Altered Steroid Δ4-Reductase Activity in Mammary Tumor-bearing Rats

Yusuf J. Abul-Hajj

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The effect of mammary tumors on steroid Δ4-reductase activity was investigated using in vitro and in vivo studies in three transplantable rat mammary tumors. Steroid Δ4-5α-reductase activity was measured spectrophotojnetrically and was significantly decreased in the host livers from R3230AC and MT/W9a-B but was increased in 7,12-dimethylbenz(a)anthracene-induced No. 14 tumor-bearing rats. There were no significant alterations of 5β-reductase activity in all animals investigated. In vivo studies using [14C]testosterone showed a similar pattern for saturation of the 4(5-double bond but that the more than doubled increase in 4,5-reduced metabolites observed in the in vivo studies in 7,12-dimethylbenz(a)anthracene-induced tumor-bearing rats cannot be explained by the increase observed in hepatic enzyme activity. Incubations with mammary tumor tissues showed that 7,12-dimethylbenz(a)anthracene-induced tumors have a very active Δ4-5α-reductase enzyme which accounts for the observed increases in in vivo results. The surgical removal of the tumor abolishes the impairment in Δ4-reductase activity.

Original languageEnglish (US)
Pages (from-to)1329-1333
Number of pages5
JournalCancer Research
Issue number4
StatePublished - Apr 1 1981


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