- 1/89 +/- 1 mmHg) or on insulin (156 +/- 1/89 +/- 1 mmHg) treatments. Serum sodium level was found to be lower (P < 0.05) in patients treated with any kind of sulphonylureas (138 +/- 1 mmol/l) than in the other patients (143 +/- 1 mmol/l). During an observation period, 576 of patients died, 412 of them due to cardiovascular or renal failures. Among the diabetic subjects suffering from coronary heart disease no difference could be detected in risk factors except for higher systolic blood pressure. The shorter survival time of patients treated with first-generation sulphonylureas might be explained by the arrhythmogenic activity of first-generation sulphonylureas. Improvement in therapy, metabolic and cardiovascular alterations during the survey can not be responsible for the shorter survival time of patients treated with first generation-sulphonylureas.

Is malondialdehyde a marker of the effect of oxygen free radicals in rat heart tissue?

We tested the effect of exogenous purine derived free radicals and H2O2 vs ischemia and reperfusion on the thiobarbituric-acid (TBA)-reactive material and malondialdehyde (MDA) formation in isolated rat hearts using the thiobarbituric acid test and high performance lipid chromatography (HPLC). We could not detect increased thiobarbituric-acid-reactive material or MDA production during 6 mM H2O2 infusion, during free radical generation by purine-derived free radicals, or using ischemia and reperfusion. Increased thiobarbituric-acid-reactive material and MDA tissue levels were detected only during infusion of 12 mM H2O2 (p less than 0.001). We conclude that the generally used thiobarbituric acid assay for MDA is susceptible to artifacts and unsuited as an indirect measure for low-to-medium-levels of oxygen free radicals. Using HPLC assay, which accurately measures MDA, no evidence was found that MDA is a primary and direct lipid peroxidation product of exogenous or endogenous reactive oxygen species.

Direct effect of hypoglycemic sulphonylureas on the cardiovascular system of dogs.

The effects of first generation sulphonylurea compounds carbutamide, gliclazide and tolbutamide as well as second generation compounds glibenclamide and glipizide on the cardiovascular system were investigated in dogs. Six dogs received each compound intravenously at cumulative dose levels of 74, 296, 1184 mumol/kg of carbutamide and tolbutamide, 0.4, 2.0, 10.0 mumol/kg of glibenclamide and glipizide, and 16, 48 and 144 mumol/kg of gliclazide. Mean arterial blood pressure, myocardial contractile force, cardiac output and heart rate were measured. The rate of change of myocardial contractile force development (positive dF/dt), as well as of myocardial relaxation (negative dF/dt) were measured. The first generation sulphonylureas were found, in dogs, to exert a positive inotropic effect in contrast to second generation compounds. The clinical importance of our findings may be in the potential for the malfunction of the cardiovascular system (based on cardiopathy, neuropathy, atherosclerosis, and obesity), developing in diabetes, to be further impaired by the first generation sulphonylureas. Therefore, second generation sulphonylureas should be preferred in the therapy of type 2 diabetics, if satisfactory metabolic control cannot be achieved by dietary management alone and sulphonylurea treatment becomes necessary.

Increased vasoconstrictor response to noradrenaline in femoral vascular bed of diabetic dogs. Is thromboxane A2 involved?

STUDY OBJECTIVE: The aim was to determine the role of cyclo-oxygenase products in the vasoconstrictor response of femoral arterial bed to noradrenaline and to analyse the role of vascular adrenoceptors in the synthesis of cyclo-oxygenase products. DESIGN: The influence of intra-arterially injected cyclo-oxygenase inhibitors indomethacin and acetylsalicylic acid on alterations in conductance of femoral arterial bed induced by noradrenaline was compared in metabolically healthy and alloxan diabetic dogs. PGI2 and TXA2 synthesising ability of isolated femoral arterial rings was measured with and without inhibition of alpha adrenoceptors by phentolamine. SUBJECTS: 18 metabolically healthy and 18 alloxan (560 mumol.kg-1) diabetic dogs of either sex, weight 16-28 kg, were studied. MEASUREMENTS AND MAIN RESULTS: Noradrenaline produced greater (p less than 0.01) pressor effects in the femoral arterial bed of alloxan diabetic dogs than in the hind limb of control animals. Blockade of cyclo-oxygenase either by indomethacin 10 mumol.kg-1 or by acetylsalicylic acid 140 mumol.kg-1 markedly reduced the response to noradrenaline in alloxan treated animals, but not in controls, thereby eliminating the different responsiveness of the two groups. Femoral arterial rings from diabetic animals synthesised similar amounts of PGI2 as control rings but formed more TXA2 (p less than 0.05). Phentolamine pretreatment (5 mumol.litre-1) markedly reduced the production of TXA2, but not of PGI2, in diabetic vessels. CONCLUSIONS: The results show an increased release of TXA2 by isolated diabetic femoral arteries. It is therefore suggested that an alpha adrenoceptor mediated increase in TXA2 biosynthesis may play a part in the vascular hyperreactivity of the diabetic femoral arterial bed.

