Methadone maintenance: effect of urinary pH on renal clearance in chronic high and low doses.

The subjects were 12 male patients stabilized on methadone for many months or years. A comparison was made of the plasma levels and renal clearance of methadone between patients on "high" doses (80 to 110 mg/day) and those on "low" doses (15 to 40 mg/day). A general trend to higher renal clearance was seen in the "high" -dose group, but on more detailed examination there was a direct correlation only when the patients were categorized by urinary pH. At low pHs, there was nearly a 3-fold increase in renal clearance which was associated with a decreased major metabolite to methadone ratio. No evidence for a difference in rate of metabolism between the two groups was found nor were there differences in hepatic function. It was concluded that urinary pH was a major factor in renal clearance of methadone.

Endocrine mediation of psychosocial stressor effects on mouse mammary tumor growth.

We have demonstrated that differential housing alters the growth rate of the androgen-responsive Shionogi mouse mammary carcinoma (SC115). In the present study we wished to determine if changes in plasma levels of hormones or a shift in the responsiveness of the tumor cells to hormones was responsible for the differential tumor growth rates observed. Plasma testosterone and corticosterone levels were assayed 24 h, 3 days and 1 week post tumor cell/vehicle injection. Also 3 weeks post injection androgen and glucocorticoid receptor binding capacity (Bmax) and binding affinity (Kd) and the in vitro responsiveness of tumor cells to dihydrotestosterone and hydrocortisone were measured. At 24 h post injection, plasma testosterone levels were significantly increased in mice with large tumors, but remained low in mice with small tumors. Plasma corticosterone levels were significantly elevated in mice with small tumors compared to those of mice with large tumors at all time points measured. Androgen and glucocorticoid receptor binding capacity and binding affinity of tumor cells did not differ among groups. Further, all groups tested had the ability to respond to dihydrotestosterone and hydrocortisone in vitro. These data indicate that an effect of housing condition on plasma levels of steroid hormones may, in part, mediate the differential tumor growth rates observed in this model.

Effect of flutamide on hepatic cytosolic methyltrienolone (R1881) binding kinetics and testosterone responsive hepatic drug and steroid metabolism in the adult male rat.

Flutamide was used to investigate the mechanism involved in androgen responsive hepatic microsomal drug and steroid metabolism. We compared the antiandrogenic action of flutamide on the prostate to its effect on testosterone responsive hepatic microsomal benzo[a]pyrene hydroxylase (BPH) and testosterone reductase (TR) activities. Male Wistar rats, castrated as adults, were treated with 5 mumoles.kg-1.day-1 of testosterone enanthate subcutaneously for 10 days. Co-administration of increasing doses of flutamide caused a dose-dependent reduction in prostate to body weight ratios and, in the same animals, caused significant alterations in adult male hepatic microsomal BPH and TR activities. These doses of flutamide did not affect the serum testosterone levels. To test the possibility that the action of flutamide on androgen responsive hepatic microsomal drug and steroid metabolism may be similar to that occurring in the prostate, a tissue which contains an androgen receptor, we also studied the effect of flutamide on the binding kinetics of the high affinity hepatic cytosolic [3H]R1881 binding protein in vivo. Scatchard analysis of [3H]R1881 binding data revealed a reduction in the binding capacity of the hepatic cytosolic androgen binding protein in castrated animals treated with a combination of flutamide and testosterone enanthate at doses capable of maximally altering hepatic microsomal drug and steroid metabolism. No alteration in binding affinity occurred in this treatment group. However, a decreased binding affinity was found when flutamide alone was given. The binding kinetics of the hepatic cytosolic androgen binding protein were not altered in the castrated adult male with or without testosterone treatment. When flutamide was injected daily into the intact adult female rat, no effect was observed on either hepatic microsomal BPH or TR activities. Taken together, these data indicate that flutamide reduces hepatic cytosolic R1881 binding in the adult male rat, and this may explain some of the effects of this antiandrogen on testosterone-sensitive hepatic microsomal drug and steroid metabolism.

