Cytochrome P450 probe substrate metabolism kinetics in Sprague Dawley rats.

The objective of the current study was to investigate the metabolism of cytochrome P450 (CYP) probe substrates in male Sprague Dawley rat liver microsomes and to determine their substrate specificities. Time and microsomal protein concentrations were varied to determine the linear conditions for each reaction. Appropriate substrate concentrations were chosen to determine the apparent K(m) and V(max) for 17 different reactions under initial rate conditions of protein and reaction time. All reactions appeared to follow Michaelis-Menten kinetics. Subsequently, each substrate was incubated at one to two times K(m) with each of 14 baculovirus cDNA-expressed rat CYP enzymes to determine the specificity of the reaction monitored. Of the 14 enzymes tested, seven were seen as the major rat CYP enzymes responsible for the majority of the substrate metabolism tested. Testosterone 2alpha- and 16alpha-hydroxylation reactions were conducted primarily by CYP2C11, and midazolam 4-hydroxylation and triazolam 1'-hydroxylation were preferentially catalyzed by CYP3A1/2, but specificity was otherwise generally poor. The results presented herein clearly indicate that care must be taken in interpretation of metabolism results obtained in rats using standard probe substrates, especially in extrapolation of those results to humans.

Ultrafast light-induced magnetization dynamics of ferromagnetic semiconductors.

We develop a theory of ultrafast light-induced magnetization dynamics in ferromagnetic semiconductors. We demonstrate magnetization control during femtosecond time scales via the interplay between nonlinear circularly polarized optical excitation, hole-spin damping, polarization dephasing, and Mn-hole-spin interactions. Our results show magnetization relaxation and precession for the duration of the optical pulse governed by the nonlinear optical polarizations and populations.

Inhibition of LTB4 biosynthesis in situ by CGS 23885, a potent 5-lipoxygenase inhibitor, correlates with its pleural fluid concentrations in an experimentally induced rat pleurisy model.

An intrapleural injection of carrageenan in rats induced LTB4 and LTC4/D4/E4 biosynthesis, exudate formation, and cellular influx in the pleural cavity. An injection of calcium ionophore (A23187, 100 nmol) 16-18 h after carrageenan injection augmented leukotriene biosynthesis and exudate formation, but not cellular influx. The carrageenan-induced pleurisy model modifid by A23187 administration was used to study the oral effect of CGS 23885 (N-hydroxy-N-[(6-phenoxy-2H-1-benzopyran-3-yl)-methyl]urea), a potent 5-lipoxygenase (5-LO) inhibitor, on inflammatory parameters. CGS 23885 dose-dependently (1 to 30 mg/kg) inhibited the enhanced LTB4 and LTC4/D4/E4 (1 to 10 mg/kg) biosynthesis, but had no effect on enhanced exudate formation. An inhibitory effect of CGS 23885 of small magnitude on cellular influx due to carrageenan stimulation was seen at 30 mg/kg. The concentrations of CGS 23885 in the pleural fluid were dose-related, and a positive correlation (r2=0.989) between pleural fluid concentration of LTB4 and CGS 23885 was observed. The results confirm that CGS 23885 is a specific, orally active 5-LO inhibitor which can achieve concentrations in the pleural cavity sufficient to inhibit production of LTB4 and LTC4/D4/E4 in an ongoing inflammatory response.

The effect of knot geometry on the strength of laparoscopic slip knots.

