Myocardial cell dysfunction in diabetes mellitus. A review of clinical and experimental studies.

Evidence for an abnormal myocardial cell function in diabetes mellitus, influenced by acute metabolic changes, has appeared within recent years. Few but interesting clinical studies focus on this aspect of diabetic cardiopathy, and experimental studies have delivered possible explanations at the cellular level. These are concerned with the intracellular calcium homeostasis and transsarcolemmal receptor signaling. Because these changes are reversible by short-term insulin treatment, a new aspect for the study of diabetic heart disease has appeared.

Abnormal myocardial calcium uptake in streptozocin-diabetic rats. Evidence for a direct insulin effect on catecholamine sensitivity.

Myocardial calcium uptake after isoproterenol (ISO) in the isolated, perfused heart was investigated at 24-h intervals after the injection of streptozocin (STZ) in rats. After 4 days, when hyperglycemia had persisted for 3 days, myocardial calcium uptake in response to this strong beta-adrenergic agonist fell significantly to the level of unstimulated hearts, which also was the level of propranolol-pretreated hearts exposed to ISO. Insulin, when given in vivo 60-90 min before perfusion, led to a complete normalization of this ISO response in diabetic rats (duration 8 days), while in vitro addition of insulin to the perfusate (0.1 U/ml) significantly increased, while not completely normalizing, the ISO-induced myocardial calcium uptake. Insulin, therefore, has a direct effect on this beta-adrenergic response in diabetic rats and streptozocin in itself does not cause the desensitization. Considering the essential role of this calcium transport for the electromechanical coupling in the heart, such metabolically induced changes in catecholamine sensitivity might hypothetically have relevance for the increased incidence of heart failure in diabetes.

The adrenergic beta-receptor adenylate cyclase system in heart and lymphocytes from streptozotocin-diabetic rats. In vivo and in vitro evidence for a desensitized myocardial beta-receptor.

The myocardial beta-receptor adenylate cyclase system was investigated in short-term streptozotocin-diabetic rats. Earlier reports of a decreased sensitivity of the myocardium to isoproterenol (ISO) in these animals were elucidated by measuring the in vivo production of cAMP after ISO. A substantial decrease was seen in diabetic animals compared with controls and starved animals, and thyroxine treatment, known to sensitize the myocardium to catecholamines, did not normalize the response. The desensitization was retained in a membrane fraction in such a way that ISO was unable to increase the cAMP production while stimulation via the nucleotide-binding protein (with NaF or GTP) leads to a normal cAMP response. As the beta-adrenergic receptor number and affinity turned out to be identical in control and diabetic animals, a functional uncoupling of the myocardial beta-receptor from productive adenylate cyclase activation seems thus to exist in experimental diabetes. It is unlikely that it has anything to do with the thyroid status of the animals, but the possibility of a catecholamine-induced densensitization cannot be excluded. The phenomenon is not universal as the beta-receptor-adenylate cyclase system is normal in isolated spleen lymphocytes. Whether the described phenomenon obtained in an animal study has any relevance for the increased incidence of heart failure in human diabetes mellitus is not known at present.

Irreversibility of glomerular basement membrane accumulation despite reversibility of renal hypertrophy with islet transplantation in early experimental diabetes.

A quantitative morphologic study of the glomeruli in rats after 4 wk of streptozotocin-induced diabetes showed a number of glomerular changes, as previously described. Of particular interest was the increase in the total amount of glomerular basement membrane material [from 0.94 +/- 0.13 (SD) mm3 to 1.26 +/- 0.14 mm3 per kidney]. This parameter did not change after 4 wk of normoglycemia following islet cell transplantation (1.19 +/- 0.17 mm3), nor was the total glomerular volume normalized. The contralateral kidney was weighed and used for estimating the total amounts of protein, RNA, and DNA. Four weeks of diabetes expectedly resulted in a 50% increase in kidney weight, and islet cell transplantation diminished this to 15% in excess of normal. The average cell size (protein/DNA ratio) paralleled the kidney size after diabetes and following transplantation. The average amount of RNA per cell (RNA/DNA) increased significantly after induction of diabetes and was totally normalized after transplantation. Kidney protein concentration (mg protein/mg kidney) remained constant throughout the experiment. Considering that a few weeks of diabetes provokes a large increase in basement membrane material, it is especially noteworthy that 1 mo of normoglycemia is quite insufficient to reverse the accumulation.

