Mechanisms of activation of cardiac glycogen phosphorylase in ischemia and anoxia

Unlocking the Potential of Stroke Blood Biomarkers: Early Diagnosis, Ischemic vs. Haemorrhagic Differentiation and Haemorrhagic Transformation Risk: A Comprehensive Review

Stroke, a complex and heterogeneous disease, is a leading cause of morbidity and mortality worldwide. The timely therapeutic intervention significantly impacts patient outcomes, but early stroke diagnosis is challenging due to the lack of specific diagnostic biomarkers. This review critically examines the literature for potential biomarkers that may aid in early diagnosis, differentiation between ischemic and hemorrhagic stroke, and prediction of hemorrhagic transformation in ischemic stroke. After a thorough analysis, four promising biomarkers were identified: Antithrombin III (ATIII), fibrinogen, and ischemia-modified albumin (IMA) for diagnostic purposes; glial fibrillary acidic protein (GFAP), micro RNA 124-3p, and a panel of 11 metabolites for distinguishing between ischemic and hemorrhagic stroke; and matrix metalloproteinase-9 (MMP-9), s100b, and interleukin 33 for predicting hemorrhagic transformation. We propose a biomarker panel integrating these markers, each reflecting different pathophysiological stages of stroke, that could significantly improve stroke patients' early detection and treatment. Despite promising results, further research and validation are needed to demonstrate the clinical utility of this proposed panel for routine stroke treatment.

A Pathophysiological Approach To Current Biomarkers

Biomarkers are necessary for screening and diagnosing numerous diseases, predicting the prognosis of patients, and following-up treatment and the course of the patient. Everyday new biomarkers are being used in clinics for these purposes. This section will discuss the physiological roles of the various current biomarkers in a healthy person and the pathophysiological mechanisms underlying the release of these biomarkers. This chapter aims to gain a new perspective for evaluating and interpreting the most current biomarkers.

New biomarker for acute ischaemic stroke: plasma glycogen phosphorylase isoenzyme BB

BACKGROUND

Glycogen phosphorylase is the key enzyme that breaks down glycogen to yield glucose-1-phosphate in order to restore depleted energy stores during cerebral ischaemia. We sought to determine whether plasma levels of glycogen phosphorylase BB (GPBB) isoform increased in patients with acute ischaemic stroke (AIS).

METHODS

We studied plasma GPBB levels within 12 hours and again at 48±24 hours of symptom onset in 172 patients with imaging-confirmed AIS and 133 stroke-free individuals. We determined the ability of plasma GPBB to discriminate between cases and controls and examined the predictive value of plasma GPBB for 90-day functional outcome, 90-day survival and acute lesion volumes on neuroimaging.

RESULTS

The mean (SD) GPBB levels were higher in cases (46.3±38.6 ng/mL at first measurement and 38.6±36.5 ng/mL at second measurement) than in controls (4.1±7.6 ng/mL, p<0.01 for both). The area under the receiver operating characteristic (ROC) curve for case-control discrimination based on first GPBB measurement was 0.96 (95% CI 0.93 to 0.98). The sensitivity and specificity based on optimal operating point on the ROC curve (7.0 ng/mL) were both 93%. GPBB levels increased in 90% of patients with punctate infarcts (<1.5 mL) and in all patients admitted within the first 4.5 hours of onset. There was no correlation between GPBB concentration and either clinical outcome or acute infarct volume.

CONCLUSION

GPBB demonstrates robust response to acute ischaemia and high sensitivity for small infarcts. If confirmed in more diverse populations that also include stroke mimics, GPBB could find utility as a stand-alone marker for acute brain ischaemia.

Seasonality of glycogen phosphorylase activity in crucian carp (Carassius carassius L.)

