Ionized magnesium concentrations in critically ill children

OBJECTIVE: To test the hypothesis that many critically ill children exhibit ionized hypomagnesemia despite having normal total magnesium (TMg) concentrations. DESIGN: A prospective, observational study with convenience sampling. SETTING: Pediatric and cardiovascular intensive care units of a large children's hospital. PATIENTS: Patients aged 1 day to 21 yrs admitted from January 1 to October 31, 1996. Patients with chronic renal failure or weight <3 kg were excluded. A group of healthy children involved in a school-based nutritional assessment study were also studied. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Sixty-seven patients (5.4+/-5.7 [SD] yrs) and 24 healthy children (10.84+/-0.93 yrs, p< .001) were studied. Plasma was assayed for ionized magnesium (IMg) using a blood analyzer. Forty (59%)/67 critically ill subjects had IMg concentrations <0.40 mmol/L, the lowest published normal value and the lowest value observed in our group of healthy children. Of these, 24 (60%)/40 had normal TMg concentrations. IMg was significantly (p=.00) lower in critically ill subjects than in the group of healthy children (0.37+/-0.10 mmol/L vs. 0.46+/-0.03 mmol/L). IMg did not correlate strongly with ionized calcium (r2=0.49), albumin (r2=0.09), or pH (r2=0.18). CONCLUSION: Many critically ill children exhibit ionized hypomagnesemia with normal TMg concentrations. These children would not be recognized as magnesium-deficient based on routine TMg testing. Critically ill children exhibited significantly lower concentrations of IMg than a group of healthy children.     

Hypomagnesemia and mitral valve prolapse in Cavalier King Charles spaniels

There is a high incidence of mitral valve prolapse (MVP), an abnormal displacement of one or both mitral valve leaflets during systole, in Cavalier King Charles Spaniels (CKCS). In humans, MVP is known to be associated with a low magnesium status. In this study, the plasma magnesium concentration was measured in 30 CKCS without heart failure. It was also investigated whether MVP-severity and degree of regurgitation correlated with plasma magnesium and a number of parameters of the renin-angiotensin system, and whether 4 weeks magnesium supplementation affected plasma magnesium or the high renin/low aldosterone profile associated with MVP. A high prevalence of hypomagnesemia was observed: plasma concentrations < 0.70 mmol/l were found in 15 dogs (50%) before and in 12 dogs (40%) after 4 weeks magnesium supplementation. The mean plasma level was 0.69 +/- 0.07 mmol/l before and 0.71 +/- 0.07 mmol/l after magnesium (P = 0.22). Plasma magnesium concentrations did not correlate with MVP-severity and degree of regurgitation. Plasma aldosterone levels correlated negatively with MVP-severity and positively with the degree of regurgitation, and serum angiotensin-converting enzyme activities correlated negatively with the degree of regurgitation. Magnesium supplementation had no effects on renin and aldosterone nor on the ratio between the two. In conclusion, many CKCS without heart failure have hypomagnesemia whether they are fed supplementary magnesium or not--a finding which may be associated with the high prevalence of MVP in this breed. Further studies, however, are needed to clarify the role of a low magnesium status in canine MVP.     

Intralymphocyte free magnesium in a group of subjects with essential hypertension

