Search PubMed⌕ Search

Biomedical subjects

B Alexander

Publications and source records attributed to B Alexander.

At least 91 records · Page 5Linked to original sources
PubMed1994

Intrahepatic portal occlusion by microspheres: a new model of portal hypertension in the rat.

Available experimental models of portal hypertension are based either on cirrhosis or externally applied portal vein constricting devices. A new method is described of raising portal pressure, which uses intraportally injected microspheres to block intrahepatic portal radicles, which has the advantages of retaining normal liver architecture and providing a more clinically relevant intrahepatic obstruction to portal flow. Measured aliquots of microspheres (15, 25, 50, 90 microns) or equivalent volumes of saline were injected into a peripheral portal tributary (caecal vein) of 22 normal rats. The resultant changes in arterial, portal, and splenic pulp pressures were monitored. Sequential microsphere injections produced graduated rises in portal pressure up to a peak of 18.5-22.5 mm Hg (8.7-12.4 mm Hg increase from basal), which declined gradually to a steady state pressure of 13.3-15.1 mm Hg (4.0-5.0 mm Hg increase). There was no significant difference between pressure increases produced by microspheres of differing sizes. It is concluded that portal hypertension can be produced acutely by blocking portal radicles with microspheres. The maximum pressure achieved, however, is substantially less than that obtained by total portal vein occlusion (mean: 57.6 mm Hg). This suggests the existence of functional intrahepatic portal systemic shunts not previously described in the normal liver.

Animals↗
PubMed1994

The Seattle children's bicycle helmet campaign: changes in helmet use and head injury admissions.

OBJECTIVE: To describe the impact of a community bicycle helmet campaign on helmet use and the incidence of bicycle-related head injuries. SETTING: Metropolitan community and a large health maintenance organization. INTERVENTIONS: Communitywide bicycle helmet campaign. OUTCOMES: Rate of observed bicycle helmet use in the community and incidence of bicycle-related injuries in an health maintenance organization population. RESULTS: Helmet use among school-aged children increased from 5.5% in 1987 to 40.2% in 1992. Bicycle-related head injuries decreased by 66.6% in 5- to 9-year-old and 67.6% in 10- to 14-year-old members of an health maintenance organization. CONCLUSIONS: Educational campaigns can increase helmet use and decrease the incidence of bicycle-related head injury.

Adolescent↗
PubMed1993

Effect of changes in rate of vascular perfusion on release of substances into the effluent from the brain of the rabbit.

The cerebral vasculature of five anaesthetised rabbits was perfused with a perfluorocarbon emulsion via the internal carotid arteries, and the effluent from the jugular veins analysed for ATP, substance P (SP), endothelin (ET) and arginine vasopressin (AVP). Viability of the preparation was monitored periodically by the electrocorticogram, oxygen uptake, carbon dioxide release and perfusion pressure. The basal rate of infusion of 7.8 +/- 1.26 ml.min-1 resulted in an infusion pressure of 114.0 +/- 22.1 mmHg and when increased first to 10.5 +/- 1.53 ml.min-1 and then to 15.0 +/- 1.87 ml.min-1, rose to 163.0 +/- 33.1 mmHg and to 170.0 +/- 33.2 mmHg, respectively. Between each 3-min period of increased flow the rate was returned to the basal rate for 6 min. Of the four vasoactive substances, ET was released at the largest rate during the initial period of basal flow, 65.3 +/- 10.7 pmol.min-1. This increased further when the infusion rate rose to 10.5 ml.min-1, but was significant only when the infusion rate was increased to 15.0 ml.min-1. ATP was released at 41.5 +/- 11.5 pmol.min-1 during the initial period of basal flow. Its release significantly increased with flow and peaked at 15.0 ml.min-1. SP was released at a rate of 13.3 +/- 8.2 pmol.min-1 during the initial period of basal flow. Its rate of release was increased significantly the second time the flow was increased to 10.5 ml.min-1 and increased even further when the flow was increased to 15.0 ml.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1993

Electron-immunocytochemistry of peptides in endothelial cells of rabbit cerebral vessels following perfusion with a perfluorocarbon emulsion.

