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Biomedical subjects

J Gustafsson

Publications and source records attributed to J Gustafsson.

At least 127 records · Page 7Linked to original sources
PubMed1980

Biosynthesis of cholic acid in rat liver: formation of cholic acid from 3 alpha, 7 alpha, 12 alpha-trihydroxy- and 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acids.

Conversion of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid into 3 alpha, 7 alpha, 12 alpha 24-tetrahydroxy-5 beta-cholestanoic and cholic acids was catalyzed either by the mitochondrial fraction fortified with coenzyme A, ATP, MgCl2 and NAD or by the combination of microsomal fraction and 100,000 x g supernatant fluid fortified with coenzyme A, ATP and nad. 24-hydroxylation and formation of cholic acid occurred at similar rates with the 25R- and the 25S-forms of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid. The 25R- and 25S-forms of 3 alpha, 7 alpha, 12 alpha-trihydroxy- and 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acids were administered to bile fistula rats. Labeled cholic acid was isolated from the bile. The initial specific radioactivity of cholic acid was higher and the disappearance of radioactivity more rapid after administration of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid than of 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acid. The findings are discussed in relation to the assumed pathway for side chain cleavage in cholic acid biosynthesis.

Adenosine Triphosphate↗
PubMed1980

An in vivo evaluation of the quantitative significance of several potential pathways to cholic and chenodeoxycholic acids from cholesterol in man.

The present study was designed to obtain more definitive information in man on the metabolic pathways to chenodeoxycholic acid and to cholic acid via a pathway not involving an initial 7 alpha-hydroxylation of cholesterol. Four bile fistula patients were administered consecutively two or more of the following 3H-labeled bile acid intermediates: 7 alpha-hydroxycholesterol, 7 alpha-hydroxy-4-cholesten-3-one, 5 beta-cholestane 3 alpha,7 alpha,26-triol, 26-hydroxycholesterol,7 alpha,26-dihydroxy-4-cholesten-3-one, and 5-cholestene-3 beta,12 alpha-diol. Both 7 alpha-hydroxy[7 beta-3H]cholesterol and 7 alpha-hydroxy-4-[6 beta-3H]cholesten-3-one were efficiently converted to bile acids and preferred chenodeoxycholic acid over cholic acid. The specific activity time curves indicated that a portion of cholic acid synthesis did not pass through 7 alpha-hydroxycholesterol. [3H]26-Hydroxycholesterol and [3H]-5-cholestene 3 beta,12 alpha-diol, two potential intermediates of this bypass pathway to cholic acid, were poorly converted to primary bile acids (10 to 27%). The [3H]26-hydroxycholesterol preferred chenodeoxycholic over cholic acid by about 4 to 1. The [3H]5-cholestene 3 beta,12 alpha-diol formed cholic acid in low yield (10 to 20%). It is concluded that pathways to primary acids from cholesterol through 26-hydroxycholesterol and 5-cholestene 3 beta,12 alpha-diol are probably of minor quantitative significance. A selective pathway to chenodeoxycholic acid via 26-hydroxylation of 7 alpha-hydroxy-4-cholesten-3-one was also investigated. The 5 beta-cholestane 3 alpha,7 alpha,26-triol was converted in about equal amounts to cholic and chenodeoxycholic acids. The 7 alpha-hydroxy-4-cholesten-3-one was also efficiently converted to both bile acids but preferred chemodeoxycholic acid. The most efficient precursor of chenodeoxycholic acid was 7 alpha,26-dihydroxy-4-cholesten-3-one, which was efficiently converted to primary bile acids; chenodeoxycholic acid was preferred over cholic acid by approximately 7 to 1. These findings suggest the presence of a major pathway to chenodeoxycholic acid via the 26-hydroxylation of 7 alpha-hydroxy-4-cholesten-3-one and intermediate formation of 7 alpha,26-dihydroxy-4-cholesten-3-one.

Bile↗
PubMed1979

Metabolism of 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid by rat liver in vivo and in vitro.

