L. M. A. Sassen

Angiotensin Production by the Heart A Quantitative Study in Pigs With the Use of Radiolabeled Angiotensin Infusions

BACKGROUND Beneficial effects of ACE inhibitors on the heart may be mediated by decreased cardiac angiotensin II (Ang II) production. METHODS AND RESULTS To determine whether cardiac Ang I and Ang II are produced in situ or derived from the circulation, we infused 125I-labeled Ang I or II into pigs (25 to 30 kg) and measured 125I-Ang I and II as well as endogenous Ang I and II in cardiac tissue and blood plasma. In untreated pigs, the tissue Ang II concentration (per gram wet weight) in different parts of the heart was 5 times the concentration (per milliliter) in plasma, and the tissue Ang I concentration was 75% of the plasma Ang I concentration. Tissue 125I-Ang II during 125I-Ang II infusion was 75% of 125I-Ang II in arterial plasma, whereas tissue 125I-Ang I during 125I-Ang I infusion was <4% of 125I-Ang I in arterial plasma. After treatment with the ACE inhibitor captopril (25 mg twice daily), Ang II fell in plasma but not in tissue, and Ang I and renin rose both in plasma and tissue, whereas angiotensinogen did not change in plasma and fell in tissue. Tissue 125I-Ang II derived by conversion from arterially delivered 125I-Ang I fell from 23% to <2% of 125I-Ang I in arterial plasma. CONCLUSIONS Most of the cardiac Ang II appears to be produced at tissue sites by conversion of in situ-synthesized rather than blood-derived Ang I. Our study also indicates that under certain experimental conditions, the heart can maintain its Ang II production, whereas the production of circulating Ang II is effectively suppressed.

Myofibrillar Ca2+ sensitization predominantly enhances function and mechanical efficiency of stunned myocardium.

BackgroundMyocardial stunning is characterized not only by a decreased regional postischemic function but also by a relatively high oxygen consumption (ie, decreased mechanical efficiency). Several lines of evidence suggest that the underlying mechanism may involve a decreased sensitivity of the myofibrils to calcium, but in vivo evidence is lacking. We therefore evaluated this hypothesis in vivo using EMD 60263, a calcium-sensitizing agent, which is devoid of any phospho-diesterase- inhibiting properties. Methods and ResultsWe first established the effect of two consecutive doses of EMD 60263 (0.75 and 1.5 mg/kg IV, n=7), administered at 15-minute intervals, on segment length shortening (SLS), external work index (EW; the area inside the left ventricular pressure-segment length loop), myocardial oxygen consumption (MVo2), and mechanical efficiency (EW/ MVo2) in anesthetized pigs with normal myocardium. After the highest dose of EMD 60263, SLS in the distribution area of the left anterior descending coronary artery (LADCA) increased from 13± 1% at baseline to 17± 1% (P<.05). However, EW, MVo2, and EW/MVo2 were not significantly affected (123±10%, 98±9%, and 85±13% of baseline, respectively). In 14 other anesthetized pigs, myocardial stunning was induced by two sequences of 10 minutes of LADCA occlusion and 30 minutes of myocardial reperfusion. After induction of stunning, the two doses of EMD 60263 (n=7) or saline (3 and 6 mL, n=7) were infused. In the distribution area of the LADCA, the stunning protocol caused decreases in SLS from 16±1% to 8±1% (P<.05) and in EW to 49±5% of baseline (P<.05), whereas MVo2 was only minimally affected (P<.05). Consequently, mechanical efficiency decreased to 59±8% of baseline (P<.05). Saline infusion did not affect any of these regional myocardial variables, but after administration of EMD 60263 SLS recovered dose-dependently to 15±2% after the highest dose of the drug. EW and mechanical efficiency also recovered dose-dependently to 89±4% (P<.05 versus stunning) and to 88±7% (NS versus baseline) of baseline, respectively. In the not-stunned segment, SLS increased from 15±2% (at baseline) to 18±2% (after the highest dose), and EW per beat was not changed significantly. An adrenergic mode of action of EMD 60263 was excluded by blocking the α-and β-adrenergic receptors with phentolamine and proprano-lol, respectively, 15 minutes before administration of EMD 60263 (ie, 15 minutes into the second reperfusion period) in five additional experiments. In these experiments the EMD 60263-induced increases in SLS and EW were not attenuated. Because EMD 60263 decreased heart rate from 106±4 to 76±3 beats per minute (P<.05) in the animals with stunned myocardium, we performed five experiments with the specific negative chronotropic compound zatebradine (UL-FS 49, 0.1 to 0.5 mg/kg) to rule out bradycardia as a factor contributing to the effects of EMD 60263. These zatebradine doses lowered heart rate from 116±5 to 55±1 beats per minute (P<.05) but had no effect on SLS of stunned and not-stunned myocardium. ConclusionsCalcium sensitization affects function and mechanical efficiency of stunned myocardium more profoundly than of not-stunned myocardium, lending support to the hypothesis that Ca2+ desensitization of the myofibrils is involved in myocardial stunning.