This study describes the localization of endothelin-1-, vasopressin- and substance P-like immunoreactivity in a subpopulation of endothelial cells of the basilar and posterior communicating arteries of the (i) normal rabbit brains and (ii) rabbit brains perfused with a perfluorocarbon emulsion (PFC). Following perfusion with the PFC at increased flow the endothelial cell ultrastructure appeared normal, although there was a decrease of immunoreactivity to these peptides. This suggests that these peptides may be involved in endothelial control of blood flow in cerebral vessels.

Animals↗
PubMed1993

Diminished hyperaemic response of the hepatic artery to portal venous occlusion (the buffer response) in Asian hybrid minipigs: a comparison of the response to that observed in dogs.

The hyperaemic response of the hepatic artery to portal vein occlusion (the buffer response) and the action of exogenous adenosine upon hepatic artery blood flow was studied in Asian hybrid minipigs as a potential alternative experimental model to that previously developed in dogs. Adenosine produced a dose-dependent hepatic artery vasodilatation, but of lesser extent than that observed in dogs. A greatly diminished buffer response was observed in the pigs compared to that seen in dogs, and could not be replicated consistently. The adenosine uptake inhibitor dipyridamole did not potentiate responses to adenosine or the buffer response. It is concluded that the minipig is an unsuitable alternative model for the study of the hepatic artery buffer response.

Adenosine↗
PubMed1993

Performance-based management in local health departments: measuring the success of implementation.

Six of eight local health departments in North Carolina's Southwest Perinatal Region III participated in a PBMS demonstration project also involving the state health department, the Centers for Disease Control, and the School of Public Health of the University of North Carolina at Chapel Hill. In all six counties the problem of reducing prematurity and low birthweight was selected to test this innovation. Using standardized instruments, staff awareness of and concern for low birthweight problems and programs were measured, as was level of success of implementation of PBMS. Factor analysis of three rounds of Awareness and Concern responses produced three uncorrelated factors: awareness of low birthweight problems, awareness of low birthweight programs, and concern for low birthweight. The results suggest that the PBMS increased awareness of the problem and the program, and that the project succeeded in half of the counties, helped some counties achieve some goals, and provided some benefits to some counties. The implications for Total Quality Management are discussed.

Awareness↗
PubMed1993

Disorders of sexual desire: diagnosis and treatment of decreased libido.

Decreased libido is the most common concern expressed by patients when they discuss sexual issues with their physicians. The causes of decreased libido are complex and multifactorial, requiring attention and a careful history to isolate the primary origin. Although dissatisfaction with the relationship or marriage is the most common factor in patients with depressed desire, organic causes must also be considered. Physicians must remember that depressed libido is relative and depends on the patient's definition, not on an absolute standard of how frequently people do or should have sexual relations.

Female↗
PubMed1993

Population-based study of fall injuries in children and adolescents resulting in hospitalization or death.

OBJECTIVE: To determine the incidence and characteristics of fall-related injuries to children and adolescents. DESIGN: Population-based study. SETTING: All hospital discharges in Washington State for fall-related injuries in 1989 and 1990. POPULATION: Children and adolescents 19 years and younger. RESULTS: Falls accounted for nearly one third of all trauma admissions, and fall patients tended to be younger than those with other injuries. Falls from one level to another accounted for 40% of the total. One fourth of all patients and 42% of preschoolers sustained head injury. The annual cost of these injuries in Washington State was $4.5 million.

Accidental Falls↗
PubMed1992

Tumor-associated karyotypic lesions coselected with in vitro macrophage differentiation.

