Functional differences in cholesterol ester hydrolase and acyl-coenzyme-A/cholesterol acyltransferase between the outer and inner zones of the guinea pig adrenal cortex.

Abstract

Previous studies clearly demonstrated that cells isolated from the chromatically distinct inner (primarily zona reticularis) and outer (zona fasciculata and zona glomerulosa) zones of the guinea pig adrenal cortex have vastly different steroidogenic capabilities; the outer zone produces far more cortisol than the inner zone, and mitochondrial cholesterol side-chain cleavage activity in the inner zone is not modulated by ACTH. Thus, in this study we have investigated the characteristics and properties of cholesterol ester hydrolase (CEHase) and acyl-coenzyme-A/cholesterol acyltransferase (ACAT) in the outer and inner zones of the guinea pig adrenal to clarify the zonal difference in cholesterol metabolism. CEHase showed two pH optima at around pH 4.5 and pH 7.5 in the outer zone, while optimum activity in the inner zone was found only around pH 4.5, suggesting a lack of neutral CEHase in the inner zone. The acid CEHase was found mainly in the lysosomal fraction, and the neutral CEHase was located mainly in the microsomal fraction. The neutral CEHase activity in the outer zone was significantly enhanced by ether stress, while the acid CEHase activity was not changed in either of the two zones by stress. The basal activity of ACAT was significantly higher in the outer zone than in the inner zone. The present experiments also demonstrated that the inner zone always showed lower ACAT activity than the outer zone even when added cholesterol exogenously. It is suggested that the relatively low activity of ACAT may not always be explained by the reduced content of cholesterol in the microsomal fraction of zona reticularis. ACAT activity in the outer zone was significantly decreased by ether-induced stress, but that in the inner zone was not changed. The content of esterified cholesterol in whole homogenate and the microsomal fraction was significantly decreased in the outer zone, but not in the inner zone, by ether stress. Thus, the decrease in esterified cholesterol after ether stress seems to relate to increased neutral CEHase activity and decreased ACAT activity in the outer zone. The present observation clearly indicates that the lack of neutral CEHase and the lesser activity of ACAT in the inner zone than in the outer zone may contribute to the impaired cholesterol metabolism in the inner zone.