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Biomedical subjects

R A Yeates

Publications and source records attributed to R A Yeates.

At least 37 records · Page 2Linked to original sources
PubMed1993

Single dose intravenous pharmacokinetics of fluconazole in infants.

The present report contains an open, non-comparative study of the plasma pharmacokinetics of a single intravenous dose (3 mg/kg) of the antimycotic agent fluconazole in infants, aged between 9 days and 4.4 months (n = 14), who were either suffering from or regarded as being susceptible to fungal infection. The mean volume of distribution was calculated as 1.17 l/kg, with a range between 0.76 and 2.60 l/kg; the comparable value for adult volunteers was 0.65 +/- 0.08 l/kg (1). The mean total clearance was calculated as 0.63 +/- 0.06 ml/min x kg; the comparable value for adult volunteers was 0.25 +/- 0.04 ml/min x kg (1). The terminal half-life of elimination was calculated as 22.5 +/- 2.2 h; the comparable value for adult volunteers was 30.2 +/- 3.8 h (1). It is suggested that this difference was caused by the countervailing effects of the changes with age in clearance and in volume of distribution.

Chromatography, High Pressure Liquid↗
PubMed1992

Total prevention of the development of in vitro tolerance to organic nitrates. Experiments with antioxidants.

The nearly total inhibition of development of pharmacological tolerance to an organic nitrate is reported here for the first time. The development of in vitro tolerance in the rabbit aorta to isosorbide-5-mononitrate (CAS 87-33-2) was potently inhibited by five structurally unrelated antioxidants--diaminodurol, ascorbic acid, potassium sulphite, pyrogallol and quercetin. Diaminodurol, ascorbic acid and potassium sulphite decreased, but quercetin increased, the spasmolytic activity of isosorbide-5-mononitrate. Diaminodurol, potassium sulphite, quercetin and ascorbic acid potently inhibited the spasmolytic activity of nitric oxide (NO). Quercetin also inhibited the development of in vitro tolerance to glyceryl trinitrate. It is suggested that tolerance to organic nitrates is the result of biochemical damage caused by a reactive intermediate such as NO. To test this possibility directly the effect of pretreatment with NO on the spasmolytic activity of glyceryl trinitrate (CAS 55-63-0) was examined. This pretreatment produced a small but significant tolerance to glyceryl trinitrate and to SIN-1 (3-morpholinosydnone imine), which also acts through guanylate cyclase. There was no effect on the activity of the unrelated vasodilators nitrendipine and theophylline. It is concluded that the reaction between NO and soluble quanylate cyclase is a real but minor cause of tolerance to organic nitrates. Other possible mechanisms of tolerance development are discussed.

Animals↗
PubMed1991

Comparison of isobutyl nitrate and isobutyl nitrite: tolerance and cross-tolerance to glyceryl trinitrate.

This study includes the first systematic comparison of an organic nitrate with the corresponding organic nitrite-isobutyl nitrate and isobutyl nitrite. The spasmolytic activity of the nitrite on isolated rabbit aortic strips was stronger, more rapid in onset, but less stable than the activity of the nitrate. In vitro tolerance to glyceryl trinitrate and isobutyl nitrite greatly weakened the activity of isobutyl nitrate, respectively, but had much less effect on isobutyl nitrite. Possible reasons for these differences are discussed.

Animals↗
PubMed1989

Antagonism of glycerol trinitrate activity by an inhibitor of glutathione S-transferase.

The in vitro spasmolytic activity of glycerol trinitrate was measured on the KCl-contraction of aorta strips from the rabbit. In the presence of sulphobromophthalein, a known inhibitor of glutathione S-transferase, the dose-activity curve for the nitrate was displaced to the right. Much smaller displacements were obtained with the control spasmolytic substances--papaverine and S-nitroso-N-acetylpenicillamine. It was confirmed that sulphobromophthalein inhibits glutathione S-transferase activity in aorta homogenates. Aorta extracts did not detectably catalyze the reaction between glutathione and sulphobromophthalein and the glutathione level was not decreased by treating the intact aorta with sulphobromophthalein. It is concluded that sulphobromophthalein acts as a specific antagonist of the spasmolytic activity of glycerol trinitrate, probably as a result of its inhibition of glutathione S-transferase. It thus seems probable that glutathione and glutathione S-transferase are involved in the pharmacological activation of the organic nitrates.

Animals↗
PubMed1987

Gas chromatographic assay of glycerol mononitrates in biological samples.

