Analysis of p-nitrophenol glucuronidation in hepatic microsomes from lactating rats

Inhibition of Uridine 5'-diphospho-glucuronosyltransferases A10 and B7 by vitamins: insights from in silico and in vitro studies

Uridine 5'-diphospho-glucuronosyltransferases (UGTs) have been considered as a family of enzymes responsible for the glucuronidation process, a crucial phase II detoxification reaction. Among the various UGT isoforms, UGTs A10 and B7 have garnered significant attention due to their broad substrate specificity and involvement in the metabolism of numerous compounds. Recent studies have suggested that certain vitamins may exert inhibitory effects on UGT activity, thereby influencing the metabolism of drugs, environmental toxins, and endogenous substances, ultimately impacting their biological activities. In the present study, the inhibition potential of vitamins (A, B1, B2, B3, B5, B6, B7, B9, D3, E, and C) on UGT1A10 and UGT2B7 was determined using in silico and in vitro approaches. A 3-dimensional model of UGT1A10 and UGT2B7 enzymes was built using Swiss Model, ITASSER, and ROSETTA and verified using Ramachandran plot and SAVES tools. Molecular docking studies revealed that vitamins interact with UGT1A10 and UGT2B7 enzymes by binding within the active site pocket and interacting with residues. Among all vitamins, the highest binding affinity predicted by molecular docking was - 8.61 kcal/mol with vitamin B1. The in vitro studies results demonstrated the inhibition of the glucuronidation activity of UGTs by vitamins A, B1, B2, B6, B9, C, D, and E, with IC50 values of 3.28 ± 1.07 µg/mL, 24.21 ± 1.11 µg/mL, 3.69 ± 1.02 µg/mL, 23.60 ± 1.08 µg/mL, 6.77 ± 1.08 µg/mL, 83.95 ± 1.09 µg/ml, 3.27 ± 1.13 µg/mL and 3.89 ± 1.12 µg/mL, respectively. These studies provided the valuable insights into the mechanisms underlying drug-vitamins interactions and have the potential to guide personalized medicine approaches, optimizing therapeutic outcomes, and ensuring patient safety. Indeed, further research in the area of UGT (UDP-glucuronosyltransferase) inhibition by vitamins is essential to fully understand the clinical relevance and implications of these interactions. UGTs play a crucial role in the metabolism and elimination of various drugs, toxins, and endogenous compounds in the body. Therefore, any factors that can modulate UGT activity, including vitamins, can have implications for drug metabolism, drug-drug interactions, and overall health.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-023-00182-0.

Anticancer Effect of Ruscogenin in B(a)P-Induced Lung Cancer in Mice via Modulation of Proinflammatory Cytokines and Mitochondrial Enzymes

Lung cancer, one of the most often diagnosed malignancies, is the top cause of death in both men and women globally. In both developed and emerging countries, high incidences of cancer are becoming a huge health burden. Natural resources, including plants, have always been a possible source of lead compounds in the identification of optimal medications for cancer treatment, with natural resources accounting for around half of all anticancer drugs. Ruscogenin, a natural saponin, is a major component of Radix Ophiopogon japonicus with a well-established anticancer activity. In this study, the anticancer potential of ruscogenin against a B(a)P-challenged lung cancer model in mice was assessed. The mice were categorized into four groups: group I was as the control group, group II mice were challenged with B(a)P, group III rodents were treated with ruscogenin prior to challenge with B(a)P, and group IV rodents were treated with ruscogenin after B(a)P administration. Tumor incidence was calculated, and the following parameters were analyzed: body weight, lung weight, immunoglobulin (Ig) levels (IgG, IgA, and IgM), key marker enzymes, and proinflammatory cytokines in both treated and control mice. Lung tissues were analyzed via histopathological analysis. According to our results, all the markers that favor the growth of cancer were increased in the lung cancer group. After administration of ruscogenin, all the markers returned to their original levels, revealing the anticancer potential of ruscogenin.

Induction of P-glycoprotein expression and activity by prolactin in female rat liver

AIM

P-glycoprotein (P-gp) plays a critical role in the excretion of xenobiotics into bile. Previous studies have demonstrated that prolactin (PRL) regulates biotransformation and bile salt transport. Here we investigate whether the capability of the liver to transport xenobiotics into bile is altered in hyperprolactinemic states studying the modulation of hepatic P-gp by PRL.

