THE EFFECTS OF LOCAL HORMONAL ORGAN TRANSPLANTS AND STEROID HORMONE IMPLANTS UPON THE THYMUS GLAND*

Gender-related Histological Changes in the Thymus Gland After Pinealectomy and Short-term Melatonin Treatment in Rats

Objectives

The aim of this study was to investigate the effects of pinealectomy and melatonin treatment on the rat thymus gland characteristics, taking into consideration possible gender differences.

Materials and methods

Thirty adult Wistar rats of both sexes were divided into three groups. Group C and group PX served as control groups and included sham-pinealectomized and pinealectomized animals that were treated with 10% ethanol solution (0,1ml/daily, subcutaneous). Animals from third group (group PXM) underwent pinealectomy and seven days after surgery started receiving melatonin dissolved in 10% ethanol solution (3mg/kg/daily, subcutaneous). All animals were treated for 4 weeks.

Results

Volume density of the thymus cortex showed statistically significant (p<0,05) decrease while the volume density of the thymus medulla was increased in the pinealectomized compared to the sham-pinealectomized female rats. Numerical density of macrophages as well as the distribution of blood vessels showed no gender differences. The numerical density of lymphocytes was statistically significantly decreased in female in comparison to the male pinealectomized rats. Melatonin treatment was proved to cause reverse effects in the sense that the results from the melatonin treated group corresponded to the results obtained from the control group of animals.

Conclusion

The results of this study suggest that the pinealectomy causes gender-related changes in the rat thymus. Short-term melatonin treatment showed reverse effect, equally in both sexes.

Contextual modulation of social and endocrine correlates of fitness: insights from the life history of a sex changing fish

Steroid hormones are critical regulators of reproductive life history, and the steroid sensitive traits (morphology, behavior, physiology) associated with particular life history stages can have substantial fitness consequences for an organism. Hormones, behavior and fitness are reciprocally associated and can be used in an integrative fashion to understand how the environment impacts organismal function. To address the fitness component, we highlight the importance of using reliable proxies of reproductive success when studying proximate regulation of reproductive phenotypes. To understand the mechanisms by which the endocrine system regulates phenotype, we discuss the use of particular endocrine proxies and the need for appropriate functional interpretation of each. Lastly, in any experimental paradigm, the responses of animals vary based on the subtle differences in environmental and social context and this must also be considered. We explore these different levels of analyses by focusing on the fascinating life history transitions exhibited by the bi-directionally hermaphroditic fish, Lythrypnus dalli. Sex changing fish are excellent models for providing a deeper understanding of the fitness consequences associated with behavioral and endocrine variation. We close by proposing that local regulation of steroids is one potential mechanism that allows for the expression of novel phenotypes that can be characteristic of specific life history stages. A comparative species approach will facilitate progress in understanding the diversity of mechanisms underlying the contextual regulation of phenotypes and their associated fitness correlates.

Bone-cell changes in estrogen-induced bone-mass increase in mice: dissociation of osteoclasts from bone surfaces

Early studies in certain avian and mammalian species have described estrogen-associated bone-cell changes, which were based on bone cells that were neither quantified nor identified histochemically (osteoclasts). In the experiments described here, weanling female mice were given a pharmacological dose of 17 beta-estradiol benzoate (1 mg/week) for 1 and 4 weeks, and changes in osteoclasts and osteoblasts were assessed in tibial metaphyses and diaphyses. In the proximal metaphysis, the number of osteoclasts/mm surface length was significantly reduced by estrogen at 1 week (43%) and 4 weeks (64%), which was accompanied by significant increases in the number of osteoclasts in the marrow space not in contact with bone surfaces (no./mm2: 382% and 999%, respectively). These increases, along with observations of decreased osteoclast size (19%), of changes in osteoclast morphology, and of numerous acid-phosphatase-positive fragments in the marrow space, suggest that estrogen treatment causes the dissociation and disintegration, and thus decreased activity, of osteoclasts. The above changes were accompanied by more than 48% increases in the number of trabecular osteoblasts. In the diaphysis, the number of endosteal osteoclasts was significantly decreased by estrogen at 1 week (32%), but was not significantly changed at 4 weeks. These changes were attended by significant increases in the number of osteoclasts in the marrow space not in contact with bone surfaces (no./mm2: 393% at 1 week and 342% at 4 weeks). The number of endosteal osteoblasts was also increased by estrogen at 1 week (132%), and so was the size of endosteal osteoblasts (39% at 1 week and 81% at 4 weeks). Comparable results were obtained when a lower dose of 17 beta-estradiol benzoate (20 micrograms/week) was given to ovariectomized mice. The increase in bone mass and its associated cell changes following estrogen treatment were also found in athymic nude mice, suggesting that these bone/bone cell changes are independent of the thymus.

