Effects of thyroidectomy and repeated administration of L-thyroxine on the dehydrogenases of the pentose-phosphate pathway of rat erythrocytes

The temporal variations in the activity of erythrocyte glucose 6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6-PGD) were studied on thyroidectomized rats (Group I) and upon administration of L-thyroxine to intact rats (Group II). For experiments on Group I, three periods of observation after total thyroidectomy were selected: 1st, 4th and 6th weeks; Group II was subdivided in two subgroups (a and b): (a) the administration of L-thyroxine was made by oral route, ad-libitum (250 ~g/l00 ml water) and the animals were sacrificed from the 4th to the 10th weeks of experiment; (b) The intoxication was produced by repeated intraperitoneal injections in normal rats of 5OjLg/100 g weight, 4 days/week, for a minimum of one week and maximum of four weeks. No significant differences were observed, in each period and experimental conditions, for the G6PD activities; meanwhile, in two intermediate periods of subgroup (a) the 6-PGD activity was increased. The above results have been discussed with reference to some current mechanism, proposed for the action of thyroid hormones on human red cells, suggesting that the direct oxidative pathway of G6P metabolism on rat erythrocytes is less sensitive to the effects of those hormones.Foi estudada a variação temporal da actividade das desidrogenases da glicose 6-fosfato (DG6P) e 6-fosfogliconato (D6-PG) nos eritrócitos de ratos tiroidectomizados (grupo I) ou tratados corn L-tiroxina (grupo II). Os animais do grupo I foram observados 1, 4 e 6 semanas apos a tiroidectomia cirúrgica. No grupo II consideram-se dois subgrupos (a e b): (a) incluía animais a que se administrou L-tiroxina por via oral (na agua ad libitum, 250 ~g/100 ml), decorrendo a observação entre a 4a e a 10•a semanas de tratamento; em (b) estudou-se o efeito de intoxicação rápida corn L-tiroxina (50 ~tg/l00 g peso), administrada 4 dias/semana por via intraperitoneal, durante as primeiras 4 semanas de tratamento. Para qualquer dos lotes e situações estudadas não foram verificadas diferenças significativas na actividade da DG6P, relativamente aos valores dos controlos normais. Apenas em dois períodos intervalados do subgrupo (a) houve aumento significativo na D6-PG, sendo os valores das restantes fases e situações sobreponíveis aos controlos. Estes resultados sugerem que a via das fosfopentoses nos eritrócitos de rato e menos sensível as hormonas tiroideias que a dos eritrócitos humanos, em situação equivalente de disfunção tiroideia.Este trabalho foi parcialrnente subsidiado pelo INIC (MbL2) e Servico de Ciência da Fundação Calouste Gulben kian