Despite the importance of magnesium in essential hypertension, few data are available on the ionized intracellular concentration of this ion. We therefore studied intralymphocyte free intracellular magnesium (Mgi) in 32 untreated essential hypertensive subjects and 27 normotensive control subjects by means of a fluorimetric technique based on the use of the new magnesium-sensitive dye furaptra. We also measured intralymphocyte ionized calcium (Cai) with fura 2. No statistically significant differences were found in Mgi in hypertensive compared with normotensive subjects (essential hypertensive, 0.291 +/- 0.053 mmol/L; normotensive, 0.293 +/- 0.043 [mean +/- SD]). A statistically significant inverse correlation was established between Mgi and plasma triglycerides in essential hypertensive subjects (r = -.521, P = .002). The hypertensive group was arbitrarily divided into two subgroups according to plasma triglyceride levels (> 2 [n = 10] or < 2 mmol/L [n = 22]), and Mgi proved to be significantly lower in the subgroup with high plasma triglyceride levels compared with either the subgroup with normal triglycerides (P = .009; 95% confidence interval, 0.013-0.088) or the normotensive control group as a whole (P = .03; 95% confidence interval, 0.003-0.069) (high-triglyceride hypertensive subgroup, Mgi = 0.256 +/- 0.045 mmol/L; normal-triglyceride hypertensive subgroup, Mgi = 0.307 +/- 0.049). No statistically significant differences were found in Cai in hypertensive compared with normotensive subjects (hypertensive, 53 +/- 12 nmol/L; normotensive, 54 +/- 14). We did not find statistically significant correlations between Cai and plasma triglycerides, nor did we find any differences in Cai between the subgroup of hypertensive subjects with high plasma triglyceride levels and either the subgroup of hypertensive subjects with normal triglycerides or the normotensive control group as a whole. The discrepancies between our results in lymphocytes and data relating to either erythrocytes or platelets emphasize the need for caution before the results are extrapolated from one tissue to the other. The decreased Mgi levels in the subgroup of high-triglyceride hypertensive subjects may suggest a role for magnesium in plurimetabolic syndrome.     

Secondary hyperparathyroidism is an expected consequence of parathyroidectomy for primary hyperparathyroidism: a prospective study

BACKGROUND: Parathyroidectomy for primary hyperparathyroidism (PHPT) can cause secondary hyperparathyroidism, with increased serum parathyroid hormone (PTH) and normal or low serum calcium concentrations. METHODS: A prospective study investigated 78 consecutive patients who underwent exploration for PHPT. Serum intact PTH and total calcium concentrations were measured the evening after operation and ionized Ca++ the following morning. These levels were reassayed 1 week later. RESULTS: Before operation, the mean PTH level was 138 +/- 15 pg/mL, total calcium concentration was 11.6 +/- 0.1 mg/dL, and ionized Ca++ concentration was 1.44 +/- 0.02 mmol/L. On the night of the operation, the PTH level was 11 +/- 2 pg/mL, and the total calcium concentration was 8.9 +/- 0.1 mg/dL. Fifty-five patients had hypoparathyroidism, with a PTH level less than 10 pg/mL. The day after the operation, the ionized Ca++ level was 1.14 +/- 0.01 mmol/L. One week later, PTH, ionized Ca++, and total serum calcium concentrations returned to normal levels. In 9 patients (12%), PTH levels were increased (98 +/- 16 pg/mL), although ionized Ca++ concentrations were normal (1.18 +/- 0.02 mmol/L), demonstrating secondary hyperparathyroidism. Risk factors for postoperative secondary hyperparathyroidism included older age, symptomatic hyperparathyroidism, higher preoperative PTH and alakaline phosphatase levels, and lower serum phosphorous levels. In 70% of these patients, PTH levels returned to normal in 3 to 12 months. CONCLUSIONS: Secondary hyperparathyroidism occurs in 12% of patients after surgical treatment of PHPT. It is transient, possibly compensating for relative hypocalcemia.     

Product activation of human erythrocyte AMP deaminase

Maternal magnesium requirements increase during pregnancy because of the synthesis of new tissue--both fetal and maternal. Magnesium takes part in almost 300 enzymatic reactions in the human body and regulates membrane permeability and protein bio-synthesis by promoting initiation and dissociation factors. The absorption velocity of magnesium differs from one tissue to another in animal experiments. It is highest in the liver, kidney, heart and is low in skeletal muscle, the brain and erythrocytes. It obeys and follows the Michaelis-Menten Kinetic law. 15 mmol of magnesium is consumed daily depending on the types of food takenin. The main sources of magnesium are vegetables and meats. Many Nigerian women are not able to afford enough of these. The amount of magnesium reabsorbed depends on the magnesium intake and not on magnesium needed which is about 10-40% of the intake. In this study, we examined the short-term effect of magnesium asphat HCL (614.18 mgMG), magnesium diasporal (magnesium citrate 610 mg + magnesium laevalitat 30 mg = 100 mg magnesium = 8.2 mval), ferrous gluconate (300 mg) plus folic acid and chemiron, a new combination hematinic agent (ferrous fumarate 300 mg, folic acid 5 mg, vitamin B12 10 mg, vitamin C 25 mg, magnesium sulfate 0.3 mg and zinc sulfate 0.3 mg) on plasma magnesium concentration during early pregnancy in Nigerian women. Significant increases of plasma magnesium concentrations were found in these groups (magnesium asphat HCL, 0.83 +/- 0.12 to 0.96 +/- 0.14 mmol/l, magnesium diasporal 0.843 +/- 0.14 to 0.891 +/- 0.14 mmol/l and chemiron 0.848 +/- to 0.866 +/- 0.16 mmol/l after five days. The ferrous gluconate and folic acid treated group showed no significant changes. This study shows that a chemiron supplement leads to increased magnesium plasma levels whereas ferrous gluconate and folic acid do not. These results suggest that the low level of magnesium is a normal physiological adjustment of pregnancy and that iron supplementation does not influence this unless magnesium salt is given.     

