1. Investigación

1.8 or 25 µg of L-thyroxine/100 g body wt. were compared with intact controls (C). The appearance of radioacitvity in fatty acids 30 min after the i.p. injection•of (3-14C)pyruvate was reduced in adipose tissue and enhanced in liver of T+25, being no differences between the other groups and C. ( 14C)- Fatty acids are reduced with 3 h of fasting only in the adipose tissue of T+ 1.8 and C, while 24 h produces a reduction in liver in the T+ 1.8, T+25 and C, and in adipose tissue in the T+l.8 and C animals. The highest percentage of radioactivity was observed in the liver glyceride glycerol fraction, being greater in T+25 than in the other groups. Fasting produces an increment in the ( 14C)-glyceride glycerol fraction. being significant only in the hypothyroid animals in both liver and adipose tissue. The most sensitive parameter to fasting was the formation of ( 14C)-non-saponifiable lipid in both the C and T+ 1.8 animals, while it does not change in T+0 or T+0.I, but is enhanced within 24 h in the adipose tissue of T + 25. It is proposed that most of the observed changes are due to the other endocrine disfunction s which appear in hypo- and hyperthyroidism, as the in vivo results do not comply with in vitro effects of thyroxine on lipogenesis of others.