Captopril improves oxygen and glucose extraction in pig hearts during reperfusion after cold cardioplegic storage.

The purpose of this study was to evaluate the haemodynamic and metabolic effects of captopril during reperfusion of pig hearts following 360 min global hypothermic cardioplegia and storage (HCS). The hearts were perfused with one litre of cold crystalloid cardioplegia (Bretschneider solution no. 3), excised and stored in saline at 4 degrees C for 360 min. The hearts were then reperfused with blood in a modified Langendorff model for 60 min. Left ventricular function, myocardial blood flow, and arteriovenous differences in oxygen, glucose and lactate were monitored intraoperatively and during reperfusion. Two groups of hearts were studied. Group I (captopril treated, n = 9): the pigs were pre-medicated with increasing oral doses of captopril for 3 weeks (12.5 mg-150 mg daily) and an intravenous dose (25 mg) upon arrival at the laboratory. Captopril was added to the cardioplegia (1000 microg/l) and to the reperfusion media (1000 microg/l). Group II (controls, n = 8): the pigs were given no premedication, captopril-free cardioplegia and the hearts were reperfused with captopril-free blood. Captopril increased myocardial oxygen and glucose extraction during reperfusion (p < 0.05 for both) while lactate remained unchanged after 360 min HCS. Treatments with captopril increased developed left ventricular pressure (DLVP) and relaxation (-dP/dtmax) during reperfusion (p < 0.05 for both), while contractility (+dP/dtmax) was unchanged. Heart rate was reduced in captopril-treated hearts (p < 0.05) while myocardial blood flow (MBF) was similar in the two groups. Captopril administration prior to and during HCS and postcardioplegic reperfusion improves oxygen and glucose extraction in large spontaneously beating porcine hearts during reperfusion. The underlying mechanisms seem to involve metabolic modulation, since myocardial uptake of oxygen and glucose was increased in the absence of changes in myocardial blood flow.

Captopril-induced glutamate release at the start of reperfusion after cold cardioplegic storage of pig hearts.

OBJECTIVE: We sought to evaluate the effects of captopril on glucose-related metabolism during hypothermic cardioplegic storage and subsequent reperfusion. METHODS: We compared hearts from control pigs with hearts from pigs treated with increasing oral doses of captopril for 3 weeks (12.5-150 mg daily), an intravenous bolus (25 mg) before operation, and captopril-containing cardioplegic solution (1 mg/L). The hearts were excised after infusion of cold crystalloid cardioplegic solution and stored in saline solution (4 degrees C-6 degrees C). In one series we studied myocardial blood flow and arteriovenous differences in oxygen, glucose, lactate, glutamate, and alanine during 60 minutes of postcardioplegic blood reperfusion. In this series captopril-treated hearts were reperfused with captopril-containing blood (1 mg/L). In another series we obtained biopsy specimens from the left ventricle throughout 30 hours of hypothermic cardioplegic storage and monitored tissue content of energy-rich phosphates, glycogen, glutamate, and alanine. RESULTS: Captopril increased glutamate and alanine release 11- to 17-fold at the start of reperfusion (P <.001). Furthermore, captopril increased myocardial oxygen and glucose uptake during reperfusion (P <.001 for both), whereas lactate release and myocardial blood flow were unaffected by captopril. At the start of reperfusion, there was a positive correlation between glutamate release and glucose uptake in captopril-treated hearts (r = 0.66, P =.05). We found no statistically significant differences between captopril and control hearts in tissue content of adenosine triphosphate, glycogen, glutamate, alanine, or lactate during 30 hours of cardioplegic storage. CONCLUSIONS: The metabolic effects of captopril are strictly related to reperfusion, during which oxidative metabolism of glucose is improved. The captopril-induced increase in glutamate and alanine release at the start of reperfusion after cardioplegic storage may reflect a switch in metabolism of glucose-related amino acids.

Haemodynamic and metabolic effects of gallopamil as additive to calcium-containing and calcium-free cardioplegic solutions in mature pig hearts.

