Uptake of injected 125I-ricin by rat liver in vivo. Subcellular distribution and characterization of the internalized ligand.

Subcellular-fractionation techniques were used to characterize the endocytic pathway followed by ricin in rat liver in vivo and tentatively identify the site(s) at which the ricin interchain disulphide bridge is split. After injection of 125I-ricin, hepatic uptake of radioactivity was maximum at 30 min (40% of injected dose). At 5 min, about 80% of the radioactivity in the homogenate was recovered in the microsomal (P) fraction, but later on the recovery of the radioactivity in the mitochondrial-lysosomal (ML) fractions progressively increased (50% at 30 min) at the expense of that in the P fraction. Subfractionation of the P and ML fractions on analytical sucrose-density gradients revealed a time-dependent translocation of the radioactivity from low- to high-density endocytic structures, with median relative densities at 5 and 60 min of about 1.15 and 1.16 (P fraction) and 1.19 and 1.22 (ML fraction) respectively. The late distribution of the radioactivity in the ML fraction was similar to that of the lysosomal marker acid phosphatase. Studies with co-injected lactose and mannan showed that ricin was internalized mainly via the mannose receptor. In the presence of mannan, the late recovery of radioactivity in the ML fraction was decreased, and the distribution of the radioactivity associated with the P fraction was shifted toward lower densities (median relative density 1.13), indicating a different pathway of endocytosis. Analysis of the radioactivity associated with the ML and S fractions by SDS/PAGE revealed a time-dependent increase in the amount of intact A- and B-chains and low-molecular-mass products. When ML fractions containing partially processed ricin were incubated at 37 degrees C at pH 5 or at pH 7.2 in the presence of ATP, only low-molecular-mass products were generated. We conclude that internalized ricin associates with endocytic structures whose size and density of equilibration increase with time, and that, although detectable in these structures, reduction of the ricin interchain disulphide bridge occurs to a large extent in the cytosol.

Iodinated compounds and thyroxine binding to albumin in human breast milk.

Mature human milk samples from young healthy women on an equilibrated diet contained a mean of 81 ng/ml total iodine. Iodide represented a mean of 77% of the total iodine. Of the 22 ng/ml organic iodine, there was about 1 ng thyroxine and triiodothyronine and, after pepsin hydrolysis, up to 40% of organic iodine in monoiodotyrosine form. By electrophoresis, after incubation with radioactive thyroid hormone, we found an absence of binding on thyroxine-binding globulin, but thyroxine and triiodothyronine were bound to albumin with a maximal capacity 50 times higher than in human serum. All these differences did not favor transport of iodinated compounds from maternal serum to milk. In conclusion, milk iodide was taken up by newborn thyroid to make thyroid hormones.

Serum and urine thyroid hormone levels in healthy preterm and small for date infants on the first and fifth day of life.

Serum levels of thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3), thyroxine binding globulin (TBG) and thyrotropin (TSH) were determined on the first and the fifth day of life in three groups of healthy premature infants (Group I: 26-32 weeks of gestation, Group II: 33-36 weeks, and Group III: full term but small for date). Urine T4 and T3 were also determined. T4 and T3 serum concentrations increased from Group I to Group III, but were similar on day 1 and 5 in each group. rT3 was higher in Group I on day 1. The low concentrations of T4 were not dependent on the TBG levels. TSH levels were higher on day 1 than on day 5, but the hormonal feed back mechanism was not effective on day 1. Hormonal urine excretions were similar on day 1 and 5, except a higher T4 excretion in Group III on day 5. These results were related to the maturation steps in healthy premature infants where gestational age seemed more important than body weight in respect to some thyroid hormone parameters.

Iodine and thyroid hormone levels in serum and urine of full term newborn infants.

