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 anesthetized pigs using intravenous infusions of dopamine, alone and after alpha- and beta-adrenoceptor blockade and intracoronary infusions of the selective D1 receptor agonist, fenoldopam. 2. Intravenous infusion of dopamine (2.5, 5 and 10 micrograms 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 less than 0.05), the maximal rate of rise of left ventricular pressure (LVdP/dtmax; from 2280 +/- 170 to 4800 +/- 410 mmHgs-1, P less than 0.05), mean arterial blood pressure (from 87 +/- 5 to 62 +/- 3 mmHg) and systemic vascular resistance (from 40 +/- 4 to 28 +/- 2 mmHgl-1 min, P less than 0.05). The increases in heart rate and LVdP/dtmax were abolished when dopamine was infused after alpha- and beta-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 less than 0.05). This action of dopamine was not observed when dopamine was infused after blockade of the alpha- and beta-adrenoceptors. 4. Pretreatment with alpha- and beta-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 0.4g kg1- 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 +/- 4mmHg (P < 0.05) due to peripheral vasodilatation (e.g. cerebral vascular bed). Heart rate, LVdP/dt,.,, 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 4jug kg1 min 1, but again there was no evidence for coronary vasodilatation. 6. We conclude that the intravenous infusion of dopamine after alpha- and beta-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/dt.mx and on regional myocardial segment length shortening also indicates that fenoldopam does not exhibit any inotropic action in this species.

Cardiovascular profile of 5 novel nitrate-esters: a comparative study with nitroglycerin in pigs with and without left ventricular dysfunction

1. Four cumulative 10 min intravenous infusions of 0.05, 0.2, 0.5 and 2.0 mg min-1 were used to compare the cardiovascular profile of 5 novel nitrate-esters dissolved in Intralipid 10% to that of nitroglycerin (GTN) in conscious pigs. 2. Infusion of Intralipid 10% alone had no effect on any of the systemic haemodynamic parameters. GTN infusions decreased mean arterial blood pressure dose-dependently from 94 +/- 2 mmHg to 79 +/- 3 mmHg (P less than 0.05) and raised cardiac output from 2.74 +/- 0.09 l min-1 to 3.40 +/- 0.18 l min-1 (P less than 0.05) due to an increase in heart rate (by up to 43 +/- 3%), as stroke volume decreased slightly. Systemic vascular resistance decreased (by 32 +/- 3%) and left ventricular end-diastolic pressure fell from 5.2 +/- 0.4 mmHg to 2.2 +/- 0.5 mmHg (both P less than 0.05). 3. The novel compounds CEDO 8811, CEDO 8834 and CEDO 8901 increased cardiac output only at the highest dose (7%, 8% and 9%, respectively). There was no change in mean arterial blood pressure as the increase in cardiac output was counterbalanced by arterial vasodilatation. All three compounds reduced left ventricular end-diastolic pressure slightly. 4. CEDO 8816 was a more potent arterial and venodilator than the aforementioned CEDO compounds, as the decreases in systemic vascular resistance and left ventricular end-diastolic pressure were already significant at lower doses. The fall in stroke volume was fully compensated by the increase in heart rate and as a result cardiac output increased by 11 +/- 3% (P less than 0.05) at the highest dose. 5. CEDO 8956 was the most potent vasodilator of the novel compounds and exhibited a cardiovascular profile similar to that of GTN. Left ventricular end-diastolic pressure decreased significantly during infusion of 0.2mgmin-'. Mean arterial blood pressure decreased by 11 +/- 2% (P < 0.05) in spite of an increase in cardiac output by up to 20 +/- 2% (P < 0.05), due to a decrease (by 27 +/- 1%, P <0.05) in systemic vascular resistance. The increases in heart rate (20 +/- 5%, P < 0.05) and LVdP/dtmax (38 +/- 4%, P < 0.05) were, however, considerably less after CEDO 8956 than after GTN. 6. The potential of CEDO 8956 in the treatment of chronic left ventricular dysfunction was evaluated during administration to conscious pigs (21-23 kg), in which the left circumflex coronary artery was ligated 4 weeks earlier. In these animals, baseline values for cardiac output and LVdP/dtx were lower and those of systemic vascular resistance and left ventricular end-diastolic pressure were higher than in the first group of experiments. 7. Both GTN and CEDO 8956 in doses of 0.05 to 2.0 mg inm increased cardiac output dosedependently (by up to 34% and 19%, respectively). The decrease in systemic vascular resistance was larger with GTN (35%) than with CEDO 8956 (17%), which resulted in a 13% decrease in mean arterial pressure during infusion of GTN, whereas there was no change in mean arterial pressure during infusion of CEDO 8956. Both compounds increased LVdP/dt,,,,X (by 48% and 30%, respectively) and lowered left ventricular end-diastolic pressure to normal levels. 8. At a dose of 1.0Omg min- 1, both GTN and CEDO 8956 increased left ventricular blood flow parallel to the increase in myocardial oxygen demand. At this dose, GTN also caused vasodilatation in the vascular beds of the brain, kidneys and adrenals. With CEDO 8956 no significant changes were achieved. 9. We conclude that the cardiovascular profile of CEDO 8956 in both normal animals and in animals with chronic left ventricular dysfunction warrants further study on its usefulness in the treatment of a number of cardiovascular disorders.

