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Biomedical subjects

G Toth

Publications and source records attributed to G Toth.

At least 55 records · Page 3Linked to original sources
PubMed1992

Laboratory methods for assessing human semen in epidemiologic studies: a consensus report.

It is clear that additional methodologic work needs to be performed. Some data gaps described above are being actively investigated. Other standards were not addressed at this meeting; statistical handling of the data, differences among CASA machines, and factors to consider as potential confounders in analysis are just a few. These may be the subject of future workshops, which will also review progress made in the existing knowledge base. For now, this effort represents a first attempt to share information and to use it to encourage investigators in different laboratories to employ similar methods. In this way more direct comparisons among studies can be made, and our collective data base can be strengthened.

Computers↗
PubMed1992

Conformationally biased analogs of oxytocin.

Four diastereomeric analogs of oxytocin containing substituted phenylalanine in position 2 were synthesized. This modified phenylalanine side chain contained one methyl group attached to the beta-carbon and the second one at the 2' position of the aromatic ring. All analogs were found to be inhibitors of uterotonic activity of oxytocin with pA2 values ranging from 6.0 to 8.3; the most potent one (pA2 = 8.3) contained dimethylphenylalanine of the D-erythro configuration.

Amino Acid Sequence↗
PubMed1991

Influence of peptidase inhibitors on the apparent agonist potency of delta selective opioid peptides in vitro.

Several peptides of diverse structure, reported to possess high affinity and selectivity for the delta opioid receptor, were studied using the mouse isolated vas deferens preparation to determine the effect of peptidase inhibition on their apparent potency. The peptides evaluated included [Leu5] enkephalin, the cyclic enkephalin analogs [D-Pen2,D-Pen5]enkephalin (DPDPE) and [D-Pen2,p-F-Phe4,D-Pen5]enkephalin (F-DPDPE), the linear enkephalin analogs [D-Ala2,D-Leu5]enkephalin (DADLE) and [D-Ser2(O-tBu), Leu5,Thr6]enkephalin (DSTBULET), and the naturally occurring amphibian peptides Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2 (dermenkephalin), Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2 (deltorphin I) and Tyr-D-Ala-Phe-Glu-Val-Val-Gly-NH2 (deltorphin II). Concentration-response curves were determined for each peptide in the absence and presence of a combination of the peptidase-inhibiting agents bacitracin, bestatin, and captopril. A wide range of potencies was observed, both in the control state and in the presence of peptidase inhibition. The synthetic enkephalin analogs demonstrated small increases in potency with peptidase inhibition (no increase in the case of DPDPE), whereas the naturally occurring peptides were markedly increased in potency, up to as much as 123-fold for dermenkephalin. In the presence of peptidase inhibition, deltorphin II was the most potent peptide tested (IC50 = 1.13 x 10(-10) molar), and as such is the most potent delta opioid agonist reported to date. Stability to metabolism must be considered in the design and evaluation of in vitro experiments using peptides of this type.

Amino Acid Sequence↗
PubMed1991

Opioid receptor labeling with the chloromethyl ketone derivative of [3H]Tyr-D-Ala-Gly-(Me)Phe-Gly-ol (DAMGO) II: Covalent labeling of mu opioid binding site by 3H-Tyr-D-Ala-Gly-(Me)Phe chloromethyl ketone.

Opioid receptors of rat brain membranes were prelabeled with 3H-Tyr-D-Ala2-(Phe4)-Gly-CH2Cl, a chloromethyl ketone derivative of enkephalin, and solubilized in 1% digitonin. Hydrodynamic parameters of the receptor detergent complex derived from gel filtration and sucrose density gradient ultracentrifugation were found to be 51 A and 8.7 S, respectively, and the size was estimated to be about 200 kDa. Sodium dodecyl sulfate gel electrophoresis followed by fluorography revealed specific alkylation of a major protein at 58 kDa.

Amino Acid Chloromethyl Ketones↗
PubMed1991

The effects of receptor blockers on atrial natriuretic peptide-induced action on passive avoidance behavior in rats.

In previous experiments, it was shown that rat atrial natriuretic peptide (rANP1-28) is able to increase the passive avoidance latency in a dose-dependent manner in the learning and consolidation phase (3). In order to clarify whether ANP has a direct action on this behavioral paradigm, or whether the action is mediated by neurotransmitters, rats were pretreated with different receptor blockers. The selected doses of the different receptor blockers could themselves not influence the behavioral paradigms. Haloperidol or atropine blocked the action of ANP on the consolidation of the passive avoidance response. Phenoxybenzamine, propranolol, methysergide, bicuculline and naloxone were ineffective. The data suggest that dopaminergic and cholinergic mediations are involved in the action of ANP on the passive avoidance response.

Animals↗
PubMed1991

Topographically designed analogues of [D-Pen,D-Pen5]enkephalin.

