Efeito da associação hipertireoidismo-castração no osso de ratas adultas

Abstract

The relationship between thyroid, gonads and bone morphology was investigated in 5 month-old Wistar rats, castrated and kept in hyperthyroid or euthyroid state for periods of 30, 60 and 90 days. A non-castrated control group was maintained in the same condition. At the end of each period, plasma concentrations of free T4, progesterone and estradiol were measured. The bones from each group were submitted to radiological and histological analysis. Hyperthyroidism in intact rats caused variation in bone morphology throughout the experiment, leading to loss of trabecular bone tissue at day 60, due to increased bone resorption. At day 90 there was no bone loss, because the increase in bone resorption was accompanied by higher bone apposition. In castrated euthyroid rats reduction in progesterone levels inhibited the bone apposition, causing a slight loss of trabecular bone tissue in vertebrae and alveolar bone at day 30, which was intensified at days 60 and 90, affecting cortical bone tissue. The administration of thyroxine to castrated rats reversed osteopenia at days 30 and 60, which did not occur at day 90 when bone loss was more extensive. In conclusion, hypoprogesteronism and hypoestrogenism alter bone metabolism and the bone response to hyperthyroidism depends on the plasma profile of sex steroids, time of exposure and bone tissue configuration.

Effects of excess maternal thyroxin on the bones of rat offspring from birth to the post-weaning period

“…This finding was described in adults rats with hyperthyroidism (14). According to some researchers, thyroid hormones stimulate osteoblast synthesis and, thus, the voluminous aspect observed in the osteoblasts of offspring of rats treated with thyroxin may be a reflex of this action (30,31).…”

“…It is known that bone responses related to experimental hyperthyroidism depend on the dose of thyroxin and the course of the disease (14). Therefore, this result is probably due to the fact that these animals were affected by excess maternal thyroid hormones throughout pregnancy and lactation, once the passage of these hormones to the placenta (16) and milk (9) has been proven, with exposure of the offspring to the interference caused by these hormones.…”

“…The control group received 5 mL of distilled water as a placebo treatment. In both groups, animals were treated daily at the same time of the day using an orogastric tube, according to protocols determined elsewhere (14,15). Before mating, five rats of each group were anesthetized (2.5% Thionembuthal), followed by intracardiac puncture for serum samples that were used in free T4 determination in commercial chemiluminescence kits (Immulite Free T4, Siemens Medical Solutions Diagnostics, Malvern, PA, USA).…”

Histomorfometria óssea de ratas hipertireóideas lactantes e não-lactantes

“…Já foi estudado o efeito do hipertireoidismo associado à osteopenia pós-castração em modelos animais (7,8) e em associação à osteopenia pós-menopausa (9,10). Os resultados destes estudos permitiram concluir que o hipertireoidismo deve ser considerado fator de risco para a osteoporose causada pela deficiência dos hormônios sexuais (9,10), e que os efeitos da administração de tiroxina são dose e tempo dependentes, variando entre os diferentes sítios do esqueleto (8).…”

“…Os resultados destes estudos permitiram concluir que o hipertireoidismo deve ser considerado fator de risco para a osteoporose causada pela deficiência dos hormônios sexuais (9,10), e que os efeitos da administração de tiroxina são dose e tempo dependentes, variando entre os diferentes sítios do esqueleto (8). Mas a literatura carece de informações sobre o efeito da associação hipertireoidismo-lactação no tecido ósseo.…”