METHODS

We used lactating post-partum rats (PP), as a model of physiological hyperprolactinemia (15 and 21 days after delivery: PP15 and PP21, respectively), and ovariectomized rats treated with PRL (300 μg/day, 7 days, via osmotic minipumps, OVX + PRL). Hepatic P-gp expression and activity were evaluated by western blotting and using rhodamine 123 as substrate in vivo, respectively. Since P-gp is encoded by Mdr1a and Mdr1b in rodents, we quantified their expression by qPCR in primary hepatocyte cultures exposed to 0.1 μg/ml of PRL after 12 h. To further study the mechanism of hepatic P-gp modulation by PRL, hepatocytes were pretreated with actinomycin D and then exposed to PRL (0.1 μg/ml) for 12 h.

KEY FINDINGS

We found increased hepatic P-gp protein expression and activity in PP15 and OVX + PRL. Also, a significant increase in Mdr1a and Mdr1b mRNA levels was observed in primary hepatocyte cultures exposed to PRL, pointing out the hormone direct action. Actinomycin D prevented these increases, confirming a transcriptional up-regulation of P-gp by PRL.

SIGNIFICANCE

These findings suggest the possibility of an increased biliary excretion of xenobiotics substrates of P-gp, including therapeutic agents, affecting their pharmaco/toxicokinetics in hyperprolactinemic situations.

Altered drug metabolism during pregnancy: hormonal regulation of drug-metabolizing enzymes

IMPORTANCE OF THE FIELD

Medication use during pregnancy is prevalent, but pharmacokinetic information of most drugs used during pregnancy is lacking in spite of known effects of pregnancy on drug disposition. Accurate pharmacokinetic information is essential for optimal drug therapy in mother and fetus. Thus, understanding how pregnancy influences drug disposition is important for better prediction of pharmacokinetic changes of drugs in pregnant women.

AREAS COVERED IN THIS REVIEW

Pregnancy is known to affect hepatic drug metabolism, but the underlying mechanisms remain unknown. Physiological changes accompanying pregnancy are probably responsible for the reported alteration in drug metabolism during pregnancy. These include elevated concentrations of various hormones such as estrogen, progesterone, placental growth hormones and prolactin. This review covers how these hormones influence expression of drug-metabolizing enzymes (DMEs), thus potentially responsible for altered drug metabolism during pregnancy.

WHAT THE READER WILL GAIN

The reader will gain a greater understanding of the altered drug metabolism in pregnant women and the regulatory effects of pregnancy hormones on expression of DMEs.

TAKE HOME MESSAGE

In-depth studies in hormonal regulatory mechanisms as well as confirmatory studies in pregnant women are warranted for systematic understanding and prediction of the changes in hepatic drug metabolism during pregnancy.

Protective role of mangiferin against Benzo(a)pyrene induced lung carcinogenesis in experimental animals

In recent years, considerable emphasis has been focused on identifying new chemopreventive agents which could be useful for the human population. In the present study, we examined the protective role of mangiferin during experimental lung carcinogenesis with reference to its effect on DNA-damage and the detoxification enzyme system. The activities of detoxifying enzymes such as glutathione transferase (GST), quinone reductase (QR) and uridin 5'-diphosphate-glucuronosyl transferase (UDP-GT) were found to be decreased while the lipid peroxidation level was increased in the lung cancer bearing animals. Supplementation of mangiferin (100 mg/kg b.wt) enhanced the detoxification enzymes and reduced DNA damage as determined by single cell electrophoresis. Furthermore, the DNA-protein cross links which was found to be high in lung cancer bearing animals was also modulated upon supplementation with mangiferin. Our present results explain the unique association between the anti-oxidant effect of mangiferin and ultimately the capability of mangiferin to prevent cancer.

Tissue-specific, Inducible, and Hormonal Control of the Human UDP-Glucuronosyltransferase-1 (UGT1) Locus

