Biomedical subjects
Publications and source records attributed to R C Webb.
Reactive hyperemia was induced in hindlimbs of rats by occlusion of the femoral artery. Using fluorescein dye as a peripheral vascular marker, we observed that there was an increase in the number of flowing capillaries supplying the muscle fibres following release of the occlusion. The results indicate that the number of flowing capillaries is not dependent on the duration of occlusion (2-10 min).
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We present evidence in accord with the observations of S. Kalsner (Br. J. Pharmacol. 36: 582-593, 1969) that in the rabbit aorta, desoxycorticosterone (DOC) potentiates the contractile response to certain catecholamines by inhibiting their degradation by catechol-O-methyltransferase. In contrast, DOC depresses the contractile responses in rat aorta and tail arteries. To elucidate the mechanism of this depression the effect of DOC was evaluated under various conditions. DOC depressed the contractile response to epinephrine, phenylephrine, KCl, and angiotensin II. The depression was unaltered by ouabain or by a potassium-free solution, indicating that DOC did not produce its depression by altering Na-K-ATPase activity. The depression is unaltered in a chloride-free solution, demonstrating that the DOC effect is not caused by a change in membrane permeability to chloride. Radioisotope studies demonstrate that DOC does not alter membrane permeability to potassium. Removal of extracellular calcium with EGTA (ethylene glycol-bis (beta-aminoethyl ether) N, N'-tetraacetic acid) significantly reduced the magnitude of the DOC depression. Indirect evidence is presented suggesting that DOC might increase calcium binding to the plasma membrane, resulting in its stabilization and hence in a depression of the contractile response.
Helical strips of tail artery from spontaneously hypertensive (SHR) and Kyoto Wistar normotensive rats (WKY) were observed to relax in response to potassium after contraction induced by norepinephrine in potassium-free solution. Helical strips from SHR consistently showed greater relaxation in response to the addition of potassium than did those from WKY. The amplitude of potassium-induced relaxation is believed to be an index of the activity of electrogenic sodium-potassium transport and hence of sodium-potassium ATPase. Thus, the sodium-potassium ATPase activity of SHR vascular smooth muscle is increased as compared to WKY. This interpretation is supported by the observation that ouabain eliminated potassium-induced relaxation in both SHR and WKY strips. Potassium-induced relaxation in SHR was more sensitive to ouabain inhibition than in WKY. Relaxation induced by potassium in SHR and WKY strips was also shown to vary with: (1) the length of incubation in potassium-free solution, and (2) the concentration of potassium added back. The results of these experiments on potassium-induced relaxation serve as evidence that SHR have either an increased intrinsic sodium-potassium ATPase activity, or an enzyme activity that has been stimulated to a greater degree by an elevated intracellular sodium concentration which resulted from the incubation in potassium-free solution.
A brief history of the Australian Pharmaceutical Benefits Scheme is given. Available statistics in recent years have been analyzed indicating the more frequently prescribed drugs both individually and in the major pharmacological groups. Part 1, which covers antibiotics and analgesics was published in AFP, February, 1979.
A brief history of the Australian Pharmaceutical Benefits Scheme is given. Available statistics in recent years have been analyzed indicating the more frequently prescribed drugs both individually and in the major pharmacological groups.
Effects of sensorimotor training on intelligence and adaptive skills of profoundly retarded young adult residents of a state institution were investigated during a 6-month intensive training program. Comparison of pre- and posttraining test scores showed that the training group made significant gains in awareness (p less than .01) and gross-motor skills (p less than .001) as well as in intellectual (p less than .02) and adaptive skills (p less than .01). No significant gains in fine-motor and imitation skills were found nor were significant changes observed in the attention (control) group. Results were interpreted in terms of sensorimotor-training integration patterns, and they substantiated previous findings that gross-motor functioning and adaptive skills improve with sensorimotor training done in the living unit.
In this study we observed relaxation in helical strips of rat tail artery in response to high concentrations of calcium after contraction induced by 10(-7) g/ml norepinephrine. This action of calcium on vascular smooth muscle contraction is referred to as the "membrane-stabilizing effect" of calcium. The current study demonstrates that changes caused by many of the variables that alter this relaxation induced by calcium parallel changes in relaxation in response to potassium; both are attenuated by ouabain, low sodium, reduced temperature, and low potassium. Relaxation produced by manganese is not similarly affected. Because potassium has been shown to cause relaxation of vascular smooth muscle by increasing the activity of sodium-potassium ATPase, we conclude that the relaxation produced by high concentrations of calcium is dependent on the activity of sodium-potassium ATPase; that produced by manganese is not.
The role of adenosine 3',5'-monophosphate (cyclic AMP)-dependent membrane phosphorylation in the regulation of microsomal calcium transport in rat aortic smooth muscle was studied. Cyclic AMP-dependent protein kinase augmented the phosphorylation of serine residues in a microsomal protein component with a molecular weight of about 44,000 (determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and the majority of 32P incorporation was in serine residue(s). The phosphorylated protein had stability characteristics of a phosphoester. The phosphorylated substrate was not extracted from the trichloroacetic acid (TCA) precipitate with organic solvents or by suspension in hot TCA; and the demonstrated hydroxylamine insensitivity suggested that the substrate was not lipid or nucleic acid. Intrinsic phosphoprotein phosphatase cleaved the labeled phosphate from the cyclic AMP-stimulated microsomes in the first 5 min of incubation. Microsomes phosphorylated in the presence of 1 micron cyclic AMP or 1 micron cyclic AMP plus 0.1 mg/ml protein kinase exhibited enhanced calcium uptake. We suggest that reversible phosphorylation of microsomal membranes may play an important role in the regulation of aortic microsomal calcium transport by cyclic AMP.
Helical strips of rat tail artery were observed to relax in response to potassium after contraction induced by 10(-7) g/ml norepinephrine in potassium-free solution. After several minutes of relaxation, the strips showed an abrupt redevelopment of tension. The amplitude of the potassium-induced relaxation was employed as an index of the activity of the electrogenic sodium-potassium pump and hence of the Na+-K+ ATPase. This assumption seemed justified because the observed amplitude of potassium-induced relaxation paralleled known effects of the following variables on Na+-K+ ATPase: (1) intracellular sodium concentration; (2) ouabain administration; (3) magnesium; (4) temperature, and (5) potassium concentration. The relaxation that occurred in response to potassium is suggested to be due to an enhanced Na+-K+ ATPase resulting in increased electrogenic transport of sodium and potassium and, consequently, hyperpolarization. We propose that potassium-induced relaxation of rat tail artery may be used as a functional indicator of Na+-K+ ATPase activity in vascular smooth muscle.
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Every year we see an increasing number of people travelling overseas. Whilst many confine their travel to Europe, South East Asia and North America, more and more people are visiting other less familiar countries where diseases not encountered in Australia occur. An awareness of the existence of such diseases and appropriate precautions against them should minimize the risk of infection.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.