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A Holt

Publications and source records attributed to A Holt.

At least 37 records · Page 2Linked to original sources
PubMed1994

Location of the active site of rat vascular semicarbazide-sensitive amine oxidase.

Semicarbazide-sensitive amine oxidase (SSAO) activity in rat vascular smooth muscle cells is associated extensively with the plasmalemma. To determine which side of the plasmalemma the active sites of these enzymes face, the non-permeating agent, diazotised sulphanilic acid (DSA; 4.4 mM) was perfused through the isolated mesenteric arterial bed of the rat, in an attempt to inactivate only those active sites facing extracellularly. DSA perfusion abolished the pressor responses to noradrenaline via inactivation of extracellular alpha 1 receptors but had no effect on cytosolic lactate dehydrogenase activity. SSAO activity, estimated by perfusing [14C] benzylamine, was reduced following DSA perfusion to 55.9 +/- 4.9% of that in control beds and to 52.4 +/- 6.0% in homogenates of these vessels. These results suggest that almost half of SSAO active sites in rat mesenteric arteries face outwards.

Amine Oxidase (Copper-Containing)↗
PubMed1994

The ex vivo effects of procarbazine and methylhydrazine on some rat amine oxidase activities.

Monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO) activities were examined in homogenates of various rat tissues following i.p. administration of procarbazine or methylhydrazine. Both compounds inhibited SSAO in a dose-dependent manner in all tissues examined, with methylhydrazine the more potent agent in this respect. Little inhibition of MAO could be detected in most cases. However, hepatic MAO-B activity was potentiated significantly in rats receiving methylhydrazine and both drugs caused a dose-dependent potentiation of MAO-A in homogenates of brown adipose tissue. The potential use of these compounds in vivo as selective SSAO inhibitors is discussed.

Adipose Tissue, Brown↗
PubMed1994

Derivatization with acetic anhydride: applications to the analysis of biogenic amines and psychiatric drugs by gas chromatography and mass spectrometry.

Acetylation with acetic anhydride, under both aqueous and anhydrous conditions, has been utilized to derivatize various biogenic amines and psychotropic drugs for subsequent analysis by gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS). Under basic aqueous conditions, acetic anhydride derivatizes phenols and amines but not alcohols; under anhydrous conditions, all three functions are acetylated. Primary amines, once derivatized with acetic anhydride, can be further derivatized with other reagents; these diderivatives have proven useful for subsequent analysis by GC or GC-MS. Examples of applications of derivatization with acetic anhydride to analysis of biogenic amines, antidepressants, antipsychotics, and some of their metabolites are presented.

Acetic Anhydrides↗
PubMed1993

Maxon is an optimal suture for bile duct anastomoses in pigs.

BACKGROUND: Three commonly used sutures were tested in a pig model of bile duct anastomosis to assess their relative contributions to inflammation and scarring. METHODS: Thirty pigs were randomised to bile duct division and anastomosis with either polyglyconate (Maxon), polyglactin 910 (Vicryl) or polypropylene (Prolene). Half the animals were sacrificed at two weeks and the remainder at 23 weeks. Anastomoses were assessed by cholangiography, scanning electron microscopy and light microscopy. RESULTS: There was less short term histological reaction with the two monofilament materials, Prolene and Maxon, compared to the braided suture Vicryl. Maxon was associated with less long term inflammation than Prolene, was found to handle better, and has an advantage over Prolene by being absorbable. CONCLUSION: Maxon is an optimal suture for bile duct anastomoses. Its long term absorption characteristics make it suitable for situations where bile duct healing may be delayed.

Anastomosis, Surgical↗
PubMed1992

Characteristics of procarbazine as an inhibitor in-vitro of rat semicarbazide-sensitive amine oxidase.

Procarbazine (N-isopropyl-alpha-(2-methyl hydrazino)-p-toluamide hydrochloride) inhibited more powerfully the deamination of benzylamine by semicarbazide-sensitive amine oxidase (SSAO) of rat brown adipose tissue than the deamination of 5-hydroxytryptamine and benzylamine by rat liver monoamine oxidase-A or -B activities, respectively. Inhibition of SSAO, but not monoamine oxidase, was time-dependent. Use of metabolic inhibitors, and an enzyme dilution technique, suggested that any conversion of procarbazine to an active species must be as a result of the action of SSAO itself and not of any other enzyme. The non-competitive kinetics and the time-dependence of inhibition were indicative of a suicide interaction between procarbazine and SSAO. The slow reversal of inhibition by dialysis was evidence in favour of the involvement of tight binding, rather than covalent bonding. High concentrations of benzylamine afforded the enzyme significant protection from the action of procarbazine, indicating that the interaction is at or near the active site. If the properties of procarbazine, evident in in-vitro studies, are retained in-vivo, these data suggest that procarbazine might be suitable for the examination of SSAO activities, both in-vivo and ex-vivo.

Adipose Tissue, Brown↗
PubMed1992

Effects in-vitro of procarbazine metabolites on some amine oxidase activities in the rat.

The effects were examined of four metabolites of the anticancer agent, procarbazine (N-isopropyl-alpha-(2-methyl hydrazino)-p-toluamide hydrochloride) on semicarbazide-sensitive amine oxidase (SSAO) and monoamine oxidase-A and -B (MAO-A and -B) activities in rat brown adipose tissue and liver homogenates, respectively. Azoprocarbazine (AZO) and monomethylhydrazine (MMH) inhibited selectively the deamination of benzylamine by SSAO, when compared with their effects on MAO activities. The IC50 values against SSAO, of 32.7 nM (AZO) and 7.0 nM (MMH), were more than three orders of magnitude lower than those exhibited against MAO. Neither isomer of azoxyprocarbazine was an effective inhibitor of rat amine oxidase activities. The inhibition of SSAO by AZO was reversed very slowly by dialysis, in contrast to results seen for MMH. The non-competitive kinetics of MMH and the ability of B24, a rapidly reversible SSAO inhibitor, to protect SSAO against inhibition by MMH are consistent with the view that this compound binds to the enzyme cofactor at, or near, the active site.