The human UDP-glucuronosyltransferase 1 (UGT1) locus spans nearly 200 kb on chromosome 2 and encodes nine UGT1A proteins that play a prominent role in drug and xenobiotic metabolism. Transgenic UGT1 (Tg-UGT1) mice have been created, and it has been demonstrated that tissue-specific and xenobiotic receptor control of the UGT1A genes is influenced through circulating humoral factors. In Tg-UGT1 mice, the UGT1A proteins are differentially expressed in the liver and gastrointestinal tract. Gene expression profiles confirmed that all of the UGT1A genes can be targeted for regulation by the pregnane X receptor activator pregnenolone-16alpha-carbonitrile (PCN) or the Ah receptor ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In addition, the selective induction of glucuronidation activity toward lamotrigine, ethinyl estradiol, chenodeoxycholic acid, and lithocholic acid by either PCN or TCDD in small intestine from Tg-UGT1 mice corresponded to expression of the locus in this tissue. Induction of UGT1A1 by PCN and TCDD is believed to be highly dependent upon glucocorticoids, because submicromolar concentrations of dexamethasone actively promote PCN and TCDD induction of UGT1A1 in Tg-UGT1 primary hepatocytes. The role of hormonal control of the UGT1 locus was further verified in pregnant and nursing Tg-UGT1 mice. In maternal 14-day post-conception Tg-UGT1mice, liver UGT1A1, UGT1A4, and UGT1A6 were induced, with the levels returning to near normal by birth. However, maternal liver UGT1A4 and UGT1A6 were dramatically elevated and maintained after birth, indicating that these proteins may play a critical role in maternal metabolism during lactation. With expression of the UGT1 locus confirmed in a variety of mouse tissues, these results suggested that the Tg-UGT1 mice will be a useful model to examine the regulatory and functional properties of human glucuronidation.

Shift from Biliary to Urinary Elimination of Acetaminophen-Glucuronide in Acetaminophen-Pretreated Rats

Despite its toxicity, acetaminophen (APAP) is used increasingly as an analgesic, antipyretic, and anti-inflammatory agent. We examined the effect of prior exposure to APAP on its biliary and urinary elimination. The biliary and urinary elimination of a test dose of APAP (150 mg/kg i.v.) was determined in male Wistar rats 24 h after pretreatment with vehicle, a single dose (1.0 g/kg i.p.), or increasing daily doses (0.2, 0.3, 0.6, and 1.0 g/kg/day i.p.) of APAP. Although elimination of the parent APAP was minimally affected, biliary excretion of APAP glucuronide was significantly decreased 70 and 80%, whereas urinary excretion was significantly increased 90 and 100% in the groups pretreated with single and repeated doses of APAP, respectively, relative to vehicle controls. Western analysis and confocal immunofluorescent microscopy indicated a marked increase in hepatic expression of multidrug resistance-associated protein 3 (Mrp3) in both groups pretreated with APAP, relative to expression of Mrp2. ATP-dependent transport of [3H]taurocholate, an Mrp3 substrate, was significantly increased in basolateral liver plasma membrane vesicles from rats pretreated with repeated doses of APAP relative to controls. Enterohepatic recirculation of APAP glucuronide after administration of the same test dose of the drug was significantly decreased in rats pretreated with repeated doses of APAP. These data indicate that APAP pretreatment induced a shift from biliary to urinary elimination of APAP glucuronide, consistent with the increased expression of Mrp3 in the basolateral domain of the hepatocyte. We postulate that decreased enterohepatic recirculation contributes to decreased APAP hepatotoxicity by reducing liver exposure.

Oral supplementation of piperine leads to altered phase II enzymes and reduced DNA damage and DNA-protein cross links in Benzo(a)pyrene induced experimental lung carcinogenesis

In recent years, considerable emphasis has been focused on identifying new chemopreventive agents, which could be useful for the human population. Piperine is a pure, pungent alkaloid constituent of black and long peppers (piper nigrum and piper longum), which is a most common spice used throughout the world. In the present study, we examined the protective role of piperine during experimental lung carcinogenesis with reference to its effect on DNA damage and detoxification enzyme system. The activities of detoxifying enzymes such as glutathione transferase (GST), quinone reductase (QR) and UDP-glucuronosyl transferase (UDP-GT) were found to be decreased while the hydrogen peroxide level was increased in the lung cancer bearing animals. Supplementation of piperine (50 mg/kg bwt) enhanced the detoxification enzymes and reduced DNA damage as determined by single cell electrophoresis. Furthermore, the DNA-Protein cross links which was found to be high in lung cancer bearing animals was also modulated upon supplementation with piperine. Our present results explain the understanding of unique association between anti-peroxidative effect of piperine and ultimately the capability of piperine to prevent cancer.