The metabolism of 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid was studied in the bile fistula rats and in preparations from rat liver homogenates. In the bile fistula rats, the main products were chenodeoxycholic acid, alpha-muricholic acid, and beta-muricholic acid. Only small amounts of cholic acid were formed. Incubations of 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid with microsomes and NADPH yielded as the main product 3 alpha, 6 beta, 7 alpha-trihydroxy-5 beta-cholestanoic acid. The formation of small amounts of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid was shown. The major product in incubations of 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid with microsomes and the 100,000 g supernatant fluid fortified with ATP was identified as 3 alpha, 7 alpha, 24 xi-trihydroxy-5 beta-cholestanoic acid. This compound was converted into chenodeoxycholic acid and its metabolites in the bile fistula rat.

Animals↗
PubMed1978

On the stereospecificity of microsomal "26"-hydroxylation in bile acid biosynthesis.

The stereospecificity of microsomal "26" -hydroxylation in bile acid biosynthesis was studied. Cholesterol was biosynthesized from [2-14C] mevalonate by a rat liver preparation. The cholesterol was converted stepwise into 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestan-26-oic acid by microsomal and soluble fractions of rat liver homogenate. The 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestan-26-oic acid was decarboxylated chemically and the carbon dioxide was assayed for 14C. The amount of radioactivity in the liberated carbon dioxide was assayed for 14C. The amount of radioactivity in the liberated carbon dioxide was such as to indicate complete stereospecificity of the microsomal "26" -hydroxylase system. The system hydroxylates the methyl group in position C-26 (the 25-pro-R methyl group) and its stereospecificity is opposite that of the mitochondrial "26" -hydroxylase system which hydroxylates the methyl group in position C-27 (the 25-pro-S methyl group).

Animals↗
PubMed1978

Effect of biliary obstruction on 26-hydroxylation of C27-steroids in bile acid synthesis.

The effect of biliary obstruction on side chain hydroxylations in the biosynthesis and metabolism of bile acids was studied in the rat. For comparison, several other hydroxylation reactions in bile acid biosynthesis and metabolism were assayed. Biliary obstruction inhibited microsomal 26-hydroxylation of 5beta-cholestane-3alpha,7alpha-diol and microsomal 25- and 26-hydroxylation of 5beta-cholestane-3alpha,7alpha-12alpha-triol. Microsomal 7alpha-hydroxylation of cholesterol and 6beta-hydroxylation of lithocholic acid acid increased significantly, whereas the increase in microsomal 12alpha-hydroxylation of 5beta-cholestane-3alpha,7alpha-diol was less. Mitochondrial 26-hydroxylation of cholesterol, 5-cholestene-3beta,7alpha-diol, and 7alpha-hydroxy-4-cholesten-3-one was stimulated, whereas 26-hydroxylation of 5beta-cholestane-3alpha,7alpha-diol was not affected and that of 5beta-cholestane-3alpha,7alpha,12alpha-triol was markedly inhibited. The results indicate that mitochondrial 26-hydroxylation, particularly of substrates that primarily are precursors of chenodeoxycholic acid, plays a more important role in bile acid biosynthesis under conditions of biliary obstruction than under normal conditions.

Animals↗
PubMed1977

Prolonged induction of germfree bile acid pattern in conventional rats by antibiotics.

Male conventional rats have been treated for five days with benzylpenicillin, neomycin, kanamycin, erythromycin, bacitracintneomycin, succihylsulfathiazole or metronidazole. Total fecal bile acids were analyzed in samples collected during periods of three days during the pretreatment period and during the eight weeks following drug treatment. Metronidazole or succinylsulfathiazole had no or minor effects on the conventional bile acid pattern and the "bile acid index" (ratio beta-muricholic acid/deoxycholic acid) remained low. Benzylpenicillin, neomycin or kanamycin induced a germfree bile acid pattern, i.e. increased the relative amounts of alpha-and beta-muricholic acid in feces and eliminated deoxycholic acid and hyodeoxycholic acid from feces. The high bile acid index was normalized within three weeks after termination of drug treatment but the excretion of alpha- and beta-muricholic acid was not normalized until a normal flora had been established by giving an enema with intestinal contents from intact, oncentional rats. Treatment with eythromycin or bacitracintineomycin also produced a germfree bile acid pattern. In these cases, the bile acid index was not back to normal until after five to eight weeks and the excretion of the muricholic acids was not normalized until an enema with intestinal bacteria had been given. It is suggested that these long-lasting effects of antibiotics on the metabolism of bile acids in the intestinal tract should be considered after short-term antibiotic therapy in humans.

Animals↗
PubMed1976

Specificity of neonatal, androgen-induced imprinting of hepatic steroid metabolism in rats.