Endothelium dependent vasodilatation following brief ischaemia and reperfusion in anaesthetised swine

STUDY OBJECTIVE

The aim as to compare the responses of intracoronary infusions of ATP, an endothelium dependent vasodilator, with adenosine following brief ischaemia (10 min) and reperfusion in a model of myocardial stunning.

DESIGN

In group 1 (n = 6), coronary blood flow and endocardial (endo) and epicardial (epi) percent segment length shortening were measured in the distribution of the left anterior descending coronary artery before and during maximal intracoronary infusions of either adenosine or ATP (20 micrograms.kg-1.min-1). Measurements were obtained before and after myocardial stunning both at control heart rate and during atrial pacing (150 beats.min-1). In group 2 (n = 6), myocardial blood flows by microspheres and arterial-venous lactate and oxygen differences were determined following the same ischaemia-reperfusion protocol to characterise transmural changes in blood flow and metabolism in this model of stunning.

EXPERIMENTAL MATERIAL

The experiments were done on 12 anaesthetised swine, weight 25-39 kg.

MEASUREMENTS AND MAIN RESULTS

In group 1, baseline endo and epi segment length shortening were 16(SD 3)% and 14(6)% and following reperfusion were reduced to 10(4)% and 8(6)% respectively (p less than 0.05). Prior to stunning, minimal coronary resistances during adenosine and ATP were 0.81(0.40) and 0.76(0.25) mm Hg.min.ml-1 respectively and following reperfusion were 0.86(0.31) (NS) and 0.85(0.23) (NS) mm Hg.min.ml-1 respectively. Infusion of either vasodilator enhanced function by 30% following reperfusion whereas no such effect was observed prior to ischaemia. In group 2, no maldistribution of blood flow was observed following the same ischaemia-reperfusion protocol to account for this vasodilator enhancement in function. Percent lactate extraction values were 29(11)% and 25(14)% at preischaemic control and paced heart rates respectively, and following reperfusion were lowered to 0(12)% without pacing (p less than 0.05) and -1(34)% during pacing (p less than 0.05).

CONCLUSIONS

Brief ischaemia and reperfusion in swine induces myocardial stunning without altering the vasodilator responses of either ATP, an endothelium dependent vasodilator, or adenosine. Recruitment in postischaemic segment length shortening was observed during infusions of both vasodilators at a time when maldistribution of flow was not observed. Possible mechanisms include either enhanced washout of lactate from the reperfused myocardium or greater utilisation of substrates during higher blood flows.

L-propionylcarnitine increases postischemic blood flow but does not affect recovery of energy charge

Effects of pretreatment with L-propionylcarnitine (50 mg/kg, n = 9) or saline (n = 10) were studied in open-chest anesthetized pigs, in which ischemia was induced by decreasing left anterior descending coronary artery blood flow to 20% of baseline. After 60 min of ischemia, myocardium was reperfused for 2 h. In both groups, flow reduction abolished contractile function of the affected myocardium and caused similar decreases in ATP (by 55%) and energy charge [(ATP + 0.5ADP)/(ATP + ADP + AMP); decrease from 0.91 to 0.60], mean arterial blood pressure (by 10-24%), the maximum rate of rise in left ventricular pressure (by 26-32%), and cardiac output (by 20-30%). During reperfusion, "no-reflow" was attenuated by L-propionylcarnitine, because myocardial blood flow returned to 61 and 82% of baseline in the saline- and L-propionylcarnitine-treated animals, respectively. Cardiac output of the saline-treated animals further decreased (to 52% of baseline), and systemic vascular resistance increased from 46 +/- 3 to 61 +/- 9 mmHg.min.l-1, thereby maintaining arterial blood pressure. In L-propionylcarnitine-treated pigs, cardiac output remained at 75% of baseline, and systemic vascular resistance decreased from 42 +/- 3 to 38 +/- 4 mmHg.min.l-1. In both groups, energy charge but not the ATP level of the ischemic-reperfused myocardium tended to recover, whereas the creatine phosphate level showed significantly more recovery in saline-treated animals. We conclude that L-propionylcarnitine partially preserved vascular patency in ischemic-reperfused porcine myocardium but had no immediate effect on "myocardial stunning." Potential markers for long-term recovery were not affected by L-propionylcarnitine.

