Keyhole sign: how specific is it for the diagnosis of posterior urethral valves?

OBJECTIVES: Posterior urethral valves (PUV) are the most common cause of renal impairment in boys during early childhood. Although antenatal suspicion of this pathology has become quite common in recent years, prenatal diagnosis remains challenging. The aim of this study was to evaluate the predictive value of different ultrasound criteria currently used to diagnose PUV. METHODS: We reviewed the antenatal and postnatal files of 54 male patients referred to our center from 2000 to 2006 after detection of fetal bilateral hydronephrosis. The following ultrasound criteria were evaluated in relation to the postnatal diagnosis of PUV: amniotic fluid volume, bladder wall thickness, bladder dilatation and the presence of the 'keyhole sign'. RESULTS: Forty-two fetuses (77.8%) were suspected to have PUV on prenatal examination. Out of these, 29 (69.0%) had PUV confirmed postnatally. The sensitivity and specificity of the antenatal diagnosis of PUV were 94% and 43%, respectively. Increased bladder wall thickness and bladder dilatation were highly associated with the diagnosis of PUV (P < 0.001). However, a thick-walled bladder was observed in 39.1% and a dilated bladder in 47.8% of the infants with a postnatal diagnosis other than PUV. The presence of the keyhole sign was not found to predict a diagnosis of PUV (P = 0.27). CONCLUSION: In this series the use of classical prenatal ultrasound signs to diagnose PUV showed high sensitivity but low specificity. The best diagnostic indicators were increased bladder wall thickness and dilatation of the bladder. The keyhole sign was not found to be a reliable predictor of PUV.

The outcome in newborns with congenital diaphragmatic hernia in a Norwegian region.

AIM: To evaluate the therapeutic strategies used in neonates with congenital diaphragmatic hernia (CDH) during the last 15 years in our department. METHOD: A retrospective study of 27 neonates with CDH treated at the Neonatal Intensive Care Unit at Ullevaal University Hospital between 1992 and 2006. Since 1992 we have used delayed operative repair and high-frequency ventilation (HFV). Because surfactant replacement and inhaled nitric oxide (iNO) therapy have been used since 1997, we divided the patients into two groups; group 1 from 1992 to 1996 (9 patients) and group 2 from 1997 to 2006 (18 patients). RESULTS: The overall survival was 70%. Group 1 had an exceptionally good outcome, 100% survival versus 56% in the last group. CONCLUSION: Pulmonary hypoplasia and pulmonary hypertension are still the most challenging factors in treatment of neonates with CDH, despite novel therapeutic modalities, such as HFV, surfactant and iNO. Delayed surgery in CDH allows pre-operative stabilization. Extracorporeal membrane oxygenation must be considered in the most severe cases.

Prenatal extravasation of urine seems to preserve renal function in boys with posterior urethral valves.

INTRODUCTION: A posterior urethral valve (PUV) may lead to extravasation of urine, resulting in prenatal ascites and/or perirenal urinoma. Extravasation has been presumed to act as a pop-off mechanism, preserving renal function, but previous reports addressing this presumption have been inconclusive. AIM OF STUDY: The present study compares renal function in patients with PUV with and without extravasation. MATERIAL AND METHODS: Sixty boys with a confirmed diagnosis of PUV as neonates (gestational age [GA]<44 weeks) throughout 2001-2016 were included. Clinical data were collected from medical records. Renal function was assessed by nadir plasma creatinine, creatinine at the last follow-up, and glomerular filtration rate (GFR) at the last follow-up. The GFR was estimated using the Schwartz formula. Renal function was classified according to the kidney disease: improving global outcomes (KDIGO) guidelines' grades of chronic kidney disease (CKD). Glomerular filtration rate > 90 ml/min/1.73m2 at the last follow-up was classified as normal renal function. RESULTS: Twelve patients (20%) had ascites and/or urinoma, and 48 (80%) did not. GA and birth weight were not different in patients with and without extravasation. PUV was suspected from prenatal ultrasound findings in 66.7% of the patients in both groups. Median nadir creatinine was 21 (range, 11-33) µmol/L in boys with ascites/urinoma, and all values were within the age-adjusted reference values. Nadir creatinine was 23 (14-199) µmol/L in boys without extravasation, and it was above the normal range in 14 boys. The incidence of elevated nadir creatinine was significantly different in the two groups (p < 0.025). One of the 12 patients with extravasation developed chronic renal failure (CKD 3). In the group of 48 patients without extravasation, 20 (42%) had chronic renal failure grade 2-5, and among these, 5 patients have had a renal transplant (CKD grade 5). The prevalence of CKD grade 2-5 was statistically different in the two groups (p = 0.03). These findings are presented in the summary figure. CONCLUSION: Extravasation of urine was found in 12 of 60 (20%) boys with PUV. These patients had significantly lower prevalence of CKD at the last follow-up than patients without extravasation. This finding is important in prenatal counseling. It also indicates that prenatal decompression of the bladder and upper tract is beneficial in patients with PUV, which is relevant to the discussion of prenatal intervention in these fetuses.