In 19 full term newborn boys serum levels of thyroxine (T4), triiodothyronine (T3), thyrotropin (TSH) and thyroxine binding globulin (TBG) were determined on the first and fifth day of life using radioimmunoassays. T4 and T3 were also measured in 24-h urine collections as well as total iodine in urine and in breast milk. A significant decrease occurred in serum concentrations of T4, T3 and TSH from day 1 to 5 while TBG remained unchanged. At the same time an increase of total iodine (1.7 to 4.1 micrograms), T4 (35.7 to 141 ng) and T3 (44.9 to 69.9 ng) was observed in the 24-h urine assay from day 1 to 5. The hormone concentration in urine was higher in the first urine excretion than in the total first day collection. The 24-h urine assay of the fifth day showed results which were similar to the T3 measurements in the 16th to 52nd day urine analysis in neonates of a control group. Breast milk iodine intake of newborn infants was similar to the excreted urine iodine concentration. Breast milk therefore provides an adequate intake of total iodine in euthyroid neonates.

[Thyroid function in a child with nephrotic syndrome evolving to renal failure (author's transl)]. / Fonction thyroïdienne d'un enfant atteint de néphrose evoluant vers l'insuffisance rénale.

The case of a 6 1/2 year old boy with a severe nephrotic syndrome unresponsive to corticotherapy is described; hemodialysis was necessary one year after detection of the nephrosis. Because of clinical symptoms of hypothyroidism, thyroid function was evaluated during the different steps of nephrosis and hemodialysis. Total protein and iodine, albumin, thyroxine binding protein, free and total thyroxine, triiodothyronine and thyreostimuline determinations were performed in serum and/or urine. Thyroid hormone concentrations were very low during the nephrotic syndrome: they increased slightly when hemodialysis was started. Thyreostimuline values did not seem dependent on hormone concentrations. Thyroxine excretion was very much increased when compared to that of normal children, a finding present at all times.

[Triiodothyronine radioimmunoassay. Comparison of the different factors between two technics (author's transl)]. / Dosage radio-immunologique de la triiodothyronine. Comparaison des divers paramètres entre deux méthodes.

Triiodothyronine concentration was determined in human serum and in thyroid extracts by two radioimmunoassay technics. Both antibodies, radioactive T3, stable T3, protein-binding-hormone inhibitors, methods used to separate the free from the bound fractions were different. Each factor from a method was substituted to the homologue of the other method. The results occasionally showed a variation of 32 p. cent in the first method and 50 p. cent in the second one. However the results gave a correct interpretation of the triiodothyronine values measured in human serum and in thyroid extracts.

The iodine content of amniotic fluid and placental transfer of iodinated drugs.

Determinations of total iodine content, levels of thyroxine (T4) and triiodothyronine (T3), and protein concentrations were made on amniotic fluid. A total of 218 samples obtained at various stages of pregnancy, from both normal and pathological pregnancies, were studied. Normal values for the iodine and hormone concentrations are presented. Several amniotic fluid samples showed greatly elevated iodine levels, thought to be the result of maternal iodine intake. This study demonstrated that such elevated levels can be produced by urography with an iodinated medium, by thyroid extract therapy, and by vaginal therapy with an iodinated agent. Levels of T4 and T3 in amniotic fluid decreased slightly from the second to the third trimester and were unrelated to the total iodine levels. Despite reports in the literature of fetal hypothyroidism produced by amniography with a fat-soluble medium, no thyroid defect was observed in this series in the presence of elevated amniotic fluid iodine levels or when a water-soluble iodinated medium was used for amniography.

[Levels of triiodothyronine and reverse triiodothyronine in the thyroid glands of man and swine at different stages of development]. / Teneurs en triiodothyronine et triiodothyronine inverse de thyroïdes d'Hommes et de porcs à divers stades du développement.

3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (rT3) were measured by radioimmunoassay in saline extracts of neonates and human adult thyroid tissues and of fetuses, Piglets and adult Swine thyroid tissues. In all these extracts, T3 content was higher than rT3 content whatever the period of development. Both triiodoamino acids represent a small percentage of the iodinated protein in thyroid tissues.