Effects of Hypo- and Hyper-Thyroidism on In Vivo Lipogenesis in Fed and Fasted Rats[*]

Abstract

Thyroidectomized rats (T) daily injected with either 0, 0.1, 1.8 or 25 µg of L-thyroxine/100 g body wt. were compared with intact controls (C). The appearance of radioactivity 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+1.8 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+0.1, but is enhanced within 24 h in the adipose tissue of I + 25. It is proposed that most of the observed changes are due to the other endocrine disfunctions which appear in hypo- and hyperthyroidism, as the in vivo results do not comply with in vitro effects of thyroxine on lipogenesis of others.

Key words

Lipogenesis - Hypothyroidism - Hyperthyroidism - Adipose Tissue - Liver

1 Supported by a grant from the "comisión Asesora de Investigación Cientificay Técnica, Presidencia del Gobierno", Spain

1 Supported by a grant from the "comisión Asesora de Investigación Cientificay Técnica, Presidencia del Gobierno", Spain

2 Postdoctorate research fellow of the Juan March foundation, Spain.