Conjugation of para-nitrophenol by the isolated perfused neonatal sheep liver

We examined the metabolism of para-nitrophenol (PNP) in the isolated perfused neonatal sheep liver (n = 8, 0.25-11 days) and compared the findings with our previous data from the perfused near-term fetal sheep liver (Ring, J. A., et al. Drug Metab Dispos 1996, 24, 1378). A three-step dosage regimen was used (72, 144, and 288 micromol of PNP). At the end of each dosage phase, PNP had fallen below detectable levels, and 101 +/- 16% of the dose was accounted for as PNP conjugates. Elimination of PNP from perfusate varied with dose. Elimination was first order with the 72-micromol dose; with the 144-micromol dose, elimination was first order in four livers but Michaelis-Menten kinetics in the remaining four. With all the 288-micromol doses, elimination was Michaelis-Menten and gave the following biochemical parameters: K(m) = 255 +/- 138 microM (fetal = 14.7 microM, P < 0.01), V(max) = 515 +/- 285 nmol/min/g liver (fetal = 34.3 nmol/min/g liver, P < 0.01), and intrinsic hepatic clearance = 2.36 +/- 1.21 mL/min/g liver (fetal = 4.74 mL/min/g liver, P > 0. 05). The mean shunt-corrected hepatic extraction ratio of PNP was 0. 82 (range, 0.40-1.0) and strongly correlated with neonatal age (r = 0.90, P < 0.05). We conclude that PNP is highly extracted by the isolated perfused neonatal sheep liver at much higher efficiency than in the near-term fetal sheep, reflecting a maturation of conjugation that progresses further in the early neonatal period.

Fetal hepatic drug elimination

The majority of studies of fetal hepatic elimination have concentrated on the expression and activity of the metabolizing enzymes, but the unique physiologic milieu of the fetal liver should also be considered. The basic structure of the liver is formed by the end of the first trimester. The fetal hepatic circulation differs substantially from that of the adult in that there is an extra input vessel, the umbilical vein, and there is shunting of 30-70% of hepatic blood flow via the ductus venosus. The left and right lobes of the fetal liver seem to function independently with respect to a variety of biochemical parameters, due at least in part to the lower oxygen supply to the right lobe. The zonation of drug-metabolizing enzymes along the hepatic acinus, which is prominent in the adult liver, is absent in the fetal liver. Unlike rodent species, the human fetal liver has a significant capacity for drug metabolism. Of the oxidative enzymes, CYP3A7 accounts for up to 50% of total fetal hepatic cytochrome P450 content. Expression of this enzyme decreases dramatically after birth. CYP1A1 and CYP2D6 have also been detected in human fetal liver, but whether CYP2E1 is expressed remains controversial. Several other cytochrome P450s have been identified and await characterization. Fetal hepatic drug conjugation may prolong fetal exposure to the metabolites produced, which, being more water soluble, do not readily cross the placenta back to the mother and, if excreted in fetal urine, can be recycled in the fetus via amniotic fluid and fetal swallowing. Limited activity of glucuronidation enzymes has been demonstrated in human fetal liver in contrast to the activity of sulfation enzymes, which is significant. Limited in vivo studies in fetal sheep have demonstrated significant fetal hepatic drug elimination, and this has been confirmed in studies of the isolated perfused fetal sheep liver. Our understanding of fetal hepatic elimination processes has advanced steadily over the years. Future developments, however, should consider more fully the influence of the unique physiological milieu of the fetal liver, in addition to the expression and activity of drug metabolizing enzymes.

Comparing the relative role of perforin/granzyme versus Fas/Fas ligand cytotoxic pathways in CD8+ T cell-mediated insulin-dependent diabetes mellitus

