Inhibitory Effect of Pentobarbital on Biliary Excretion of Diclofenac in a Rat Liver Perfusion System

The effect of pentobarbital on the biliary excretion of diclofenac was investigated in a rat liver perfusion system following a pulse input of the drug. Without albumin in the perfusate, a trace amount of diclofenac was detected in the outflow from the liver (< 0.1%). The total biliary excretion of diclofenac (intact diclofenac plus its glucuronide) decreased from 23.8% (diclofenac 6.01, glucuronide 17.8%) to 16.3% (diclofenac 5.09, glucuronide 11.2%) with an increase in the perfusate concentration of pentobarbital from 0 to 2.5 μg mL^?1. At pentobarbital concentrations exceeding 2.5 μg mL^?1, the biliary excretion of diclofenac and its glucuronide (14% total diclofenac) was not reduced further. The mean local excretion times of both diclofenac and its glucuronide were approximately 17 min and were unchanged at all pentobarbital concentrations tested. The ratios of biliary excreted diclofenac and its glucuronide to total diclofenac were 22 and 78%, respectively, and these values were virtually constant at all concentrations of pentobarbital in the perfusate. These results suggest that the glucuronidation of diclofenac and the biliary excretion of its glucuronide are rapid processes and that pentobarbital blocks a step before glucuronidation.     

Nasal myoepithelioma removed through endonasal endoscopic surgery: a case report

Myoepithelioma is a rare neoplasm that can occur in either the major or minor salivary gland and accounts for less than 1% of salivary gland neoplasms. We report a rare case of a nasal myoepithelioma that originated from the nasal inferior turbinate. The tumor, measuring 50 × 30 × 20 mm, was in the right nasal cavity and had a necrotic surface. We removed the tumor through endonasal endoscopic surgery. The tumor had spindle-shaped cells and was positive for cytokeratin, (AE1/AE3), vimentin, S-100β, and MIB-1 but was negative for CD34, desmin, neuron-specific enolase, and synaptophysin. Slight immunoreactivity for smooth muscle actin was noted in some tumor cells. There has been no evidence of tumor recurrence in the 18 months following surgery.     

High-Performance Frontal Analysis of the Binding of Thyroxine Enantiomers to Human Serum Albumin Binding of Thyroxine Enantiomers to Human Serum Albumin Kimura

No HeadingPurpose. The aim of this study was to characterize the binding property between thyroxine and human serum albumin (HSA) qualitatively and enantioselectively using high-performance frontal analysis (HPFA).Methods. An on-line HPLC system consisting of an HPFA column, an extraction column, and an analytical HPLC column was developed to be used to determine the unbound concentrations of thyroxine enantiomers.Results. Both enantiomers were bound to human serum albumin at two high-affinity sites with similar affinities. The binding constant (K) and the number of binding sites on an HSA molecule (n) evaluated from Scatchard plot analysis were K = 1.01 × 10⁶m^-1 and n = 1.90 for l-thyroxine, and K = 9.71 × 10⁵ m^-1 and n = 1.97 for d-thyroxine. The binding sites were identified using phenylbutazone and diazepam as site-specific probes for sites I and II, respectively, and each enantiomer was found to bind to both sites. Incorporation of a chiral HPLC column into the on-line system permitted the investigation of enantiomer-enantiomer interactions, which revealed that both enantiomers competitively bind to the same binding sites without significant allosteric effects.Conclusions.     

Suppression of insulin signalling by a synthetic peptide KIFMK suggests the cytoplasmic linker between DIII-S6 and DIV-S1 as a local anaesthetic binding site on the sodium channel