Increased number of myocardial voltage-gated Ca2+ channels and unchanged total beta-receptor number in long-term streptozotocin-diabetic rats.

In order to elucidate further the abnormal myocardial Ca2+ metabolism in diabetes mellitus, voltage-gated Ca2+ channels and beta-receptors were quantified in myocardial membranes of short- and long-term diabetic rats. Diabetes was induced by an injection of streptozotocin (STZ). Animals were killed 2, 4, 7, 90 and 200 days after STZ. A group of diabetic animals were treated with insulin for 20 days following 180 days of untreated diabetes. Diabetic animals developed low triiodothyronine syndrome. During short-term diabetes, the maximum binding capacity (MBC) for Ca2+ channels was reduced by 25% at day 4 (p < 0.05) and the beta-receptor MBC was reduced by 48% (p < 0.05). A normalizing tendency was observed at day 7 for both receptor types; insulin-treated rats did not differ from controls at that time. After 90 and 200 days of untreated diabetes the Ca2+ channel MBC had increased by 36% and 27%, respectively (p < 0.05). Twenty days of strictly regulated blood glucose following 180 days of untreated diabetes totally normalized the Ca2+ channel MBC. This is in contrast to a previous report where insulin treatment did not normalize the Ca2+ channel MBC. Total beta-receptor MBCs did not differ from control values 90 and 200 days after STZ. In conclusion, an increase in rat myocardial Ca2+ channel MBC during long-term diabetes was fully normalized by short-term insulin treatment. The increase in sarcolemmal Ca2+ channels could serve to compensate for a defect coupling of the beta-receptor to adenylate cyclase. An elevated Ca2+ channel number may, at least theoretically, lead to increased Ca2+ flow across the cardiac sarcolemma and in this way contribute to the diabetic cardiomyopathy by increasing the intracellular Ca2+ concentration.

Regression of glycogen nephrosis in experimental diabetes after pancreatic islet transplantation.

Glycogen nephrosis, i.e. the Armanni-Ebstein lesion which manifests itself by intracellular accumulation of beta-glycogen has been studied in two groups of streptozotocin diabetic rats and compared to controls. One diabetic group was left untreated and the other diabetic group received pancreatic islet transplantation after 4 weeks duration of diabetes. The kidneys were studied after another 4 week period with normoglycemia. In the non-transplanted diabetic animals glycogen containing tubules comprised 43% of the distal tubule length in the cortex but in the transplanted animals no abnormal, glycogen containing cells could be recovered at the light microscope level. Measurements of the total distal tubule length in the non-transplanted diabetic animals showed that the distal tubules increased in length by 24%. In the transplanted diabetic animals distal tubule length remained the same as in the non-transplanted diabetic animals in spite of normalization of the tubular morphology. This finding could possibly be responsible for the incomplete normalization of kidney weight after treatment.

[Allergic myocarditis in clozapine treatment]. / Allergisk myocarditis ved klozapinbehandling.

Clozapine is a high-dose neuroleptic, which is recommended only for those cases in which patients have failed to respond adequately to standard antipsychotic drugs. This report describes a 45 year old man with ischaemic heart disease who died of cardiogenic shock 11 days after starting treatment with clozapine. Autopsy showed apart from coronary atherosclerosis and interstitial fibrosis a considerable infiltration of eosinophilic granulocytes in the myocardium suggesting myocarditis as the cause of death.

[Atypical meningococcal disease diagnosed with meningococcal antibody test]. / Atypisk meningokoksygdom diagnosticeret ved hjaelp af meningokokantistoftest.

The case histories of three patients with atypical meningococcal disease in whom the diagnosis was established by means of a meningococcal antibody test (MAT) are presented. One patient had clinically atypical, but bacteriologically verified meningococcal disease; the other two patients were primarily suspected of having viral infections. The usefulness of investigation for meningococcal antibodies in serum from patients with assumed meningococcal disease or with fever of unknown origin is stressed.

[Left ventricular diastolic function assessment by transthoracic Doppler echocardiography]. / Venstre ventrikels diastoliske funktion vurderet med transtorakal Doppler-ekkokardiografi.

