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Biomedical subjects

J G Hamilton

Publications and source records attributed to J G Hamilton.

At least 19 recordsLinked to original sources
PubMed1995

Purification and characterization of an acyclic monoterpene primary alcohol:NADP+ oxidoreductase from catmint (Nepeta racemosa).

A soluble monoterpene primary alcohol:NADP+ oxidoreductase has been purified to apparent homogeneity from leaves of the catmint, Nepeta racemosa. The purified enzyme consisted of two polypeptides, with molecular masses of 42,000 and 40,000 Da, and contained zinc ions. A number of monoterpene alcohols (geraniol, nerol, citronellol, and their hydroxylated derivatives) were substrates, but the enzyme was inactive toward ethanol. The enzyme required NADP(H) as cofactor, with NAD(H) ineffective. Gas chromatographic and coupled mass spectrometric analysis of the reaction products showed that 10-hydroxygeraniol and 10-hydroxynerol were oxidized by the enzyme in the presence of NADP+, at both C-1 and C-10. These results are consistent with a role for this enzyme in the biosynthesis of iridoid monoterpenes.

Alcohol Oxidoreductases↗
PubMed1995

The effect of female body size on male mounting behaviour in Dermacentor variabilis and D. andersoni.

This study was undertaken to determine if body size of female ticks was an important factor in eliciting the mating behaviour of Dermacentor variabilis and D. andersoni males. Dummy female ticks (DFTs) representing varying sizes of feeding females were prepared from plastic beads. Size of DFT was shown to be important in determining both the time spent by males in contact with DFTs and the extent of male mating response released. Dermacentor variabilis males preferred the smaller-sized DFT, whereas D.andersoni males preferred the larger sizes. Males of both species were able to discriminate between size of DFT only when mounting sex pheromone (MSP) was present. Size of the DFT was more important than the composition of the MSP extract in determining the time males spent in contact with DFTs. Males of both species were sensitive to variations in concentration of extract, and spent 2-6 times longer in contact with DFTs when the concentration was optimal than when it was not. No significant difference in the male's mating response was seen in response to variation in concentration of heterospecific extract. Male mating response, i.e. the behaviour of the male as it progresses through the initial contact, climbing onto the dorsal surface and turning onto the venter, was shown not to be dependent upon how long the male spent in contact with the DFT. Male D. andersoni had a much lower mating response to DFTs than D. variabilis males, suggesting that some further stimulus may be required.

Animals↗
PubMed1995

Needle phobia: a neglected diagnosis.

Needle phobia is a recently defined medical condition that affects at least 10% of the population. Because persons with needle phobia typically avoid medical care, this condition is a significant impediment in the health care system. The etiology of needle phobia lies in an inherited vasovagal reflex of shock, triggered by needle puncture. Those who inherit this reflex often learn to fear needles through successive needle exposure. Needle phobia is therefore both inherited and learned. In a family practice, needle phobia can be managed by reassurance and education, avoidance of needles, postural and muscle tension techniques, benzodiazepines, nitrous oxide gas, and topical anesthesia applied by iontophoresis.

Family Practice↗
PubMed1994

Evidence for a mounting sex pheromone in the brown ear tick Rhipicephalus appendiculatus, Neuman 1901 (Acari: Ixodidae).

The presence of a mounting sex pheromone was demonstrated on the surface of fed female Rhipicephalus appeniculatus. This pheromone, which is present on the female cuticle, allows the male to recognise the female. The pheromone was removed by cleaning the female in hexane, resulting in the loss of male mating behaviour in in vitro experiments. Male mating behaviour was resumed when extract made from fed female cuticle was replaced on cleaned females. When the extract was transferred to inanimate objects typical male mating behaviour was released. Preliminary chemical analyses indicated that the active component of the extract was contained in the sterol ester fraction of the extract.

Animals↗
PubMed1994

Chemical analysis of a putative sex pheromone from Lutzomyia pessoai (Diptera: Psychodidae).

Lutzomyia pessoai has been named as a probable vector of Leishmania braziliensis in southern Brazil. Males of this species have recently been shown to have pheromone-disseminating structures on their abdomen. Chemical analysis of extracts from the glands associated with these structures has revealed the presence of a possible sex pheromone. Although this compound has been partially characterized as a monocyclic diterpene with the same molecular weight as the Lu. longipalpis diterpene sex pheromone, mass spectral evidence indicates that it is different compound. This, the first evidence for a possible sex pheromone in any phlebotomine species other than Lu. longipalpis, indicates that such semiochemicals may be widely distributed in this group.

Animals↗
PubMed1994

Attraction of Lutzomyia longipalpis to human skin odours.

Male and female Lutzomyia longipalpis sandfiles showed attraction to human skin emanations placed on warmed glass Petri dishes. Unfed virgin females were more strongly attracted than males, which also showed attraction. Four human subjects were tested and significant variation was found between the numbers of sandflies attracted to their skin emanations. This suggests that some individuals were more attractive than others. There was a significant difference between the response shown by sandflies from the Jacobina and Lapinha regions of Brazil, suggesting that sandflies from the Jacobina region were more anthropophilic. In addition, sandflies from Jacobina had a significantly higher level of activity than those from Lapinha. The role of sandfly attraction to humans as a risk factor in Leishmania transmission is considered.

