Tissue distribution,metabolism, and elimination of perfluorooctanoic acid in male and female rats

The elimination, tissue distribution, and metabolism of [1-¹⁴C]perfluorooctanoic acid (PFOA) was examined in male and female rats for 28 days after a single ip dose (9.4 μmol/kg, 4 mg/kg). A sex difference in urinary elimination of PFOA-derived ¹⁴C was observed. Female rats eliminated PFOA-derived radioactivity rapidly in the urine with 91% of the dose being excreted in the first 24 hr. In the same period, male rats eliminated only 6% of the administered ¹⁴C in the urine. The sex-related difference in urinary elimination resulted in the observed difference in the whole-body elimination half-life (t_1/2) of PFOA in males (t_1/2 = 15 days) and females (t_1/2 < 1 day). Analysis of PFOA-derived ¹⁴C in tissues showed that the liver and plasma of male rats and the liver, plasma, and kidney of female rats were the primary tissues of distribution. The relatively high concentration of PFOA in the male liver was further examined using an in situ nonrecirculating liver perfusion technique. It was shown that 11% of the PFOA infused was extracted by the liver in a single pass. The ability of the liver to eliminate PFOA into bile was examined in rats whose renal pedicles were ligated to alleviate sex differences in the urinary excretion of PFOA. In a 6-hr period following IP administration of PFOA, there was no apparent difference in biliary excretion, where both males and females eliminated less than 1% of the PFOA dose via this route. We hypothesized that the sex difference in the persistence of PFOA was due to a more rapid formation of a PFOA-containing lipid (i.e., a PFOA-containing mono-, di-, or triacylglycerol, cholesteryl ester, methyl ester, or phospholipid) in the male rat. Also, the increased urinary elimination of PFOA in females may have been due to increased metabolism to a PFOA-glucuronide or sulfate ester. However, no evidence that PFOA is conjugated to form a persistent hybrid lipid was obtained, nor were polar metabolites of PFOA in urine or bile detected. In addition, daily urinary excretion of fluoride in male and female rats before or after PFOA treatment were similar, suggesting that the parent compound is not defluorinated. Thus, the more rapid elimination of PFOA from female rats is not due to formation of a PFOA metabolite.     

Induction by perfluorinated fatty acids with different carbon chain length of peroxisomal beta-oxidation in the liver of rats

The potency of the induction of peroxisomal beta-oxidation was compared between perfluorinated fatty acids (PFCAs) with different carbon chain lengths in the liver of male and female rats. In male rats, perfluoroheptanoic acid (PFHA) has little effect, although perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) potentially induced the activity. By contrast, PFHA and PFOA did not induce the activity of peroxisomal beta-oxidation in the liver of female rats while PFNA and PFDA effectively induced the activity. The induction of the activity by these PFCAs was in a dose-dependent manner, and there is a highly significant correlation between the induction and hepatic concentrations of PFCAs in the liver regardless of their carbon chain lengths. These results strongly suggest that the difference in their chemical structure is not the cause of the difference in the potency of the induction. Hepatic concentrations of PFOA and PFNA was markedly higher in male compared with female rats. Castration of male rats reduced the concentration of PFNA in the liver and treatment with testosterone entirely restored the reduction. In contrast to the results obtained from the in vivo experiments, the activity of peroxisomal beta-oxidation was induced by PFDA and PFOA to the same extent in cultured hepatocytes prepared from both male and female rats. These results, taken together, indicate that difference in accumulation between PFCAs in the liver was responsible for the different potency of the induction of peroxisomal beta-oxidation between PFCAs with different carbon chain lengths and between sexes.     