Cardiovascular profile of the new dihydropyridine derivative S12968

The cardiovascular profile of S12968 was evaluated in anaesthetized pigs, using cumulative 15-min i.v. infusions of 1.25, 2.5, 5, 10 and 20 micrograms.kg-1.min-1 (n = 7) or equal volumes of its solvent (n = 7). S12968 decreased mean arterial blood pressure from 94 +/- 4 to 66 +/- 3 mm Hg (P less than 0.05) and cardiac output from 2.7 +/- 0.2 to 2.2 +/- 0.2 l.min-1 (P less than 0.05), had no effect on heart rate and left ventricular end-diastolic pressure, but decreased maxLVdP/dt (maximal rate of rise in left ventricular pressure) by up to 35 +/- 3% (P less than 0.05). With doses higher than 10 micrograms.kg-1.min-1 transmural left ventricular blood flow increased by up to 49 +/- 22% (P less than 0.05), favouring the subepicardium over the subendocardium. Myocardial oxygen consumption decreased by 22 +/- 7 and 32 +/- 8% (P less than 0.05) during infusion of 10 and 20 micrograms.kg-1.min-1, respectively. Heart rate, left ventricular end-diastolic pressure and arterial blood pressure were not affected, but maxLVdP/dt (partially) and cardiac output returned to pre-drug values a during a 60-min post-infusion period. In conclusion, S12968 exhibited a negative inotropic effect at low doses. However, with higher doses and after discontinuation of the infusion, vasodilatation occurred, while the negative inotropy disappeared. It is possible that an active metabolite, acting preferentially on the vasculature, was responsible for the vasodilatation.

Cardiovascular effects of elgodipine in conscious pigs with a normal coronary circulation and in conscious pigs with a healed myocardial infarction

The cardiovascular effects of the phenyldihydropyridine derivative elgodipine (0.3, 1, 3, 10, and 30 microgram/kg/min) were studied in normal conscious pigs and in pigs with chronic left ventricular dysfunction (LVD, caused by coronary artery occlusion) without and after beta-adrenoceptor blockade with propranolol (0.5 mg/kg + 0.5 mg/kg/h). In normal pigs, elgodipine increased cardiac output from 2.57 +/- 0.09 to 5.21 +/- 0.24 L/min (p less than 0.05) as a result of a doubling of the heart rate. Mean arterial blood pressure decreased from 94 +/- 2 to 76 +/- 3 mm Hg (p less than 0.05) as a result of a decrease in systemic vascular resistance. Left ventricular (LV) dP/dtmax increased (by up to 78 +/- 9%), but left ventricular end-diastolic pressure (LVEDP) remained unchanged. After propranolol administration elgodipine did not increase LV dP/dtmax, and the increase in heart rate was attenuated, resulting in a smaller increase in cardiac output (from 2.11 +/- 0.13 to 3.09 +/- 0.23 L/min, p less than 0.05), but an unchanged vasodilator response. In pigs with LVD, elgodipine increased cardiac output and LV dP/dtmax less than in normal animals, but the vasodilator response was not affected. LVEDP decreased from 14.6 +/- 1.6 to 11.7 +/- 2.5 mm Hg (p less than 0.05). In animals with LVD, propranolol caused a more severe depression of systemic hemodynamics, but did not modify the cardiovascular responses to elgodipine. Its cardiovascular profile suggests that elgodipine may not only be useful in the treatment of cardiovascular disorders for which other dihydropyridines are already in use, but also in mild chronic heart failure.

Coronary stenting with a new, radiopaque, balloon-expandable endoprosthesis in pigs

BACKGROUND

Intracoronary stents may be effective when used as "bail-out" devices for acute complications after percutaneous transluminal coronary angioplasty. Furthermore, preliminary reports have demonstrated some promising results with stents with regard to the reduction of restenosis. Several stent devices are available for preclinical and clinical evaluation. The use of these stainless-steel stents has been limited by poor visibility during fluoroscopy and thrombogenicity during the first days to weeks after implantation. We therefore investigated the immediate and short-term effects on arterial patency of a new, radiopaque, balloon-expandable coil stent in normal coronary arteries of pigs.

METHODS AND RESULTS

In 10 animals, a stent was placed in two of the three epicardial coronary arteries. During the implantation procedure, the animals received heparin; after the procedure, no antithrombotic drugs were administered. After 1 week (five animals and 10 stents) or 4 weeks (five animals and 10 stents), repeat angiography was performed, followed by pressure-fixation of the coronary arteries for light and electron microscopic examination. Angiographic analysis revealed that all stented coronary segments were patent and without signs of intraluminal defects. Scanning electron microscopy showed complete endothelial covering of all stents within 7 days. Light microscopy showed a reduced tunica media locally under the stent wires, which resulted from exerted pressure. The neointima on top of the stent wires measured 56 microns (range, 42-88 microns) after 1 week and 139 microns (range, 84-250 microns) after 4 weeks.

CONCLUSIONS

Results from this study show that this radiopaque endoprosthesis can be safely placed in normal coronary arteries of pigs. After 4 weeks, all stents were patent and there was no need for additional antithrombotic treatment, whereas neointimal proliferation was limited.

