Effect of 1 alpha,25-dihydroxy vitamin D3 and vitamin E on insulin-induced glucose uptake in rat adipocytes.
Vitamin E, an antioxidant, improves insulin sensitivity through the suppression of conventional PKC in vascular smooth muscle cells. It has been reported that vitamin E reduces platelet aggregation through the suppression of PKC alpha and beta (Diabetes 47 (1998) 1494). On the other hand, 1 alpha,25-dihydroxy vitamin D3 (1,25D3) activates conventional PKC and may subsequently cause insulin resistance. Against this background, we examined the effect of vitamin E and 1,25D3 on PKC beta and PKC zeta/lambda activities in vitro and 10 nM insulin-induced glucose uptake in rat adipocytes. In vitro PKC beta activity of adipocytes was slightly decreased by the addition of 1 microM vitamin E, but not PKC zeta/lambda activity. In contrast, a 10-1000 nM 1,25D3 dose responsively activated PKC beta activity of adipocytes (ED 50%, 10 nM), but not PKC zeta/lambda activity. Pretreatment with 1 microM vitamin E for 60 min did not improve the insulin-induced glucose uptake. On the other hand, pretreatment with a 10-1000 nM 1,25D3 dose responsively suppressed insulin-induced glucose uptake. Moreover, 1,25D3 increased membrane-associated PKC beta immunoreactivity for 60 min, but no additional increase in membrane-associated PKC beta immunoreactivity during treatment with insulin was observed. These results suggest that 1,25D3 reduces insulin-induced glucose uptake via activation of PKC beta, but not vitamin E in rat adipocytes.
Huang
Yannan
Y
The Third Department of Internal Medicine, Gifu University School of Medicine, Tsukasamachi 40, Gifu 500-8705, Japan.
Ishizuka
Tatsuo
T
Miura
Atsushi
A
Kajita
Kazuo
K
Ishizawa
Masayoshi
M
Kimura
Mika
M
Yamamoto
Yoritsuna
Y
Kawai
Yasunori
Y
Morita
Hiroyuki
H
Uno
Yoshihiro
Y
Yasuda
Keigo
K
D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002117:Calcitriol / Q000494:pharmacology*; D003847:Deoxyglucose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D064546:Protein Kinase C beta; D051381:Rats; D017208:Rats, Wistar; D014810:Vitamin E / Q000494:pharmacology*
D000975:Antioxidants; D007328:Insulin; D007527:Isoenzymes; D014810:Vitamin E; D003847:Deoxyglucose; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D002117:Calcitriol; D005947:Glucose