OBJECTIVE: To evaluate and compare the strength of six different knot geometries used in laparoscopic slip knots. METHODS: The strength of six extracorporeal slip knots used in laparoscopic surgery was measured using a tensiometer. Two multiple-throw laparoscopic square knots (the intracorporeal two-turn flat square knot and the extracorporeal sliding square knot) were used as controls. Each knot type was tied five times, and each type was tied in random order by the same primary and assisting surgeons using a laparoscopic pelvic surgery training model. One-way analysis of variance was performed to detect significant differences in knot strengths, and the variability in knot strength for each knot type was determined by Tukey's multiple comparison test. RESULTS: A statistically significant effect for knot geometry was identified. The mean knot strengths +/- standard deviation (SD), measured in newtons, from strongest to weakest, were: 4S knot (28.01 +/- 11.45), fisherman's knot (22.45 +/- 6.89), modified Roeder knot (19.86 +/- 9.30), Roeder knot (15.77 +/- 7.02), Weston knot (7.28 +/- 7.96), and Duncan knot (6.55 +/- 0.95). The mean knot strengths for the multiple-throw control square knots were as follows: intracorporeal two-turn flat square knot (41.21 +/- 2.69) and extracorporeal sliding square knot (27.81 +/- 16.27). The intracorporeal two-turn flat square knot (control) was significantly stronger (P < .05) than all slip knots except the 4S and fisherman's knot. CONCLUSION: The 4S and fisherman's knots are the strongest laparoscopic slip knots and are the only slip knots similar in strength to multiple-throw square knots.

A simple modification to add strength to the Roeder knot.

The Roeder knot is commonly used during laparoscopic suturing because it may be tied extracorporeally and slid down to the target tissue with a single pass of a knot pusher. However, it is significantly weaker than extracorporeally tied knots with several throws. We compared the usual Roeder knot to one that was modified by adding a fourth loop around the standing end of the suture and a second half-hitch to the completed knot. The modified knot (26.6 newtons +/- 15.3) was significantly stronger (p <0.05) than the standard Roeder knot (18.0 newtons +/- 12.1). If a single-pass extracorporeal knot is to be used, we recommend a modified Roeder knot when ligating pedicles at laparoscopy.

Laparoscopic knot strength: a comparison with conventional knots.

OBJECTIVE: To compare the strength of laparoscopic knots with those used at laparotomy. METHODS: Three types of laparoscopic knots commonly used (Roeder, extracorporeal sliding square, and intracorporeal two-turn flat square) and three widely used conventional knots (flat square, surgeon's square, and sliding square) were tied using seven suture materials. Each knot was tied five times in random order by a single surgeon in a pelvic training model. Knot strengths were scored by tensiometer readings. A two-way analysis of variance was performed to uncover differences in mean knot strength. Turkey multiple-comparisons test was performed to determine the variability in strength of different knot geometries. Knot strength was measured in newtons. RESULTS: Significant main effects for knot geometry (P < .05) and material (P < .05) as they contribute to differences in knot strength were identified, as well as an interaction for knot geometry with material (P < .05). The laparoscopic Roeder knot was significantly weaker than all other laparoscopic and conventional knots tested. The laparoscopic extracoporeal sliding square knot was significantly weaker than the conventional surgeon's square knot, and the conventional sliding square knot was significantly weaker than the conventional flat square knot and the surgeon's knot. The laparoscopic intracorporeal two-turn flat square knot was as strong as the strongest conventional knot. A significant main effect was discovered for knots with eight throws. CONCLUSION: When performing laparoscopic procedures that result in significant tension on suture lines, consideration should be given to using the stronger laparoscopic knots, such as the intracorporeal two-turn flat square knot and the extracorporeal sliding square knot, instead of the weaker Roeder knot.

Development of tolerance to the antihypertensive effects of highly selective adenosine A2a agonists upon chronic administration.

