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Biomedical subjects

R Barnett

Publications and source records attributed to R Barnett.

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

Cost containment: the Americas. Canada.

Resources allocated for health care in Canada are about to be decreased. In recent years, the Canadian healthcare system has been consuming a progressively greater share of the country's gross domestic product. Due to recession, less revenue is available for health care. The need to contain and limit national healthcare spending has begun to affect resource allocation in Canadian ICUs. Increasing efficiency and reducing inappropriate use may not be enough to contain costs. More difficult decisions need to be made.

Canada↗
PubMed1991

The number of positively charged amino acids in the basic domain of Tat is critical for trans-activation and complex formation with TAR RNA.

The basic domain of Tat is required for trans-activation of viral gene expression. We have performed scanning peptide studies to demonstrate that only this domain is capable of binding to the TAR RNA stem-loop. Strikingly, the basic domain of the other human immunodeficiency virus trans-acting factor, Rev, but no other region, is also capable of binding to TAR. Peptide derivatives of Tat do not require the highly conserved glutamine residue at position 54 for TAR binding, since it may be substituted or deleted. In addition, the two lysine residues may be replaced by arginines. Analysis of binding and trans-activation demonstrated that homopolymers of arginine can completely substitute for the basic domain. Such homopolymers have high affinity for wild-type TAR RNA and lower affinity for mutant TAR. Homopolymers of six to nine arginines substituting for the basic domain of Tat enable full trans-activation in vivo. Homopolymers of at least seven arginines are required for detectable in vitro complex formation, although approximately 30% trans-activation is achieved with a mutant Tat containing only five arginines.

Amino Acid Sequence↗
PubMed1991

Critical chemical features in trans-acting-responsive RNA are required for interaction with human immunodeficiency virus type 1 Tat protein.

The human immunodeficiency virus type 1 Tat protein binds to an RNA stem-loop structure called TAR which is present at the 5' end of all human immunodeficiency virus type 1 transcripts. This binding is centered on a bulge within the stem of TAR and is an essential step in the trans-activation process which results in a dramatic increase in viral gene expression. By analysis of a series of TAR derivatives produced by transcription or direct chemical synthesis, we determined the structural and chemical requirements for Tat binding. Tat binds well to structures which have a bulge of two to at least five unpaired bases bounded on both sides by a double-stranded RNA stem. This apparent flexibility in bulge size is in contrast to an absolute requirement for an unpaired uridine (U) in the 5'-most position of the bulge (+23). Substitution of the U with either natural bases or chemical analogs demonstrated that the imido group at the N-3 position and, possibly, the carbonyl group at the C-4 position of U are critical for Tat binding. Cytosine (C), which differs from U at only these positions, is not an acceptable substitute. Furthermore, methylation at N-3 abolishes binding. While methylation of U at the C-5 position has little effect on binding, fluorination reduces it, possibly because of its effects on relative tautomer stability at the N-3 and C-4 positions. Thus, we have identified key moieties in the U residue that are of importance for the binding of Tat to TAR RNA. We hypothesize that the invariant U is involved in hydrogen bond interactions with either another part of TAR or the TAR-binding domain in Tat.

Base Composition↗
PubMed1991

Characterization of endothelin 1 receptor and signal transduction mechanisms in rat medullary interstitial cells.

Previous autoradiographic studies have delineated the renal medullas the predominant site of renal endothelin (ET) receptors. Accordingly, cultured rat renal medullary interstitial cells (RMICs) were studied as a target tissue for ET action. Scatchard analysis revealed presence of a single class of high-affinity receptor sites (Kd, 57 +/- 10 pM; receptor density, 749 +/- 124 fmol/mg protein). Relative potency order for displacing 125I-ET-1 was ET-1 greater than ET-2 greater than sarafotoxin greater than big endothelin (human) = big endothelin (porcine). ET-3, unrelated pressor substances, vasodilators, Ca2+ channel antagonists, atrial natriuretic factor, GTP, and GppNHp did not inhibit binding. Challenge of monolayers with ET-1 evoked a biphasic elevation in cytosolic free Ca2+ concentration [Ca2+]i). Initial transient rise in [Ca2+]i observed in absence of extracellular Ca2+ and accumulation of inositol trisphosphate (IP3) was consistent with activation of phosphatidylinositol-specific phospholipase C (PI-PLC). Half-maximal activation concentration of ET-1 for the process was 0.5 and 1 nM for [Ca2+]i and IP3, respectively. The late sustained phase in [Ca2+]i elevation was completely blocked by Ni2+, unperturbed by nimodipine, and accompanied by influx of Mn2+, indicating presence of receptor-operated Ca2+ channels. Ca2+ channel opening was detected at 10(-16) MET-1, whereas greater than 10(-12) M agonist was required to mobilize Ca2+ from intracellular stores and/or stimulate phosphoinositol hydrolysis, indicating that ET activation of PI-PLC and Ca2+ channel opening were independent events. ET-1 markedly stimulated prostaglandin E2 synthesis in a concentration-dependent manner that paralleled PI-PLC activation and mobilization of [Ca2+]i. In summary, cultured rat RMICs possess ET receptors that are linked to PI-PLC, Ca2+ channels, and perhaps phospholipase A2.