Seasonal changes in the activity of glycogen phosphorylase (GP), a rate-limiting enzyme of glycogen degradation, were examined in an anoxia-tolerant fish species, the crucian carp (Carassius carassius L.). In muscle and brain, the activity of GP remained constant throughout the year when tested at 25°C. In contrast, the activities of liver and heart GP displayed striking increases in summer. When seasonal temperature changes are taken into account, the activity of GP during the anoxic mid-winter is only 4-6% of its summer time activity in the muscle, heart and liver, and 13% in brain. In winter-acclimatized fish, experimental anoxia (1-6 weeks) caused sustained depression of the GP activity in heart and gills. In liver and muscle, a transient depression of GP activity occurred during the first week of anoxia but later GP activity recovered back to the normoxic level. GP of the brain was completely resistant to anoxia. In all studied tissues, the constitutive activity of GP is more than sufficient to degrade glycogen deposits during winter anoxia without anoxia-induced activation of GP. The seemingly paradoxical summer-time increase in the activity of liver and heart GP could be related to active life-style of the summer-acclimatized fish (growth, reproduction), the increased demand of energy and molecular precursors of anabolic metabolism being satisfied by preferential degradation of glycogen. The high glycogen content of winter-acclimatized crucian carp is not associated with the elevated GP activity or anoxic activation of GP.

Glycogen phosphorylase isoenzyme BB in diagnosis of myocardial ischaemic injury and infarction

This review deals with glycogen phosphorylase (GP) and its isoenzyme BB in the diagnosis of ischaemic myocardial injury. Early identification and confirmation of acute myocardial infarction is essential for correct patient care and disposition decision in the emergency department. In this respect, glycogen phosphorylase isoenzyme BB (GPBB) based on its metabolic function is an enzyme for early laboratory detection of ischaemia. In the aerobic heart muscle GPBB together with glycogen is tightly associated with the vesicles of the sarcoplasmic reticulum. Release of GPBB, the main isoform in the human myocardium, essentially depends on the degradation of glycogen, which is catalyzed by GP. Ischaemia is known to favour the conversion of bound GP in the b form into GP a, thereby accelerating glycogen breakdown, which is the ultimate prerequisite for getting GP into a soluble form being able to move freely in the cytosol. The efflux of GPBB into the extracellular fluid follows if ischaemia-induced structural alterations in the cell membrane become manifest. The clinical application of GPBB as a marker of ischaemic myocardial injury is a very promising tool for extending our knowledge of the severity of myocardial ischaemic events in the various coronary syndromes. The rational roots of this development were originated from Albert Wollenberger's research work on the biochemistry of cardiac ischaemia and the transient acceleration of glycogenolysis mainly brought about by GP activation.

Crucial role of intracellular effectors on glycogenolysis in the isolated rat heart: potential consequences on the myocardial tolerance to ischemia

The role played by glycogenolysis in the ischemic heart has been recently put into question because it is suspected that a slowing down of this process could be beneficial for the tolerance of the myocardium to ischemia. The role of the intracellular effectors that control the rate of glycogenolysis has therefore regained interest. We aimed to understand the role played by those intracellular effectors which are directly related to the energy balance of the heart. To this end, we review some of the previously published data on this subject and we present new data obtained from P-31 and C-13 NMR spectroscopic measurement on isolated rat heart. Two conditions of ischemia were studied: 15 min global no-flow and 25 min low-flow ischemia. The hearts were isolated either from control animals or from rats pre-treated with isoproterenol (5 mg.kg-1 b.w. i.p.) 1 h before the perfusion in order to C-13 label glycogen stores. Our main results are as follows: (1) the biochemically determined glycogenolysis rate during the early phase of ischemia (up to 10-15 min) was larger in no-flow ischemia than in low-flow conditions for both groups, (2) direct measurement of the glycogenolysis rate, as determined by C-13 NMR, after labelling of the glycogen pool in the hearts from isoproterenol-treated rats, confirms the estimations from the biochemical data, (3) glycogenolysis was slower in the hearts from pre-treated animals than in control hearts for both conditions of ischemia, (4) the total activity of glycogen phosphorylase (a + b) increased, by 50%, after 5 min no-flow ischemia, whereas it decreased by 42% after the same time of low-flow ischemia. However, the ratio phosphorylase a/a + b was not altered, whatever the conditions, (5) the concentration of inorganic phosphate (Pi) increased sharply during the first minutes of ischemia, to values above 8-10 mM, under all conditions studied. The rate of increase was larger during no-flow ischemia than during low-flow ischemia. The concentration of Pi was thereafter higher in controls than in the hearts from isoproterenol-treated animals. The calculated cytosolic concentration of free 5'AMP increased sharply at the onset on ischemia, reaching in a few minutes values above 30 microM in controls and significantly lower values around 15 microM, in the hearts from isoproterenol-treated rats. (6) The hearts from isoproterenol-treated rats displayed a reduced intracellular acidosis, when compared to controls, under both conditions of ischemia. We conclude that the intracellular effectors, mainly free AMP, play an essential role in the control of glycogenolysis via allosteric control of phosphorylase b activity. The alteration in the concentration of free Pi, the substrate of both forms of phosphorylase, can be considered as determinant in the control of the rate of glycogenolysis. The attenuation of ischemia-induced intracellular acidosis in the hearts from isoproterenol-treated rats could be a consequence of a reduced glycogenolytic rate and is likely to be related to a better resumption of the mechanical function on reperfusion.