Effects of 5-hydroxytryptamine on capillary and arteriovenous anastomotic blood flow in the human hand and forearm and in the pig hind leg

The effects of intraarterially infused serotonin (5-HT) on capillary and arteriovenous anastomotic (AVA) blood flow were investigated in the hand and forearm of 19 healthy volunteers, and in the hind leg of six anesthetized pigs using radioactive microspheres with a diameter of 15 microns. The 5-HT2-receptor antagonist ketan-serin was used in an attempt to identify the receptors involved. None of the drugs in the doses used induced systemic hemodynamic effects. Low doses of 5-HT significantly increased forearm blood flow with a maximum response at the dose of 1 ng/kg/min (68 +/- 14%, p less than 0.05), whereas only at the highest dose of 80 ng/kg/min was a net decrease in forearm blood flow measured (-28 +/- 6%, p less than 0.05). Conversely, finger blood flow was not influenced by the lower doses of 5-HT, whereas a major reduction was observed at the highest dose (-90 +/- 3%). Ketanserin increased both total forearm blood flow and AVA blood flow. The drug blunted the constrictor response to 5-HT in the forearm but only slightly attenuated this response in the finger. The percentage AVA blood flow in the human hand and forearm was not influenced by an infusion of 5-HT at 80 ng/kg/min alone. However, after pretreatment with ketanserin, which itself increased the AVA component, this dose of 5-HT significantly reduced AVA flow. In the pig, total femoral blood flow was not influenced by 5-HT, but AVA blood flow was significantly reduced and capillary skin blood flow increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nisoldipine on recovery of coronary blood flow, sarcoplasmic reticulum function and other biochemical parameters in post-ischaemic porcine myocardium

The effects of nisoldipine (0.1 micrograms/kg/min; n = 9) or its solvent (n = 9) were studied in pigs, in which left anterior descending coronary artery (LADCA) blood flow in both groups was reduced to 20% of baseline for 60 min and reperfused for 2 hr. Infusions were started at 30 min of ischaemia and lasted throughout reperfusion. In both groups, flow reduction abolished regional contractile function and caused similar decreases in the level of creatine phosphate (CP; by 70%) and the energy charge (from 0.91 to 0.69), mean arterial blood pressure (by 25%), LVdP/dtmax (by 30%) and cardiac output (by 30%). During ischaemia LADCA blood flow slightly increased (from 14 +/- 8 to 24 +/- 6 mL/min/100 g; P less than 0.05) in the nisoldipine-treated animals, resulting in an increase in CP to 91 +/- 24% of baseline and preventing further decreases in energy charge, as observed in the solvent-treated animals. After 2 hr of reperfusion in neither group return of contractile function of the post-ischaemic myocardium was observed. Post-ischaemic blood flow in the nisoldipine-treated pigs increased from 24 +/- 6 mL/min/100 g to 76 +/- 14 mL/min/100 g and from 19 +/- 6 mL/min/100 g to 41 +/- 6 ml/min/100 g in the solvent-treated animals (P less than 0.05) after 2 hr of reperfusion. Myocardial work was significantly higher in the nisoldipine-treated animals (111 +/- 15 mmHg.L/min as compared to 69 +/- 14 mmHg.L/min in the solvent-treated pigs after 2 hr of ischaemia). The energy charge of the post-ischaemic myocardium was similar for both groups (0.84 +/- 0.02 for the nisoldipine-treated and 0.83 +/- 0.03 for the solvent-treated animals). The rate of sarcoplasmic reticular Ca2+ uptake of the non-ischaemic segment of the nisoldipine-treated animals was 61% higher (P less than 0.05) than that of the solvent-treated animals. In the post-ischaemic myocardium similar rates of Ca2+ uptake were found in both groups, but the activities were markedly lower as compared to the non-ischaemic myocardium. It is concluded that nisoldipine increases blood flow during reperfusion, which may have been caused by coronary vasodilatation. However, attenuation of the "no-reflow" phenomenon also contributed, since more rapid rephosphorylation of ADP leading to an increase in CP during ischaemia may have preserved jeopardized cells. Moreover, nisoldipine increases the sarcoplasmic reticular Ca2+ pump activity independent of ischaemia, which may have contributed in reducing the Ca2+ overload.

Effects of dilevalol in the anesthetized pig with a partially occluded coronary artery

The beta-adrenoceptor antagonist dilevalol in a total dose of 430 micrograms/kg i.v., potently suppressed isoprenaline-induced increases in heart rate and max LVdP/dt (dose ratios of 42 +/- 6 and 38 +/- 5, respectively, in anesthetized pigs), but a dose of 1430 micrograms/kg did not appreciably modify phenylephrine-induced increases in arterial blood pressure (dose ratio less than 4) in both anesthetized and conscious pigs. The actions of dilevalol on ischemic myocardium of anesthetized pigs were investigated following a reduction of left anterior descending artery flow by 85-90%. Dilevalol (300 micrograms/kg), administered after 15 minutes of ischemia, did not affect the ischemia-induced changes in systemic hemodynamics (such as heart rate, max LVdP/dt and cardiac output), myocardial perfusion, and wall-thickening of the ischemic segment during the following 15 minutes of ischemia and 2 hours of reperfusion. The reasons for the lack of antiischemic actions are most likely the absence of negative chronotropy and an absence of afterload reduction by dilevalol.

