Biomedical subjects

K Liewendahl

Publications and source records attributed to K Liewendahl.

At least 109 records · Page 6Linked to original sources

PubMed1976

Effect of fatty acids on thyroid function tests in vitro and in vivo.

Addition of long-chain fatty acids to serum increased thyroxine (T4), measured by a competitive protein binding assay, and triiodothyronine (T3) uptake by Sephadex or resin (T3U tests). This is compatible with the assumption that fatty acids compete with thyroxine for binding sites on T4-binding proteins. When equimolar concentrations of various saturated and unsaturated fatty acids were added to serum it was observed that the effectiveness in raising tests based on protein binding of thyroid hormones incrreased serum T3 determined by radioimmunoassay (RIA). T4(RIA) was not significantly influenced by either saturated or unsaturated fatty acids. Serum T4(CPB) rose during storage at 22degreesC and 37degreesC but was stable at 4degreesC and --20degreesC for periods up to two weeks. The proportional increase in T4(CPB) and free fatty acids (FFA) indicated that this phenomenon was due, at least partly, to the interference from FFA formed during storage of the serum. There was also a small, significant increase in T3U, T3(RIA) and CT4I (a free thyroxine estimate) after storage of serum at room temperature or higher for one to two weeks. Serum T4(RIA) did not alter during two weeks of storage. In five subjects with raised serum FFA after eating a fat meal followed by a heparin injection an increase in T4(CPB), T3U, T3(RIA) and CT4I that was proportional to the increase in FFA was observed. This effect on the thyroid tests was small until the increase in FFA concentration exceeded 2 mmol/l. T4(RIA) did not respond to the increase in FFA. In ten patients with raised levels of FFA due to uncontrolled diabetes T4(CPB), T4(RIA) and T3(RIA) decreased while T3U increased. These unexpected alterations were probably related to the severe, chronic illness in these patients. Increased FFA in vivo seem to be of little importance for the interpretation of thyroid tests in clinical practice.

Adult↗

PubMed1976

Studies on proteolytic activity and function of the thyroid gland in rats administered excess iodide.

Thyroid auto-proteolytic activity in rats increased significantly only after several weeks of treatment with 1 mg iodide per day. Iodide added in vitro did not activate thyroid auto-proteolysis, nor was inhibition observed. Thyroid proteolytic activity was also tested using 131I-labelled heat-inactivated thyroid homogenate from control rats as substrate. Significantly increased proteolytic activity was again demonstrated in thyroid glands from rats on excess iodide for several weeks. The increased proteolytic activity is therefore probably not due to a decreased proteolytic resistance of thyroglobulin in the iodide-treated rats. Increased synthesis or decreased degradation of thyroid proteolytic enzymes is a more likely explanation for this phenomenon. These findings are at variance with those of some previous studies showing decreased proteolytic activity in thyroid glands from rats administered excess iodide. Since the rats remained euthyroid the increased auto-proteolysis, which occurred quite late, was considered an unexpected finding and it is at present not certain whether this is related to the successful adaptation. Treatment with iodide did not alter the thyroid and hypophyseal weight or histology. Serum free thyroxine level and thyrotropin concentration were also unaffected by excess iodide. The adaptation of the imtact rat thyroid to prolonged and excess iodide intake seems to occur without the assistance of an altered thyrotrophin secretion.

Animals↗

PubMed1976

Triiodothyronine binding to lymphocytes from euthyroid subjects and a patient with peripheral resistance to thyroid hormone.

Triiodothyronine (T3) binding to Ficoll-Isopaque purified human lymphocytes was studied. During incubation of lymphocytes with [125I]T3 in a calcium-free medium at 37 degrees C, maximal uptake of T3 in nuclei occurrred after 2 h and declined after prolonged incubationd incubation . Incubation of lymphocytes with T3 concentrations ranging from 1 X 10(-11) TO 1 X 10(-9) mol/l and subsequent treatment with Triton X-100 to strip off [125I]T3 bound with low affinity was used for the estimation of affinity and capacity of nuclear T3 binding sites. The mean equilibrium affinity constant (Ka) estimated with the Scatchard method in 11 euthyroid healthy subjects was 4.5 X 10(9) l/mol, and the mean maximal binding capacity 25 X 10(-5) mol/100 mug DNA. In a female patient with peripheral resistance to thyroid hormone action, the estimated Ka was 3.5 X 10(9) l/mol and the number of T3 binding sites 37 X 10(-15) mol/100 mug DNA. Although not statistically different from the mean value in euthyroid subjects, this Ka value was outside the range of control values observed and was considered presumptive evidence that the nuclear T3 receptors in this patient have abnormally low affinity for its ligand. The nuclear T3 binding capacity in this patient was significantly increased.

Adult↗

PubMed1976

Thyroxine, triiodothyronine, and thyrotropin in serum during long-term diphenylhydantoin therapy.

Clinical laboratory tests for assessment of thyroid function were performed in 31 patients receiving long-term diphenylhydantoin (DPH) therapy. Reduced serum total thyroxine and free thyroxine index were found. The decrease in serum total triiodothyronine and free triiodothyronine index was smaller but statistically significant. DPH had no significant effect on the serum thyrotropin (TSH) concentration and maximal TSH response to TSH-releasing hormone. The absence of reciprocal changes in TSH and serum thyroxine might be due to the near-normal triiodothyronine concentration. Such an explanation would also conform with previous findings that the pituitary contains specific receptors for triiodothyronine but not thyroxine.

Adolescent↗

PubMed1975

Comparison of serum free thyroxine indices and "corrected" thyroxine tests.

A dual competitive protein-binding assay for serum thyroxine (T4) is described. The assay is called the "corrected" T4 index and can be performed simultaneously with the determination of total T4. This method correlated significantly with the free T4 index and the effective T4 ratio. The "corrected" T4 index was compared for precision and diagnostic accuracy with the effective T4 ratio and two different free T4 indices. Improved modifications of the thyroxine and triiodothyronine Sephadex uptake tests, used for calculation of the free T4 indices, are also reported. In spite of better precision, the "corrected" T4 index and effective T4 ratio gave twice as many incorect classifications of both hyper- and hypothyroidism as the free T4 indices. Previous reports on the effective T4 ratio and other basically similar tests might give an overly optimistic view of what can be expected in routine clinical practice. The free T4 index, which is a good estimate of the free T4 concentration, may still be the thyroid function test of choice when serum T4 and clinical impression are not in conformity.

Adult↗

PubMed1975