The conformationally restricted, cyclic disulfide-containing delta opioid receptor selective enkephalin analogue [D-Pen2,D-Pen5]enkephalin (1, DPDPE) was systematically modified topographically by addition of a methyl group at either the pro-S or pro-R position of the beta carbon of an L-Phe4 or D-Phe4 residue to give [(2S,3S)-beta-MePhe4]DPDPE (2), [(2R,3R)-beta-MePhe4]DPDPE (3), [(2S,3R)-beta-MePhe4]DPDPE (4), and [(2R,3S)-beta-MePhe4]DPDPE (5). The four corresponding isomers were prepared in which the beta-methylphenylalanine residue was p-nitro substituted, that is with a beta-methyl-p-nitrophenylalanine (beta-Me-p-NO2Phe) residue, to give [(2S,3S)-beta-Me-p-NO2Phe4]DPDPE (6), [(2R,3R)-beta-Me-p-NO2Phe4]DPDPE (7), [(2S,3R)-beta-Me-p-NO2Phe4] DPDPE (8), and [(2R,3S)-beta-Me-p-NO2Phe4]DPDPE (9), respectively. The potency and selectivity (delta vs mu opioid receptor) were evaluated by radioreceptor binding assays in the rat brain using [3H]CTOP (mu ligand) and [3H]DPDPE (delta ligand) and by bioassay with mouse vas deferens (MVD, delta receptor assay) and guinea pig ileum (GPI, mu receptor assay). The eight analogues of DPDPE showed highly variable binding and bioassay activities particularly at the delta opioid receptor (4 orders of magnitude), but also at the mu opioid receptor, which led to large differences (3 orders of magnitude) in receptor selectivity. For example, [(2S,3S)-beta-MePhe4]DPDPE (2) is 1800-fold selective in binding to the delta vs mu receptor, making it one of the most selective delta opioid receptor ligands in the enkephalin series as assessed by the rat brain binding assay, whereas the corresponding (2R,3R)-beta-Me-p-NO2Phe-containing analogue 9 is only 4.5-fold selective (nonselective) in this same assay. On the other hand, in the bioassay systems, [(2S,3S)-beta-Me-p-NO2Phe4]DPDPE (5) is more potent than DPDPE and 8800-fold selective for the MVD (delta receptor) vs the GPI (mu receptor), making it the most highly selective ligand in this series for the delta opioid receptor on the basis of these bioassays. In these assay systems, the (2R,3S)-beta-MePhe4-containing analogue 5 had very weak potency and virtually no receptor selectivity (4.4-fold). These results demonstrate that topographical modification alone in a conformationally restricted peptide ligand can significantly modulate both potency and receptor selectivity of peptide ligands that have multiple sites of biological activity and suggest that this approach may have general application to peptide ligand design.

Amino Acid Sequence↗
PubMed1991

Severe hypoglycemia in type I diabetic patients with impaired kidney function.

OBJECTIVE: To assess the frequency and possible risk indicators of severe hypoglycemia in insulin-dependent (type I) diabetic patients with impaired kidney function. RESEARCH DESIGN AND METHODS: Retrospective follow-up examination of case subjects and control subjects with mean follow-up periods of 2.9 and 1.3 yr, respectively. The setting was the diabetes center at the Düsseldorf University hospital. Subjects were consecutive type I diabetic patients. Case subjects consisted of 44 patients with initial serum creatinine levels of greater than or equal to 133 microM and pathological proteinuria. Control subjects consisted of 46 patients with normal serum creatinine levels matched for age, duration of diabetes, and hypertension; 57% of case subjects and 67% of control subjects were being treated with beta-blockers. Incidence of severe hypoglycemia (cases/patient-yr) was assessed through an interviewer-administered questionnaire. RESULTS: At comparable levels of HbA1c (7.9 +/- 1.8 vs. 7.6 +/- 1.1%), case subjects had a fivefold higher incidence of severe hypoglycemic episodes (1.28 vs. 0.25 cases/patient-yr, P less than 0.02) than control subjects. Within the group with impaired kidney function, patients with severe hypoglycemic episodes had lower HbA1c levels (7.4 +/- 1.6 vs. 8.7 +/- 2.0%, P less than 0.03) and a lower body mass index (22.0 +/- 3.4 vs. 24.4 +/- 3.8 kg/m2, P less than 0.04) than those without severe hypoglycemic episodes, whereas serum creatinine levels, body weight-related insulin dosage (U x kg-1 x day-1), prevalence of blindness, autonomic neuropathy, and treatment with beta-blockers were comparable. CONCLUSIONS: Type I diabetic patients with impaired kidney function are at an excessively high risk of severe hypoglycemia. In addition to low HbA1c levels, a low body mass index appears to be a risk indicator for this adverse effect of insulin therapy.

