Aryl hydrocarbon (benzo[a]pyrene) hydroxylase development in rat mammary tissue

Aryl Hydrocarbon Hydroxylase Activity in Spontaneous Mammary Tumors in Rat

“…The only differences in enzyme activities in var ious tissues of the rats were found between age groups: either AHH or NCR activities were lower in old than in young rats' liver, lungs or tumors. The decrease of activity with old age is well known in liver and is also found in mammary tissue [19].…”

“…the activity observed in the absence of any inducing agents, is normal ly suppressed by the activity of the negative regulatory element [25], Kimura et al [26] reported elevated P 4 5 0 I A I mRNA levels without foreign chemi cal stimulation during differentiation in mouse embryos, embryonal carcinoma cells 30 Pyykkö/J aakkola/Södcrst röm/ Lamminen AHH in Rai Mammary Tumors and in regenerating mouse liver after partial hepatectomy. Fysh and Okey [ 19] found a sig nificant twofold increase in constitutive mammary AHH activity in control female Sprague-Dawley rats at about the time of pu berty, between days 28 and 35. The common feature of these unstimulated elevations of gene expression is that they occurred in tissue or cells which are in the active growth and/or differentiation phase.…”

“…The basal AHH activity level in nontumorous mammary gland tissue is extremely low: AHH activities of 10-60 fmol/min/mg have been reported for noninduced adult rats [9,18,19]. In cultured mammary carcinoma cells, the basal level of cytochrome P450IAI is reported to be undetectable when measured by AHH activity assay [20] or immunocytochemically [21], or by analysis of P450IAI mRNA expression [22,23].…”