Enzymatic radioiodination of porcine thyroid-stimulating hormone

Thyrotropin receptor-adenylate cyclase system in plasma membranes from normal and diseased human thyroid glands

Thyrotropin binding characteristics and adenylate cyclase (AC) activity of thyroid plasma membranes were studied in 52 tissues from normal and diseased human thyroids. Data from normal glands, Graves' goiters, non toxic multinodular goiters and nodular and perinodular tissue of toxic nodular goiters show the same basal, TSH- and NaF- stimulated adenylate cyclase activities (no. = 45; 34.1 +/- 3.2 (m +/- SE), 378 +/- 43, 298 +/- 48 pmol cAMP x min-1 x mg membrane protein-1), the same stimulability of AC by TSH (11.3 +/- 1.4--fold over basal level) and by NaF (8.1 +/- 1.8-fold), the same apparent TSH binding equilibrium constants (5.6 +/- 0.7 and 406 +/- 57 nM) and the same TSH binding site concentrations (2.2 +/- 0.4, 27.8 +/- 5.9 pmol x mg membrane protein-1). Alterations of the TSH receptor and of the AC were detected in membranes from tumoral and metastatic lymph node tissues from thyroid papillary carcinoma and in the thyroid tissue from post-radioiodide therapy thyroiditis. These observations suggest that: (i) hyperthyroidism in Graves' disease or toxic nodular goiter does not result in and is not a consequence of an alteration in the TSH receptor-adenylate cyclase system; (ii) there is no evidence supporting a relationship between the studied membrane properties and clinical or histological status; (iii) membrane abnormalities detected in thyroid carcinoma vary widely; (iv) studies of these membrane alterations might be of interest in the therapeutic management of thyroid carcinoma and may lead to a better understanding of the receptor-adenylate system.

Modulation of adenylate cyclase/cyclic AMP response by thyrotropin and prostaglandin E2 in cultured thyroid cells. 1. Negative regulation

Isolated porcine thyroid cells, cultured in the presence of thyrotropin (greater than or equal to 0.25 mU/ml) or prostaglandin E2 (greater than or equal to 0.1 micron), showed decreased adenosine 3':5'-monophosphate (cyclic AMP) response to further thyrotropin or prostaglandin E2 stimulation, respectively. Kinetics of the refractory process to thyrotropin and prostaglandin E2 are different: (a) maximal refractoriness to prostaglandin E2 was attained after 2--6 h exposure to prostaglandin E2 while refractoriness to thyrotropin was maximal only after 12--24 h; (b) the degree of refractoriness to prostaglandin E2 was much greater than that to thyrotropin. Refractoriness to thyrotropin or prostaglandin E2 is characterized: by specificity for each thyroid stimulator; by dependence upon the dose of thyrotropin or prostaglandin E2 in culture, e.g. induction of high degree of refractoriness with 0.5 mU/ml thyrotropin (or 1 micron prostaglandin E2), which elicits only a small cyclic AMP increase; by time requirement for induction; by partial effect; by changes of maximum activation of cyclic AMP response; by reversibility. This refractoriness of the cyclic AMP response was not induced by dibutyryl adenosine 3':5'-monophosphate. It was not attributed to increased cyclic AMP-phosphodiesterase activity, but to alterations in the receptor-adenylate cyclase system. Prevention of refractoriness to thyrotropin or prostaglandin E2 by incubation of cells in the presence of actinomycin D, puromycin and cycloheximide suggests that new RNA and protein syntheses are required for the development of the refractory state.

Thyrotropin binding to and adenylate cyclase activity of porcine thyroid plasma membranes

Plasma membranes have been purified from porcine thyroid gland homogenate by discontinuous sucrose gradient centrifugation. The preparations contained specific binding sites for thyrotropin but not for luteinizing hormone or the beta subunits of thyrotropin and luteinizing hormone. Optimum conditions of 125I-labeled thyrotropin binding were pH 6.0-6.5 and 37 degrees C. Thyrotropin binding was reduced by divalent (Ca2+, Mg2+) and monovalent cations (Na+, K+, Li+), 50% inhibition being obtained at 10 mM and 50 mM respectively. Displacement curves of 125I-labeled bovine or porcine thyrotropin by the unlabeled hormone from three species was in the order of increasing concentrations (bovine greater than porcine greater than human) which is the order of decreasing biological activity of these hormone preparations in the assay in vivo in the mouse. The validity of the results was established by controlling that porcine membranes bound the native and the 125I-labeled hormones with equal affinity. A single type of high-affinity (Kd = 0.28 nM) binding sites was detected for bovine and porcine thyrotropins. In contrast, porcine plasma membranes bound human thyrotropin with a lower affinity (Kd = 70 nM). A good correlation was found at equilibrium and in the conditions of the cyclase assay, between receptor occupancy and adenylate cyclase activation for the three hormones.

Active transport of iodide in isolated porcine thyroid cells. Application to an in vitro bioassay of thyrotropin

Porcine thyroid cells were cultured for 2 days with or without dibutyryl cyclic AMP or thyrotropin (TSH). Then they were isolated post-culture by a gentle treatment with a calcium chelating agent. Some characteristics of the iodide transport system were studied in these thyroid cell suspensions. Iodide influx is a saturable, temperature- and energy-dependent phenomenon. It is blocked by ouabaïn, N-ethylmaleimide, dinitrophenol, cardiotoxin, low Na+ concentration and harmaline. Only 3% of the intracellular iodide is trichloracetic-acid-insoluble at equilibrium. The apparent Michaelis constant (Km) of the transport system is 30 micronM. For monolayer cells, the decrease of C/M ratio, increase of apparent Km, and decrease of Vmax between day 0 (freshly isolated cells) and day 6, indicate a loss of iodide-trapping ability up to passive diffusion. To the contrary, high values of C/M and normal Km (30 micronM) are observed in TSH follicles from reassociated cells. At iodide equilibrium, thryotropin, prostaglandins E1 and E2 and long-acting thyroid stimulator (LATS), induce a fast release of iodide. This release is dose-dependent in the first 5 min. It has been used to develop a bioassay of TSH and a fast detection of LATS.

Thyrotropin-specific binding to human peripheral blood monocytes and polymorphonuclear leukocytes

[125I]Labeled thyrotropin binding to leukocytes has been studied using lymphocyte-, monocyte- and polymorphonuclear leukocytes-enriched preparations obtained by centrifugation of Ficoll-Angiocontrix gradients and Sephadex G-10 adherence. From the relation between thyrotropin binding and phagocytosis as shown by latex beads ingestion, it is concluded that the hormone binds essentially to monocytes and polymorphonuclear leukocytes. Equilibrium association constants of the high-affinity, low-capacity sites (1 nM-1) are similar to those found in isolated thyroid cells or in thyroid plasma membranes. The role of thyrotropin in the regulation of phagocytosis by leukocytes is discussed.