Influence of ischaemia and reperfusion on cardiac signal transduction. G protein content, adenylyl cyclase activity, cyclic AMP content, and forskolin and dibutyryl cyclic AMP-induced inotropy in the rat Langendorff heart

We investigated whether post-receptor alterations contribute to the diminished beta-adrenergic inotropic effects in the rat Langendorff heart following ischaemia (I) and reperfusion (R). We quantitated immunodetectable Gs and Gi protein alpha-subunit content, basal and stimulated adenylyl cyclase activity and cyclic AMP (cAMP) content in normoxic, ischaemic (30 min) and ischaemic reperfused (30 min) hearts. In addition, we measured the inotropic response of normoxic and reperfused Langendorff hearts to forskolin and dibutyryl cAMP (db-cAMP). Immunodetectable Gs and Gi alpha-subunits were unaltered by I or R. Basal adenylyl cyclase activity was decreased during I, but recovered during R. In membranes from normoxic hearts, isoprenaline, GTP, Gpp(NH)p, NaF, forskolin or Mn2+ enhanced adenylyl cyclase activity. This increase in activity was diminished in ischaemic hearts, but could be restored by R. cAMP content decreased time-dependently during I and did not recover by R, indicating ATP depletion. Forskolin and db-cAMP induced an inotropic response in normoxic hearts, which was virtually abolished after I and R. We conclude that adenylyl cyclase responsiveness is impaired during I. Since adenylyl cyclase responsiveness recovers during R, whereas inotropic responses to forskolin and db-cAMP are virtually absent in reperfused hearts, an additional mechanism downstream of cAMP formation appears to be defective during R, which prevents recovery of inotropic responses to hormonal stimulation.

Cyclic GMP in the perfused rat heart. Effect of ischaemia, anoxia and nitric oxide synthase inhibitor

Working rat hearts perfused with 5.5 mM glucose were submitted to a 10-min period of no-flow ischaemia or anoxia. Both conditions stimulated glycogenolysis, activated phosphorylase and increased cyclic GMP content, although the time course of these changes differed in anoxia and ischaemia. Changes in cyclic GMP content were not correlated with glycogenolysis or phosphorylase activation. Perfusion with 1 microM L-nitroarginine methylester, an inhibitor of nitric oxide synthase, decreased cGMP concentration under normoxic conditions and abolished the ischaemia-induced increase in cGMP. The inhibitor decreased the coronary flow without affecting the overall working performance of the hearts under normoxic conditions.