Sex hormone-regulated renal transport of perfluorooctanoic acid

The biological half-life (t1/2) of perfluorooctanoic acid (PFOA) in male rats is 70 times longer than that in female rats. The difference is mainly due to the difference in renal clearance (CL(R)), which was significantly reduced by probenecid, suggesting that PFOA is excreted by organic anion transporter(s). Castration of male rats caused a 14-fold increase in the CL(R) of PFOA, which made it comparable with that of female rats. The elevated PFOA CL(R) in castrated males was reduced by treating them with testosterone. Treatment of male rats with estradiol increased the CL(R) of PFOA. In female rats, ovariectomy caused a significant increase in CL(R) of PFOA, which was reduced by estradiol treatment. Treatments of female rats with testosterone reduced the CL(R) of PFOA as observed in castrated male rats. To identify the transporter molecules that are responsible for PFOA transport in rat kidney, renal mRNA levels of organic anion transporter 1 (OAT1), OAT2, OAT3, organic anion transporting polypeptide 1 (oatp1), oatp2 and kidney specific organic anion transporter (OAT-K) were determined in male and female rats under various hormonal states and compared with the CL(R) of PFOA. The level of OAT2 mRNA in male rats was only 13% that in female rats. Castration or estradiol treatment increased the level of OAT2 mRNA whereas treatment of castrated male rats with testosterone reduced it. In contrast to OAT2, mRNA levels of both oatp1 and OAT-K were significantly higher in male rats compared with female rats. Castration or estradiol treatment caused a reduction in the levels of mRNA of oatp1 and OAT-K in male rats. Ovariectomy of female rats significantly increased the level of OAT3 mRNA. Multiple regression analysis suggests that the change in the CL(R) of PFOA is, at least in part, due to altered expression of OAT2 and OAT3.     

Renal excretion of perfluorooctanoic acid in male rats: Inhibitory effect of testosterone

There is a marked sex difference in the whole-body elimination of perfluorooctanoic acid (PFOA) in rats, with females excreting the perfluorinated acid much more rapidly (half life [t_1/2] < 1 day) than males (t_1/2=15 days). Our objective was to determine if androgens or estrogens are involved in causing this sex difference in PFOA elimination. Castration of males greatly increased the elimination of [1-¹⁴C]PFOA (9.4 μmiol/kg, i.p.) in urine, demonstrating that a factor produced by the testis was responsible for the slow elimination of PFOA in male rats. Castration plus 17β-estradiol had no further effect on PFOA elimination whereas castration plus testosterone replacement at the physiologic level reduced PFOA elimination to the same level as rats with intact testes. Thus, in male rats, testosterone exerts an inhibitory effect on renal excretion of PFOA. In female rats, neither ovariectomy nor ovariectomy plus testosterone affected the PFOA urinary elimination, demonstrating that the inhibitory effect of testosterone on PFOA renal excretion is a male-specific response. Probenecid decreased the high rate of PFOA renal excretion in castrated males but had no effect on male rats with intact testes. We conclude that testosterone is a key determinant of the sex difference in PFOA elimination in rats.     

Comparison of the elimination between perfluorinated fatty acids with different carbon chain length in rats

Elimination in urine and feces was compared between four perfluorinated fatty acids (PFCAs) with different carbon chain length. In male rats, perfluoroheptanoic acid (PFHA) was rapidly eliminated in urine with the proportion of 92% of the dose being eliminated within 120 h after an intraperitoneal injection. Perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) was eliminated in urine with the proportions of 55, 2.0 and 0.2% of the dose, respectively. By contrast, four PFCAs were eliminated in feces with the proportion of less than 5% of the dose within 120 h after an injection. In female rats, the proportions of PFOA and PFNA eliminated in urine within 120 h were 80% and 51% of the dose, respectively, which were significantly higher compared with those in male rats. There was the tendency that PFCA with longer carbon chain length is less eliminated in urine in both male and female rats. Fecal elimination of PFCAs was not different between PFCAs in female rats and comparable to those in male rats. The rates of biliary excretion of PFCAs in male rats were slower than those in female rats. Sex-related difference in urinary elimination of PFOA was abolished when male rats had been castrated. On the contrary, treatment with testosterone suppressed the elimination of PFOA in urine in both castrated male rats and female rats. The effect of testosterone was in a time- and dose-dependent manner. These results suggest that PFCAs are distinguished by their carbon chain length by a renal excretion system, which is regulated by testosterone.     

Evidence for the involvement of multiple forms of cytochrome P-450 in the occurrence of sex-related differences of drug metabolism in the rat

Multiple forms of cytochrome P-450 in liver microsomes of untreated male and female rats could be divided into several fractions by the use of ω-amino-n-octyl Seph. 4B and DE-52 columns. Male cytochrome P-450 fractions (I-b - I-e) differed from female fractions (I-b - I-e) with respect to absorption peaks in carbon monoxide difference spectra and 7-prop-oxycoumarin O-depropylation activities. Although male and female I-a fractions showed quite similar protein bands on SDS-polyacrylamide gel electrophoresis, some protein bands in other male fractions (I-b - I-e) were absent in corresponding female fractions. Immunochemical examinations using immunoglobulin G raised to cytochrome P-450 purified from untreated male rats also showed that liver microsomes from male and female rats contain different forms of cytochrome P-450. Based on these results, we propose that sex-related differences of drug metabolizing activities in liver microsomes are caused by multiple forms of cytochrome P-450.     