Development and regression of atherosclerosis in pigs. Effects of n-3 fatty acids, their incorporation into plasma and aortic plaque lipids, and granulocyte function.

Fifty-one pigs were fed a low-cholesterol basal diet, to which either 10% (by weight) of lard fat (group INORM, n = 7), 2% cholesterol plus 8% lard fat (group II, n = 33), or 2% cholesterol plus 4% lard fat plus 4% fish oil (group IIIPREV, n = 11) was added. In all pigs, the left anterior descending coronary artery and the abdominal aorta were denuded at 1 month. In the first 24 hours thereafter, three animals in group II and two in group IIIPREV died suddenly. After 3 months, 0.5% bile acids was added to the diet in groups II and IIIPREV. After 8 months the degree of atherosclerosis was evaluated in groups INORM and IIIPREV and in 14 animals from group II (IIIND). At 4 months, one animal from Group II died of pneumonia. For the next 4 months (postinduction period), the remaining 15 animals from group II received the basal diet, to which either 10% lard fat (group IILF, n = 6) or 5% lard fat plus 5% fish oil (group IIFO, n = 9) was added. The hypercholesterolemic diet increased plasma cholesterol from 2 to 9-12 mM after 8 months. Fish oil had no major effects on plasma lipids during both induction and postinduction. Superoxide production by granulocytes in response to the membrane receptor-dependent N-formyl-methionyl-leucyl-phenylalanine (fMLP) gave a higher response in group IIIND than in group INORM. In group IIIPREV, the response to phorbol myristate acetate (PMA) and fMLP was lowered, while in groups IIFO and IILF the responses to PMA and fMLP were not affected. The response to serum-treated zymosan was similar in all groups. Abrasion caused increases in free cholesterol (40%) and phospholipids (46%) in the abdominal aortas of group INORM animals. Hypercholesterolemia increased both free and esterified cholesterol in the entire aorta. Fish oil prevented accumulation of free cholesterol in the nonabraded ascending aorta during induction and further accumulation of free cholesterol and phospholipids in the abdominal aorta during postinduction. In the nonabraded ascending aorta, triglycerides were significantly (almost five times) lower in group IIFO than in group IILF. During both induction and postinduction, a large incorporation of n-3 polyunsaturated fatty acids (up to 20%) occurred in plasma and aortic cholesterol esters and phospholipids of groups IIFO and IIIPREV.(ABSTRACT TRUNCATED AT 400 WORDS)

Nicorandil-induced changes in the distribution of cardiac output and coronary blood flow in pigs

SummaryThe present investigation was conducted to study systemic and regional haemodynamic effects of nicorandil, a potent coronary vasodilator, after intravenous or local intracoronary administration in anaesthetized or conscious pigs. Intravenous infusions of nicorandil for 10 min in both anaesthetized (15, 30, 75 and 150 μg · kg−1 · min−1) and conscious (20, 40 and 80 μg · kg−1 · min−1) pigs reduced arterial blood pressure, stroke volume, left ventricular end-diastolic pressure (LVEDP) and systemic vascular resistance, but increased heart rate and maxLVdP/dt. Since nicorandil decreased LVEDP at doses which did not affect arterial blood pressure, the drug may be considered as a more potent venodilator than arterial dilator. Nicorandil increased cardiac output only in conscious animals due to a more marked tachycardia (85% after 80 μg · kg−1 · min−1) than in anaesthetized animals (30% after 75 μg · kg−1 · min−1). The nicorandil-induced increase in heart rate and maxLVdP/dt, being substantially attenuated in conscious pigs after treatment with propranolol, can be ascribed to a reflex activation of the sympathetic nervous system following the fall in arterial pressure. Although cardiac output did not change in anaesthetized animals, intravenous infusions of nicorandil did cause a redistribution of blood flow in favour of organs such as the heart, adrenals, spleen, small intestine and brain at the expense of that to the stomach and kidneys; hepatic artery and skeletal muscle blood flow did not change. The increase in myocardial blood flow, primarily to the subepicardial layers, was associated with an enhancement in coronary venous oxygen content and was also noticed after intracoronary infusions of nicorandil (0.6, 1.5, 3 and 6 μg · kg−1 · min−1). The above cardiovascular profile suggests a possible usefulness of nicorandil in angina pectoris as well as congestive heart failure. However, caution is needed because the strong hypotensive action and reflex-mediated tachycardia may under certain conditions aggravate myocardial ischaemia, particularly in the subendocardial layers.