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 micrograms 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 less than 0.05), and stroke volume decreased from 30 +/- 2 ml to 21 +/- 2 ml (P less than 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 microgram 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.

Adverse hemodynamic effects and echocardiographic consequences of pericardial closure soon after sternotomy and pericardiotomy

The acute hemodynamic and echocardiographic effects of pericardial closure on cardiac function were studied in 11 pigs during steady-state anesthesia and ventilation. Observations were made after sternotomy, both while the pericardium was open and after it had been closed, and then after closure of the chest, after the pericardium had been reopened by removing the pericardial suture through the chest wall. In five pigs, further observations were made when a suture was tightened to close the pericardium while the chest remained closed. Closure of the pericardium when the chest was open reduced cardiac output by 14% and mean stroke volume by 19% (both p less than 0.05). Systemic vascular resistance increased by 15% when the pericardium was closed while the chest was open (NS), and increased by 19% when it was closed while the chest was closed (p less than 0.05). Heart rate did not change significantly, and the systemic blood pressure was maintained (-8%, NS). All these effects were reversed by opening the pericardium. Intrathoracic epicardial echocardiographic monitoring of the left ventricle showed that its end-diastolic dimension increased (by 11%, p less than 0.05) when the pericardium was opened. After chest closure, paradoxical motion of the interventricular septum was consistently demonstrated only during ventilation, and it was not related to whether or not the pericardium was open. This study suggests that cardiac function may be impaired by pericardial closure after cardiac surgery because of some degree of constriction of the heart chambers, although acute circulatory responses compensate for the mild decrease in stroke volume. Monitoring of blood pressure alone cannot document the subtle circulatory changes induced by pericardial closure, and therefore it is not a reliable guide to decisions of whether to close the pericardium or leave it open in individual patients.

Redistribution of cardiac output caused by opening of arteriovenous anastomoses by a combination of azaperone and metomidate

The effects of the butyrophenone, azaperone 5 mg kg-1 i.m. alone and after addition of the imidazole derivative metomidate 6 mg kg-1 i.v. were studied in eight conscious pigs. Fifteen minutes after administration of azaperone, systemic arterial pressure was reduced by 35% as a result of a 45% increase in systemic vascular conductance and 10% decrease in cardiac output (Q). After azaperone, 23% of the radioactive labelled microspheres (15 (SD 1) microns) injected into the left atrium were detected in the lungs as a result of opening of arteriovenous anastomoses (baseline 3%). The increase in arteriovenous anastomotic blood flow was at the expense of the nutritional (= capillary) channels. Flow to the brain was maintained, but that to the left ventricle decreased in parallel with the reduction in arterial pressure. Vascular conductance of most other organs, except the skin, increased or was maintained. The addition of metomidate had no effect on Q because an increase in stroke volume (by 30%) compensated for the decrease in heart rate. Systemic vascular conductance decreased, most noticeably in the brain, left ventricle and skeletal muscle. We conclude that azaperone alone and in combination with metomidate had only a moderate effect on Q, but caused a redistribution in favour of arteriovenous anastomoses.

Nisoldipine improves blood flow to skeletal muscles in conscious pigs with chronic heart failure

We studied the acute effects of the calcium antagonist nisoldipine in 10 conscious pigs with chronic heart failure. Left ventricular dysfunction was induced by permanent ligation of the left circumflex coronary artery. Two to three weeks after myocardial infarction the effects of four consecutive 10 min intravenous infusions of nisoldipine (0.05; 0.1; 0.25 and 0.5 micrograms kg-1 min-1) or its solvent on systemic haemodynamics were evaluated. In addition, we used the radioactive microsphere technique to study the distribution of cardiac output after each dose of nisoldipine. Nisoldipine significantly (P less than 0.05) increased heart rate (from 144 +/- 9 to 161 +/- 8 beats min-1), cardiac output (from 2.1 +/- 0.1 to 2.9 +/- 0.2 l min-1), stroke volume (from 14 +/- 1 to 18 +/- 1 ml) and left ventricular dP/dtmax (from 2600 +/- 100 to 3500 +/- 250 mmHg s-1), but had no effect on arterial blood pressure. Left ventricular end-diastolic pressure (from 19 +/- 2 to 16 +/- 1 mmHg) and systemic vascular resistance (from 52 +/- 3 to 37 +/- 3 mmHg min l-1) decreased after nisoldipine. The nisoldipine-induced increase in cardiac output did not affect blood flow to the kidneys, brain, liver or skin, but perfusion of the stomach (84%), adrenals (84%) and normal myocardium (from 200 +/- 25 to 321 +/- 38 ml min-1 100 g-1) as well as infarcted myocardium (from 41 +/- 8 to 61 +/- 19 ml min-1 100 g-1) increased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Nimodipine has no effect on the cerebral circulation in conscious pigs, despite an increase in cardiac output

