Chronic catecholamine depletion switches myocardium from carbohydrate to lipid utilisation.

PURPOSE: Chronic cardiac transplantation denervation (i.e., global sympathetic denervation with myocardial catecholamine depletion, plus parasympathetic denervation) is known to inhibit myocardial oxidation of glucose. It is not known whether this is due to increased utilization of lactate, lipid or ketone bodies. The purpose of the present study was to test the hypothesis that the extraction and contribution of blood-borne fatty acids (FA) to overall oxidative energy conversion is increased. METHODS: In anaesthetised dogs (control n = 6, cardiac denervated n = 6), we investigated fatty acid (FA) utilization. The studies were made at least four weeks after surgical cardiac denervation. Measurements were made of total FAs and with a radio-labelled tracer (U-14C palmitate). RESULTS: The contribution of FA utilisation to overall substrate oxidation rose from 31% (control) to 48% (cardiac denervated). The increase in the ratio (%) of CO2 production from palmitate oxidation to total CO2 production increased from 4.0 +/- 1.8 (control) to 10.6 +/- 5.8 (denervated, p = 0.04). The time from uptake of FA to release of CO2 product was unaltered. CONCLUSION: We conclude that the contribution of FA oxidation to overall energy conversion is increased in chronically denervated hearts, which is postulated to result from a decline in the active form of pyruvate dehydrogenase. This would appear to be a result of chronic catecholamine depletion.

Thrombosis in one coronary artery causes generalized coronary vasoconstriction in a dog model of unstable angina.

We investigated the effect of thrombosis in one coronary artery upon the vascular resistance of another coronary artery. In previous investigations, using an animal model of unstable angina, we have observed increased resistance downstream from thrombus within a left circumflex coronary artery (LCx) stenosis and vasoconstriction of collateral vessels from the left anterior descending artery (LAD) supplying the distal LCx vascular bed. In the present paper, we induced thrombosis within a stenosis of the LCx of 16 beagle dogs, and observed the changes in blood flow to the myocardium supplied by the LAD using the radioactive microsphere technique. This blood flow decreased with thrombosis (P = 0.005) in these animals, whereas it did not do so in three time-control experiments. The pressures across the coronary vascular bed, i.e. arterial pressure to coronary venous pressure (coronary sinus catheter), did not change. Thus the vascular resistance of the LAD bed increased significantly from 147 +/- ll.5 mmHg/ml/sec/g of tissue to 172 +/- 13.4 mmHg/ml/sec/g of tissue (P = 0.02). As the LAD territory is not perfused with blood from the artery containing thrombus, we conclude that the effect observed is caused either by release of vasoconstrictors from the thrombus into the general circulation, or by activation of a neural reflex vasoconstriction. The study suggests that unstable angina involving thrombosis in one coronary artery is a global coronary vascular disease.

Measurement of coronary collateral flow and resistance in the presence of an open critical stenosis, and the response to intra-arterial thrombosis.

OBJECTIVE: (1) Can one measure coronary collateral flow around an open critical stenosis? (2) Does intracoronary platelet thrombosis affect native coronary collateral vessels? METHODS: We measured regional myocardial blood flow by the radioactive microsphere technique in seven anaesthetised dogs with an ultrasonic flowmeter on the circumflex branch of the left coronary artery (LCx). Measurements were made (a) in a control period, (b) after induction of a tight stenosis on the LCx, and (c) after additional arterial damage at the stenosis to induce intraluminal thrombosis. Collateral flow was calculated from LCx tissue flow(in ml/min/g tissue) minus LCx flowmeter flow which is in ml/min. Therefore, it was necessary to use scaling by reference back to the control measurements and conversion to ml/min/g tissue equivalent. RESULTS: LCx stenosis induced collateral flow from the other coronary arteries into the LCx area of supply, which decreased (mean+/-S.E.) from 0.23+/-0.03 to 0.15+/-0.05 ml/min/g tissue with thrombosis. Collateral resistance correspondingly increased with thrombosis from 187.6+/-18. 2 to 1069+/-544 mmHg/ml/min/g (P<0.02). CONCLUSION: Coronary collateral flow around an open stenosis can be measured by reference back to control conditions. The coronary collaterals vasoconstrict in the presence of thrombosis even though they are in the stream of blood coming from normal coronary arteries.