Growth hormone regulation and developmental expression of rat hepatic CYP3A18, CYP3A9, and CYP3A2.

The present study investigated the role of growth hormone (GH) in hepatic CYP3A18 and CYP3A9 expression in prepubertal and adult male rats. For comparison, the effects of GH on CYP3A2 expression were also measured. Initial experiments demonstrated that CYP3A18 mRNA levels were greater during puberty and adulthood than during the prepubertal period, CYP3A9 mRNA was not expressed until puberty and its expression increased in adulthood, and CYP3A2 mRNA levels were relatively constant from prepuberty to adult life. Hypophysectomy, which results in the loss of multiple pituitary factors including GH, increased CYP3A2 and CYP3A18 mRNA expression 3- to 4-fold, but it did not affect CYP3A9 mRNA levels or CYP3A-mediated testosterone 2beta- or 6beta-hydroxylase activity in adult rats. GH administered as twice daily s.c. injections (0.12 microg/g body weight) to hypophysectomized or intact adult rats did not affect CYP3A18 or CYP3A9 mRNA expression. The same treatment decreased CYP3A2 mRNA and protein and testosterone 2beta- and 6beta-hydroxylase activity levels in intact but not hypophysectomized rats. However, in intact prepubertal rats, intermittent GH administration decreased CYP3A18 and CYP3A2 mRNA levels, but a higher dosage (3.6 microg/g) was required to suppress CYP3A2. Overall, the present study demonstrated that: (a) the constitutive expression of CYP3A18, CYP3A9, and CYP3A2 does not require the presence of GH, (b) CYP3A18 is more sensitive than CYP3A9 to GH modulation in adult rats; and (c) CYP3A2 is less sensitive to the suppressive influence of GH during the prepubertal period than during adult life.

Differential effects of diabetes on microsomal metabolism of various substrates. Comparison of streptozotocin and spontaneously diabetic Wistar rats.

We have examined the effect of recent onset diabetes on several aspects of hepatic microsomal metabolism in both streptozotocin (STZ)-induced and spontaneously diabetic BioBreeding (BB) male and female Wistar rats. Differential alterations of the diabetic state on hepatic microsomal enzyme activities were observed. Female diabetic rats exhibited no change in benzo [a]pyrene (BP) hydroxylase activity, a decrease in testosterone delta 4-hydrogenase, and an increase in aniline hydroxylase. On the other hand, male diabetic rats demonstrated a decrease in hepatic BP hydroxylase activity, no change in testosterone delta 4-hydrogenase, and an increase in aniline hydroxylase. Insulin treatment corrected these effects. No change in kidney BP hydroxylase activity was apparent in either female or male diabetics. There were no marked differences between the chemically induced and genetic models of diabetes with respect to the metabolism studies. Serum testosterone levels were significantly lower than control in male BB diabetics, whereas no change was apparent in female diabetics. Light microscopy and serum insulin determinations indicated that the spontaneously diabetic animals we examined were not severely diabetic. From electrophoresis of hepatic microsomal proteins we determined that spontaneous diabetes of short duration does alter the protein distribution in the cytochrome P-450 region. We conclude that the acute effects of STZ-induced and spontaneous diabetes on hepatic microsomal metabolism are quantitatively and qualitatively similar, despite probable differences in etiology of the diabetic state.

Impact of tamoxifen on peripubertal androgen imprinting of rat hepatic cytochrome P450 2C11, cytochrome P450 3A2, and steroid 5 alpha-reductase.

