DIETARY PROTEIN QUALITY AND β-CAROTENE SUPPLEMENTATION AFFECT THE ACTIVITY OF HEPATIC ACYL CoA: RETINOL ACYLTRANSFERASE IN CHICKS

Abstract

To study the effect of protein quality and β-carotene supplementation on the activity of intestinal and hepatic enzyme i.e. Acyl CoA: retinol acyl transferase (ARAT), one-day-old male leghom chicks were used. Afier feeding the chicks on vitamin—A deprived diet for 10 days to lower and equalise hepatic retinol storage, 28 chicks with similar average body weight were assigned into four groups to receive diet containing: 1) 20% gluten protein supplemented with 1.5 pg B-carotene/g diet, 2) 20% gluten protein supplemented with 15 pg β-carotene/g diet, 3) 20% casein protein supplemented with 1.5 pg B-carotene diet, 4) 20% casein protein supplemented with 15 ug β-carotene/g diet. Each experimental group consisted of seven replicate chicks. The experimental diet was performed for two weeks. Serum retinol, hepatic retinol and hepatic B-carotene content and the activity of intestinal and hepatic enzyme i.e. Acyl CoA:retinol acyl transferase (ARAT) were measured to estimate the fate of retinol converted from β-carotene. The results showed that regardless of protein quality, increase β-carotene supplementation raised liver retinol and β-carotene content significantly. These raise was followed byincreased activity of intestinal and hepatic ARAT activity. Comparing the efiect of protein quality at the same level of β-carotene supplementation it cou.ld be observed that there was no sigriificant difference in intestinal ARAT activity. However, a striking difierence was found when comparing serum retinol and the activity of hepatic ARAT in gluten groups and casein groups each supplemented with 15 pg β-carotene. Serum retinol content was higher up to 65.0 i 14.3 pg/dl in casein groups supplemented with 15 pg β-carotene compared to 15.2 at 4.6 pg/dl in gluten groups supplemented with the same amount of β-carotene. Hepatic ARAT activity was also increased up to 114.2 i13.3 pmol/minute/mg in these casein groups compared to 51.5 $9.1 pmol/minute/mg in gluten groups. These results suggested that when the level of β-carotene supplementation and dietary protein is sufificient (20%), good quality of protein enhanced the esterification rate of retinol in liver and might suggest its influence in retinol release from the liver and its consequent increase in serum retinol.