THE UPTAKE OF S35-L-METHIONINE INTO THE BRAIN OF EUTHYROID AND HYPERTHYROID NEONATAL RATS

Abstract

Five day old male suckling rats were made hyperthyroid by the intraperitoneal administration of 20 [mu]g of L-thyroxine daily for 5 days. On the tenth day of life, L-methionine S35 (2 [mu]c [microcurie]/2 gm body weight) was given intravenously to both the hyperthyroid rat and its euthyroid control. Ten minutes, 60 minutes, and 22 hours later, the radioactivity of the whole brain and its bound protein fraction was assayed in terms of the per cent of the administered dose of S35/mg of tissue. It was found that in the 10 and 60 minute hyperthyroid group, there was a statistically significant higher concentration of radioactive sulphur in the whole brain and in its bound protein fraction. A similar, though statistically not significant trend was observed in the 22 hour hyperthyroid group. Although these findings suggest that in short term experiments thyroxine increases protein synthesis in the brain of suckling rats, similar results could also be obtained from either an increased turnover rate of sulfur containing amino acids or from an increased concentration of S35 in the precursor amino acid pool or a very active fraction of the protein pool.