CD8+ cytotoxic T cells play a critical role in initiating insulin-dependent diabetes mellitus. The relative contribution of each of the major cytotoxic pathways, perforin/granzyme and Fas/Fas ligand (FasL), in the induction of autoimmune diabetes remains controversial. To evaluate the role of each lytic pathway in beta cell lysis and induction of diabetes, we have used a transgenic mouse model in which beta cells expressing the influenza virus hemagglutinin (HA) are destroyed by HA-specific CD8+ T cells from clone-4 TCR-transgenic mice. Upon adoptive transfer of CD8+ T cells from perforin-deficient clone-4 TCR mice, there was a 30-fold increase in the number of T cells required to induce diabetes. In contrast, elimination of the Fas/FasL pathway of cytotoxicity had little consequence. When both pathways of cytolysis were eliminated, mice did not become diabetic. Using a model of spontaneous diabetes, which occurs in double transgenic neonates that express both clone-4 TCR and Ins-HA transgenes, mice deficient in either the perforin or FasL/Fas lytic pathway become diabetic soon after birth. This indicates that, in the neonate, large numbers of autoreactive CD8+ T cells can lead to destruction of islet beta cells by either pathway.

Antigen concentration and precursor frequency determine the rate of CD8+ T cell tolerance to peripherally expressed antigens

Expression of transgene-encoded proteins in the pancreatic islets can cause peripheral deletion of T cells. However, tolerance has not been observed in all transgenic models. It has been proposed that the determining factor for successful peripheral tolerance is the amount of Ag cross-presented by quiescent APCs. Using InsHA mice, which demonstrate peripheral tolerance to the influenza virus hemagglutinin (HA) expressed in the pancreatic islet beta cells, we have investigated the consequences when different amounts of HA are expressed. As compared with InsHA mice that are heterozygous for the InsHA transgene, homozygous InsHA mice demonstrated enhanced activation and proliferation of Kd-restricted HA-specific CD8+ T cells in the pancreatic lymph nodes. However, despite such activation, insulitis was not observed, and the T cells were gradually functionally deleted. Deletion of these activated cells occurred much more rapidly in homozygous than in heterozygous InsHA mice. These data demonstrate that there is a direct correlation between the amount of HA expressed in the periphery, and both the degree of T cell proliferation in the pancreatic lymph nodes and the rate of tolerance of HA-specific CD8+ T cells. This strongly supports the hypothesis that activation of T cells through cross-presentation of peripheral Ags in a noninflammatory environment is an important part of the normal mechanism of tolerance to Ags expressed in the pancreatic islets.

Age-related abnormalities in arterial compliance identified by pressure pulse contour analysis: aging and arterial compliance

The objective of this study was to evaluate age-related changes in pulsatile arterial function. Aging alters arterial pulsatile function and produces consistent changes in the pressure pulse contour. A reduced systemic arterial compliance that can be derived from analysis of the pulse contour is regarded as the best clinical index of impaired pulsatile arterial function and may mark the presence of early vascular damage. We analyzed intra-arterial brachial artery waveforms in 115 healthy normotensive volunteers (83 men, 32 women) and radial artery waveforms obtained with the use of a calibrated tonometer device in 212 healthy volunteers (147 women, 65 men). A computer-based assessment of the diastolic pressure decay and a modified Windkessel model of the circulation were used to quantify changes in arterial waveform morphology in terms of large artery or capacitive compliance, oscillatory or reflective compliance in the small arteries, inertance, and systemic vascular resistance. Large artery compliance and oscillatory compliance correlated negatively with age for both invasive and noninvasive groups (r=-0.50 and r=-0.55; r=-0.37 and r=-0.66; P<0.001 for all). The slopes of the regression lines for the decline in oscillatory compliance with age were significantly steeper than those recorded for large artery compliance estimates. The change in blood pressure with age independently contributed to the decrease in large artery compliance but not oscillatory compliance in both groups. Consistent age-related changes were found in the pressure pulse contour by analysis of waveforms obtained invasively or noninvasively from the upper limb. The change in the oscillatory or reflective compliance estimate was independent of blood pressure change and may represent a better marker than large artery or capacitive compliance of the degenerative aging process in altering pulsatile arterial function.

Determination of lamotrigine in human plasma by high-performance liquid chromatography

The method involves precipitation of plasma proteins with acetonitrile and analysis of the supernatant by high-performance liquid chromatography using a 5 microm Zorbax C8 column. Quantitation was performed by measurement of the UV absorbance at a wavelength of 306 nm. The method was linear in the range of 1-20 microg/ml, with a mean coefficient of determination (r2=0.998). The limit of detection was 0.6 microg/ml and the lower limit of quantitation was 1 microg/ml using 200 microl of plasma. Within- and between-day accuracy and precision were below 6% at all analysed concentrations except at the limit of quantitation. No interfering peaks were found by commonly monitored antiepileptic drugs. Recovery was found to be > or =99%. Satisfactory performance was obtained in the evaluation of epileptic patient samples, whose results of plasma concentration measurements are briefly discussed. We conclude that this is a reliable method for the routine monitoring of lamotrigine concentration in plasma in the clinical setting.

