No 17a hydroxylase activity has been detected in the brain but its activity in this tissue has been inferred from the accumulation of dehydroepiandrosterone (DHEA) and its sulfate ester in brains of adrenalectomized and castrated rats (12). RT-PCR revealed the presence of P45017 mRNA throughout the brain at very low levels (14). According to the criteria previously listed, there is not enough information available to assign a physiological meaning of this RT-PCR detection. The relevance of the PCR detection is particularly troubling because there was a signal, larger than that in the brain regions, detected in the liver. The liver has no measurable 17a hydroxylase activity. One possible explanation for the presence of P45017 mRNA and not protein could be that P45017 was functional early in embryogenesis and is no longer necessary in the adult. In agreement with this concept, Compagnone et al. (61) have found that P45017 is expressed in the nervous system of the developing rodent embryo. In this case the mRNA could be detected by RT-PCR in the head of E15.5 to E19.5 rat embryos and immuno-
cytochemically detectable P450c17 protein was expressed in the nervous system as early as embryonic d E10.5
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