Induction of P-450 isoenzyme activities in Syrian golden hamster liver compared to rat liver as probed by the rate of 7-alkoxyresorufin-O-dealkylation

The activities of 7-ethoxyresorufin-O-deethylase (EROD), 7-pentoxyresorufin-O-deethylase (PROD), 7-ethoxycoumarin-O-deethylase (ECOD) and aromatic hydrocarbon hydroxylase (AHH) were measured in hepatic microsomes from male and female Wistar rats and Syrian golden hamsters in order to probe the basal activity and the inducibility by phenobarbital (PB) and 3-methylcholanthrene (MC) of different P-450 isoenzymes. The basal activities of EROD and ECOD, but not PROD and AHH, were higher in male hamsters than in male rats. No sex-related difference in enzyme activities was observed with hamsters, whereas male rats had a higher ECOD and AHH activity than female rats. Induction by PB led to a 450-fold and 250-fold increase in PROD activity in male and female rat liver microsomes, respectively, while MC had a more pronounced inductive effect on EROD activity in this species. In hamsters, EROD activity was induced by MC but not by PB. Unexpectedly PROD activity in male and female hamster liver microsomes was only moderately induced by PB, the extent being lower than on induction by MC. Therefore, the activity of PROD, which is useful as a specific enzymatic assay for P-450 IIB in the rat liver, cannot be used to probe PB-like inducers in the hamster liver.     

Sex-related differences in cadmium-induced lipid peroxidation in the rat

Male and female rats were dosed once a day for 2 days injection with 1.5 mg of Cd/kg as CdCl₂. 24 hr after administration of cadmium, lipid peroxidation determined by estimation of malondialdehyde (MDA) was greatly increased in male rat liver, but was not in female rats. Cadmium in a larger dose of 4.5 mg/kg, subcutaneous single injection, significantly increased content of MDA in female rat liver. These results suggest that sex-related differences exist in the ability of cadmium to induce MDA formation in rat liver, although administration of cadmium causes the enhancement of MDA formation in both male and female rats. The reason why sex-related differences exist in lipid peroxidation of rat liver is discussed.     

Ontogenesis of hepatic growth hormone receptors in the rat

Detailed ontogenic studies of the binding of human (hGH) and bovine growth hormone (bGH) have been performed in liver preparations from male and female rats during the neonatal, weanling, pre- and post-pubertal periods. Specific binding of both hormones was readily detected at all ages, with no apparent interference due to occupancy by endogenous hormones. No sex difference in binding was observed prior to weaning (22 days) for hGH, which binds to both somatotrophic and lactogenic sites. However, after weaning a marked sex-related dissociation in the pattern of binding did occur, with female rats binding 3-4 times more hGH than in the pre-weaning period and male rats binding hGH to only half their pre-weaning levels. A very similar pattern was seen for binding of bGH (which binds only to somatotrophic sites) except that in male rats, the post-weaning levels did not fall. Binding patterns for either hGH or bGH prior to weaning did not mirror the known age-related pattern of circulating rat GH levels, suggesting the absence of a definitive auto-regulation system for the GH-GH receptor system under normal circumstances in vivo. The possible role of the weaning process per se in the post-weaning changes of GH binding seen in male and female rats still requires elucidation.     

Induction of microsomal 1-acylglycerophosphocholine acyltransferase by peroxisome proliferators in rat kidney; co-induction with peroxisomal beta-oxidation

Induction of microsomal 1-acyl-glycerophosphocholine (GPC) acyltransferase in rat tissues by four peroxisome proliferators, clofibric acid, tiadenol, DEHP and PFOA, was examined. Among the nine tissues examined, kidney, liver and intestinal mucosa responded to the challenges by the peroxisome proliferators to induce the enzyme. The treatment of rats with various dose of clofibric acid, tiadenol, DEHP or PFOA resulted in an induction of kidney microsomal 1-acyl-GPC acyltransferase in a dose-dependent manner. Despite the structural dissimilarity of peroxisome proliferators, the induction of microsomal 1-acyl-GPC acyltransferase was highly correlated with the induction of peroxisomal beta-oxidation. The activity of microsomal 1-acyl-GPC acyltransferase was not affected by changes in hormonal (adrenalectomy, diabetes, hyperthyroidism and hypothyroidism) and nutritional (starvation, starvation-refeeding, fat-free-diet feeding and high-fat-diet feeding) states. The induction of renal microsomal 1-acyl-GPC acyltransferase was seen in mice subsequent to the administration of clofibric acid and tiadenol and in guinea pigs subsequent to the administration of tiadenol. These results may indicate that kidney microsomal 1-acyl-GPC acyltransferase is a highly specific parameter responsive to the challenges by peroxisome proliferators and may suggest that the possibility that the inductions by peroxisome proliferators of microsomal 1-acyl-GPC acyltransferase and peroxisomal beta-oxidation in kidney are co-regulated.     

