Albumin-dependent digoxin transfer in isolated perfused human placenta.

OBJECTIVE: To determine the effects of albumin (BSA) concentration in perfusion medium on digoxin transfer in isolated perfused human placental cotyledon. STUDY DESIGN: Isolated placental cotyledons from 13 normal human placentas were dually perfused after cannulating artery and vein of the chorionic plate and piercing 4 catheters through the corresponding basal plate with M199 medium enriched with BSA and glucose. Flow rates were 12 and 6 ml/min in the maternal and fetal circuits, respectively. Digoxin was added to the maternal reservoir at a final concentration of 5.51 +/- 1.00 ng/ml. BSA in maternal and fetal perfusate was kept at 3 concentrations: 1, 3 and 5 mg/ml (Groups I, II, III). Transplacental passage of digoxin was calculated from repeated fetal and maternal perfusate samples collected over 3 hours in the 3 groups. Digoxin levels were measured by FPIA (TDx, Abbott). RESULTS: There was no transfer of digoxin from the maternal to fetal compartment when the concentration of BSA was 1 mg/ml. Increasing the concentration of BSA led to a substantial increase in the transfer of digoxin to the fetal compartment. Steady state levels of digoxin in the fetal compartment were 0.61 +/- 0.19 ng/ml at 3 mg/ml of BSA. CONCLUSION: Maternal and fetal serum concentration of BSA affect digoxin transfer in isolated perfused human placentas. Three mg/ml are considered to be the optimal albumin concentration.

Thiopurine methyltransferase activity in the Jewish population of Israel.

OBJECTIVE: 6-Mercaptopurine is used therapeutically for its immunosuppressant and cytotoxic properties. It is deactivated by thiopurine methyltransferase (TPMT), which shows genetic polymorphism in many populations. In North American populations, TMPT activity exhibits a trimodal activity pattern. In Oriental populations, TPMT shows almost a unimodal pattern of activity. The purpose of the present study was to assess the activity of TPMT in a Jewish male population sample in Israel. METHODS: The study was approved by the Israeli Ministry of Health. Blood samples of 2.5 ml were collected in heparinized tubes from 134 males. The red blood cell (RBC) fraction of each individual was washed and hemolyzed. TPMT activity in the RBC hemolysate was determined using a radioactive assay with tritiated S-adenosyl methionine as a methyl donor. RESULTS: The activity of TPMT ranged from 3.2 nmol/h/ml to 42.9 nmol/h/ml packed RBCs with mean and median activities of 18.6 nmol/h/ml and 17.9 nmol/h/ml packed RBCs, respectively. The distribution frequency of TPMT was very close to the unimodal by analysis of normal distribution. CONCLUSION: The pattern of distribution of TPMT in the Jewish population of Israel is closer to that of East Asian populations than European and North American populations. This observation may have relevance for the usage of 6-mercaptopurine and azathioprine as therapeutic agents in the Jewish population.

Drug metabolizing enzymes in the ostrich (Struthio camelus): comparison with the chicken and the rat.

The activities of selected hepatic and renal drug-metabolizing enzymes of the ostrich, chicken and rats were compared. The concentration of glutathione in the liver and kidneys of the avian species was significantly lower than in the rat. The activity of ostrich hepatic glutathione S-transferase was 2-fold higher than that of the chicken and the rat and the renal glutathione S-transferase of the ostrich was 10 times higher than that of the rat. The activity of ostrich hepatic UDP-glucuronyl transferase was significantly lower than that of the rat. The activities of hepatic cytochrome P450 1A and 2B1/2 as measured by the dealkylation of ethoxy- and methoxyresorufin, respectively, were higher int he avian species than the rat; no difference was noticed in the activity of aniline hydroxylase. The results show that the activity of ostrich drug-metabolizing enzyme system is quantitatively different from the rat and in many cases also from the chicken.

Red blood cell permeability to thiol compounds following oxidative stress.