Expression of sex-dependent rat hepatic cytochromes P450 and steroid 5 alpha-reductase is regulated mainly by the sex-specific pattern of growth hormone (GH) secretion and is subject to androgen imprinting. Since tamoxifen suppresses GH pulse amplitude and nadir levels, we investigated the effect of tamoxifen on peripubertal testosterone imprinting of hepatic CYP2C11, CYP3A2, CYP2A1, and steroid 5 alpha-reductase. Prepubertal tamoxifen administration (5 mg once daily s.c. on days 28 and 29 of age) to non-ovariectomized female Sprague-Dawley rats did not affect hepatic microsomal CYP2C11-dependent testosterone 2 alpha-hydroxylase, CYP3A-mediated testosterone 6 beta-hydroxylase, CYP2A1-dependent testosterone 7 alpha-hydroxylase, or steroid 5 alpha-reductase activity in adult rats. Testosterone treatment (5 mumol/kg, s.c., once daily) of intact female rats during either puberty (days 35-49 of age) or adult life (days 69-77 of age) had no effect on these enzyme activities in adult (78-day-old) female rats, but the same treatment given during both of these periods induced the male-specific testosterone 2 alpha- and 6 beta-hydroxylase activities and suppressed the female-predominant testosterone 7 alpha-hydroxylase and steroid 5 alpha-reductase activities, indicating that peripubertal testosterone administration imprints the adult androgen responsiveness but not the basal levels of these enzyme activities in non-ovariectomized female rats. However, peripubertal androgen imprinting of the basal levels of testosterone 2 alpha-hydroxylase and steroid 5 alpha-reductase activities was observed in female rats administered tamoxifen prepubertally. Tamoxifen pretreatment also enhanced testosterone imprinting of the adult androgen responsiveness of testosterone 2 alpha- and 6 beta-hydroxylase and steroid 5 alpha-reductase activities. The enhanced testosterone hydroxylase activities were, however, not associated with an increase in microsomal NADPH-cytochrome P450 reductase activity, but were accompanied by elevated hepatic CYP2C11 and CYP3A2 protein levels. Overall, the present study indicates that prepubertal tamoxifen administration does not interfere with the normal sex differentiation of the gender-dependent hepatic cytochromes P450 and steroid 5 alpha-reductase, but this drug modulates peripubertal androgen imprinting of CYP2C11, CYP3A2, and steroid 5 alpha-reductase in adult female rats.

Testosterone metabolism in rat liver cytosolic androgen binding assays.

Testosterone metabolism was studied in vitro, using incubation conditions similar to those employed in some adult male rat liver cytosolic androgen receptor assays. Following extraction, thin layer chromatography, and gas chromatography-mass spectrometric analysis, it was observed that testosterone was significantly metabolized in vitro to 5 beta-androstane-3 alpha, 17 beta-diol. These results indicate that gross inaccuracies can be made when estimating the free testosterone concentrations in hepatic cytosolic androgen binding studies.

Hepatic microsomal ethoxyresorufin O-deethylase-inducing potency in ovo and cytosolic Ah receptor binding affinity of 2,3,7,8-tetrachlorodibenzo-p-dioxin: comparison of four avian species.

The hepatic microsomal ethoxyresorufin O-deethylase (EROD)-inducing potency in ovo of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was determined in the domestic chicken (Gallus gallus), domestic pigeon (Columba livia), great blue heron, and double-crested cormorant. Dose-response curves were produced by injecting various doses of [3H]TCDD into the air sac of developing eggs during the latter third part of incubation. Hepatic EROD activities were measured in day-old hatchlings. Liver, yolk, and whole blood were analyzed for [3H]TCDD; no distributional differences among species were found. The ED50 for EROD induction was between one and two orders of magnitude lower in the chick (0.1 microgram/kg egg) than in the heron and cormorant (3-10 micrograms/kg egg). Consistent with this, the apparent affinity of TCDD for the hepatic cytosolic Ah receptor was about 15 times higher in the domestic chick (Kd = 0.75-1.6) than in the other avian species (pigeon, Kd = 11-14; heron, Kd = 10-20; cormorant, Kd = 12-16). Receptor binding affinities in the pigeon, heron, and cormorant were of the same order of magnitude as that reported for human placenta (D.K. Manchester, S.K. Gordon, C.L. Golas, E.A. Roberts, and A.B. Okey, 1987, Cancer Res. 47, 4861-4868). Subcutaneous edema was observed in TCDD-treated hatchlings of the chick, heron, and cormorant, but not of the pigeon, within the dose range examined. The laboratory dose-response relationships demonstrated that the heron and cormorant hatchlings that were exposed to TCDD and related chemicals in the Strait of Georgia (J.T. Sanderson, R.J. Norstrom, J.E. Elliott, L.E. Hart, K.M. Cheng, and G.D. Bellward (1994b) J. Toxicol. Environ. Health 41, 245-263; and J.T. Sanderson, J.E. Elliott, R.J. Norstrom, P.E. Whitehead, L.E. Hart, K.M. Cheng, and G.D. Bellward (1994a) J. Toxicol. Environ. Health 41, 435-450) had hepatic EROD activities at the lower end of the linear part of their respective dose-response curves. A further increase in levels of TCDD and related compounds in the environment would lead to a large increase in EROD activity and further increases in TCDD-induced toxicities, such as body weight loss and subcutaneous edema.