Adult↗
PubMed1991

[D-Pen2,4'-125I-Phe4,D-Pen5]enkephalin: a selective high affinity radioligand for delta opioid receptors with exceptional specific activity.

[D-Pen2,4'-125I-Phe4,D-Pen5]enkephalin ([125I]DPDPE) is a highly selective radioligand for the delta opioid receptor with a specific activity (2200 Ci/mmol) that is over 50-fold greater than that of tritium-labeled DPDPE analogs. [125I]DPDPE binds to a single site in rat brain membranes with an equilibrium dissociation constant (Kd) value of 421 +/- 67 pM and a receptor density (Bmax) value of 36.4 +/- 2.7 fmol/mg protein. The high affinity of this site for delta opioid receptor ligands and its low affinity for mu or kappa receptor-selective ligands are consistent with its being a delta opioid receptor. The distribution of these sites in rat brain, observed by receptor autoradiography, is also consistent with that of delta opioid receptors. Association and dissociation binding kinetics of 1.0 nM [125I] DPDPE are monophasic at 25 degrees C. The association rate (k + 1 = 5.80 +/- 0.88 X 10(7) M-1 min-1) is about 20- and 7-fold greater than that measured for 1.0 nM [3H DPDPE and 0.8 nM [3H] [D-Pen2,4'-Cl-Phe4, D-Pen5]enkephalin, respectively. The dissociation rate of [125I]DPDPE (0.917 +/- 0.117 X 10(-2) min-1) measured at 1.0 nM is about 3-fold faster than is observed for either of the other DPDPE analogs. The rapid binding kinetics of [125I]DPDPE is advantageous because binding equilibrium is achieved with much shorter incubation times than are required for other cyclic enkephalin analogs. This, in addition to its much higher specific activity, makes [125I]DPDPE a valuable new radioligand for studies of delta opioid receptors.

Animals↗
PubMed1990

Differentiation between rat brain and mouse vas deferens delta opioid receptors.

Certain enkephalin analogues, including those which contain the conformationally restricted amino acid E-(2R,3S)-cyclopropylphenylalanine [2R,3S)-delta E Phe), have been shown to have high affinity for brain delta opioid receptors but are much less active in mouse vas deferens bioassays. To investigate whether there are differences between delta opioid receptors in brain and mouse was deferens, the ability of a selective delta opioid compound, [D-Pen2,pCl-Phe4,D-Pen5]enkephalin (pCl-DPDPE), and [D-Ala2,(2R,3S)-delta E Phe4,Leu5]enkephalin methyl ester (CP-OMe), to inhibit [3H]pCl-DPDPE binding in both rat brain and mouse vas deferens were measured. pCl-DPDPE recognized brain and mouse vas deferens binding sites with equal affinity, however, CP-OMe showed 33 fold lower affinity in mouse vas deferens compared to brain. This suggests that mouse vas deferens delta opioid receptors may be distinct from brain delta opioid receptors.

Animals↗
PubMed1990

A radiopharmaceuticals schedule for imaging in paediatrics. Paediatric Task Group European Association Nuclear Medicine.

There is no standard schedule for the amounts of radiopharmaceutical administered to children at present. Various alternative methods are currently in practice, all with some support from the literature. Optimization of the amount of radiopharmaceutical to be administered is discussed in relation to the radiation burden of such an examination. The Paediatric Task Group of the European Association of Nuclear Medicine has investigated the current situation and now suggests a method for standardization of administered amounts of radiopharmaceutical in paediatrics. The fraction of the adult amount of radiopharmaceutical to be administered should be calculated from the child's body weight according to the accompanying table. In small infants, the minimum amount of a radiopharmaceutical is discussed and suggested amounts to be administered are presented.

Body Weight↗
PubMed1990

[D-Pen2,D-Pen5]enkephalin analogues with increased affinity and selectivity for delta opioid receptors.

The conformationally restricted, cyclic disulfide-containing enkephalin analogue [D-Pen2,D-Pen5]enkephalin (DPDPE) was modified by halogenation (F, Cl, Br, I) of the phenylalanine-4 residue in the para position. The potency and selectivity of these analogues for the delta opioid receptor was greater than that of the parent peptide. The analogues possessed greater potency and affinity for the delta receptors than DPDPE in the mouse vas deferens assay and in radioreceptor assays (against [3H]DPDPE), respectively. [p-ClPhe4]DPDPE was the most selective in the radioligand binding assays (IC50(mu)/IC50(delta) = 574), being about 5-fold more delta opioid receptor selective than DPDPE in this assay, whereas [p-IPhe4]DPDPE was the most selective in the classical bioassay systems using the mouse vas deferens and guinea pig ileum assays (IC50(GPI)/IC50(MVD) = 17,374), making it nearly 9-fold more selective than DPDPE in direct comparisons using the same assay conditions.