1. Acetyl-KIFMK-amide (KIFMK) restores fast inactivation to mutant sodium channels having a defective inactivation gate. Its binding site with sodium channels could be considered to be the cytoplasmic linker (III-IV linker) connecting domains III and IV of the sodium channel alpha subunit. There is a close resemblance of the amino-acid sequences between the III-IV linker and the activation loop of the insulin receptor (IR). This resemblance of the amino-acid sequences suggests that KIFMK may also modulate insulin signalling. In order to test this assumption, we studied the effects of KIFMK and its related (KIYEK, KIQMK, and DIYET) and unrelated (LPFFD) peptides on tyrosine phosphorylation or dephosphorylation of IR in vitro. 2. Purified IR was phosphorylated in vitro with insulin in the presence of various synthetic peptides and lignocaine. The phosphorylation level of IR was then evaluated after SDS-PAGE separation, followed by Western blot analysis with antiphosphotyrosine antibody. 3. KIFMK and KIYEK inhibited insulin-stimulated autophosphorylation of IR. Lignocaine showed similar effects, but at a higher order of concentration. KIYEK and DIYET, but not KIFMK, dephosphorylated the phosphorylated tyrosine residues. The structurally unrelated peptide LPFFD had no effect either on phosphorylation or dephosphorylation of IR. 4. These results indicate that KIFMK, KIYEK, and lignocaine bind with the autophosphorylation sites of IR. 5. The present findings also suggest that KIFMK and lignocaine bind with the III-IV linker of sodium channel alpha subunit.     

Evaluation of Intestinal Absorption into the Portal System in Enterohepatic Circulation by Measuring the Difference in Portal–Venous Blood Concentrations of Diclofenac

Purpose. We evaluated the first-pass effects in vivo by the intestine and liver during enterohepatic circulation (EHC) by simultaneously measuring the portal and venous plasma concentrations of the rat. Methods. The venous and upper portal blood vessels were cannulated through the jugular and the pyloric veins, respectively, to obtain simultaneously blood samples from both sites. After diclofenac was injected as a bolus through the jugular vein, the concentrations of diclofenac in the portal and jugular veins were measured at time intervals. The absorption rate from the intestinal tract into the portal system was determined using the portal–venous difference in plasma concentrations of diclofenac, considering 40% partitioning of diclofenac into erythrocytes. Results. After one hour, the plasma concentration in the portal vein was always higher than that in the jugular vein in awakening rats with intact EHC (portal–venous blood concentration difference). No portal–venous difference was observed in awakening rats with bile-duct cannulation. Therefore, it was concluded that this portal–venous concentration difference was not due to the hepatic clearance but to diclofenac reabsorption from the intestinal tract. Conclusions. Appropriately 40% of the dose of diclofenac was reabsorbed over 8 hours from the intestinal tract into the portal system. By comparing the reabsorbed amounts in the portal system and in the systemic circulation, the hepatic extraction ratio in vivo (F_H) of diclofenac was estimated to be 63%.     

Effect of Coadministered Uridine on Intestinal First-Pass Metabolism of 5′-Deoxy-5-Fluorouridine in Conscious Rats—An Evaluation by Method of Portal-Systemic Concentration Difference

Purpose. The effect of uridine (UR) coadministration on the intestinal metabolism from 5-deoxy-5-fluorouridine (5-DFUR) to 5-fluorouracil (5-FU) was evaluated by a method of concentration difference between portal and systemic bloods in conscious rats (PS method). Methods. 5-DFUR (100 mg/kg) alone (Group A), or 5-DFUR + UR (100 mg/kg each) (Group B) was orally administered to conscious rats. The portal and arterial bloods were simultaneously withdrawn from two canulas at appropriate time intervals, and blood concentrations of 5-DFUR, 5-FU, UR and uracil (U) were assayed by HPLC. The concentration-time profiles of these drugs and its metabolites were analyzed by local moment analysis. Results. UR coadministration made the local absorption ratio (F_a) of 5-DFUR decrease significantly from 60.1 ± 10.5% to 38.0 ± 18.6% of dose. Though the local absorption ratios (F_a ^m) of the metabolite (5-FU) were the same between Group A and Group B (8.3 ± 1.9 and 8.7 ± 4.0% of 5-DFUR, respectively), AUC of arterial 5-FU in Group B was 5 times greater than that in Group A. UR was not detected in the portal blood, and F_a ^m of U was estimated to be 41.9 ± 26.8% of UR in Group B. Conclusions. It is predicted that a large portion of 5-FU generated from 5-DFUR is further degraded in the intestine in Group A, and U generated from UR blocks 5-FU degradation in the intestine and the systemic circulation in Group B.     

