Prostaglandin E1-associated pathology of pulmonary microvasculature in newborn pups: similarity to findings in prostaglandin E1-treated human newborns

Prostaglandin E1 (PGE1) administration is a useful therapeutic measure for short-term maintenance of ductal patency in patients with obstructions to pulmonary or systemic blood flow. Such treatment is not without complications, however, and a report of three infants from our institution with abnormalities of the pulmonary microvasculature after varying periods of PGE1 therapy was recently published (Heffelfinger et al., Pediatr Pathol 1987;7:165-73). The vascular abnormalities appeared to be temporally related to the PGE1 administration. To test this hypothesis, we investigated the effects of PGE1 in newborn beagles by infusing PGE1 for periods of up to 21 days in four experimental pups. Two control pups were infused with saline for the same period of time. Five of the animals developed respiratory infection during the course of the infusions. One PGE1-treated pup was not infected. Both the PGE1- and saline-treated pups had bronchopneumonias of similar severity; however, pulmonary arteritis occurred only in the PGE1-treated pups. The severity of the arteritis varied with the amount of pulmonary parenchymal inflammation and not with the duration of PGE1 administration. Inflammatory and vascular lesions were found in organs other than the lung only in two pups receiving longer courses of PGE1 treatment. We conclude that systemic PGE1 infusion at therapeutic levels plays a role in the development of arterial lesions in small muscular arteries and that this is potentiated by the presence of infection.

Structural states in the Z band of skeletal muscle correlate with states of active and passive tension

In skeletal muscle Z bands, the ends of the thin contractile filaments interdigitate in a tetragonal array of axial filaments held together by periodically cross-connecting Z filaments. Changes in these two sets of filaments are responsible for two distinct structural states observed in cross section, the small-square and basketweave forms. We have examined Z bands and A bands in relaxed, tetanized, stretched, and stretched and tetanized rat soleus muscles by electron microscopy and optical diffraction. In relaxed muscle, the A-band spacing decreases with increasing load and sarcomere length, but the Z lattice remains in the small-square form and the Z spacing changes only slightly. In tetanized muscle at sarcomere lengths up to 2.7 micron, the Z lattice assumes the basketweave form and the Z spacing is increased. The increased Z spacing is not the result of sarcomere shortening. Further, passive tension is not sufficient to cause this change in the Z lattice; active tension is necessary.

Mechanism of complement activation after coronary artery occlusion: evidence that myocardial ischemia in dogs causes release of constituents of myocardial subcellular origin that complex with human C1q in vivo

To evaluate whether ischemic myocardium releases molecules that react with the first component of complement, we studied cardiac lymph from eight dogs before and at intervals after coronary artery occlusion and reperfusion. Before occlusion, the dogs were injected intravenously with radiolabeled human C1q. Labeled C1q could be detected in the cardiac lymph within minutes following injection. Rabbit antisera, prepared against substances precipitated from postreprefusion cardiac lymph by anti-human C1q, also reacted with specific constituents of isolated cardiac sarcoplasmic reticulum and mitochondria. To evaluate whether mitochondria are the source of these C1q-binding proteins, we isolated intramyofibrillar and subsarcolemmal mitochondria from canine heart and incubated sonicates of these with purified C1q, immobilized on nitrocellulose. Molecules bound to the immobilized C1q were removed with 0.1% sodium dodecyl sulfate, fractionated under reducing conditions by polyacrylamide gel electrophoresis, and transferred electrophoretically to nitrocellulose paper. Antisera prepared against postreperfusion lymph reacted with a 31,000-32,000-dalton protein in these nitrocellulose paper replicas. Since this protein originates from mitochondria, binds to C1q, and is recognized by antibodies made against postreperfusion lymph, this protein is likely to be one of the subcellular constituents that, upon release from ischemic cells, activates the complement cascade. To evaluate the clinical relevance of these observations, we tested sera from 53 patients obtained 48-72 hours after hospitalization for suspected myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

An animal model to examine the response to environmental stress as a factor in sudden cardiac death

