ABSTRACT
The present study was conducted to characterise the transporter(s) responsible for the uptake of cyclic nucleotides to human erythrocytes. Western blotting showed that hRBC expressed OAT2 (SLC22A7), but detection of OAT1 (SLC22A6), or OAT3 (SLC22A8) was not possible. Intact hRBC were employed to clarify the simultaneous cyclic nucleotide egression and uptake. Both these opposing processes were studied. The Km -values for high affinity efflux was 3.5 ± 0.1 and 39.4 ± 5.7 µM for cGMP and cAMP, respectively. The respective values for low affinity efflux were 212 ± 11 and 339 ± 42 µM. The uptake was characterised with apparently low affinity and similar Km -values for cGMP (2.2 mM) and cAMP (0.89 mM). Using an iterative approach in order to balance uptake with efflux, the predicted real Km -values for uptake were 100-200 µM for cGMP and 50-150 µM for cAMP. The established OAT2-substrate indomethacin showed a competitive interaction with cyclic nucleotide uptake. Creatinine, also an OAT2 substrate, showed saturable uptake with a Km of 854 ± 98 µM. Unexpectedly, co-incubation with cyclic nucleotides showed an uncompetitive inhibition. The observed Km -values were 399 ± 44 and 259 ± 30 µM for creatinine, in the presence of cGMP and cAMP, respectively. Finally, the OAT1-substrate para-aminohippurate (PAH) showed some uptake (Km -value of 2.0 ± 0.4 mM) but did not interact with cyclic nucleotide or indomethacin transport.
Subject(s)
Cyclic AMP/metabolism , Cyclic GMP/metabolism , Erythrocytes/metabolism , Nucleotides/metabolism , Organic Anion Transporters, Sodium-Independent/metabolism , Biological Transport/physiology , HumansABSTRACT
OBJECTIVE: Acute liver failure (ALF) is haemodynamically characterized by a hyperdynamic circulation. The aims of this study were to investigate the systemic and regional haemodynamics in ALF, to measure changes in nitric oxide metabolites (NOx) and to evaluate whether these haemodynamic disturbances could be attenuated with albumin dialysis. MATERIAL AND METHODS: Norwegian Landrace pigs (23-30 kg) were randomly allocated to groups as controls (sham-operation, n = 8), ALF (hepatic devascularization, n = 8) and ALF + albumin dialysis (n = 8). Albumin dialysis was started 2 h after ALF induction and continued for 4 h. Systemic and regional haemodynamics were monitored. Creatinine clearance, nitrite/nitrate and catecholamines were measured. A repeated measures ANOVA was used to analyse the data. RESULTS: In the ALF group, the cardiac index increased (PGT < 0.0001), while mean arterial pressure (PG = 0.02) and systemic vascular resistance decreased (PGT < 0.0001). Renal resistance (PG = 0.04) and hind-leg resistance (PGT = 0.003) decreased in ALF. There was no difference in jejunal blood flow between the groups. ALF pigs developed renal dysfunction with increased serum creatinine (PGT = 0.002) and decreased creatinine clearance (P = 0.02). Catecholamines were significantly higher in ALF, but NOx levels were not different. Albumin dialysis did not attenuate these haemodynamic or renal disturbances. CONCLUSIONS: The haemodynamic disturbances during the early phase of ALF are characterized by progressive systemic vasodilatation with no associated changes in metabolites of NO. Renal vascular resistance decreased and renal dysfunction developed independently of changes in renal blood flow. After 4 h of albumin dialysis there was no attenuation of the haemodynamic or renal disturbances.
Subject(s)
Albumins/pharmacology , Creatinine/blood , Liver Failure, Acute/physiopathology , Liver Failure, Acute/therapy , Renal Dialysis , Algorithms , Analysis of Variance , Animals , Blood Pressure/drug effects , Catecholamines/blood , Disease Models, Animal , Female , Hepatorenal Syndrome/blood , Liver Failure, Acute/blood , Nitrates/blood , Nitrites/blood , Random Allocation , Renal Dialysis/instrumentation , Renal Dialysis/methods , Swine , Vascular Resistance/drug effectsABSTRACT
OBJECTIVE: Although water-soluble drugs can be removed by haemofiltration/haemodialysis, morbidity and mortality from intoxication with protein-bound drugs remains high. The present study investigates whether albumin dialysis in the form of the Molecular Adsorbents Recirculating System (MARS) is effective in removal of protein-bound drugs. DESIGN: Prospective animal study. SETTING: Surgical research laboratory in a university hospital. SUBJECTS: Seven female Norwegian Landrace pigs. INTERVENTION: We studied whether midazolam (97% albumin-bound) and fentanyl (85% alpha-1-acid glycoprotein-bound), administered as anaesthetics to pigs with induced acute liver failure, could be removed by MARS dialysis lasting for 4 h. MEASUREMENTS: After 4 h of dialysis, total and free anaesthetic concentrations were measured in the blood and dialysate from different segments of the MARS circuit. MAIN RESULTS: Midazolam: total plasma concentrations fell by 47.1+/-2.1% (in 4 h) across the MARS filter ( p<0.01). The charcoal component of the system reduced the total dialysate drug concentration by 16.4+/-2.2% ( p<0.05). Free midazolam removal followed a similar pattern. Fentanyl: total plasma concentrations fell by 56.1+/-2.4% (in 4 h) across the MARS filter ( p<0.01). Clearance of fentanyl from the dialysate by the charcoal was 70+/-0.7% at 4 h ( p<0.001). CONCLUSIONS: The results of the study show that MARS can remove both albumin and other protein-bound drugs efficiently from the plasma, and it may have a place for the treatment of patients suffering from intoxication with this class of compounds.