1. We studied the effects of four doses of nimodipine (0.5, 1, 2 and 4 micrograms kg-1 min-1) on systemic haemodynamics and on regional vascular beds, in particular the cerebral circulation, in conscious pigs. 2. Nimodipine caused dose-dependent, probably reflex-mediated, increases in heart rate (42% with the highest dose) and cardiac output (54%), while arterial blood pressure was only minimally affected. Left ventricular end-diastolic pressure and systemic vascular resistance decreased dose-dependently (35-40% at the highest dose) while stroke volume remained unchanged. 3. Total brain blood flow was not affected by the drug. Furthermore, we could not demonstrate any regional cerebral differences, as blood flows to both cerebral hemispheres as well as the diencephalon, cerebellum and brain stem remained unchanged. 4. Blood flow to the kidneys, liver, small intestine and skin also did not change. Nimodipine caused dose-dependent increases in blood flow to the stomach (95%), myocardium (97%) and adrenal glands (102%), while blood flow to skeletal muscles (267%) increased most. 5. It is concluded that in the conscious pig, nimodipine is an arterial vasodilator which shows some selectivity for the skeletal muscle vasculature but does not increase total or regional cerebral blood flow.

Effects of administration of L-propionylcarnitine during ischemia on the recovery of myocardial function in the anesthetised pig

The effects of L-propionylcarnitine (50 mg/kg) were studied in open-chest anesthetized pigs in which the blood flow in the left anterior descending coronary artery was reduced to 20% of baseline. A group of 7 animals given L-propionylcarnitine after 30 minutes of ischemia was compared with a group of 8 animals treated only with saline. After 60 minutes of ischemia the myocardium was reperfused for 2 hours. In both groups, the reduction of coronary artery blood flow abolished contraction of the affected myocardium and caused similar decreases in mean arterial blood pressure, the maximal rate of rise in left ventricular pressure, cardiac output, and ATP level and energy charge of the affected zone. L-propionylcarnitine did not affect any of these changes. Two hours of reperfusion caused further deterioration of systemic hemodynamics in both groups, although the decreases in cardiac output (P greater than 0.05) and mean arterial blood pressure (P less than 0.05) were smaller in the animals treated with L-propionylcarnitine. Left ventricular work, which decreased similarly in both groups during ischemia, deteriorated further in the saline treated group during reperfusion. This decrease was significantly attenuated by L-propionylcarnitine. Two hours of reperfusion resulted in only a partial return of blood flow to the reperfused ischemic myocardium, amounting to 53% of baseline in the saline-treated and to 72% of baseline in the L-propionylcarnitine-treated animals. The energy charge increased in both groups, but the increment tended to be less (P greater than 0.05) in the animals which had received L-propionylcarnitine.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of diltiazem to suppress cholesterol-induced atherogenesis of endothelium-denudated arteries in pigs

To investigate the effect of diltiazem on the development of atherosclerosis, 15 pigs were fed a fat-poor basal diet to which 8% (w/w) lard fat and 2% (w/w) cholesterol were added for 8 months. To enhance the formation of atherosclerotic plaques endothelium of the aorta and the left anterior descending coronary artery was removed after 1 month and 0.5% (w/w) bile acids were added to the diet after 3 months. Seven animals served as control, while 8 animals also received diltiazem (the first 2 months 10 mg/kg twice daily and during the remainder of the dietary period 5 mg/kg twice daily). The diet-induced increases in plasma level of total cholesterol were not affected by diltiazem. Triglyceride levels did not change in the control group but decreased significantly in the diltiazem-treated animals. Collagen-induced (1 microgram/ml) platelet aggregation was increased by diltiazem. The sum of free and esterified cholesterol was increased in the lesions of the aortic wall in the diltiazem-treated animals (9.8 +/- 1.3 micrograms/g wet weight vs. 6.3 +/- 1.0 mumol/g wet weight in the untreated animals), but coverage of the aorta with sudanophilic lesions was similar for both groups (40 +/- 4% for the treated and 34 +/- 9% for the control animals). Narrowing of the previously abraded coronary arteries was similar for the diltiazem-treated (median 7.1%, ranges 2.6-29.0%) and the control group (median 10.0%, ranges 2.3-24.1%). It is concluded that the dose range of diltiazem of 5-10 mg/kg twice daily, which is close to that used in the clinical setting, had no effect on the experimentally induced atherogenesis in pigs.

