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The biosynthesis of androst-16-enes in boar testis tissue.

ABSTRACT: 1. The metabolism of [4-(14)C]pregnenolone to androst-16-enes has been studied in short-term incubations of boar testis tissue. With fresh tissue androsta-5,16-dien-3beta-ol (8%) and 5alpha-androst-16-en-3beta-ol (2%) were formed. Tissue that had been stored at -20 degrees C was still capable of metabolizing pregnenolone to androsta-5,16-dien-3beta-ol. 2. NADPH was essential for the formation of androsta-5,16-dien-3beta-ol from pregnenolone; NADH had less activity and ATP was not necessary for the reaction. 3. [4-(14)C]Androsta-5,16-dien-3beta-ol, prepared biosynthetically from [4-(14)C]pregnenolone, was shown to be converted by boar testis preparations into androsta-4,16-dien-3-one (31%) if NAD(+) was present or into 5alpha-androst-16-en-3beta-ol (4%) if NADPH was present. 4. 17alpha-Hydroxyandrost-4-en-3-one and 3beta,17alpha-dihydroxypregn-5-en-20-one were considered as possible precursors for androst-16-ene formation, but both were shown to be ineffective. 5. No radioactivity was incorporated into androst-5-en-3beta-ol used to trap any corresponding (14)C-labelled compound formed from [4-(14)C]pregnenolone.

SUBMITTER: Katkov T

PROVIDER: S-EPMC1178957 | biostudies-other | 1970 Apr

REPOSITORIES: biostudies-other

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Project description:1. In one experiment [7alpha-(3)H]pregnenolone was infused continuously for 12min into the left spermatic artery of a sexually mature boar and blood was collected during this period by continuous drainage from the spermatic vein. After infusion, the testis was removed and immediately cooled to -196 degrees C. 2. From both the testicular tissue and the spermatic venous plasma, (3)H-labelled 16-unsaturated C(19) steroids were isolated and characterized and their radiochemical purity was established. 5alpha-Androst-16-en-3alpha- and 3beta-ol occurred mainly as sulphate conjugates and to a lesser extent as free steroids. Only traces of these alcohols occurred as glucosiduronate conjugates. 5alpha-Androst-16-en-3-one was found in the free (ether-extractable) fraction. 3. The isotope concentration of each of the (3)H-labelled 16-unsaturated C(19) steroids in testicular tissue was different from that in spermatic venous plasma. 4. The ratios of tritiated 5alpha-androst-16-en-3alpha- and 3beta-ol (free steroids) to their respective sulphate conjugates in the testicular tissue were less than the ratios of the same compounds in the spermatic venous plasma. The possibility that the sulphates are partially hydrolysed by testicular sulphatases before secretion is discussed. 5. In a second experiment, a continuous close-arterial infusion of [7alpha-(3)H]pregnenolone into the left testis was performed over a 200min period and all the urine that accumulated during the infusion was collected for analysis. 6. No (3)H-labelled 16-unsaturated C(19) steroids were detected in the urine as free steroids. Only a trace of 5alpha-androst-16-en-3alpha-ol was detected conjugated as glucosiduronate, whereas the corresponding 3beta-alcohol occurred mainly as glucosiduronate and to a lesser extent as sulphate. 7. The absence of 5alpha-androst-16-en-3beta-ol glucosiduronate in the spermatic venous blood and its presence in considerable amount in the urine may be attributed to hepatic glucuronyl transferase activity.

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The biosynthesis of androst-16-enes in boar testis tissue.

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