Children with Alagille syndrome show high serum cholesterol (15-20 mmol/L). To establish correlation of this unusual level of cholesterol with the regulation of cholesterol metabolism, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) activity and synthesis of cholesterol, fatty acids and acidic steroids from [14C]acetate were determined in cultured skin fibroblasts from 2-3 year old children. Prostaglandin E2 (PGE2) synthesis and nucleic acid synthesis were determined in cells when they were growing in medium containing normal, Alagille or fetal bovine serum. These values were similar to values of controls. HMGR activity was found to be similar in cells of control and children with the syndrome, whether the cells were incubated in lipoprotein-deficient or normal medium. Incorporation of acetate into cholesterol was inhibited to a greater extent by lipoprotein-containing medium in control than in children with the syndrome. Fatty acid synthesis was similar in all conditions. 1-7% of the recovered lipid radioactivity in cells and medium separated as acidic steroids. Serum from a donor patient, when included in the medium, did not affect PGE2 or nucleic acid synthesis compared with normal human or fetal bovine serum. The data suggest that cells of children with Alagille syndrome may have a membrane defect of transfer of cholesterol (LDL receptor defect) leading to excessive cholesterol synthesis. Also, synthesis of acidic steroids (bile acid-like material) and their secretion into the medium occurs in normal fibroblasts and those from children with the syndrome.

The present study was undertaken to investigate the effect of 17 β-estradiol (E₂) administration on in vitro prolactin (PRL) release and intracellular phosphoinositide metabolism. The incorporation of [³H]inositol (Ins) into phosphatidylinositol (PtdIns), phophatidylinositol-4-phosphate [PtdIns(4)P] and phosphatidylinositol-4,5-bisphophate [PtdIns(4,5)P₂], and the generation of inositol phosphate (InsP₂) following thyrotropin-releasing hormone (TRH) stimulation were studied in primary cultures of anterior pituitary cells obtained from ovariectomized rats. Administration of polyestradiol phosphate (PEP) to ovariectomized rats produced a significant increase (p < 0.05) in serum PRL levels. This treatment also enhanced significantly (p < 0.01) the in vitro release of PRL in a progressive manner during 24, 48 and 72 h of culture of dispersed anterior pituitary cells. The radioisotopic labeling by [³H]Ins of all species of phosphoinositides was progressive throughout 72 h of culture, and a good correlation was observed between intracellular phosphoinositide synthesis and PRL release from these cells. PEP treatment enhanced significantly (p < 0.05–0.01) [³H]Ins incorporation into Ptdlns and PtdIns(4)P after 48 and 72 h of culture, although it did not alter [³H]Ins incorporation into PtdIns(4,5)P₂. Furthermore, this treatment caused a small, but significant increase (p < 0.01) in InsP_x generation following TRH stimulation. However, the increased [³H]Ins incorporation into phosphoinositide and InsP_x generation that we observed after TRH stimulation was significantly (p < 0.01) less than the increased amount of in vitro PRL release following PEP treatment. There was no significant correlation between the percentage increases in PRL release and phosphoinositide metabolism following the same treatment. These data suggest that phosphoinositide metabolism is enhanced in the anterior pituitary cells of ovariectomized rats by treatment with PEP, but this system does not appear to be tightly coupled or causally related to the much greater production of PRL release.

The aim of this study was to determine how small differences in dietary fats affect cholesterol metabolism in mice hypo- (CBA/J) and hyperresponsive (C57BR/cdJ) to diet-induced hypercholesterolemia. Six-wk-old male mice were fed either a diet corresponding to the U.S. average gross composition (US74, 40% of total energy as fat, 347 mg cholesterol/1000 Kcal, P/S = 0.24) or a modified-fat diet (30% of total energy as fat, 46 mg cholesterol/1000 Kcal, P/S = 0.91). After 8 wk of feeding, neither strain had developed hypercholesterolemia. CBA/J mice had higher concentrations of serum total and high-density lipoprotein (HDL) cholesterol and a higher esterified-to-free cholesterol ratio than did C57BR/cdJ mice. CBA/J mice maintained a constant serum cholesterol concentration mainly by adjusting the hepatic hydroxymethylglutaryl coenzyme A reductase (HMGR) activity, whereas C57BR/cdJ mice did so by changing the fecal excretion of cholesterol. Compared to the modified-fat diet, the US74 diet caused an increase in the ratio of total to HDL serum cholesterol, liver microsomal free cholesterol, fecal cholesterol and hepatic microsomal cholesterol 7 alpha-hydroxylase activity and a decrease in hepatic microsomal HMGR activity. We conclude that the metabolic responses to small differences in dietary fat are different in CBA/J and C57BR/cdJ mice.

INTRODUCTION 43 METHODS 44 Animals 44 Experimental Diets 46 Serum Cholesterol Determination 46 Hydroxymethylglutaryl CoA Reductase Assay 46 RESULTS 49

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