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 micrograms kg-1 min-1) and intracoronary (0.3, 0.9, 3.0 and 4.5 micrograms 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 micrograms kg-1 min-1) both LV dP/dtmax and segment length shortening decreased by less than 10%. With 0.9 micrograms kg-1 min-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 3.0upg kg - I 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 yg kg - ' min- 1 the vasodilatation in the renal vascular bed was more pronounced in the inner than in the outer cortex, but, at 0 pyg kg-1 min-, 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 yg kg- I min - ' 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 pg kg'- 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.

Nicorandil and cardiovascular performance in anaesthetized pigs with a concentric coronary artery stenosis

The present investigation compares the systemic and regional haemodynamics in nicorandil-treated and solvent-treated pigs with a concentric stenosis around the left anterior descending coronary artery. The stenosis per se led to a decrease in mean arterial blood pressure, cardiac output, stroke volume, maximum rate of rise in left ventricular pressure and transmural (more marked in the endocardium than in the epicardium) blood flow to and myocardial wall motion in the post-stenotic segment. Infusions of nicorandil (15 and 30 micrograms.kg-1.min-1, intravenously) decreased arterial blood pressure, cardiac output and the maximum rate of rise in left ventricular blood pressure. There was a tendency for epicardial blood flow in the non-stenotic segment to increase but blood flow to the ischaemic myocardium (epicardium as well as endocardium) was further compromised. Using the postsystolic wall thickening as an index for the viability of the myocardium and the Bretschneider formula for myocardial oxygen demand and the calculated myocardial oxygen consumption, we found that nicorandil further compromised the oxygen balance but did not jeopardize the viability of the myocardium. Regionally, nicorandil decreased renal blood flows but enhanced blood flows to the brains and adrenals. It is concluded that nicorandil lacks beneficial effects on the ischaemic myocardium in pigs with a concentric coronary artery stenosis. Apparently, the potential adverse effect (decrease in coronary perfusion pressure) of nicorandil outweighs its potential salutary effects (coronary vasodilatation and decrease in myocardial oxygen consumption due to peripheral vasodilatation.

The 5-HT1-like receptor mediating reduction of porcine carotid arteriovenous shunting by RU 24969 is not related to either the 5-HT1A or the 5-HT1B subtype

Using the radioactive microsphere technique in anaesthetized pigs, we studied the systemic and carotid haemodynamic effects of intracarotid infusions (0.3, 1, 3 and 10 micrograms/kg.min) of 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole succinate (RU 24969), a drug with high affinity for 5-HT1A and 5-HT1B recognition sites. Unlike in the rat, RU 24969 did not elicit hypotension in the pig. Instead, the two highest doses of the drug caused a slight increase in blood pressure. RU 24969 reduced common carotid artery blood flow by decreasing the non-nutrient, arteriovenous anastomotic blood flow; the nutrient, arteriolar blood flow was mildly increased. The decrease in common carotid and arteriovenous anastomotic blood flow was only slightly attenuated in animals pretreated with the 5-HT2 receptor antagonist, ketanserin (0.5 mg/kg i.a.), but was markedly reduced in animals pretreated with the 5-HT1-like and 5-HT2 receptor antagonist, methiothepin (1.0 mg/kg i.a.). However, these responses were not modified after pretreatment with the putative 5-HT1A and 5-HT1B receptor antagonist, (+/-)-pindolol (4.0 mg/kg i.v.). The slight increase in arteriolar blood flow was attenuated in the animals pretreated with either ketanserin, methiothepin or (+/-)-pindolol. It is concluded that the RU 24969-induced reduction in common carotid and arteriovenous anastomotic blood flow is mediated mainly by 5-HT1-like receptors, which do not seem to correspond to either the 5-HT1A or 5-HT1B receptor subtypes.

Intimal proliferation in coronary arteries of normolipidaemic pigs with a fixed stenosis: the effects of fish oil

In order to investigate the effect of fish oil on intimal proliferation of coronary arteries with a fixed stenosis, piglets were fed a diet to which either 9% (w/w) lard fat (L, n = 8) or 4.5% (w/w) lard fat and 4.5% (w/w) mackerel oil (ML, n = 8) was added for 4 months. The stenosis was applied by implanting a Teflon constrictor around the left anterior descending coronary artery (LADCA) after the animals had been on their diet for two months. Levels of plasma cholesterol and triglycerides did not change in L, but decreased in ML, while ADP-induced platelet aggregation in whole blood was higher in L than in ML. At the end of the dietary period the animals were anaesthetized and myocardial perfusion and systolic segment length shortening (SLS) were measured while the hearts were paced at 160 pulses min-1. Transmural blood flow to the non-LADCA nourished zones were normal and similar for L and ML, but impaired in the LADCA-perfused myocardium. In particular the subendocardial layers of L were hypoperfused resulting in a larger loss of SLS in L than in ML. A significantly higher encroachment due to intimal proliferation was found in L (62 +/- 7%) than in ML (11 +/- 4%) at the site of the constrictor while this was less than 2% adjacent to the constrictor. We conclude that the presence of the constrictor causes intimal proliferation and that the fish oil-induced changes in platelet aggregation may play a role in determining the extent to which this occurs.