Sudden cardiac death is the leading mode of death in adults in the United States. While it appears intimately associated with coronary artery disease, the factors that render some subjects vulnerable to sudden cardiac death, while others with the same coronary disease do not die suddenly, are unknown. An approach is described which considers that sudden cardiac death represents a separate syndrome of coronary artery disease within certain vulnerable subjects. It is suggested that the response to psychosocial stress in vulnerable subjects results in deleterious cerebral cortical influences on the autonomic control of the heart which render it more vulnerable to ischemia-induced ventricular fibrillation. Studies in the pig, an animal known to be susceptible to sudden death resulting from an environmental stress, demonstrate that cerebral cortical influences on autonomic centers play a central role in vulnerability to ventricular fibrillation after coronary artery occlusion. In this model, the incidence of ventricular fibrillation can be reduced by psychologic adaptation of the animal to his environment, cryoblockade of frontal cortical brain stem pathways and by central administration of propranolol. The relative role of adrenergic and cholinergic innervation of the heart is an important consideration.

Lipoxygenase inhibitor nafazatrom fails to attenuate postischaemic ventricular dysfunction

The role of lipoxygenase activation in the genesis of postischaemic myocardial dysfunction was investigated in open chest dogs undergoing a 15 min occlusion of the left anterior descending artery followed by 4 h of reperfusion. Treated animals (n = 9) received nafazatrom, a potent lipoxygenase inhibitor, 10 mg.kg-1 orally 4 h before occlusion followed by intravenous boluses of 1.5 mg.kg-1 and 0.5 mg.kg-1 5 min before occlusion and 1 min before reperfusion respectively. Control animals (n = 10) received saline. No discernible haemodynamic effects were produced by the drug. Collateral flow to the ischaemic zone (radioactive microspheres) was 0.14(0.02) ml.min-1.g-1 in the control group and 0.16(0.05) ml.min-1.g-1 in the treated group. The size of the occluded bed as determined by postmortem perfusion was 25.5(0.8)% of the left ventricle in the control and 24.3(1.3)% in the treated group. Histological examination showed a decrease in neutrophil infiltration of the non-ischaemic myocardium and, to a lesser extent, of the reperfused myocardium in nafazatrom treated animals, suggesting lipoxygenase inhibition. Systolic wall thickening (an index of regional function) was assessed using an epicardial pulsed Doppler probe. The two groups exhibited comparable systolic thickening under baseline conditions. Though treated animals showed less dyskinesis during coronary occlusion (p less than 0.05), recovery of function was not enhanced over controls and in both groups the reperfused myocardium was still dyskinetic at 4 h. Thus nafazatrom failed to improve postischaemic ventricular dysfunction, suggesting that leukotrienes do not contribute importantly to this phenomenon.

A hemodynamic load in vivo induces cardiac expression of the cellular oncogene, c-myc

To establish whether a hemodynamic load that causes cardiac hypertrophy in the intact animal might interact with cellular pathways that are thought to transduce growth signals in model systems, we have analyzed expression of the cellular oncogene, c-myc, after a systolic pressure load. Aortic constriction increased c-myc mRNA abundance in both the atria and left ventricle of 28-day rats, but did not activate a second "competence" gene, r-fos, whose expression by cardiac cells ceases upon termination of mitotic growth. In 80-day rats, c-myc was induced in the atria alone. Induction of c-myc by aortic constriction in vivo may correlate with the respective capacity of atrial and ventricular myocytes to replicate DNA during cardiac hypertrophy. Activation of c-myc was not sufficient to account for inhibition of muscle creatine kinase (mck) mRNA, which was decreased only in 28-day rats.

Z band dynamics as a function of sarcomere length and the contractile state of muscle

The Z band in skeletal muscle has two distinct structural states--a relaxed (small square or ss) form and a maximally activated (basket weave or bw) form. We have examined by electron microscopy and optical diffraction Z lattice forms and dimensions and A band spacings in relaxed, tetanized, stretched, and stretched-and-tetanized rat soleus muscle. We have tested the independent contributions of passive load, active tension, and sarcomere length to Z band state. As the A band spacing decreased with increasing load and increasing sarcomere length in the untetanized muscles, the Z lattice remained in the ss form and the Z spacing changed only slightly. Computer-enhanced images from digitized electron micrographs showed that the ss Z lattice resisted deformation regardless of load or method of stretching. In contrast, when the muscle was tetanized at sarcomere lengths of up to 2.7 microns, the Z lattice assumed the bw form and the Z spacing was increased by 20%. Regardless of lattice form, Z spacing did not vary significantly with sarcomere length. Images from freeze-substituted preparations showed both lattice forms comparable to those in images from glutaraldehyde-fixed muscles. Thus, Z band state appears to be a function of the presence (or absence) of active tension. Our previous three-dimensional model is compatible with these observations and with the sub-structures revealed by computer-enhanced images of both lattice forms.

