The importance of employing homologous serum free of thyronines in radioimmunoassays to assess circulating thyroid hormones in rainbow trout

Although abundant, available information regarding the values of circulating thyronines in the rainbow trout is misleading and confusing. The present study demonstrates the importance of maintaining species serum-homology when measuring thyronines with RIA to avoid spurious results. The utilization of homologous (trout) serum free of thyronines in the standard curve allowed the standardization of accurate and specific radioimmunoassays to quantitate circulating T3 and T4 levels in 10 microliters of rainbow trout serum. Detection limit was 50 pg for both thyronines. Inter- and intra-assay coefficients of variation were minor to 10%. Mean values for T3 and T4 +/- SEM in the trout population studied (n = 34) were 23.6 +/- 1.2 and 12.0 +/- 2.3 ng/ml respectively. A positive and significant correlation (p < 0.005) between body weight and T3 was observed, confirming the active participation of this thyronine in growth processes.

Proton nuclear magnetic resonance assignments of thyroid hormone and its analogues

1H NMR data of a series of thyroid hormone analogues, e.g., thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), 3,5-diiodothyronine (3,5-T2), 3',5'-diiodothyronine (3',5'-T2), 3-monoidothyronine (3-T1), 3'-monoiodothyronine (3'-T1), and thyronine (TO) in dimethylsulfoxide (DMSO) have been obtained on a 300 MHz spectrometer. The chemical shift and coupling constant are determined and tabulated for each aromatic proton. The inner tyrosyl ring protons in T4, T3, and 3,5-T2 have downfield chemical shifts with respect to those of the outer phenolic ring protons. Four-bond cross-ring coupling has been observed in all the monoiodinated rings. However, this long-range coupling does not exist in T4, diiodinated on both rings, and T0, containing no iodines on the rings. There is no evidence that at 30 degrees C these iodothyronines have any motional constraint in DMSO solution. In addition to identification of the hormones, the potential use of some characteristic peaks as probes in binding studies is discussed.

[Effect of different infusion regimens on the hormonal and metabolic reaction before, during and after cholecystectomy]

18 metabolically healthy female patients with cholelithiasis, who had to undergo cholecystectomy, were divided into 3 groups and studied for a 4-day period. Group I, n = 6, received beginning on the operationday 0,19 g/kg BW X h of a polyol-mixture-solution (Sorbitol/Xylitol 1:1) and 0,86 g 1-crystalline amino acids (AA)/kg BW X day. Group II, n = 6, received beginning 24 h preoperatively only 1,14 g 1-crystalline AA/kg BW X day. Group III, n = 6, received beginning 24 h preoperatively 0,07 g Xylitol/kg BW X h, 0,03 g Glucose/kg BW X h and 1,14 g 1-crystalline AA/kg BW X day. In this study we could demonstrate that the pre-, intra- and postoperative hormonal and metabolic response is strongly influenced by different infusion regimens. Only by the simultaneous infusion of carbohydrate together with AA during the preoperative period a significant drop of triiodothyronine can be avoided. The rise of insulin and cortisol in the early postoperative period is augmented by the infusion of carbohydrates together with AA. There was no difference in growth hormone response to surgery between group I-III. All 3 groups showed a continuous fall of cholesterol during the study period.

