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L Lack

Publications and source records attributed to L Lack.

At least 37 records · Page 2Linked to original sources
PubMed1987

Rat hepatic bile acid sulfotransferase: enzyme response to androgens and estrogens.

Rat liver bile sulfotransferase activity can be divided into a fraction that reacts with a monoclonal antibody (PK1B) and another fraction that does not. This work was performed to analyze the known response of hepatic bile acid sulfotransferase activity to androgens and estrogens by determining the effect of treatment on the proportion of bile acid sulfotransferase activity that possessed the epitope for PK1B monoclonal antibody. Activity in treated animals was further characterized by high-performance liquid chromatography (HPLC) analysis following purification by PK1B-immunoadsorption chromatography. The results indicate that estrogens and androgens affect the subset of enzyme activity that has the PK1B epitope more than the population that does not. HPLC demonstrates that increases and decreases in activity that follow treatment with androgens and estrogens are mirrored by the proportion of the PK1B-reactive protein that exhibits a relative molecular weight (Mr) greater than 170,000. Radial immunodiffusion assays of hepatic supernatant using a polyclonal antibody raised against PK1B-reactive bile acid sulfotransferase show that changes in specific activity that follow treatment are the result of changes in enzyme protein concentration.

Androgens↗
PubMed1984

Positional requirements for anionic charge for ileal absorption of bile salt analogues.

Previous structure-activity studies of the ileal bile salt cotransport system have suggested the idea that a coulombic interaction occurs between the negative charge of the bile salt and a cationic site on the carrier. Evidence included observations that modified bile salts with uncharged, cationic, or zwitterionic side chains were poorly transported. They did interact with this system as evidenced by their abilities to inhibit transport. Another prerequisite for coulombic interaction is positional (side-chain) specificity for the anionic grouping. [14C]chenodeoxycholyl-N-ethanolamide-O-sulfate and the 3 alpha-sulfate ester of chenodeoxycholyl-N-ethanolamide were tested for their in vivo absorption from the jejunums and ileums of anesthetized guinea pigs. Active ileal transport was estimated by subtracting jejunal absorption (passive) from ileal absorption (active and passive). Translocation of the anionic SO4(-) radical from the side chain to the 3 alpha position of the steroid decreased active ileal absorption by 95%, demonstrating a positional requirement for the anionic group for optimal transport.

Absorption↗
PubMed1983

Inhibitory effects of some steroidal 6-methylene derivatives on 5 alpha-reductase activity in human and rat prostate.

Using a short-term organ culture assay, some 6-methylene derivatives of progesterone and testosterone have been evaluated for their effects on testosterone metabolism in rat and human prostatic tissues, and on DNA synthesis in explants from 7-day castrated rats. Comparative studies showed that the ability to inhibit 5 alpha-reductase activity was fairly specific with respect to structural requirements. Methylene substitution at the C6 position of the progesterone molecule was associated with high inhibitory activity. In explants prepared from human prostates, 6-methylene progesterone (II) had 70-85% (mean of 79% for 4 BPH tissues) of the potency of unmodified progesterone (I). Its 17 alpha-acetoxy-6-methylene analog (III), however, had only 32-73% (mean of 53% for 5 BPH specimens) of the activity of (I). The degrees of inhibition in rat and human prostatic tissues were similar. Inhibition of 5 alpha-reductase activity in cultured explants by 6-methylene progesterone (II) could not be reversed by change in media. The 6-methylene derivatives had little or no effect on DNA synthesis. Histological examination confirmed a lack of effect on basal cell proliferation. However, morphological alterations affecting epithelial cell height and secretory activity were clearly evident. These results indicate that, under our experimental conditions, the main effect of inhibition of 5 alpha-reductase activity in prostatic tissues by 6-methylene derivatives of progesterone is related to suppression of differentiated function.

5-alpha Reductase Inhibitors↗
PubMed1983

Prostatic cancer--II. Inhibitors of rat prostatic 4-ene-3-ketosteroid 5 alpha-reductase derived from 6-methylene-4-androsten-3-ones.