Attenuation of dysfunction in the postischemic 'stunned' myocardium by dimethylthiourea

The mechanism for the prolonged contractile dysfunction observed in myocardium reperfused after reversible regional ischemia ("stunned" myocardium) is unclear. Recent studies suggest that myocardial stunning may be mediated by oxygen-derived free radicals, but the precise molecular species involved remain unknown. Thus we explored the role of the highly cytotoxic hydroxyl radical in regional postischemic dysfunction by using dimethylthiourea (DMTU), an effective and highly permeable hydroxyl radical scavenger. Open-chest dogs undergoing a 15 min occlusion of the left anterior descending coronary artery followed by 4 hr of reperfusion received either DMTU (0.5 g/kg iv over 45 min starting 30 min before occlusion, n = 14) or saline (n = 15). Control and treated dogs were comparable with respect to variables that may affect postischemic dysfunction, including heart rate, aortic pressure, left atrial pressure, arterial blood gases and hemoglobin concentration, size of the occluded bed (determined by postmortem perfusion), and collateral blood flow (determined by radioactive microspheres). Regional myocardial function was assessed by measuring wall thickening with an epicardial Doppler probe. The two groups exhibited comparable systolic thickening under baseline conditions and similar degrees of dyskinesis during ischemia. After reperfusion, however, wall thickening (expressed as percent of baseline) was considerably greater in treated as compared with control dogs: 53 +/- 9% (mean +/- SEM) vs 9 +/- 14% (p less than .03) at 1 hr, 55 +/- 9% vs 23 +/- 13% (p less than .05) at 2 hr, 60 +/- 9% vs 28 +/- 14% (p less than .05) at 3 hr, and 67 +/- 5% vs 36 +/- 13% (p less than .05) at 4 hr. Thus DMTU produced a significant and sustained improvement in recovery of contractile function. In concentrations greater than the plasma levels attained in vivo, DMTU did not scavenge either hydrogen peroxide or superoxide anion in vitro. These results suggest that the myocardial dysfunction occurring after a brief episode of regional ischemia is mediated in part by the hydroxyl radical.

Evidence for a pathogenetic role of xanthine oxidase in the "stunned" myocardium

Recent evidence suggests that postischemic myocardial dysfunction (or myocardial "stunning") may be mediated by oxygen free radicals, but the mechanism for their production remains unknown. To explore the role of xanthine oxidase as a potential source of free radicals, open-chest dogs undergoing a 15-min occlusion of the left anterior descending coronary artery (LAD) followed by 4 h of reperfusion (REP) received intravenously either allopurinol (50 mg/kg 48 h, 20 h, and 30 min before occlusion, 10 mg/kg 1 min before REP, and 6.25 mg X kg-1 X h-1 throughout REP, n = 13) or saline (n = 14). The two groups were similar with respect to occluded bed size (postmortem perfusion) and collateral flow (radioactive microspheres). In controls, the transcardiac difference in plasma uric acid (great cardiac vein - arterial concentration) increased 199 +/- 70% (means +/- SE) during ischemia (P less than 0.02) and remained elevated for 5 min after REP; no increase was observed in treated dogs. Regional myocardial function was assessed by measuring systolic wall thickening with an epicardial Doppler probe. The two groups exhibited comparable systolic thickening under base-line conditions and similar degrees of dyskinesis during ischemia. Following REP, however, recovery of contractile function (expressed as percent of preocclusion values) was considerably greater in allopurinol-treated as compared with control dogs: 57 +/- 14 vs. -22 +/- 16 (P less than 0.01) at 1 h, 70 +/- 13 vs. -15 +/- 15 (P less than 0.001) at 2 h, 65 +/- 14 vs. -28 +/- 13 (P less than 0.001) at 3 h, and 68 +/- 13 vs. -17 +/- 14 (P less than 0.001) at 4 h. These differences could not be ascribed to hemodynamic factors. The results suggest that xanthine oxidase is a source of the oxygen free radicals responsible for myocardial stunning following a brief episode of reversible regional ischemia.

