Biomedical subjects
H Thomann
Publications and source records attributed to H Thomann.
Combined proton T1N and CPMG T2N studies of water saturated sandstone core plugs.
Diffusion dynamics for water in a series of sandstone core plugs with a broad range of permeabilities was studied using both the Carr-Purcell-Meiboom-Gill (CPMG) and inversion recovery experiments. Both the transverse and longitudinal magnetization curves were found to fit well to stretched exponential relaxation kinetics. At short times, the transverse magnetization is well described by an expression for free diffusion averaged over a distribution of pore sizes. The stretch exponents for the transverse and longitudinal magnetization are shown to be simply related to the width of the pore size distribution. A cross over from free to restricted diffusion is evident in the dependence of T2 with increasing diffusion time set by the interpulse spacing tau in the CPMG experiment. The T2(tau) data is fit to a model which interpolates between the limits of free and restricted diffusion. A length derived from this model is shown to provide a simple estimate of the absolute fluid flow permeability.
[School dental care: when economies become expensive].
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[School dental care: the need for a consensus].
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Pulsed electron nuclear multiple resonance spectroscopic methods for metalloproteins and metalloenzymes.
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[Unavoidable diseases as compulsory benefits. The revision of the health insurance law].
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Endothelium-dependent relaxant effect of neurokinins on rabbit aorta is mediated by the NK1 receptor.
Several neurokinins, namely substance P, neurokinin A, neurokinin B, [beta-Ala8]neurokinin A-(4-10) and senktide, were tested on noradrenaline-precontracted rabbit aortic rings to characterize the receptor mediating their endothelium-dependent relaxant effect in this preparation. CP-96,345, the new nonpeptide antagonist selective for the NK1 receptor, was also studied. Substance P, neurokinin A and neurokinin B, in that order of potency, were effective in relaxing precontracted rings, indicating the involvement of the NK1 receptor; [beta-Ala8]neurokinin A-(4-10) and senktide, which are selective agonists for NK2 and NK3 receptors, respectively, had no significant relaxant effect. The relaxant effects of substance P, neurokinin A and neurokinin B were competitively antagonized by nanomolar concentrations of CP-96,345. These findings support the view that the NK1 receptor mediates the endothelium-dependent relaxant effect of the neurokinins in rabbit aorta.
Sensitivity and reactivity to endothelin-1 in mesenteric beds and aortic rings of 4-week-old spontaneously hypertensive rats.
The vasoconstrictor effects of endothelin-1 were studied in perfused mesenteric vascular beds (MVB) and aortic rings of 4-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). Mean blood pressure (124 +/- 4 vs. 97 +/- 3 mmHg) and initial perfusion pressure in the MVBs (25 +/- 2 vs. 19.7 +/- 1.2) were significantly higher in SHR. Reactivity to endothelin-1 was increased in MVBs of SHR, as indicated by the maximum perfusion pressure obtained (223 +/- 8 vs 155 +/- 7 mmHg, p less than 0.001), whereas there was no significant difference in sensitivity between the two strains (EC50 values: 50 +/- 12 and 80 +/- 15 pmol, respectively). By contrast, in aortic rings reactivity and sensitivity to endothelin-1 were similar in both strains, (EC50s: 1.8 +/- 0.12 and 1.4 +/- 0.1 nM). Reactivity to norepinephrine was increased in MVBs, but reduced in aortic rings of SHR. The unchanged sensitivity to endothelin-1 and the unspecifically increased reactivity in the MVBs of SHR to endothelin-1 and norepinephrine indicate rather a change in vascular structure and not a functional abnormality. These results suggest that hyperreactivity to endothelin-1 may not be a primary hypertensive mechanism in genetic hypertension.
["We must resist far too strong encroachments of the state". Interview by Kurt Venner].
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N coordination of FeMo cofactor requires His-195 of the MoFe protein alpha subunit and is essential for biological nitrogen fixation.