Reduced prostaglandin release from the stunned porcine heart--significance for attenuated reactive hyperaemia.

STUDY OBJECTIVE: Since both reactive hyperaemia and membrane phospholipids are altered even after short lasting ischaemic periods, the release of PGE2 and PGI2 in the basal state and during early reperfusion was examined to determine whether it was changed in the stunned myocardium. The effect of prostaglandin synthesis inhibition on reactive hyperaemia was also examined. DESIGN: The distal left anterior descending coronary artery was occluded for brief periods and coronary flow was recorded by Doppler flowmetry. In subgroups: (1) a shunt was established draining the ischaemic region for determination of myocardial prostaglandin release associated with 2 min of ischaemia before and after a 10 min occlusion; (2) prostaglandin synthesis was blocked between two 2 min occlusions by infusing indomethacin into the left anterior descending artery; and (3) segment lengths were measured in the left anterior descending artery region subjected to consecutive periods of 2, 10, and 2 min of ischaemia, and in a control region. EXPERIMENTAL MATERIAL: 21 pentobarbitone sodium anaesthetised pigs, weight 21-30 kg, were used. MEASUREMENTS AND MAIN RESULTS: 30 min after the 10 min occlusion, systolic shortening was reduced by 38(18-57)% (median +95% confidence interval; p less than 0.05). Concomitantly, basal PGE2 and PGI2 release was reduced by 69(30-77)% (p less than 0.05) and 58(7-81)% (p less than 0.05), respectively. During early reperfusion after 2 min of ischaemia, PGE2 release was reduced by 53(17-86)% (p less than 0.05) after development of stunning, whereas PGI2 release remained unaltered. Blockade of prostaglandin synthesis did not affect reactive hyperaemia either in normal or in stunned myocardium. CONCLUSIONS: Prostaglandin release from the stunned myocardium is reduced. Since indomethacin did not affect reactive hyperaemia, the attenuated PGE2 release during early reperfusion in stunned myocardium cannot explain the concomitant reduction in reactive hyperaemia.

Coronary reactivity in the porcine heart after short lasting myocardial ischaemia: effects of duration of ischaemia and myocardial stunning.

STUDY OBJECTIVE: The aim was to characterise reactive hyperaemia and endothelium dependent (ADP) and independent (adenosine) vasodilatation after ischaemic periods of increasing duration, and in the stunned myocardium. DESIGN: The left anterior descending coronary artery was occluded 5-7 cm distal from its origin for consecutive periods of 2, 2, 5, 10, and 2 min separated by 30 min of reperfusion. Coronary flow was continuously measured by Doppler flowmetry proximal to the occlusion site. ADP and adenosine were infused into the left coronary artery proximal to the flowprobe. EXPERIMENTAL MATERIAL: 11 domestic pigs, weight 25-36 kg, were used. MEASUREMENTS AND MAIN RESULTS: In the stunned myocardium maximal reactive hyperaemia after 2 min of ischaemia was preserved, whereas all other variables describing reactive hyperaemia were diminished: time to maximal hyperaemia by 40% (p less than 0.01), duration of hyperaemia by 44% (p less than 0.001), volume of hyperaemia by 53% (p less than 0.001), and repayment of flow debt by 43% (p less than 0.001). The vasodilating effects of ADP and adenosine (dose-response curves) were not altered after development of stunning. CONCLUSIONS: Preserved maximal hyperaemia and vasodilation during ADP and adenosine infusion, but reduced volume of hyperaemia, indicate normal coronary reactivity but diminished release in the stunned myocardium of the vasodilator(s) responsible for the prolonged postischaemic flow increase.