Myocardial haemodynamic and metabolic effects of the calcium-channel blocker gallopamil as additive to calcium-containing (St Thomas Hospital, STH) and calcium-free (Bretschneider procaine-containing, BRT) crystalloid cardioplegic solutions were evaluated. Adult pig hearts (weight 0.033 kg) were randomized to four groups and perfused with 1 litre of cold (4 degrees C) cardioplegic solution; group A: BRT without gallopamil, n = 9, group B: BRT with gallopamil (0.4 microM), n = 8, group C: gallopamil-free STH, n = 8, and group D: STH with gallopamil (0.4 microM), n = 8. After storage at 4 degrees C for 6 hours the hearts were reperfused with blood/Ringer solution in a modified Langendorff model for 60 min. Developed left ventricular pressure, rate-pressure product and +dP/dt were lower in gallopamil-treated hearts during reperfusion (p < 0.05), as were oxygen extraction and oxygen uptake (p < 0.05) and lactate release (p < 0.05). Myocardial blood flow was greater in gallopamil-treated hearts (p < 0.05). In hearts comparable in size and anatomy to the human heart, gallopamil added to both cardioplegic solutions reduced cardiac function and oxygen uptake despite increased myocardial blood flow. The findings suggest reduced myocardial protection after addition of gallopamil to cardioplegic solutions.

Effect of verapamil in intermittent claudication A randomized, double-blind, placebo-controlled, cross-over study after individual dose-response assessment.

BACKGROUND: The calcium antagonist verapamil is a vasodilator drug that has been shown to increase oxygen extraction of ischemic tissues in coronary and peripheral vascular disease. METHODS AND RESULTS: Since the balance between the positive and the negative effects of vasodilation may be delicate in ischemic diseases a dose-response study (dose range, 120 to 480 mg) was established to determine optimal, individual dosages of slow-release verapamil in 44 patients with stable intermittent claudication (Fontaine classification stage II) with respect to walking capacity. A randomized, double-blind, placebo-controlled, cross-over study (4 weeks) was performed to assess clinical and hemodynamic effects of verapamil. The optimal daily dose of verapamil on maximal walking ability was 120 (8 patients), 240 (8 patients), 360 (14 patients), and 480 mg (14 patients). Walking distances were measured at a metronome-controlled speed of 60 steps per minute on level surface. Optimal individual doses of verapamil increased mean pain-free walking distance by 29% from 44.9 to 57.8 meters (P < .01) and maximal walking distance by 49% from 100.7 to 149.8 meters (P < .001) compared with placebo. The increase in maximal walking distance correlated positively only with initial systolic ankle pressure (r = .49, P < .001) and ankle/brachial pressure index (r = .37, P < .013). Verapamil had no effect on systolic ankle pressure, ankle/brachial pressure index, peripheral leg temperature, or blood pressure, which suggests that the drug may have extrahemodynamic effects, possibly brought about through improved oxygen metabolism. CONCLUSIONS: Verapamil showed significant clinical benefits in patients with moderate intermittent claudication in this short-term study. Individual optimization of drug dosage should be considered an option both in trials and in the clinical setting in these patients.

Animal model of the univentricular heart and single ventricular physiology.

The univentricular heart complexes are a fairly common and potentially lethal set of congenital cardiac anomalies. Progress in developing new therapeutics has been hampered by a lack of suitable animal models. The authors developed a stable, closed heart preparation to systematically examine potential interventions. Using neonatal piglets (3.5-6.0 kg), a 6-mm PTFE graft was anastomosed end to end to the innominate artery and end to side to the pulmonary artery. An atrial septostomy was made, using a Rashkind septostomy catheter passed transvenously. With the same catheter, the tricuspid valve was rendered incompetent. Occlusion of the right ventricular outflow tract completed a univentricular circuit. All cardiac output exited from the left ventricle, and pulmonary blood flow was maintained via the innominate artery-to-pulmonary artery shunt. Pressure transducers measured central venous (mid inferior vena cava), aortic, and pulmonary arterial pressures. Oximetric probes recorded systemic venous and arterial oxygen saturations. Transit-time flow probes measured total cardiac output and pulmonary flows. Systemic flow was calculated by subtracting pulmonary flow from total cardiac output. This model has been completed in 30 animals. Minimal pressure drops have been recorded across the innominate-to-pulmonary artery graft. Pulmonary flows up to 700 +/- 52 mL/min were seen. Total cardiac outputs are as high as 1370 +/- 88 mL/min. Mean ratios of pulmonary to systemic flow (Qp/Qs ratio) range from 1.29 +/- 0.08 to 0.41 +/- 0.09. The model allows for full continuous monitoring of systemic and pulmonary pressures and flows and for accurate characterization of the physiological effects of respiratory and pharmacological interventions. In addition, mechanical constriction of the graft may allow direct alteration of the Qp/Qs ratio, with determination of an optimum value for this ratio.