The permeability of red blood cells (RBCs) to thiol containing compounds, reduced glutathione (GSH) and N-acetyl cysteine (NAC), has been studied in control adult and neonatal cells and after oxidative stress. NAC penetrates the cell membrane easily while GSH hardly permeates. We measured their capacity to enhance intracellular non-protein thiols (NPSH), after inducing damage to the membrane by formation of defects. Diamide, phenazine methosulfate (PMS) and t-butyl hydroperoxide (BHP) were chosen as exogenous oxidants, each inducing damage by a different mechanism. Our data indicate that although neonatal cells are more sensitive to oxidative stress, only membrane damage induced by diamide, renders adult and neonatal cells permeable to GSH. NAC treatment enhances thiol levels in cells exposed to oxidizing agents, as well as in control cells.

The bioavailability of febantel in dehydrated camels.

In the present study the bioavailability of febantel paste and febantel suspension was investigated in the fully hydrated and the dehydrated camel. The serum concentrations of febantel and its metabolites, fenbendazole, oxfendazole and fenbendazole sulfone were determined by high performance liquid chromatography following extraction with ether. The exposure to febantel and its metabolites in fully hydrated camels was significantly higher in camels dosed with febantel paste compared to febantel suspension, as measured by AUC and Cmax. The AUC and Cmax of fenbendazole and oxfendazole were significantly lower in dehydrated camels as compared to control camels dosed with febantel paste. The systemic availability of febantel suspension in control and dehydrated camels was very low and differences between dehydration and control phases were insignificant. The low systemic availability of febantel in camels dosed with febantel suspension may cause nematodes to become resistant to this anthelmintic. It is, thus, suggested to increase the dose of febantel paste in dehydrated camels in order to increase the exposure to febantel and its metabolites. The binding of febantel, fenbendazole, oxfendazole and fenbendazole sulfone to camels' serum proteins was over 85%. Oxfendazole was only about 70% bound. Dehydration of 10 days did not affect the binding of these benzimidazole derivatives to serum proteins.

Lidocaine elimination and monoethylglycinexylidide formation in the dehydrated camel.

The elimination kinetics and the formation of the monoethylglycinexylidide (MEGX), a major metabolite of lidocaine, were studied in camels deprived of water for 14 days. The study was conducted on four camels in a crossover design. Lidocaine was administered intravenously at a dose of 1 mg/kg to adult female camels when water was given ad libitum (stage 1) and to the same camels after 14 days of dehydration. Blood samples were taken up to 6 h after dosing. Serum lidocaine and MEGX levels were analysed by polarization fluorescence immunoassay. The elimination profiles of lidocaine and the formation of the metabolite MEGX in the two phases of the study were essentially identical. No difference in any pharmacokinetic parameter was noticed between normally hydrated and water-deprived camels. It is thus concluded that dehydration does not affect the cytochrome P450 isozymes involved in degradation of lidocaine to MEGX nor does it affect the hepatic blood flow, which is a major determinant in the clearance of lidocaine. The very low clearance of lidocaine in the camel in comparison with other ruminant or monogastric mammals may be associated with the camel's ability to survive drought in the desert.

Disposition kinetics of tylosin tartrate administered intravenously and intramuscularly to normal and water-deprived camels.

The disposition kinetics of tylosin tartrate administered intravenously (i.v.) at 10 mg/kg and intramuscularly (i.m.) at 20 mg/kg were studied in normal camels and in the same camels at the end of a 14 day water-deprivation period. After i.v. treatment, serum tylosin concentrations in the water-deprived camels were significantly higher, rate of drug elimination was slower, the volume of distribution was significantly smaller, and total body clearance was significantly slower than in the normal camels. On the other hand, serum drug concentrations were lower in the water deprived camels after i.m. dosing, the mean absorption time was significantly shorter and the i.m. availability was significantly smaller than in the normal camels. Water-deprivation was thought to cause reduced rate of tylosin elimination by the liver, as was shown for antipyrine--a drug which is eliminated from the body exclusively by the liver. Redistribution of tylosin in tissues concomitant with a greater proportion of drug in blood and extracellular fluid of water-deprived camels was suggested as a partial explanation for the higher serum drug levels seen after i.v. dosing. The low i.m. availability observed in the water-deprived camels implies that i.v. is the route of choice for tylosin administration to ill, dehydrated camels.

Antipyrine disposition in the dehydrated camel.

