The expression of cytochrome P450scc, encoded by the CYP11A gene, was investigated in the rat kidney from birth to adulthood. In the male and female rat kidneys, the corresponding mRNA was detected by semi-quantitative reverse transcriptase and polymerase chain reaction (RT-PCR) analysis with specific primers, resulting in higher levels of expression during the first 15 days from birth. RT-PCR and sequence analysis showed that the P450scc mRNA coding region was the same for both kidney and testis, whereas 5'-RACE analysis (rapid amplification of cDNA ends) demonstrated that the renal transcription utilizes a distal transcription start site (TSS) located 76 b upstream of that used in ovarian and testicular P450scc mRNA expression, which is placed 43 b upstream of the first ATG. The 5'-UTR sequence of renal P450scc cDNA exactly matched the contiguous upstream untranslated region of the gene, suggesting that alternative splicing was not involved in the synthesis of this transcript. Northern hybridization detected a specific transcript only in the newborn male, but not in adult rat kidney, confirming the higher levels of expression in the first days of the rat's life. Positive immunodetections of cytochrome P450scc were found in renal cortical distal tubules and the results were confirmed by Western blotting analysis. As demonstrated by semi-quantitative RT-PCR, the male kidney also expresses the messengers corresponding to the steroidogenic acute regulatory (StAR) and steroidogenic factor 1 (SF-1) proteins, which are normally required for steroidogenesis in steroidogenic tissues, such as gonads and adrenal cortex. These studies suggest that the rat kidney has the capability for local steroid hormone production, although the physiological significance of the pregnenolone eventually produced remains to be established.