Electron spin echo envelope modulation (ESEEM) spectroscopy, a pulsed electron spin resonance technique, was used to analyze the N coordination of the iron-molybdenum (FeMo) cofactor contained within the nitrogenase MoFe protein. Comparison of spectra obtained from whole cells and purified MoFe protein established that the N coordination of the FeMo cofactor provided by the MoFe-protein polypeptide matrix can be unambiguously recognized in whole cells. ESEEM spectra of altered MoFe proteins, which were produced in certain mutant strains of Azotobacter vinelandii, showed that the N coordination to FeMo cofactor requires His-195 of the MoFe protein alpha subunit. Moreover, this requirement for His-195 was shown to be essential for biological nitrogen fixation.
Effect of covalent dimer conjugates of angiotensin II on receptor affinity and activity in vitro.
Angiotensin II [1-8 or 2-8] analogues and [4-8] fragments were dimerized through the amino- or carboxy-terminal groups in order to try to increase their potency as reported for other hormones. The binding affinity to the angiotensin II receptor subtypes A (A IIA) and B (A IIB) was tested and compared to the potency in rabbit aortic ring. The [2-8] dimers coupled through the N-terminus show no significant change in potency in aortic ring. The [4-8] fragments coupled through the N-terminus are inactive in the ring. They have however a significantly increased affinity for the A IIA receptor, the specific function of which has not yet been reported. When angiotensin II analogues or fragments are coupled through the C-terminus, there was a significant drop in affinity and potency, confirming the importance of the free carboxyl group in position 8 for binding and activity. It is concluded that binding to the A IIB receptor correlates well with the effectiveness in aortic ring. However, in contrast to the beneficial effect reported for a large number of other hormones, dimerization of angiotensin II or its fragments is not accompanied by an increased biological activity in aortic ring.
Sarmesin is a partial agonist of angiotensin-II receptors in rabbit, but not in rat, aortic rings.
Sarmesin, [Sar1, Tyr(Me)4]angiotensinII], has been reported to be a competitive angiotensin II (AII) receptor antagonist in rat smooth muscle preparations (Scanlon et al., (1984), Life Science 34, 317-321). In the present study, sarmesin displaced AII from its binding sites in rat aortic smooth muscle cells and in a rabbit aorta membrane preparation (IC50 5 and 6 nM resp.; Ki 4.1 and 5.3 resp.) In rabbit aortic rings, sarmesin (0.003-3 microM) produced concentration-dependent contractions (ED50 89 nM) and this effect was inhibited by saralasin. No contraction was observed in the rat aorta up to 100 microM. In rabbit aortic rings, sarmesin, at the same concentrations that produced contraction, inhibited contractions induced by AII in a competitive manner (pA2 7, 26). These results indicate that, in rabbit aortic rings sarmesin is a partial agonist of AII receptors.
Binding characteristics and vascular effects of various angiotensin II antagonists.
Subtypes of angiotensin II (Ang II) receptors have been recently identified using specific ligands (see Whitebread et al. Biochem Biophys Res Comm 1989; 163:284-291). The present study compares the binding characteristics of different structural classes of Ang II receptor ligands in rat aortic smooth muscle cells (Ang IIB subtype) and in human uterus (Ang IIA subtype) and their effects on the constrictor response to Ang II in isolated rabbit aortic rings. Saralasin and [Sar1 Ile8]-Ang II displayed similar affinity for the two subtypes. In contrast, CGP 42112A bound with high affinity to the uterus (Ki 0.24 nM), but showed a low affinity for the aortic receptor (Ki 1,760 nM). Compound 89 displayed affinity for the aortic receptor only (Ki 26 nM) whereas Ex 169 recognized specifically the uterus receptor (Ki 310 nM). In rabbit aortic rings, saralasin, [Sar1 Ile8]Ang II, CGP42112A and compound 89 inhibited Ang II-induced contractions at concentrations similar to those required to bind to the Ang IIB receptor subtype. IC50s were 3, 0.7, 1,850, and 23 nM respectively. Ex 169 was ineffective in concentrations up to 100 microM. There was a highly significant correlation between inhibition of Ang II-induced contraction in aortic rings and binding to smooth muscle cells. This correlation does not exist with human uterus. Our results indicate that the Ang IIB receptor subtype is responsible for vascular contractions. Antagonists of this vascular receptor subtype are potential antihypertensive agents.