Falsely high ionized magnesium results by an ion-selective electrode method in severe hypomagnesemia

Changes in serum total and ionized magnesium (Mg and Mg2+) and calcium (Ca and Ca2+) were monitored in three patients who transiently developed severe (total Mg < 0.50 mmol/l) to profound hypomagnesemia (total Mg < 0.35 mmol/l) due to cisplatin or interleukin-2 therapies. Mg2+ and Ca2+ were measured with the Nova ion-selective electrodes at 37 degrees C and all results were normalized to pH 7.40. Independent of the etiology, the Mg2+ fraction (Mg2+/total Mg) increased as the concentration of the serum total Mg decreased in all three patients. When the total Mg was around or below 0.35 mmol/l the Mg2+ approached or exceeded total Mg, suggesting an error in the measurement of Mg2+. The findings were extended by including a group of 31 additional patients whose serum total Mg, Mg2+, total Ca, and Ca2+ concentrations varied from abnormally low to above normal. The serum total and ionized concentrations strongly correlated for both Mg (r2 = 0.88) and Ca (r2 = 0.92). The Mg2+ fraction rapidly increased with a fall in the total Mg concentration (r2 = 0.76) and total Mg/total Ca ratio (r2 = 0.71). In fact, with decreasing total Mg concentrations or total Mg/total Ca ratios, the Mg2+ fraction progressively increased to 93-128% of the total, confirming an error in the Mg2+ determinations. The Ca2+ fraction showed a slight and insignificant decrease with falling total Ca concentrations and total Mg/total Ca ratios. The Mg2+ concentration was directly related (r2 = 0.62), whereas the Ca2+ concentration showed a complex relationship to the total Mg/total Ca ratio. Whether this latter relationship represents a technical artifact or a true biological phenomenon requires further study. The apparent overestimation of Mg2+ at very low total Mg concentrations, and in the presence of a very low total Mg/total Ca ratio, could be due to improper chemometric correction of the Ca effect on the Mg electrode, non-linearity, and inadequate calibration. Whatever the mechanism, the failure of this method to correctly measure very low serum Mg2+ concentrations in the sera of patients with severe hypomagnesemia, or likely in any patient with an unusually low total Mg/total Ca ratio, erodes its diagnostic usefulness.     

Determination of ionized magnesium in platelets and correlation with selected variables

We describe a method for determining the intracellular ionized magnesium concentration ([Mg2+]i) in platelets by using the fluorescent probe FURAPTRA. We determined the dissociation constant (KD) of FURAPTRA for Mg2+ (2.26 +/- 0.29 mmol/L), within-day assay variability (CV = 6.8%), among-day intraindividual variability (CV = 11.0%), variability after a 4-h delay in processing the blood specimen (t = 1.2, P >0.2; F = 6.2, P <0.02), and the reference interval (0.23-0.59 mmol/L) for this assay. We also evaluated the correlation between platelet [Mg2+]i and concentrations of selected serum electrolytes, proteins, and total cholesterol; age; body mass index; and gender. Only the inverse correlation between platelet [Mg2+]i and serum total cholesterol concentration in men was significant (r=-0.66, P <0.005).     