Oxygen free radical injury and Gs mediated signal transduction in the stunned porcine myocardium.

OBJECTIVE: The aim was to investigate involvement of oxygen free radicals and any changes in the Gs mediated beta adrenergic signalling system of stunned porcine myocardium. METHODS: Myocardial stunning was induced in eight pentobarbitone anaesthetised pigs by brief occlusions of the distal left anterior descending coronary artery for periods of up to 10 min. Segment length function was measured in the ischaemic region and in a control region supplied by the circumflex artery. Left ventricular biopsies were obtained from the two regions 1 h after the last occlusion for ultrastructural and biochemical studies. Timolol has been used to prevent arrhythmia during ischaemia. RESULTS: At the time when biopsies were obtained, percent systolic shortening was reduced to 58% in the region subjected to ischaemia and was only minimally reduced in the control region. In the biopsies from the stunned region: (1) electron microscopy showed mild and reversible intracellular changes in the stunned myocardium; (2) the activities of superoxide dismutase and glutathione peroxidase were decreased by 66% and 52%, respectively; (3) the content of malondialdehyde was increased by 49%; (4) neither density nor affinity of beta adrenoceptors showed any changes; (5) there were no alterations in messenger RNA encoding for the alpha subunit of the stimulatory guanine nucleotide binding protein (Gs), demonstrated by northern and dot-blot hybridisations; (6) ELISA technique utilising a specific antipeptide antibody showed no quantitative change in Gs; (7) the activity of adenyl cyclase was unchanged. CONCLUSIONS: Even though the stunned porcine myocardium showed substantial evidence of free radical injury, the beta adrenergic signalling system was intact.

Nocturnal periodic breathing at altitudes of 6,300 and 8,050 m.

Nocturnal periodic breathing was studied in eight well-acclimatized subjects living at an altitude of 6,300 m [barometric pressure (PB) 350-352 Torr] for 3-5 wk and in four subjects during one night at 8,050 m altitude (PB 281-285 Torr). The measurements at 6,300 m included tidal volume by inductance plethysmography, arterial O2 saturation by ear oximetry (calibrated by arterial blood samples), electrocardiogram (ECG), and electrooculogram. At 8,050 m, periodic breathing was inferred from the cyclical variation in heart rate obtained from a night-long ECG record. All subjects at 6,300 m altitude showed well-marked periodic breathing with apneic periods. Cycle length averaged 20.5 s with 7.9 s apnea. Minimal arterial O2 saturation averaged 63.4% corresponding to a PO2 of approximately 33 Torr, i.e., approximately 6 Torr lower than the normal value at rest during daytime. This was probably the most severe hypoxemia of the 24-h period. At 8,050 m altitude, the cycle length averaged 15.4 s, much longer than predicted by a theoretical model. Cyclical variations in heart rate caused by periodic breathing occurred in all subjects, but abnormal cardiac rhythms such as ventricular premature contractions were uncommon. The severe arterial hypoxemia caused by periodic breathing may be an important determinant of tolerance to these great altitudes.

Calcium-induced net potassium uptake of pig hearts in vivo.

To determine whether the catecholamine-induced myocardial potassium uptake could be mimicked by increasing extracellular and intracellular calcium concentrations in vivo, we measured changes in myocardial potassium balance in nine anaesthetized open-chest pigs with PVC-valinomycin electrodes in arterial and coronary sinus blood. CaCl2 infusion (200-400 mumol min-1) into the left coronary artery increased coronary sinus blood calcium concentration from 2.29 (2.19-2.42) to 4.63 (3.76-5.67) mmol l-1 (median, 95% confidence interval, P = 0.01) indicating a similar increment in myocardial extracellular calcium concentration. The contractility measure LV dP/dt increased 95 (76-147) %, indicating a substantial increment in intracellular calcium concentration. During the CaCl2 infusion coronary sinus potassium concentration declined to a nadir 0.12 (0.09-0.17) mmol l-1 below baseline (P = 0.008) whereas arterial concentration remained unchanged. Peak myocardial potassium uptake was 18 (7-32) mumol min-1 100 g-1 and occurred 150 (110-195) s after start of infusion. The response remained unaltered after adrenoceptor blockade by prazosin and propranolol. Prolonged CaCl2 infusion caused a net myocardial potassium loss which was accompanied by metabolic and haemodynamic indications of myocardial ischaemia. These findings are consistent with enhanced Na-K pump activity in the intact beating pig heart in response to increased extracellular and intracellular calcium concentrations.