Inhibition of rat liver UDP-glucuronosyltransferase by silymarin and the metabolite silibinin-glucuronide

The inhibitory effects of silymarin, its main constituent silibinin and the metabolite silibinin-glucuronide on UDP-glucuronosiltransferase (UGT) were evaluated in rat hepatic microsomes. Three substrates were chosen to cover both UGT1A and UGT2B family isozymes: bilirubin (substrate of UGT1A1), p-nitrophenol (UGT1A6) and ethinylestradiol (UGT2B1 and 2B3 for position C17 and UGT1A1 for position C3). The study of p-nitrophenol and bilirubin glucuronidation indicated that silymarin (SM) and silibinin glucuronide (SB-G) were enzyme inhibitors. The kinetic analysis showed that the type of inhibition was competitive in all cases and the Ki obtained were: for p-nitrophenol glucuronidation, KiSB-Gapp: 14+/-1 microg/ml and KiSMapp: 51+/-10 microg/ml and for bilirubin glucuronidation, KiSB-Gapp: 16+/-3 microg/ml. In turn, ethinylestradiol glucuronidation was not affected by any of the compounds studied suggesting that the inhibitory effect was restricted to UGT1A isozymes. Similar studies performed using human hepatic microsomes showed that SM and SB-G were also inhibitors of human UGT1A isozymes. In conclusion, administration of silymarin or its main constituent silibinin could lead to the decrease in the glucuronidation of substrates whose conjugation depends on UGT1A isozymes in a process mediated by silibinin-glucuronide, though their effect in humans needs further investigation.

Effect of spironolactone on the expression of rat hepatic UDP-glucuronosyltransferase

Spironolactone (SL) increases the glucuronidation rate of several compounds. We analyzed the molecular basis of changes occurring in major rat liver UDP-glucuronosyltransferase (UGT) family 1 isoforms and in UGT2B1, a relevant isoform of family 2, in response to SL. UGT activity toward bilirubin, ethynylestradiol and p-nitrophenol was assayed in native and activated microsomes. Protein and mRNA levels were determined by Western and Northern blotting. The lipid composition and physicochemical properties of the microsomal membrane were also analyzed. Glucuronidation rates of bilirubin and ethynylestradiol (at both 3-OH and 17 beta-OH positions), determined in UDP-N-acetylglucosamine-activated membranes, were increased in SL group. Western blot analysis revealed increased levels of UGT1A1 and 1A5 (bilirubin and 3-OH ethynylestradiol conjugation), and 2B1 (17 beta-OH ethynylestradiol conjugation). Northern blot studies suggested transcriptional regulation by the steroid. Analysis of UGT activity in native vs. alamethicin-activated microsomes indicated increased latency, which was not associated to changes in physicochemical properties of the microsomal membrane. p-Nitrophenol glucuronidation rate and mRNA and protein levels of UGT1A6, the main isoform conjugating planar phenols, were not affected by the inducer. The data suggest transcriptional regulation of specific isoforms of hepatic UGT by SL, thus explaining previously reported increases in UGT activity toward selective substrates.

Decreased hepatic drug metabolising enzyme activity in rats with nitrosamine-induced tumours

N-Methyl N-benzyl nitrosamine (MBNA), which requires P450-dependant activation to be mutagenic, has been shown to produce squamous cell carcinoma of rat oesophagus. The aim of this study was to determine the effects of tumour induction on hepatic cytochrome P450 (CYP) and phase II enzyme activity. Female Wistar rats were given MBNA (2.5 mg/kg) by gavage, twice weekly for 12 weeks. At the end of 12 weeks they were sacrificed; livers and oesophagi were removed. The activity of hepatic CYP and phase II enzymes was determined by incubation of liver microsomes with appropriate CYP substrates. All rats receiving MBNA developed oesophageal lesions. Hepatic CYP1A2 activity (phenacetin 5 microM) in tumour-bearing rats was significantly decreased to 53% of the controls (p <0.05). CYP2E1 (p-nitrophenol hydroxylase), CYP2D (debrisoquine hydroxylase) and CYP3A (quinine hydroxylase) activity was significantly (p <0.05) reduced. Microsomal UDP-glucuronosyl transferase activity was also found to be markedly decreased while glutathione-S-transferase activity remained almost unchanged. Alteration of the activities of drug metabolising enzymes in rats with chemically induced tumours could be an important factor in determining resistance or susceptibility to xenobiotics and antitumour drugs.

