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Biomedical subjects

H Seifert

Publications and source records attributed to H Seifert.

At least 145 records · Page 8Linked to original sources
PubMed1989

M-mode echovenography: a new technique for the evaluation of venous wall and valve motion.

The M-mode technique which is widely used in echocardiography allows continuous recording of spontaneous venous wall movements. Compliance of the vein can be quantified. The diameter of the normal vein changes with respiration, while only minor changes are induced by cardiac function. Distensibility and compressibility of the common femoral vein (CFV) were documented. During Valsalva manoeuvre the mean diameter of the CFV increased from 1.05(SD 0.18) cm to 1.52(0.25) cm (p less than 0.01) in the recumbent position and from 1.50(0.20) cm to 1.63(0.17) cm (NS) in the upright position. A patent vein can be completely compressed by the scan head, a thrombosed vein is incompressible. The valve of the normal subclavian vein describes a characteristic M-shaped tracing. The waveform is modulated by cardiac and respiratory function. The study of venous wall movement and venous valve motion provides new insights into venous physiology.

Adult↗
PubMed1988

[Duplex sonography in the diagnosis of peripheral arterial circulation disorders].

From January 1984 to June 1986, 621 duplex scans of the arteries of the lower extremities were performed. 54.8% of the examinations were performed for clinical reasons. In 45.2% the indication was strictly scientific. Clinical and non-invasive examinations including pulse-volume recordings and Doppler pressure measurements preceded duplex-scanning. The analysis shows that duplex scanning may replace arteriography in patients with localized stenosis and short occlusions where catheter therapy is possible. Patients with insignificant stenosis or long occlusion may be selected for conservative treatment without arteriography.

Adolescent↗
PubMed1988

Analysis of flow motion by the laser Doppler technique in patients with peripheral arterial occlusive disease.

Laser Doppler flux was measured at the forefoot in 12 healthy subjects and in 36 patients with different degrees of ischemia due to peripheral arterial occlusive disease. Two characteristic patterns of flow motion waves were observed: Large waves with a mean amplitude of 0.77 +/- 0.4 arbitrary units and a mean frequency of 3.03 +/- 1.0 c/min (0.051 +/- 0.02 Hz) and small waves with a mean amplitude of 0.21 +/- 0.1 arbitrary units and a mean frequency of 21.7 +/- 4.2 c/min (0.362 +/- 0.07 Hz). The prevalence of large waves tended to decrease with more advanced ischemia, whereas small waves occurred almost exclusively in ischemia and most frequently in severe cases. Large flow motion waves were enhanced during reactive hyperemia after arterial occlusion or appeared after peak flux had been reached. Time to peak flux or to vasomotion were reliable parameters for characterizing skin ischemia. The previously undescribed small flow motion waves might represent a compensatory mechanism involved in pathophysiology of ischemia.

Adult↗
PubMed1987

Laser-Doppler probes for the evaluation of arterial ischemia.

Rhythmic variations of microvascular flux have been studied at the forefoot of patients with arterial occlusive disease by laser-Doppler flowmetry. Two patterns of flow motion with characteristic amplitudes and frequencies could be observed. The prevalence of small waves with a mean amplitude of 0.21 +/- 0.1 AU and a frequency of 21.7 +/- 4.2 c/min increased with the degree of ischemia. Big flow motion waves with a mean amplitude of 0.77 +/- 0.4 AU and a frequency of 3.0 +/- 1.0 c/min were found in both controls and patients with different degrees of ischemia. The small waves may represent a compensatory mechanism in skin ischemia.

Blood Flow Velocity↗
PubMed1986

Down-regulation of growth hormone releasing factor receptors following continuous infusion of growth hormone releasing factor in vivo.

The in vivo chronic infusion of growth hormone releasing factor (GRF) results in a loss of the pituitary growth hormone (GH) response to GRF as well as in a substantial depletion of pituitary GH content. To evaluate if the loss in response is due to the down-regulation of GRF receptors the specific GRF binding capacity of pituitary homogenates prepared from rats infused with saline or GRF (1 or 15 micrograms/h for 24 h) was determined. The pituitary binding capacity of animals infused with GRF was significantly reduced as compared to animals infused with saline.

Animals↗
PubMed1986

Desensitization to growth hormone-releasing factor (GRF) is associated with down-regulation of GRF-binding sites.

The time course, concentration dependence, and mechanism of rat anterior pituitary desensitization to GRF were studied. Chronic stimulation of cultures of rat anterior pituitary cells with rat GRF (rGRF) resulted in desensitization to a subsequent challenge with the peptide. Despite a slight enhancement of GH synthesis, prolonged exposure to GRF caused substantial depletion of cellular GH pools. As a result, acute secretory responses were markedly blunted. Depletion was accompanied by a time-dependent decrease in sensitivity to rGRF; GRF EC50 values for GH release of 0.5 nM rGRF-pretreated cells were 24.8 +/- 6 (+/- SEM) pM after 2 h, 46.2 +/- 2.4 pM after 4 h, and 154.7 +/- 31 pM after 8 h compared to 9.2 +/- 0.6 pM for control cells. The process of desensitization was complete within 8 h, as cells pretreated for 24 h exhibited sensitivity to rGRF comparable to that of cells pretreated for 8 h. Desensitization was associated with a time-dependent decrease in rat anterior pituitary cell GRF-binding capacity; a 48% loss of binding sites was evident after a 2-h pretreatment with 0.5 nM rGRF, with a maximum loss occurring after 8 h. The dose of rGRF required to produce an attenuation of responsiveness did not completely correlate with the dose requirement for down-regulation of binding sites. The decrease in GRF-binding sites was not associated with any alteration of apparent Kd values, which were 0.36 (0.18-0.72) nM in control and 0.1 (0.01-0.82) nM after 8 h of exposure to 0.5 nM rGRF. Both the reduction in GRF-binding capacity and decreased sensitivity to GRF were reversible after 24 h, although cellular GH pools were not restored to control levels. These results suggest that rat anterior pituitary cells become desensitized to rGRF after chronic stimulation with a maximal concentration of the peptide. One mechanism for this decrease in apparent sensitivity to rGRF may be the pronounced reduction or down-regulation of GRF-binding sites.