Mechanical efficiency of stunned myocardium is modulated by increased afterload dependency

OBJECTIVE Oxygen consumption (MVO2) of stunned myocardium is relatively high compared to, and poorly correlated with, systolic contractile function. The aim of this study was to investigate whether an increased afterload dependency, induced by the decreased contractility of the stunned myocardium, contributes to the large variability in the mechanical efficiency data. METHODS In 13 anaesthetised open thorax pigs undergoing two cycles of 10 min occlusion of left anterior descending coronary artery and 30 min reperfusion, segment shortening, the slope of end systolic pressure segment length relationship (Ees), external work (EW, derived from the area inside the left ventricular pressure segment length loop), the efficiency of energy conversion (EET, = EW/PLA x 100%, where PLA = total pressure-segment length area), mechanical efficiency (EW/MVO2), and their dependency on left ventricular end systolic pressure (Pes) were determined before and after induction of stunning, and during subsequent inotropic stimulation with dobutamine (1 and 3 micrograms.kg-1.min-1 over 15 min). RESULTS The stunning protocol not only caused significant decreases in segment shortening, external work, energy conversion efficiency, and EW/MVO2 but also increased the afterload dependency of these variables. Before stunning an increase in Pes from 100 to 160 mm Hg decreased segment shortening from 18(SEM 1)% to 14(2)% (P > 0.05) and increased external work from 206(18) to 254(32) mm Hg.mm (P < 0.05). After induction of stunning the same increase in Pes caused a decrease in segment shortening from 9.5(1.8)% to -4.6(2.1)% (P < 0.05) and in external work from 149(21) to -11(10) mm Hg.mm (P < 0.05). The afterload dependency of the PLA was not altered by stunning, but the afterload dependency of energy conversion efficiency increased, since efficiency decreased from 67(3)% to 59(5)% as Pes was increased from 100 to 160 mm Hg before stunning, but from 57(5) to -7(5)% after induction of stunning (P < 0.05). Furthermore, the same increase in Pes resulted in an 8% decrease of EW/MVO2 before stunning and 107% after induction of stunning. Infusion of dobutamine not only restored segment shortening, external work, energy conversion efficiency, and EW/MVO2 of the stunned myocardium, but also attenuated their afterload dependency to pre-stunning levels. CONCLUSIONS Myocardial stunning increases the afterload dependency of segment shortening, external work, energy conversion efficiency, and mechanical efficiency, which can be attenuated by inotropic stimulation with dobutamine. However, the decrease in left ventricular end systolic pressure, which accompanies the induction of stunning, counteracts the decrease in these variables. These two mechanisms can explain most of the reported scatter in mechanical efficiency.

