Papers by Fritz Sixtus Keck
Thyroidology / A.P.R.I.M, 1991
The intracellular 5'deiodination (5'D) of T4 and rT3 has been investigated in human adipo... more The intracellular 5'deiodination (5'D) of T4 and rT3 has been investigated in human adipose tissue. We studied 5'D in intact adipose tissue, its morphological components and in 3T3-L1-cells. 5'D as assessed by T3-production out of T4 and by rT3-decomposition was not inhibited by propylthiouracil (PTU), but by iopodate (IOP). The apparent Michaelis constants were kM = 3 nM for rT3 and kM = 1 microM for T4. The rT3-degradation was linear over 25 h (115 pg/h.mg (prot.)) both at 37 degrees C and at 4 degrees C. The same type of 5'D was observed in adipocytes, stromal-vascular cells and in 3T3-L1-cells regarding T4 to T3 degradation (244 +/- 30, 181 +/- 27, 227 +/- 37 pg T3/mg.min), resp.; PTU did not exert any influence upon 5'D in the cells investigated. We conclude, that i. the intracellular generation of T3 in adipose tissue does not derive from type I deiodination; ii. 5'D in adipocyte precursors and differentiated adipocytes is identical and iii. there i...
Arzneimittel-Forschung, 1994
The effect of corticotropin releasing factor (CRF) on atrial natriuretic peptide (ANP) release an... more The effect of corticotropin releasing factor (CRF) on atrial natriuretic peptide (ANP) release and its possible modulation by indomethacin, norepinephrine, propranolol and nitro-L-arginine (an inhibitor of the endothelium-derived relaxing factor (EDRF) release) was investigated, using an isolated perfused rat heart preparation. Bolus injection of 5 micrograms CRF, dissolved in 100 microliters perfusion buffer, provoked a significant (p < 0.01 vs. control) short-time increase of ANP release. Indomethacin (3 x 10(-5) mol/l) inhibited the CRF-stimulated increase of ANP release and decreased the basal ANP secretion (p < 0.01 vs. CRF group). Norepinephrine (10(-9) mol/l) slightly, but not significantly, decreased the CRF-stimulated ANP release and did not change the basal ANP output. Propranolol (3 x 10(-6) mol/l) did not alter ANP release. Nitro-L-arginine (3 x 10(-5) mol/l) increased the basal ANP release (p < 0.01 vs. CRF group) and prolonged the CRF-induced rise of the ANP s...
Hormone and Metabolic Research, 1993
The recent introduction of third generation assays for TSH has led to a considerable improvement ... more The recent introduction of third generation assays for TSH has led to a considerable improvement of assay sensitivity. To assess the clinical significance of subnormal basal TSH (b-TSH) values (&lt; 0.2 microU/ml), we investigated b-TSH and TRH-stimulated TSH (r-TSH) by means of a new, highly sensitive immunochemiluminometric assay in 105 euthyroid subjects, 45 patients with overt hyperthyroidism and 18 patients suspected of having subclinical hyperthyroidism. A weak, albeit statistically significant, correlation (r = 0.48) was found between b-TSH and r-TSH and also between b-TSH and delta-TSH (r = 0.31) in euthyroid subjects. Consideration of b-TSH alone correctly identified 90 % of euthyroid subjects in this group; 10 of 105 apparently euthyroid subjects presented delta-TSH suggesting subclinical hyperthyroidism. While b-TSH was detectable (&gt; 0.04 microU/ml) in 8 of 45 (18%) of hyperthyroid patients, all (100%) were abnormal in both b-TSH and r-TSH. 14 of 18 (78%) of patients with subclinical hyperthyroidism exhibited a blunted TSH response to stimulation (delta-TSH &lt; 2 microU/ml). These results suggest that although the new generation of TSH assays can be a valuable addition to the diagnostic arsenal of thyroid function tests, certain limitations must still be accepted. Specifically, b-TSH in the &quot;grey zone&quot; (0.1-0.2 microU/ml) appears to be a less than reliable predictor of thyroid function.
Frontiers in Thyroidology, 1986
The reciprocal changes of triiodothyronine (T3) serum concentrations and (SC) and thyroxine (T4) ... more The reciprocal changes of triiodothyronine (T3) serum concentrations and (SC) and thyroxine (T4) SC observed in patients with varying degrees of primary hypothyroidism are well known. T3 SC are often still within normal limits, when T4 SC have already reached low-normal or subnormal levels. The patients do not have clinical evidence of hypothyroidism at that time (1). Considering the other extreme of the spectrum, most athyroid patients have a negative TRH test only if T4 SC are raised to levels beyond the normal range by large doses of T4. This is associated with T3 SC in the upper normal range. These patients do not appear to be clinically hyperthyroid (2). These findings suggest that a non-thyroidal mechanism accounts for the reciprocal changes in T4 SC and T3 SC. The purpose of this clinical study was to clarify the role of these non-thyroidal mechanisms in regulating T3.