In the present study the effects of water deprivation in the camel (Camelus dromedarius) on the pharmacokinetic profile of antipyrine were assessed. A cross-over design was used. The pharmacokinetics of antipyrine in adult and young camels were compared. Antipyrine was administered intravenously to young and adult female camels when water was available ad libitum and to the adult camels after 14 days of dehydration. The elimination half-life of antipyrine in watered adult camels was 136.5 +/- 16.7 min. The half-life of elimination and the mean residence time of antipyrine were significantly prolonged following dehydration. The observed effects of water deprivation were not a function of age, as the pharmacokinetic profile of antipyrine in young camels was similar to that of the adults, but more likely due to the changes in oxidative metabolic capacity of the liver as a result of a reduced general metabolism. The results of the present study also show that the intrinsic clearance of antipyrine is proportional to the camel's body weight, as previously shown for other mammalian species.

Loperamide effects on hepatobiliary function, intestinal transit and analgesia in mice.

Loperamide effects on hepatobiliary function, analgesia and gut transit were studied in mice. Varying doses of the antidiarrheal drug, loperamide, were administered to mice by intracerebroventricular, intravenous, subcutaneous and intragastric routes. Gut motility was determined by intestinal transit of India ink, analgesia by warm water tail flick latency, and hepatobiliary function by retention of the anionic dye, sulfobromophthalein in plasma and liver. When given by all routes at modest doses, loperamide slowed intestinal transit. Analgesia, a centrally mediated opiate effect, was only detected after intracerebroventricular or subcutaneous loperamide at high, near-toxic doses. Elevations of plasma and liver sulfobromophthalein were noted at routes and doses which slowed gut transit, well below those needed for analgesia. Intragastric loperamide at one fortieth its LD50 caused marked elevation of sulfobromophthalein levels and gut slowing, but no analgesia. Sulfobromophthalein elevation and gut slowing by intragastric loperamide were not affected by spinal cord transection but were reversed by naltrexone, an opiate antagonist. Non-toxic doses of loperamide slow gut transit and modify hepatobiliary function in mice by opiate actions at peripheral sites.

Effects of clonidine and IBMX on sulfobromophthalein disposition in rats.

Clonidine, an alpha 2-adrenoceptor agonist, inhibited the biliary excretion, reduced the plasma clearance and increased the hepatic retention of sulfobromophthalein (BSP) in a dose related fashion in rats. The maximal effects of clonidine on BSP disposition occurred about 4 h after pretreatment. The effects of clonidine on biliary excretion and hepatic retention of BSP were retained following laparotomy (with or without bile duct cannulation); however, the effect of clonidine on plasma disappearance profile was not retained following abdominal surgery. Isobutylmethylxanthine (IBMX) affected BSP disposition in a similar fashion as clonidine, in rats without bile duct cannulation only; no effect of IBMX could be observed in bile duct cannulation rats. Yohimbine, an alpha 2-adrenoceptor antagonist, reversed the effects of clonidine, but not of IBMX, on BSP disposition. It thus seems that clonidine and IBMX exert their effects on BSP disposition by different mechanisms and probably at different sites.

Bromosulfophthalein disposition in chronically bile duct obstructed rats.

The disposition of bromosulfophthalein was studied in chronically bile duct obstructed rats. In this model a catheter was inserted into the common bile duct and the distal tip was sealed. Resumption of bile flow was achieved with great ease. Obstruction of bile duct for 18 days in rats resulted in elevated bilirubin, ALT, AST, and alkaline phosphatase levels. Portal hypertension developed within this period (11.6 +/- 0.5 in obstructed rats vs. 8.6 +/- 0.6 mm Hg in sham-operated group). After the bile duct obstruction was opened, the half-life time for elimination of bromosulfophthalein (42.30 +/- 6.47 min) was longer than in sham-operated rats (21.23 +/- 3.34 min). Plasma clearance was reduced by 70% in bile duct obstructed rats. In spite of increased bile flow rate, biliary excretion of the dye was reduced by 40% in chronically bile duct obstructed rats. Hepatic glutathione levels were significantly reduced by 20% in this model. The specific activity of glutathione S-transferase with chlorodinitrobenzene and styrene oxide, as substrates, was reduced by 50% and 30%, respectively. However, the percent of conjugated bromosulfophthalein in bile was similar to that of sham-operated rats.