Temperature/light dependent development of selective resistance to photoinhibition of photosystem I

BACKGROUND: Circulating magnesium exists in the ionized state and in the undissociated form, either bound to albumin, or complexed to various anions. Until recently, only the measurement of total plasma magnesium has been possible. Now circulating ionized magnesium can be assessed as well. METHODS: Total and ionized plasma magnesium were determined in 43 patients on maintenance hemodialysis (dialysate composition: calcium 1.75 mmol/l, magnesium 0.75 mmol/l) before a dialysis session and in a group of 23 healthy subjects. RESULTS: The total (1.16 [1.03-1.31] versus 0.81 [0.78-0.89] mmol/l; median and interquartile range) and the ionized (0.71 [0.66-0.78] versus 0.54 [0.53-0.59] mmol/l) plasma magnesium levels were significantly higher (p < 0.01) and the ionized plasma magnesium fraction lower (0.61 [0.58-0.65] versus 0.67 [0.64-0.70]; p < 0.02) in patients than in controls. CONCLUSION: The determination of circulating ionized magnesium using selective electrodes is an attractive method to evaluate extracellular magnesium in kidney disease.     

Intralymphocyte free magnesium and plasma triglycerides

To evaluate the relative effect of hypertension and plasma triglycerides on intralymphocyte magnesium we measured ionized intralymphocyte magnesium (Mg(i)) concentration by means of a fluorimetric method based on the dye Furaptra in 4 groups of subjects: 18 normotensive normotriglyceridemic controls (NTNC), 9 hypertriglyceridemic normotensive patients (HTN), 8 hypertriglyceridemic essential hypertensive patients (HTEH), 17 normotriglyceridemic essential hypertensive patients (NTEH). Hypercholesterolemic, diabetic patients and alcoholics were excluded from the study. Mg(i) was found to be statistically reduced (ANOVA test F=10.41, P=0.0001) in both HTN and HTEH (M+/- SD, HTN: 0.235 +/- 0.01, HTEH: 0.236 +/- 0.01 mmol/l) as compared to both NTNC and NTEH (M +/- SD, NTNC: 0.294 +/- 0.008, NTEH: 0.297 +/- 0.009 mmol/l). A statistically significant negative correlation was found in the population as a whole between Mg(i) and plasma triglycerides (n=52, R= -541, P=0.00004). Our data suggest that hypertriglyceridemia per se and possibly the so-called plurimetabolic syndrome is characterized by low intralymphocyte free magnesium.     

Contribution of D-(-)-3-hydroxybutyrate to the energy expenditure of neonatal pigs

In vivo oxidation rate of arterially infused D-(-)-3-hydroxybutyrate (3HB) was measured in 1-2-d-old-piglets. Twelve piglets (1.4 kg) were randomly assigned to a 12 h continuous infusion of 3HB at 19.5, 37.8, 55.8 or 74.5 mumol/min along with -31 kBq/h of [3-14C]3HB. Piglets were housed in respiration chambers allowing collection of total expired CO2 over 20-min intervals for the 12 h infusion and 6 h washout. Oxidation of 3HB was calculated from the quantity and specific radioactivity of expired CO2 for 20-min collection periods at 6, 9 and 12 h for each piglet and collectively plotted against plasma 3HB concentration measured in blood drawn during those 20-min periods. A Lineweaver-Burk plot of these data yielded a Km of 0.62 +/- 0.07 mmol/L and Vmax of 0.74 +/- 0.02 mmol ATP equivalents/(min.kg 0.75) (parameter estimate +/- SD), which could account for 32% of the piglet mean total ATP turnover of 2.3 mmol/(min.kg 0.75). These data show that 3HB oxidation is a linear function of plasma concentration in the physiologic range measured in piglets (0.006 mmol/L to 0.1 mmol/L) and within this range would account for 0.3% to 4.5% of piglet energy requirement. Oxidation of 3HB can meet a maximum of 30 to 40% of piglet energy requirement at unphysiologically high 3HB concentrations (> 3 mmol/L).     