Comparative effects of oxygen supplementation on theophylline and acetaminophen clearance in human cirrhosis

BACKGROUND & AIMS

Sinusoidal capillarization in cirrhosis may impair the transfer of oxygen into hepatocytes; this may contribute to impaired oxidative drug metabolism. The aim of this study was to test this hypothesis by comparing the effects of oxygen supplementation in cirrhotic patients on the clearance of theophylline, which is dependent on hepatic oxidative metabolism, with its effect on the clearance of acetaminophen, which is reliant on hepatic conjugation reactions.

METHODS

Ten cirrhotic patients awaiting liver transplant and 5 control subjects were studied. Oral acetaminophen (1000 mg) and intravenous theophylline (3 mg/kg) were administered simultaneously on two separate occasions, 7 days apart. Subjects were randomized to breathe either room air or oxygen via face mask at 12 L/min for 9 hours of blood sampling.

RESULTS

Theophylline and acetaminophen clearances were significantly reduced by a mean of 54% and 50%, respectively, in cirrhotic patients compared with controls. Oxygen supplementation improved plasma theophylline clearance in cirrhotic patients by a mean of 34% (P = 0. 001), whereas acetaminophen clearance remained unchanged.

CONCLUSIONS

These findings indicate that, in cirrhosis, impaired hepatocyte oxygenation contributes to reduced oxidative drug metabolism and that oxidative drug metabolism can be improved by oxygen supplementation.

Clonidine and cardiac surgery: haemodynamic and metabolic effects, myocardial ischaemia and recovery

Clonidine may have beneficial effects in patients undergoing major surgery. We enrolled 156 patients having elective CABG surgery in a double-blind, randomized trial. Patients were randomized to receive either two doses of placebo (Group PP) or clonidine 5 micrograms/kg (Group CC). Perioperative measurements included haemodynamics, anaesthetic and analgesic drug usage, creatinine clearance, cortisol excretion, recovery times and quality of life (SF-36) after surgery. Overall, there was no significant difference with time to tracheal extubation (median [10-90 centile]): CC 7.1 (3.4-18) h vs PP 8.0 (4.3-17) h, P = 0.70; but there was a higher proportion of patients extubated within four hours: CC 20% vs. PP 8%, P = 0.038. Clonidine resulted in a number of significant (P < 0.05) haemodynamic changes, particularly pre-CPB: less tachycardia and hypertension, more bradycardia and hypotension. Clonidine was associated with a significant (P < 0.05) reduction in anaesthetic drug usage, higher creatinine clearance, lower cortisol excretion and improvement in some aspects of quality of life. This study lends support to consideration of clonidine therapy in patients undergoing CABG surgery.

Uptake and excretion of sodium taurocholate by the isolated perfused neonatal sheep liver

We present a model for perfusion of the isolated perfused neonatal sheep liver which allows examination of drug disposition by the intact organ. We studied the disposition of sodium taurocholate (TC) in seven neonatal lambs (ages 2-11 days) and compared the results with earlier data from the perfused fetal sheep liver (Ring, J. A. et al. Biochem. Pharmacol. 1994, 48, 667-674). Measurements of perfusion pressure, oxygen consumption, lactate:pyruvate ratio, bile flow, and liver histology indicated that the preparation was both viable and stable over a 2 h period. [14C]-labeled TC was added to the reservoir by constant infusion (30 micromol/h) and the ductus venosus shunt quantitated by injection of [153Gd]-labeled microspheres. Shunt-corrected hepatic extraction ratio of TC was 0. 56 +/- 0.14 (fetal 0.23 +/- 0.16, p < 0.005) and clearance of TC was 0.92 +/- 0.35 mL/min/g liver (fetal 0.44 +/- 0.23 mL/min/g, p < 0. 01). We conclude that the isolated perfused neonatal sheep liver is a useful experimental model which will facilitate the study of the developmental physiology and pharmacology of the liver. There is considerable maturation of the biliary excretion of TC between the late fetal and early neonatal periods in the lamb.

