monoiodotyrosine and Adenoma

To better understand the state of dopamine (DA) neurotransmission in the tuberoinfundibular DA system (TIDA), monoiodotyrosine (3-iodo-L-tyrosine, MIT), a potent inhibitor of DA synthesis, was acutely administered to 8 normal women, 7 postpartum women, 8 women with pathological hyperprolactinemia and 5 women after successful removal of a prolactinoma. The effects on plasma prolactin (PRL) and thyrotropin (TSH) were compared to those induced in the same subjects by the DA receptor antagonist domperidone (DOM). MIT (1 gpo) and DOM (10 mg iv) induced qualitatively similar hormonal responses, although the PRL- and TSH-releasing effects of DOM were always greater than those of MIT. In control subjects, MIT treatment induced a consistent rise in plasma PRL (peak increment 45.2 +/- 13 ng/ml at 120 min); in the same subjects DOM induced a prompter and higher PRL response, (peak increment 147.8 +/- 26 ng/ml at 30 min). MIT failed to alter plasma TSH levels, while DOM induced a significant rise in plasma TSH. In postpartum women MIT induced a prompter and higher PRL rise than that occurring in controls (peak increment 180.3 +/- 20 ng/ml at 90 min), though also in this instance DOM proved to be a more potent PRL releaser (peak increment 345.7 +/- 88 ng/ml at 30 min) than MIT. MIT was unable to stimulate TSH secretion, while DOM induced a significant rise in plasma TSH. In women with pathological hyperprolactinemia MIT failed to alter baseline PRL levels while DOM slightly increased them (peak increment 14.7 +/- 3 ng/ml at 30 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenoma; Adult; Animals; Binding, Competitive; Domperidone; Dopamine; Female; Humans; In Vitro Techniques; Male; Monoiodotyrosine; Pituitary Gland, Anterior; Pituitary Neoplasms; Postpartum Period; Pregnancy; Prolactin; Rats; Rats, Inbred Strains; Receptors, Dopamine; Thyrotropin

Iodoamino acid content and distribution were measured in adenomas, nodular goiters, thyroiditis and carcinomas and compared to thyroids from patients who died suddenly and normal thyroid tissues originally adjacent to diseased tissue. Tissues were hydrolyzed with Pronase, derivatized and analyzed by gas chromatography as had previously been reported for rat thyroids. Considerable overlap in values was found among adenomas, nodular goiters and papillary and follicular carcinomas as compared to values in normal thyroid tissue, but low values were also found in several diseased tissues. MIT/DIT and T3/T4 ratios were essentially constant in most tissues, even when T4 values were low. MIT/DIT ratios were, however, high and iodothyronines undetectable in all Hurthle cell neoplasms, clearly differentiating them from other thyroid conditions.

Topics: Adenoma; Carcinoma; Humans; Monoiodotyrosine; Thyroid Gland; Thyroid Neoplasms; Thyroiditis, Autoimmune; Thyroxine; Triiodothyronine

Topics: Adenoma; Diiodotyrosine; Humans; Long-Acting Thyroid Stimulator; Monoiodotyrosine; Thyroid Function Tests; Thyroid Hormones; Thyroid Neoplasms; Thyrotropin; Triiodothyronine

Topics: Adenine; Adenoma; Adenylyl Cyclases; Adult; Carbon Isotopes; Cyclic AMP; Diiodotyrosine; Enzyme Activation; Female; Glucose; Humans; Iodides; Iodine Isotopes; Monoiodotyrosine; Thyroid Neoplasms; Thyrotropin; Thyroxine; Triiodothyronine; Tritium

Benign and malignant nodules in human thyroid glands, which did not concentrate iodide in vivo, were also unable to accumulate iodide in vitro. The mean thyroid-to-medium ratio (T/M) in seven benign nodules was 0.8+/-0.2 compared with 7+/-2 in adjacent normal thyroid tissue. In four malignant thyroid nodules, the mean T/M was 0.5+/-0.1 compared with 11+/-4 in adjacent normal thyroid. Despite the inability of such nodules to concentrate iodide, iodide organification was present but was only one-half to one-third as active as in surrounding normal thyroid. Thyroid-stimulating hormone (TSH) increased iodide organification equally in both benign nodules and normal thyroid although it had no effect in three of the four malignant lesions. The reduction in organification is probably related to the absence of iodide transport, since incubation of normal thyroid slices with perchlorate caused similar diminution in iodide incorporation but no change in the response to TSH. Monoiodotyrosine (MIT) and di-iodotyrosine (DIT) accounted for most of the organic iodide in both the nodules and normal tissue. The MIT/DIT ratio was similar in normal and nodule tissue. The normal tissue contained much more inorganic iodide than the nodules, consistent with the absence of the iodide trap in the latter tissue. The thyroxine content of normal thyroid was 149+/-17 mug/g wet wt and 18+/-4 mug/g wet wt in the nodules. The transport defect in the nodules was not associated with any reduction in total, Na(+)-K(+)- or Mg(++)-activated ATPase activities or the concentration of ATP. Basal adenylate cyclase was higher in nodules than normal tissue. Although there was no difference between benign and malignant nodules, the response of adenylate cyclase to TSH was greater in the benign lesions. These studies demonstrate that nonfunctioning thyroid nodules, both benign and malignant, have a specific defect in iodide transport that accounts for their failure to accumulate radioactive iodide in vivo. In benign nodules, iodide organification was increased by TSH while no such effect was found in three of four malignant lesions, suggesting additional biochemical defects in thyroid carcinomas.

Topics: Adenoma; Adenosine Triphosphatases; Adenosine Triphosphate; Adenylyl Cyclases; Animals; Biological Transport; Carcinoma, Papillary; Cattle; Diiodotyrosine; Humans; Iodides; Iodine Radioisotopes; Magnesium; Monoiodotyrosine; Ouabain; Perchlorates; Potassium; Sodium; Thyroid Gland; Thyroid Neoplasms; Thyroxine

Topics: Adenoma; Autoradiography; Chromatography; Goiter; Histological Techniques; Humans; In Vitro Techniques; Iodine Radioisotopes; Methods; Monoiodotyrosine; Thyroid Gland; Thyroid Hormones; Thyroid Neoplasms; Tyrosine

Topics: Adenocarcinoma; Adenoma; Adult; Aged; Centrifugation, Density Gradient; Chromatography; Diiodotyrosine; Female; Goiter; Humans; Iodides; Iodine; Iodine Radioisotopes; Iodoproteins; Male; Metabolic Diseases; Middle Aged; Monoiodotyrosine; Spectrophotometry; Thyroglobulin; Thyroid Gland; Thyroid Neoplasms