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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1996;16:1088.)
© 1996 American Heart Association, Inc.

Articles

Effect of Estrogen and Progesterone on the Expression of Hepatic and Extrahepatic Sterol 27-Hydroxylase in Baboons (Papio sp)

Rampratap S. Kushwaha; Bharathi Guntupalli; Evelyn M. Jackson; Henry C. McGill, Jr

the Department of Physiology and Medicine, Southwest Foundation for Biomedical Research, San Antonio, Tex.

Correspondence to Rampratap S. Kushwaha, PhD, Southwest Foundation for Biomedical Research, Department of Physiology and Medicine, PO Box 760549, San Antonio, TX 78245-0549.

Abstract

Sterol 27-hydroxylase plays an important role in cholesterol metabolism in hepatic and extrahepatic tissues. To determine whether female sex steroid hormones influence its expression, we measured plasma and hepatic 27-hydroxycholesterol, hepatic mRNA levels, activity of sterol 27-hydroxylase, and adrenal mRNA levels of this enzyme in baboons (n=6 per group) treated with placebo, estrogen, estrogen + progesterone, and progesterone. We also measured hepatic cholesterol concentration and hepatic acyl coenzyme A:cholesterol acyltransferase (ACAT) activity to determine their relationship with hepatic sterol 27-hydroxylase activity. Plasma 27-hydroxycholesterol concentration was increased by estrogen and estrogen + progesterone and was negatively correlated with plasma (P=.090) and LDL (P=.026) cholesterol concentrations. Similarly, hepatic sterol 27-hydroxylase activity was increased by estrogen and estrogen + progesterone and was negatively correlated with plasma (P=.056) and LDL (P=.052) cholesterol concentrations but was positively correlated with hepatic and plasma 27-hydroxycholesterol concentrations (P<.001). Hepatic ACAT activity was increased by progesterone (P<.004) and was positively correlated with plasma (P=.002) and LDL (P=.009) cholesterol concentrations but was negatively correlated with hepatic sterol 27-hydroxylase activity (P=.035). Hepatic and adrenal gland mRNA levels for sterol 27-hydroxylase were increased by estrogen alone or in combination with progesterone (P<.05). Hepatic sterol 27-hydroxylase activity was positively correlated with hepatic mRNA levels (P<.001), an observation suggesting that estrogen increases the activity of sterol 27-hydroxylase by increasing its synthesis. Hepatic cholesterol concentration was not influenced by the hormone treatment. These observations suggest that estrogen alone or in combination with progesterone increases the synthesis of sterol 27-hydroxylase in hepatic and extrahepatic tissues, and the increased activity of hepatic sterol 27-hydroxylase resulting from the increased synthesis is associated with a hypolipidemic effect on plasma LDL levels. Furthermore, progesterone alone increases the hepatic ACAT activity, but given in combination with estrogen progesterone does not have the same effect on hepatic ACAT activity. The effect of estrogen on hepatic ACAT activity may be mediated by sterol 27-hydroxylase and its effect on cholesterol metabolism (decreased cholesterol synthesis and increased output of cholesterol in the bile) in liver.

Key Words: dietary cholesterol • dietary saturated fat • female sex steroid hormones • 27-hydroxycholesterol • acyl coenzyme A:cholesterol acyltransferase

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