Inhibition of ischemia-induced glutamate release in rat striatum by dihydrokinate and an anion channel blocker

BACKGROUND AND PURPOSE: Increased activation of excitatory amino acid (EAA) receptors is considered a major cause of neuronal damage. Possible sources and mechanisms of ischemia-induced EAA release were investigated pharmacologically with microdialysis probes placed bilaterally in rat striatum. METHODS: Forebrain ischemia was induced by bilateral carotid artery occlusion and controlled hypotension in halothane-anesthetized rats. During 30 minutes of ischemia, microdialysate concentrations of glutamate and aspartate were measured in the presence of a nontransportable blocker of the astrocytic glutamate transporter GLT-1, dihydrokinate (DHK), or an anion channel blocker, 4,4'-dinitrostilben-2,2'-disulfonic acid (DNDS), administered separately or together through the dialysis probe. RESULTS: In control striata during ischemia, glutamate and aspartate concentrations increased 44+/-13 (mean+/-SEM) times and 19+/-5 times baseline, respectively, and returned to baseline values on reperfusion. DHK (1 mmol/L in perfusate; n=8) significantly attenuated EAA increases compared with control (glutamate peak, 9. 6+/-1.7 versus control, 15.4+/-2.6 pmol/ microL). EAA levels were similarly decreased by 10 mmol/L DHK. DNDS (1 mmol/L; n=5) also suppressed EAA peak increases (glutamate peak, 5.8+/-1.1 versus control, 10.1+/-0.7 pmol/ microL). At a higher concentration, DNDS (10 mmol/L; n=7) further reduced glutamate and aspartate release and also inhibited ischemia-induced taurine release. Together, 1 mmol/L DHK and 10 mmol/L DNDS (n=5) inhibited 83% of EAA release (glutamate peak, 2.7+/-0.7 versus control, 10.9+/-1.2 pmol/ microL). CONCLUSIONS: These findings support the hypothesis that both cell swelling-induced release of EAAs and reversal of the astrocytic glutamate transporter are contributors to the ischemia-induced increases of extracellular EAAs in the striatum as measured by microdialysis.     

Platelet adhesion to collagen type IV under flow conditions

Collagen type IV is a sheet-forming collagen and a major constituent of the vessel wall. To find out which conditions are important for platelet adhesion to collagen type IV, we performed perfusion studies with anticoagulated blood in parallel plate perfusion chambers. The role of divalent cations was investigated by using plasmas with variable concentrations of Mg2+ and Ca2+ ions. When Mg2+ concentration was decreased from 2.00 mmol/L to 0.25 mmol/L at a fixed Ca2+ concentration of 1.25 mmol/L, platelet coverage on the collagen type IV surface decreased from 22.8% +/- 1.8% (n = 4) to 4.6% +/- 0.6% (n = 4) at a shear rate of 1,600 s-1. Also, platelet aggregate formation on collagen type IV was strongly impaired. A monoclonal antibody against the glycoprotein (Gp) Ib receptor and von Willebrand factor (vWF)-depleted plasma reduced the platelet coverage to collagen type IV to, respectively, 10% and 45% of the control value. Electron microscopy showed that vWF was only present between platelets and between the platelet and the collagen type IV surface, but did not bind elsewhere to collagen type IV. These data indicate that collagen type IV is a reactive collagen for platelets. Differences in physiologic plasma magnesium concentrations may in part explain the differences in platelet reactivity to collagen type IV between individuals, and perhaps contribute to differences in the risk for thrombosis.     

Blood concentrations of dopexamine in patients during and after orthotopic liver transplantation

Blood concentrations of dopexamine were measured in five female patients during and after orthotopic liver transplantation. Each patient received a continuous infusion of the drug (2 micrograms kg-1 min-1), starting at induction of anaesthesia and finishing 48 h afterwards. Blood concentrations of dopexamine increased rapidly at the start of the infusion, to a mean (range) value of 64 (40-150) ng ml-1 after 20 min. Blood concentrations of dopexamine increased further during the anhepatic period of surgery, to 236 (180-410) ng ml-1. On reperfusion of the donor liver, concentrations of dopexamine decreased rapidly, reaching similar values to the maximum seen during the dissection period. Steady-state was not reached during either the dissection or anhepatic periods. From 1-2 h after revascularisation the mean (range) steady-state concentration was 85 (69-102) ng ml-1 corresponding to a mean (range) clearance of 24 (20-29) ml min-1 kg -1. These results suggest that the liver plays a significant role in the clearance of dopexamine.     