Evidence against a role for dopamine D1 receptors in the myocardium of the pig

1 We investigated the presence of dopamine D1 receptors in the myocardium of anaesthetized pigs using intravenous infusions of dopamine, alone and after α‐ and β‐adrenoceptor blockade and intracoronary infusions of the selective D1 receptor agonist, fenoldopam. 2 Intravenous infusion of dopamine (2.5, 5 and 10 μg kg−1 min−1 for 10 min, n = 6) caused dose‐dependent changes in heart rate (from 94 ± 6 to 132 ± 10 beats min−1, P < 0.05), the maximal rate of rise of left ventricular pressure (LVdP/dtmax; from 2280 ± 170 to 4800 ± 410 mmHgs−1, P < 0.05), mean arterial blood pressure (from 87 ± 5 to 62 ± 3 mmHg) and systemic vascular resistance (from 40 ± 4 to 28 ± 2 mmHg l−1 min, P < 0.05). The increases in heart rate and LVdP/dtmax were abolished when dopamine was infused after α‐ and β‐adrenoceptor blockade. The vasodilator response was, however, only minimally affected. 3 Intravenous infusions of dopamine decreased coronary vascular resistance from 0.90 ± 0.06 to 0.53 ± 0.07 mmHg ml−1 min 100 g (P < 0.05). This action of dopamine was not observed when dopamine was infused after blockade of the α‐ and β‐adrenoceptors. 4 Pretreatment with α‐ and β‐adrenoceptor blockade had no effect or only slightly attenuated the dopamine‐induced decrease in vascular resistance of the brain, kidneys, adrenals and small intestine. 5 In 7 animals, intracoronary doses of 0.04, 0.1, 0.2 and 0.4 μg kg−1 min−1 of fenoldopam had no effect on coronary venous oxygen content, local myocardial oxygen consumption, coronary blood flow or coronary vascular resistance. However, systemic effects were observed at the highest two doses, as manifested by a drop in mean arterial blood pressure from 82 ± 4 to 72 ± 4 mmHg (P < 0.05) due to peripheral vasodilatation (e.g. cerebral vascular bed). Heart rate, LVdP/dtmax, regional myocardial segment length shortening and left ventricular end‐diastolic pressure were not affected at these doses. In 2 animals the infusion rate was increased to 4 μg kg−1 min−1, but again there was no evidence for coronary vasodilatation. 6 We conclude that the intravenous infusion of dopamine after α‐ and β‐adrenoceptor blockade and the intracoronary infusion of fenoldopam provided no evidence for a major role of D1 receptors in the coronary circulation of pigs. The absence of any effect of the employed doses of fenoldopam on LVdP/dtmax and on regional myocardial segment length shortening also indicates that fenoldopam does not exhibit any inotropic action in this species.

Haemodynamic profile of the potassium channel activator EMD 52692 in anaesthetized pigs.

1 The systemic and regional haemodynamic effects of the potassium channel activator EMD 52692 or its solvent were investigated after intravenous and after intracoronary administration in anaesthetized pigs. 2 Consecutive intravenous 10 min infusions of EMD 52692 (0.15, 0.30, 0.60, 1.20 μg kg−1 min−1; n = 7) dose‐dependently decreased mean arterial blood pressure by up to 50%. This was entirely due to peripheral vasodilatation, since cardiac output did not change. Heart rate increased by up to 50%, while left ventricular end diastolic pressure decreased dose‐dependently from 6 ± 1 mmHg to 3 ± 1 mmHg (P > 0.05), and stroke volume decreased from 30 ± 2 ml to 21 ± 2 ml (P > 0.05). Left ventricular dP/dtmax was not affected. 3 Although cardiac output did not change, EMD 52692 caused a redistribution of blood flow from the arteriovenous anastomoses to the capillary channels. Blood flow to the adrenals, small intestine, stomach, bladder, spleen and brain increased, while renal blood flow decreased and blood flow to several muscle groups and skin were not altered. Vascular conductance was increased dose‐dependently in all organs, except for the kidneys, where after the initial increase, vascular conductance returned to baseline with the highest dose. Particularly striking were the effects on the vasculature of the brain. With the highest dose of EMD 52692 blood flow more than doubled, while vascular conductance increased four fold. 4 Transmural myocardial blood flow increased slightly, which was entirely due to an increase in subepicardial blood flow. Myocardial O2‐consumption and segment length shortening were not significantly affected. 5 After consecutive 10 min intracoronary infusions (0.0095, 0.019, 0.0375 and 0.075 μg kg−1 min−1; n = 7) into the left anterior descending coronary artery (LADCA), mean arterial blood pressure was maintained with the lowest two doses, but decreased by up to 15% with the higher doses, whereas heart rate increased by up to 24%. Blood flow to the LADCA‐perfused myocardium doubled with the highest dose, the subepicardium benefitting the most. Coronary venous O2‐saturation increased dose‐dependently from 23 ± 2% to 60 ± 4%, while myocardial O2‐consumption of the LADCA‐perfused myocardium was not affected by the drug. 6 It is concluded that EMD 52692 is a potent vasodilator, with particularly pronounced effects on vasculature of the brain. Its selectivity for vascular smooth muscle cells exceeds that for the myocytes, since with doses that are much higher than those of potential clinical interest no negative inotropic effects were observed. The compound primarily dilates arteries but some venodilatation may also occur.