The thymus in congenital heart disease

Some cases of thymus developmental defects (DiGeorge's syndrome) are associated with the development of defects of the heart and great vessels. To see if anomalies of the heart are also associated with anomalies of the thymus, a material of thymus tissue removed during operation for congenital heart disease was compared with thymus tissue from a forensic autopsy material representing the same age group, but without cardiac lesions. Among 27 cases of congenital heart disease, occurrence in the thymus of solid epithelial cords were seen in 6 and cyst- or duct-like structures were found in 7. Among 47 forensic cases, 1 showed cords and another showed duct-like structures. Of these, one had congenital anomalies in the form of hepatic hamartomas and nesidioblastosis, whereas the other had died from morbilli, raising the possibility of congenital immune deficiency. Anyhow, a striking occurrence of minor morphological deviations in the structure of the thymus was found in children with congenital heart disease. Such material therefore may be less suitable for studying the morphology and biology of the normal thymus gland.

Short-term and long-term effects of estrogen on lymphoid tissues and lymphoid cells with some remarks on the significance for carcinogenesis

Estrogens have long been thought to play a role in regulating the immune system. The difference in some types of immune responses between males and females is well-known, as is the pronounced thymic involution induced by exogenous estrogens. Estrogens stimulate some aspects of macrophage activity and, depending on dose and mitogen, inhibit or stimulate lymphocyte proliferative response in vitro. Another example is the estrogen effect on the delayed type hypersensitivity response. A broad review is given of such estrogen effects on lymphoid tissue and immune response. Most of the studies published so far are phenomenological. However, the recent description of estrogen receptors in the thymus and in some lymphocyte subpopulations, as well as a deeper understanding of regulating factors in the immune system, open the possibility of a more detailed understanding of the estrogen mechanism of interference. Estrogen effects in adults are reversible. After treating neonatal mice with the synthetic estrogen diethylstilbestrol (DES), disturbances are induced in lymphocyte populations and lymphocyte functions which are permanent and irreversible. Lymphocytes from adult, neonatally DES-treated female mice have a reduced mitogen response to ConA and LPS (T and B cell mitogen) and the delayed type hypersensitivity response is depressed. A detailed analysis demonstrated a decreased T helper cell population. The activity of Natural Killer cells is permanently reduced and this functional impairment is related to a decreased number of these cells, in turn determined at the bone marrow level. The same animals have an increased sensitivity to chemical carcinogens (methylcholanthrene) and they spontaneously develop epithelial changes in the uterine cervix which morphologically are similar to adenocarcinoma. The association between estrogen-associated malignancy and estrogen effects in lymphocyte functions deserves further study.

Effect of gonadectomy and oestrogen administration on the response of lymph-node post-capillary venules to infection with Toxoplasma gondii

The effects of gonadectomy and oestrogen administration on the response of lymph-node post-capillary venules to infection with Toxoplasma gondii have been studied in mice. The endothelial cells of the post-capillary venules were significantly higher in the female than in the male controls. Oophorectomy had no significant effect while orchidectomy increased the height of the cells. However, hexoestrol administration resulted in a rise of the height to maximum levels in the female and in the male gonadectomised animals. The endothelial cells of male and female control and gonadectomised mice were higher after infection with Toxoplasma while in the infected hexoestrol-treated animals, lower cells were seen. The number of lymphocytes passing through the post-capillary venule wall was increased by gonadectomy and decreased by hexoestrol administration in both sexes. The same pattern was seen in the infected groups. The influence of sex hormones on the post-capillary venules and its possible contribution to the differences seen in the immune response between the two sexes is discussed.

Fine structure of epithelial thymus cysts in dogs

Epithelial thymus cysts in dogs were investigated by electron microscopy. Epithelial cells from one and the same cyst showed morphological differences. Regular columnar or cuboidal epithelial cells predominated. These had an elongated nucleus, poor in chromatin but with abundant cytoplasmic organelles, e.g. mitochondria, and a Golgi region with sacs and vacuoles. Other cells possesed a narrower, indented nucleus richer in chromatin, a cytoplasm with numerous tonofilaments and cell membranes showing interdigitations with other cell membranes. Some cysts displayed a pseudostratified epithelium. In these cells the same organelles were present as were seen in the cuboidal cells. Abundant cilia and microvilli were present in the lumenal cells. All these different morphological characteristics were considered to be different functional aspects of the same kind of thymus epithelial cell. The cells had a structure indicating a secretory-activity.

Orchidectomy and the immune response. I. Effect of orchidectomy on lymphoid tissues of mice

The effects of pre- and postpuberal orchidectomy on the lymphoid tissues of mice have been studied. Prepuberal orchidectomy delayed the normal rate of thymic involution and caused relative hypertrophy of the thymus which was maximal 1 month after surgery. There was also enlargement of the peripheral lymph nodes to reach a sustained maximum by 6 weeks and also an increase of spleen size. Histological examination of the enlarged thymus showed widening of the cortex and medulla with increased cell density. The enlarged peripheral lymph nodes showed widening of the paracortical area which is thymus dependent. Synchronous thymectomy and orchidectomy prevented the lymph node enlargement that follows orchidectomy alone, but it did not affect the increase of spleen size until 3 months after surgery. After postpuberal orchidectomy thymic size increased to a maximum at 1 month and the increase of peripheral lymph node mass and spleen mass was less than the changes following prepuberal surgery ; only 3 months after operation was the lymph node mass of orchidectomized mice significantly greater than controls and changes in spleen mass were only apparent after correction for changes in body mass.