Effects of hemodynamic variables on myocardial K+ balance during and after shortlasting ischemia.

Ischemia-induced myocardial potassium loss and post-ischemic potassium reuptake was quantitated in 8 open chest pigs during control conditions and during hemodynamic alterations which have been shown to increase steady state sarcolemmal potassium fluxes. Myocardial K+ balance was continuously computed before, during and after a 90 s occlusion of a branch of the circumflex artery during control (CTR), during pacing tachycardia (PACE: 34% increase in heart rate), during proximal aortic constriction (AC; 28% increase in LVSP), and during isoprenaline infusion (ISO; 135% increase in LVdP/dt and 35% increase in heart rate). Ischemia-induced potassium loss increased significantly (40%) during ISO only. Higher basal metabolic rate, increased sarcolemmal K+ conductance, or ischemia-induced depression of a more active Na/K-pump during ISO are possible explanations to why increased K+ loss appeared in this situation. The maximal rate of post-ischemic potassium reuptake was not different from CTR during PACE and ISO, but it was reduced during AC, which might be due to persisting subendocardial ischemia in early reperfusion when ventricular wall stress is high. The extent of potassium restoration was not different from CTR during AC, PACE and ISO.

Role of adenosine for reactive hyperemia in normal and stunned porcine myocardium.

The role of adenosine for reactive hyperemia in normal and stunned myocardium was examined in 16 open-chest barbiturate-anesthetized pigs. Interstitial adenosine concentration was reduced or enhanced by intracoronary infusion of adenosine deaminase or the nucleoside transport inhibitor R 75231, respectively. In normal myocardium, adenosine deaminase reduced volume of hyperemia (Doppler flowmetry) after a 30-s left anterior descending coronary artery (LAD) occlusion by 20% (6-34%; P < 0.05), whereas R 75231 increased volume of hyperemia by 15% (2-24%; P < 0.05). Adenosine deaminase reduced volume of hyperemia after a 2-min LAD occlusion by 27% (13-37%; P < 0.001), whereas R 75231 increased volume of hyperemia by 66% (53-159%; P < 0.001). Adenosine deaminase and R 75231 did not affect maximal hyperemia. Volume of hyperemia after a 2-min LAD occlusion was reduced in stunned myocardium (%systolic segment length shortening reduced by approximately 45%, ultrasonic technique) but not further altered by either adenosine deaminase or R 75231. These findings show that adenosine contributes to reactive hyperemia after 30-120 s of ischemia in normal myocardium and indicate that the reduced reactive hyperemia in stunned myocardium is due to reduced accumulation of adenosine during ischemia.

Atrial contractile dysfunction after short-term atrial fibrillation is reduced by verapamil but increased by BAY K8644.

BACKGROUND: Reduced atrial contractility occurs after cessation of atrial fibrillation. Its mechanism is unknown, and no pharmacological treatment exists. It has been hypothesized that this atrial contractile dysfunction results from intracellular calcium overload due to rapid depolarizations during fibrillation. Accordingly, we examined the effects of drugs that reduce or increase transsarcolemmal calcium influx on postfibrillation atrial dysfunction. Furthermore, we examined whether the dysfunction could be attributed to atrial ischemia. METHODS AND RESULTS: Atrial contractility after atrial fibrillation was examined in open-chest pigs paced with a constant ventricular rate after complete AV block. Atrial contractility was computed as systolic shortening of left atrial diameter divided by atrial preload. Three groups of six pigs each were subjected to two 5-minute periods of atrial fibrillation separated by 1 hour of AV pacing. Verapamil or the calcium channel agonist BAY K8644 was administered intravenously before the second fibrillation period. The degree and duration of postfibrillation atrial contractile dysfunction were reduced with verapamil but increased with BAY K8644. In a control group, parallel changes occurred after the first and second fibrillation periods. Atrial tissue content of creatine phosphate declined slightly during fibrillation, whereas the tissue content of ATP and lactate remained unchanged. CONCLUSIONS: Atrial contractile dysfunction after short-term atrial fibrillation is reduced by the calcium antagonist verapamil, which suggests that transsarcolemmal calcium influx contributed to this dysfunction. The calcium agonist BAY K8644 increased postfibrillation atrial contractile dysfunction. Atrial ischemia was not observed during fibrillation.