Expression and immunohistochemical localization of heat-shock protein-70 in preconditioned porcine myocardium

Brief periods of ischemia not only cause a long lasting (hours to days) myocardial contractile dysfunction (stunning) but also increase the tolerance for irreversible damage during a subsequent ischemic episode, a phenomenon called ischemic preconditioning.1J Heat-shock proteins, in particular HSP-70, have been postulated in myocardial protection against irreversible damage due to i~chemia .~ It is known that in vivo as well as in vim, metabolic stressors (e.g., ischemia) and heat lead to the rapid synthesis of 70 kD heat-shock protein (HSP-70) family.3.4 However, the cellular distribution and its potential role in ischemic preconditioning have not yet been well established. Brief periods of myocardial ischemia in rabbits also cause a rapid expression of HSP-70, which is detectable at the protein level within 2 h.4 Recently, we have shown that porcine myocardium responds to ischemia and repehsion by inducing a battery of genes.5-7 In this study, we examined the expression pattern and cellular distribution of HSP-70 in a porcine model of myocardial stunning and preconditioning achieved by two cycles of 10 min of ischemia and 30 min of reperfusion followed by additional 90 and 180 min of reperfusion.

The central and regional cardiovascular responses to intravenous and intracoronary administration of the phenyldihydropyridine elgodipine in anaesthetized pigs.

1 The central and regional cardiovascular responses to intravenous (0.3, 1.0, 3.0 and 10.0 μg kg−1 min−1) and intracoronary (0.3, 0.9, 3.0 and 4.5 μg kg−1 min−1) infusions of elgodipine, a phenyldihydropyridine, and its solvent were studied in anaesthetized pigs. 2 Elgodipine (i.v.) caused dose‐dependent decreases in arterial blood pressure (up to 44%) and systemic vascular resistance (up to 48%), whereas heart rate, LV dP/dtmax, left ventricular filling pressure, cardiac output and segment length shortening did not change. The absence of a negative inotropic effect with the employed doses was confirmed by the intracoronary infusions; with the lowest dose (0.3 μg kg−1 min−1) both LV dP/dtmax and segment length shortening decreased by less than 10%. With 0.9 μg kg−1min−1 (intracoronary) the negative inotropic properties of the drug became apparent as LV dP/dtmax and segment length shortening decreased by 20% and 33%, respectively, whereas heart rate and left ventricular filling pressure were not affected. 3 Transmural myocardial blood flow did not change during intravenous infusion of elgodipine, as vasodilatation, more pronounced in the subepicardial than in the subendocardial layers, compensated for the decrease in arterial perfusion pressure. The intracoronary infusions revealed that the decrease in normalized subendocardial/subepicardial blood flow ratio was not secondary to the fall in arterial blood pressure. 4 Myocardial oxygen consumption decreased during both the i.v. and the intracoronary administration of elgodipine. With the i.v. administration the decrease was secondary to the hypotensive action of the drug, whereas with the intracoronary administration the negative inotropic properties played the dominant role. 5 Elgodipine (i.v.), although not affecting total cardiac output, caused a redistribution in favour of the nutritional blood flow at the expense of the arteriovenous anastomotic (AVA) blood flow. Up to an infusion rate of 3.0 μg kg−1 min−1 the decrease in AVA‐flow was due to a fall in arterial blood pressure, but at the highest infusion rate both the decrease in arterial perfusion pressure and an increase in their resistance contributed to a further decrease in AVA blood flow. 6 The skeletal muscles benefited most from the elgodipine(i.v.)‐induced increase in nutritional blood flow, but vasodilatation was not uniform for all muscle groups. Up to an infusion rate of 3 μg kg−1 min−1 the vasodilatation in the renal vascular bed was more pronounced in the inner than in the outer cortex, but, at 10 μg kg−1 min−1, vascular resistances of both cortical layers returned to baseline values. In all regions of the brain, blood flow was maintained until the highest infusion rate was given. With 10 μg kg−1 min−1 only flow to the vital parts of the brain (diencephalon and brain stem) was maintained. Blood flows to the skin and various abdominal organs were well maintained up to 3 μg kg−1 min−1 but, at the highest dose, a decrease was observed in blood flow to the adrenals and spleen. Vascular resistances of all these organs and tissues decreased dose‐dependently. 7 The potent systemic and coronary vasodilator actions of elgodipine during i.v. administration, which were not accompanied by negative inotropic and positive chronotropic properties or decreases in the perfusion of vital organs, warrant further study as this compound could be useful in the treatment of essential hypertension, myocardial ischaemia and, possibly, moderate chronic heart failure.