Animals↗
PubMed1990

Atrial natriuretic factor alters phospholipid metabolism in mesangial cells.

The mechanism for the vasorelaxant effect of atrial natriuretic factor (ANF) remains to be clarified. Recent evidence suggests that this agent can antagonize the action of angiotensin II (ANG II) by affecting intracellular calcium metabolism. The biochemical basis for this phenomenon was investigated in cultured rat mesangial cells (MCs), a preparation which exhibits the contractile properties of smooth muscle cells and is responsive to ANG II and ANF. Preincubation of MCs with ANF significantly inhibited ANG II-induced release of inositol trisphosphate (IP3) resulting from hydrolysis of phosphatidylinositol 4, 5-bisphosphate. Similarly, ANG II-stimulated increases in cytosolic free Ca2+ [( Ca2+]i), 45Ca efflux, as well as 45Ca influx were diminished by ANF. In addition, these alterations in Ca2+ kinetics were associated with ANF-mediated antagonism of ANG II-induced phospholipid turnover and prostaglandin (PG) E2 release. Sodium nitroprusside (SNP), which augmented guanosine 3',5'-cyclic monophosphate (cGMP) accumulation to a degree comparable to ANF, likewise inhibited ANG II action on the phosphoinositide (PI) pathway, Ca2+ regulation, and PGE2 production. Collectively our results indicate that the effects of ANF on [Ca2+]i in MCs relate to cGMP-induced alterations of PI metabolism. In this fashion cGMP-elevating agents may influence a variety of calcium-dependent biochemical pathways including prostaglandin synthesis.

1-Methyl-3-isobutylxanthine↗
PubMed1988

Hybrid FES orthosis incorporating closed loop control and sensory feedback.

A hybrid functional electrical stimulation (FES) orthosis is described, comprising a rigid ankle-foot brace, a multi-channel FES stimulator with surface electrodes, body mounted sensors, a 'rule-based' controller and an electro-cutaneous display for supplementary sensory feedback. The mechanical brace provides stability, without FES activation of muscles, for standing postures normally adopted by patients. This avoids inducing muscle fatigue during prolonged upright activity. However, stability is conditional upon the position of the ground reaction vector (GRV) relative to the knee joint. The finite state FES controller reacts automatically to destabilizing shifts of the GRV by stimulating appropriate anti-gravity musculature to brace the leg. The FES system also features a control mode to initiate and terminate flexion of the leg during forward progression. A simple mode of supplementary sensory feedback was used during the laboratory standing tests to assist the patient in maintaining a set posture. Preliminary results of laboratory tests for two spinal cord injured subjects are presented.

Adult↗
PubMed1987

Methods for developing relative need criteria to accompany a health care capital expenditure limit.

In recent years capital spending in the health care industry has escalated tremendously, and most forecasters agree that needs will increase at an even faster rate throughout the 1990s. As a result of this trend, there is a dire need to develop effective and equitable controls on capital spending in health care. One of the capital payment options under consideration is the establishment of a lid on capital expenditures and the concomitant allocation of capital to health care providers whose applications are the most meritorious. The purpose of this article is to present some ideas and methods for the development of a relative need system to accompany a capital expenditure limit and to supplement and expand the absolute need determinations of the typical CON process.

Capital Expenditures↗
PubMed1987

Comparison of glomerular and mesangial prostaglandin synthesis and glomerular contraction in two rat models of diabetes mellitus.

Enhanced prostaglandin production is postulated to contribute to altered vascular reactivity and glomerular hyperfiltration in early insulin-deficient diabetes mellitus. Rats with streptozocin-induced diabetes (STZ-D) show glomerular hyperfiltration and develop renal disease. BB rats with genetic diabetes (BB-D) also hyperfilter but have only minor renal lesions. We therefore compared glomerular and mesangial prostaglandin E2 (PGE2) production and glomerular contractility in response to pressors as a reflection of in vitro vascular reactivity in these models. Glomeruli isolated from rats with 3 wk of STZ-D produced significantly more PGE2 under basal and ionophore A23187-stimulated conditions than those from control rats. Glomeruli from BB-D rats under basal and stimulated conditions, however, generated amounts of PGE2 that were comparable to either those of nondiabetic littermates or of normal Wistar rats. Mesangial cells cultured from glomeruli of STZ-D, BB-D, and control rats all had identical prostaglandin profiles judged by conversion of [14 C]arachidonic acid. They also produced comparable amounts of PGE2 under basal conditions and after stimulation with angiotensin II or A23187, as determined by radioimmunoassay. Planar surface area of glomeruli isolated from control rats showed a dose-dependent decrease in response to angiotensin II (10(-11)-10(-9) M). This response to angiotensin II was at least as great in glomeruli from STZ-D rats. Contraction of glomeruli from control and STZ-D rats was also comparable after vasopressin or norepinephrine. Similarly, glomeruli from BB-D and BB control rats contracted in a comparable fashion to angiotensin II and norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1986

Effects of leukotrienes on isolated rat glomeruli and cultured mesangial cells.