Ontogeny of T cell tolerance to peripherally expressed antigens

Transgenic expression of the influenza virus hemagglutinin (HA) in the pancreatic islet beta cells of InsHA mice leads to peripheral tolerance of HA-specific T cells. To examine the onset of tolerance, InsHA mice were immunized with influenza virus A/PR/8 at different ages, and the presence of nontolerant T cells was determined by the induction of autoimmune diabetes. The data revealed a neonatal period wherein T cells were not tolerant and influenza virus infection led to HA-specific beta cell destruction and autoimmune diabetes. The ability to induce autoimmunity gradually waned, such that adult mice were profoundly tolerant to viral HA and were protected from diabetes. Because cross-presentation of islet antigens by professional antigen-presenting cells had been reported to induce peripheral tolerance, the temporal relationship between tolerance induction and activation of HA-specific T cells in the lymph nodes draining the pancreas was examined. In tolerant adult mice, but not in 1-week-old neonates, activation and proliferation of HA-specific CD8(+) T cells occurred in the pancreatic lymph nodes. Thus, lack of tolerance in the perinatal period correlated with lack of activation of antigen-specific CD8(+) T cells. This work provides evidence for the developmental regulation of peripheral tolerance induction.

Effect of cirrhosis on sulphation by the isolated perfused rat liver

BACKGROUND/AIMS

There is evidence to suggest that not all pathways of drug metabolism are similarly affected in cirrhosis. The effect of cirrhosis on drug oxidation and glucuronidation has been extensively investigated but little is known of the effect of cirrhosis on drug sulphation. The aim of this study was to investigate the effect of cirrhosis on sulphation.

METHODS

We investigated the effect of cirrhosis on p-nitrophenol sulphation and compared this with the effect of cirrhosis on p-nitrophenol glucuronidation as well as on d-propranolol oxidation simultaneously in the single-pass isolated perfused rat liver. The perfusate contained added inorganic sulphate to maximise production of p-nitrophenol sulphate.

RESULTS

About 77% and 59% of p-nitrophenol was eliminated as the sulphate conjugate by the healthy (n=6) and cirrhotic (n=7) livers, respectively. Mean total p-nitrophenol clearance was decreased in cirrhosis (healthy: 18.5+/-0.2 vs. cirrhotic 15.3+/-4.0 ml/min; p<0.05). The decrease in total clearance of p-nitrophenol was due solely to the decrease in sulphate formation clearance, which was significantly decreased (healthy: 14.1+/-1.9 vs. cirrhotic: 9.27+/-3.33 ml/min; p<0.05). Mean glucuronide formation clearance (healthy: 5.11+/-0.94 vs cirrhotic: 5.79+/-0.85 ml/ min; p>0.05) was not significantly altered. Mean total propranolol clearance was decreased in cirrhosis (healthy: 19.9+/-0.1 vs. cirrhotics: 18.0+/-1.5 ml/min; p<0.05).

CONCLUSIONS

We have shown that in cirrhosis there is significant impairment of drug oxidation and sulphation, whilst glucuronidation is spared. The decreased sulphation of p-nitrophenol was most likely due to a decrease in phenol sulphotransferase and/or decrease in cofactor synthesis.

A comparison of the use of Papanicolaou-stained cervical cytological smears with Gram-stained vaginal smears for the diagnosis of bacterial vaginosis in early pregnancy