Amino Acid Sequence↗
PubMed1989

A high affinity, highly selective ligand for the delta opioid receptor: [3H]-[D-Pen2, pCl-Phe4, d-Pen5]enkephalin.

Binding characteristics of a new, conformationally constrained, halogenated enkephalin analogue, [3H]-[D-penicillamine2, pCl-Phe4, D-penicillamine5]enkephalin ([3H]pCl-DPDPE), were determined using homogenized rat brain tissue. Saturation binding studies at 25 degrees C determined a dissociation constant (Kd) of 328 +/- 27.pM and a receptor density (Bmax) of 87.2 +/- 4.2 fmol/mg protein. Kinetic studies demonstrated biphasic association for [3H]pCl-DPDPE, with association rate constants of 5.05 x 10(8) +/- 2.5 x 10(8) and 0.147 +/- 10(8) +/- 0.014 x 10(8) M-1 min-1. Dissociation was monophasic with a dissociation rate constant of 2.96 x 10(-3) +/- 0.25 x 10(-3) min-1. The average Kd values determined by these kinetic studies were 8.4 +/- 2.7 pM and 201 +/- 4 pM. Competitive inhibition studies demonstrated that [3H]pCl-DPDPE has excellent selectively for the delta opioid receptor. [3H]pCl-DPDPE binding was inhibited by low concentrations of ligands selective for delta opioid receptor relative to the concentrations required by ligands selective for mu and kappa sites. These data show that [3H]pCl-DPDPE is a highly selective, high affinity ligand which should be useful in characterizing the delta opioid receptor.

Animals↗
PubMed1989

Effects of oxymorphazone in frogs: long lasting antinociception in vivo, and apparently irreversible binding in vitro.

Oxymorphazone (at doses of 50-200 mg/kg) was found to be a relatively weak antinociceptive drug in intact frog (Rana esculenta) when acetic acid was used as pain stimulus. Frogs remained analgesic for at least 48 hrs following oxymorphazone (200 mg/kg) administration. The ligand increased the latency of wiping reflex in spinal frogs too. These effects were blocked by naloxone. In equilibrium binding studies (3H)oxymorphazone had high affinity to the opioid receptors of frog brain and spinal cord as well (apparent Kd values were 8.9 and 10.6 nM, respectively). Kinetic experiments show that only 25% of the bound (3H)oxymorphazone is readily dissociable. Preincubation of the membranes with labeled oxymorphazone results in a washing resistant inhibition of the opioid binding sites. At least 70% of the (3H)oxymorphazone specific binding is apparently irreversible after reaction at 5 nM ligand concentration, and this can be enhanced by a higher concentration of tritiated ligand.

Analgesics↗
PubMed1988

No evidence of a genetic polymorphism in the oxidative metabolism of midazolam.

The benzodiazepine midazolam is rapidly eliminated by oxidative metabolism. In young healthy volunteers elimination half-life (t1/2) is about 2.4 hours. A recent study showed a prolonged t1/2 from 8 to 22 hours in 6.5% of surgical patients, and a genetic polymorphism of midazolam's metabolism has been suggested. Therefore, we measured in 168 surgical patients the elimination of midazolam and its major hydroxylated metabolite (alpha-OH-midazolam) in blood and urine. Co-medication, disease status, smoking habits and alcohol intake were recorded; normal liver and kidney functions were assessed by routine laboratory tests. Midazolam was administered intravenously (0.1 to 0.2 mg/kg) for the induction of anaesthesia. Blood was drawn 1.5, 3, 4.5 and 6 hours after application and urine was collected for 6 hours. Plasma protein binding of midazolam was determined by equilibrium dialysis. Midazolam and alpha-OH-midazolam were measured in plasma by specific gas-liquid chromatography and in urine by high performance liquid chromatography. Data for the dose-corrected area under plasma-level curve of midazolam (AUC-midazolam/dose: 1.23 +/- 961 x 10(5) h/ml; mean +/- SD) and for the metabolic plasma ratio (AUC of alpha-OH-midazolam/AUC-midazolam: 0.52 +/- 0.28) demonstrated a log-normal distribution. Likewise, the percentage of the unbound fraction of midazolam in plasma (5.0 +/- 2.4%), urinary excretion of alpha-OH-midazolam (55.9 +/- 22.7% of dose) and the values for t1/2 (2.9 +/- 1.1 hours) did indicate a unimodal distribution. Age, comedication and smoking habits did not affect the disposition of midazolam. However, patients with regular intake of alcohol had a higher (p less than 0.05) metabolic ratio. Only in 3 patients could a prolonged t1/2 of midazolam from 7.5 to 10.2 hours be detected, but plasma levels and urinary excretion of alpha-OH-midazolam in those individuals were found to be normal. Therefore it is very unlikely that the oxidative metabolism of midazolam exhibits a genetic polymorphism.

Age Factors↗