Adrenocorticotropic Hormone↗
PubMed1986

[The purification and characterization of Cordemcura].

3-Amino-5-(4-pyridinyl)-1,2-dihydro-pyrid-2-one (1) is an amphoteric compound and forms one crystalline sodium salt and two hydrochlorides. Physicochemical properties UV, NMR and MS are described. TLC has been used mainly and is the most sensitive method for estimation of 1-byproducts. Coloured byproducts, generated by hypochlorite or air oxidation during synthesis and handling in solution, are monitored by vis-spectra, diminished by sulfite addition and removed by alkaline precipitation. The purification procedure is able to produce 1 with only 0.1% of precursors or byproducts.

Aminopyridines↗
PubMed1985

Binding sites for calcitonin gene-related peptide in distinct areas of rat brain.

Calcitonin gene-related peptide (CGRP) binding sites were localized in rat brain and spinal cord by an in vitro labeling light microscopic technique using [125I]rCGRP as radioligand. Specific rCGRP binding with a dissociation constant (Kd) of 0.53 nM to membrane preparations from rat brain cortex was characterized. The presence and the selective distribution of specific high affinity CGRP binding sites in the central nervous system suggest a role for this recently predicted peptide as a neurotransmitter.

Animals↗
PubMed1985

Vasoactive intestinal peptide receptor localization in rat forebrain by autoradiography.

Vasoactive intestinal peptide (VIP) receptors were localized in rat forebrain by in vitro labeling light microscopic autoradiography with 125I-labeled VIP. Binding sites for VIP were found in discrete areas of rat forebrain including lamina I of the neocortex and pyriform cortex, caudate-putamen, the hippocampus and molecular layer of the dentate gyrus, basolateral nucleus of the amygdala, several thalamic nuclei and the magnocellular paraventricular and supraoptic nuclei of the hypothalamus. These results are consistent with earlier findings on the immunohistochemical distribution and proposed sites of action of VIP, and reinforce the concept that endogenous VIP may function as a neuromodulator in brain.

Animals↗
PubMed1985

Receptor for calcitonin gene-related peptide: binding to exocrine pancreas mediates biological actions.

In the present study we demonstrate by immunohistochemical techniques that calcitonin gene-related peptide (CGRP) is present in nerve terminals in the islets of Langerhans. Furthermore, binding studies with 125I-CGRP indicate that dispersed acini from guinea pig pancreas contain a single class of high-affinity binding sites for CGRP with an apparent dissociation constant of 18 nM. Vasoactive intestinal peptide (VIP), rat growth hormone-releasing factor (rGRF), cholecystokinin octapeptide (CCK-OP), and bombesin do not interact with these receptors. Interaction of CGRP with these receptors leads to release of amylase from the acinar cells. Amylase release is half maximal at 0.3 nM CGRP and maximal at 3 nM CGRP. Maximal amylase release with CGRP is one-third of that observed with VIP. CGRP-induced amylase release is dependent on theophylline in the incubation medium. CGRP potentiates the amylase release stimulated by bombesin and CCK-OP but has no effect on amylase release stimulated by VIP, rGRF, and natural glucagon. CGRP stimulates a 25% increase in basal cellular cAMP. These results indicate that guinea pig pancreatic acinar cells contain a novel receptor for CGRP and that interaction of CGRP with this receptor leads to digestive enzyme secretion through a cAMP-mediated pathway. The presence of CGRP in the islets of Langerhans suggests a pathway for CGRP to reach the exocrine pancreas through an insuloacinar portal system.

Amylases↗
PubMed1985

Growth hormone-releasing factor binding sites in rat anterior pituitary membrane homogenates: modulation by glucocorticoids.

Specific high affinity binding sites for growth hormone releasing factor (GRF) were described in rat anterior pituitary homogenates with use of the analog [His1-mono-125I-Tyr10,Nle27]-hGRF(1-32)-NH2 as radioligand. Computerized analysis of competition experiments indicated one class of specific high affinity binding sites with a dissociation constant of 0.19 nM. The relative binding affinities of rGRF, hGRF(1-40) and various analogs correlated well with their in vitro biological potencies. Further, the number binding sites was drastically decreased after adrenalectomy; chronic dexamethasone treatment of these animals restored GRF binding capacity to control without changing binding affinity. These results may in part explain the enhanced responsiveness of the somatotroph after dexamethasone treatment.

Adrenalectomy↗
PubMed1984

Growth hormone-releasing factor stimulates pancreatic enzyme secretion.

Growth hormone-releasing factors (GRF's) from two human pancreatic tumors (hpGRF's) that caused acromegaly and from the rat hypothalamus ( rhGRF ) were recently isolated and characterized. Although these peptides are potent growth hormone secretagogues, they have not until now been described to have actions outside the pituitary. These GRF's were shown to stimulate digestive enzyme secretion from an exocrine pancreatic preparation in vitro, rhGRF being more than 100 times as potent as hpGRF. Adenosine 3',5'-monophosphate mediates this action of the GRF's.

Amylases↗