Downstream resistance effects of intracoronary thrombosis in the stenosed canine coronary artery.

OBJECTIVE: The presence is well established in unstable angina of intracoronary thrombosis in a stenosed epicardial coronary artery. The effects of the thrombus formation on the distal microcirculation are however still unclear. METHODS: We adapted the Folts canine model of left circumflex coronary arterial stenosis and intracoronary thrombosis by the insertion of a pressure catheter distal to the stenosis and by the use of 15 microns radioactive microspheres for measurement of regional myocardial blood flow. This permitted measurement during circumflex artery occlusion of collateral flow, downstream vascular resistance and collateral resistance. RESULTS: Distal circumflex resistance, obtained by dividing the distal circumflex coronary pressure gradient by the collateral flow, significantly increased with thrombosis (94.47 +/- 35.72 to 120.06 +/- 34.47; p = 0.0018) mmHg/ml/min/g. Changes in collateral flow and resistance in the presence of thrombosis, during maximum ischaemic vasodilatation, were inconsistent. CONCLUSION: Thrombosis causes increased vascular resistance in the microcirculation distal to the site of injury. This may be of clinical relevance in unstable angina, characterised by episodes of thrombus growth and embolization, in which ischaemic episodes may be worsened by generalised downstream vascular changes.

Tachycardia-induced failure alters contractile properties of canine ventricular myocytes.

OBJECTIVE: Rapid cardiac pacing has been used as a model for experimentally-induced cardiomyopathy. However, its relevance to human heart failure is not clear at present because little is known about changes in size and function of ventricular myocytes. We have therefore studied the responses to graded increases in frequency and calcium in canine ventricular myocytes from failing hearts. The aim of our study was to evaluate the resemblance between canine pacing-induced and human end-stage heart failure. METHODS: Myocytes were isolated from the left ventricular wall of dogs that were in heart failure after 6 weeks of pacing at 250 beats/min. Cell shortening was measured by edge detection. RESULTS: Clinical signs of failure included dyspnea, ascites, and heart dilatation; the hemodynamic parameters were: LVdP/dtmax 1613 +/- 149 vs. 4713 +/- 304 mmHg/s in 6 control dogs; LVEDP 17.2 +/- 4.4 vs 5.6 +/- 1.1 mmHg; LV volume 60.5 +/- 6.2 vs. 30-35 ml. Myocytes from failing hearts were longer and thinner than those from controls (from factor: 0.40 +/- 0.01 vs. 0.47 +/- 0.01, P < 0.001, > 30 cells/heart). With 6 mM Ca2+ and at 0.5 Hz, contraction amplitude was significantly attenuated in myocytes from failing hearts: 6.6 +/- 0.9% cell shortening vs. 10.0 +/- 0.8% in controls (P < 0.05). This deficit was exacerbated at higher stimulation rates. Time-to-peak contraction and time-to-50% relaxation were not altered. There was no difference in sensitivity to thapsigargin. CONCLUSION: As with cells from human failing hearts, contraction amplitude showed rate-dependent depression in this animal model, whereas features like slowing of contraction and relaxation and reduced sensitivity to thapsigargin, were not reproduced.

Failure of thrombin inhibition to prevent intracoronary thrombosis in the dog.

