Kinetics of endogenous leukotriene B4 and E4 production following injection of the chemotactic peptide FMLP in the rabbit

The kinetic profiles of leukotriene B4 (LTB4) and E4 (LTE4) after intravenous administration (30 nmol/kg) of the inflammatory peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) were evaluated in male rabbits. LTB4 and LTE4 reached the maximal concentration of 84.2 +/- 60.0 and 162.2 +/- 51.4 nmol/L (mean +/- s.d.), at 2 and 5 min, respectively. The first elimination phase for LTB4 and LTE4, after FMLP administration, showed an apparent half-life of 24.6 +/- 6.7 and 36.9 +/- 13.0 min, respectively. The area under the blood concentration-time curve (AUC, nmol min/L) of LTB4 and LTE4 was 2178 +/- 1591 and 7627 +/- 3052, respectively. LTE4 and N-ac-LTE4 were the major components excreted in the urine, mostly in the first time interval (0-12 h) of urinary collection after FMLP treatment; 11-trans-LTE4 was recovered in the second interval (12-24 h). Two other more polar compounds, potential metabolites, were recovered in the first interval of urine collection. Knowledge of the kinetic characteristics of endogenously produced leukotrienes may be useful in understanding the role of these eicosanoids in inflammatory and thrombotic disease, as well as in evaluating the efficacy of drugs designed to modulate their production and effect.     

Detection and quantitation of human papillomavirus by using the fluorescent 5' exonuclease assay

Some 1-aryl-4-[(5-methoxy-1,2,3, 4-tetrahydronaphthalen-1-yl)-n-propyl]piperazines and their alkylamino and alkylamido analogues, previously studied as 5-HT1A ligands, were prepared in enantiomerically pure form, and their absolute configuration was determined by chemical correlation or by chiroptical properties. They were evaluated for in vitro 5-HT1A, D2, and alpha1 receptor affinity by radioligand binding assays, to study the influence of the chiral carbon atom of the tetrahydronaphthalene nucleus on the 5-HT1A affinity and selectivity. Results indicated that, as regarding the 5-HT1A receptor affinity, there was no difference in affinity between (-)- and (+)-enantiomers as well as the racemate of each compound. The stereochemistry, instead, influenced the selectivity: all (-)-enantiomers displayed affinity values higher than those of (+)-isomers at D2 receptors, and conversely, all (+)-enantiomers displayed affinity values higher than those of (-)-isomers at alpha1 receptors. As a result of this trend, it is not possible to predict the isomer with a better selectivity profile. However, compounds (S)-(+)-2, (S)-(+)-4, and (R)-(+)-6 displayed high affinity for the 5-HT1A receptor (IC50 values ranging between 7.0 and 2.3 nM) and good selectivity (>/=250-fold) versus both D2 and alpha1 receptors. Furthermore, compounds (S)-(+)-4 and (R)-(-)-4 were submitted to the [35S]GTPgammaS binding assay for a preliminary evaluation of their intrinsic activity on the 5-HT1A receptor.     

Initial reactions in the oxidation of 1,2-dihydronaphthalene by Sphingomonas yanoikuyae strains

The substrate oxidation profiles of Sphingomonas yanoikuyae B1 biphenyl-2,3-dioxygenase and cis-biphenyl dihydrodiol dehydrogenase activities were examined with 1,2-dihydronaphthalene and various cis-diols as substrates. m-Xylene-induced cells of strain B1 oxidized 1,2-dihydronaphthalene to (-)-(1R,2S)-cis-1,2-dihydroxy-1,2-3,4-tetrahydronaphthalene as the major product (73% relative yield). Small amounts of (+)-(R)-2-hydroxy-1,2-dihydronaphthalene (15%), naphthalene (6%), and alpha-tetralone (6%) were also formed. Strain B8/36, which lacks an active cis-biphenyl dihydrodiol dehydrogenase, formed (+)-(1R,2S)-cis-1,2-dihydroxy-1,2-dihydronaphthalene (51%), in addition to (-)-(1R,2S)-cis-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene (44%) and (+)-(R)-2-hydroxy-1,2-dihydronaphthalene (5%). The cis-biphenyl dihydrodiol dehydrogenase of strain B1 oxidized both enantiomers of cis-1,2-dihydroxy-1,2-dihydronaphthalene, but only the (+)-(1S,2R)-enantiomers of cis-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene and cis-1,2-dihydroxy-3-phenylcyclohexa-3,5-diene. The results show that biphenyl dioxygenase expressed by S. yanoikuyae catalyzes dioxygenation, monooxygenation, and desaturation reactions with 1,2-dihydronaphthalene as the substrate, and cis-biphenyl dihydrodiol dehydrogenase catalyzes the enantioselective dehydrogenation of (+)-(1S,2R)-cis-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene and (+)-(1S,2R)-cis-1,2-dihydroxy-3-phenylcyclohexa-3,5-diene.     