Inotropes in the hypoplastic left heart syndrome: effects in an animal model.

BACKGROUND: Despite substantial changes in the surgical treatment of children born with the hypoplastic left heart syndrome, overall mortality remains high. Although further improvements in outcomes appear to depend on more effective perioperative care, few experimental data exist to guide appropriate pharmacologic therapy in these infants. Because different inotropic agents may have different effects on the ratio of pulmonary to systemic flow (Qp/Qs), we hypothesize that they may not be equally effective at increasing oxygen delivery. METHODS: In neonatal piglets (n = 6; 3.5 to 6.5 kg), we placed an innominate artery-to-pulmonary artery shunt, created an atrial septal defect, and then occluded right ventricular outflow. We examined the effects of a number of commonly used inotropic agents, administering high and low concentrations of dopamine (5 and 15 micrograms.kg-1 .min-1), dobutamine (5 and 15 micrograms.kg-1.min-1), and epinephrine (0.05 and 0.1 microgram /min). RESULTS: Dobutamine at 15 micrograms.kg-1.min-1 increased the Qp/Qs ratio from 1.03 +/- 0.6 at baseline to 2.52 +/- 0.55 (p < 0.05) and decreased oxygen delivery from 50 +/- 4.3 to 36 +/- 1.7 mL/min (p < 0.1). The arterial-venous oxygen difference increased as oxygen delivery went down, going from 44% +/- 1% to 48% +/- 2% (p < 0.1). Epinephrine at 0.1 microgram.kg-1.min-1 decreased the Qp/Qs ratio from 1.23 +/- 0.21 to 0.82 +/- 0.08 (p < 0.05) and increased oxygen delivery from 40 +/- 9.7 to 56 +/- 1.7 mL/min (p < 0.05). Systemic venous oxygen saturation increased from 36% +/- 4.8% to 50% +/- 8.6% (p < 0.05). Although dopamine decreased the Qp/Qs ratio and increased oxygen delivery, these changes were not statistically significant. CONCLUSIONS: Dopamine, dobutamine, and epinephrine all increased cardiac output but had substantially different effects on the Qp/Qs ratio and on oxygen delivery, possibly due to differential effects on systemic and pulmonary vascular resistances. This suggests that inotropic agents may not be equally beneficial in the clinical setting. Systemic venous oxygen saturation and the arteriovenous oxygen difference may help determine if a given inotrope improves oxygen delivery.

Improved recovery after cold crystalloid cardioplegia using low-dose glutamate enrichment during reperfusion after aortic unclamping: a study in isolated blood-perfused pig hearts.

Increased glutamate utilization is a part of the metabolic adaptation to oxygen deprivation by the heart. The effect of low-dose L-glutamate (2 mmol/L) during continuous reperfusion after aortic unclamping on postcardioplegic recovery was studied in pig hearts similar in size, anatomy, and function to the human adult heart. After cold crystalloid cardioplegic arrest (CCC) with Bretschneider solution no 3, hearts were excised from pigs weighing 70-80 kgs (heart weight, average +/- SEM: 308 +/- 4 grams), and reperfused in an isolated blood-perfused heart model for 120 minutes. Three groups of hearts were compared. One group of hearts was subjected to 30 minutes of CCC only (30 min group; n = 9), another group of hearts to 90 minutes of CCC and storage (Control group: n = 16), and a third group to 90 minutes of CCC and storage, but with L-glutamate added to the blood reperfusate (2 mmol/L) (Glutamate group: n = 18). In the Control group 14 of 16 hearts (88%) needed electrical defibrillation after start of reperfusion, significantly more (p < 0.05) than the 8 of 18 (44%) in the Glutamate group; the difference between the 30-min (2 of 9 [22%]) and the Glutamate group was not significant (p = 0.48). Developed left-ventricular pressure (DLVP) and positive dP/dtmax (+dP/dtmax) was significantly higher in the Glutamate group than in the Control group during early reperfusion (DLVP: p < 0.05: +dP/dtmax: p < 0.01) and the entire reperfusion (DLVP and +dP/dtmax: p < 0.05), while reperfusion responses in the Glutamate and 30-min groups were not significantly different. Furthermore, myocardial oxygen uptake was significantly higher in the Glutamate group than in the Control group (p < 0.001), but not higher than that in the 30-min group. Decreased lactate release was found in the Glutamate group compared to the Control group during early reperfusion (p < 0.01), and the entire reperfusion (p < 0.001). No differences were found between the Control and Glutamate groups in alanine exchange. Thus, L-glutamate has a beneficial effect in pig hearts on both functional and metabolic recovery after cold crystalloid cardioplegia and storage when present in a concentration even as low as 2 mmol/L during continuous reperfusion after aortic unclamping. A possible mechanism is a glutamate-induced stimulation of the malate-aspartate shuttle leading to increased intramyocardial lactate utilization.