The specificity of the neonatal, andreogen-induced, irreversible programming of hepatic steroid metabolism in the rat was investigated. 5-alpha-Dihydrotestosterone propionate and estradiol benzoate were as efficient as testosterone propionate in inducing a male type of liver metabolism in the adult animal, whereas epitestosterone propionate, etiocholanolone propionate, and o,p'-DDT were practically inactive in this respect. These findings indicate that different mechanisms are involved in neonatal imprinting of hepatic steroid metabolism and in the well-known neonatal androgenic and estrogenic induction of persistent estrus and acyclic gonadotropin secreqion.

Androgens↗
PubMed1976

On the heterogeneity of the mitochondrial C27-steroid 26-hydroxylase system.

Mitochondrial 26-hydroxylation of exogenous cholesterol, endogenous cholesterol, and 5beta-cholestane-3alpha,7alpha,12alpha-triol was studied. 26-Hydroxylation of endogenous cholesterol was measured by mass fragmentography. NADPH and isocitrate stimulated 26-hydroxylation of endogenous as well as exogenous cholesterol. 26-Hydroxylation of endogenous cholesterol was linear with time for 15 min, whereas that of exogenous cholesterol was linear with time for at least 40 min. This finding indicates that the fractions of exogenous and endogenous cholesterol that were 26-hydroxylated did not equilibrate. Mg2+ stimulated isocitrate- and NADPH-dependent 26-hydroxylation of exogenous cholesterol but inhibited in the case of endogenous cholesterol. Ca2+ stimulated NADPH-dependent and inhibited isocitrate-dependent 26-hydroxylation of both exogenous and endogenous cholesterol. It is suggested that the differing effect of Mg2+ on the 26-hydroxylation of exogenous and endogenous cholesterol is related to transfer of the steroid to the enzyme. Isocitrate- and NADPH-dependent 26-hydroxylation of exogenous 5beta-cholestane-3alpha,7alpha,12alpha-triol differed from that of exogenous cholesterol in response to Mg2+ and Ca2+. 26-Hydrocylation of 5beta-cholestane-3alpha,7alpha,12alpha-triol was stimulated by Mg2+ in low concentrations but inhibited by Mg2+ and Ca2+ in high concentrations. Mg2+ had the same influence on the 26-hydroxylation of three dioxygenated C27-steroids known to be intermediates in bile acid biosynthesis. The results are not only compatible with heterogeneity of the mitochondrial 26-hydroxylase system but also with differences in the transport of cholesterol and 5beta-cholestane-3alpha,7alpha,12alpha-triol to the enzyme. The finding of a differing effect of Mg2+ on 26-hydroxylation of exogenous and endogenous cholesterol seems to favor differences in transport rather than heterogeneity of the 26-hydroxylase as an explanation of the results.

Animals↗
PubMed1975

Influence of cholesterol feeding on liver microsomal metabolism of steroids and bile acids in conventional and germ-free rats.

The present investigation has aimed at defining the factor responsible for the differences in microsomal metabolism of steroids between germ-free and conventional rats. Cholesterol, cholic acid, taurocholic acid, and chenodeoxycholic acid were fed to conventional and germ-free male rats and the effects on liver microsomal metabolism of 4-[4-14C]androstene-3,17-dione, 5alpha-[4-14C]androstane-3alpha,17beta-diol, [4-14C]-cholesterol, 7alpha-hydroxy-4-[6beta-3H]cholesten-3-one, and [24-14C]lithocholic acid were studied. The most consistent effects were found with dietary cholesterol that stimulated the activities of several of the hydroxylases active on 4-androstene-3,17-dione and 5alpha-androstane-3alpha,17beta-diol and that decreased the 5alpha reduction of 4-androstene-3,17-dione, increased the 7alpha hydroxylation of cholesterol, decreased the 12alpha hydroxylation of 7alpha-hydroxy-4-cholesten-3-one, and increased by 6beta hydroxylation of lithocholic acid. These effects of cholesterol feeding on the microsomal metabolism of steroids in conventional rats made the pattern of microsomal enzyme activities resemble that characteristic of germ-free rats. Cholesterol feeding led to a pronounced increase in the intestinal concentration of beta-muricholic acid in conventional rats. Furthermore, cholesterol feeding to conventional animals led to an intestinal ratio of chenodeoxycholic acid (including its metabolites alpha- and beta-muricholic acid and hyodeoxycholic acid) to cholic acid (including deoxycholic acid) that was almost identical to that in germ-free rats. Conventionalization of germ-free rats for a period of up to 56 days led only to a partial normalization of the liver microsomal metabolism of 5alpha-[4-14C]androstane-3alpha, 17beta-diol and 7alpha-hydroxy-4-[6beta-3H]cholesten-3-one and of the liver microsomal concentration of cytochrome P-450. The concentration of cholesterol was higher in both total liver homogenate and liver microsomal fraction of germ-free rats than in corresponding preparations from conventional rats. In conclusion, it is suggested that cholesterol is one of the factors responsible for the different microsomal metabolism of steroids in germ-free and conventional rats. It is also suggested that cholesterol may play a role as regulator of microsomal enzyme activities.

