Efeito do excesso de tiroxina materna e pós-natal sobre o perfil proliferativo, angiogênico e de síntese das cartilagens de crescimento de ratos

• Ano de defesa: 2016
• Autor(a) principal: Lorena Gabriela Rocha Ribeiro
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Angiogênese; Proliferação; Matriz extracelular; Cartilagens de crescimento; Tiroxina; Rato; Ciência animal
• Link de acesso: http://hdl.handle.net/1843/SMOC-A9TJTN

Three different experiments were developed to evaluate in vivo effects of excess maternal and postnatal thyroxine in bone growth and growth cartilages. Sixteen female adult Wistar rats were used. The rats mated and, they were divided into two groups control and treated with eight animals each on the first day of gestation. L-thyroxine (50g/animal) was orally administered daily for female rats in the treated group and distilled water for the control group during pregnancy and lactation. Three offspring were separated from each rat, the first was euthanized at birth and the second at 20-days-old. The third offspring was weaned at 20-day-old and received a daily dose of L-thyroxine or distilled water, depending on the group, until 40 days old. The aim of the first study was to evaluate the effects of excess of maternal thyroxine on the growth cartilage of neonatal and weanling rats, analyzing the proliferative activity by CDC-47 expression and angiogenic profile by VEGF, Flk-1, Ang1, Ang2, and Tie2 expression. The second experiment evaluated the effects of excess of maternal thyroxine associated with postnatal hyperthyroidism on the proliferative and angiogenic profile of cartilage growth of 40-day-old rats. The third experiment evaluated the effects of excess of maternal and postnatal thyroxine on the synthesis activities of the cartilage matrix in neonatal, 20-day-old and 40-day-old rats based on histochemistry of the cartilage matrix by Safranin-O, alcian blue, and PAS stainings and expression of gene transcripts for Sox9, Runx2, aggrecan, Col I, Col II, Caspase3, alkaline phosphatase, Mmp2, Mmp9 and Bmp2 by real-time RT-PCR. Data were analyzed using Students t-test. Free T4 was significantly higher only in the treated female rats and in treated 40-day-old rats, but the height of the follicular epithelium of the thyroid offspring was significantly lower in the treated group regardless of age. The excess of maternal thyroxine significantly reduced the body weight and length of the femur in treated neonates and 20-day-old rats. The treated 40-day-old rats showed reduction in width of the bone shaft. There was a significant increase in thickness of the trabecular bone and a change in thickness of the zones of the growth plate in treated neonates and 20-day-old rats. In treated 40-day-old rats it was observed an altered morphology of the epiphyseal plate and reduction in the thickness of the articular cartilage. Furthermore, excessive maternal thyroxine caused reduction in both cell proliferation and VEGF expression in the growth cartilage in all offspring ages. There was also a decrease in immunohistochemical expression of Tie2 in the cartilaginous epiphysis of the newborns and Flk-1 in the articular cartilage of 20-day-old rats and significant reduction in gene transcripts for Ang1 in articular cartilage of 40-day-old rats. Histomorphometry of cartilage growth plates showed a lower percentage of chondrocytes/area in the cartilaginous epiphysis of newborns and in the articular cartilage of treated 40-day-old rats. Excess of maternal and postnatal thyroxine was also associated to reduction of intracellular glycogen and glycosaminoglycans and non-sulfated proteoglycans in the cartilage growth and gene transcripts for Sox9, Mmp2, Mmp9, Col II, and Bmp2 in all treated offspring. It is concluded that the reduced endochondral bone growth caused by excessive maternal thyroxine is associated with reduction in proliferation rate and the VEGF expression in the growth cartilage of in all ages, Flk-1 and Tie2 receptors in the growth cartilages in neonates and at 20-day-old and reduction of Ang1 expression in growth plate of 40-day-old rats. Moreover, excess of maternal thyroxine influences the ECM composition of growth cartilages, to reduce the amount of proteoglycans, glycosaminoglycans, collagens proteins and metalloproteinases, and gene transcripts for Sox9, Mmp2, Mmp9, Col II, and Bmp2 in all treated offspring, and changed differently with the age, the expression of gene transcripts as Runx2, Aggrecan, Col I, and Caspase3.