Assessment of the role of the renin-angiotensin system in cardiac contractility utilizing the renin inhibitor remikiren.

1 The role of the renin‐angiotensin system in the regulation of myocardial contractility is still debated. In order to investigate whether renin inhibition affects myocardial contractility and whether this action depends on intracardiac rather than circulating angiotensin II, the regional myocardial effects of systemic (i.v.) and intracoronary (i.c.) infusions of the renin inhibitor remikiren, were compared and related to the effects on systemic haemodynamics and circulating angiotensin II in open‐chest anaesthetized pigs (25–30 kg). The specificity of the remikiren‐induced effects was tested (1) by studying its i.c. effects after administration of the AT1‐receptor antagonist L‐158,809 and (2) by measuring its effects on contractile force of porcine isolated cardiac trabeculae. 2 Consecutive 10 min i.v. infusions of remikiren were given at 2, 5, 10 and 20 mg min−1. Mean arterial pressure (MAP), cardiac output (CO), heart rate (HR), sytemic vascular resistance (SVR), myocardial oxygen consumption (MVO2) and left ventricular (LV) dP/dtmax were not affected by remikiren at 2 and 5 mg min−1, and were lowered at higher doses. At the highest dose, MAP decreased by 48%, CO by 13%, HR by 14%, SVR by 40%, MVO2 by 28% and LV dp/dtmax by 52% (mean values; P<0.05 for difference from baseline, n=5). The decrease in MVO2 was accompanied by a decrease in myocardial work (MAP x CO), but the larger decline in work (55% vs. 28%; P<0.05) implies a reduced myocardial efficiency ((MAP x CO)/MVO2). 3 Consecutive 10 min i.c. infusions of remikiren were given at 0.2, 0.5, 1, 2, 5 and 10 mg min−1. MAP, CO, MVO2 and LV dP/dtmax were not affected by remikiren at 0.2, 0.5 and 1 mg min−1, and were reduced at higher doses. At the highest dose, MAP decreased by 31%, CO by 26%, MVO2 by 46% and LV dP/dtmax by 43% (mean values; P<0.05 for difference from baseline, n=6). HR and SVR did not change at any dose. 4 Thirty minutes after a 10 min i.v. infusion of the AT1 receptor antagonist, L‐158,809 at 1 mg min−1, consecutive 10 min i.c. infusions (n=5) of remikiren at 2, 5 and 10 mg min−1 no longer affected CO and MVO2, and decreased LV dP/dtmax by maximally 27% (P<0.05) and MAP by 14% (P<0.05), which was less than without AT1‐receptor blockade (P<0.05). HR and SVR remained unaffected. 5 Plasma renin activity and angiotensin I and II were reduced to levels at or below the detection limit at doses of remikiren that were not high enough to affect systemic haemodynamics or regional myocardial function, both after i.v. and i.c. infusion. 6 Remikiren (10−10 to 10−4 m) did not affect contractile force of porcine isolated cardiac trabeculae precontracted with noradrenaline. In trabeculae that were not precontracted no decrease in baseline contractility was observed with remikiren in concentrations up to 10−5 m, whereas at 10−4 m baseline contractility decreased by 19% (P<0.05). 7 Results show that with remikiren i.v., at the doses we used, blood pressure was lowered primarily by vasodilatation and with remikiren i.e. by cardiac depression. The blood levels of remikiren required for its vasodilator action are lower than the levels affecting cardiac contractile function. A decrease in circulating angiotensin II does not appear to be the sole explanation for these haemodynamic responses. Data support the contention that myocardial contractility is increased by renin‐dependent angiotensin II formation in the heart.