Triiodothyronine increases rat apolipoprotein A-I synthesis and alters high-density lipoprotein composition in vivo.
The effects of altered serum 3,3',5-triiodothyronine levels on rat lipoprotein metabolism were examined. Daily injections of the hormone (50 micrograms/100 g body mass) over a period of six days led to an increase of 6.4-fold in the hepatic mRNA level for apolipoprotein(apo)A-I, and a 21% increase in serum apoA-I levels. 12h after a single injection of 3,3',5-triiodothyronine the rate of [14C]leucine incorporation into apoA-I increased 2.1 fold. Conversely, in hypothyroid rats there was a decrease in hepatic mRNA levels for apoA-I and a decreased rate of [14C]leucine incorporation into apoA-I. The increase in hepatic apoA-I mRNA levels following 3,3',5-triiodothyronine treatment occurred prior to significant changes in serum triacylglycerol levels. High-density lipoprotein (HDL) particles isolated from the serum of hyperthyroid rats were smaller and enriched in apoA-I compared to apoA-IV and apoE. Similar changes in HDL composition were observed following in vitro incubations of normal rat serum with purified rat apoA-I. The results suggest that during altered thyroid status, changes in serum HDL size and composition occur in association with significant changes in apoA-I gene expression.
Apostolopoulos
J J
JJ
Russell Grimwade School of Biochemistry, University of Melbourne, Australia.
Marshall
J F
JF
Howlett
G J
GJ
D000818:Animals; D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000096:biosynthesis* / Q000097:blood / Q000235:genetics; D002784:Cholesterol / Q000097:blood; D015870:Gene Expression; D006980:Hyperthyroidism / Q000378:metabolism; D007037:Hypothyroidism / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011915:Rats, Inbred BUF; D013997:Time Factors; D014280:Triglycerides / Q000097:blood; D014284:Triiodothyronine / Q000494:pharmacology*
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D008075:Lipoproteins, HDL; D012333:RNA, Messenger; D014280:Triglycerides; D014284:Triiodothyronine; D002784:Cholesterol