The Z-band lattice in skeletal muscle before, during and after tetanic contraction

Electron micrographs and optical diffraction patterns of the Z-band were studied in rat soleus muscle fixed before, during, and after tetanic contraction. We compared the morphology (small square or basketweave pattern) and dimensions of the Z-lattice of control and tetanized muscles near rest length. Z-bands of muscle fixed at rest and of muscle allowed to rest after a tetanic contraction exhibited the small square pattern. Z-bands from muscle fixed during tetanic contraction exhibited the basketweave pattern. Concomitant with the transition to basketweave, we observed an average increase of 20% in spacing between the axial filaments of the Z-lattice. Optical diffraction measurements of the A-band d10 spacing revealed that the Z/A ratio remained constant during the transition. We have modelled the small square to basketweave transformation as resulting from a change of curvature of constant length cross-connecting Z-filaments when the axial filaments increase their separation.

Myocardial ischemia: platelet and thromboxane concentrations in cardiac lymph and the effects of ibuprofen and prostacyclin

Blood platelets have been implicated in several mechanisms leading to and/or modifying myocardial ischemia. Cardiac lymph examination allows insight into the extracellular fluid that is in equilibrium with the capillary blood. In order to obtain an index of platelet activation during coronary artery events in the awake chronic animal, we wished to ascertain whether evaluation of cardiac lymph would detect changes in platelet activation resulting from a vascular occlusion. The study used conscious dogs in which cardiac lymph vessels had been previously cannulated by open-chest surgical protocol. The concentrations of immunoreactive thromboxane B2 and platelet counts were assessed in the cardiac lymph during the control period, the 10-60 minute occlusions, and the reperfusion periods. The same protocols were effected on another series of dogs after infusion of ibuprofen or prostacyclin. Initially, immunoreactive thromboxane B2 concentrations in the systemic blood and cardiac lymph were identical. A three-fold increase in immunoreactive thromboxane B2 concentrations occurred in untreated animals and was accompanied by a fall in platelet count in the lymph. The infusion of ibuprofen or prostacyclin, which inhibit platelet aggregation by different mechanisms, prevented both the decrease in platelets and the increase in immunoreactive thromboxane B2. In this study, intravascular events resulting from coronary occlusion invoke a rapid rise of immunoreactive thromboxane B2 in the extravascular fluid. A decrease in platelet escape into the extravascular compartment is interpreted as a result of intravascular aggregation promoting decreased platelet numbers. Thus, examination of continuously flowing cardiac lymph allows rapid detection of intravascular activation of platelets in the awake animal in the absence of surgical trauma.

Selective accumulation of the first component of complement and leukocytes in ischemic canine heart muscle. A possible initiator of an extra myocardial mechanism of ischemic injury

Myocardial concentrations of C1q, a subunit of the first component of complement, were measured 5-120 minutes after ligation of a coronary artery in dogs injected with 125I-labeled human C1q and 131I-labeled human albumin. The 131I-labeled human serum albumin was used as a plasma protein marker. Ischemic regions of myocardium were defined by measuring regional myocardial blood flow by the reference sample method at intervals after coronary artery occlusion. Significant accumulations of 125I-C1q were demonstrated in the ischemic myocardium after coronary artery occlusions lasting 45 minutes. Some localization of C1q in ischemic myocardium was observed after a 15-minute occlusion, but the accumulations of C1q achieved in this case were not statistically significant. After coronary artery occlusions lasting greater than or equal to 45 minutes, left ventricular concentrations of C1q correlated reciprocally with regional myocardial blood flow. Moreover, high concentrations of C1q persisted in formerly ischemic segments after reperfusion. Radiolabeled neutrophils also accumulated selectively in ischemic segments relatively rich in C1q. It is suggested that complement activation may initiate the neutrophil-dependent portion of ischemic injury, delineated in recent years, that is associated with free radical release by phagocytic cells.