Release of atrial natriuretic factor during selective cardiac alpha- and beta-adrenergic stimulation, intracoronary Ca2+ infusion, and aortic constriction in pigs.

The effects of alpha- and beta-adrenergic stimulation on release of atrial natriuretic factor (ANF) were examined in seven anesthetized, open-chest pigs. The alpha-adrenergic agonist phenylephrine (28.0 micrograms/min) and the beta-adrenergic agonist isoproterenol (0.3 micrograms/min) were infused into the proximal part of the circumflex coronary artery to stimulate the left atrial adrenoceptors without concomitant changes in left and right atrial filling pressures (v wave). Isoproterenol reduced plasma immunoreactive ANF (irANF) by 15 +/- 7 pg/ml (20%) from 76 +/- 10 pg/ml despite a rise in left atrial systolic pressure (a wave). A comparable rise in left atrial systolic pressure, induced by intracoronary infusion of calcium chloride (8.0 mg/min), increased plasma irANF by 33 +/- 10 pg/ml (53%) from 62 +/- 7 pg/ml. Phenylephrine increased plasma irANF by 9 +/- 4 pg/ml (14%) from 66 +/- 10 pg/ml without altering right and left atrial pressures. A rise in left atrial filling pressure of 3.2 +/- 0.5 mm Hg, induced by constricting the ascending aorta, increased plasma irANF by 83 +/- 35 pg/ml (141%) from 59 +/- 11 pg/ml. This increase was nine times that during phenylephrine infusion. In conclusion, alpha-adrenergic stimulation increases and beta-adrenergic stimulation inhibits ANF release by a direct action on the atrial myocytes. The direct effects of alpha- and beta-adrenergic stimulation on ANF release in vivo are small compared with the effect of a moderate rise in atrial filling pressure.

Characteristics and development of myocardial stunning in the pig.

Regional left ventricular function associated with consecutive ischemic periods of 2, 2, 5, 10, and 2 min was recorded by ultrasonic technique in pentobarbital-anesthetized pigs. All systolic and diastolic derangements first appeared after 5 min of ischemia, and all worsened after 10 min of ischemia. Percent systolic segment length shortening reached nadirs 23 (17-29)% (P less than 0.001) and 54 (45-65)% (P less than 0.001) below baseline 30 min after 5 and 10 min of ischemia. During reperfusion all recorded systolic and diastolic variables transiently recovered and then deteriorated with a closely similar time course. This covariance indicates that systolic and diastolic derangements are causally related, and because diastolic compliance was preserved in stunned myocardium we conclude that all derangements largely result from reduced systolic tension development. Transient postischemic hypercontractility followed all occlusions and was not attenuated by beta-blockade and not mimicked by hyperemia alone. Postischemic hypercontractility was greatly enhanced in stunned myocardium, and we hypothesize that more pronounced and sustained postischemic elevation of intracellular Ca2+ concentration explains this observation.

Myocardial potassium balance associated with regional ischaemia in the pig: effects of beta-adrenoceptor blockade, duration of ischaemia and preceding ischaemic periods.