Several cytogenetic lesions in chromosomes 2, 5, 12, and 16 have been repeatedly coselected with in vitro macrophage differentiation in a clonal murine thymic tumor cell line. Parental-type subclones, which show an extremely immature hemopoietic phenotype, do not carry the aberrations. The frequency of the stable differentiated variants is elevated by 5-azacytidine and bromodeoxyuridine, consistent with chromosome breakage being responsible for the phenotype. The frequency is also raised by dexamethasone. Since variants are 300-3,000-fold more resistant to dexamethasone than parental clones, we interpret this to be largely due to selection. Three of the lesions, on chromosome 2, match those previously described as associated specifically with in vivo-generated murine myeloid tumors, induced by X irradiation and corticosteroid treatment. Several implications follow from these observations. (1) In vitro differentiation in clonal tumor cell lines can be used to select for tumor-associated lesions. This should allow genetic and molecular analysis of the chromosome 2 lesions and of others that may pinpoint genes critical to macrophage differentiation and transformation. (2) Myeloid and lymphoid tumors that occur in response to X irradiation may diverge from a common initiating tumor. (3) The hemopoietic lineage switch phenomenon, previously described by several authors, may be caused by similar or identical chromosome aberrations.

Abelson murine leukemia virus↗
PubMed1992

An isolated dual-perfused rabbit liver preparation for the study of hepatic blood flow regulation.

An original, isolated dual-perfused rabbit liver preparation was developed for investigations into mechanisms that control the hepatic vascular tone. The hepatic artery (HA) and portal vein (PV) were perfused at constant flows of 0.16 +/- 0.01 and 0.64 +/- 0.05 mL/g/min (n = 5), respectively. Responses of the hepatic arterial and portal venous vascular beds to noradrenaline (NA) were measured as changes in perfusion pressure. Noradrenaline injected directly into the hepatic artery and portal vein produced dose-dependent increases in pressure in the respective vascular beds, the maximum response in the hepatic arterial bed being two to three times greater than that in the portal venous bed. A restricted transmission of vasoconstrictor stimulus between the intrahepatic portal venous and hepatic arterial vasculature was demonstrated. The results demonstrate the suitability of the dual-perfused rabbit liver model for detailed studies of the control of hepatic vascular tone.

Animals↗
PubMed1992

An investigation of the composite resin/porcelain interface.

Failures at composite resin/porcelain interfaces under shear-like loading were examined. Porcelain surfaces were treated with hydrofluoric acid and/or one of two silane coupling agents, using two different composite resin cements. The results showed that after seven days storage, bond strengths of specimens which had undergone porcelain surface treatment were greater than the cohesive strength of the porcelain itself, resulting in brittle fracture of the porcelain. The diluted restorative composite resin performed as well as the commercial composite resin cement. Silane pretreatment of porcelain was important as the bond strength of etched/silane primed specimens was significantly higher than the etched only specimens. However, one primer appeared to be more efficient than the other in bond promotion. Some explanations for the differences in bond strengths are offered.

Acid Etching, Dental↗
PubMed1991

Central nervous system action of endothelin-3 to inhibit water drinking in the rat.

Endothelin-3, a vasoconstrictor peptide produced not only in endothelial cells but also within the brain interstitium in magnocellular neurons of the hypothalamo-neurohypophysial system, exerted significant, dose-related, inhibitory effects on water intake when administered into the third cerebroventricle of rats exposed to exogenous and endogenous stimuli for drinking. Passive immunoneutralization of endogenous endothelin-3 accentuated water drinking in response to angiotensin II administration suggesting a physiological role for the peptide in the central control of fluid and electrolyte homeostasis.

Angiotensin II↗
PubMed1991

Isolation and identification of Bacillus sphaericus strains pathogenic for mosquito larvae.

Three selective media for the isolation of Bacillus sphaericus have been compared. BATS medium and a formulation employing adenosine as the principal carbon source were the most effective for the recovery of spores of strain 1593. Anthranilic acid as the principal carbon source was less efficient. Eighty-four strains were isolated from mud samples using these media and were identified by computer. Identifications were confirmed for representative strains using DNA sequence homology. Most were B. sphaericus sensu stricto or members of an unnamed group. However, one strain (BSE 18) was identified as the DNA homology group IIB and this organism was found to be highly toxic toward larvae of Culex pipiens. Southern hybridization of BSE 18 DNA to a probe prepared from the cloned toxin gene from strain 1593 revealed that BSE 18 contained a typical gene for the 41.9-kDa toxin.