Protection of canine cardiac mitochondrial function by verapamil-cardioplegia during ischemic arrest

Hemodynamic and mitochondrial function recover following 60 minutes of ischemic arrest and reperfusion in hearts pretreated with verapamil. The present study was carried out to determine whether verapamil prevents the onset of mitochondrial oxidative impairment after 60 minutes of ischemic arrest without reperfusion. Two preparations of mitochondria isolated following Polytron homogenization and subsequent treatment of the myofibrillar pellet with Nagarse were examined for phosphorylating respiration. The Polytron mitochondria were more sensitive to ischemic arrest than were the Nagarse mitochondria with either glutamate-malate (57% vs. 22% inhibition), succinate (+ rotenone) (41% vs. 14% inhibition), or palmitoylcarnitine (57% vs. 27% inhibition) as respiratory substrates. Verapamil pretreatment significantly increased oxidation of all substrates by the subsequently isolated Polytron mitochondria, but only succinate-supported respiration returned to control levels. In contrast, the small amount of respiratory inhibition exhibited by the Nagarse mitochondria after ischemic arrest was insensitive to verapamil pretreatment. We conclude that the Polytron preparation of mitochondria is more susceptible to ischemia than the Nagarse mitochondria, and this susceptibility correlates with a striking sensitivity to verapamil protection. In general, oxidation of NADH-linked substrates, including palmitoylcarnitine, is more affected by ischemic arrest than succinate, and only oxidation of the latter substrate is totally protected by verapamil. The beneficial action of verapamil on mitochondrial function occurs prior to reperfusion. The data suggest that alterations in calcium homeostasis occur during the ischemic period, as well as in the subsequent reperfusion period.

Creatine kinase and phosphorylase in cardiac lymph: coronary occlusion and reperfusion

Cardiac lymph, collected from conscious dogs, was monitored for glycogen phosphorylase and creatine kinase (CK) enzymatic activity during control state, circumflex coronary artery (CFX) occlusion, and reperfusion. CFX occlusions, lasting for intervals as short as 10 min, initiated a release of phosphorylase and CK into the cardiac lymph, which was immediately observed during reperfusion of the ischemic tissue. Blood plasma levels did not appear for several hours. In the absence of reperfusion, the appearance of enzymes in cardiac lymph was delayed and peaked later. Glycogen phosphorylase and CK entered the lymph in greater quantities with reperfusion as the length of occlusion was increased. Histological examination of multiple sections of the reperfused hearts showed infarcts in hearts where CFX occlusions lasted 20 min or longer; occlusions of 10-15 min showed evidence of cell injury and death in two hearts and no definable infarct in the majority. Ischemic intervals of short duration release functionally active glycogen phosphorylase and CK, which reflect changes in myocardial cell egress of macromolecules and/or cell death.

Age-related changes in tetanic contraction of ventricular myocardium

Developmental changes of myocardial function have been described in a number of animal species. The purpose of these experiments was to assess the role of activation mechanisms in the age-related differences in twitch tension. We produced tetanic contraction of isolated ventricular trabeculae obtained from adult dogs and 4- and 25-day-old puppies. Tetanic contraction was produced using electrical stimulation at 10 Hz in modified Ringer's solution containing caffeine (10(-2)M) and calcium (10, 20, and 30 mM). This study demonstrated significant differences in the responses of adult and puppy myocardia to caffeine and calcium. The most striking finding was that active tension of puppy myocardium did not increase with tetanic contraction, whereas active tension of adult myocardium increased significantly during tetanic contraction.