The effects of beta-adrenoceptor blockade, duration of ischaemia and preceding ischaemic periods on ischaemia-induced changes in myocardial K+ balance were studied in 12 open-chest pigs. Coronary venous blood was directed through a shunt from the coronary sinus to the right atrium. Continuous recordings of arterial, shunt blood [K+] and shunt flow enabled us to compute myocardial K+ balance during and after consecutive 2-, 2-, 5-, 10- and 2-min periods of regional ischaemia separated by 30 min of reperfusion. beta-adrenoceptor blockade (propranolol 1 mg kg-1 i.v.) given between the first and second ischaemic period did not alter the effects of 2 min ischaemia on myocardial K+ balance. Total K+ losses induced by 2, 5 and 10 min of ischaemia were 67.1 (40.6-93.3), 106.7 (69.4-176.8) and 192.2 (117.7-332.6) mumol 100 g-1, respectively. Thus, the plateau observed in extracellular [K+] between 2 and 10 min of regional ischaemia could, at least partly, be explained by continuous drainage of K+ from ischaemic myocardium into the surrounding normally perfused tissue. The total K+ loss induced by the second and last 2-min ischaemic period were 67.1 (40.6-93.3) and 35.6 (23.1-53.6) mumol 100 g-1 (P less than 0.001), respectively. This reduction shows that ion homeostasis during ischaemia was greatly changed in myocardium which had been 'preconditioned' and 'stunned' by 5 plus 10 min of ischaemia. Total amount, maximal rate and duration of post-ischaemic K+ reuptake increased with the duration of the preceding ischaemia. Moreover, K+ re-uptake after 2 min of ischaemia and the number of sarcolemmal Na/K pumps ([3H]ouabain binding), were normal in stunned myocardium. From these observations we conclude that progressive stimulation of the Na/K-pump occurred when ischaemia was prolonged from 2 to 10 min, and that Na/K-pump function was preserved in stunned myocardium.

Myocardial K+ repletion and rise in contractility after brief ischemic periods in the pig.

Potassium loss from the myocardium during brief ischemic periods is well documented, but whether intrinsic myocardial mechanisms restore this loss during reperfusion is unclear. To address this question, we established a shunt from the coronary sinus to the right atrium in seven open-chest pigs. Shunt flow and arterial and coronary sinus potassium concentrations were measured continuously in order to determine myocardial potassium balance. Thirty, 60 and 120 s occlusions of the mid-LAD coronary artery were repeated four times each at 10 min intervals with reproducible metabolic and hemodynamic responses. A myocardial K+ reuptake amounting to 51 to 77% of K+ release during ischemia occurred between 20 and 140 s of reperfusion. The maximal rate of K+ reuptake was 1.4 (0.7 to 3.6), (median and 95% confidence interval), 4.3 (2.5 to 9.6) and 7.3 (4.9 to 13.4) mumol/100 g min after occlusion periods of 30, 60 and 120 s, respectively. Concomitant with the K+ reuptake a progressive rise in LV dP/dt occurred. Adrenoceptor stimulation could not explain these findings since catecholamine release declined during occlusion and reperfusion. We suggest that increased intracellular Na+ concentration in early reperfusion stimulates the Na,K-pump and favours Ca++ entry through Na+/Ca++ exchange, thereby mediating K+ reuptake and the rise in contractility.

Na,K-pump concentration in hypertrophied human hearts.

Several studies have associated myocardial dysfunction with reduced myocardial Na,K-pump concentration, but whether impaired Na,K-pump capacity is a pathogenetic factor or an epiphenomenon related to accompanying cardiac hypertrophy is not established. We measured Na,K-pump concentrations in 10 hypertrophied and 11 normal weighted hearts obtained at autopsy using [3H]ouabain as ligand. Specific [3H] ouabain binding site concentration (OBC) in the left ventricle (LV) averaged 449 +/- 40 (pmol.g-1 wet weight; mean +/- SEM) in hypertrophied and 598 +/- 36 in normal weighted ventricles (P = 0.02). A trend towards lower LV OBC (-19%; P = 0.25) was found in hypertrophied hearts from patients with congestive heart failure as compared with non-failing hypertrophied hearts. In multivariate analysis with 18 variables including age and heart failure, only LV weight correlated independently with LV OBC (r = -0.61; P = 0.003). When OBC was related to either dry weight or to protein content, a 25-35% reduction was consistently found in hypertrophied LV, whereas RV OBC was similar in both groups. In conclusion, myocardial Na,K-pump concentration and thus the capacity to maintain homeostasis is reduced in LV, but not in RV, of hypertrophied hearts. Whether the moderately reduced myocardial Na,K-pump concentration is a pathogenetic factor in LV dysfunction remains to be determined.

Density of L-type calcium channels in ischaemically preconditioned porcine heart regions.