A new gas chromatographic analysis of glycerol 1-nitrate and glycerol 2-nitrate is described. The method is suitable for a variety of biological samples and can detect down to the low nanogram range. An extract of the sample to be analysed is treated with phenylboronic acid. The glycerol mononitrates rapidly form cyclic boronates, with five- and six-membered rings, respectively, which can then be separated by gas chromatography and detected by an electron-capture detector.

Animals↗
PubMed1987

[The pharmacology and pharmacokinetics of glycerol-2-nitrate].

Glyceryl 2-nitrate (G-2-N), which is the major metabolite of glyceryl trinitrate (GTN, Nitro Mack, glyceryl 1-nitrate (G-1-N) and isosorbide-5-nitrate (IS-5-N, Mono Mack) were examined in a comparative study. The haemodynamic and antianginal properties and the spasmolytic activity on blood vessels were investigated in the rat and dog. Also examined were the pharmacokinetics of G-2-N in the rat and of oral GTN in the dog. Strips of rat aorta contracted with potassium chloride or with norepinephrine were relaxed by G-2-N, but somewhat more weakly than with IS-5-N or G-1-N. After oral administration to the anaesthetized rat or to the conscious dog G-2-N exhibited antianginal and hypotensive activity for 6 h. The duration of action of orally administered GTN in the dog depended on the concentration used and was between 15 and 360 min. The half-life of elimination of G-2-N in the rat came to 2 h, and the substance was 100% bioavailable. The concentrations of G-2-N found in the walls of rat vena cava caudalis and rat aorta abdominalis were twice as high as those in blood or plasma. After oral administration of GTN to the conscious dog, G-2-N is the main metabolite, followed by G-1-N, glyceryl 1,2-dinitrate (1,2-GDN), and glyceryl 1,3-dinitrate (1,3-GDN). After a large oral dose of GTN (30 mg/kg), G-2-N contributes to the pharmacodynamic effect from the 3rd h or earlier.

Angina Pectoris↗
PubMed1986

Pharmacokinetics of oral glycerol-1-nitrate.

The plasma kinetics and urinary excretion of glycerol-1-nitrate (G-1-N), a water soluble metabolite of glycerol trinitrate with anti-anginal potential, have been investigated in healthy human volunteers following oral doses of 10, 20 and 40 mg tablets and 20 mg as drops. In all volunteers G-1-N was rapidly absorbed. The mean concentration-time curves peaked 40 min after administration of tablets at 144 ng/ml (10 mg), 308 ng/ml (20 mg) and 573 ng/ml (40 mg). After the drops the peak of 324 ng/ml occurred at 1 h. The areas under the G-1-N concentration-time curve and the G-1-N peak heights were linear with dose. Tablets and drops can be regarded as bioequivalent with respect to area under the curve and elimination half-life. The bioavailability of the 20 mg tablet relative to the 20 mg drops was 98.6% in terms of area under the curve. The mean apparent half-life of G-1-N elimination from plasma was 2.69 +/- 0.67 h (n = 46). The mean residence time of G-1-N in the body was 4.65 h compared to 0.28 h for glycerol trinitrate after buccal administration. Female volunteers were found to have significantly lower areas under the curve than male volunteers. The difference was probably due to differences in body weight. Renal excretion does not play an important role in the elimination of oral G-1-N from the body. An overall average of 5.42% of the G-1-N dose was excreted in the urine; free drug accounted for 4.02% and conjugated drug for 1.40%.

Adult↗
PubMed1986

Preliminary study of the pharmacokinetics of desmethyldiazepam administered as drops or tablets.

Desmethyldiazepam (Vegesan) was administered in the form of 5-mg and 10-mg tablets and of 10-mg drops to 4 male and 4 female young healthy volunteers. The plasma levels of desmethyldiazepam were measured over 168 h. The time courses could be fitted to the one- or to the two-compartment model. The mean half-lives of elimination came to 75.3 +/- 32.0 (SD) h (5-mg tablets), 66.5 +/- 21.0 (SD) h (10-mg tablets) and 78.4 +/- 33.2 (SD) h (10-mg drops). The bioavailability of desmethyldiazepam from tablets and from drops was practically the same. The bioavailability appeared to be independent of dose in this range. A significantly higher total plasma clearance was calculated for the male than for the female volunteers after all three dosage forms (p less than 0.05). The total plasma clearance lay between 4.8 and 13.0 ml/min for the female and 12.4 and 24.3 ml/min for the male volunteers. Ingestion of the contraceptive pill is suggested as a possible cause of the sex differences.