Dose proportionality and comparison of single and multiple dose pharmacokinetics of fexofenadine (MDL 16455) and its enantiomers in healthy male volunteers

The pharmacokinetics and dose proportionality of fexofenadine, a new non-sedating antihistamine, and its enantiomers were characterized after single and multiple-dose administration of its hydrochloride salt. A total of 24 healthy male volunteers (31 +/- 8 years) received oral doses of 20, 60, 120 and 240 mg fexofenadine HCl in a randomized, complete four-period cross-over design. Subjects received a single oral dose on day 1, and multiple oral doses every 12 h on day 3 through the morning on day 7. Treatments were separated by a 14-day washout period. Serial blood and urine samples were collected for up to 48 h following the first and last doses of fexofenadine HCl. Fexofenadine and its R(+) and S(-) enantiomers were analysed in plasma and urine by validated HPLC methods. Fexofenadine pharmacokinetics were linear across the 20-120 mg dose range, but a small disproportionate increase in area under the plasma concentration-time curve (AUC) (< 25%) was observed following the 240 mg dose. Single-dose pharmacokinetics of fexofenadine were predictive of steady-state pharmacokinetics. Urinary elimination of fexofenadine played a minor role (10%) in the disposition of this drug. A 63:37 steady-state ratio of R(+) and S(-) fexofenadine was observed in plasma. This ratio was essentially constant across time and dose. R(+) and S(-) fexofenadine were eliminated into urine in equal rates and quantities. All doses of fexofenadine HCl were well tolerated after single and multiple-dose administration.     

The CAG repeat within the androgen receptor gene and benign prostatic hyperplasia

Thalidomide, a glutamic acid derivative, has recently been shown to inhibit in vitro angiogenesis, the process of formation of new blood vessels. This Phase II study examined the pharmacokinetics of thalidomide in patients with clinically progressive hormone-refractory prostate cancer. Patients (aged 55 to 80 years) were randomized to two different arms, low dose versus high dose. Patients in the low-dose group were given 200 mg of thalidomide and patients in the high-dose group received 200 mg of thalidomide, with subsequent dose escalations to 1200 mg. Serial serum or blood samples were obtained for pharmacokinetic assessment after administration of a single oral dose or multiple daily dosing of thalidomide and were assayed by reversed-phase HPLC. Pharmacokinetic parameters for both the single and multiple dosing were calculated with ADAPT II. A one-compartment model best fit the data. After single dosing, the oral clearance and apparent volume of distribution for the low-dose regimen (n = 13) were 7.41 +/- 2.05 L/h and 66.93 +/- 34.27 L, respectively, whereas for the high-dose regimen (n = 11), these values were 7.21 +/- 2.89 L/h and 165.81 +/- 84.18 L, respectively. The elimination half-lives for the low and high dose were 6.52 +/- 3.81 and 18.25 +/- 14.08 h, respectively. After the multiple dosing of thalidomide, the oral clearance and apparent volume of distribution for the low-dose group (n = 10) were 6.35 +/- 1.64 L/h and 64.63 +/- 23.20 L, respectively, whereas for the high-dose group (n = 11), these values were 7.73 +/- 2.27 L/h and 167.85 +/- 82.08 L, respectively. The elimination half-lives for the low and high dose were 7.08 +/- 1.87 and 16.19 +/- 9.57 h, respectively. For both the single and multiple dosing of thalidomide, the apparent volume of distribution and half-life were significantly higher for the high-dose group than those for the low-dose group. The higher apparent volume of distribution may be attributable to several factors, such as change in absorption, protein binding, etc. A dose-proportional increase in thalidomide steady-state concentrations was seen after multiple daily dosing of thalidomide.     