Three highly A2a-selective adenosine agonists were examined for their effects on blood pressure during chronic administration in conscious spontaneously hypertensive rats. Sodium 4-[2-[[6-amino-9-(N-ethyl-beta-D-ribofuranuronamidosyl)-9H-purin-2 -yl] amino]ethyl]benzenepropionate (CGS 21680C) 2-[(2-cyclohexyl-ethyl)amino]adenosine (CGS 22492) and 2-[[2-(1-cyclohexen-1-yl)ethyl]amino]adenosine (CGS 22989) were administered at a rate of 0.25 and 0.5 micrograms/kg/min i.v. for 2 weeks using osmotic minipumps. Significant systolic blood pressure reductions were seen in the A2a agonist-treated groups compared to vehicle-treated (50% dimethyl sulfoxide) animals. Maximum effects occurred on days 1 and 2 in the treated animals. However, the antihypertensive effect diminished with time such that no differences between treatments were seen at 2 weeks. In contrast, a sustained antihypertensive effect was evident with benazeprilat (an angiotensin converting enzyme inhibitor). Tolerance was associated with a decrease in Bmax values (375 +/- 22, 410 +/- 18 and 548 +/- 17 fmol/mg of protein in the CGS 21680C, CGS 22989- and vehicle-treated spontaneously hypertensive rats, respectively) without affecting the Kd value. In addition to a reduction in A2 receptor number, increased heart rates were seen on day 1 and 2 in both the CGS 21680C- and CGS 22989-treated animals and a mild stimulation of the renin angiotensin system occurred with CGS 21680C. In separate acute experiments using identical infusion rates, plasma concentrations of CGS 21680C were 157 +/- 41 ng/ml compared to 30.4 +/- 8.8 ng/ml after chronic administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Automated-extraction, high-performance liquid chromatographic method and pharmacokinetics in rats of a highly A2-selective adenosine agonist, CGS 21680.

CGS 21680 (2-[p-(2-carboxyethyl)phenylethylamino]-5'-N- ethylcarboxamidoadenosine, I) is a highly A2-selective (A2/A1 = 140), high-affinity adenosine agonist. A method has been devised to extract the compound from biological matrices with automated solid-phase extraction using C18 bonded silica columns. This is followed by reversed-phase, paired-ion chromatography on a Supelco LC-18-S column with fluorescence detection. The limit of quantitation is 5 ng/ml, but 1 ng/ml (five times the signal-to-noise ratio) can readily be detected. Tritium-labeled compound was used to study the pharmacokinetics in rats. After an intravenous dose of 0.3 mg/kg, biphasic elimination kinetics were observed for parent I, characterized by half-lives of 1.8 min (distribution) and 15 min (elimination). The volume of distribution in the terminal phase (V beta) was low (0.27 l/kg) and plasma clearance was moderate (0.83 l/kg/h). Although the compound was rapidly absorbed (mean Tmax = 13 min), low concentrations (mean Cmax = 94 ng/ml) were observed after an oral dose of 3.0 mg/kg, and bioavailability was only approximately 1.4%. Radioactivity persisted in plasma longer than parent compound after either dose, but levels were too low for isolation and structure identification of drug-derived compounds.

Response latency measurements to visual cognitive tasks by normal hearing and deaf subjects.

Visual cognitive differences between hearing (N = 16) and deaf (N = 32) high-school and middle-school students were studied. Visual tasks were presented on a microcomputer and response latencies were collected. Significant differences were noted between the deaf and normal groups but not between total communication deaf and oral deaf students. These differences support the hypothesis that deaf students prefer a visual cognitive strategy. Implications for educating the deaf are discussed.

Bleomycin for the cure of Trypanosoma brucei brucei infections in mice: lack of pulmonary toxicity.

Although bleomycin is a known pulmonary toxin, results presented herein indicate its relative safety for treatment of trypanosomiasis. More than 4 times the curative dose in this acute model of infection does not induce significant alterations of lung hydroxyproline levels, which are known to directly correlate with histopathological criteria of pulmonary fibrosis.

Comparison of meclizine levels in the plasma of rats and dogs after intranasal, intravenous, and oral administration.