Cerebral blood flow and experimental intraventricular hemorrhage

We evaluated the effects of acute hypovolemic hypotension followed by rapid, corrective blood infusion upon sequential regional cerebral blood flows (rCBF) in nine anesthetized 24-48-h-old beagle pups using the radioactive microsphere technique. After 5 min of hemorrhagic hypotension, during which time systemic arterial blood pressures were reduced 35-45%, cerebral blood flow to all regions increased by 31-42% over steady-state values. After blood reinfusion, rCBF increased by 39-88% over control values. Highest blood flows during hypovolemia were in the medulla and pons; slightly lower values were in the cerebellum, midbrain, cortex, and thalamus; and the lowest flows were in the white matter. These flows paralleled the hierarchy of flows to these regions in the steady state. Increases in blood flow during hemorrhagic hypotension were statistically significant when compared with the control values in the medulla (P less than 0.01), pons (P less than 0.01), midbrain (P less than 0.01), cerebellum (P less than 0.01), and cortex (P less than 0.01). One minute after reinfusion of the withdrawn blood volume, blood flows further increased by substantial margins in the medulla and pons; by moderate degree in the thalamus, midbrain, and cerebellum; and mildly in the cortex and white matter. Reinfusion state flow increases were significant when compared with control values in the medulla (P less than 0.01), pons (P less than 0.01), midbrain (P less than 0.01), cerebellum (P less than 0.01), cortex (P less than 0.05), and white matter (P less than 0.01). After flow values were corrected to compensate for variations in PCO2, the increases remained significant during both hypovolemia and reperfusion for medullary, thalamic, cortical, and white matter flows. Three of the nine puppies had macroscopic intraventricular hemorrhages at autopsy.

Doppler measurement of myocardial thickening with a single epicardial transducer

To eliminate the need for intramyocardial transducers in measuring regional left ventricular (LV) function we have developed a pulsed Doppler technique utilizing a single epicardial transducer. Wall thickening is evaluated by digitally integrating the velocity of myocardial layers passing through the sample volume located at a selected depth. Thickening fraction (TF) can then be estimated by dividing the systolic excursion by the sample volume depth. The Doppler method was compared with the transit-time method in three acute dogs by placing the 4-mm-diameter epicardial Doppler transducer over a 2-mm-diameter endocardial crystal tunneled through the LV wall. With the sample volume set to 1 mm less than the minimum LV thickness, simultaneous measurements of TF by the Doppler and transit-time methods showed good agreement (r = 0.95) during control, ischemia, volume overload, shock, and anoxia. In 28 chronically instrumented piglets signals were obtained for longer periods with Doppler transducers than with transit-time segment-length crystals. We conclude that the Doppler technique provides a high-fidelity wall thickening waveform and a good estimate of TF with minimal disturbance to the ventricle and that the technique is suitable for use in both acute and chronically instrumented animals.

Sodium-calcium exchange in dog heart mitochondria: effects of ischemia and verapamil

Na+ - Ca2+ exchange was studied in two preparations of dog heart mitochondria isolated from normal and ischemic muscle following occlusion of the circumflex (CFX) coronary artery with or without prior verapamil infusion. Na+ - Ca2+ exchange in mitochondria isolated using polytron homogenization showed sigmoidal kinetics with phosphate, whereas mitochondria isolated using gentle nagarse treatment showed hyperbolic kinetics and a Vmax 60% greater than the polytron preparation. Nagarse did not alter the sigmoidal kinetics or exchange velocities of the polytron mitochondria observed with phosphate. With acetate, both preparations exhibited hyperbolic kinetics, and the sodium required for half-maximum activity was increased. Verapamil inhibited Na+ - Ca2+ exchange in both preparations with phosphate, but not with acetate. Thirty or sixty minutes of acute ischemia following CFX occlusion produced significant epicardial surface S-T elevation in the ischemic area and a decrease in myocardial segment shortening. Na+ - Ca2+ exchange of both ischemic preparations was depressed, and the kinetics of the polytron preparation changed to hyperbolic. Pretreatment of the experimental animals with verapamil (0.3 mg/kg) before 60 min of ischemia protected the exchange rates in both preparations, and the sigmoidicity of the polytron mitochondria was retained.

Comparative response of the developing canine myocardium to inotropic agents

Developmental changes in cardiac muscle function were assessed in isolated dog ventricular muscle strips obtained from dogs of three age groups: 2 day, 4 wk, and adult. Active tension (AT) and maximum rate of contraction and relaxation (+dT/dt, -dT/dt) increased significantly with age. Total contraction time increased with age. Time to peak tension increased between 4 wk and adulthood, and relaxation time increased between 2 day and 4 wk (P less than 0.05). The degree of post-"extra stimulus" potentiation in response to a single premature extra stimulus (SPES) or to sustained paired stimulation (SPS) was similar in all age groups. However, a longer period of SPS was necessary to reach peak AT in young animals than in adults. AT, +dT/dt, -dT/dt, and (-dT/dt)/T increased significantly in all age groups in response to increasing concentrations of isoproterenol. However, while (+dT/dt)/T increased significantly in the 4-wk and adult groups, it remained unchanged from control in the 2-day group with increasing concentration of isoproterenol. The ED50 of isoproterenol was significantly greater in the 2-day and 4-wk groups than in the adult group. AT increased significantly in young muscles but not in adult muscles when additional calcium was added to the bath containing the highest concentration of isoproterenol. In adult muscles SPS produced the greatest AT but not in the 2-day group, which required increased calcium concentration as well as isoproterenol. Maturation of several membrane systems is implicated.