Our objective is to compare the efficacy of using Papanicolaou (PAP)-stained cervical cytology smears with a standardized method of interpreting Gram-stained vaginal smears for the diagnosis of bacterial vaginosis (BV) in pregnancy. High vaginal smears were Gram-stained and examined by a single observer to characterize 3 grades of vaginal flora and diagnose BV. Cervical smears were PAP-stained and examined for characteristic patterns of vaginal flora including evidence of BV by either a number of cytotechnicians or a single cytopathologist. The results of the 2 methods were compared. Seven hundred and forty-seven women attending an antenatal clinic in a district general hospital who consented to have a smear of vaginal secretions and cervical cytology in early pregnancy. The main outcome measure is the diagnosis of BV by different methods in a pregnant population. Compared with the Gram-stain method for the diagnosis of BV, there was good agreement between PAP-stain interpretation by a single observer but the agreement was not as good with PAP-stain interpretation by multiple cytotechnicians. When the grades were consolidated to normal (grade I) and abnormal flora (grades II and III), compared to Gram-stained smears, PAP cytology undertaken by several cytotechnicians had a sensitivity of 80.7% and a specificity of 90.7%. The sensitivity and specificity increased to 87% and 97%, respectively, when the PAP-stained smears were read by a single cytopathologist. Using kappa scores, only those readings made by a single cytopathologist were reliable. The setting in a cytopathology laboratory comprises multiple cytotechnicians, so that PAP-stain analysis of vaginal smears for the diagnosis of BV is likely to provide results which are less reliable than those obtained by Gram staining. The latter should be the first choice and every effort should be made to set up this service.

Retention of heroin and morphine-6 beta-glucuronide analgesia in a new line of mice lacking exon 1 of MOR-1

Morphine produces analgesia by activating mu opioid receptors encoded by the MOR-1 gene. Although morphine-6 beta-glucuronide (M6G), heroin and 6-acetylmorphine also are considered mu opioids, recent evidence suggests that they act through a distinct receptor mechanism. We examined this question in knockout mice containing disruptions of either the first or second coding exon of MOR-1. Mice homozygous for either MOR-1 mutation were insensitive to morphine. Heroin, 6-acetylmorphine and M6G still elicited analgesia in the exon-1 MOR-1 mutant, which also showed specific M6G binding, whereas M6G and 6-acetylmorphine were inactive in the exon-2 MOR-1 mutant. These results provide genetic evidence for a unique receptor site for M6G and heroin analgesia.

Relationships among liver and kidney volumes, lean body mass and drug clearance

AIMS

To determine whether lean body mass (LBM), a possible surrogate of liver and kidney volumes, correlates with hepatic and renal drug clearances.

METHODS

Twenty-one disease-free patients with a history of cancer and with normal hepatic and renal function were studied. Salivary pharmacokinetics of oral antipyrine (1200 mg) and 24 h creatinine clearance were determined following the determination of LBM by dual energy X-ray absorptiometry and the determination of liver and kidney volumes by helical CT scanning.

RESULTS

Liver volume correlated with LBM (r2=0.21, P=0.04), body surface area (BSA) (r2=0.54, P<0.001), and total body weight (TBW) (r2=0.61, P<0.001). Kidney volume correlated with LBM (r2=0.49, P<0.001), BSA (r2=0.43, P=0.002) and TBW (r2=0.24, P=0.03). Stepwise multiple regression analysis, incorporating the independent variables of age, height, weight, sex, BSA, LBM, alcohol consumption, smoking status and liver volume and the dependent variable antipyrine clearance, indicated that LBM was the only independent correlate of antipyrine clearance. A stepwise multiple regression analysis with kidney volume in the independent variables, and creatinine clearance as dependent variable, showed that kidney volume and age were the only independent correlates of creatinine clearance. A nomogram using serum creatinine and LBM was comparable with the Cockcroft and Gault nomogram in calculating creatinine clearance.

CONCLUSIONS

Of the anthropometric variables tested, LBM was the only determinant of antipyrine clearance, but this was not due to a relationship between LBM and liver volume. By contrast, the relationship between creatinine clearance and LBM appeared to be due to a relationship between LBM and kidney volume.

Phase I and pharmacokinetic study of KRN8602 alone and with filgrastim in patients with advanced cancer

PURPOSE

To determine the recommended dose, toxicity profile, and pharmacokinetics of KRN8602 (MX2-hydrochloride), a novel morpholino anthracycline with potent cytotoxicity against anthracycline-sensitive and resistant experimental tumors in vitro and in vivo.

PATIENTS AND METHODS

KRN8602 was administered alone in increasing doses to patients with advanced cancer or high-grade gliomas until dose-limiting toxicity (DLT) was observed in three or more of five patients treated in a dose level. Because neutropenia was dose limiting, further escalation was investigated with filgrastim support.