Thyrotropin suppression by 3,5-dimethyl-3'-isopropyl-L-thyronine in man

The thyromimetic activity of 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT), a nonhalogenated thyroid analog, was studied in adult men using suppression of TRH-induced TSH release to assess this activity. In nine men, aged 30-58 yr, the TSH increment after 500 microgram TRH iv was compared to the TSH response to TRH 24 h after oral administration of 1 mg DIMIT. Eight euthyroid subjects had normal baseline TSH levels of 1.5 +/- 0.2 (SE) microunit/ml that fell significantly to 0.7 +/- 0.2 microunit/ml 24 h after DIMIT (P less than 0.005). Their TSH increments after TRH fell from 15.3 +/- 2.8 to 6.7 +/- 1.6 microunit/ml 24 h after DIMIT (P less than 0.001). One subject with probable Hashimoto's thyroditis had an elevated TSH of 18 microunit/ml, with an exaggerated TSH response to TRH of 72 microunit/ml. His basal TSH fell to 7.6 and his TSH increment fell to 14.3 microunit/ml 24 h after DIMIT. The suppression of TSH was relatively prolonged. In four subjects, the TSH response to TRH was still blunted from 5-12 days after DIMIT. In one subject, the TSH increment returned to normal 15 days after DIMIT. DIMIT had no significant effect on PRL secretion. There was no evidence of toxicity in patients receiving DIMIT. DIMIT has effective thyromimetic activity in man, as shown by its significant and prolonged suppression of TSH secretion.

[Investigation on the synthesis of 125I labelled triiodothyronine and thyroxine of high specific radioactivity (author's transl)]

The reaction conditions of the monoiodination of L-diiodothyronine and L-triiodothyronine by nonradioactive iodide have been investigated by separation of the reaction mixture on sephadex G-25 with sodium hydroxide 10 mmol/l as eluent and quantitative iodine estimation in the eluate. When labelling with 125I was performed under optimal conditions, a good yield of chromatographically pure L-triiodothyronine or L-thyroxine was obtained with a specific radioactivity between 2 and 3 Ci/mg. The synthesized labelled hormones were tested by radioimmunoassay. They enable a detection of less than 2 pg T3 and less than 5 pg T4.

Isolation of desialylated and low-iodinated thyroglobulin in an experimental rat thyroid tumour

In an experimental rat thyroid tumour (Wollman line 1-1C2) thyroglobulin (TG) was isolated from soluble iodoproteins by ammonium sulphate fractionation and density gradient ultracentrifugation. The isolated TG was characterized by polyacrylamide gel electrophoresis, microimmunodiffusion, immunoelectrophoresis, analytical ultracentrifugation and by chemical determination of sialic acid and iodine content.

Tumour thyroglobulin has a sedimentation coefficient of 17.7S, which is similar to that of enzymatically desialylated thyroglobulin (18.4S) in the normal rat; tumour TG shows a slower electrophoretic mobility than native TG and similar to rat desialylated TG.

In double immunodiffusion tumour TG is shown to precipitate with an identity reaction with both native and desialylated rat TG; in immunoelectrophoresis it has a slower migration than native TG and is very close to that of enzymatically desialylated TG. Tumour TG has an iodine content of 0.02 % and a sialic content of 0.15 %. Chromatography of the 125I-labelled tumour TG revealed the presence of mono- and diiodothyrosines, a very small amount of triiodothyronine but no thyroxine.

These results suggest that tumour TG, isolated in the experimental rat thyroid tumour, previously shown not to incorporate sialic acid into thyroglobulin, has a different electrophoretic mobility from native TG but is very similar to desialylated rat TG and has a very low sialic acid and iodine content as well as a striking decrease in thyroxine.

Hydrolysis of 125-I-labelled thyroglobulin by pancreatin, pronase and pepsin

1. Pancreatin or Pronase hydrolysis of partially purified heat-denatured (125)I-labelled thyroglobulin does not release all the iodoamino acids from peptide linkage. 2. The addition of thyroidal proteases is essential to obtain maximum hydrolysis of thyroglobulin. 3. Pronase plus a fresh non-radioactive thyroid homogenate gives the best hydrolysis results, but peptide ;mapping' shows that about 10% of the radioactivity remains in the form of peptides. 4. These peptides have approximately the same R(F) as the iodotyrosines on one-dimensional chromatograms developed in butan-1-ol-2n-acetic acid (1:1, v/v). 5. Peptic hydrolysis of thyroglobulin releases virtually all of the iodothyronines but little of the iodotyrosines, in contrast with the action of pancreatin. 6. Hydrolysis of thyroglobulin with pepsin followed by Pronase plus a source of thyroidal proteases is satisfactory, but the results are not superior to those obtained by using Pronase plus a source of thyroidal proteases.