Androstane-3,17-diol↗
PubMed1975

Biosynthesis of cholic acid in rat liver. 24-Hydroxylation of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid.

Conversion of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-[7beta-3H]cholestanoic acid into 3alpha, 7alpha, 12alpha, 24-tetrahydroxy-5beta-cholestanoic acid in rat liver was catalyzed either by the mitochondrial fraction fortified with the 100,000 times g supernatant fluid or the microsomal fraction fortified with 100,000 times g supernatant fluid and ATP. The microsomal system was more active than the mitochondrial system. With the microsomal system the rate of reaction was considerably faster with free 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid as substrate than with the corresponding coenzyme A ester. Addition of coenzyme A inhibited the activity. Addition of cofactors other than ATP and coenzyme A did not markedly influence the reaction. The 100,000 times g supernatant fluid could be substituted with a protein fraction obtained by ammonium sulfate precipitation and Sephadex chromatography of the 100,000 times g supernatant fluid. The reaction was not catalyzed by a mixed function oxidase since there was no incorporation of 18O into the product when the reaction was performed in an atmosphere containing 18O2. On the other hand, oxygen may be obligatory since there was almost complete inhibition when the reaction was performed in an atmosphere consisting of nitrogen. Carbon monoxide did not inhibit the reaction. One atom of deuterium was incorporated into the product when the reaction was performed in a medium containing deuterated water. It was concluded that microsomal 24-hydroxylation of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid involves the combined action of a desaturase and a hydratase. The reaction catalyzed by the hydratase appears to be stereospecific since the 24alpha epimer of 3alpha, 7alpha,12alpha-trihydroxy-5beta-cholestanoic acid was the predominant product. In contrast to the microsomal system, the mitochondrial system was not stimulated by the addition of ATP and was not inhibited by coenzyme A. The coenzyme A ester of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid was 24-hydroxylated more efficiently than the free acid.

Animals↗
PubMed1975

Biosynthesis of bile acids in man. Hydroxylation of the C27-steroid side chain.

The first step in the degradation of the steroid side chain during biosynthesis of bile acids from cholesterol in man was studied in microsomal and mitochondrial fraction of homogenate of livers from 14 patients. The microsomal fraction was found to catalyze an efficient 25-hydroxylation of 5,8-cholestane-3a,7a,12atriol. A small extent of 23-, 24-, and 26-hydroxylation of the same substrate was observed. 53-Cholestane-3a,7adiol was hydroxylated in the 25-position only to a very small extent. The mitochondrial fraction was found to catalyze 26-hydroxylation of cholesterol, 5-cholestene-3P,7a-diol, 5P-cholestane-3a,7a-diol, 7a-hydroxy-4-cholesten-3-one, and 5,0-cholestane-3a,7a,12a-triol. Addition of Mg++ stimulated the 26-hydroxylation of cholesterol but had no effect or an inhibitory effect on 26-hydroxylation of the other substrates, indicating a heterogeneity of the mitochondrial 26-hydroxylating system. The level of 26-hydroxylase activity towards different substrates varied considerably with different mitochondrial preparations. The roles of the microsomal and mitochondrial 26- hydroxylations as well as the microsomal 25-hydroxylation in biosynthesis of bile acids in man are discussed. The results indicate that microsomal 26-hydroxylation is less important than mitochondrial 26-hydroxylation under normal conditions. The possibility that microsomal 25-hydroxylation is important cannot be ruled out.

Adult↗