Quantitative cytoarchitecture of the liver of the shrew Crocidura russula (fam. Soricidae). Ultrastructural and morphometric comparison with rat liver.

The livers of two groups of the shrew Crocidura russula, kept under standardized physiological conditions, were investigated with electron microscopy and morphometry. The adaptations to the extremely high basal metabolism of these small mammals are reflected in the architectural characteristics of the hapatocytes, which, in comparison with those of the rat, show a smaller cell volume of the mononuclear hepatocytes (3,800 micrometers3), and increased number of cells per cm3 of liver tissue (250 X 10(6)), and a relative larger liver volume (4.85 ml per 100 g body weight). The ground substance is reduced by the other cell compartments to 4%. The volume density of the glycogen differs from 5-15% and the variation of the SER is from 10-20%. The RER (constant at about 35%) and the mitochondria (around 30%) form the main part of the cytoplasm of the hepatocyte. The mean volume of individual mitochondria amounts to 2.5 micrometers3. The chrondriome in the cell shows important numerical-volumetrical transformations, i.e, an increase in the individual volume of mitochondria correlating with a decrease in the number of the mitochondria per volume unit and vice versa. The adaptations to the high basal metabolism and the special conditions of life (short phases of activity, long resting times) are considered in relation to the possible functional activity of the megamitochondria.

Iodine, thyroxine (T4), triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (T2) in normal human thyroids. Effect of excessive iodine exposure.

20 Normal glands obtained from euthyroid subjects at autopsy were analysed for total iodine (Tl), PBl, L-thyroxine (T4), 3,3',5-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (T2) after pronase hydrolysis. The mean Tl was 325.1+-47.2 micrograms/g wet tissue, giving a total iodine per gland of 10.01 mg. Pretreatment of iodine containing X-ray drugs in 8 patients did not significantly affect these results with the exception of Lipiodol. The mean T4, T3 and T2 values were 93.0+-23.1 micrograms/g, 5.25+-0.99 micrograms/g, 5.54+-1.05 micrograms/g and 0.60+-1.19 micrograms/g, respectively. In contrast to goitrous tissue, normal thyroid tissue showed no dependence of the T4/T3 ratio on the Tl. Compared with goitrous tissue PBI consisted of much more T4-l in normal tissue. The corresponding values were 47.7+-11.8% and 12.7+-3.4%, respectively. A positive relationship was found between Tl and T4, T3, rT3 but not with T2. The rT3 concentration corresponds to that of T3 in a remarkable way. The ratios of T3 or rT3 were similar, suggesting that thyroidal T3 and rT3 production is a random process. T2 represents only 0.73% of T4-l. Our results in normal thyroid tissue clearly show that the difference in iodine concentrations is only one factor among others in comparison to goitrous tissue.

The thyroidal production of reverse triiodothyronine in autonomous adenoma.

The ratios of reverse triiodothyronine (rT3) to triiodothyronine (T3) concentrations were similar (0.89 +/- 0.09) in twenty-three autonomous thyroid nodules (fourteen decompensated, nine compensated) and paranodular tissues (0.82 +/- 0.08), whereas the serum ratio was significantly lower (0.098 +/- 0.014). This is compatible with the hypothesis that thyroidal rT3 and T3 production from mono- and diiodotyrosine may be a random process in contrast to non-random extrathyroidal rT3 and T3 formation.

The thyroidal T4/T3 ratio and its regulation in non-toxic goitre.

In 35 patients with non-toxic goitre, surgically resected thyroid tissue was hydrolyzed with Pronase under anaerobic conditions in the presence of methylmercaptoimidazole. Total iodine, PBI, L-thyroxine (T4-RIA and T4 (D)) as well as triiodothyronine (T3-RIA) were determined in the tissue hydrolysates. The data obtained were compared with T4/T3 ratios in the serum, TRH test and thyroidal 131I uptake before operation. The total iodine, amounted to 112.6 +/- 14.6 ug/g tissue. The T4/T3 ratio was 11.37 +/- 1.80. Using this procedure of tissue hydrolysis and RIA assays for iodothyronines, the yield for T4 and T3 is considerably higher than the one obtained with previous methods. As in animal experiments, evidence was given for human goitre that T3 is predominantly produced first in the case of decreased T4 production. Second in the case of iodine deficiency, and third in cases of increased TSH response after TRH. Patients with a large amount of iodine and T4 in their thyroids have a much smaller increase in serum TSH after TRH than do subjects with a much lower thyroidal T4 concentration. This occurs even though the thyroid hormone levels in serum in these groups are not different. No correlation between thyroidal T4/T3 ratio and serum T4/T3 ration could be demonstrated even under extreme conditions. This finding favors the assumption of a predominant extrathyroidal regulation for T4/T3 ratio in serum.