RESULTS

Fifty-six assessable patients completed at least one cycle of chemotherapy. The recommended dose of KRN8602 alone was 40 mg/m2. Dose escalation was limited by neutropenia. The recommended dose of KRN8602 with filgrastim was 70 mg/m2, and limiting toxicities were neutropenia, diarrhea, and vomiting. The most commonly experienced nonhematologic toxicity was nausea and vomiting. Alopecia and mucositis were infrequent and mild. Pharmacokinetic parameters showed substantial variation, although the area under the plasma concentration-time curve (AUC) and maximum concentration both increased with dose. There was no relationship between pharmacokinetic parameters and toxicity.

CONCLUSION

KRN8602 at doses of 40 mg/m2 when administered alone and 70 mg/m2 when administered with filgrastim appeared to be manageable. The major DLTs were neutropenia and, at higher doses, diarrhea and vomiting. The efficacy of this drug is currently being tested in phase II studies.

Effect of filgrastim on the pharmacokinetics of MX2 hydrochloride in patients with advanced malignant disease

PURPOSE

To investigate the effect of granulocyte colony-stimulating factor (G-CSF) on the pharmacokinetics and pharmacodynamics of the new morpholino anthracycline drug MX2.

METHODS

A total of 25 patients with advanced malignant disease participated in a dose-escalation study in the first cycle of treatment given i.v. at doses of 50-80 mg/m2 (74-152 mg) with concomitant filgrastim (G-CSF, 5 microg/kg) given daily beginning at 24 h after the dose of MX2.

RESULTS

The mean fast distribution half-life (1.5 +/- 1.0 min) and the mean plasma clearance (2.18 +/- 0.95 l/min) were significantly lower than the respective mean values found in a previous study in which 27 patients had received MX2 (16.8-107.5 mg) alone (3.3 +/- 2.2 min and 2.98 +/- 1.68 l/min, respectively; P < 0.05). There was no correlation between plasma clearance and the delivered dose for the combined MX2-alone and MX2-filgrastim groups, indicating that the lower clearance observed in the G-CSF group was probably not due to the higher dose. Elimination half-lives of the metabolites M1 and M4 were significantly greater in the filgrastim group (19.8 +/- 14.7 and 11.8 +/- 5.0 h for M1 and 14.8 +/- 4.1 and 12.3 +/- 6.3 h for M2, respectively). Unlike the MX2-alone group, there was no relationship in the MX2-filgrastim group between the relative nadir neutrophil count and the dose or between the duration of grade IV neutropenia and the dose of MX2.

CONCLUSIONS

This study shows that filgrastim decreased the plasma clearance of MX2 by approximately 25%, possibly by inhibition of metabolism.

Compatibility of ketamine and morphine injections

The compatibility of ketamine and morphine mixture was studied. In addition, pH adjustment to minimise local tissue irritation led to no change in stability of the mixture up to pH 5.9. It appears that ketamine and morphine mixtures are stable over a 24 h period.

The importance of arterial compliance in cardiovascular drug therapy

Arterial compliance, defined as a change in dimension in response to a given change in stress, is becoming an increasingly important clinical parameter. Related concepts, such as distensibility, elasticity, and stiffness, and more traditional concepts such as resistance, afterload, and impedance need to be differentiated from compliance, although they are frequently (inappropriately) used interchangably. Many studies cannot differentiate between compliance changes due to a drug's effect on blood pressure and those due to a drug's effect on vessel wall integrity. This differentiation is important because a more physiologic therapy, one that benefits pulsatile and nonpulsatile flow, should be of greater clinical benefit than a therapy that only lowers blood pressure. A number of methods have been used to estimate compliance, but to date there is no generally agreed-on best method. There also are no longitudinal studies that relate abnormal compliance and drug effects to outcome. Nonetheless, patients at risk from a variety of disease states, such as hypertension, diabetes mellitus, and hypercholesterolemia, may benefit from earlier recognition of abnormal compliance. Earlier recognition may lead to interventions that would reduce their risk. This review includes a discussion of compliance and related estimates of blood vessel function and attempts to summarize the data currently available regarding the effects of cardioactive drugs on arterial compliance.