The lack of effect of chronic metabolic acidosis on 25-OH-vitamin D metabolism and serum parathyroid hormone in humans

We evaluated the turnover of the plasma 25-OH-vitamin D pool, acid, and mineral balances in paired balance studies of 6 normal subjects during normal acid base conditions and during stable chronic metabolic acidosis induced by NH4Cl. Positive acid balances and negative Ca balances due to hypercalciuria were observed as previously reported. Plasma 25-OH-D pool turnover averaged 6.1+/-0.4 nmol/day during control and did not change during acidosis (6.5 +/- 0.5 nmol/day) nor were any significant increments in net intestinal absorption of Ca, PO4, or Mg, the physiological expression of vitamin D action, observed during acidosis. In 3 other subjects, repetitive measurements of serum iPTH during 7 control days and 24 days of stable NH4Cl acidosis showed no changes. We interpret the data to support the hypothesis that neither PTH nor vitamin D and its metabolites mediates the increase in net bone resorption that must accompany chronic metabolic acidosis.     

Enantioselective determination of isradipine in human serum using chiral stationary phase liquid chromatography and gas chromatography with nitrogen selective detection

rac-Isradipine is a dihydropyridine type calcium antagonist. Its calcium entry blocking effect is due primarily to the (+)-(S)-enantiomer. This study describes a sensitive enantioselective method for the determination of isradipine in human serum. Following alkaline extraction into hexane, the enantiomers of isradipine are separated quantitatively by high-performance liquid chromatography on a Chiralcel OJ column at 39 degrees C. The collected fractions were evaporated and assayed using capillary gas chromatography on a HP 50+ column with nitrogen selective detection. Using 2.0 ml of serum, 0.7 nmol/1 (0.26 ng/ml) of each enantiomer could be determined with acceptable precision. The method has successfully been used to measure (+)-(S)- and (-)-(R)-isradipine concentrations in samples from volunteers after intravenous and oral administration of isradipine.     

Pharmacokinetics of imipenem-cilastatin in critically ill patients undergoing continuous venovenous hemofiltration

The pharmacokinetics of imipenem-cilastatin were investigated in 12 critically ill patients with acute renal failure (ARF) managed by continuous veno-venous hemofiltration (CVVH) while receiving a fixed combination of 500 mg of imipenem-cilastatin intravenously three or four times daily. No adverse drug reactions were observed. Plasma and hemofiltrate samples were taken at specified times during one dosing interval, and the concentrations of imipenem and cilastatin were determined by high-performance liquid chromatography. Pharmacokinetic variables were calculated by a first-order, two-compartment pharmacokinetic model for both substances. Total clearances of imipenem and cilastatin (mean +/- standard deviations) were 122.2 +/- 28.6 and 29.2 +/- 13.7 ml/min, respectively, with hemofiltration clearances of 22.9 +/- 2.5 and 16.1 +/- 3.1 ml/min, respectively, and nonrenal, nonhemofiltration clearances of 90.8 +/- 26.3 and 13.2 +/- 13.9 ml/min, respectively. Mean imipenem dosage requirements were approximately 2,000 mg/24 h (2,111.8 +/- 493.4 mg/24 h). They were calculated in order to achieve an average steady-state concentration of 12 mg/liter to ensure that concentrations in plasma exceeded the MICs at which 90% of intermediately resistent bacteria are inhibited (8 mg/liter) during the majority of the dosing interval. By contrast, the recommended dosage for patients with end-stage renal failure (ESRF) and infections caused by intermediately resistant bacteria is 1,000 mg/24 h. This remarkable difference may be due (i) to differences in the nonrenal clearance of imipenem between patients with ARF and ESRF and (ii) to the additional clearance by the hemofilter. Since the total clearance of cilastatin was low, marked accumulation occurred, and this was particularly pronounced in patients with additional liver dysfunction. Thus, in patients with ARF managed by CVVH, rather high imipenem doses are required, and these inevitably result in a marked accumulation of cilastatin. The doses of imipenem recommended for patients with ESRF, however, will lead to underdosing and inadequate antibiotic therapy.     