Lactate metabolism of subcutaneous adipose tissue studied by open flow microperfusion

Open flow microperfusion and a novel calibration technique (ionic reference technique) were evaluated for the frequent measurement of the absolute lactate concentration in sc adipose tissue. Furthermore, the influence of the plasma insulin concentration on the lactate concentration of sc adipose tissue was investigated during hyperglycemia. Sixteen lean healthy young men participated in the studies. In the postabsorbtive state the mean sc lactate concentrations were 1.29 and 1.36 mmol/L for the ionic reference technique and the no net flux protocol, respectively (not significant, P > 0.05). The simultaneously measured arterialized plasma lactate concentration was significantly lower at 0.77 mmol/L (P < 0.05). Both the sc lactate concentration (1.8+/-0.33 mmol/L) and the plasma lactate concentration (0.96+/-0.03 mmol/L) were significantly elevated during a hyperinsulinemic euglycemic clamp experiment. During a hyperglycemic clamp experiment the sc lactate concentration reached a significantly elevated plateau (2.15+/-0.27 mmol/L) that was not influenced by the increasing plasma insulin concentration. It is concluded that 1) open flow microperfusion combined with the ionic reference technique enables frequent measurement of the sc lactate concentration; 2) sc adipose tissue is a significant source of lactate release in the postabsorbtive state as well as during hyperinsulinemic clamp conditions; and 3) insulin concentrations greater than 180 pmol/L have no further influence on adipocyte stimulation of sc adipose tissue with respect to lactate release.     

Enhancement of postischemic myocardial stunning by calcium overload in hearts of diabetic rats

The effects of Ca2+ concentration on postischemic myocardial stunning were studied in isolated working hearts of rats with streptozotocin-induced diabetes and of age-matched control rats. During reperfusion after 10 min of ischemia, hearts from control rats showed complete recovery of cardiac function of Ca2+ concentrations of 1.25, 1.88, and 2.50 mmol/L, while the recovery of diabetic rats was decreased only at a Ca2+ concentration of 2.50 mmol/L. Although myocardial Na+ and Ca2+ concentrations were comparable between control and diabetic rats, only diabetic rats showed increases in myocardial concentration of Na+ during ischemia and Ca2+ during reperfusion at a Ca2+ concentration of 2.50 mmol/L. Results suggest that diabetic rat hearts are vulnerable to postischemic stunning via an overload of calcium.     

Relation of the levels of systemic prostaglandins and hemodynamic changes present during orthotopic transplant of the liver]

The aim of this study is to investigate the role of prostaglandins (PGI2 and TXA2) in relation with the hemodynamic alterations occuring after graft reperfusion in patients undergoing OLT. A total of 40 patients with liver cirrhosis were studied. Systemic 6-keto-PGF1 alpha and TXB2, stable metabolites of PGI2 and TXA2 respectively, were determined at the radial artery, at four different surgical stages: basal, hepatectomy, anhepatic, and 10 minutes after graft reperfusion. Overall results showed that 6-keto-PGF1 alpha levels were significantly elevated during hepatectomy (1143 +/- 204) when compared to values in the basal stage (p = 0.007). During hepatectomy, 6-keto-PGF1 alpha levels did not correlate to systemic vascular resistance index (SVRI), neither with the cardiac index (IC) nor with the medial arterial pressure (MAP) in the same stage. During the anhepatic stage, only IRVS was inversely correlated with 6-keto-PGF1 alpha levels (p = 0.004): there was no relation with MAP and CI. During reperfusion no correlations were observed between 6-keto-PGF1 alpha levels and MAP, CI or SVRI. We conclude that systemic PGI2 levels are very high in cirrhotic patients undergoing OLT. The absence of correlation between the magnitude of changes in hemodynamic parameters and 6-keto-PGF1 alpha levels during reperfusion of the new liver suggests that other factors must play a role in these hemodynamic changes.     

