EFFECT OF L-TRIIODOTHYRONINE ON LIVER MICROSOMAL DELTA-6 AND DELTA-5 DESATURASE ACTIVITY OF MALE-RATS

The effect of different doses of L-triiodothyronine (T3) on the activity of DELTA6 and DELTA5 desaturases and lipid fatty acid composition was studied in liver microsomes of male rats. The activity of DELTA6 and DELTA5 desaturases was decreased 24 and 28%, respectively, in animals administered a daily intraperitoneal dose of 1000mug T3/100g body wt. for 5 days, whereas with 500mug T3/100g body wt. only DELTA6 desaturase activity was decreased. On the other hand, no enzyme activity changed at a shorter period of hormone treatment. Changes in microsomal fatty acid composition did not seem to be a direct consequence of desaturation activity since after 1 and 5 days of T3 treatment, the concentrations of 18:2 (n-6) and 20:3 (n-6) decreased and only after 1 day that of 20:4 (n-6) increased in spite of unchanged or decreased DELTA6 and DELTA5 desaturase activities. Other factors than desaturation activity must be involved in fatty acid composition of thyroid hormone-treated rats, such as diet, membrane lipid synthesis and degradation, fatty acid turn-over and oxidation.