Myocardial effect compartment modeling of metoprolol and sotalol: importance of myocardial subsite drug concentration

We have recently reported the time course of acute myocardial drug uptake and simultaneous pharmacodynamic effects for metoprolol (4 mg; n = 12) and sotalol (20 mg; n = 10) in patients with ischemic heart disease. The acute pharmacodynamic effects of the two drugs included reductions in both spontaneous heart rate and the contractile index peak positive rate of left ventricular pressure rise and prolongation of the electrocardiographic PR interval, all of which exhibited an equilibration delay compared with myocardial drug content. The objective of the current study was to analyze the relationship between myocardial drug content and effect for both metoprolol and sotalol using an effect compartment model, to examine the potential for the two drugs to share a common subsite of action in the myocardium. The time course of myocardial drug content was best described by a one-compartment model for metoprolol and a two-compartment model for sotalol. A linear pharmacodynamic model, relating the amount of drug at the effect-site (Ae) with each of the three effects, was used in the effect compartment modeling. The slope of each of these effects as a function of Ae was considerably flatter for sotalol than for metoprolol, reflecting the relative beta-adrenoceptor antagonistic potencies of the two drugs. The exit rate constant from the effect compartment (K(eo)) did not differ significantly from each other or from the exit rate constant from the "peripheral" compartment (K21) for sotalol. The results suggest that the effect compartment within the myocardium for both drugs may correspond to a "peripheral" compartment, even though a "peripheral" pharmacokinetic compartment for myocardial metoprolol content was not apparent. Thus, the effect compartment for many cardioactive drugs may correspond to a pharmacokinetically "peripheral" compartment, irrespective of localization of effect to a small (e.g. sinoatrial node) or large (e.g. ventricular myocardium) region of the heart.

Propranolol elimination by right and left fetal liver: studies in the intact isolated perfused fetal sheep liver

Propranolol extraction in vivo by the left lobe of the fetal sheep liver is greater than that by the right lobe, and this may be due to the fact that oxygenation of the left lobe is greater than that of the right lobe. To explore this hypothesis, we studied the elimination of (R)-(+)-propranolol (PROP) by right and left lobes of the intact isolated perfused fetal sheep liver model, in which there is equal oxygenation of both liver lobes. After isolation of the liver, near-term fetal sheep livers (n = 11) were perfused (2.68 +/- 1.05 ml/g liver/min) in situ via the umbilical vein in a 1-liter recirculating system. PROP was infused (1.2 mg/hr) into the reservoir after an initial bolus dose (2.3 mg). Perfusate samples were taken from the common and right and left hepatic veins every 10 min for determination of PROP concentrations and oxygen consumption over the 180-min experimental period. Mean ductus venosus shunt through the liver was 42 +/- 21% of perfusate flow. Oxygen consumption was not significantly different between the left and right lobes of the liver (0.79 +/- 0.46 and 0.67 +/- 0.44 micromol/g liver/min, respectively, P > .05), nor was there any significant difference between lobes in PROP hepatic extraction at steady state (0.25 +/- 0.20 and 0.25 +/- 0.23, respectively, P > .05). This supports the hypothesis that the difference between lobes in PROP extraction in vivo may be due to the difference in degree of oxygenation of the left and right lobes that is known to be present in vivo.

A priming dose of propranolol reduces the availability of a subsequent dose in the isolated perfused rat liver preparation

1. A 50 microL bolus dose containing (+/-)-propranolol hydrochloride (200 microg) and [14C]-sucrose, or antipyrine (2 mg) and [14C]-sucrose, or [14C]-taurocholate sodium was injected into the portal vein of the isolated perfused rat liver preparation and perfusate outflow samples were collected frequently for the next 30 min. After a 20 min washout period this procedure was repeated. 2. [14C]-Sucrose, antipyrine and [14C]-taurocholate each eluted as a single peak at 18, 31 and 28 s, respectively, after each dose. In contrast, propranolol eluted with two peaks at approximately 18 and 128 s after dosing. 3. There was no significant difference in dose-corrected area under the outflow curve (AUC) for [14C]-sucrose, antipyrine or [14C]-taurocholate between the first and second doses whereas the mean propranolol AUC for the second dose was only 0.577+/-0.439 that for the first dose (P<0.05). 4. Unmetabolized propranolol accounted for more than 80% of the drug in hepatic tissue for the first and second doses at 18 s and greater than 50% at 128 s, and there was no significant difference in these values at each time between the first and second doses. 5. These findings suggest that for an avidly extracted drug, such as propranolol, systemic availability of orally administered drug will be highly dependent on factors that influence the hepatic tissue binding of the drug.