Reactivity and sensitivity of mesenteric vascular beds and aortic rings of spontaneously hypertensive rats to endothelin: effects of calcium entry blockers.
1. The vasoconstrictor effects of endothelin-1 were studied in perfused mesenteric vascular beds (MVB) and aortic rings of 14-16 week-old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). 2. Reactivity to endothelin-1 was increased in MVBs of SHR, as indicated by the maximum perfusion pressure obtained (264 +/- 8 and 141 +/- 9 mmHg respectively) (P less than 0.001), whereas sensitivity was not significantly different between the two strains (EC50 171 +/- 21 and 102 +/- 19, respectively). 3. In aortic rings, in contrast, reactivity to endothelin-1 was reduced in SHR as compared to WKY, whereas sensitivity was similar (EC50 0.78 +/- 0.08 and 0.87 +/- 0.09 nM). 4. As with endothelin-1, reactivity to noradrenaline and potassium chloride was increased in MVBs, but not in aortic rings of SHR. Endothelin-1 was 30 times more potent than noradrenaline in MVBs of SHR, and 15 times more potent than noradrenaline in aortic rings. 5. In both strains, nifedipine and nitrendipine almost completely blocked potassium-induced contractions in MVB and aortic rings, respectively, whereas contractions induced by endothelin-1 or noradrenaline were only partially inhibited. 6. It is concluded that calcium influx via the voltage-operated calcium channel is only partially responsible for the vasoconstrictor action of endothelin-1 in MVBs and aortic rings of SHR and WKY rats. The increased reactivity of the MVB of SHR to endothelin-1 at this stage of the hypertensive process is most likely to be the result of a change in vascular structure rather than due to a primary hypertensive mechanism.
Sensitivity to endothelin-1 in mesenteric beds and aortic rings of 4-week-old spontaneously hypertensive rats.
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Blockade of endothelin-induced contractions by dichlorobenzamil: mechanism of action.
Contractions of intact rat aortic rings induced by endothelin were totally inhibited by the amiloride analogue dichlorobenzamil (DCB) at concentrations known to block Na-Ca exchange (IC50 = 30 microM). Amiloride (100 microM) was ineffective. Ca-channel blockers and a K-channel opener elicited only partial inhibition. These results could indicate that the Na-Ca exchanger plays an important role in endothelin-induced contractions. Endothelin, however, had no effect on the kinetics of the exchanger, and, in addition, contractions also occurred in Na-depleted vessels. The endothelin-induced contractions produced by Ca release from intracellular pools were also completely inhibited by DCB. In fact, the latter compound was found to block contractions induced by Ca itself in the presence of Ca ionophore or detergent. We conclude that DCB acts directly on Ca-induced activation of myofilaments in smooth muscle.
[Curing ability of polymerization lights for composite materials].
An in-vivo study has been conducted with four different brands of activator light sources. 38 light units in service by different dental practitioners were compared with new light sources. Curing depth profiles were obtained using Knoop microhardness measurements. It was observed that with an exposure time of up to 60 s the polymerization was not sufficient below 2 mm of depth. The "old" light sources showed worse curing properties than the new ones, especially below this depth. Generally, the polymerization units with rigid glass fiber light guide showed better results than the units with a flexible fiber-optic cable. Other reasons for insufficient polymerization were polymerized composite material at the end of the light guide, a defect in the cooling system of the light source and, for two brands of light sources, a reduction of the voltage below 220 V.
Observation of triplet hole pairs and glassy spin waves in La2-x-zSrxCuO4-y by electron spin resonance.
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