Synthesis of steroids in pancreas: evidence of cytochrome P-450scc activity.
In pancreas, the activities of several sex steroid-transforming enzymes have been reported. Data have been obtained in perfused organs, total tissue homogenates, and subcellular organelles. These data, concurrent with the description of the presence of ligand-regulated steroid receptors, as well as the sexually dimorphic behavior of some pancreatic tumors, are clear evidence in support of the participation of steroid hormones in the pancreatic function. In this study, the steroidogenic ability of the pancreas was demonstrated by two different methods: (a) in tissue homogenates, by the identification of cytochrome P-450scc gene (CYP11A) transcripts after reverse transcription-polymerase chain reaction amplification (RT-PCR); and (b) in isolated mitochondria by the glutethimide-dependent inhibition of cholesterol-pregnenolone biotransformation. The results obtained in a series of independent experiments showed that (a) the pancreatic tissue possessed transcriptional activity of the CYP11A gene, although to a lesser extent than the typical steroidogenic tissues, and (b) isolated mitochondria obtained from the pancreas were able consistently to synthesize pregnenolone; furthermore, the addition of the specific inhibitor aminoglutethimide (AMG) blocked its synthesis. On the whole, these findings are interpreted as clear evidences of the activity of the cytochrome P-450scc enzymatic complex (P450scc), responsible for the transformation of cholesterol into pregnenolone and considered the first and limiting step in steroid biosynthesis.
Department of Reproductive Biology, Instituto Nacional de la Nutrición Salvador Zubirán, Tlalpan, DF México.
A
A
Morales
A
A
Cuéllar
J
J
Ramírez
F
F
Vilchis
V
V
Díaz-Sánchez
D000616:Aminoglutethimide / Q000494:pharmacology; D000818:Animals; D001711:Biotransformation / Q000187:drug effects; D002458:Cell Fractionation; D002784:Cholesterol / Q000096:biosynthesis*; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers / Q000737:chemistry; D004285:Dogs; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009710:Nucleotide Mapping; D010179:Pancreas / Q000201:enzymology*; D011284:Pregnenolone / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D017931:DNA Primers; D012333:RNA, Messenger; D000616:Aminoglutethimide; D011284:Pregnenolone; D002784:Cholesterol; D002786:Cholesterol Side-Chain Cleavage Enzyme