Analysis of enterohepatic circulation of cefixime in rat by fast inverse Laplace transform (FILT)

The enterohepatic circulation of cefixime in rat was evaluated by a nonlinear least square analysis program, MULTI(FILT), into which the fast inverse Laplace transform (FILT) was incorporated. The plasma time course in the bile duct-cannulated rat exhibited a biexponential curve after the rapid iv administration of cefixime. Several pharmacokinetic models for the enterohepatic circulation were constructed based on the recirculatory concept and the Laplace-transformed equations corresponding to these models were derived by means of the method of transfer function. The transformed equations were simultaneously fitted to the time courses of plasma concentration in rats with laparotomy and with bile duct cannula. The optimum model was selected based on the Akaike's information criterion (AIC). The local moment characteristics for a single pass through enterohepatic circulation were further calculated from the time courses of both the plasma concentration and the amount excreted into the bile. The recovery ratio (F_c and the mean circulatory time (¯t_c through a single pass of enterohepatic circulation were estimated 27.9% and 1.07 hr, respectively. The recovery ratio (F_a and the mean absorption time (¯t_a for the absorption process from the intestinal tract into the systemic circulation were 68.3% and 0.0234 hr, respectively. The recovery ratio (F_b and the mean transit time (¯t_b)for the disposition process through the systemic circulation into the bile were 40.8% and 1.05hr, respectively.Notation A _i coefficient - a _i exponent - (s) Laplace transform of the time course of plasma following intravenous dose - (s) Laplace transform of the time course of plasma following oral administration dose - (s) Laplace transform of the time course of plasma concentration without EHC - CL_b clearance into the bile - CL¹ total clearance through the single EHC (=CL_b/F_b) - D_iv intravenous dose - D_po oral administration dose - F_a recovery (availability) from intestinal tract to systemic circulation - F_b recovery from systemic circulation to intestinal tract - F_a recovery from oral dose (absolute availability) - F_c recovery through a single pass of EHC - F_g recovery through the stomach - (s) transfer function corresponding to the process outside the body through the intestinal tract - (s) transfer function for oral dose - (s) transfer function through the systemic circulation into the bile - (s) transfer function for a single pass of EHC - (s) transfer function through the stomach - f_i(t) weight function for the processi - (s) Laplace transform off _t (t) - (s) transfer function corresponding to the recirculatory process - k_a absorption rate constant - s Laplace variable - mean transit time for the absorption process from the intestinal tract - _a mean transit time for oral dose (=MAT) - mean transit time for the disposition process in the body - mean transit time for a single pass of EHC - t ₀ gap time     

Influence of Pentobarbitone on In-vivo Local Disposition of Diclofenac in Rat Liver

Because the liver is the main organ eliminating many drugs from the body and because pentobarbitone and other analogues can inhibit biliary secretion, the influence of pentobarbitone on hepatic local disposition of diclofenac has been investigated. Diclofenac was infused into the portal and femoral veins of non-anaesthetized rats (group A) and rats anaesthetized with pentobarbitone (group B) and the plasma concentration of diclofenac and the total amount of diclofenac excreted in the bile (in both cases intact diclofenac plus its glucuronide) were simultaneously monitored by HPLC at appropriate time intervals. The time-courses of plasma concentration and amount excreted in the bile were evaluated by moment analysis with trapezoidal integration. The hepatic recovery ratio (F_H) was calculated by comparing the area under the curve (AUC) of plasma concentration after intravenous infusion with that after intraportal infusion. The mean biliary transit time (t_b) was estimated by subtracting the mean residence time (MRT) of the plasma data from the mean biliary residence time (MRT_b) of the biliary excretion data. The F_H values of diclofenac were 0.664 in group A and 0.643 in group B. The biliary excretion ratio (F_b) of total diclofenac after intravenous administration was 27.0% in group A and 14.1% in group B. The t?_b values for total diclofenac were estimated to be 0.192 h (intravenous) and 0.159 h (intraportal) in group A, and 0.174 h and 0.238 in group B. Analysis of variance showed that differences among these four t?_b values were insignificant at the 5% level. The differences in the mean residence time (MRT), total clearance (CL) and distribution volume at steady state (V_SS) were insignificant between groups A and B. Whereas total and the hepatic clearance of diclofenac were not affected by pentobarbitone, biliary clearance was extensively reduced. It took a relatively long time for diclofenac to move from the sinusoid into the bile and the time was not affected by pentobarbitone.