Left ventricular diastolic dysfunction is currently recognized in patients with different heart diseases. Three abnormal filling patterns of the left ventricle detected by pulsed-Doppler echocardiography are observed in patients with heart disease. Each filling pattern is characterised by different symptoms, and by differences in function and dimension of the left atrium and filling pressures. Mitral and pulmonary venous flow velocities and durations obtained by pulsed Doppler technique can be used to evaluate left ventricular diastolic function in patients with different heart diseases. However, several factors affect the transmitral and pulmonary venous flow such as age, heart rate, positioning of the sample volume and aortic- and mitral valve insufficiency. These factors must be taken into consideration when the diastolic function is evaluated by pulsed Doppler technique.

Acute insulin treatment normalizes the resistance to the cardiotoxic effect of isoproterenol in streptozotocin diabetic rats. A morphometric study of isoproterenol induced myocardial fibrosis.

The acute effect of insulin treatment on the earlier reported protective effect of streptozotocin diabetes against the cardiotoxic effect of high doses of isoproterenol (ISO) was investigated in rats. Thirty to 135 min after the injection of crystalline insulin, ISO was given subcutaneously and when ISO induced fibrosis in the myocardium was morphometrically analyzed 7 days later, a highly significant correlation (r = 0.83, 2 p = 0.006) to the slope of the fall in blood glucose after insulin treatment appeared. The myocardial content of catecholamines was estimated in these 8 day diabetic rats. The norepinephrine content was significantly increased while epinephrine remained unchanged. An enhanced sympathetic nervous system activity with a consequent down regulation of the myocardial beta-adrenergic receptors could, therefore, explain this catecholamine resistance. The rapid reversion after insulin treatment excludes the possibility that streptozotocin in itself causes the ISO resistance and points towards a direct insulin effect on myocardial catecholamine sensitivity in diabetic rats. The phenomenon described might elucidate pathogenetic mechanisms behind toxic myocardial cell degeneration and may possibly have relevance for acute cardiovascular complications in diabetic patients.

Myocardial calcium uptake in streptozotocin diabetic and control rats after dibutyryl-cAMP; alpha-adrenergic stimulation and calcium deprivation.

Previous studies have shown a decreased myocardial calcium uptake after beta-adrenergic stimulation with isoproterenol in isolated perfused hearts from streptozotocin diabetic rats. Abnormalities in the beta-receptor-adenylate cyclase system could explain this but in order to circumvene the receptor we studied the effect of the permeable cAMP analogue, dibutyryl-cAMP on this calcium uptake. A marked increase was seen in control hearts while no increase could be registered in diabetic hearts. Defects in the protein kinase phosphorylation system or in the protein kinase substrate in the sarcolemma are suggested. alpha-Adrenergic stimulation with phenylephrine, being a cAMP independent positive inotropic agent, was also tested but no increase in calcium uptake was seen in either control or diabetic hearts. This could be due to a different effect on calcium currents during action potential after alpha-stimulation compared to the beta-adrenergic effect. Reexposure to calcium after calcium deprivation leads to excessive myocardial calcium uptake (calcium paradox), but the increase was significantly smaller in diabetic hearts, suggesting a differential responsiveness to the damage induced by this procedure. Early biochemical abnormalities in the basement membrane or in the composition and calcium binding ability of the sarcolemma could possibly constitute a common final site for the defect myocardial calcium uptake after isoproterenol, db-cAMP and calcium deprivation in streptozotocin diabetic rats.

Renal glucosuria and aminoaciduria.

A follow-up examination of five patients in whom renal glucosuria had been diagnosed 7-15 years previously, showed that the condition was unchanged. There was no indication of hormonal abnormalities. Oral glucose tolerance test, with determination of insulin, growth hormone and free fatty acids, showed no difference between the patients and a group of normal subjects. The urinary excretion of insulin and albumin was normal, but two patients turned out to have an increased excretion of certain amino acids, aspartic acid in one and glutamic acid, citrulline and alanine in the other.

Lack of cardiotoxic effect of isoproterenol in streptozotocin diabetic rats. A morphometric study of isoproterenol induced fibrosis.