Alterations in plasma magnesium concentrations during liver transplantation

Plasma magnesium concentrations were monitored during orthotopic liver transplantation. Magnesium supplementation was not given, although intraoperative calcium, potassium, and sodium bicarbonate were given as required. We found that there were significant falls in magnesium concentration to below our laboratory lower limit of normal, occurring chiefly during the anhepatic phase of surgery. Two patients with hypomagnesemia but normal potassium and calcium ion concentrations developed ventricular extrasystoles. Magnesium is a smooth muscle relaxant, dilating coronary arteries and peripheral vessels. It also exerts an antiarrhythmic effect and may have a permissive effect on the actions of catecholamines. Magnesium supplementation may be indicated during orthotopic liver transplantation because of the potentially beneficial effects and to avoid possible deleterious effects of hypomagnesemia. However, magnesium levels need to be monitored to avoid the unwanted side effects of hypermagnesemia.     

Human gallbladder mucosal function: effects on intraluminal fluid and lipid composition in health and disease

OBJECTIVES: Fructose-1,6-diphosphate is a glycolytic intermediate that has been shown experimentally to cross the cell membrane and lead to increased glycolytic flux. Because glycolysis is an important energy source for myocardium during early reperfusion, we sought to determine the effects of fructose-1,6-diphosphate on recovery of postischemic contractile function. METHODS: Langendorff-perfused rabbit hearts were infused with fructose-1,6-diphosphate (5 and 10 mmol/L, n = 5 per group) in a nonischemic model. In a second group of hearts subjected to 35 minutes of ischemia at 37 degrees C followed by reperfusion (n = 6 per group), a 5 mmol/L concentration of fructose-1,6-diphosphate was infused during the first 30 minutes of reperfusion. We measured contractile function, glucose uptake, lactate production, and adenosine triphosphate and phosphocreatine levels by phosphorus 31-nuclear magnetic resonance spectroscopy. RESULTS: In the nonischemic hearts, fructose-1,6-diphosphate resulted in a dose-dependent increase in glucose uptake, adenosine triphosphate, phosphocreatine, and inorganic phosphate levels. During the infusion of fructose-1,6-diphosphate, developed pressure and extracellular calcium levels decreased. Developed pressure was restored to near control values by normalizing extracellular calcium. In the ischemia/reperfusion model, after 60 minutes of reperfusion the hearts that received fructose-1,6-diphosphate during the first 30 minutes of reperfusion had higher developed pressures (83 +/- 2 vs 70 +/- 4 mm Hg, p < 0.05), lower diastolic pressures (7 +/- 1 vs 12 +/- 2 mm Hg, p < 0.05), and higher phosphocreatine levels than control untreated hearts. Glucose uptake was also greater after ischemia in the hearts treated with fructose-1,6-diphosphate. CONCLUSIONS: We conclude that fructose-1,6-diphosphate, when given during early reperfusion, significantly improves recovery of both diastolic and systolic function in association with increased glucose uptake and higher phosphocreatine levels during reperfusion.     

Enflurane and isoflurane, but not halothane, protect against myocardial reperfusion injury after cardioplegic arrest with HTK solution in the isolated rat heart