[Enzyme activity of cardiac glycogen metabolism: study of an in situ hypoxia protocol in the rat]

Myocardial hypoxia, induced by arrest of the artificial ventilation of anaesthetized open-chest rats, was utilized in order to study some aspects of the regulation of myocardial glycogen metabolism. Atenolol, a cardioselective beta-adrenergic receptor antagonist, and verapamil, an inhibitor of sarcolemmal calcium transfer, were used to determine the respective role of adenosine 3', 5'-cyclic monophosphate (cAMP) and calcium in the activation of the enzymes of glycogen phosphorolysis and synthesis. Glycogen degradation is reduced by atenolol treatment, as a consequence of a reduced activation of glycogen phosphorylase. Verapamil treatment has no significant effect, neither on the enzyme activation nor on the glycogen utilization. The activation of glycogen synthase, expressed by the conversion of the enzyme from the D to the I form, which results from the decrease in glycogen stores during hypoxia, is lowered under the effect of both drugs. However, in the beta-blocker treatment case, this effect results from a lower glycogen depletion while this effect is more specific in hearts from rats treated with verapamil. Under the effect of verapamil, the reduction of synthase activation, for a similar depletion of glycogen stores, was confirmed by experiments using isolated rat hearts submitted to ischaemia. These results show that: 1. the glycogenolysis in the hypoxic myocardium in situ is mainly controlled by a cAMP-dependent enzyme conversion or by metabolic allosteric effectors; 2. the activation of myocardial glycogen synthase, which is essentially correlated to the reduction of glycogen stores, is also calcium-dependent and most probably totally cAMP-independent.

Cardiac contractility, cAMP concentration, cAMP-dependent protein kinase, and phosphorylase activation during acute pressure overload

The relationship between increases in myocardial contractility and cAMP and protein kinase activity were studied for hearts of normal rats and those with altered sympathectic capacity produced by the combined treatments of adrenalectomy, and 6-hydroxydopamine and propranolol injections. Increases in myocardial contractility, evaluated from intra-ventricular pressure changes, were produced by occlusion of the ascending aorta for 15, 20, or 25 s. Resting peak left ventricular pressure and the rate of rise of left ventricular pressure were lower (P less than 0.05) in sympathectomized animals, however, aortic occlusion abolished these differences. Time to peak tension and the relationship between end-diastolic pressure and developed pressure were unchanged by sympathectomy. ATP and CP concentrations in freeze clamped samples of the myocardium were lower (P less than 0.05) in both groups after aortic occlusion whereas lactate was elevated (P less than 0.05). Sympathectomy delayed and reduced the magnitude of the increase in the phosphorylase a/a + b ratio produced by aortic occlusion. Myocardial cAMP concentration was increased in the normal rats but decreased in sympathectomized animals after aortic occlusion. cAMP-dependent protein kinase activity followed the pattern of cAMP. The results demonstrate that heart possesses the capacity to increase its contractility to an acute, short-term overload even when devoid of sympathetic control.

Changes in serum cyclic nucleotide concentration during open-heart surgery

Changes in serum cyclic AMP and GMP concentrations were studied in 14 patients undergoing open-heart surgery with cold cardioplegia. Blood samples were taken on total bypass from the radial artery and from the coronary sinus before aortic cross-clamping and 1 and 9 min after declamping. The samples were analyzed for cyclic nucleotides. The cAMP levels showed no pronounced change in the arterial samples, but were significantly increased in the coronary sinus samples after declamping of the aorta. The cGMP values showed the same trend of change in the arterial and the coronary sinus samples, viz. significant fall after aortic release, and after 9 min an increase. The cAMP/cGMP ratio after clamp removal showed pronounced increase in the first minute and some reduction at 9 min. All the changes were statistically significant. Beating recommenced spontaneously in seven hearts. The cAMP levels were lower in this group than in the patients without spontaneous recovery. The outset cGMP levels and the cAMP/cGMP ratio were higher in the latter group. Absence of increase in the cGMP level may be due to effectiveness of cardioplegia in reducing the energy requirements of the ischemic myocardium. The study indicates that hearts without spontaneous recovery of beating react more sensitively to hypoxia and have to use up more of their energy resources for restoration of function.