Sex-dependent pharmacokinetics of S(-)-hydroxyhexamide,a pharmacologically active metabolite of acetohexamide,in rats

The pharmacokinetic profile of S(-)-hydroxyhexamide (S-HH), a pharmacologically active metabolite of acetohexamide, was examined in male and female rats. S-HH was eliminated more rapidly from plasma in the males than in the females. A significant sex difference was observed in the pharmacokinetic parameters of S-HH in rats. Testectomy caused significant alteration in these parameters of S-HH in male rats, whereas ovariectomy did not in the females. The co-administration of sulfamethazine significantly decreased the plasma clearance (CL(p)) of S-HH in male rats, but had no effect in the females. The plasma concentrations of acetohexamide generated from S-HH showed no sex-related difference. Furthermore, there was no difference in the accumulation of S-HH by renal cortical slices from male and female rats. We propose the possibility that the sex-dependent pharmacokinetics of S-HH in rats is mediated through the male-specific hydroxylation of the cyclohexyl ring catalyzed by a major cytochrome p450 (CYP) isoform (CYP2C11), although the detailed mechanism remains to be elucidated.     

The sex difference in the regulation of liver regeneration after partial hepatectomy in the rat

The increases in the activity of hepatic thymidylate synthetase and thymidine kinase, which catalyzes the formation of thymidylate via the de novo and salvage pathways, respectively, were significantly suppressed 24 h after 70% partial hepatectomy in female rats administered either alpha- or beta-adrenoreceptor antagonists. The injection of beta-antagonist to male or ovariectomized female rats had no effect on the activities of these enzymes. Only alpha-adrenoceptor antagonist depressed these enzymatic activities of 24-h-regenerating liver in male and ovariectomized female rats. The decrease of the activities of thymidylate synthetase and thymidine kinase was accompanied by a concomitant reduction of DNA content in 24-h-regenerating liver. It is concluded that catecholamine regulates the female rat liver regeneration through both alpha- and beta-adrenergic pathways by the inductions of thymidylate synthase and thymidine kinase, while in adult male and ovariectomized female rats, only the alpha-mediated pathway is involved.     

Age- and sex-related changes in type-1 iodothyronine deiodinase messenger ribonucleic acid in rat liver and kidney.

To evaluate the age- and sex-related changes in Type 1 iodothyronine deiodinase gene expression in the liver and kidneys, we measured 5'-deiodinating activity and deiodinase mRNA in developing rats. The activity in the liver increased after birth, and that in neonates was approximately half that in adults. In contrast, the activity in neonatal kidneys remained very low. The relative importance of activity in male kidneys compared to the liver increased from the ages of 1 to 20 days. The male adult rat liver showed a higher level of activity than the female liver. Deiodinase mRNA in the male liver gradually increased from 1 to 20 days, in correlation with the activity. In kidneys, deiodinase mRNA was low before day 20, and there was no significant sex difference in all age groups. In orchiectomized male rats, the activity and mRNA in the liver was similar to the low levels found in females; however, the levels in the kidneys were not significantly different than those of normal males. These data suggest that the age- and sex-related changes in iodothyronine deiodinase gene expression are regulated mainly at the pretranslational level, and that the relative importance of kidneys to liver in iodothyronine deiodinase increases from birth to age 20 days due to the difference in the gene expression.     

Sex differences in the metabolism of essential fatty acids studied in isolated rat liver cells

The triacylglycerol synthesis from exogenous linoleic acid (18:2(n-6], linolenic acid (18:3(n-3], dihomogammalinolenic acid (20:3(n-6], eicosapentaenoic acid (20:5(n-3] and oleic acid (18:1(n-9] was observed to be significantly increased in isolated liver cells from female rats compared with males. The rate of fatty acid oxidation and phospholipid biosynthesis was concomitantly more important in male cells. With the C22-polyenoic fatty acids, adrenic acid (22:4(n-6] and docosahexaenoic acid (22:6(n-3), only a minor sex-related difference in fatty acid metabolism was found.     

