Decreased hepatic retinyl palmitate hydrolase activity in protein-deficient rats

Abstract

Abstract28-day-old weanling rats were fed a diet containing 3% casein as the only source of protein for eight weeks to induce protein deficiency. When compared to control animals (fed a diet containing 25% casein), these rats had significantly lowered body (5.2-fold reduction) and liver (2.5-fold reduction) weights. The circulatory level of retinol (nmoi per ml plasma) as well as retinol (nmol per g tissue) in the liver of these protein-deficient animals were also reduced significantly, although their liver concentration of retinyl palmitate (nmol per g tissue) was comparable to that of the control group. Assay of liver tissue for retinyl palmitate hydrolase activity revealed a 4-fold reduction (compared to that of control animals) of specific enzyme activity (nmol retinol formed per g protein per h). These findings suggest that severe protein deficiency results in a decreased hydrolysis of retinyl esters in the liver, which may be in part responsible for the reduced level of metabolically 'active' retinoids available for normal physiological functions.

Iron Deficiency in Young Rats Alters the Distribution of Vitamin A between Plasma and Liver and between Hepatic Retinol and Retinyl Esters

“…It may be possible that during iron deficiency the balance might be shifted to an increase of holo-CRBP with a subsequent reduction of hydrolysis and might thereby limit the availability of retinal for the production of VA metabolites (Ross 1995). In support of a reduced hydrolysis of hepatic VA, Tsin et al (1986) showed that hepatic retinyl palmitate hydrolase activity was reduced to 30% of controls in rats consuming a diet containing 3% casein, and Sharma et al (1987) demonstrated that the hepatic release of VA was only 70% of control in rats consuming a diet containing 10% casein.…”