Psychological stress activates phosphorylase in the heart of the conscious pig without increasing heart rate and blood pressure

The present study uses a technique that enables the collection of multiple freeze-biopsy samples from the myocardium of the conscious pig (i.e., through a thoracic window). This technique enables sequential analysis of the metabolic state of the myocardium during different behavioral conditions. The results demonstrate that with daily adaptations to an unfamiliar environment (i.e., stress reduction), the phosphorylase activation ratio (phosphorylase a/total phosphorylase) in the quiescent pig declines steadily from approximately 80% to 30% (r = -0.91, P less than 0.01). This decline occurs with both the mean resting heart rate and left ventricular blood pressure remaining constant. The decline is seen within individual subjects during the whole adaptation sequence as well as between subjects whose samples were taken either early or late in the adaptation series. The dissociation of hemodynamic functional and metabolic activation in the unadapted, psychologically stressed pig may be associated with the occurrence of increased vulnerability of the ischemic heart to ventricular fibrillation, a phenomenon previously observed under the same behavioral conditions.

The metabolic role of endogenous catecholamines in acute myocardial infarction: effects of reserpinization and of infused noradrenaline

A significant decrease of the noradrenaline content of the ischemic as well as non-ischemic parts of the myocardium was found in rats after ligation of the left coronary artery. The eventual role of released noradrenaline in the anaerobic metabolism of the heart was investigated. A highly significant decrease of ATP and glycogen was obtained in the ischemic myocardium 10 min after coronary ligation whereas glucose-6-phosphate (g-6-p) was significantly increased. Catecholamine depletion by reserpine pretreatment did not reduce the loss of ATP, although the hearts had broken down rather higher amounts of glycogen. Glycolytic energy production was obviously inhibited, as the accumulation of g-6-p was significantly greater than in non-reserpinized animals. However when a high breakdown of glycogen was induced by noradrenaline infusion into coronary ligated animals, the g-6-p levels were no higher than those in untreated coronary-ligated rats. The results suggest that the ischemic breakdown of glycogen is independent of endogenous noradrenaline. The metabolic conversion of g-6-p, however, may need sufficient catecholaminergic stimulation to become fully activated.

Cyclic nucleotides and changes in protein kinase activity ratio in the ischemic and nonischemic myocardium

Following coronary artery ligation (CAL), levels of cAMP and the activity ratio of cAMP-dependent protein kinase, of phosphorylase kinase, and of phosphorylase are significantly elevated in both ischemic and nonischemic areas of the canine left ventricle. The aerobic level of cAMP was found to be 0.4 to 0.6 pmol/mg myocardium only after a precooled clamp or a cryobiopsy device was employed to guarantee tissue freezing in situ. Maximal changes in response to ischemia are observed within 2 min in both parts of the heart. Twenty minutes after the onset of ischemia, different responses have been found in the nonischemic and ischemic tissue. Whereas the levels of cAMP and the activity ratio of protein kinase, of phosphorylase kinase, and of phosphorylase returned to aerobic values in the nonischemic area, these parameters remained elevated in the ischemic area. The changes in the levels of myocardial cAMP and in the cAMP-dependent protein kinase activity ratio following CAL could be prevented by propranolol.

A simple technique for determining contractility, intraventricular pressure, and heart rate in the anesthetized guinea pig

This paper describes a rapid technique for the continuous recording of intraventricular pressure, dP/dt, and heart rate in the anesthetized guinea pig. A 21g needle, attached to a pressure transducer, is inserted through the chest wall into the left ventricle. This provides continuous monitoring of intraventricular pressure; the first derivative of this pressure pulse is dP/dt, an index of inotropic state. The ventricular signal is also used to trigger a cardiotach for the continuous recording of heart rate. Since major surgery is not required, experimental set-up can be completed in 15-20 min with a minimum of trauma to the animal. This model is ideally suited for the determination of cardiovascular parameters following the administration of drugs by several routes (intravenous, oral, intramuscular, subcutaneous). The effects of three distinct inotropic agents: isoproterenol, AR-L57, and ouabain, have been evaluated in this system. Isoproterenol increased heart rate and dP/dt, and caused a transient increase in peak intraventicular pressure. AR-L57 and ouabain increased dP/dt and intraventricular pressure; their effects on heart rate were minimal. Ouabain was active following either oral or intravenous administration.