Divergent cardiac effects of the first and second generation hypoglycemic sulfonylurea compounds.

The effects of first and second generation hypoglycemic sulfonylureas on the incidence of ventricular ectopic beats and on the duration of transitional ventricular fibrillation in the ischemic rat heart were investigated. First generation sulfonylurea compounds (tolbutamide, carbutamide and gliclazide) in 105 preparations increased, while second generation sulfonylurea compounds (glibenclamide and glipizide) in 50 preparations decreased in a dose-dependent manner both the number of ventricular ectopic beats and the duration of transitional ventricular fibrillation during the first 30 min after ligation of the left anterior descending coronary artery. Therefore, second generation sulfonylureas should be preferred in the treatment of type 2 diabetics with ischemic heart diseases, if satisfactory metabolic control cannot be achieved by a treatment regimen and diet alone.

[Effect of antidiabetic treatment in ischemic heart diseases]. / Az antidiabetikus kezelés hatásának vizsgálata az ischaemiás szívelváltozásokra.

In a retrospective study of 962 diabetic (male: 441, female: 521) patients in the Diabetic Outpatient Clinic of the National Institute of Cardiology between 1st November 1967 and 31st October 1988 the survival time of diabetics treated with first generation sulphonylureas was considerably less after the first attack of angina pectoris or acute myocardial infarction compared with that of individuals controlled with regime alone or being on glibenclamide or insulin treatments. The systolic blood pressure proved to be higher in diabetics treated with first generation sulphonylureas. During the observation, among the 183 patients on insulin- as well as in the 262 individuals on first and 230 on second generation sulphonylurea treatments, and in the 287 diabetics controlled with regime alone, 547 (male: 241, female: 306) patients died, 403 of them due to cardiovascular and renal failures. Between the diabetics suffering from ischaemic heart diseases no difference could be detected relating the risk factors except the higher systolic blood pressure. The alterations in the cardiovascular states during the survey, the improvement of therapeutical interventions, the alterations in the carbohydrate and lipid metabolism are not supposed to be involved in the shorter survival time of diabetics treated with first generation sulphonylureas. The shorter survival time might be explained by the arrhythmogenic activity of first generation sulphonylureas described in earlier studies. On this basis we are tempted to draw the conclusion that second generation sulphonylureas must be selected in the diabetes care, if the metabolic state could not be normalized by diet and regime only.

Effects of first and second generation sulphonylureas on cardiotoxicity of strophanthidin in rabbits.

The effects of the first generation sulphonylurea compound gliclazide and the second generation sulphonylurea compound glipizide on strophanthidin toxicity was investigated in rabbits. The sulphonylurea pretreated animals were intravenously infused with 23 mumol/kg strophanthidin until the appearance of the first ventricular ectopic beat and continued thereafter until the appearance of ventricular fibrillation. The first generation sulphonylurea gliclazide increased, while the second generation sulphonylurea glipizide decreased the strophanthidin toxicity in a dose dependent manner. It was concluded that instead of first generation sulphonylureas, second generation sulphonylureas must be preferred in cardiac glycoside treated diabetics, when sulphonylurea treatment is necessary.

Insulin induced reversibility of altered responsiveness in femoral arterial bed of diabetic dogs.

The altered reactivities of femoral arterial bed to noradrenaline, phenylephrine, adenosine and prostacyclin were compared in 18, clinically manifest but aketotic, alloxan diabetic mongrel dogs. Alloxan treatment markedly increased the vasoconstrictor responses to noradrenaline and phenylephrine, as well as the adenosine-induced vasodilation in the femoral vasculature. These changes were prevented or normalized, respectively, in the early or late insulin-treated alloxan diabetic animals. In the case of noradrenaline not only a normalization but also an explicit overcompensation could be observed by insulin treatment. The altered reactivity to prostacyclin could not be influenced by insulin therapy. These results indicate a significant difference in the effect of insulin treatment on the altered diabetic vascular responsiveness to catecholamines and adenosine or to prostacyclin.

Relationship between vascular adrenergic receptors and prostaglandin biosyntheses in canine diabetic coronary arteries.