Ischaemic preconditioning by brief ischaemic episodes could be explained by reduced cellular calcium ion (Ca2+) influx, reduced cytosolic Ca2+ overload and delayed cell-injury during subsequent long-lasting ischaemia. L-type calcium channels (LCC) regulate sarcolemmal Ca2+ influx in myocardial cells. The aim of this study was to investigate if preconditioning was associated with reduced density or altered state of LCC in the preconditioned region of the heart. To test this we compared the density and the dissociation constant of (+)-[3H]isradipine binding to LCC in membranes from preconditioned and control regions of porcine hearts. Eight porcine hearts were regionally preconditioned by two 10-min occlusions of the mid left anterior descending artery, and each occlusion was followed by 30 min of reperfusion. Biopsies were taken from the preconditioned regions and control regions supplied by the circumflex artery at the end of the last reperfusion, and (+)-[3H]isradipine binding to membranes made from the biopsies was measured. The differences in density and dissociation constant of (+)-[3H]isradipine binding to LCC in membranes from preconditioned and control regions were not significant. In conclusion, the proposed effect of ischaemic preconditioning to reduce Ca2+ influx, does not involve local changes in density or state of LCC that could be detected by (+)-[3H]isradipine binding.

Nitric oxide regulates coronary blood flow at various coronary arterial pressures in intact porcine hearts.

Nitric oxide (NO) is known to regulate basal coronary blood flow (CBF). The objective of the present study was to examine the importance of NO in CBF regulation at various coronary arterial pressures (CAPs) in vivo. Experiments were performed in 11 open-chest pentobarbitone sodium anesthetized pigs. CAP was reduced in steps by a hydraulic occluder on the mid left anterior descending coronary artery (LAD) before and after a 5-min intracoronary infusion of the inhibitor of NO synthesis, NG-nitro-L-arginine (NOARG, 30 mumol min-1). CAP was recorded and NOARG infused through a catheter inserted into the LAD just distal to the occluder. CBF was measured by Doppler flowmetry on the LAD. NOARG significantly reduced CBF by 11 +/- 4, 20 +/- 5, 10 +/- 3, 15 +/- 4, 19 +/- 2, 25 +/- 4 and 25 +/- 5 mL min-1 100 g-1 (mean +/- SE) at CAPs of 30 (n = 6), 40 (n = 9), 50 (n = 9), 60 (n = 9), 70 (n = 9), 80 (n = 8) and 90 (n = 6) mmHg, respectively. These decrements were not statistically different, but the percentage reductions in CBF after infusion of NOARG were significantly greatest at the lowest CAPs. The slight haemodynamic alterations induced by NOARG could not explain the reductions in CBF. Thus, the reductions in CBF after infusion of NOARG were caused by inhibition of a continuous NO release from the coronary endothelium. Coronary NO contributes significantly to CBF at all CAPs between 30 and 90 mmHg. The pronounced reduction in CBF during NO inhibition at the lower CAPs indicates an important vasodilating role of intact endothelium in a region supplied by a stenosed coronary artery.

Cardiac contractile function following repetitive brief ischemia: effects of nucleoside transport inhibition.

The effects of nucleoside transport inhibition on cardiac contractile function were examined in anesthetized pigs subjected to five 6-min left anterior descending coronary artery (LAD) occlusions, separated by 20-min reperfusion, and followed by 150-min reperfusion. In group 1 (n = 8), saline was infused. In group 2 (n = 9), endogenous myocardial accumulation of adenosine was increased by intracoronary infusion of the specific nucleoside transport inhibitor R-75 231. Left ventricular segment lengths were recorded by ultrasonic crystals in the inner one-third of the myocardium. Percent systolic segment length shortening (SS) (normalized to percent of preischemic value) was significantly better maintained in the R-75 231 group compared with the saline group after each occlusion. SS in the saline group reached a nadir of 30% (22-40) at 30-min reperfusion after the last occlusion compared with 66% (54-73) in the R-75 231 group. In the R-75 231 group, but not in the saline group, maximal postischemic decline in SS and decline at 20-min reperfusion were significantly reduced following the last occlusion. We conclude that R-75 231, which inhibits nucleoside transport, attenuates contractile dysfunction following repetitive brief ischemia and results in a preconditioning-like effect against stunning in the pig. On the basis of the well-documented biochemical effects of R-75 231, increased accumulation of endogenous adenosine most likely explains these findings.