Regulation of guinea pig heart phosphorylase kinase by cAMP, protein kinase, and calcium

In skeletal muscle the activation of phosphorylase kinase (PK) associated with phosphorylation of the enzyme can be measured as an increase in the pH 6.8:8.2 activity ratio. Phosphorylation leads to a 20- to 30-fold increase in PK activity (PKA) at pH 6.8 and a large decrease in the Km for phosphorylase. Perfused guinea pig hearts exposed to isoproterenol (0.3 microM) showed an increase in PKA, but without an increase in the pH 6.8:8.2 activity ratio. In a 10-fold dilution of guinea pig heart cytosol exposed to cAMP + methylisobutylxanthine, PKA was stimulated twofold at pH 7.5. Addition of exogenous protein kinase stimulated PKA fourfold. Both methods of activation were reversible and were blocked by the heat-stable inhibitor of protein kinase. Guinea pig heart PK was Ca2+-dependent requiring 0.6 microM Ca2+ for half-maximal activity. Kinetic studies indicate that the Km of guinea pig heart PK for phosphorylase b at pH 6.8 is not markedly reduced after in vitro activation (35%). This could explain the observed lack of increase in the pH 6.8:8.2 activity ratio after exposure of hearts to isoproterenol. The time course for the activation of inotropic state and the glycogenolytic pathway in perfused guinea pig hearts by isoproterenol showed that these processes were maximally activated within 25 s. However, PK remained activated for 2 min, long after the other biochemical and physiological parameters had returned to control values. These data suggest that Ca2+, not phosphorylation state, is important in regulating the return of dP/dt to control levels after beta-adrenergic stimulation.

Protective action of amiodarone against ventricular fibrillation in the isolated perfused rat heart

The pretreatment of rats with amiodarone for 2 minutes to 3 weeks before the excision of their hearts caused a dose-related decrease in heart rate and an increase in the ventricular fibrillation threshold both before and after coronary arterial ligation. Similarly, amiodarone decreased the incidence of ventricular premature extrasystoles, ventricular tachycardia and fibrillation during the period of regional ischemia after coronary arterial ligation and also after reperfusion of the ischemic myocardium. There was no evidence of a metabolic protective effect on ischemic myocardium because tissue high energy phosphate content decreased to a similar extent in ischemic myocardium from control and amiodarone-treated rats. Instead, the protective effect of amiodarone against fibrillation was accompanied by attenuation of the increase in tissue cyclic adenosine monophosphate in ischemic myocardium after coronary arterial ligation. It is proposed that amiodarone exerts a potent antifibrillatory effect by decreasing tissue cyclic adenosine monophosphate in ischemic myocardium.

Myocardial extraction of cyclic AMP during pacing-induced angina

The application of cyclic AMP as a marker of myocardial ischemia in humans with coronary artery disease has been investigated during pacing-induced angina. Cyclic AMP was determined by a radioimmunoassay. In 15 patients myocardial lactate extraction at rest (20 +/- 12%) converted to production levels (-30 +/- 23%) during angina (p less than 0.0005). Insignificant changes occurred in coronary venous plasma cyclic-AMP levels. The mean myocardial cyclic-AMP extraction at rest (0.3 +/- 8.7%) converted to small release values (-6.0 +/-11%) during angina (= n.s.). No significant correlation was found between myocardial lactate and cyclic-AMP uptake or release. Therefore, cyclic AMP is an insensitive marker in the evaluation of myocardial ischemia.