CCAAT displacement protein (CDP/cut) binds a negative regulatory element in the human tryptophan hydroxylase gene

BACKGROUND: The pharmacokinetics of low-dose subcutaneous methotrexate have not been determined throughout the standard weekly dosing interval. It is not known whether methotrexate concentrations in the gastrointestinal tract are sufficient for pharmacologic activity in inflammatory bowel disease. METHODS: Ten patients with inflammatory bowel disease participated in the study. After the patients started taking 15 or 25 mg subcutaneous methotrexate once a week, erythrocyte methotrexate concentration was measured every 2 weeks. The absorption, rectal distribution, metabolism, and elimination of methotrexate were measured. The effect of methotrexate on proliferation of an intestinal epithelial cell line was determined. RESULTS: After weekly subcutaneous administration of methotrexate was begun, trough erythrocyte concentration rose to reach a plateau after 6 to 8 weeks, ranging from 150 to 300 nmol/L. More than 90% of subcutaneously administered methotrexate was rapidly excreted in the urine. The methotrexate plasma time course after subcutaneous administration fit a 2-compartment first-order model with biphasic elimination and trough concentration of about 1 nmol/L. Trough and peak methotrexate concentrations (mean value +/- SD) were 64 +/- 33 and 206 +/- 64 fmol/mg in the rectal mucosa and 4 +/- 3 and 51 +/- 26 nmol/L in the rectal lumen. These methotrexate concentrations were in the range found to be pharmacologically active against Caco-2 cell growth, that is, a 50% inhibitory concentration from 10 to 46 nmol/L. CONCLUSION: Subcutaneous methotrexate was well absorbed and distributed to the site of the lesions in patients with inflammatory bowel disease. Methotrexate was concentrated intracellularly in blood and in the rectum. The methotrexate concentration in the rectal mucosa remained within a pharmacologically active range throughout the dosing interval. The findings represent a pharmacologic explanation for the sustained efficacy of weekly methotrexate therapy.     

Synthesis of beta-difluorine-containing amino acids

This single-dose, randomized, crossover study was carried out to investigate the potential effect of ranitidine on the pharmacokinetics of chlorpheniramine. The study also afforded an opportunity to add to the limited data currently available on the stereoselective pharmacokinetics of chlorpheniramine. Healthy subjects received a single oral 4 mg dose of racemic chlorpheniramine on two separate occasions: alone, and on day 6 of dosing with ranitidine 75 mg b.i.d. for 8 days. Serum concentrations and urinary recovery of (S)-(+)- and (R)-(-)-chlorpheniramine were unaffected by administration of ranitidine, indicating no pharmacokinetic drug-drug interaction. The observed chlorpheniramine pharmacokinetic data were consistent with previous data and indicated approximately 2.5-fold higher serum concentrations of the (S)-(+) enantiomer. Previously reported high variability in chlorpheniramine pharmacokinetics was greatly reduced by well-controlled food and fluid intake.     

Evidence for disturbed S-adenosylmethionine : S-adenosylhomocysteine ratio in patients with end-stage renal failure: a cause for disturbed methylation reactions?