Effect of cimetidine on hepatic cytochrome P450: evidence for formation of a metabolite-intermediate complex.

Cimetidine is an inhibitor of hepatic cytochrome P450 (CYP) in vivo and in vitro in both rats and humans. However, the concentrations of cimetidine required to inhibit drug metabolism in hepatic microsomes in vitro are 100-1000-fold higher than those associated with a similar degree of inhibition in vivo. Recently, we provided evidence indicating that cimetidine selectively inhibits CYP2C11 in the rat and that it acts by forming a metabolite-intermediate (MI) complex. To investigate this further, optical-difference spectroscopy was performed with the use of microsomes from uninduced and phenobarbital-induced male rats treated with cimetidine in vivo or, after a preincubation step, in vitro. In microsomes from uninduced rats treated with cimetidine in vivo or in vitro, a spectral peak at 428-430 nm was observed that was not dissociated by the addition of potassium ferricyanide. The spectral peak obtained with cimetidine in vitro was dependent on the presence of NADPH and on the concentration of cimetidine in the reaction mixture, indicating the presence of an MI complex. The magnitude of this complex was reduced in microsomes from phenobarbital induced rats that were administered cimetidine either in vivo or in vitro. The formation of the complex was also inhibited by preincubation of the microsomes with anti-rat CYP2C11 immunoglobulin. These results are consistent with the hypothesis that cimetidine inhibits CYP in vivo in the rat by forming an MI complex, largely with CYP2C11, and that this complex can be generated in vitro by incubating microsomes with cimetidine in the presence of NADPH.

In ovo 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure in three avian species. 1. Effects on thyroid hormones and growth during the perinatal period.