The well known cardiotoxic effect of isoproterenol (ISO) was investigated in normal and streptozotocin diabetic rats. Seven days after the subcutaneous injection of ISO (15 mg/kg) the hearts were perfusion fixed and 12 sections from each heart were stained (Masson's trichrome). ISO induced myocardial fibrosis was quantified at the light microscopic level according to established morphometric principles. Pulse rate and ST elevation were recorded by EEC (3 standard leads) before and after the ISO injection. Non-diabetic control animals showed marked fibrosis after ISO, but surprisingly the diabetic animals showed no fibrosis after ISO treatment. These findings were in accordance with an ISO induced ST elevation seen only among control animals although both groups showed the same degree of tachycardia. Insulin treatment prevented the protection against ISO and when streptozotocin was injected 24 h after the ISO a normal quantitative and qualitative appearance of the scar tissue was seen. It thus seems that streptozotocin diabetic rats are protected against the toxic effect of ISO, leaving the haemodynamic response unaffected. Which factor in the diabetic metabolism is responsible for the present phenomenon is not known, but a defect in the signal transmission from the beta-receptor to the adenylcyclase is suggested as a possible explanation.

Decreased myocardial calcium uptake after isoproterenol in streptozotocin-induced diabetic rats. Studies in the in vitro perfused heart.

Myocardial calcium uptake in response to isoproterenol (ISO, 10(-4) M) was investigated in control and streptozotocin-induced diabetic rats using an in vitro heart perfusion model. An initial labeling with 45Ca added to the perfusate (with or without ISO) was followed by a cold calcium-free washout, thus clearing the myocardial interstitium of 45Ca. In this way the remaining 45Ca was an estimate of the myocardial calcium uptake during the labeling period. In control rats ISO induced a statistically significant increase in myocardial calcium uptake within the first 5 minutes, as well as from the 5th to the 15th minutes after exposure to this strong beta-receptor agonist. In contrast to this, diabetic hearts showed no increase in calcium uptake during any of these periods. The toxic effect of ISO was expressed by a leak of creatinine phosphokinase to the perfusate. In control rats the concentration of creatinine phosphokinase increased after ISO with a statistically significant correlation to the calcium uptake, whereas no enzymatic leak was seen after perfusion of the diabetic hearts. This abnormal response to strong beta-receptor stimulation in experimental diabetes is in accordance with our earlier in vivo finding of a myocardial protection against toxic doses of ISO. These results indicate a decreased catacholamine-induced calcium transport through the myocardial sarcolemma in streptozotocin-induced diabetic rats. This might hypothetically have relevance for diabetic heart disease as well as diabetic neuropathy.

Abnormal changes in transmitral flow after acute exposure to nitroglycerin and nifedipine in uncomplicated insulin-dependent diabetes mellitus: a Doppler echocardiographic study.

To study the left ventricular (LV) diastolic function in uncomplicated insulin-dependent diabetic patients without hypertension (n = 25) and comparable controls (n = 15), the effect of acute administration of nitroglycerin and nifedipine on cavity dimensions and transmitral flow pattern was investigated by Doppler echocardiography. At baseline no significant differences in any of the LV Doppler echocardiographic parameters were seen in the two groups. Only in diabetics did nitroglycerin diminish LV diastolic and systolic diameter significantly (p < 0.0002 and 0.004, respectively), reducing the stroke volume from 70 +/- 16 to 64 +/- 20 ml, p < 0.01. The decrease in stroke volume correlated significantly to hemoglobin (Hb) A1c level (r = 0.42, p = 0.036). An excessive preload reducing effect on venous capacitance vessels is assumed in diabetes, and this preload reducing effect was also reflected in transmitral flow pattern where E-wave/A-wave ratio decreased significantly only in the diabetic subjects (p < 0.0005). Nifedipine induced the same degree of sympathetic activation in the two groups, but an increase in LV early peak filling rate (E wave) was seen in diabetes only (63.3 +/- 13.5 to 66.8 +/- 13.5 mm, p < 0.01). The atrial filling of LV (A wave) was increased significantly in both groups. Thus an abnormal LV diastolic function can be disclosed by these pharmacologic challenges. Regulation of preload and its influence on transmitral flow pattern in diabetes deserves further investigation, as does the influence of calcium antagonists on early relaxation in the diabetic myocardium.