The studied 6-methylene-4-androsten-3-ones proved to be significantly inferior to 6-methylene-4-pregnene-3,20-dione and its 17-acetoxy derivative described in Part 1 as inhibitors of 4-ene-3-ketosteroid 5 alpha-reductase [1] in vitro. Surprisingly, the 6-methylene derivative of testosterone was only weakly active until acetylated, when an effective inhibitor was obtained. Etherification of the hydroxyl-group, its replacement by a hydrocarbon chain, or introduction of a substituent at C17 or on the methylene group led to virtual loss of activity. 17 alpha-Chloro-6-methylene-4-androstene-3-one had ca 60-70% of the potency of progesterone, but was inactive as enzyme inhibitor in explants of rat prostate in tissue culture and in in vivo studies. 6-Methylenetestosterone acetate was weakly active as enzyme inhibitor in explants of human prostate in tissue culture and produced a histological picture closely resembling testosterone and differing from that of cyproterone acetate. In vivo in the rat it had 80% of the androgenic activity of testosterone propionate. The foregoing data have been used to define some structural characteristics necessary for enzyme inhibition and to draw some conclusions regarding the architecture of the androgen and progesterone receptors and of the enzyme active site.

5-alpha Reductase Inhibitors↗
PubMed1981

Prostatic cancer. I. 6-Methylene-4-pregnen-3-ones as irreversible inhibitors of rat prostatic delta 4-3 ketosteroid 5 alpha-reductase.

Some derivatives of 6-methylene-4-pregnen-3-one were studied as inhibitors of delta 4-3-ketosteroid 5 alpha-reductase. Maximum inhibitory activity was shown by 17-acetoxy-6-methylene-4-pregnene-3,20-dione (AMPD). Irreversible inactivation was observed following preincubation of the enzyme with NADPH and AMPD. This inactivation was found to occur only in the presence of NADPH. As such enzyme inactivation was not due to the formation of a more inhibitory metabolic product, or to the formation of superoxide via a cytochrome P-450/NADPH pathway, it seemed likely that the observed inactivation was derived from an irreversible combination of the enzyme with AMPD. That this was probably the case was established by kinetic studies which revealed a pattern compatible with a kcat type of mechanism.

5-alpha Reductase Inhibitors↗
PubMed1980

Identification of the 3-sulfate isomer as the major product of enzymatic sulfation of chenodeoxycholate conjugates.

Thin layer and high performance liquid chromatography identified the 3-monosulfate ester as the predominant product of in vitro enzymatic sulfation of glyco- and taurochenodeoxycholate by rat liver and kidney and hamster liver. The rate of synthesis of the 7-sulfate ester was less than 20% that of the 3-sulfate isomer; in vitro synthesis of the 3,7-disulfate was not definitely seen. Reaction of the enzymatic products with 7 alpha-hydroxysteroid dehydrogenase indicated a molar ratio of 7 alpha-hydroxyl function and SO4 which further supported the identification of the 3-sulfate isomer as the major product.

Animals↗
PubMed1980

Effects of sulfation patterns on intestinal transport of bile salt sulfate esters.

The absorption of 14C-labeled 3 alpha-, the 7 alpha- and the 3 alpha,7 alpha-sulfate esters of taurochenodeoxycholate by guinea pig small intestine was studied using in vivo and in vitro preparations. In vivo ileal perfusions showed that sulfation markedly decreased uptake by the ileal bile salt transport system and that the position and number of the sulfate radicals affected the degree of transport inhibition. The following relationships were found: transport of taurochenodeoxycholate (TCDC) greater than TCDC-3-sulfate greater than TCDC-7 sulfate greater than TCDC-3,7-disulfate with a decrease of approximately 90% between each pair. In vitro, jejunal perfusions demonstrated that sulfation also decreased passive flux. By use of an everted gut sac technique, the ability of ileum to move the sulfated bile salts against a concentration gradient was measured. Under these conditions transport of TCDC-3-sulfate was minimal, and that of the 7-sulfate and 3,7-disulfate was not observed. In view of the reported increased levels of sulfated bile salts after total or partial biliary tract obstruction, our results support the concept of sulfation as an adaptive mechanism for enhancing fecal elimination of bile salts.

Animals↗
PubMed1979

The synthesis of diazo, halo, and sulfoxy bile acid derivatives: potential affinity labels.

Bile acid derivatives, with and without C-3 sulfate groups, and having either the diazo- or halomethylketone moieties, have been synthesized in good yield and purity. The synthetic sequence, COOH leads to COC1 leads to COCHN2 leads to COCH2X, was used with deoxycholic and cholic acids, which requires carefully controlled quench, work-up, and purification procedures, especially for the 3-sulfate esters (made from deoxycholic acid derivatives only). The pure title compounds are anticipated to be useful chemical probes (affinity labels), especially the completely water soluble sulfates, toward our studies of ileal active transport of bile salts. A new use for Sephadex LH-20 as a sulfate ester protecting group is reported. Also developed were the use of acetamide hydrochloride complex as a mild hydrochlorination reagent and a neutral desalting method for sulfate esters of deoxycholic acid derivatives.