Microspheres in cardiac lymph: control and ischemic states

The cardiac lymph from conscious animals was monitored for the presence or absence of radiolabelled 15 micrometer microspheres during: 1) control periods after left atrial injection of microspheres and b) after circumflex coronary artery (CFX) occlusions (10--20 min total or less than 40 mins 50% of control flow) followed by full reperfusions. Microspheres (15 mu) numbering 7--150 were present in the lymph within 2 hrs after the occlusions; and in three experiments, the presence of a small number in the lymph on the following day implied continual release overnight. No microspheres were present in 8--48 hr lymph samples prior to occlusions. This study suggests that some microspheres escape from the intravascular space of the myocardium and are channeled into the cardiac lymphatics; this is apparent even after short-term ischemic events.

Hydralazine: effect on contraction mechanics of WKY and SHR rat heart muscle

Chronic hydralazine treatment (2 weeks) in 22-week-old normotensive (WKY) and spontaneously hypertensive rats (SHR) significantly lowered the systolic blood pressure in both groups. Left ventricular papillary muscles from nontreated and treated WKY and SHR were placed in an isometric myography, and contractile indices monitored. Nontreated WKY and SHR were not statistically different comparing: tension, maximum contraction and relaxation rates, time to maximum tension, total contraction time, or passive and active length-tension curves. Hydralazine-treated WKY and SHR had significantly reduced tension and maximum rates of tension development and relaxation; passive length-tension characteristics were not altered. Stressing the papillary muscles with increased frequency of electrical stimulation (0.1-2 Hz) did not differentiate the various groups. Significant (p less than 0.05) alteration with isoproterenol (10(-9)-10(-5) M) occurred with the hydralazine-treated WKY, which responded with a greater increase in relaxation rate than the hydralazine-treated SHR. It is suggested that the clinically very useful drug, hydralazine, causes a distinct contractile state alteration in rat myocardium after treatment sufficient to lower SHR blood pressure to a normal range.

Mitochondrial water in myocardial ischemia: investigation with nuclear magnetic resonance

Nuclear magnetic resonance studies of mitochondria isolated from ischemic hearts after coronary vessel occlusion indicated a decrease in water proton relaxation times. This change coincided with a decrease in the hydration of the samples. It is suggested that in ischemia, changes in macromolecular hydration may be one of the first mechanisms to alter function in the mitochondria, which are vital to the energy-transducing process in heart muscle.

Cardiac lymph flow in conscious dogs

The cardiac lymphatic duct was cannulated in dogs and the exteriorized cannula allowed chronic collection of lymph during the awake state for as long as 3 wk. The surgical methodology and inherent difficulties in the technique are describ:d. Cardiac lymph flow ranged from 0.45--5.6 ml/h in the control state in 14 dogs. An occluding device and flow probe were placed on the circumflex coronary artery (CFX); ultrasonic segment length crystals were placed in the left ventricular free wall in 4 dogs. Occlusion of the CFX in these conscious dogs caused lymph flow to fall as great as 46% below control during the 1st half-hour. Reperfusion of the occluded vessel caused an increase in lymph flow as great as 67% above control. The effect on cardiac lymph flow was demonstrated for a few select drugs that have known effects on the cardiovascular system. Cardiac lymph flow was altered from control as follows: isoproterenol, 42 +/- 11% increase; RO 2-2985, 118 +/- 8% increase; verapamil, 101 +/- 10% increase; propranolol caused no significant change. The conscious dog with cardiac lymph vessel cannulated should provide a model to further study the complexities of cardiac metabolism and physiology without interference of anesthesia and surgical stress.