Adipose Tissue, Brown↗
PubMed1990

Some aspects of the pharmacology of semicarbazide-sensitive amine oxidases.

Semicarbazide-sensitive amine oxidase enzymes (SSAO) are found in animals, plants, fungi and bacteria. In vertebrates, their distribution in tissues and blood plasma varies between species. Studies of the SSAO enzymes have concentrated on their biochemical identities separate from those of MAO. Attention is now being paid to their possible physiological and pharmacological significance. These may include, besides the scavenging of circulating amines, functions dependent upon the hydrogen peroxide these enzymes produce. Modulation, by SSAO, of blood vessel tone may be due to the control of amine concentration itself or to actions of released peroxide. In the plasma the activity of SSAO may be susceptible to hormonal control as well as being an indicator of copper status of the animal. However, SSAO may convert xenobiotics to more toxic metabolites. Use of highly selective SSAO inhibitors, such as procarbazine and B24 should enable these preliminary observations to be examined further.

Amine Oxidase (Copper-Containing)↗
PubMed1990

Further studies on the metabolism of methylamine by semicarbazide-sensitive amine oxidase activities in human plasma, umbilical artery and rat aorta.

An ion exchange radiochemical assay has been developed to study the deamination of [14C]methylamine (MA) in homogenates of rat aorta and human umbilical artery, as well as in samples of human plasma. MA metabolism was found to be inhibited almost completely by 1 mM semicarbazide, but virtually unaffected by 0.1 mM clorgyline, suggesting that MA is a substrate for the semicarbazide-sensitive amino oxidase (SSAO) activities which also metabolize benzylamine (BZ) in these sources. Mean Km values for MA metabolism by aorta, umbilical artery and plasma were 182, 832 and 516 microM, respectively, with corresponding Vmax values in aorta and umbilical artery of 100 and 590 nmol (mg prot.)-1 h-1, and in plasma of 48 nmol (mL serum)-1 h-1. Kinetic constants determined for [14C]BZ metabolism in plasma (by an organic solvent extraction assay) and in umbilical artery (by the ion exchange assay) yielded mean Km values of 225 microM (plasma), 222 microM (umbilical artery), and Vmax values of 28 nmol (mL serum)-1 h-1 (plasma) and 377 nmol (mg prot.)-1 h-1 (umbilical artery). The deamination of [14C]MA was inhibited competitively by unlabelled BZ, with Ki values in umbilical artery and plasma of 220 and 172 microM, respectively. Also, metabolite formation from mixtures of [14C]BZ (200 microM) and [14C]MA (800 microM) was extremely close to that predicted for a single enzyme capable of metabolizing two alternative substrates in a competitive fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminopropionitrile↗
PubMed1985

Latamoxef: single agent prophylaxis in colorectal surgery.

To assess the suitability of latamoxef (moxalactam) as single agent chemoprophylaxis in elective colorectal surgery, 120 consecutive patients were randomized to receive latamoxef (L) 1 g or cephazolin 1 g and metronidazole 500 mg (CM) administered intravenously at induction of anaesthesia and 6 and 12 h postoperatively. The groups were well matched for age, sex, pathology and procedures. Serum and tissue levels of latamoxef were well above the MIC90 for most bowel organisms. Inpatient stay was similar for both groups. Pyrexia was seen in 44 patients (11 L, 23 CM) and eight developed a wound infection (3 L, 5 CM). Major intra-abdominal sepsis occurred in seven patients (2 L, 5 CM), secondary to anastomotic leakage in four (1 L, 3 CM). Twenty patients developed a chest infection (5 L, 15 CM) and eight urinary sepsis (2 L, 6 CM). No bleeding complication occurred, and there was no difference in clotting function between the two groups. Six patients died prior to follow-up at six weeks (1 L, 5 CM), two from anastomotic dehiscence. All but three wounds had healed (1 L, 2 CM) and one further patient had an incisional hernia (CM). These results suggest that latamoxef is an efficient chemoprophylactic agent in elective colorectal surgery, and is marginally better than cephazolin plus metronidazole.

Adult↗
PubMed1980

Comparison of sensititre dried microtitration trays with a standard agar method for determination of minimum inhibitory concentrations of antimicrobial agents.

A total of 222 clinical isolates were used to test the accuracy of Sensititre dried microtitration trays for determining minimum inhibitory concentrations (MICs) of antimicrobial agents. In comparison with an agar dilution technique, 89.5% of all the pairs of results were within one doubling dilution. The 2,420 pairs of MIC results with finite values gave a corresponding figure of 86.8%. Exclusion of sulfisoxazole results, which demonstrated a significant interlaboratory variation in accuracy, raised this value to 89.1%. Very good differentiation of beta-lactamase-producing strains of Staphylococcus aureus (24 of 24 giving an MIC greater than or equal to 0.25 micrograms/ml) and Haemophilus influenzae (3 of 3 giving an MIC greater than or equal to 32 micrograms/ml) was obtained with the Sensititre system. This method also clearly distinguished erythromycin-resistant S. aureus strains (7 of 7 giving an MIC greater than 32 micrograms/ml) from the susceptible strains (26 of 28 giving an MIC less than or equal to 0.5 microgram/ml plus 1 strain at 1.0 microgram/ml and 1 at 2.0 micrograms/ml). Sensititre offers an accurate and convenient method of determining MICs comparable to those obtained with the agar dilution procedure, with the advantage of an extended shelf life when stored at room temperature.

Aminoglycosides↗