Thyroid hormones are important in the perinatal growth and development of avian species, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds have been shown to cause alterations in these hormones in laboratory animals. Since the decreased reproductive success in certain fish-eating bird populations exposed to TCDD and related compounds is characterized by high embryo and hatchling mortality, we examined the effects of in ovo TCDD exposure on plasma thyroid hormone concentrations (total T3, total T4) and body and skeletal growth during the perinatal period in the domestic chicken (Gallus gallus), domestic pigeon (Columba livia), and great blue heron (Ardea herodias). Hepatic ethoxyresorufin O-deethylase (EROD) activity was also determined as an enzymatic marker of cytochrome P450IA induction by TCDD. [3H]TCDD was injected into the air cell of chicken eggs (21-day incubation period) on Embryonic Day 4.5 (0.1 microgram/kg egg), pigeon eggs (18-day incubation period) on Embryonic Day 3.5 (1 microgram/kg egg) and Embryonic Day 14 (3 microgram/kg egg), and heron eggs (28-day incubation period) at approximately the midpoint of incubation (2 microgram/kg egg). Chickens were euthanized on Embryonic Days 17 and 19, day of hatch (Embryonic Day 21), and Days 2 and 4 after hatch. Pigeons and herons were euthanized either at hatch (Embryonic Days 18 and 28, respectively), or fed an uncontaminated diet for 7 days prior to sacrifice. Although hepatic EROD activity was induced 13- to 43-fold above controls in chickens, there was no effect of TCDD exposure on hatchability, body growth, subcutaneous edema, or plasma thyroid hormone levels. In pigeons exposed to TCDD on Embryonic Day 3.5, EROD was induced 6- to 15-fold, hatchability was decreased, liver to body weight ratio was elevated, and body and skeletal growth were decreased (p < 0.01); however, there was no effect of TCDD exposure on plasma thyroid hormone levels. Similarly, in pigeons exposed to TCDD on Embryonic Day 14, EROD was induced 10- to 14-fold, liver to body weight ratio was elevated, and body and skeletal growth were decreased (p < 0.01), but there was no effect of TCDD treatment on plasma thyroid hormone levels. In herons, hepatic EROD activity was induced 2- to 3-fold above control birds, similar to EROD activities measured in heron hatchlings exposed to environmental levels of TCDD and related chemicals in the Strait of Georgia, British Columbia. However, this level of TCDD exposure had no effect on plasma thyroid hormone levels or body growth in herons. Collectively, these results suggest that perinatal plasma thyroid hormone levels cannot be used as relatively noninvasive biomarkers of TCDD exposure during embryonic development in chickens, pigeons, and great blue herons.

In ovo 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure in three avian species. 2. Effects on estrogen receptor and plasma sex steroid hormones during the perinatal period.

As opposed to mammals, the heterogametic sex in birds is female, and sexual differentiation of the central nervous system away from the intrinsic male pattern is dependent on ovarian estrogen secretions during the perinatal period. The contamination of aquatic systems with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds has been suggested to be responsible for decreased reproductive success in certain wild fish-eating bird populations. Since TCDD has been shown to alter estrogenic status in laboratory animals, we determined the effects of in ovo TCDD exposure on hepatic estrogen receptor (ER) concentrations and affinities, and plasma estradiol concentrations during the perinatal period in the domestic chicken (Gallus gallus), domestic pigeon (Columba livia), and great blue heron (Ardea herodias). Plasma testosterone levels were also determined in herons as an indication of androgenic status. [3H]TCDD was injected into the air cell of chicken eggs on Embryonic Day 4.5 (0.1 microgram/kg egg), pigeon eggs on Embryonic Day 3.5 (1 microgram/kg egg) and Embryonic Day 14 (3 micrograms/kg egg), and heron eggs at approximately Embryonic Day 13 (2 micrograms/kg egg). Chickens were euthanized on Embryonic Days 17 and 19, hatch, and Days 2 and 4 after hatch. Pigeons and herons were either euthanized at hatch or fed an uncontaminated diet for 7 days prior to termination. Between 5 and 10% of the injected [3H]TCDD dose was measured in the liver of hatchlings. There was no effect of in ovo TCDD exposure on hepatic ER levels or plasma estradiol concentrations in female chickens and pigeons exposed early in incubation. In female pigeons exposed during the latter third part of incubation to a TCDD dose that would cause high embryo lethality if injected early in incubation, hepatic ER concentrations were elevated (p < 0.001) and plasma estradiol concentrations were decreased (p < 0.01) at hatch. There was no effect of TCDD exposure on plasma estradiol levels in male pigeons. In herons, TCDD exposure had no effect on hepatic ER levels or plasma estradiol and testosterone concentrations at either time point. We conclude that in chicken, pigeon, and great blue heron hatchlings exposed early in incubation to low doses of TCDD, hepatic ER levels and plasma estradiol concentrations are not biomarkers of toxicity.

Peripubertal androgen imprinting of rat hepatic cytochrome P450 2C11 and steroid 5 alpha-reductase: pretranslational regulation and impact on microsomal drug activation.