Reduced left ventricular afterload and increased contractility in children with insulin-dependent diabetes mellitus: an M-mode and Doppler-echocardiographic evaluation of left ventricular diastolic and systolic function.

Twenty-three children with diabetes mellitus, their ages ranging from 0.2-9.8 years, but with no sign of diabetic microvascular disease were investigated by M-mode and Doppler echocardiography, along with a comparable group of control subjects. In the diabetics, the fractional shortening and the mean velocity of fractional shortening were 14 and 18% higher, respectively, whereas the left ventricular end-systolic wall stress, an indicator of left ventricular afterload, was markedly reduced (22%). Assuming an unchanged preload in the two groups, this indicates a reduced afterload in these children. Systolic and diastolic time intervals, heart rate, and blood pressure were similar in diabetics and controls. Doppler-derived transmitral left ventricular filling indices were also similar. Thus, in these diabetic children no signs of left ventricular diastolic abnormality were detected. The state of hypercontractility of the left ventricle is considered to be due to a reduced afterload in early insulin-dependent diabetes.

Abnormal left ventricular diastolic function during cold pressor test in uncomplicated insulin-dependent diabetes mellitus.

1. Insulin-dependent diabetes mellitus is a known risk factor for congestive heart failure and an early diastolic dysfunction has been described. In order to see if diabetes itself and not complications like hypertension, nephropathy or ischaemic heart disease can be considered responsible for the abnormal diastolic function of the left ventricle, 17 young patients with uncomplicated insulin-dependent diabetes mellitus and 12 control subjects were exposed to a cold pressor test. 2. Blinded echo-Doppler examination was performed before and during the test. During basal conditions, left ventricular dimensions and volumes were smaller in diabetes and atrial contributions to left ventricular filling were increased. 3. During the cold pressor test, isovolumic relaxation time increased, peak early filling velocity (E) decreased, E deceleration time decreased and atrial contribution (A) increased significantly in diabetes, while only A increased in the control group. A marked increase in left atrial ejection force was seen in diabetes only (P < 0.002). This difference was seen in spite of comparable reductions in mitral area and atrioventricular compliance in the two groups. 4. The hyperfunction of the left atrium in diabetes is hypothesized to be due to reduce size of the left ventricle combined with incipient autonomic neuropathy.

The rate of synthesis and breakdown of glomerular basement membrane material at the transition 'normal to diabetes' and 'diabetes to normal'.

A considerable enlargement of the renal glomeruli is present very early after the acute onset of juvenile diabetes mellitus. In the hypertrophied glomeruli the surface area of the capillary walls, the filtration surface, is increased, and thereby also the amount of basement membrane in the capillary wall. The rate of development of this type of diabetic basement membrane accumulation has been studied in streptozotocin diabetic rats with 4- and 47-day duration of diabetes. During the first 4 days a 40% increase in the total amount of peripheral basement membrane material occurs, whereas the following period up to 47 days shows no further change. The structural changes of the glomerular capillaries seen in conjunction with the basement membrane accumulation comprise an enlargement of the filtration surface and capillary luminal volume. In another experiment, 4-week diabetic animals were transplanted with pancreatic islets. The renal structures were studied quantitatively after 4 weeks of normalization. It was found that the increased amounts of basement membrane material were still present.

Time course of myocardial viability after acute myocardial infarction: an echocardiographic study.

The recognition of dysfunctional but viable myocardium after acute myocardial infarction (MI) may be of importance for both patient prognostication and the decision for revascularization. Low-dose dobutamine echocardiography (LDDE) has been shown to be a reliable technique in detecting reversibility of dysfunctional myocardium. The aim of the present study was to assess by LDDE possible time-dependent changes in myocardial viability and to evaluate the value of LDDE used in the postinfarction period. Twenty-seven patients with acute MI underwent LDDE on day 6, 30, and 90. At LDDE day 6, 41% of the affected segments showed a positive response to LDDE. At later examination on day 30 and 90, only 32% and 18%, respectively, of the dysfunctioning segments responded to dobutamine stimulation, with a significant decline in response (p < 0.0001), indicating loss of viability. Spontaneous segmental outcome was significantly better for LDDE-responding segments than for nonresponding segments (p = 0.0001). This study indicated that myocardial viability may be temporary and that a time-dependent loss of viability may take place during the first months after MI.