BACKGROUND: Elevated homocysteine concentrations have been associated with premature arteriosclerosis and with impairment of key methylation reactions through accumulation of the homocysteine metabolite S-adenosylhomocysteine. In end-stage renal failure high homocysteine concentrations are commonly found but thus far the concentrations of related adenosylated metabolites in plasma have not been assessed. METHODS: In this prospective study we determined plasma homocysteine and related metabolites in 25 patients on regular haemodialysis, and in 40 healthy volunteers. Blood samples from patients were drawn immediately before and in 10 patients additionally after the dialysis session. RESULTS: Folic acid and vitamin B12 in plasma were similar in patients (mean +/- SEM 25+/-2 nmol/l and 400+/-41 pmol/l respectively) and controls (24+/-3 and 324+/-23 respectively). In patients plasma homocysteine, S-adenosylmethionine and S-adenosylhomocysteine were markedly elevated (36.6+/-3.6 micromol/l, 381+/-32nmol/l and 1074+/-55 nmol/l respectively) compared to the control values (6.8+/-0.4 micromol/l, 60+/-3 nmol/l and 24.4+/-1.1 nmol/l respectively) whereas the molar ratio of plasma S-adenosylmethionine and S-adenosylhomocysteine was significantly decreased (0.36+/-0.02 and 2.7+/-0.2 in patients and controls respectively). Haemodialysis failed to normalize the abnormal levels of these metabolites. CONCLUSION: Since the ratio of S-adenosylmethionine : S-adenosylhomocysteine is closely linked to the activity of numerous enzymatic methylation reactions, these results suggest that methylation may be impaired in these patients.     

The enantiomers of phenprocoumon: pharmacodynamic and pharmacokinetic studies

The pharmacodynamics and pharmacokinetics of the optical enantiomers of phenprocoumon were studied in 5 normal subjects and compared to the racemic mixture. Each subject received a single oral dose of 0.6 mg/kg of racemic, S(-), and R(+) phenprocoumon. S(-) phenprocoumon was 1.6 to 2.6 times as a potent as R(+) phenprocoumon when the area under the effect/time curve was used to quantify the total anticoagulant effect per dose. Comparing the plasma concentrations that elicited the same anticoagulant effect, S(-) phenprocoumon was 1.5 to 2.5 times as potent as R(+) phenprocoumon. The anticoagulant activity of the racemic mixture was between that of the enantiomers. There was no distinct difference in the rate of elimination between the enantiomers. The apparent volume of distribution and the plasma clearance for S(-) phenprocoumon were less than those for R(+) phenprocoumon. When the binding of the enantiomers to human serum albumin was compared, S(-) phenprocoumon was more highly bound than R(+) phenprocoumon. The protein binding of racemic phenprocoumon was between that of the enantiomers. The results show that S(-) phenprocoumon is more potent anticoagulant than R(+) phenprocoumon and that the pharmacokinetic differences between the enantiomers are due mainly to differences in their distribution.     

Characterization of 5-HT1A receptor-mediated [35S]GTPgammaS binding in rat hippocampal membranes

Stimulation of [35S]GTPgammaS binding by serotonin (5-hydroxytryptamine, 5-HT) receptor ligands was characterized in rat hippocampal membranes. The optimized assay contained 30-50 microg protein, 300 microM GDP and 0.1 nM [35S]GTPgammaS, incubated at 37 degrees C for 20 min. At 10 microM, the 5-HT1A receptor agonist R(+)-8-hydroxy-2-(di-n-propylamino)tetralin [R(+)-8-OH-DPAT] stimulated GTPgammaS binding from 27.1 +/- 2.5 to 45.7 +/- 4.2 fmol/mg protein. Increasing the protein concentration did not affect the absolute difference between basal and maximal GTPgammaS binding nor the EC50, but decreased the percent stimulation. The non-selective agonists serotonin and 5-carboxamidotryptamine were 30-35% more efficacious, whereas the partial agonists buspirone and S(-)-8-hydroxy-2-(di-n-propylamino)tetralin stimulated GTPgammaS binding by 19 +/- 1 and 43 +/- 3%, respectively, compared to R(+)-8-OH-DPAT. Neither the 5-HT2 receptor agonist [(+/-)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl] (DOI) nor the 5-HT1A receptor antagonists WAY 100,635 (n-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-n-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride) and spiperone altered basal GTPgammaS binding. WAY 100,635 abolished the effect of R(+)-8-OH-DPAT, but only reduced the effect of serotonin by 88 +/- 3%. Finally, methiothepin antagonized R(+)-8-OH-DPAT-stimulated GTPgammaS binding and reduced basal GTPgammaS binding by itself. The reduction was not affected by WAY 100,635. We have characterized a method to assess functional activity at 5-HT1A receptors in rat hippocampal membranes by measuring agonist-induced [35S]GTPgammaS binding.     