1. Recurrent occlusion after thrombolysis may be caused by thrombin receptor-mediated platelet thrombosis occurring in a residual stenosis. To test the relative importance of the platelet thrombin receptor under conditions of high shear and endothelial damage (the Folts model of intracoronary thrombosis) we used the specific thrombin inhibitor recombinant hirudin. 2. A critical coronary artery stenosis overlying an area of crushed endothelium was used in a repeated measures study of eight open-chest anaesthetized dogs. In the control period, recurrent thrombosis occurred at an average rate (+/- SD) of 4.4 +/- 1.4 ml/min2. Infusion of recombinant hirudin at 1.6 mg h-1 kg-1 abolished recurrent thrombosis in three dogs, but the thrombosis rate averaged 4.7 +/- 2.9 ml/min2 in the remaining five animals. 3. Haematological measurements demonstrated the activity of recombinant hirudin: thrombin time rose from 13 +/- 3 s to > 165 s universally (P < 0.01), partial thromboplastin time rose from 14 +/- 2 s to 29 +/- 10 s (P < 0.01). Bleeding time rose from 2.3 +/- 0.8 min to 4.7 +/- 1.8 min (P < 0.05). 4. It is concluded that specific thrombin inhibition, despite affecting coagulation, is relatively ineffective in preventing intracoronary thrombosis under conditions of high shear.

Effects of trimetazidine on in vivo coronary arterial platelet thrombosis.

We used Folts' model of critical coronary artery stenosis with endothelial damage, which measures platelet-rich thrombus accumulation from cyclic flow reductions (CFRs). This paper reports results applied to trimetazidine, a member of the piperazine group. Trimetazidine at a dose of 1 mg/kg completely abolished CFRs caused by accumulating thrombus in the circumflex coronary artery in 4 of 8 open-chest anesthetized beagles. More trimetazidine (up to 5 mg/kg) abolished CFRs in two more and attenuated them in the remaining two dogs. There were no systemic hemodynamic effects observed. Adrenaline was then infused to stimulate platelet activation. At a rate of 0.4 microgram/kg/min, CFRs were restored in one dog only. Adrenaline given at 1.6 micrograms/kg/min resulted in restoration or increase in the slope of CFRs in all animals. A further six nonoperated dogs were anesthetized and given trimetazidine 3 mg/kg. Routine coagulation studies were not altered. However, aspirin 5 mg/kg significantly increased bleeding time, whereas trimetazidine alone did not. These findings suggest that trimetazidine is effective in preventing intracoronary platelet aggregation in this model. Because of its demonstrated sparing of coagulation factors and its lack of effect on bleeding time, the cause is unlikely to be inhibition of the fibrinogen or thrombin receptors, or interference with arachidonic acid metabolism.

Advantages of a narrow-range, medium molecular weight hydroxyethyl starch for volume maintenance in a porcine model of fecal peritonitis.

OBJECTIVE: To compare the effectiveness of two hydroxyethyl starch solutions of different molecular weight ranges for volume maintenance in a porcine model of fecal peritonitis. DESIGN: Randomized prospective trial. SETTING: Laboratory investigation. SUBJECTS: Adolescent female pigs weighing approximately 30 kg. INTERVENTIONS: We compared diafiltered 6% pentastarch with 6% high molecular weight hetastarch for volume maintenance in a porcine model of fecal peritonitis. The number average molecular weight of pentastarch is higher than hetastarch, although the weight average molecular weight is lower, i.e., a narrow range of medium weight molecules. The infusion rate of each agent was adjusted to maintain baseline arterial Hct for less than or equal to 7 hr after instrumentation and induction of fecal peritonitis. MAIN OUTCOME MEASUREMENTS: The volume of fluid required to maintain arterial Hct was compared along with comparisons of hemodynamic and histologic responses associated with the two agents. RESULTS: Significantly less pentastarch was required to prevent hemoconcentration than hetastarch (109 +/- 22.8 vs. 150 +/- 10.3 mL/kg; p less than .05) while hemodynamics, colloid osmotic pressure, and oxygen transport responses were similar. Capillary patency was greater (21.99 +/- 3.68 vs. 10.09 +/- 1.17%; p less than .05) and mean alveolar capillary barrier thickness was less (2.36 +/- 0.13 vs. 3.06 +/- 0.17 microns; p less than .05) with pentastarch than with hetastarch, as judged by electron microscopy. CONCLUSIONS: These data suggest that pentastarch is better retained in the circulation in capillary leak syndromes compared with hetastarch.