Disposition of hexobarbitone and antipyrine in DOCA-hypertensive rats.

The disposition of antipyrine and hexobarbitone, and their effects on drug metabolizing hepatic enzymes have been investigated in DOCA-hypertensive rats. Antipyrine pharmacokinetic parameters were the same in hypertensive and control animals. Hexobarbitone sleeping time was longer in hypertensive rats compared with controls, while the activity of hepatic hexobarbitone hydroxylase was the same in both groups. Hepatic aminopyrine-N-demethylase activity was elevated in hypertensive rats while aniline hydroxylase and aryl hydrocarbon hydroxylase were lower. Glucuronyl transferase was the same in both groups. The sensitivity of the central nervous system of hypertensive rats to hexobarbitone was not altered, as determined by hexobarbitone concentration in blood and in brain. The total hepatic blood flow (arterial and portal) was significantly increased. Thus it is suggested that the difference in the disposition of the two drugs is probably not due to drug metabolizing enzyme activity. It is likely that the increase in total hepatic blood flow and rapid saturation of hepatic hexobarbitone metabolizing enzymes have significant roles in the slower metabolism and increased activity of hexobarbitone in hypertensive rats as compared with control rats.

Association of hematuria and mycobacterial infection.

Hematuria has been noted to be a presenting symptom of urinary tuberculosis. In the last few decades because of the decreasing incidence of tuberculosis in the United States, the association of tuberculosis and hematuria has been neglected. Now that the incidence of tuberculosis is again on the rise, it is timely to remind the medical community of this association. We present 3 children with hematuria associated with positive tuberculin tests. Mycobacterium tuberculosis was cultured from the urine of one patient. Mycobacterium avium-intracellulare was cultured from a second patient. All 3 patients showed clearing of their hematuria with antituberculosis therapy. A tuberculin test should once again be considered part of the standard work-up of hematuria.

Hepatobiliary effects of morphine are mediated in the brain.

Morphine slows hepatobiliary elimination of sulfobromophthalein in rodents, raising dye levels in plasma and liver. Earlier studies showed these effects to be independent of other opiate effects such as bile duct spasm, hypothermia or blood gas changes resulting from respiratory depression. Because opiate receptors are distributed throughout the body, within the central nervous system and at peripheral sites including the gastrointestinal tract, experiments were performed to ascertain whether central or peripheral sites mediate the hepatobiliary effects of morphine. Sulfobromophthalein was administered intravenously to mice and its levels were measured in plasma and liver. Tail-flick latency indicated centrally mediated analgesia. Inhibited intestinal transit of India ink reflected an opiate effect with a significant peripheral component. When injected into a cerebral ventricle morphine was much more potent in producing analgesia and raising sulfobromophthalein levels than when administered intravenously or intraperitoneally. An intravenous dose of naloxone that reversed morphine analgesia also prevented sulfobromophthalein elevation but did not prevent gut slowing. Naltrexone injected in a cerebral ventricle also reversed analgesia and sulfobromophthalein elevation but not intestinal slowing. The polar opiate agonist N-methylmorphine did not cause analgesia or raise sulfobromophthalein levels at peripheral intraperitoneal doses to 100 mg/kg. When given in a central ventricle at 4 x 10(-3) mg/kg, this agent produced analgesia and raised sulfobromophthalein but did not slow intestinal transit. After spinal cord transection, intravenous morphine did not retard the tail-flick response or affect sulfobromophthalein disposition, but peripherally mediated intestinal transit was slowed as it was in intact mice. These experiments demonstrate parallel opiate effects on analgesia and on BSP disposition but not on intestinal transit.(ABSTRACT TRUNCATED AT 250 WORDS)

Monitoring phenytoin therapy using citric acid-stimulated saliva in infants and children.