Adult↗
PubMed1986

[Comparative pharmacology of glycerol-1-nitrate and glyceryl trinitrate in various species].

The present studies yield that all 4 metabolites of glyceryl trinitrate (Nitro Mack, GTN) cause the same typical pharmacological effects as the parent substance. Continuous infusion of 4 mg/kg/min of glyceryl 1-nitrate (G-1-N) in the conscious dog results in a drop in blood pressure which is maintained for at least 20 min after stopping the infusion. Under comparable conditions the reduction in blood pressure caused by glyceryl 2-nitrate (G-2-N) (infused at 16 mg/kg/min) decreases by only 3 mmHg. The drop in blood pressure caused by a continuous infusion with GTN (8 micrograms/kg/min) disappeared 10 to 12 min after the end of the infusion. GTN is active in rat, dog and man for 15 to 30 min. Our experiments indicate that after oral administration to the rat or dog glyceryl 1,2-dinitrate (1,2-GDN) and glyceryl 1,3-dinitrate (1,2-GDN) are active for 3 h. Earlier experiments have shown that the administration of high oral doses of 1,2-GDN or 1,3-GDN (280 mg/kg) to the rat increases the time of action to 5-6 h. This is taken as indication that the dinitrates form pharmacologically active metabolites. 1,3-GDN (70 mg/kg p.o.) and 1,2-GDN (140 mg/kg p.o.) exhibited antianginal activity in the rat for 3 or 2 h, respectively. Orally administered GTN is only active for 15 min in the rat or dog. Its pharmacological activity after this time and up to 2-3 h on the rat (280 mg/kg p.o.) and on the dog (4 mg/kg p.o.) is brought about by the dinitrate metabolites (1,2-GDN, 1,3-GDN) and after this time probably only by G-1-N.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1986

[Hypotensive, antianginal action and pharmacokinetics of glyceryl-1-nitrate in rats and dogs].

The antianginal and hypotensive activity and the pharmacokinetic properties of glyceryl 1-nitrate (G-1-N) were examined in the rat and in the dog. The level and duration of antianginal and hypotensive activity were the same after single or repeated oral dosage of G-1-N to the anaesthetized rat. The haemodynamic activity of intravenously administered G-1-N in the anaesthetized and thoracotomized dog was dose-dependent. A bolus injection of G-1-N or glyceryl trinitrate (GTN, Nitro Mack) antagonized the cardiovascular activity of intravenously injected dihydroergotamine (DHE) in the anaesthetized and thoracotomized dog. The bioavailability of G-1-N in the rat and in the dog is practically 100%. After intravenous or oral administration to the rat the concentrations of G-1-N in the walls of the vena cava caudalis were markedly higher and in the aorta abdominalis somewhat higher than in the blood or in the other organs examined. G-1-N was eliminated more slowly from the walls of the animals veins than from the walls of the aorta abdominalis or from the blood.

Angina Pectoris↗
PubMed1986

[Comparative hemodynamics action of glycero-2-nitrate and glycerol trinitrate in various species and the pharmacokinetics of glycerol-2-nitrate in the dog].

Comparative Hemodynamic Activity of Glyceryl 2-Nitrate and Glyceryl Trinitrate in Various Species and Pharmacokinetics of Glyceryl 2-Nitrate in Dog A single dose of glyceryl 2-nitrate (G-2-N) had practically identical hypotensive and cardiovascular activity when administered intravenously or enterally to the anaesthetized rabbit, cat or dog. In all three species the hypotensive and also cardiovascular activity of G-2-N lasted much longer than that of glyceryl trinitrate (GTN, Nitro Mack). In the rabbit, cat and dog enterally active doses of GTN were 500-1000 times greater than parenterally active doses. In all species enterally administered GTN was about 8 times more active than enterally administered G-2-N. G-2-N is 100% bioavailable in the conscious dog.

Animals↗
PubMed1985

The reaction between organic nitrates and sulfhydryl compounds. A possible model system for the activation of organic nitrates.