Properties of epinephrine-induced activation of cardiac adenosine 3',5'-monophosphate-dependent protein kinase

The effects of epinephrine on cyclic AMP content and protein kinase activity were examined in an in situ rat heart preparation. Bolus injection of epinephrine into the superior vena cava caused an increase in the activity ratio (-cyclic AMP/"cyclic AMP) of 12 000 X g supernatant protein kinase. The increase was significant within 5 s and maximal in 10 s. Epinephrine produced a dose-dependent increase in both protein kinase activity ratio and cyclic AMP content. The increases in both parameters exhibited a high degree of correlation. The increase in protein kinase activity ratio observed with low doses of epinephrine (less than or equal to 1 microgram/kg) resulted from an increase in independent protein kinase activity (-cyclic AMP) without a change in total protein kinase activity (+cyclic AMP). However, the increase in the activity ratio observed with higher doses of epinephrine (greater than 1 microgram/kg) was due mainly to a decrease in total protein kinase activity rather than a further increase in independent protein kinase activity. The loss of supernatant total protein kinase activity could be accounted for by an increase in activity associated with particulate fractions obtained from the homogenates. A similar redistribution of protein kinase could be demonstrated by the addition of cyclic AMP to homogenates prepared from hearts not stimulated with epinephrine. These results demonstrate that epinephrine over a wide dose range produces a parallel increase in the content of cyclic AMP and the activation of soluble protein kinase. The findings also suggest that protein kinase translocation to particulate material may depend on the degree of epinephrine-induced enzyme activation.

The role of cyclic adenosine 3', 5'-monophosphate and calcium in the regulation of contractility and glycogen phosphorylase activity in guinea pig papillary muscle

We studied the relationships between the positive inotropic effects of isoproterenol, increased frequency of contraction or paired electrical stimulation, and cyclic AMP concentration and phosphorylase activity in isolated guinea pig papillary muscles. The minimum concentration of isoproterenol (10 nM) that augmented isometric force development increased cyclic AMP concentration. However 100 nM isoproterenol was required to increase the phosphorylase activity ratio (-AMP/+AMP) from 0.15 +/- 0.03 to 0.25 +/- 0.03. After addition of 1 muM isoproterenol to the bath, cyclic AMP increased within 0.5 minute from 0.58 +/- 0.03 to 1.04 +/- 0.13 mol/kg (wet weight), peak contractile force was elevated 2-fold at 1 minute, and the phosphorylase activity ratio rose to 0.40 +/- 0.02 in 4 minutes. Although an increase in contraction frequency (6/min to 36/ min) and paired stimulation produced more than a 3-fold increase in peak contractile force, there were no changes in cyclic AMP and phosphorylase activity. The cyclic AMP concentration during diastole was 0.60 +/- 0.04 and in midsystole, 0.55 +/- 0.03 mumol/kg. Anoxia increased the phosphorylase activity ratio from 0.19 +/-0.02 to 0.41 +/- 0.04 without elevation of cyclic AMP concentration. Removal of Ca2+ from the bathing medium prevented active force development and the anoxic increase in phosphorylase activity, but did not prevent the isoproterenol-induced increase in cyclic AMP and phosphorylase. These results suggest that cyclic AMP is a factor in the catecholamine-induced enhancement of inotropic state. However, it does not appear to play a role in the maintained augmentation of inotropic state produced by increased contraction frequency and paired stimulation, nor does the concentration of the cycle nucleotide appear to vary during the contraction cycle or during anoxia. Extracellular Ca2+ is required for contraction, the positive inotropic aciton of catecholamines and phosphorylase b to a conversion by anoxia.

Cyclic adenosine monophosphate, ventricular fibrillation, and antiarrhythmic drugs

It is proposed that the development of ventricular fibrillation in the context of ischaemic heart-disease and myocardial infarction can be related to accumulation of cyclic adenosine 3',5' monophosphate (A.M.P.) in the ischaemic zone. The known electrophysiological and metabolic actions of cyclic A.M.P. are consonant with the hypothesis, which also provides a framework for the better understanding of the action of antiarrhythmic drugs.