Several vasoactive substances influence glomerular function in vivo and alter glomerular surface area and prostaglandin (PG) synthesis in vitro. Leukotrienes (LT) LTC4 and LTD4 may also influence glomerular function in vivo and in the isolated perfused kidney. We therefore compared the effects of LT with those of angiotensin II (ANG II), arginine vasopressin (AVP), and platelet activating factor (PAF) on planar surface area of isolated rat glomeruli and the shape change of cultured mesangial cells and their PG synthesis. ANG II, AVP, and PAF decreased the surface area of isolated rat glomeruli by 10-14% with comparable changes induced by LTC4 and LTD4. Half-maximal effects of LTs were observed at approximately 10(-7) M. Incubation of cultured rat mesangial cells with LTC4 or LTD4 at 10(-7) and 10(-8) M was also associated with shape changes of the cells resulting in significant reductions in planar surface area in a dose- and time-dependent fashion similar to that noted previously with other vasoactive agents. In cells grown on a flexible silicone rubber support, LTD4 resulted in rapid increases in wrinkling of the mobile surface indicating that the shape change may represent cell contraction. The LT-mediated decrease in surface area of glomeruli and mesangial cells was partially antagonized by the LT inhibitor FPL-55712. In contrast to the 11- and 7-fold enhancement of PGE2 synthesis in cultured mesangial cells by ANG II or PAF, neither LTC4 nor LTD4 affected PGE2 production. These results demonstrate that LTC4 and LTD4 cause mesangial shape changes that in the whole glomerulus may decrease glomerular surface area.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Dopamine attenuates the contractile response to angiotensin II in isolated rat glomeruli and cultured mesangial cells.

Recent evidence suggests that dopamine may alter kidney function by actions not only in the renal vasculature but also at the glomerular-mesangial level. We studied this phenomenon by examining the ability of dopamine to antagonize the contractile properties of angiotensin II in isolated rat glomeruli and cultured mesangial cells. In isolated rat glomeruli angiotensin II caused a decrease in the planar surface area, indicating glomerular contraction, an effect that was abolished by coincubation with dopamine. Angiotensin II also mediated shape changes in cultured mesangial cells, which resulted in a decline in their planar areas. Simultaneous addition of dopamine prevented these decreases in cell size. In mesangial cells grown on a flexible silicone rubber support, angiotensin II addition enhanced wrinkling of the mobile surface. This indicated that the angiotensin-II-induced decrease in cell size observed in cells grown on conventional substrata represented contraction. Conversely, dopamine caused a rapid reduction in wrinkling of the surfaces from control cells as well as those previously treated with angiotensin II, actions consistent with cell relaxation. The prostaglandin inhibitor indomethacin did not alter the ability of dopamine to attenuate angiotensin-II-associated reductions in mesangial cell surface area. Direct determination of mesangial cell prostaglandin-E2 production showed that dopamine did not change either basal synthesis or angiotensin-II-stimulated synthesis of prostaglandin. The results demonstrate that dopamine antagonizes the constrictor effect of angiotensin II at the glomerular-mesangial level. This action of dopamine is prostaglandin independent. These findings support a role for dopamine in the regulation of glomerular filtration and may provide a rationale for its use during states of renal vasoconstriction.

Angiotensin II↗
PubMed1981

Development of a sensitive high-performance liquid chromatographic method for detection of aflatoxins in pistachio nuts.

A very sensitive method is described for the detection of aflatoxins in pistachio nuts. The method employs the extraction procedure used in the BF method (described in the Association of Official Analytical Chemists' Book of Methods) followed by an acid alumina column clean-up to remove sample components which would otherwise interfere in the final determinative step. The quantitation of the aflatoxins is carried out by high-performance liquid chromatography on a C18 reversed-phase column after conversion of aflatoxins B1 and G1 to their more fluorescent derivatives, B2a and G2a. The limit of detection was found to be 0.5 microgram/kg. The chromatograms were found to be free of interfering peaks and multiple injections showed excellent reproducibility.

Aflatoxins↗
PubMed1979

Chromium-induced hyperglycemia in the rat.

The acute administration of chromium chloride (Cr) produces hyperglycemia in rats. Adrenalectomy prevents the hyperglycemic effect but not the glucose intolerance. Subacute exposure of rats to Cr for 7--23 days does not change the resting blood glucose nor is there an acute or subacute effect on tolerance to glucose load. Administration of Cr does not influence acute insulin hypoglycemia. Thus contrary to Cr deficient animal, at the concentrations tested, Cr appears to be a hyperglycmiec agent to rats with minimal subacute effects.

Adrenalectomy↗
PubMed1979

A method of producing improved scars following excision of small lesions of the back.

Twelve benign lesions were excised from the back using the accepted elliptical excisions with suturing. At follow-up, all scars had stretched to become much larger than the original lesion. By contrast, 12 lesions of similar size were excised with minimal margin and the resultant defect allowed to heal by contraction and epithelialization. This method was quicker and less painful, and produced significantly smaller scars than the conventional method.

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