Biomedical subjects

M H Howard

Publications and source records attributed to M H Howard.

4 recordsLinked to original sources

PubMed2001

Air insufflation: a useful adjunct to the single contrast barium enema for the evaluation of the rectum.

We examined whether insufflation of a small volume of air after a single-contrast barium enema would improve evaluation of the rectum. Eighty patients presenting for barium enema by single-contrast technique underwent examination of the colon including spot films with fluoroscopy and palpation during introduction of the barium and filled overhead views, using standard apparatus and technique. The examination was completed by draining barium from the rectum only, following which air in the barium enema bag was squeezed back into the rectum and three views of the rectum obtained (lateral, left posterior oblique, and frontal). Two reviewers then chose the best image of the rectum from each study with relevance to luminal distention and visibility of surface detail of the rectum. Following air insufflation, improved surface detail visualization was recognized by both reviewers in 69 (86%) patients and by one reviewer in 10 (12%) patients, a statistically significant observation (P < 0.0001). There was a trend towards improved rectal distention, recognized by both reviewers in 37 (46%) patients and by one reviewer in 18 cases (22%). In 25 (31%) patients neither reviewer recognized any improvement in rectal distention. Rectal abnormalities were identified in nine cases; there were two large carcinomas, two radiation strictures, two rectal fistulae, two small rectal polyps (5 and 7 mm), and one case of prolapsing rectal mucosa. All rectal abnormalities were visible on the air insufflation views. In the two cases of suspected rectal polyp and one of the cases of rectal fistula, the findings were not visible on the initial barium filled views. A normal rectum was observed in 71 cases. Follow-up of these 71 patients found no later evidence of any rectal abnormalities. Improved filling of the proximal colon following air insufflation was observed in 12 (15%) patients, an additional and unexpected benefit of this maneuver. Air insufflation is a simple addition to the SCBE study that improves visualization of the rectum.

Adult↗

PubMed2001

An electronic device for needle placement during sonographically guided percutaneous intervention.

An electronic device for guiding needle placement during sonographically directed percutaneous intervention was tested in a phantom and then in patients. In the phantom, targeting accuracy was similar for use of the needle guide alone, the needle guide with the device, and freehand techniques with the device, but all were superior to the freehand technique alone (P <.001). In 34 (79%) of 43 patients, the device worked well.

Adult↗

PubMed1997

Effects of [3H]-BIDN, a novel bicyclic dinitrile radioligand for GABA-gated chloride channels of insects and vertebrates.

1. The radiolabelled bicyclic dinitrile, [3H]-3,3-bis-trifluoromethyl-bicyclo[2.2.1]heptane-2,2-dicarbonitrile ([3H]-BIDN), exhibited, specific binding of high affinity to membranes of the southern corn rootworm (Diabrotica undecimpunctata howardi) and other insects. A variety of gamma-aminobutyric acid (GABA) receptor convulsants, including the insecticides heptachlor (IC50, 35 +/- 3 nM) and dieldrin (IC50, 93 +/- 7 nM), displaced [3H]-BIDN from rootworm membranes. When tested at 100 microM, 1-(4-ethynylphenyl)-4-n-propyl-2,6,7-trioxabicyclo[2.2.2]oct ane(EBOB), 4-t-butyl-2,6,7-trioxa-1-phosphabicy-clo[2.2.2]octane-1-thio ne (TBPS), 1-phenyl-4-t-butyl-2,6,7-trioxabicyclo[2.2.2]octane (TBOB) and picrotoxin failed to displace 50% of [3H]-BIDN binding to rootworm membranes indicating that the bicyclic dinitrile radioligand probes a site distinct from those identified by other convulsant radioligands. 2. Dissociation studies showed that dieldrin, ketoendrin, toxaphene, heptachlor epoxide and alpha and beta endosulphan displace bound [3H]-BIDN from rootworm membranes by a competitive mechanism. 3. Rat brain membranes were also shown to possess a population of saturable, specific [3H]-BIDN binding sites, though of lower affinity than in rootworm and with a different pharmacological profile. Of the insecticidal GABAergic convulsants that displaced [3H]-BIDN from rootworm, cockroach (Periplaneta americana) and rat brain membranes, many were more effective in rootworm. 4. Functional GABA-gated chloride channels of rootworm nervous system and of cockroach nerve and muscle were blocked by BIDN, whereas cockroach neuronal GABA(B) receptors were unaffected. 5. Expression in Xenopus oocytes of either rat brain mRNA, or cDNA-derived RNA encoding a GABA receptor subunit (Rdl) that is expressed widely in the nervous system of Drosophila melanogaster resulted in functional, homo-oligomeric GABA receptors that were blocked by BIDN. Thus, BIDN probes a novel site on GABA-gated Cl- channels to which a number of insecticidally-active molecules bind.

Animals↗

PubMedDate not supplied

Polycyclic dinitriles: a novel class of potent GABAergic insecticides provides a new radioligand, [3H]BIDN.

The polycyclic dinitriles are a potent class of insecticides which are non-competitive GABA (gamma-aminobutyric acid) antagonists acting at the convulsant site. Comparison with other classes of GABA convulsant site ligands using molecular modelling has shown significant structural similarities. We have developed a pharmacophore model which unifies this class and some previous classes of GABA convulsants. Key pharmacophore elements are a polarizable functionality separated by a fixed distance from two H-bond accepting elements. This model is based on information from X-ray crystal structures and Sybyl using the Tripos force field. Using this pharmacophore model, numerous structural modifications were explored to enhance understanding of structure-activity relationships at the GABA receptor convulsant site of insects and mammals. A radiolabelled bicyclic dinitrile, [3H]BIDN [3H]3,3-bis-trifluoromethyl-bicyclo[2,2,1]heptane-2,2-dicarbonitrile+ ++), was prepared from this area of chemistry and was used as a probe for the interaction of polycyclic dinitriles at the target site.

Animals↗