Leptin levels in protracted critical illness: effects of growth hormone-secretagogues and thyrotropin-releasing hormone

Prolonged critical illness is characterized by feeding-resistant wasting of protein, whereas reesterification, instead of oxidation of fatty acids, allows fat stores to accrue and associate with a low-activity status of the somatotropic and thyrotropic axis, which seems to be partly of hypothalamic origin. To further unravel this paradoxical metabolic condition, and in search of potential therapeutic strategies, we measured serum concentrations of leptin; studied the relationship with body mass index, insulin, cortisol, thyroid hormones, and somatomedins; and documented the effects of hypothalamic releasing factors, in particular, GH-secretagogues and TRH. Twenty adults, critically ill for several weeks and supported with normocaloric, continuously administered parenteral and/or enteral feeding, were studied for 45 h. They had been randomized to receive one of three combinations of peptide infusions, in random order: TRH (one day) and placebo (other day); TRH + GH-releasing peptide (GHRP)-2 and GHRP-2; TRH + GHRH + GHRP-2 and GHRH + GHRP-2. Peptide infusions were started after a 1-microgram/kg bolus at 0900 h and infused (1 microgram/kg.h) until 0600 h the next morning. Serum concentrations of leptin, insulin, cortisol, T4, T3, insulin-like growth factor (IGF)-I, IGF-binding protein-3 and the acid-labile subunit (ALS) were measured at 0900 h, 2100 h, and 0600 h on each of the 2 study days. Baseline leptin levels (mean +/- SEM: 12.4 +/- 2.1 micrograms/L) were independent of body mass index (25 +/- 1 kg/m2), insulin (18.6 +/- 2.9 microIU/mL), cortisol (504 +/- 43 mmol/L), and thyroid hormones (T4: 63 +/- 5 nmol/L, T3: 0.72 +/- 0.08 nmol/L) but correlated positively with circulating levels of IGF-I [86 +/- 6 micrograms/L, determination coefficient (R2) = 0.25] and ALS (7.2 +/- 0.6 mg/L, R2 = 0.32). Infusion of placebo or TRH had no effect on leptin. In contrast, GH-secretagogues elevated leptin levels within 12 h. Infusion of GHRP-2 alone induced a maximal leptin increase of +87% after 24 h, whereas GHRH + GHRP-2 elevated leptin by up to +157% after 24 h. The increase in leptin within 12 h was related (R2 = 0.58) to the substantial rise in insulin. After 45 h, and having reached a plateau, leptin was related to the increased IGF-I (R2 = 0.37). In conclusion, circulating leptin levels during protracted critical illness were linked to the activity state of the GH/IGF-I axis. Stimulating the GH/IGF-I axis with GH-secretagogues increased leptin levels within 12 h. Because leptin may stimulate oxidation of fatty acids, and because GH, IGF-I, and insulin have a protein-sparing effect, GH-secretagogue administration may be expected to result in increased utilization of fat as preferential substrate and to restore protein content in vital tissues and, consequently, has potential as a strategy to reverse the paradoxical metabolic condition of protracted critical illness.     

Metabotropic glutamate receptors in the ventrolateral medulla of rats

We investigated the hypothesis that stimulation of metabotropic excitatory amino acid receptors in the ventrolateral medulla evokes cardiovascular responses. Thus, (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD], a selective agonist of metabotropic excitatory amino acid receptors, was microinjected into the rostral or caudal ventrolateral medulla of halothane-anesthetized Sprague-Dawley rats. Microinjections of (1S,3R)-ACPD (100 pmol-1 nmol) into the rostral ventrolateral medulla produced dose-dependent increases in mean arterial pressure (+20 +/- 4 mm Hg by 100 pmol and +35 +/- 2 mm Hg by 1 nmol, p < 0.01 versus artificial cerebrospinal fluid) and integrated splanchnic sympathetic nerve activity (+17 +/- 3% and +46 +/- 4%, respectively, p < 0.01), whereas (1S,3+)-ACPD microinjected into the caudal ventrolateral medulla decreased mean arterial pressure (-28 +/- 2 mm Hg by 100 pmol and -48 +/- 6 mm Hg by 1 nmol, p < 0.01 versus artificial cerebrospinal fluid) and splanchnic sympathetic nerve activity (-24 +/- 4% and -49 +/- 5%, p < 0.01). The blockade of ionotropic excitatory amino acid receptors by the combined injection of 2-amino-7-phosphonoheptanoic acid (200 pmol) and 6,7-dinitroquinoxaline-2,3-dione (200 pmol), which effectively blocked the responses elicited by either N-methyl-D-aspartate (20 pmol) or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (5 pmol), failed to affect the responses evoked by either (1S,3R)-ACPD (100 pmol) or L-glutamate (2 nmol) microinjected in the rostral and caudal ventrolateral medulla. These results suggest that metabotropic receptors are present and mediate cardiovascular responses evoked by L-glutamate injections into the rostral and caudal ventrolateral medulla.     