Animals↗
PubMed1994

Isolation of oviposition pheromone from the eggs of the sandfly Lutzomyia longipalpis.

Semiochemical components of eggs of the sandfly Lutzomyia longipalpis (Diptera: Psychodidae) were separated by high performance liquid chromatography. HPLC fractions were examined quantitatively and qualitatively by gas chromatography (GC). A bioassay was used to determine the oviposition attraction of gravid L. longipalpis to each of the fractions separately and a peak responsible for the semiochemical activity was identified. Gravid flies were placed in individual oviposition tubes to determine if the peak of interest was an oviposition stimulant. The active semiochemical fraction attracted gravid flies for oviposition. Furthermore, egg laying was enhanced: gravid flies exposed to the pheromone oviposited earlier and laid more eggs than control flies. GC analysis indicated that 1200 eggs (2 days old) gave a yield of 12.75 micrograms of active pheromone. This fraction had similar HPLC and GC retention times to caryophyllene oxide, suggesting comparable polarity and molecular weight.

Animals↗
PubMed1991

Gas-chromatographic analysis of Lutzomyia longipalpis tergal pheromone gland extract.

Lutzomyia longipalpis is the vector of visceral leishmaniasis (VL) in South America. Previous gas-chromatographic (GC) analyses of tergal gland extracts of Lu. longipalpis have demonstrated two distinct pheromone types. These have been classified as a farnesene/homofarnesene type compound and a diterpene type compound. GC analysis of tergal gland extracts of Lu. longipalpis from other areas of South America demonstrates that there may be other different pheromone producing forms of this sandfly. Gland extracts are more complex than has previously been indicated, and they have been shown to differ in the chemicals present and in the ratio of these compounds to each other.

Animals↗
PubMed1988

Rapid separation of neutral lipids, free fatty acids and polar lipids using prepacked silica Sep-Pak columns.

A method is described for the separation of neutral lipid, free fatty acid and polar lipid classes using small (600 mg), prepacked silica Sep-Pak columns. Combinations of hexane and methyltertiarybutylether were used to progressively elute cholesteryl ester first then triglyceride from the column. After column acidification, fatty acids were eluted followed by cholesterol. Recoveries of these lipids were 96% or greater. Polar lipids were eluted from the column using combinations of methyltertiarybutylether, methanol and ammonium acetate. Phospholipid classes could not be separated completely from each other. Phosphatidylethanolamine and phosphatidylinositol eluted together, whereas the more polar phosphatidylcholine, sphingomyelin and lysophosphatidylcholine were eluted as a second fraction. Recoveries of each phospholipid was greater than 98%.

Chromatography↗
PubMed1988

Separation of neutral lipid, free fatty acid and phospholipid classes by normal phase HPLC.

Normal phase high performance liquid chromatography methods are described for the separation of neutral lipid, fatty acid and five phospholipid classes using spectrophotometric detection at 206 nm. Separations were accomplished in less than 10 min for each lipid class. A mobile phase consisting of hexane/methyltertiarybutylether/acetic acid (100:5:0.02) proved effective in separating cholesteryl ester and triglyceride with recoveries of 100% for radiolabeled cholesteryl oleate and 98% for radiolabeled triolein. Free fatty acid and cholesterol were separated by two different mobile phases. The first, hexane/methyltertiarybutylether/acetic acid (70:30:0.02) effectively separated free fatty acids and cholesterol, but did not separate cholesterol from 1,2-diglyceride. A mobile phase consisting of hexane/isopropanol/acetic acid (100:2:0.02) effectively separated free fatty acid, cholesterol, 1,2-diglyceride and 1,3-diglyceride. Recoveries of oleic acid and cholesterol were 100% and 97%, respectively. Five phospholipid classes were separated using methyltertiarybutylether/methanol/aqueous ammonium acetate (pH 8.6) (5:8:2) as the mobile phase. The recoveries of phosphatidylinositol, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin and lysophosphatidylcholine were each greater than 96%.

Animals↗
PubMed1984

Separation of neutral lipids and free fatty acids by high-performance liquid chromatography using low wavelength ultraviolet detection.

Normal phase, isocratic high-performance liquid chromatography methods are described for the separation of neutral lipid and fatty acid classes using low wavelength detection. Prior to high-performance liquid chromatography, methods were developed and are described for the separation of phospholipids from neutral lipids and fatty acids using small (600 mg) silica Sep-PaksTM. Recoveries of cholesteryl esters, triglycerides, fatty acids, and phospholipids from the silica columns were greater than 95%. Two mobile phases are described for lipid class separation by high-performance liquid chromatography. The first mobile phase, hexane-2-propanol-acetic acid 100:0.5:01, resulted in incomplete separation of cholesteryl ester and triglyceride but excellent separations of fatty acids and cholesterol. The second mobile phase, hexane-n-butyl chloride-acetonitrile-acetic acid 90:10:1.5:0.01, resulted in complete separation of the four lipid classes. This mobile phase also separated individual triglycerides and fatty acids based on the number of double bonds. Recoveries of radiolabeled lipids for the four lipid classes from high-performance liquid chromatography was greater than 95% with both mobile phases.

Animals↗