Two factors have limited the use of saliva in monitoring phenytoin therapy: availability of adequate volume of clear saliva and lack of a sensitive phenytoin assay. The applicability of citric acid-stimulated saliva and of a sensitive analytical assay (fluorescence polarization immunoassay, "TDx" Abbott) was evaluated in this study. Phenytoin was measured in paired plasma-saliva specimens from epileptic children during the long-term or the initial phase of phenytoin therapy. Analysis was carried out in plasma and in the clear supernatant of saliva (following centrifugation). Pooled-estimate SD of the analytical assay variability was 0.175 micrograms/ml for plasma total phenytoin, 0.063 for plasma free phenytoin, and 0.009 for saliva phenytoin. Recovery measurements of phenytoin spiked into saliva samples gave a coefficient of variation of less than 5%. Correlations between saliva and total plasma phenytoin levels and between saliva and free plasma phenytoin levels were strong and highly significant (r = 0.99, p less than 0.01). The percentage of temporal fluctuation (as determined by saliva phenytoin profiles) during 10-24 h ranged between 25.5-177 (mean, 58.3; SD, 47.3). Ratios of plasma total phenytoin/saliva phenytoin and of plasma free phenytoin/saliva phenytoin levels were 9.54 +/- 1.05 and 0.71 +/- 0.09, respectively. Dialysis experiments showed no binding of phenytoin to saliva supernatant. The greater saliva phenytoin concentrations as compared to plasma free phenytoin concentrations could be due to active transport of phenytoin from plasma to saliva. Measurement of phenytoin in citric acid-stimulated saliva by fluorescent polarization immunoassay is a reliable, noninvasive, and convenient method for monitoring phenytoin therapy in children.

Acetaminophen hepatotoxicity: is there a role for prostaglandin synthesis?

The hepatotoxicity of acetaminophen (APAP) overdose depends on metabolic activation to a toxic reactive metabolite via hepatic mixed function oxidase. In vitro studies have indicated that APAP may also be cooxidized by prostaglandin H synthetase. The present experiments were designed to assess the possible contribution of hepatic prostaglandin synthesis to APAP toxicity. Adult fed male mice were overdosed with 400 mg APAP/kg. Liver toxicity was estimated by measurement of serum transaminases. Hypertonic xylitol or sodium chloride (2250 mOsm/l), administered intragastrically to stimulate prostaglandin synthesis, increased APAP toxicity. By contrast, the cyclooxygenase inhibiting drugs aspirin (at 25 mg/kg) and indomethacin (at 10 mg/kg) protected against APAP-induced toxicity. APAP kinetics were not affected by hypertonic xylitol or indomethacin, nor were hepatic glutathione levels in overdosed mice. Imidazole, a nonspecific thromboxane synthetase inhibitor, also protected overdosed mice. This drug prolonged hexobarbital sleeping time and prevented the depletion of hepatic glutathione that followed APAP intoxication. Thus, the data support the conclusion that APAP-induced hepatoxicity may be modulated not only by inhibition of cytochrome P450 mediated oxidation, but also by controlling hepatic cyclooxygenase activity.

Interaction of clonidine and morphine with lidocaine in mice and rats.

Morphine and clonidine both elevated plasma levels of lidocaine to the same extent in mice while slowing lidocaine metabolism to deethylated products. The effects of clonidine on lidocaine disposition were reversed by yohimbine. Mice given morphine, 20 mg/kg sc, or clonidine, 0.2 mg/kg sc, had similar, 30-50%, elevation of plasma lidocaine levels at 15 min after lidocaine, 15 mg/kg iv, when compared to saline-treated animals. Despite similarity of effect on plasma lidocaine, mice treated with morphine were much more susceptible to lethal effects of lidocaine than were mice given clonidine. At iv doses of 22 mg/kg or higher, lidocaine caused death in nearly all morphine-treated mice, while even 32 mg/kg lidocaine caused only 11% mortality after saline or clonidine. Clonidine, 0.5 mg/kg sc, and morphine, 20 mg/kg sc, both raised plasma lidocaine levels in rats, but only morphine depressed respiration, causing hypoxia, hypercapnia, and acidosis and increasing lidocaine lethality. These data suggest that potentiation of lidocaine toxicity by morphine is due primarily to changes in blood gases rather than to elevation in lidocaine levels.

Liver function and protein binding in camels.

