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.

To determine adipose tissue cellularity in hypo- and hyperthyroidism, male rats were thyroidectomized after weaning (T) and injected daily with either 0, 0.1, 1. 8, or 25 µg of L-thyroxine/100 g body weight for 40 days. They were compared with intact controls (C). Both epididymal fat-pad weight and adipocyte diameter were reduced in T+0, T+0.1 and T+25 animals. When corrected per unit of body weight, the diameters of adipocytes from T+0 and T+0. l animals were larger than in the other groups. Those same animals have reduced absolute adipocyte number but not when corrected per unit of body weight. The fat-pad protein concentration varied conversely with the fat cell diameter. These findings indicate that thyroid hormone deficiency reduces thf proliferation of fat cells in parallel with body growth while hyperthyroidism causes reduction in the size, but not the number, of fat cells which corresponds to its depletion of fat storage.