Effect of herbal teas on hepatic drug metabolizing enzymes in rats

We have investigated the effect of herbal teas (peppermint, chamomile and dandelion) on the activity of hepatic phase I and phase II metabolizing enzymes using rat liver microsomes. Female Wistar rats were divided into six groups (n = 5 each). Three groups had free access to a tea solution (2%) while the control group had water. Two groups received either green tea extract (0.1%) or aqueous caffeine solution (0.0625%). After four weeks of pretreatment, different cytochrome P450 (CYP) isoforms and phase II enzyme activities were determined by incubation of liver microsomes or cytosol with appropriate substrates. Activity of CYP1A2 in the liver microsomes of rats receiving dandelion, peppermint or chamomile tea was significantly decreased (P < 0.05) to 15%, 24% and 39% of the control value, respectively. CYP1A2 activity was significantly increased by pretreatment with caffeine solution. No alterations were observed in the activities of CYP2D and CYP3A in any group of the pretreated rats. Activity of CYP2E in rats receiving dandelion or peppermint tea was significantly lower than in the control group, 48% and 60% of the control, respectively. There was a dramatic increase (244% of control) in the activity of phase II detoxifying enzyme UDP-glucuronosyl transferase in the dandelion tea-pretreated group. There was no change in the activity of glutathione-S-transferase. The results suggested that, like green and black teas, certain herbal teas can cause modulation of phase I and phase II drug metabolizing enzymes.

Tea consumption modulates hepatic drug metabolizing enzymes in Wistar rats

The antioxidant, antimutagenic and anticarcinogenic activities of green tea and its polyphenols have been reported. As bioactivation of the precarcinogens and detoxification of ultimate carcinogens are mainly carried out by hepatic metabolizing enzymes, we have investigated the modulation of these enzyme activities subsequent to tea consumption in rats. Female Wistar rats were divided into eight groups (n = 5). Six groups were given aqueous solutions (2%, w/v) of six different teas (New Zealand green tea, Australian green tea, Java green tea, Dragon green tea, Gunpowder green tea or English Breakfast black tea) as the sole source of fluid. One group was given a standard green tea extract (0.5%, w/v) while the control group had free access to water. At the end of four-weeks treatment, different cytochrome P450 (CYP) isoform and phase II enzyme activities were determined by incubation of the liver microsomes or cytosols with appropriate substrates. CYP 1A2 activity was markedly increased in all the tea treatment groups (P < 0.05). CYP 1A1 activity was increased significantly in most of the groups except for the Madura, Gunpowder, and Java green tea-treatment groups. Cytosolic glutathione-S-transferase activity was significantly increased (P< 0.05) in the New Zealand, Gunpowder, and Java green tea-treatment groups. The microsomal UDP-glucuronosyl transferase activity remained unchanged or was moderately increased in most of the groups. The balance between the phase I carcinogen-activating enzymes and the phase II detoxifying enzymes could be important in determining the risk of developing chemically-induced cancer.

Induction of phase II biotransformation reactions in rat jejunum during lactation. Possible involvement of prolactin

The effect of lactation on UDP-glucuronosyltransferase (UGT) and Glutathione S-transferase (GST) activities was studied in jejunum from mother rats, 14 (LM14) and 21 (LM21) days after delivery. p-Nitrophenol glucuronidation rate was increased in LM14 and LM21 rats while conjugation of bilirubin and estrone was not affected and androsterone glucuronidation was decreased. Additional studies, including Western blotting and microsomal lipid analysis, revealed that the enhancement in p-nitrophenol UGT activity is most likely associated with an inductive process rather than with a modification in enzyme constraint. GST activity towards 1-chloro-2,4-dinitrobenzene (CDNB) was also increased in LM14 and LM21 while activity towards 1,2-dichloro-4-nitrobenzene (DCNB) was not affected. Western blotting revealed a significant increase in the cytosolic content of mu (rGSTM2) and pi (rGSTP1) class subunits in LM14 and LM21 groups, while the alpha class subunit rGSTA2 remained unchanged. To evaluate the potential modulatory role of prolactin on the same enzyme systems, ovariectomized rats were treated with ovine prolactin (oPRL) at doses of 100, 200 and 300 microg/100 g body wt. per day for 4 days. Hormone administration affected UGT activities towards p-nitrophenol and androsterone and GST activity towards CDNB in a way and magnitude consistent with those produced in lactating rats, while conjugation of estrone, bilirubin and DCNB were unchanged. Western blotting data were also consistent with those of lactating rats. These results indicate that UGT and GST activities are increased in rat jejunum during lactation, due to induction of some specific isoforms, and that prolactin is the likely mediator of these effects.