An in vitro slice preparation of the cat lateral geniculate nucleus.

A slice preparation of the cat thalamus containing the lateral geniculate nucleus and the terminal portion of the optic tract is described. Ultrastructurally the slices remain relatively normal for only a short time after cutting. Indeed most cellular elements deteriorate quickly with time but patches of relatively intact tissue were still present even 10 h after cutting and maintenance in a storage bath. However, for 4-5 h after cutting long-lasting intracellular recordings of high quality and stability were obtained, and intrasomatic injection of horseradish peroxidase used for the morphological identification of recorded neurones as X or Y cells.

Effect of defibrinogenation on the early patency rate of experimental small calibre arterial grafts.

The effect of defibrinogenation with Arvin was studied in a new animal model of early thrombosis of a 3 mm diameter polytetrafluoroethylene (PTFE) graft with a poor run-off. Fifteen control animals were compared with fourteen animals treated with subcutaneous Arvin 20 units kg-1 body weight day-1, starting 2 days before surgery and continuing for 2 days postoperatively. The peroperative fibrinogen level in the controls was 2.8 +/- 0.9 gl-1 compared with 0.4 +/- 0.3 gl-1 in the treated group. There was no significant difference in the peroperative or postoperative platelet count or haematocrit value between the two groups. Plasma viscosity and whole blood viscosity (at a low shear rate of 0.7s-1) were significantly less during and after surgery in the defibrinogenated group. The degree of defibrinogenation in these animals produced no problems with haemostasis during surgery or in the postoperative period. The cumulative patency rates of the controls at 24 h, 48 h, and 4 days were 43 per cent, 28 per cent and 28 per cent compared with 86 per cent (P less than 0.05), 73 per cent (P less than 0.05) and 73 per cent (P less than 0.05) respectively in the defibrinogenated group. In this model of a narrow PTFE graft with a poor run-off, defibrinogenation was a safe and effective method of improving early patency of small calibre arterial grafts.

The effect of normovolaemic haemodilution on the early patency rate of small calibre vascular prostheses studied in a new animal model.

A new animal model has been developed to study early thrombosis in small calibre vascular prostheses. It consists of an ePTFE graft 2 cm long and of 3mm internal diameter inserted into a rabbit abdominal aorta in which the distal run-off is reduced by narrowing both common iliac arteries using clips with a standard gap. Scanning electron microscopy and in vivo gamma imaging of the graft using labelled autologous platelets showed that, as in the human, platelets played a primary role in the model graft thrombosis. This model was used to study the effect of haemodilution on early graft patency. Moderate normovolaemic haemodilution dramatically improved the early patency rate.

Intermittent sampling of portal venous blood and bile from guinea pigs.

A technique is described for intermittent collection of portal venous blood from guinea pigs through a catheter advanced from an ileal tributary of the cranio-mesenteric vein into the portal vein and for the collection of bile from a catheter in the gallbladder after ligature obstruction of the common bile duct.

Successful anaesthesia and small-bowel anastomosis in the guineapig.

Using methoxyflurane and paying critical attention to maintenance of body temperature, tracheal aspiration and fluid replacement, guineapigs were rendered suitable for intraperitoneal operations lasting up to 3 h. Anaesthetic mortality was less than 2%. A technique of small-bowel anastomosis was developed using interrupted soluble sutures meticulously placed 1 mm apart and taking bites 1 mm deep. Survival was 95%.

Improvement in experimental vascular graft patency by controlled defibrinogenation.

A sensitive animal model was used to investigate treatment designed to improve vascular graft patency. A Dacron graft was inserted into the infrarenal vena cava of 30 rabbits. Half were treated with subcutaneous Arvin for 28 days after operation. This produced a significant lowering of the post operative plasma fibrinogen. The patency rate of the grafts in the treated rabbits was significantly greater than in the control rabbits.