The rate of loss of the sulfhydryl group, determined with the Ellman reagent, was used to derive second order rate constants for the reaction of a series of organic nitrates with a series of sulfhydryl compounds. For the organic nitrates, increases in the rate of reaction with cysteine, in general, ran parallel both with increases in pharmacological potency (flow in the Langendorff heart) and with increases in total clearance. Cysteine was the most active sulfhydryl compound examined, which is compatible with a possible role as an important nitrate receptor. Under some conditions the rate of loss of the sulfhydryl group was much greater than the rate of formation of nitrite ion. This indicates the presence of a reaction intermediate, probably a thionitrate. It is suggested that, in vivo, a thionitrate could function as an important intermediate in the activation of guanylate cyclase.

Animals↗
PubMed1982

Adsorption of bile salts by soya-bean flour, wheat bran, lucerne (Medicago sativa), sawdust and lignin; the effect of saponins and other plant constituents.

1. The adsorption of bile salts from aqueous solution on the soya-bean flour, wheat bran, fine dry sawdust and lucerne (Medicago sativa) was measured. Adsorption on to the residuum after the first three of these substances had been extracted with organic solvents, pronase or solvents, pronase and acid (to produce lignin) was also measured. 2. The removal of saponins from soya-bean flour did not affect bile salt adsorption, and bile salts were adsorbed on to lignin and on to wheat bran (deficient in saponins). Although our methods differed from Oakenfull & Fenwick (1978) we were unable to substantiate their conclusions that saponins are responsible for most bile salt binding to fibrous substances in vitro.

Adsorption↗
PubMed1981

Ultrastructural damage of in vitro cultured ookinetes of Plasmodium gallinaceum (Brumpt) by purified proteinases of susceptible Aedes aegypti (L.).

Previous in vivo studies have implicated trypsin-like proteinases in the destruction of ookinetes of Plasmodium gallinaceum in the gut of the susceptible mosquito Aedes aegypti (Gass 1977). An in vitro study has shown that the ookinetes are destroyed by crude extracts of blood-fed A. aegypti and that this destruction is largely inhibited by an inhibitor of mosquito proteinases, lima bean trypsin inhibitor (Gass and Yeates 1979). In the present study ookinetes of P. gallinaceum have been incubated with highly purified preparations of the three principal trypsin-like proteinases of A. aegypti. It is shown that all three enzymes destroy the ookinetes and that the purified preparations are about as active as crude mosquito extracts.

Aedes↗
PubMed1980

The mosquito Aedes aegypti (L.): evidence for three new proteinases.

The effect of inhibitors was studied on the proteolytic activity of crude extracts of the mosquito Aedes aegypti (L.), prepared 25 h after blood intake. This activity is only partially inhibited by the lima bean trypsin inhibitor (LBTI) or by EDTA. Experiments with mixed inhibitors are used to indicate that, apart from the well characterized trypsin-like enzymes, at least three other proteinases are present. These are an LBTI-resistant serine proteinase, a metal chelator-sensitive proteinase, and a proteinase which can only be inhibited by the ovomucoid inhibitor. These newly described proteinases are inactive against several model substrates developed for mammalian enzymes. They are partially separable by ion-exchange chromatography.

Aedes↗
PubMed1979

Electroimmunoassay of a subunit protein in a macromolecular complex (apolipoprotein B in human plasma very low density lipoprotein); implications for other electroimmunoassay systems.

With an electroimmunoassay ("rocket") system for the apolipoprotein B component of the plasma very low density lipoprotein complex we obtained results which were similar to those obtained by a colorimetric tetramethylurea extraction method. Results were up to twice as high as those using radioimmunoassay. Low density lipoprotein containing apolipoprotein B as the only demonstrable protein component was used as the standard for these assays. This protein produced larger and higher rockets at pH 8.6 when the negative particle charge was increased by maleylation. The very low density lipoprotein complex has a higher negative charge at pH 8.6 than low density lipoprotein. These findings suggest that some apolipoprotein B in vary low density lipoprotein is not "recognised" by anti-apolipoprotein B antibodies, hence radioimmunoassay results are lower than those obtained with the tetramethylurea extraction method. The higher negative charge on very low density lipoprotein particles (compared with low density lipoprotein), as a factor tending to increase rocket area and height, is counterbalanced by reduced recognition by antiapolipoprotein B antibodies. The net result of these opposing tendencies is that the rocket electroimmunoassay of apolipoprotein B in very low density lipoprotein fortuitously gives valid results, under the specified assay conditions. We conclude that electroimmunoassays of complex proteins are not necessarily valid if protein subunits are used for standards. This has implications for the electroimmunoassay of other apolipoproteins.

Apolipoproteins↗