Activation of low avidity CTL specific for a self epitope results in tumor rejection but not autoimmunity

To determine how self-tolerance can alter the ability of the immune system to respond against tumor-associated Ags that are also expressed by normal tissue, we designed experiments in which the same protein was expressed both as a tumor Ag and as a transgene product. Unlike conventional BALB/c mice that rejected renal carcinoma cells transfected with the influenza virus hemagglutinin (Renca-HA), transgenic mice that are tolerant of HA due to its expression as a self-Ag on pancreatic islet beta cells, (Ins-HA mice) supported progressive growth of these tumor cells. However, when Ins-HA mice were immunized with a recombinant strain of vaccinia virus expressing the dominant H-2Kd peptide epitope of HA before receiving Renca-HA cells, they too were able to reject the tumor cells. Rejection of Renca-HA cells by immunized Ins-HA mice was found to be associated with the generation of CTL having much lower avidity for target cells presenting the KdHA epitope than CTL from immunized conventional BALB/c mice. Significantly, we show that self-tolerance to the HA Ag is quantitative rather then absolute, and that vaccination of Ins-HA mice can activate low avidity KdHA-specific CD8+ T cells that are able to reject tumor cells expressing high levels of HA, yet these mice remain tolerant of pancreatic islet beta cells expressing HA.

Studies of the surgical scrub

BACKGROUND

To evaluate the effectiveness of various scrub techniques in reducing bacterial skin flora, the present study was developed in three stages.

METHODS

Each stage involved fingertip bacterial colony counts measured before, immediately after and 30 min after a variety of handwashing techniques using 10% povidone iodine solution. The first compared 1, 2 or 3 non-timed washes from fingertips to elbows in 10 volunteers. The second compared two volunteers scrubbing for equal durations with or without friction rubbing, while the third involved 15 volunteers who each scrubbed for different time intervals.

RESULTS

The first stage showed that a single wash episode failed to provide lasting bacterial colony count reductions on fingertip cultures. The second showed that enduring colony count reductions occur whether friction rubbing of the hands was used or not, and the third showed that a 30 s wash was as effective as washing for longer periods in reducing fingertip flora.

CONCLUSIONS

These findings suggest that prolonged vigorous pre-operative scrubbing is unnecessary, although more than a cursory wash is required to produce lasting fingertip antisepsis.

Drug disposition in mother and foetus

1. In pregnancy, plasma protein binding of certain drugs is reduced due to a reduction in serum albumin concentration. Due to an increase in cardiac output in pregnancy there is a 50% increase of effective renal plasma flow, glomerular filtration rate and creatinine clearance. This results in a corresponding increase in renal drug clearance. 2. Placental transfer of small lipophilic molecules from the mother to the foetus is efficient because the placental membrane is a very thin lipophilic membrane, with a large surface area for exchange and high maternal and foetal placental blood flow rates. Nevertheless, placental transfer of relatively hydrophilic molecules is slow and this may limit foetal exposure to the drug where a single maternal dose is concerned. 3. Once a drug has crossed the placenta it passes via the umbilical vein to the foetal liver and then to the systemic circulation of the foetus, which creates a potential foetal hepatic first-pass effect. The activity of most foetal hepatic drug-metabolizing enzymes studied is much less than the adult activity and some enzymes do not appear to be expressed at all. The circulation of the foetal liver is unique because 30-70% of umbilical vein flow is shunted via the ductus venosus. There is also a difference in oxygenation and enzyme content between the left and right lobes of the foetal liver. 4. The foetal kidney is not a very effective route of elimination because renally excreted drug enters the amniotic fluid and recirculates via foetal swallowing. Moreover, foetal renal blood flow is only 3% of cardiac output, compared with 25% in the adult, and renal tubular anion secretion is absent. In conclusion, the extent of foetal exposure of maternally administered drug depends on numerous factors, in particular maternal and foetal elimination mechanisms and placental permeability.