Affinity Labels↗
PubMed1979

Properties and biological significance of the ileal bile salt transport system.

The properties of a specific transport system for bile salts, which is located in the ileum of the small intestine are described. The system operates by a sodium ion cotransport mechanism, and it functions in maintaining a normal enterohepatic circulation of bile salts. Analysis of structure-activity data allows us to depict our hypothesis for the interaction of bile salt and Na with the membranal recognition site of this transport system. The sequellae of metabolic disorders which can arise following disease or surgical ablation of the ileal region of the intestine which result in an interrupted bile salt enterohepatic circulation are described. We suggest that these findings hold interest to toxicologists, since it is not beyond reason that toxic agents might exist which impair the function of this transport system specifically or which could poison the ileal mucosal cell. Such agents might be detected by the presence of some of the described metabolic disorders. Finally, we discuss the ileal transport of the sulfated esters of bile salts and the possibility that this might relate to that aspect of detoxification pertaining to their enhanced excretion.

Animals↗
PubMed1977

The effect of bile salts on the formation and hydrolysis of cholesterol esters by rat liver enzymes.

To determine the effects of different bile salts on the enzymic esterification of cholesterol and the hydrolysis of cholesterol esters rat liver homogenates and rat liver microsomes were incubated with varying amounts of different bile salts. Bile salts inhibited the formation of radioactive cholesterol esters in incubations of either rat liver homogenates or rat liver microsomes containing [14C]cholesterol. Chenodeoxycholate, glycochenodeoxycholate and taurochenodeoxycholate were more potent inhibitors than their comparable cholate analogues. Bile salts stimulated the hydrolysis of cholesterol esters when incubation were carried out with the liver homogenates. The dihydroxy bile salts were again more potent in this regard than the trihydroxylated bile salts. When the effects of bile salts on cholesterol ester hydrolysis were studied in in vitro incubations of hepatic microsomes a biphasic mode of acion was observed. In the absence of Na+ or K+ bile salts stimulated the hydrolysis of cholesterol oleate. However, following the addition of either Na+ or K+ to the microsomal incubations, bile salts caused an inhibition of cholesterol ester hydrolysis. Since cholesterol esterification was also inhibited under these conditions a direct inhibitory effect (not attributable to enhanced hydrolase activity) of the bile salts on the formation of cholesterol esters by the microsomes was established. Furthermore, this inhibition takes place at the transacylation step involving the fatty acyl-CoA ester and the sterol. These results suggest that bile salts can significantly alter the cholesterol-cholesterol ester profile in the liver, and furthermore, that these effects may be influenced by small changes in the intracellular environment in the region where these reactions occur.

Acyltransferases↗
PubMed1977

Interaction of uncharged bile salt derivatives with the ileal bile salt transport system.

Two series of uncharged conjugated bile salt derivatives, N-conjugates of ethanolamine and 3-amino-1,2-propanediol were studied for interaction with the ileal bile salt transport system. Evidence for interaction is threefold. 1) In everted gut sac experiments more material was removed from the mucosal compartment when ileal sacs were used. 2) These derivatives inhibited the in vitro transport of taurocholate. 3) In vivo intestinal perfusion demonstrated greater absorption from ileum than from jejunum. Number three demonstrates that such interactions are followed by transmucosal movement. Their uphill transport was less than taurocholate transport. The Na(+) requirement for cholyl-3-amino-1,2-propanediol interaction with the system was greater than for taurocholate. This observation is similar to that previously observed with taurodehydrocholate, which had a greater Na(+) requirement for transport than taurocholate. Therefore removal of the anionic charge, as well as distortion of steroid shape, increases the Na(+) requirement for substrate interaction with the transport system. These observations support our hypothesis that this interaction involves two recognition components; one includes the steroid moiety, the other a coulombic interaction between the anionic bile salt and a cationic membrane site. Additionally the membrane would have an anionic group to accomodate the Na(+). Both factors (steroidal and coulombic) operate for optimal substrate attachment. Simultaneously the system's affinity for Na(+) increases and active transport then proceeds.

Animals↗
PubMed1976

A sterospecific synthesis of 7alpha-hydroxycholesterol.

The five step synthesis of 7alpha-hydroxycholesterol utilizes the solvolysis of 7alpha-bromocholesterol benzoate with potassium acetate in acetic acid as the key step in controlling the stereospecificity of the reaction sequence. This reaction yields 7alpha-acetoxycholesterol benzoate with retention of configuration at position seven. The diester is readily reduced with lithium aluminum to 7alpha-hydroxycholesterol.

Hydroxycholesterols↗