To characterize the dose response and time course of peripubertal testosterone imprinting of rat hepatic CYP2C11 and steroid 5 alpha-reductase and to gain further insights into the mechanism and consequences of peripubertal androgen imprinting of these enzymes, prepubertally gonadectomized female rats were injected s.c. with testosterone enanthate (5 mumol/kg/day) on days 35 to 49 (peripubertal period) or days 81 to 89 (adulthood) and then sacrificed on day 90. Androgen treatment during the peripubertal or adult period increased hepatic microsomal testosterone 2 alpha-hydroxylase activity by 4- to 5-fold and decreased steroid 5 alpha-reductase activity by 30 to 50%. By comparison, androgen administration during both periods completely masculinized these two enzyme activities. Whereas shortening the duration of treatment to 5 days during the peripubertal and adult periods resulted in only a partial masculinization of these activities, reducing the dosage of testosterone enanthate from 5 mumol/kg/day to 2.5 mumol/kg/day during both the peripubertal (15 days) and adult periods (9 days) still fully masculinized testosterone 2 alpha-hydroxylase and steroid 5 alpha-reductase activities. Northern blot analysis showed that peripubertal and adult testosterone treatment of female rats increased hepatic CYP2C11 mRNA levels, decreased steroid 5 alpha-reductase mRNA levels and did not change CYP2C6 mRNA levels. Enhanced cyclophosphamide 4-hydroxylation and ifosfamide 4-hydroxylation was found in liver microsomes isolated from adult female rats exposed to testosterone during puberty and adult life. In contrast to once daily subcutaneous injections, continuous testosterone release via subcutaneous implant was ineffective in producing the long-term changes in testosterone 2 alpha-hydroxylase and steroid 5 alpha-reductase activities. Overall, the present study establishes that peripubertal androgen imprinting of CYP2C11 and steroid 5 alpha-reductase can be achieved after daily subcutaneous testosterone administration. This occurs by a pretranslational mechanism(s), which lead to long-lasting effects on microsomal drug activation.

Effects of chronic mestranol and (or)norethindrone treatment on ethanol-associated decreases in hepatic benzo[a]pyrene hydroxylase activity and increases in central vein fat accumulation in the female Wistar rat.

Female Wistar rats were fed a liquid diet, Sustacal, which contained ethanol (40% of calories) or isocaloric sucrose. Mestranol and norethindrone in pharmacological doses were also administered via this diet. Hepatic microsomal benzo[a]pyrene (BP) hydroxylase, epoxide hydrase, aniline hydroxylase, and aminopyrine-N-demethylase activities were measured after 3 and 6 months treatment. In addition, hepatic histology and electron microscopic studies were carried out in an attempt to monitor ethanol-associated fat accumulation in the central vein region. Mestranol or norethindrone alone for 3 months produced an elevation of BP hydroxylase activity which was no longer present after 6 months treatment. When compared with the 3-month time period, BP hydroxylase activity was significantly decreased in livers of animals which had ingested ethanol (group 10 vs. group 2), ethanol plus mestranol (group 12 vs. group 4), and ethanol plus norethindrone (group 14 vs. group 6) for 6 months. However, in the steroid-treated groups, the ethanol associated decreases were not as large as that seen without ethanol over the 3-month time period (group 11 vs. group 3; group 13 vs. group 5). No decrease was observed in the combined steroid plus ethanol-treated groups. Ethanol treatment for 6 months increased hepatic epoxide hydrase activity in both the nonsteroid and mestranol-treated group. Aniline hydroxylase was increased by ethanol in the combined steroid-treated animals. Otherwise there were no significant changes in the enzyme activities measured. Hepatic histology studies carried out on the 6-month ethanol-treated animals provided evidence of fat accumulation in the central vein region of the liver lobule, as expected. However, the steroid- plus ethanol-treated groups exhibited less apparent fat accumulation in the central vein region. These data do not support the hypothesis that mestranol and (or) norethindrone will accentuate the inhibition of liver BP hydroxylase or the central vein fat accumulation produced by chronic ethanol ingestion in the female rat.