To investigate the effects of halothane, enflurane, and isoflurane on myocardial reperfusion injury after ischemic protection by cardioplegic arrest, isolated perfused rat hearts were arrested by infusion of cold HTK cardioplegic solution containing 0.015 mmol/L Ca2+ and underwent 30 min of ischemia and a subsequent 60 min of reperfusion. Left ventricular (LV) developed pressure and creatine kinase (CK) release were measured as variables of myocardial function and cellular injury, respectively. In the treatment groups (each n = 9), anesthetics were given during the first 30 min of reperfusion in a concentration equivalent to 1.5 minimum alveolar anesthetic concentration of the rat. Nine hearts underwent the protocol without anesthetics (controls). Seven hearts underwent ischemia and reperfusion without cardioplegia and anesthetics. In a second series of experiments, halothane was tested after cardioplegic arrest with a modified HTK solution containing 0.15 mmol/L Ca2+ to investigate the influence of calcium content on protective actions against reperfusion injury by halothane. LV developed pressure recovered to 59%+/-5% of baseline in controls. In the experiments with HTK solution, isoflurane and enflurane further improved functional recovery to 84% of baseline (P < 0.05), whereas halothane-treated hearts showed a functional recovery similar to that of controls. CK release was significantly reduced during early reperfusion by isoflurane and enflurane, but not by halothane. After cardioplegic arrest with the Ca2+-adjusted HTK solution, halothane significantly reduced CK release but did not further improve myocardial function. Isoflurane and enflurane given during the early reperfusion period after ischemic protection by cardioplegia offer additional protection against myocardial reperfusion injury. The protective actions of halothane depended on the calcium content of the cardioplegic solution. IMPLICATIONS: Enflurane and isoflurane administered in concentrations equivalent to 1.5 minimum alveolar anesthetic concentration in rats during early reperfusion offer additional protection against myocardial reperfusion injury even after prior cardioplegic protection. Protective effects of halothane solely against cellular injury were observed only when cardioplegia contained a higher calcium concentration.     

Nitric oxide scavenging by hemoglobin or nitric oxide synthase inhibition by N-nitro-L-arginine induces cortical spreading ischemia when K+ is increased in the subarachnoid space

We investigated the combined effect of increased brain topical K+ concentration and reduction of the nitric oxide (NO.) level caused by nitric oxide scavenging or nitric oxide synthase (NOS) inhibition on regional cerebral blood flow and subarachnoid direct current (DC) potential. Using thiopental-anesthetized male Wistar rats with a closed cranial window preparation, brain topical superfusion of a combination of the NO. scavenger hemoglobin (Hb; 2 mmol/L) and increased K+ concentration in the artificial cerebrospinal fluid ([K+]ACSF) at 35 mmol/L led to sudden spontaneous transient ischemic events with a decrease of CBF to 14+/-7% (n=4) compared with the baseline (100%). The ischemic events lasted for 53+/-17 minutes and were associated with a negative subarachnoid DC shift of -7.3+/-0.6 mV of 49+/-12 minutes' duration. The combination of the NOS inhibitor N-nitro-L-arginine (L-NA, 1 mmol/L) with [K+]ACSF at 35 mmol/L caused similar spontaneous transient ischemic events in 13 rats. When cortical spreading depression was induced by KCl at a 5-mm distance, a typical cortical spreading hyperemia (CSH) and negative DC shift were measured at the closed cranial window during brain topical superfusion with either physiologic artificial CSF (n=5), or artificial CSF containing increased [K+]ACSF at 20 mmol/L (n=4), [K+]ACSF at 3 mmol/L combined with L-NA (n=10), [K+]ACSF at 10 mmol/L combined with L-NA (five of six animals) or [K+]ACSF at 3 mmol/L combined with Hb (three of four animals). Cortical spreading depression induced longlasting transient ischemia instead of CSH, when brain was superfused with either [K+]ACSF at 20 mmol/L combined with Hb (CBF decrease to 20+/-20% duration 25+/-21 minutes, n=4), or [K+]ACSF at 20 mmol/L combined with L-NA (n=19). Transient ischemia induced by NOS inhibition and [K],ACSF at 20 mmol/L propagated at a speed of 3.4+/-0.6 mm/min, indicating cortical spreading ischemia (CSI). Although CSH did not change oxygen free radical production, as measured on-line by in vivo lucigenin-enhanced chemiluminescence, CSI resulted in the typical radical production pattern of ischemia and reperfusion suggestive of brain damage (n=4). Nimodipine (2 microg/kg body weight/min intravenously) transformed CSI back to CSH (n=4). Vehicle had no effect on CSI (n=4). Our data suggest that the combination of decreased NO. levels and increased subarachnoid K+ levels induces spreading depression with acute ischemic CBF response. Thus, a disturbed coupling of metabolism and CBF can cause ischemia. We speculate that CSI may be related to delayed ischemic deficits after subarachnoid hemorrhage, a clinical condition in which the release of Hb and K+ from erythrocytes creates a microenvironment similar to the one investigated here.