Cyclic AMP, cyclic GMP, and glucocorticoids as potential metabolic regulators of epidermal proliferation and differentiation

The two cyclic nucleotides, cyclic AMP and cyclic GMP, appear to be central to the metabolic regulation of cell proliferation and differentiation in various cells. Moreover, in many systems glucocorticoids appear to act in concert with or parallel to cyclic AMP. The available evidence suggests that these three molecular species--cyclic AMP, cyclic GMP, and glucocorticoids--may be essential to the normal regulation of epidermal proliferation and differentiation. In 1970, we suggested that perturbed epidermal homeostasis, exemplified by psoriasis, might be associated with low cellular levels of cyclic AMP and, in 1972, with high levels of cyclic GMP as well. Subsequent measurements of these two cyclic nucleotides in our laboratory showed a probable reduction in the cyclic AMP/cyclic GMP ratio in lesional psoriatic tissue. This led to the hypothesis that the cardinal features of psoriatic epidermis--glycogen accumulation, excessive proliferation, and reduced cell specialization--are the results of this reduced ratio. A corollary of this hypothesis was that a psoriatic lesion could not begin or exist without this altered cyclic nucleotide ratio. Recently, four different agents--lithium, a beta adrenergic blocking agent, antimalarials, and iodide--have been found to exacerbate psoriasis and to reduce the formation of cyclic AMP in various tissues. Consequently we believe that cyclic nucleotides are of central importance in the pathogenesis of the epidermal component of psoriasis.

Phosphorylase kinase mediating the effects of cyclic AMP in muscle

In the classic view of the control of phosphorylase b to a conversion by catecholamines, cyclic AMP acts as the second messenger stimulating the activity of cyclic AMP-dependent protein kinase to covalently modify phosphorylase kinase. Phosphorylation of phosphorylase kinase converts this enzyme form with a nonactivated to an activated form with a markedly higher activity at pH 7. There is now considerable evidence that the activity of phospphorylase kinase is also regulated by changeds in the Ca-2+ concentration. The activity of both nonactivated and activated phosphorylase kinase is stimulated by Ca-2+ in the range of concentrations that have been reported to occur in the sacroplasm of contracting muscle, with the activated pphosphorylase kinase having a lower K-alpha for Ca-2+. Thus there are at leaset two mechanisms for the regulation of phosphorylase kinase activity in muscle. These mechanisms may act independently or in concert in controlling glycogenolysis stimulated by catecholamines, anoxia, or tetanic electrical stimulation...

[Histochemical and histoenzymatic study of experimental myocardial infarction in the rat by temporary and permanent ligation of the left coronary artery (author's transl)]

The evolution of experimental myocardial infarction in the Rat with or without revascularization has been studied histochemically and histoenzymatically in 56 animals sacrified after 1, 6, 12, 24, 48 hrs and 7 days. Following permanent ischemis (14 animals), there appeared an extended transversal infarction marked by the complete disappearance of all phosphorylase activity (P-ase) after the first hour. During the first 6 hrs, changes appeared in succinodeshydrogenase (SHD) and cytochrome oxydase (Cyt-Ox). Glucose-6-phosphodeshydrogenase (G6PDH) presisted until lysis of the necrotic focus. It was possible to define a perinecrotic marginal area in which Pase activity is absent and SDH is granular "G3 in nature, characterized by continuous remodeling in the first 48 hrs. Following temporary ischemia (42 animals) the evolution was marked by rapid tissue reactions and early regression of the marginal zones. After 48 hrs and 7 days of survival, the planimetric evaluation of the infarcted area shows a definite reduction in the size of the infarctus in 50% of cases following removal of the ligature after 6 hrs, and in 66% of cases following removal of the ligature after 1 hr. It would appear probable that the revitalization of certain myocardial areas may extend from the marginal zones as is suggested by the reappearance in these zones several hrs after revascularization of P-ase and SDH activity. On the other hand, it is also true that the early restoration of blood flow does not always prevent the occurrence of an extended infarction. Certain recent observations have shown microcirculatory changes which are secondary to anoxia and should be studied further.