Animals↗
PubMed1991

Detoxification from benzodiazepines: schedules and strategies.

Management of benzodiazepine (BZD) tolerance is divided into low- and high-dose withdrawal. Low-dose withdrawal includes patients who have received manufacturer-recommended doses of BZD on a daily basis for longer than 1 month. Gradual tapering of the BZD over 4 weeks on an outpatient basis is suggested. High-dose withdrawal includes patients who have been ingesting doses of BZD greater than the equivalent of diazepam 40 mg/d for longer than 8 months. It is recommended that the patients be tolerance tested with diazepam and, if tolerant, tapered off medication as inpatients at a rate of 10% per day. Triazolobenzodiazepines may be exceptions to these recommendations. Alprazolam should be titrated at a rate of 0.5 mg three times a day regardless of whether the patient is being tapered for low- or high-dose withdrawal.

Anti-Anxiety Agents↗
PubMed1991

Nitric oxide is the mediator of ATP-induced dilatation of the rabbit hepatic arterial vascular bed.

1. Livers of 10 New Zealand White rabbits were perfused in vitro with Krebs-Bülbring buffer via the hepatic artery (HA) and portal vein (PV) at constant flows of 23 +/- 1 and 77 +/- 1 ml min-1 100 g-1 respectively. The tone of the preparation was raised with noradrenaline (concentration: 10 microM). 2. Dose-response curves for the vasodilatation produced by adenosine 5'-triphosphate (ATP), acetylcholine (ACh), adenosine, and sodium nitroprusside (SNP) were obtained following injection into the HA supply. Injections were then repeated in the presence of the L-arginine to nitric oxide pathway inhibitors N-monomethyl-L-arginine (L-NMMA, n = 6) and N-nitro-L-arginine methyl ester (L-NAME, n = 4) at concentrations of 30 microM and 100 microM for each inhibitor. 3. Both L-NMMA and L-NAME antagonized the responses to ATP and ACh; L-NAME was 2-3 times more potent than L-NMMA as an inhibitor of these endothelium-dependent vasodilatations. Neither L-NMMA nor L-NAME attenuated responses of the endothelium-independent vasodilators, adenosine and SNP. 4. These results indicate that nitric oxide is the mediator of ATP-induced vasodilatation in the HA vascular bed of the rabbit and that the receptor responsible for the release of nitric oxide, the P2y-purinoceptor, is located predominantly on the endothelium.

Acetylcholine↗
PubMed1991

Adenosine-induced dilatation of the rabbit hepatic arterial bed is mediated by A2-purinoceptors.

1. This study was carried out in order to identify the receptor responsible for adenosine-induced dilatation of the hepatic arterial vascular bed. 2. Livers of 10 New Zealand White rabbits were perfused in vitro with Krebs-Bülbring buffer via the hepatic artery and the portal vein at constant flows of 26 and 77 ml min-1 100 g-1 liver respectively. The tone of the preparation was raised by the presence of noradrenaline in the perfusate (concentration: 10(-5) M). 3. Dose-response curves for adenosine and its analogues 5'-N-ethyl-carboxamido-adenosine (NECA), the 2-substituted NECA analogue CGS 21680C, and R- and S-N6-phenyl-isopropyl-adenosine (R- and S-PIA) were obtained after their injection into the hepatic arterial supply. 4. The order of vasodilator potency of these agents was: NECA greater than CGS 21680C greater than adenosine greater than R-PIA greater than S-PIA. Their potency, expressed relative to that of adenosine, was in the approximate ratio 10:3:1:0.3:0.1, consistent with that resulting from activation of P1-purinoceptors of the A2 sub-type (which mediate vasodilatation due to adenosine). 5. The P1-purinoceptor antagonist 8-phenyltheophylline (10(-5) M) caused significant attenuation of the vasodilatation to adenosine and analogues. 6. It is concluded that adenosine-induced dilatation of the hepatic arterial vascular bed is mediated by P1-purinoceptors of the A2 sub-type.

Acetylcholine↗