Biomedical subjects

D J Morgan

Publications and source records attributed to D J Morgan.

At least 37 records · Page 2Linked to original sources

PubMed2000

Right heart failure impairs hepatic elimination of p-nitrophenol without inducing changes in content or latency of hepatic UDP-glucuronosyltransferases.

Congestive heart failure has been shown to affect oxidative drug metabolism, however, there has been little study of its effects on drug conjugation. Using the isolated perfused livers from rats with right ventricular failure (RVF) due to pulmonary artery constriction, we studied the effects of RVF on hepatic elimination of p-nitrophenol (PNP) under controlled flow and oxygen delivery conditions. Hepatic clearance of the drug was found to be significantly impaired in RVF as compared with the sham group (0.80 +/- 0.23 versus 1.28 +/- 0.26 ml/min/g of liver). The impairment of PNP clearance in RVF occurred in parallel with significant reduction in metabolic formation clearance of p-nitrophenyl-beta-D-glucuronide; the major metabolite of PNP (0.51 +/- 0.12 versus 1.03 +/- 0.26 ml/min/g of liver). The intrinsic drug-glucuronidation capacity of livers was evaluated by measuring the microsomal content and activity of the UDP-glucuronosyltransferase(s) (UDP-GT) toward p-nitrophenol. There was no significant difference between sham and the RVF groups in either the content or the activity of the UDP-GT. The latency of the UDP-GT enzymes in microsomes was measured and was found to be similar between the two groups. The results of this study show that RVF impairs hepatic elimination of PNP and that this appears to be independent of changes in hepatic perfusion and oxygenation or alterations in hepatic content, activity, and latency of the UDP-GT.

Animals↗

PubMed1999

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.

Adoptive Transfer↗

PubMed1999

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.

Animals↗

PubMed1999

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.

Adult↗

PubMed1999

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.

Aging↗

PubMed1999

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.

Acetaminophen↗

PubMed1999

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.

Animals↗

PubMed1999

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.

Animals↗

PubMed1999

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.

Aging↗

PubMed1999

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.

Analgesics, Opioid↗

PubMed1999

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.

Adult↗

PubMed1999

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.

Adrenergic alpha-Agonists↗

PubMed1999

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.

Cervix Uteri↗

PubMed1998

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.

Animals↗

PubMed1998

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.

Adrenergic beta-Antagonists↗

PubMed1998

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.

Antibiotics, Antineoplastic↗

PubMed1998

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.

Drug Combinations↗

PubMed1998

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.

Adrenergic beta-Antagonists↗