Arterial bypass graft spasm: an examination of the role of high flow demands and endothelial function in the porcine GEA.

This study examined why an artery becomes vulnerable to spasm when used as a bypass graft. We hypothesized that high flow demands would decrease pressure distally in the conduit (afterload), thus increasing the sensitivity to vasoconstrictors. Furthermore, perioperative endothelial dysfunction would additionally sensitize the artery to constrictors. Six gastroepiploic arteries (GEA, 1.0-1.5 mm diameter, 11 cm length) were harvested from adult pigs (110-125 kg) and mounted on a computer-controlled perfusion system. The inflow pressure was set at 80 mmHg and outflow resistance was adjusted to simulate normal (in situ) or high (coronary bypass graft) flow demands. Gastroepiploic flow and distal pressures were measured at baseline [B] and after adding norepinephrine (NE, 10(-9) M to 10(-5) M). Under normal flow demand, a minimal pressure drop existed across the GEA and flow decreased only at high NE concentrations. High flow demand decreased distal GEA pressure and increased the sensitivity to NE. To block endothelial function N-Monomethyl-L-Arginine, Monoacetate (L-NMMA, 10(-5) M) was then added. Under high flow demand, blocking endothelial function resulted in an additional fivefold increase in sensitivity to NE (ED50 from 9.75 10(-8) M to 2.11 10(-8) M, P < 0.05). It was shown that in long narrow arterial grafts, high flow demands cause cumulative pressure losses. Even with normal endothelial function, these pressure losses render the artery responsive to vasoconstrictors. Endothelial dysfunction additionally increases the sensitivity of the artery. Anastomosis of a small arterial graft to a large myocardial perfusion bed may result in reduced distal conduit pressure and may predispose to the development of myocardial ischemia even when low doses of vasoconstrictors are used. Perioperative endothelial dysfunction may exacerbate this effect.

Superiority of acid extractable glycogen for detection of metabolic changes during myocardial ischaemia.

Various methods for extraction and isolation of myocardial glycogen show different yields and identify different glycogen subsets. The aim of the present study was to identify a glycogen fraction exposed to changes during myocardial ischaemia. Endomyocardial biopsies from 10 pigs were sampled before cardioplegia, after cardioplegic arrest, and after reperfusion. Glycogen yields were compared following five extraction procedures: (1) hot alkaline tissue digestion, (2) homogenization in perchloric acid and subsequent determination in homogenate, (3) homogenization in perchloric acid and subsequent determination in supernatant, (4) homogenization in perchloric acid and subsequent determination in the precipitate redissolved in hot alkaline and (5) homogenization in homogenisation buffer with lysating capacity. Glycogen was isolated on filter-paper and determined enzymatically. Hot alkaline tissue digestion yielded the highest glycogen amounts (63.5 +/- 18.3 nmol/mg wet weight). Glycogen yields in perchloric homogenate and supernatant were 51%, perchloric precipitate 47%, and buffer 30% of these obtained with hot alkaline. Glycogen yields in hot alkaline were comparable to the sum of those obtained in perchloric supernatant ("acid extractable glycogen") and redissolved precipitate ("heavily extracted glycogen") confirming that glycogen yields obtained with hot alkaline digestion represent "total glycogen". Acid extractable glycogen showed superior analytical characteristics compared with the other methods. Acid extractable glycogen demonstrated a consistent decrease during ischaemia whereas total glycogen and glycogen extracted in homogenization buffer tended to decrease. Glycogen in perchloric precipitate remained unchanged during ischaemia. These findings support a revival of the concept that tissue contains two forms of glycogen. Decreases in myocardial glycogen content during myocardial ischaemia are best observed with acid extractable glycogen.