Kinetics of 8-2 fluorotelomer alcohol and its metabolites, and liver glutathione status following daily oral dosing for 45 days in male and female rats

Fluorotelomer alcohols (FTOHs) are raw materials used in the manufacture of polymeric and surfactant products. Based on previous findings from single oral dosing in rats with radiolabeled 8-2 FTOH, glutathione (GSH) depletion and/or the presence of perfluorinated/polyfluorinated acids and aldehyde metabolites was hypothesized to account for the hepatocellular lesions observed in male rats from a 90-day subchronic oral dosing study. Further, the reported nephropathy in female rats from the subchronic experiment was hypothesized to have been initiated by a thiol metabolite produced by degradation of GSH conjugates. In the current investigation, the kinetics of 8-2 FTOH and its metabolites along with liver GSH status were evaluated in the rat following daily oral dosing with 8-2 FTOH for 45 days at 5 and 125 mg/kg/day. Liver GSH stores 1-2 h after dosing were unaffected, suggesting that GSH depletion is not likely a relevant mode of action in the liver. The tissue metabolite data indicate that the liver toxicity mode of action is likely associated with elevated levels of perfluoroalkyl acids found in males, since other polyfluorinated metabolites and 8-2 FTOH were present in livers from female rats at comparable or higher levels. Detection of the N-acetyl cysteine conjugate of the unsaturated parent telomer alcohol in urine from female rats and not male rats provides some evidence to support the mechanistic basis for the observed kidney effects. Further, the increasing levels of perfluorooctanoic acid (PFOA) in plasma from female rats over the 45-day dosing phase, while unexpected, may reflect an increased net absorption of 8-2 FTOH, slow elimination of intermediates in the metabolic pathway between 8-2 FTOH and PFOA, or altered kidney clearance. The results of this study have enhanced our understanding of 8-2 FTOH kinetics and metabolism and potential modes of action in the rat, which will guide the design of future studies for FTOHs and our need to define the mechanistic basis for the observed effects.     

Comparison of metabolism of free fatty acid by isolated perfused livers from male and female rats.

Livers from normal, fed male and female rats were perfused with different amounts of [1-14C]oleate under steady state conditions, and the rates of uptake and utilization of free fatty acid (FFA) were measured. The uptake of FFA by livers from either male or female rats was proportional to the concentration of FFA in the medium. The rate of uptake of FFA, per g of liver, by livers from female rats exceeded that of the males for the same amount of FFA infused. The incorporation by the liver of exogenous oleic acid into triglyceride, phospholipid, and oxidation products was proportional to the uptake of FFA. Livers from female rats incorporated more oleate into triglyceride (TG) and less into phospholipid (PL) and oxidation products than did livers from male animals. Livers from female rats secreted more TG than did livers from male animals when infused with equal quantities of oleate. The incorporation of endogenous fatty acid into TG of the perfusate was inhibite) by exogenous oleate. At low concentrations of perfusate FFA, however, endogenous fatty acids contributed substantially to the increased output of TG by livers from female animals. Production of 14CO2 and radioactive ketone bodies increased with increasing uptake of FFA. The partition of oleate between oxidative pathways (CO2 production and ketogenesis) was modified by the availability of the fatty acid substrate with livers from either sex. The percent incorporation of radioactivity into CO2 reached a maximum, whereas incorporation into ketone bodies continued to increase. The output of ketone bodies was dependent on the uptake of FFA, and output by livers from female animals was less than by livers from male rats. The increase in rate of ketogenesis was dependent on the influx of exogenous FFA, while ketogenesis from endogenous sources remained relatively stable. The output of glucose by the liver increased with the uptake of FFA, but no difference due to sex was observed. The output of urea by livers from male rats was unaffected by oleate, while the output of urea by livers from females decreased as the uptake of FFA increased. A major conclusion to be derived from this work is that oleate is not metabolized identically by livers from the two sexes, but rather, per gram of liver, livers from female rats take up and esterify more fatty acid to TG and oxidize less than do livers from male animals; livers from female animals synthesize and secrete more triglyceride than do livers from male animals when provided with equal quantities of free fatty acid.     