Intra-individual comparison of 3(R)-BMIPP and 3(S)-BMIPP isomers in humans

The racemic 15-(p-iodophenyl)-3(R,S)-methylpentadecanoic acid (BMIPP) is currently used at several centers for myocardial metabolic imaging with SPECT. Recently, the 3(R)-BMIPP isomer showed a 20%-25% higher myocardial uptake and lower liver uptake than 3(S)-BMIPP in fasted rats. The aim of this study was to determine if these differences in myocardial and liver uptake also occur in humans. METHODS: Iodine-123-labeled 3(R)-BMIPP and 3(S)-BMIPP isomers were injected at rest, on two separate days, in six patients with stable coronary artery disease. Dual-head, whole-body scintigraphy was performed 20 min and 3 hr after injection. SPECT cardiac imaging was performed 60 min after injection. RESULTS: Myocardial activity averaged (% injected dose +/- s.d.) 3.15 +/- 0.49 versus 3.01 +/- 0.44 at 20 min (p = ns) and 2.64 +/- 0.38 versus 2.55 +/- 0.41 at 3 hr postinjection (p = ns) for the 3(R)-BMIPP and 3(S)-BMIPP isomers, respectively. Liver activity averaged 9.50 +/- 1.18 versus 9.44 +/- 0.66 at 20 min and 5.33 +/- 0.64 versus 5.43 +/- 0.66 at 3 hr, respectively (p = ns). SPECT showed no difference in the distribution of the two isomers between normal and infarcted myocardium. CONCLUSION: There is no significant difference in myocardial and liver distribution of the 3(R)-BMIPP and 3(S)-BMIPP isomers in humans.     

Intrapulmonary steady-state concentrations of clarithromycin and azithromycin in healthy adult volunteers

The steady-state concentrations of clarithromycin and azithromycin in plasma were compared with concomitant concentrations in epithelial lining fluid (ELF) and alveolar macrophages (AM) obtained in intrapulmonary samples during bronchoscopy and bronchoalveolar lavage from 40 healthy, nonsmoking adult volunteers. Mean plasma clarithromycin, 14-(R)-hydroxyclarithromycin, and azithromycin concentrations were similar to those previously reported. Clarithromycin was extensively concentrated in ELF (range of mean +/- standard deviation concentrations, 34.4 +/- 29.3 microg/ml at 4 h to 4.6 +/- 3.7 microg/ml at 24 h) and AM (480 +/- 533 microg/ml at 4 h to 99 +/- 50 microg/ml at 24 h). The concentrations of azithromycin in ELF were 1.01 +/- 0.45 microg/ml at 4 h to 1.22 +/- 0.59 microg/ml at 24 h, and those in AM were 42.7 +/- 28.7 microg/ml at 4 h to 41.7 +/- 12.1 microg/ml at 24 h. The concentrations of 14-(R)-hydroxyclarithromycin in the AM ranged from 89.3 +/- 52.8 microg/ml at 4 h to 31.3 +/- 17.7 microg/ml at 24 h. During the period of 24 h after drug administration, azithromycin and clarithromycin achieved mean concentrations in ELF and AM higher than the concomitant concentrations in plasma.     

