Vitamin A regulation of stearoyl-CoA desaturase mRNA levels and fatty acid composition in sheep tissues

The effect of vitamin A (retinol) on ovine stearoyl-CoA desaturase (SCD) mRNA levels and fatty acid composition was investigated. Sheep adipose tissue explants were maintained in culture for 24 h in the presence of all-trans retinoic acid ( RA). Tissue SCD mRNA levels were increased with 25 mumol/l RA but the levels of SCD mRNA in tissue treated with 100 mumol/l RA were not different from control. The effect of vitamin A supplement on SCD mRNA levels in vivo was then characterized: growing lambs were given a concentrate diet (2 kg/day) containing 0, 0.225, 1.125 and 3.375 mg vitamin A per kg diet for 21 days. Treatment resulted in a concentration-dependent increase in adipose tissue and liver SCD mRNA levels, although the greatest effect was seen in the liver. SCD mRNA levels were highest in tissue from animals given 0.225 mg vitamin A per kg diet and further increases in vitamin A supplementation were not accompanied by corresponding increases in SCD gene expression. Fatty acid composition was also determined. Overall, tissue from animals given vitamin A had greater levels of both palmitoleic and oleic acid relative to their precursors. These data clearly show that SCD gene expression in adipose tissue and liver is regulated by retinoic acid and the liver appears to be most responsive. However, although significant, the change in the proportion of oleic acid was only small indicating that dietary manipulation with vitamin A is not a suitable method for increasing the unsaturated fat content of sheep meat.