Retina Maturation Following Administration of Thyroxine in Developing Rats: Effects on Polyamine Metabolism and Glutamate Decarboxylase

Abstract

The effects of s.c. daily treatment with thyroxine on cell proliferation, differentiation, polyamines, and GABA metabolism in the rat retina were studied during the first 20 postnatal days. The retinal layers of the treated rats displayed an enhanced cell differentiation which reached its maximum 9-12 days from birth; but this effect stopped very quickly and was finished by the 20th postnatal day. Primarily there was an increase in ornithine decarboxylase [ODC] activity which was accompanied by an increase in putrescine, spermidine and spermine levels. S-Adenosylmethionine decarboxylase was induced later than ODC; corresponding with the enhanced synaptogenesis, glutamate decarboxylase increased 15-fold between the 4th and 15th days. Thyroxine may exert some of its effects by inducing the enzymes which regulate polyamine metabolism and synaptogenesis.