Stereoselective effects of etomidate optical isomers on gamma-aminobutyric acid type A receptors and animals

BACKGROUND: The intravenous anesthetic etomidate is optically active and exists in two mirror-image enantiomeric forms. However, although the R(+) isomer is used as a clinical anesthetic, quantitative information on the relative potencies of the R(+) and S(-) isomers is lacking. These data could be used to test the relevance of putative molecular targets. METHODS: The anesthetic concentrations for a half-maximal effect (EC50) needed to induce a loss of righting reflex in tadpoles (Rana temporaria) were determined for both etomidate enantiomers. The effects of the isomers on gamma-aminobutyric acid (GABA)-induced currents in stably transfected mouse fibroblast cells was also investigated using the patch-clamp technique. In addition, the effects of the isomers on a lipid chain-melting phase transition were determined. RESULTS: The EC50 concentrations for general anesthesia for the R(+) and S(-) isomers were 3.4 +/- 0.1 microM and 57 +/- 1 microM, with slopes of n = 1.9 +/- 0.1 and n = 2.9 +/- 0.2, respectively. The R(+) isomer was also much more effective than the S(-) isomer at potentiating GABA-induced currents, although the degree of stereoselectivity varied with anesthetic concentration. R(+) etomidate potentiated the GABA-induced currents by increasing the apparent affinity of GABA for its receptor. Both isomers were equally effective at disrupting lipid bilayers. CONCLUSIONS: These data are consistent with the idea that the GABA(A) receptor plays a central role in the actions of etomidate. Etomidate exerts its effects on the receptor by binding directly to a specific site or sites on the protein and allosterically enhancing the apparent affinity of GABA for its receptor.     

Bioavailability of escin after administration of two oral formulations containing aesculus extract

In a steady-state cross-over study in 18 healthy volunteers, the relative bioavailability of beta-escin (CAS 11072-93-8) after oral administration of a new immediate release enteric-coated test formulation containing aesculus extract was evaluated in comparison with a prolonged-release reference preparation. The subject received the test and the reference preparation in randomised sequence for 7 days each with no washout period in between. The daily dose was 50 mg escin b.i.d. Blood samples for pharmacokinetic profiling were taken on the 7th treatment day of each period over a full 24-h cycle of two successive dosing intervals. For the determination of beta-escin serum concentrations, a highly specific radioimmunoassay (RIA) was used. Generally, escin serum concentrations were lower during the second dosing interval (night) than during the first interval, probably indicating a drug by food interaction. (The morning dose was given after overnight fasting whereas the evening dose was given between meals). Test and reference demonstrated bioequivalence with regard to the extent of absorption; for the AUC (0-24 h p.a.), the 90% confidence interval ranged from 84% to 114% (point estimate: 98%). The differences observed for rate parameters can be disregarded due to the generally slow elimination and the wide therapeutic concentration range of escin.     

Comparative repellency of commercial formulations of deet, permethrin and citronellal against the mosquito Aedes aegypti, using a collagen membrane technique compared with human arm tests

The plasma concentrations and urinary excretions of bisoprolol enantiomers in four Japanese male healthy volunteers after a single oral administration of 20 mg of racemic bisoprolol were evaluated. The AUC(infinity) and elimination half-life of (S)-(-)-bisoprolol were slightly larger than those of (R)-(+)-bisoprolol in all subjects. The metabolic clearance of (R)-(+)-bisoprolol was significantly (P < 0.05) larger than that of (S)-(-)-bisoprolol (S/R ratio: 0.79+/-0.03), although the difference was small. In contrast, no stereoselective in vitro protein binding of bisoprolol in human plasma was found. An in vitro metabolic study using recombinant human cytochrome P450 (CYP) isoforms indicated that oxidation of both bisoprolol enantiomers was catalyzed by the two isoforms, CYP2D6 and CYP3A4. CYP2D6 metabolized bisoprolol stereoselectively (R > S), whereas the metabolism of bisoprolol by CYP3A4 was not stereoselective. The S/R ratio of the mean clearance due to renal tubular secretion was 0.68, indicating a moderate degree of stereoselective renal tubular secretion. These findings taken together suggest that the small differences in the pharmacokinetics between (S)-(-)- and (R)-(+)-bisoprolol are mainly due to the stereoselectivity in the intrinsic metabolic clearance by CYP2D6 and renal tubular secretion.