1. Dehydration of camels for 10 days resulted in reduction of liver functions, expressed in longer half life and reduced clearance of bromosulfophthalein (BSP), elevated AST (ALT levels were below the limit of detection of the method) and reduced serum albumin concentrations. 2. Binding of BSP to camel serum proteins by gel permeation chromatography and by equilibrium dialysis showed very strong binding. 3. Binding parameters of various drugs to camels serum by equilibrium dialysis showed close similarities both qualitatively and quantitatively to those of humans. 4. Albumin seems to be the major serum binding protein of BSP.

Clonidine effects on disposition of xenobiotics in rats: inhibited elimination of flow-limited but not extraction-limited agents.

1. The alpha 2-adrenoceptor agonist, clonidine, reduces the hepatobiliary clearance of the anionic dye, sulphobromophthalein (BSP) in rodents. We now compare the effects of clonidine on BSP elimination with its effects on disposition of compounds which are metabolized by hepatic microsomal mixed function oxidases. 2. BSP, 100 mg kg-1 was administered i.v. to rats at 4 h after s.c. saline or clonidine, 0.2 mg kg-1. Thirty min later, plasma BSP levels were 121.4 +/- 2.25 micrograms ml-1 in saline-treated rats, while in clonidine-treated rats they were 631.5 +/- 141.0 micrograms ml-1. Clonidine raised hepatic BSP levels from 256.0 +/- 28.9 micrograms g-1 tissue to 568.5 +/- 86.5 micrograms g-1. 3. Acute administration of clonidine (0.2 mg kg-1 s.c.) or repeated clonidine dosing (0.2 mg kg-1, s.c. twice daily for 10 days) did not affect the disposition of intravenously administered [14C]-antipyrine (15 mg kg-1). 4. Activities of the P450 mixed function oxidase enzymes, aniline hydroxylase and aminopyrine N-demethylase, were identical in liver microsomes from saline-treated rats and in microsomes from rats given single or multiple s.c. doses of clonidine (0.2 mg kg-1). 5. Addition of clonidine or other 2-substituted imidazoles at concentrations up to 2 microM did not affect the activities of aniline hydroxylase or of aminopyrine N-demethylase in suspensions of rat liver microsomes. Other substituted imidazoles, including cimetidine, clotrimazole and metronidazole, at concentrations of 0.2 microM or higher, inhibited the activities of these microsomal enzymes. 6. Clonidine slowed BSP elimination, which is probably hepatic blood flow-limited, but not the extraction-limited elimination of antipyrine, which is metabolized by hepatic microsomal enzymes.

Morphine effects on gentamicin disposition and toxicity in mice.

Morphine has been shown to reduce renal and hepatic clearance of several xenobiotics in rodents. After iv administration of gentamicin, 10 to 30 mg/kg, its plasma levels were elevated in mice given morphine, 20 mg/kg sc. Plasma clearance of gentamicin was nearly halved by morphine, due primarily to lowering of the elimination constant of gentamicin from 0.03 to 0.02 min-1 (p less than 0.01). Morphine also significantly reduced urine levels of gentamicin and urine volume. In mice given naloxone, 2 mg/kg sc, morphine did not significantly raise plasma levels of gentamicin nor reduce its elimination into urine. Mice were made tolerant by morphine administration for 9 days at ascending doses to 100 mg/kg twice daily. An acute challenge with morphine, 20 mg/kg, was less effective in raising plasma levels of gentamicin or lowering its urinary elimination in tolerant mice than after chronic saline treatment. Partial tolerance to acutely administered morphine and reversal of morphine effects by naloxone suggest opioid receptor-mediated reduction of glomerular filtration by morphine in mice. Despite marked elevation of plasma gentamicin levels in morphine-treated mice, narcotic administration did not significantly increase the acute toxicity of a single dose of gentamicin. LD50 of acutely administered iv gentamicin was 51.6 mg/kg after saline and 45.3 mg/kg after treatment with morphine, 20 mg/kg sc. However, this dose of morphine enhanced the lethality of intravenously infused gentamicin. Morphine administration significantly reduced the dose of infused gentamicin needed to achieve the critical lethal plasma level.