Primäre Diagnostik und Verlaufskontrolle der Struma. 9. Konferenz über die menschliche Schilddrüse, Homburg-Saar, 1990
Münchener medizinische Wochenschrift, 1989
4th International Symposium, Munich, October 1992, 1993
Thyroidology / A.P.R.I.M, 1991
We investigated thyrotropin releasing hormone (TRH) degradation in terms of half-life (t1/2) and ... more We investigated thyrotropin releasing hormone (TRH) degradation in terms of half-life (t1/2) and metabolic clearance rate (MCR) in eight subjects with insulin dependent diabetes mellitus (IDDM) before and after strict metabolic control. The results were compared with those of six healthy control subjects. The basal plasma TRH-IR levels (31 +/- 9 fmoles/ml) were on the lowest normal limit in the IDDM patients and were not considerably changed (24 +/- 10) after strict metabolic control. The basal and delta max rise of TSH to TRH (200 micrograms i.v.) were not significantly different before or after improved metabolic control in IDDM and as compared to controls. The TRH-degradation curves showed similar exponential decay before and after improvement of metabolic control (t1/2: 7.6 +/- 0.4 min and 7.3 +/- 0.3 respectively; 6.5 +/- 0.4 min for the controls). The MCR of exogenously administered TRH in IDDM before (65.5 +/- 8.6 l/m2/day) and after (65.0 +/- 8.9) control was not different c...
Endocrinology of the Heart, 1989
The secretion of atrial natriuretic peptide (ANP) is depended mainly by volume loading and atrial... more The secretion of atrial natriuretic peptide (ANP) is depended mainly by volume loading and atrial stretch. Different humoral factors such as acetylcholine, epinephrine, calcium and sodium ions stimulate the release of ANP [1, 2]. Medicaments which can alter the intracellular Ca++ may influence the secretion of ANP. It was the aim of this study to determine influences of selective and non selective calcium channel blockers on the secretion of human ANP.
The Endocrinology of Aging
The Endocrinology of Aging
Journal of Endocrinological Investigation, 1991
We describe the clinical application of a radioimmunoassay combined with fast protein liquid Chro... more We describe the clinical application of a radioimmunoassay combined with fast protein liquid Chromatography (FPLC) for measuring TRH immunoreactivity (TRH-IR) in blood samples extracted previously with methanol or with Sep Pak C 18 cartridges. Sensitivity of the RIA was 3 fmol/tube, displacement at 50% B/Bo was achieved by 55 fmol of unlabelled TRH. Our specific antibody K2B7 (km = 2.2 fM) showed no cross reaction with other peptides. No difference was observed between the mean values of TRH-IR in 19 euthyroid, 22 hyperthyroid, 18 hypothyroid and 10 hypophysectomised patients (45 ± 17.{3, 58 ± 30,40 ± 22 and 36 ± 12 fmol/ml, mean ± SD, respectively), whereas TRH-IR was significantly lowered (p < 0.05) in 6 euthyroid pancrea-1This work was supported by a research grant from the Deutsche Forschungsgemeinschaft (Pf 38/3-1).
The Journal of Clinical Endocrinology & Metabolism, 1982
TRH measurements have been carried out in human peripheral blood and rat peripheral and portal bl... more TRH measurements have been carried out in human peripheral blood and rat peripheral and portal blood by RIA in conjunction with affinity chromatography. Human peripheral blood TRH appeared to be identical to synthetic TRH by immunological, chromatographic, and enzymatic criteria. TRH concentrations in normal subjects ranged from 24-138 pg/ml, with a mean of 78 pg/ml. Moreover, TRH concentrations were not altered from normal in either thyrotoxic or hypothyroid subjects. TRH measurements in selected venous compartments in the rat, in conjunction with previously reported kinetic data, suggest that most of the TRH in peripheral blood is derived from nonhypothalamic sources.
The thyroid state is an important determinant of cardiac performance. This study examines the eff... more The thyroid state is an important determinant of cardiac performance. This study examines the effects of acute hypothyroidism on left ventricular diastolic function.
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Papers by Fritz Sixtus Keck