Using highly purified unconjugated [3H]bilirubin (UCB), we measured UCB binding to delipidated human serum albumin (HSA) and its uptake by basolateral rat liver plasma membrane vesicles, in both the absence and presence of an inside-positive membrane potential. Free UCB concentrations ([Bf]) were calculated from UCB-HSA affinity constants (K'f), determined by five cycles of ultrafiltration through a Centricon-10 device (Amicon) of the same solutions used in the uptake studies. At HSA concentrations from 12 to 380 microM, K'f (litre/mol) was inversely related to [HSA], irrespective of the [Bf]/[HSA] ratio. K'f was 2.066 x 10(6) + (3.258 x 10(8)/[HSA]). When 50 mM KC1 was isoosmotically substituted for sucrose, the K'f value was significantly lower {2.077 x 10(6) + (1.099 x 10(8)/[HSA])}. The transport occurred into an osmotic-sensitive space. Below saturation ([Bf] < or = 65 nM), both electroneutral and electrogenic components followed saturation kinetics with respect to [Bf], with K(m) values of 28 +/- 7 and 57 +/- 8 nM respectively (mean +/- S.D., n = 3, P < 0.001). The Vmax was greater for the electrogenic than for the electroneutral component (112 +/- 12 versus 45 +/- 4 pmol of UCB. mg-1 of protein. 15 s-1, P < 0.001). Sulphobromophthalein trans-stimulated both electrogenic (61%) and electroneutral (72%) UCB uptake. These data indicate that: (a) as [HSA] increases, K'f decreases, thus increasing the concentration of free UCB. This may account for much of the enhanced hepatocytic uptake of organic anions observed with increasing [HSA]. (b) UCB is taken up at the basolateral membrane of the hepatocyte by two systems with K(m) values within the range of physiological free UCB levels in plasma. The electrogenic component shows a lower affinity and a higher capacity than the electroneutral component. (c) It is important to calculate the actual [Bf] using a K'f value determined under the same experimental conditions (medium and [HSA]) used for the uptake studies.

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b-Cyclodextrin is a compound that forms inclusion complexes with a variety of molecules, specially bile acids and sterols. This study examines the effects of b-cyclodextrin on cholesterol and bile acid metabolism in hypercholesterolaemic rats. Male Wistar rats were divided into 4 groups that received during 7 weeks: control diet, 2% cholesterol diet (A), Aπ2.5% b-cyclodextrin (B) and Aπ5% b-cyclodextrin (C). The cholesterol-rich diet induced hepatomegaly and fatty liver and significantly reduced cholesterol, bile acid and phospholipid secretion. Addition of b-cyclodextrin normalised biliary lipid secretion. Moreover, when compared to A, b-cyclodextrin significantly lowered plasma phospholipid concentration (B: ª21%; C: ª29%) and the liver free/total cholesterol molar ratio (B: ª40%; C: ª38%), increased bile acid faecal output (B: π17%; C: π62%) and enhanced cholesterol 7a-hydroxylase activity (B:π50%; C: π100%) and mRNA levels (B: π14%; C: π29%). 5% b-cyclodextrin also reduced plasma triglycerides concentration (ª38%). However, ALT and AST activities were significantly increased (B: π140% and π280%; C: π72% and π135%) and there was a high incidence of cell necrosis with portal inflammatory cell infiltration. Addition of b-cyclodextrin to a cholesterol-rich diet results in a triglyceride-lowering action, enhancement of bile acid synthesis and excretion, and normalization of biliary lipid secretion, but produces a marked hepatotoxic effect.

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The eects of physical conditioning on antipyrine clearance were studied in two groups of subjects. Healthy men not engaged in the systematic practice of any sport were compared with endurance runners (de®ned as men running >80 km/week). Studies were carried out at three dierent periods of the annual plan training at 4-month intervals. Antipyrine was administered orally and pharmacokinetic parameters were obtained from saliva samples by the multiple-sample method. Endurance performance, expressed in terms of the maximal oxygen uptake ( O 2 max ), the ventilatory threshold and the 4-mM á l A1 lactate threshold (OBLA), was higher in trained than in control subjects at each of the three periods. Antipyrine clearance was also signi®-cantly elevated and antipyrine half-life reduced in runners during all periods. No signi®cant dierence in O 2 max or antipyrine clearance was found between the various periods in either trained or control subjects. Both ventilatory threshold and OBLA increased significantly along the training period in conditioned subjects. Signi®cant correlations were found between antipyrine clearance and O 2 max , ventilatory threshold and OBLA. In summary, these results indicate an association between aerobic conditioning and increased hepatic oxidative metabolism of low-clearance drugs.

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