Before the onset of histologically detectable alterations of diabetic arteries, a considerable decrease of vasodilation ability develops. The role of an altered prostaglandin biosynthesis in this phenomenon was investigated in connection to the altered vascular adrenergic mechanisms. The effect of phenylephrine on prostacyclin production of isolated coronary arterial rings (100 mumol/l) as well as on conductivity of the coronary arterial bed (7.5-15-30-60 pmol. kg-1.min-1) were compared in 12 metabolically healthy and 12 alloxan-diabetic (560 mumol/kg) dogs. Furthermore, the effect of phentolamine (5 mumol/l) on the prostacyclin and thromboxane productions of the isolated vessels (coronary, femoral and basilar arteries) was investigated by radioimmunoassay. Although the basal prostacyclin amounts synthesized by healthy and diabetic coronary vessels were not different (5.1 +/- 1.6 and 4.9 +/- 1.4 pg/mg vessel/30 min), similarly to femoral and basilar arteries, the diabetic arterial rings produced significantly (p less than 0.05) more thromboxane than the control rings. The alpha-adrenergic blockade by phentolamine did not influence the prostacyclin production in the healthy arteries, but considerably (p less than 0.05) increased it in the diabetic coronary arteries. Phentolamine normalised the thromboxane synthesis in the diabetic group (p less than 0.01) and enhanced (p less than 0.05) it in the metabolically healthy group. Phenylephrine was ineffective (98 +/- 6%) on the prostacyclin production in vitro versus the stimulated (150 +/- 22%) prostacyclin synthesis detected in the metabolically healthy group; and in vivo induced a more significant (p less than 0.05) decrease in the coronary conductivity in diabetic than in control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins and altered diabetic vasoregulation.

In previous studies an enhanced tendency to vasconstriction could be demonstrated in special regions, first of all in the coronary arterial bed of the diabetic vasculature. Analysing the role of prostaglandins in this phenomenon, the present work demonstrates that in vivo the dose-dependent decrease in the conductivity of the coronary arterial bed induced by PGF2 alpha (3, 6, 12, 24, 48 nmol/kg) administration in alloxan- (560 mumol/kg) diabetic dogs (n = 6) proved to be more expressed after indomethacin (10 mumol/kg) treatment compared with metabolically healthy (n = 6) animals. In the presence of indomethacin (3 mumol/l) PGF2 alpha (1, 3, 10, 30 mumol/l) evoked also considerably higher vasoconstriction in the isolated coronary rings of the diabetic dogs in comparison to the metabolically healthy state. The data are referring to the contribution of an altered prostaglandin biosynthesis in the diabetic coronaries to their increased tendency to vasoconstriction induced by PGF2 alpha.

Influence of diabetic state on coronary vasoregulation in myocardial hypoxia.

It is a matter of common knowledge that under ischaemic or hypoxic conditions the oxygen demand of the myocardium could only be satisfied by enhancement of collateral blood flow. It is demonstrated that in a diabetic state an elevation of the myocardial blood flow could not develop due to lack of proper vasodilation in the coronary arterial bed.

Effects of hypoxia and adrenergic stimulation induced alterations in PGI2 synthesis by diabetic coronary arteries.

Before the onset of histologically detectable alterations in diabetic arteries, a considerable decrease in vasodilatory potential is seen. While analyzing this phenomenon, the role of altered PGI2 synthesis in rings of coronary arteries from metabolically healthy and alloxan-diabetic dogs was measured by radioimmunoassay during baseline, under the influence of phenylephrine (100 mumol/L), and during hypoxia with or without the presence of the alpha adrenergic blocker phentolamine (5 mumol/L). Basal levels of PGI2 synthetized by healthy and diabetic coronaries were no different (7.9 +/- 2.1 and 6.4 +/- 1.4 pg/mg vessel). Phenylephrine potentiated PGI2 synthesis in controls (150 +/- 22%), while it proved to be ineffective in the diabetic animals (98 +/- 6%). Under hypoxic conditions, PGI2 production of healthy coronaries (152 +/- 24%) increased, while that in the diabetic ones (82 +/- 7%) decreased (p less than 0.01). In the presence of phentolamine no difference could be detected between the two groups. Given all these data, the decreased ability of the diabetic coronaries to vasodilate develops due to diminished PGI2 production, presumably controlled by adrenergic mechanisms. Furthermore, the more severe outcome of ischaemic heart disease in diabetes mellitus might be explained by the lack of an enhanced coronary PGI2 synthesis under hypoxic conditions.

Species specificity of thrombin-induced changes in vascular tone.

We studied the effects of acetylcholine and human thrombin on the tone of rabbit and dog isolated femoral arteries and aortas with intact endothelium. Acetylcholine (10(-9)-10(-6) mol/l) produced relaxation in the vessels from both species whereas thrombin (10(-9)-3 X 10(-8) mol/l) relaxed only canine arterial smooth muscle. Thrombin pretreatment increased significantly the relaxant potency of acetylcholine in femoral arteries of dogs. The results suggest an interspecies difference in the thrombin-induced endothelium-dependent vasorelaxation.