A comparative study of benzo[a]pyrene hydroxylase and epoxide hydrolase derived from isolated rat hepatic nuclei and microsomes.

Several properties of benzo[a]pyrene hydroxylase (AHH) and epoxide hydrolase (EH) in isolated rat hepatic nuclei were investigated. Comparisons were made with microsomal AHH and EH in order to determine whether the nuclear enzymes were distinct from those of endoplasmic reticulum origin. The ratio of EH to AHH in the nuclei of adult male rats was 4.5 compared to 1.6 in the microsomes. Phenobarbital increased AHH in nuclei from immature males and females. However, the increase were markedly lower than those observed in the microsomes. In contrast, 3-methylcholanthrene increased nuclear AHH to a greater extent than the microsomal enzyme. The age and sex dependence, the inhibition by SKF 525-A, the stimulatory and inhibitory effects of 7,8-benzoflavone and the decrease produced by trans-stilbene oxide administration were the same for both nuclear and microsomal AHH. Phenobarbital, l-alpha-acetyulmethadol, and trans-stilbene oxide increased nuclear EH. The increases were approximately 3-fold lower than observed in the microsomes. EH activity in both nuclei and microsomes was inhibited by 1,2-epoxy-3,3,3-trichloropropane. The data indicate that both the constitutive and induced form(s) of AHH in isolated nuclei and endoplasmic reticulum have a number of common properties. The constitutive form(s) of microsomal and nuclear EH also appear to be similar. However, AHH and EH in isolated nuclei differ from their microsomal counterparts in quantitative inducibility. These differences in inducibility support the suggestion that AHH and EH are located in isolated nuclei rather than resulting from contamination by endoplasmic reticulum.

Differential sensitivity of hepatic microsomal aryl hydrocarbon hydroxylase to the inhibitory effect of SKF 525-A in rats of varying age, hormonal- and drug-induced status.

The inhibition of hepatic microsomal aryl hydrocarbon hydroxylase (AHH) activity by SKF 525-A in vitro was studied in hepatic microsomes from rats of varying age, sex hormone status, and drug treatment. The concentration of SKF 525-A required to produce a 50% inhibition of AHH activity, the IC50, was determined for the various microsomal preparations. Microsomes from adult female and immature rats exhibited a similar sensitivity to SKF 525-A. However, microsomes from adult male rats were significantly more sensitive to the inhibitory effect of the drug. AHH activity from pseudohermaphroditic male rats was found to have the same sensitivity to SKF 525-A as in the female littermates. Microsomes obtained from adult rats that had been pretreated with various cytochrome P-450 inducing agents yielded significantly different IC50 values from untreated controls. These differences in IC50 values indicated that the predominant form(s) of cytochrome P-450 that hydroxylate benzo(a)pyrene varied with the age, hormonal, and induced status of the animal.

Effects of perinatal exposure of Wistar rats to l-alpha-acetylmethadol.HCl on hepatic microsomal mixed-function oxidase enzyme activity in the adult.

I-alpha-Acetylmethadol (LAAM) was administered via the drinking water to female Wistar rats throughout pregnancy and lactation. Controls were pair-fed and watered. After weaning, pups received lab chow and water ad lib. until maturity. The apparent KM and Vmax were determined for benzo[a]pyrene hydroxylase (BPH), aminopyrine N-demethylase (AP), ethylmorphine N-demethylase (ET) and aniline hydroxylase (AN) from the hepatic microsomal fraction of the mature male and female offspring. The dose of LAAM administered was low enough to produce no symptomatology. In the adult male, pre- and neonatal exposure to LAAM resulted in decreases in KM for AP and Vmax for AN, and increase in the KM and Vmax for BPH. For the female, LAAM produced an increase in KM for AP and a decrease in Vmax for ET and BPH. That is, long-term changes occurred in the enzyme parameters measured; the direction of the changes were sex- and substrate-dependent.