Differential effects of n-3 fatty acids on the regression of atherosclerosis in coronary arteries and the aorta of the pig

Atherosclerosis was induced in 13 Yorkshire pigs (4 weeks; 7-10 kg) by endothelial balloon denudation of the aorta and left anterior descending coronary artery and a diet containing 2% (wt/wt) of cholesterol, 8% (wt/wt) of lard fat and 0.5% (wt/wt) of bile acids. After 8 months 7 animals (group I) were sacrificed to determine the extent to which atherosclerosis had developed. The other 6 animals (group R) received a diet (no cholesterol, 5% (wt/wt) of lard fat and 5% (wt/wt) of fish oil) for 4 months. In I plasma cholesterol increased from 2.29 to 9.02 mmol l-1 after 8 months and in R it returned to 1.89 mmol l-1 after 12 months. Less marked changes occurred in plasma HDL cholesterol and triglycerides. ADP-induced platelet aggregation and the number of platelets remained constant in I whereas both parameters were reduced in R after 12 months. In the lesions of the abdominal aorta of I, cholesterol, cholesterol ester, phospholipid and triglyceride contents were 4.97, 2.08, 4.20 and 0.77 micrograms g-1 wet wt, respectively, whereas in R these values (3.02, 0.47, 2.70 and 0.44 micrograms g-1 wet wt, respectively), were close to the values measured in non-abraded vessel wall specimens. The Sudan IV-positive area of the aorta was 34 +/- 9% in I and 10 +/- 4% in R (P less than 0.05). Luminal encroachment of the denudated left anterior descending coronary artery was 11 +/- 3% in I and 13 +/- 3% in R (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Discrete interactions between phosphatidylethanolamine-N-methylation and phosphatidylinositolbisphosphate hydrolysis in rat myocardium

Both phosphatidylethanolamine(PE)-N-methylation and phosphatidyl-inositol bisphosphate (PI-bisphosphate) breakdown potentially modify the microdomains in the sarcolemmal lipid bilayer. In this study the possibility of a mutual interaction between the enzymes responsible for these phospholipid reactions is examined. In sarcolemma purified from rat heart, prior hydrolysis of PI lipids by exogenous specific phospholipase C inhibited (to 75, 59 and 78% of control for sites I, II and II, respectively) the PE-N-methyltransferase system. In cultured rat cardiomyocytes the addition of L-methionine, a precursor for the methyl donor S-adenosylmethionine, stimulated PE-N-methylation in a concentration (0.2-300 microM)-dependent manner. Methionine (50 microM) decreased the basal rate of PI-bisphosphate hydrolysis (to 72% of control), but had no effect on the phenylephrine-stimulated PI-bisphosphate hydrolysis. Maximal activation of the PI-bisphosphate breakdown by 30 microM phenylephrine did not affect the rate of PE-N-methylation in the presence of exogenous methionine (50 microM). These findings support the existence of interactions, although discrete, between the enzymes involved in the PE-N-methylation and PI turnover.

Acute hemodynamic effects of nisoldipine and pimobendan in conscious pigs with chronic heart failure

The acute systemic hemodynamic effects of the calcium antagonist nisoldipine and the pyridazinone-derivative pimobendan, a phosphodiesterase inhibitor with vasodilating as well as positive inotropic properties, were studied in conscious pigs with chronic heart failure. Left ventricular (LV) dysfunction, manifested by a 25% decrease in cardiac output (CO), a 35% increase in systemic vascular resistance (SVR), and a doubling of the left ventricular filling pressure, was induced by a proximal ligation of the left circumflex coronary artery. Two to three weeks after myocardial infarction, cumulative 10-min infusions of either nisoldipine (0.05, 0.1, 0.25, and 0.5 micrograms/kg/min), pimobendan (2.5, 5, 12.5, and 25 micrograms/kg/min) or the solvents were administered. Infusion of the solvents did not affect any of the hemodynamic variables. Both nisoldipine and pimobendan normalized CO and exhibited a similar cardiac profile [systemic vasodilatation, reduction in left ventricular filling pressure, and an increase in heart rate (HR)] except for the significantly (p less than 0.05) larger increase in LVdP/dtmax with pimobendan (85%) than with nisoldipine (45%). In animals with heart failure, lower doses of both nisoldipine (twice) and pimobendan (four times) were needed to elicit a 30% reduction in SVR than in animals with normal pump function. For both drugs, the slope of the line describing the vasodilatory and positive inotropic properties shifted more in favor of the vasodilatory actions during heart failure (p less than 0.05). We conclude that in swine with chronic LV dysfunction nisoldipine, despite its lack of inotropic properties, appeared to improve ventricular function to the same extent as the primary positive inotropic agent pimobendan.