Melatonin increases survival of HaCaT keratinocytes by suppressing UV-induced apoptosis.

Melatonin is a potent antioxidant and direct radical scavenger. As keratinocytes represent the major population in the skin and UV light causes damage to these cells, the possible protective effects of melatonin against UV-induced cell damage in HaCaT keratinocytes were investigated in vitro. Cells were preincubated with melatonin at graded concentrations from 10(-9) to 10(-3) m for 30 min prior to UV irradiation at doses of 25 and 50 mJ/cm2. Biological markers of cellular viability such as DNA synthesis and colony-forming efficiency as well as molecular markers of apoptosis were measured. DNA synthesis was determined by [3H]-thymidine incorporation into insoluble cellular fraction, clonogenicity through plating efficiency experiments and apoptosis by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. DNA synthesis experiments showed a strong protective effect by preincubation with melatonin at concentrations of 10(-4) m (P < 0.01) and 10(-3) m (P < 0.001). Additional postirradiation treatment with melatonin showed no increase in the pre-UV incubation protective effect. These results indicate that preincubation is a requirement for melatonin to exert its protective effects. The mechanism of melatonin's protective effect (10(-6) to 10(-3) m) includes inhibition of apoptosis as measured by TUNEL assay. Moreover, the biological significance of these effects is supported by clonogenic studies showing a significantly higher number of colonies in cultures treated with melatonin compared to controls. Thus, pretreatment with melatonin led to strong protection against UVB-induced damage in keratinocytes.

The influence of maternal hypothyroidism and radioactive iodine on rat embryonal development: thyroid C-cells.

There have been no works devoted to the study of the influence of (131)I and maternal (131)I-induced hypothyroidism on the state of the C-cells in the thyroid gland of the developing embryos. A study was made on the effect of a dose of 150 microCi (131)I (0.5 Gy) leading to hypothyroidism in rats, on 35 mother rats and 168 newborn pups. The mother rats were divided into control and four treated groups which were injected with (131)I before pregnancy, on gestation days 5, 10, and 16, respectively. Immunohistochemically, the thyroid gland was examined for calcitonin-positive cells. Maternal hypothyroidism induced by (131)I leads to the development of hyperplasia and hyperthrophy of calcitonin-positive cells in the pups at the time of birth. The discovery of separate C-cells in the peripheral zone of the thyroid lobe may be evidence of an unbalance in the development of the medial and lateral source of the thyroid. There is a verifiable increase in the quantity of C-cells per 1 mm(2) field of the localization in the central zone of the gestation days 10 and 16 groups. This might be a compensatory mechanism for regulating the activity of the thyroid gland under induced hypothyroidism. Thus, in cases when there is a breakdown in the normal external regulation of the embryonic morphogenesis, a reduction in the level of maternal thyroid hormones and also direct exposure to (131)I, there is also a change in the foetus' internal regulatory systems. A change in C-cell system could lead to the appearance of endocrinological disorders later in life.

[Proliferating cell nuclear antigen of the rat thyroid gland before and after birth]. / Iadernyi antigen kletochnoi proliferatsii shchitovidnoi zhelezy krys do i posle rozdeniia.

We were studied the proliferative activity of the thyroid gland's cells of embryo and adult Wistar rats due to using the antiserum against the cell nuclear antigen (PCNA). The 100% of cells in thyroid's embryo was a positive on the 16th, 17th, 18th stages of the embryonic development (stages by Kornegy). The percent of PCNA-positive cells considerably increased to 67% on the 19th stage. This fact the 20th and 21th stages of prenatal development relatively the previous stage coordinate with starting of the thyroid hormones in fetal thyroid gland and the first follicles formation. The small increasing of number of PCNA-positive cells detected on the 20th and 21th stages of prenatal development relatively the previous stage. Considerable elevation of the proliferating cells to 75% immediately before the birth (22th stage). An infant rats had have the 39% of proliferating cells. The 51% cells divided on the 5th day of postnatal development. Considerable decreased of the cell's division was occurred until the postnatal day 60. Using of the PCNA antiserum allowed to study cell proliferation in thyroid gland during pre- and postnatal rat development.

Immunohistochemical study of fibronectin and thyroglobulin in the thyroid gland of female rats after exposure to radioactive iodine.

The aim of this work was to study the effect of a dose of 150 microCi 131I on the barrier properties of the thyroid epithelium in pregnant female rats. Thirty-five female Wistar rats were divided into a control and four experimental groups (each distinguished by the time of 131I injection: group I--no less then 12 days before mating; groups II, III, and IV--on 5th, 10th, and 16th days of gestation, respectively). The thyroid glands were fixed in Bouin's fluid, embedded in paraffin, and stained immunohistochemically for thyroglobulin and fibronectin. In group IV the appearance of follicles with fibronectin-positive colloid demonstrates the penetration of blood plasma into the follicular lumen. There are more fibronectin positive follicles in group III. Regardless of the nature of the follicles' contents, numerous thyrocytes with an intensive fibronectin positive reaction begin to appear in the follicles. In group II the number of fibronectin positive follicles and thyrocytes is clearly reduced, and in group I only a few remain. In group IV there is a noticeable reduction in the quantity of colloid inside the follicles and often an absence of any thyroglobulin positive reaction. There are thyrocytes in which thyroglobulin positive granules localized in the basal zone. There is thyroglobulin positive staining in the stroma and blood vessels. In group II thyroglobulin is no longer found in the stroma. Small doses of 131I provoke a serious breakdown in the thyroid epithelium's barrier properties, although these changes are of a transient nature. The central zone of the thyroid gland reacts more actively and dynamically to exposure to radioactive iodine than the peripheral zone.

Some morphological changes in the rat thyroid gland during experimental hyperphenylalaninemia.

BACKGROUND: Little is known about the effect of phenylketonuria on the thyroid gland. In the present study, this problem was investigated by using a defined experimental model of hyperphenylalaninemia (HPA). METHODS: The experimental group was subjected to an HPA regimen (Matsuo and Hommes, 1988. Neurochem. Res., 13:867-870) from the 5th day of postnatal development. The pups were decapitated on the 7th, 14th, 21st, 28th, and 35th days. The thyroid glands were fixed in Bouin's fluid and routinely embedded in paraffin. The staining techniques used were Mallory-Slinchenko's method, toluidin blue, silver impregnation of the basement membrane, immunohistochemical staining of the proliferating cell nuclear antigen (PCNA), and neuron-specific enolase (NSE). RESULTS: The size of the follicles was less than that in the control group. There were no substantial changes in the epitheliomer structures. In almost all of the treated groups, a reduction in the number of PCNA+, NSE+, and mast cells was observed until the 28th day. On the 28th day of HPA, the level of mast cell degranulation was higher (61%) than that in the control group. On the 35th day, these parameters began to reach normal levels. From the 28th day, degenerative changes in the thyroid glands of treated animals were observed in the NSE+ cells. CONCLUSIONS: The HPA condition mainly has an influence on the number and structure of the NSE+ cells of the thyroid gland. One may assume that under HPA the increase in mast cell degranulation plays a significant role in the normalisation of the parameter of the thyroid gland.