Sex-related difference of kinin level in rat pituitary gland

The kinin level in the pituitary glands was compared in adult male and female rats. A sex-related difference in the bradykinin (BK)-like immunoreactivity was found in the posterior lobe. The posterior pituitaries of female rats contained a higher concentration of the immunoreactive kinin than those of males. Ovariectomy of female rats resulted in the disappearance of a sex difference in the posterior kinin level and about a 3-fold increase in the anterior one. Orchidectomy of adult male rats failed to alter the kinin levels in both lobes. Moreover, the constitution of pituitary kinins was determined using HPLC. The pituitary kinins consisted of BK, Lys-BK (L-BK) and Met-Lys-BK (ML-BK) in different proportions in both lobes of male and female rats. The gonadectomy altered the proportions of these kinins. These results suggest that the pituitary kinin system may be regulated by circulating gonadal steroid hormones.     

Interference of sex-related factors in the response of liver cells to experimental mitotic stimuli.

Stimulation of liver cell multiplication was obtained under two different experimental conditions. (1) A single injection of casein solution resulted in (a) an identical synchronized mitotic wave response in 10-day old male and female rats and (b) a significantly lower response in adult male rats compared to females, a difference which was reduced by castration of males at birth but essentially maintained if animals were operated when 10 days old. (2) Partial hepatectomy shortly after puberty resulted in active hepatocyte multiplication occurring 3 hr earlier in females were ovariectomized at birth and significantly reduced when they were spayed at a later age. Hepatocytes of castrated females entered actively into S phase 2 hr later than the sham-operated controls. Unilateral ovariectomy on the other hand indicated that during compensatory and/or hypercompensatory activity of the single ovary there was a maximum difference between the male and female rate of [3H]thymidine uptake in liver nuclei 20 hr after hepatectomy. A further kinetic study (t = 25, 30,40, 65, 90 hr) indicated no significant sex-related difference in the number of S phases per 10,000 cells. The DNA content of regenerating versus control livers was comparable in both sexes at t = 22 and 90 hr but higher in females at t = 40 and 65 hr. A possible early postnatal interference of certain hormonal mechanisms in the receptivity to mitotic stimuli is postulated and discussed.     

Covalent binding of perfluorinated fatty acids to proteins in the plasma, liver and testes of rats.

Perfluorinated fatty acids alter hepatic lipid metabolism and are potent peroxisome proliferators in rodents. Two such perfluorinated acids, perfluorodecanoic acid (PFDA) and perfluorooctanoic acid (PFOA), were examined to determine if they covalently bind cellular proteins. PFDA and PFOA were found to covalently bind proteins when administered to rats in vivo. The liver, plasma and testes of male rats treated with [1-14C]PFDA or PFOA (9.4 mumol/kg) contained detectable levels of covalently bound 14C (0.1-0.5% of the tissue 14C content). Characterization of PFDA covalent binding to albumin in vitro showed that cysteine significantly decreased binding with no effect of methionine, suggesting protein sulfhydryl groups are involved. In cytosolic and microsomal incubation there was no effect of the addition of CoA, ATP or NADPH on the magnitude of the covalent binding of PFDA. Therefore PFDA need not be metabolically activated to form covalent adducts. Despite demonstration of covalent binding of PFDA and PFOA to proteins both in vivo and in vitro, the role of this macromolecular binding in perfluorinated fatty acid toxicity is not known.     

Sex differences in spironolactone induction of rat intestinal and hepatic p-nitrophenol UDP-glucuronyltransferase

In the present study we analyzed the effect of spironolactone administration on hepatic and intestinal p-nitrophenol-UDP-glucuronyltransferase activity. We used microsomal preparations from male and female Wistar rats to establish whether or not this effect was sex dependent. Enzyme activity was measured in the presence of UDP-N-acetylglucosamine, a presumed physiological activator of the enzyme. Female but not male microsomes showed an increase in enzyme activity of both hepatic and intestinal tissue preparations in response to the inducer pretreatment. In addition, the inducer effect observed in female rats showed a tissue-related difference, since percent increase in the intestinal enzyme activity was greater than that in the liver (127 and 52%, respectively). These results suggest that factors regulating enzyme activity or mechanisms involved in the inducer effect of spironolactone could be different in the intestinal mucosa in comparison to the liver. A possible explanation of sex-related response to spironolactone administration was discussed.