Meclizine, used prophylactically for the prevention of motion sickness and vertigo, is presently available only in oral form. We report herein that, when given intranasally, meclizine dihydrochloride is absorbed in rats about half as effectively as when given intravenously, but about six times more effectively than after oral administration, as estimated by the area under the plasma concentration-time curve. The mean times to peak levels in plasma are about 8.5 min after an intranasal dose and 49.0 min after oral delivery. We extended these studies to a second species, the beagle dog, and achieved qualitatively similar results with a new formulation (Mecnazone; Nastech Pharmaceutical Co., Inc.). The fraction absorbed intranasally was about 0.89 that of an equivalent intravenous dose but about four times that of an equivalent oral administration. In these studies, the mean times to peak levels in plasma was 11.9 min after an intranasal dose and 70.0 min after an oral dose. Terminal elimination kinetics were the same for all routes within each species. Intranasal delivery of meclizine therefore appears to be superior to the oral route for the more rapid achievement of substantial levels in plasma at a reduced dose.

Reversed-phase paired-ion high-performance liquid chromatographic method for the separation and quantification of multiple bleomycin congeners.

A rapid, linear gradient chromatographic technique for separating and quantifying copper(II)-chelated bleomycin congeners is described. This method is also capable of separating divalent from trivalent metal chelates; determining the purity of many chemically modified bleomycins; and assaying bleomycin hydrolase activity on complex mixtures. Quantification at 280 nm is sensitive to 50 pmol and is linear at least up to 10 nmol per injection.

Bleomycin pulmonary toxicity: production of fibrosis by bithiazole-terminal amine and terminal amine moieties of bleomycin A2.

We have previously demonstrated that endotracheal administration of the terminal amines of several bleomycins, when administered as the free amines, produce pulmonary fibrosis of severity comparable to the intact drug. In the present report, bleomycin A2 and its sulfonium ion-containing terminal substituents, with and without the bithiazole rings, were administered to mice endotracheally. The incidence and severity of epithelial metaplasia was greater with the intact drug in comparison to the terminal substituents. In contrast, the terminal substituents and intact drug produced similar degrees of fibrosis. These results underscore the importance of the variable bleomycin terminal substituents in the pathogenesis of pulmonary fibrosis.

Effect of taurine on calcium paradox and ischemic heart failure.

The loss of mechanical function in rat hearts subjected to either the calcium-paradox or global ischemia heart failure models was found to correlate with decreases in myocardial taurine levels. Therefore, the effect of taurine treatment was assessed in the two failure procedures. The presence of taurine protected against loss of mechanical function resulting from the calcium paradox and prevented both the large decline in sarcolemmal ATPase activities and the increase in sarcolemmal calcium binding normally associated with this model. Parallel studies on reperfused, taurine-untreated ischemic hearts showed only minor changes in these sarcolemmal functions. Taurine treatment normalized the slight increase in calcium binding associated with ischemia, but had no observable effect on recovery of mechanical function. Although taurine returns selected parameters of the sarcolemma toward normal in both models, it only improves mechanical function in the paradox model. This suggests that calcium paradox-induced heart failure is more closely associated with sarcolemmal dysfunction than ischemic heart failure.

Regulation of calcium homeostasis in the heart by taurine.

The role of taurine in maintaining calcium and potassium homeostasis in excitable tissues is discussed. These effects of taurine appear to be related to its interaction with a low affinity binding protein of the cell membrane. This conclusion is based on the observation that the sulfinic acid analog of taurine, hypotaurine, also interacts with this protein and mimics these actions of taurine, whereas two other analogs, beta-alanine and isethionic acid, have little affinity for the binding protein and fail to exhibit taurine-like activity. The possibility that a relationship exists between the low affinity protein and sarcolemmal calcium pools is considered.

Taurine enhancement of calcium binding to rat heart sarcolemma.

The effect of taurine on calcium binding to isolated rat heart sarcolemmal membrane was examined. Taurine was observed to increase calcium binding to the low affinity sites in both high sodium-low potassium and low sodium-high potassium buffers. Taurine was also seen to antagonize the inhibition of calcium binding to the sarcolemma caused by both verapamil and lanthanum. Nevertheless, membrane structural changes due to taurine could not be detected using the spin label ESR probe 2N14. A possible regulatory role of taurine is discussed.