Glucuronidation: a dual control

1. Glucuronidation is a major detoxication process catalyzed by uridine diphosphate glucuronosyltransferases. 2. The amount of enzyme can be modulated by numerous foreign compounds, such as common chemical inducers already implicated in the induction of other detoxication enzymes. 3. Hormones such as thyroid hormones or growth hormone also are implicated in the control of glucuronidation. 4. Because glucuronidation enzymes (isozymes) are anchored in the endoplasmic reticulum membrane, with their active site likely being located on the lumenal side of the membrane, the membrane environment of these enzymes was shown to modulate their functional state as evaluated by the conjugating activity per enzymatic molecular unit. 5. In accord with a first, previously proposed model, it seems that this modulation can be attributed to different conformational states of the enzymes, depending on the physicochemical state of the membrane. 6. In accord with a second model, the membrane may act as a barrier between the enzymes and the cosubstrate UDP-glucuronic acid, which is a polar and charged molecule synthesized in the cytosol. This would imply a transporting process for this molecule through the reticulum membrane, which has been characterized in vitro and could be of importance in vivo. 7. Glucuronidation is under the control of a dual regulation, by means of a specific isozyme expression level and by the modulation of their functional state.

The influence of age and some inducers on UDP-glucuronyltransferase activity

UDP-glucuronyltransferase (UDP-GT) activity was examined in male Wistar rats aged 0.5, 1, 2, 4, 8, 12, 20, and 28 months. The rats were treated with phenobarbital (75 mg/kg, 72 and 48 h before death), beta-naphthoflavone or dexamethasone (40 mg/kg and 20 mg/kg, respectively, for three days before death). Prior to decapitation the rats were fasted for 12 h. Hepatic microsomes were prepared according to the method of Dallner. UDP-GT activity was determined by the method of Burchell and Weatherill. p-Nitrophenol was used as an aglucone. UDP-GT activity decreased rapidly in the control rats aged from two weeks to four months. In the older control rats the activity tended to increase. Two-week-old rats treated with phenobarbital showed a slightly increased UDP-GT activity. In the older animals (up to one year) UDP-GT activity increased to 150% of the control value and stayed at this level in the remaining age groups. beta-Naphthoflavone was a more potent inducer of UDP-GT than phenobarbital. The activity of beta-naphthoflavone-induced UDP-GT was low in the youngest rats. It was about 180% in two-month-old rats and reached 260% of the control value in eight-month-old rats. Although the activity decreased in the older rats, it still exceeded 200%. Dexamethasone did not affect UDP-GT activity. Only in two-week-old and two-month-old rats did we observe a slight increase in the activity of UDP-GT.

Gender-related differences in the amount and functional state of rat liver UDP-glucuronosyltransferase

The basis for gender-dependent differences in rates of glucuronidation of xenobiotics is uncertain. To clarify this issue, the glucuronidation of p-nitrophenol was compared in liver microsomes from adult male and female rats. The activity of native UDP-glucuronosyltransferase was 47% higher in microsomes from male than from female rats. Immunoblotting of microsomal protein with anti-UDP-glucuronosyltransferase antiserum revealed 66% more immunoreactive protein in male microsomes. A kinetic method for measuring glucuronidating enzyme content confirmed the result of the immunoblot. Responses of UDP-glucuronosyltransferase to activation by palmitoyllysophosphatidylcholine or high pressure indicated that the activity of the enzyme was more latent in male than in female microsomes. Differences in enzyme latency could be due to differences in membrane structure. A comparison of microsomal fatty acid composition revealed significantly higher levels of oleic and linoleic acids and lower levels of stearic and docosahexaenoic acids in male than in female microsomes. The phospholipid composition, ratio of cholesterol:phospholipid, and membrane fluidity were similar in male and female microsomes. These results indicate that gender-dependent differences in UDP-glucuronosyltransferase activity are due to differences in both the amount and functional state of the enzyme.

Enhancement of cytosolic and microsomal glutathione S-transferase activities in liver and small intestine from female rats during lactation

The influence of lactation on hepatic and intestinal glutathione S-transferase activities in mother rats was studied. Cytosolic and microsomal activities were assessed 7, 14 and 21 days after delivery, using 1-chloro-2,4-dinitrobenzene as substrate. Cytosolic and microsomal activities from liver and small intestine determined 7 days post partum did not differ from those of virgin female rats. The hepatic cytosolic activity was significantly increased with respect to that of virgin females 14 days after delivery and tended to revert to the control value on day 21 of lactation, whereas the intestinal activity was increased on day 14 and remained augmented even 21 days post partum. Although the respective microsomal activities showed percent increases higher than those of the cytosolic enzymes, they both exhibited a similar pattern of stimulation in response to lactation.