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Cytochrome P450 (CYP) enzymes have well characterized functions in dispositionand pharmacokinetics of xenobiotics as well as in biosynthesis and/or metabolismof endogenous compounds, such as steroid hormones, bile acids, arachidonic acid andits derivatives. Cytochrome P450 mediated metabolic activation is known to be a prerequisitefor the cytotoxic and mutagenic activity of many environmental toxins and procarcinogens.Xenobiotic and steroid-metabolizing P450 enzymes are found in many tissues in thebody, although at lower levels than in the liver and adrenal glands. It is the majorhypothesis of this thesis that cell-specific expression of P450 can influence hormonemetabolism and xenobiotic toxicity in target cells. In order to test this theorywe have investigated P450 mediated activation of procarcinogens in the lung and characterizedthe P450 content of rat and human breast. Environmental factors have been implicated in the etiology of both lung and breastcancer. Heterocyclic amines are a group of dietary procarcinogens, that produce tumorsat multiple sites in experimental animals and that have been proposed to play a rolein human cancer. The capacity of rat and mouse lung microsomes to activate the heterocyclicamines IQ, MelQx and PhlP was demonstrated using the Ames mutagenicity test. Withinhibitory antibodies it was shown that CYP2A3 mediated a large part of the activationof IQ in rat lung microsomes. CYP2A3 has been detected in rat lung and nasal mucosa,but not in the liver and thus these studies underscore the importance of studyingextrahepatic reactions. The mammary gland is characterized by its hormonal regulation of growth and differentiation.In studies on rat breast, we could show that the P450 profile also varies with ageand endocrine status of the animals. Quantitation of enzyme levels was achieved afterpartial purification of P450 and expression of P450 enzymes was analysed by Westernblot of the protein in combination with RT PCR of mRNA. The studied P450

This study was undertaken to examine the effect on the rat embryonic heart of two experimental drugs (AZA and AZB) which are known to block the sodium channel Nav1.5, the hERG potassium channel and the L-type calcium channel. The sodium channel blockers bupivacaine, lidocaine, and the L-type calcium channel blocker nifedipine were used as reference substances. The experimental model was the gestational day (GD) 13 rat embryo cultured in vitro. In this model the embryonic heart activity can be directly observed, recorded and analyzed using computer assisted image analysis as it responds to the addition of test drugs. The effect on the heart was studied for a range of concentrations and for a duration up to 3 h. The results showed that AZA and AZB caused a concentration-dependent bradycardia of the embryonic heart and at high concentrations heart block. These effects were reversible on washout. In terms of potency to cause bradycardia the compounds were ranked AZB > bupivacaine > AZA > lidocaine > nifedipine. Comparison with results from previous studies with more specific ion channel blockers suggests that the primary effect of AZA and AZB was sodium channel blockage. The study shows that the short-term rat whole embryo culture (WEC) is a suitable system to detect substances hazardous to the embryonic heart.

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Cytochrome P450 (CYP) enzymes have well characterized functions in disposition and pharmacokinetics of xenobiotics as well as in biosynthesis and/or metabolism of endogenous compounds, such as steroid hormones, bile acids, arachidonic acid and its derivatives. Cytochrome P450 mediated metabolic activation is known to be a prerequisite for the cytotoxic and mutagenic activity of many environmental toxins and procarcinogens. Xenobiotic and steroid-metabolizing P450 enzymes are found in many tissues in the body, although at lower levels than in the liver and adrenal glands. It is the major hypothesis of this thesis that cell-specific expression of P450 can influence hormone metabolism and xenobiotic toxicity in target cells. In order to test this theory we have investigated P450 mediated activation of procarcinogens in the lung and characterized the P450 content of rat and human breast. Environmental factors have been implicated in the etiology of both lung and breast cancer. Heterocyclic amines are a group of dietary procarcinogens, that produce tumors at multiple sites in experimental animals and that have been proposed to play a role in human cancer. The capacity of rat and mouse lung microsomes to activate the heterocyclicamines IQ, MelQx and PhlP was demonstrated using the Ames mutagenicity test. With inhibitory antibodies it was shown that CYP2A3 mediated a large part of the activation of IQ in rat lung microsomes. CYP2A3 has been detected in rat lung and nasal mucosa, but not in the liver and thus these studies underscore the importance of studying extrahepatic reactions. The mammary gland is characterized by its hormonal regulation of growth and differentiation. In studies on rat breast, we could show that the P450 profile also varies with age and endocrine status of the animals. Quantitation of enzyme levels was achieved after partial purification of P450 and expression of P450 enzymes was analysed by Western blot of the protein in combination with RT PCR of m