Effect of oral contraceptive cycle on dry socket (localized alveolar osteitis).

Use of oral contraceptives was associated with a significant increase in the frequency of dry socket after extraction of mandibular third molars. The probability of dry socket increases with the estrogen dose in the oral contraceptive. The risk of dry socket associated with oral contraceptives can be minimized by performing extractions during days 23 through 28 of the tablet cycle.

PIP: A patient population consisting of women currently taking oral contraceptives (OCs) and who were scheduled to undergo extraction of third molars was examined to establish any connection between postoperative sequelae, specifically higher incidence of dry socket (localized alveolar osteitis) in dental patients using OCs. 71 third molar extractions were performed on 47 OC users. Mandibular third molars extracted during Days 1-22 of the OC cycle (Day 22 was considered the last day of estrogen influence) had significantly higher frequency of dry socket than those removed during Days 23-28. Of the 58 extractions during Days 1-22, 18 (31%) resulted in dry sockets compared with none of the 13 extractions during Days 23-28 (P=.0145). The effect of estrogen dose on frequency of dry socket was also computed. The risk of dry socket increased with increased estrogen dose in the OCs (P .01). Therefore, the risk of dry socket can be minimized by performing extractions during Days 23-28 of the OC tablet cycle.

Cholesterol 7 alpha-hydroxylase from human liver: partial purification and reconstruction into defined phospholipid-cholesterol vesicles.

Cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme for bile acid synthesis, was shown to be copurified with human liver microsomal cytochrome P-450. When these cytochrome P-450 species were reconstituted in phospholipid-cholesterol vesicles together with NADPH-cytochrome P-450 reductase, high cholesterol 7 alpha-hydroxylase activity was obtained in the presence of NADPH. The activity represented a twofold enrichment relative to cytochrome P-450 and 43-fold enrichment relative to total microsomal protein. Availability of such a preparation will allow further characterization of the enzyme and will also allow studies of its mechanisms of regulation.

Characterization of chylomicron remnant binding to rat liver membranes.

The binding of chylomicron remnants to rat liver membranes was investigated using radioiodinated lipoproteins. The specific activity of binding increased in parallel with increased enrichment in plasma membrane markers. The yield of receptor activity, however, decreased with enrichment. Accordingly, a partially purified plasma membrane preparation was used for routine studies. Binding was saturable, with half maximal binding achieved at 4.6 micro g tetramethylurea-precipitable protein per ml. The rate of binding was time- and temperature-dependent. It could be inhibited only moderately by 10 mM EDTA. Chylomicron remnants appeared to bind to the membrane as a unit. The bound particle was richer in apoproteins of 20,000-50,000 molecular weight relative to low molecular weight apoproteins than the particles that were not bound. Lipoprotein particles containing only human apoB did not bind to liver membranes nor did they compete for the remnant binding site. Rat lipoproteins of d 1.019-1.063 g/ml did compete for remnant binding. When they were separated into apoB-rich (LDL) or apoE-rich (HDL(c)) fractions by block electrophoresis, the apoE-rich fraction was a more potent competitor. ApoE purified and reconstituted into dimyristoyl phosphatidylcholine vesicles was a potent competitor for the remnant binding site. Vesicles containing (125)I-labeled apoE bound to the membranes, and they could be displaced by unlabeled remnants. Dimyristoyl phosphatidylcholine vesicles themselves did not compete with either remnants or apoE-phospholipid vesicles. These results offer strong support for the hypothesis that the liver membrane chylomicron remnant receptor recognizes apoE with a high affinity, and this initiates the rapid removal of lipoproteins that contain this apoprotein.-Cooper, A. D., S. K. Erickson, R. Nutik, and M. A. Shrewsbury. Characterization of chylomicron remnant binding to rat liver membranes.

Rat liver acyl-coenzyme A:cholesterol acyltransferase: its regulation in vivo and some of its properties in vitro.

To gain insight into the role of the enzyme acyl-coenzyme A:cholesterol acyltransferase (ACAT) in cellular cholesterol homeostasis, its regulation in rat liver was investigated both in vivo and in vitro. In vitro assay conditions were optimized and some properties of the microsomal enzyme in vitro was also studied. Arrhenius plots of microsomal ACAT activity showed discontinuities at about 28-29 degrees C and 16-17 degrees C. Detergents above their critical micelle concentrations and organic solvents both inhibited the enzyme. Addition of progesterone or SC 31769, a 7-keto-cholesterol analogue, to microsomes inhibited activity while addition of 25-hydroxycholesterol increased the rate of cholesterol esterification, suggesting that the enzyme is susceptible to both negative and positive modulation by steroids, steroid analogues, or their metabolic products. Increasing the rate of cholesterol biosynthesis had a variable effect on ACAT activity. It was higher at the circadian peak of sterol biosynthesis than at the nadir. Increasing sterol biosynthesis by intragastric administration of mevalonolactone resulted in increased activity. In contrast, increasing the rate of sterol biosynthesis by feeding cholestyramine or administration of Triton WR 1339 had little effect on ACAT. Increasing hepatic cholesterol content by feeding cholesterol, cholate, or an atherogenic diet, fasting or intragastric administration of mevalonolactone all resulted in increased ACAT activity. ACAT activity showed a positive correlation with changes in microsomal free and esterified cholesterol contents. The response of ACAT to changes in hepatic cholesterol concentration in vivo and its response to changes in the rate of cholesterol synthesis support the hypothesis that this enzyme plays an important role in maintenance of hepatic cholesterol homeostasis.