Effect of insulin, glucagon or dexamethasone on the production of apolipoprotein A-IV in cultured rat hepatocytes.
We studied the effects of insulin, glucagon or dexamethasone on the production of apolipoprotein A-IV (apo A-IV) by cultured rat hepatocytes, using specific radioimmunoassay for rat apo A-IV. We also compared the effect of these hormones on the production of apo A-IV with those of albumin and apo A-I, reported previously. In the absence of hormones, apo A-IV and albumin in culture medium increased almost linearly for periods up to 24 h. The rates of accumulation of apo A-IV and albumin in the medium were 15.4 ng/mg cell protein per h and 1.2 micrograms/mg cell protein per h, respectively. The concentration of intracellular apo A-IV remained constant during the incubation. Insulin stimulated the production of albumin, but inhibited the production of apo A-IV dose-dependently. Glucagon inhibited the production of both albumin, and apo A-IV dose-dependently. Dexamethasone showed no significant effects on albumin production, but stimulated apo A-IV production. Thus, apo A-IV production in hepatocytes is regulated by several hormones with different effects on albumin production. The regulatory effects of these hormones on apo A-IV production were almost identical with the effects observed in a course of apo A-I synthesis, suggesting that the production of the two apoproteins are regulated by similar mechanisms.
Uchida
E
E
Third Department of Internal Medicine, Faculty of Medicine, Kyushi University, Fukuoka, Japan.
Masumoto
A
A
Sakamoto
S
S
Koga
S
S
Nawata
H
H
D000418:Albumins / Q000096:biosynthesis; D000818:Animals; D001054:Apolipoproteins A / Q000096:biosynthesis*; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D005934:Glucagon / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism*; D008297:Male; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains
D000418:Albumins; D001054:Apolipoproteins A; D007328:Insulin; C022205:apolipoprotein A-IV; D003907:Dexamethasone; D005934:Glucagon