Chronic low-level lead toxicity in the rat: I. Maternal toxicity and perinatal effects

The first in a series of studies on the chronic exposure of rats to lead (Pb) is reported here. Weanling females were provided semipurified diets containing no detectable Pb, and drinking water containing 0, 0.5, 5, 25, 50, or 250 ppm Pb (as Pb-acetate). Rats were exposed to Pb-acetate for 6–7 weeks, then mated and exposed continuously throughout gestation and lactation. No statistically significant change in food or water consumption was noted in any exposure group. Females in the 50- and 250-ppm groups exhibited significant growth retardation within 1 to 3 weeks after exposure began. In addition, vaginal opening was significantly delayed in the 50- and 250-ppm groups, and to a lesser extent in the 25-ppm group. The level of Pb exposure used here did not affect the ability to conceive, to carry a normal litter to term, or to deliver the young. The percentage of malformed fetuses, resorptions, and postpartum pup deaths to weaning were unaffected by Pb exposure. Body lengths of female offspring in the 250-ppm exposure group were significantly shorter than those of controls, and there was a tendency for all young in this group to be smaller. The estimated dose of Pb consumed (mg/kg) indicated that groups were exposed to different amounts of Pb, and tissue (blood, brain, and bone) Pb concentrations indicated dose-related patterns. Urinary aminolevulinic acid concentrations were significantly dose related and were significantly correlated with blood Pb concentrations. Maternal toxicity occurred in groups exposed to 25 ppm Pb or higher and was associated with a minimum blood Pb concentration of 20 μg/dl.     

Chronic low-level lead toxicity in the rat: III. An integrated assessment of long-term toxicity with special reference to the kidney

Male and female rats whose mothers had been exposed to Pb before and during pregnancy and lactation at exposure levels of 0, 0.5, 5, 25, 50, and 250 ppm Pb as Pb-acetate in drinking water were continued on the respective regimens for 6 or 9 months. Body weights of males and females were not significantly different from controls at 6 months of age; however, female body weights were significantly decreased at 250 ppm at 9 months of age. In males at 9 months of age, spleen weights were significantly increased at 250 ppm Pb and kidney weights were increased at 0.5 ppm Pb and above; in females the liver, pituitary, and heart weights were affected at 250 ppm Pb. No significant Pb effects were found in sperm counts or sperm morphology, hematology profiles, or serum chemistries. Blood, brain, femur, and kidney Pb levels as well as urinary ALA excretion were all significantly dose related. Histopathological lesions were noted in the spleen (250 ppm) and in the kidney as evidenced by cytomegaly/karyomegaly (beginning at 5 ppm in males; 25 ppm in females), nuclear inclusion body formation and increased numbers of iron-positive granules within renal proximal tubule cells. These effects were more marked after 9 months exposure. Ultrastructural studies revealed mitochondrial swelling and the presence of increased numbers of lysosomes within renal proximal tubule cells. Energy-dispersive X-ray microanalysis, performed on adjacent sections, showed the highest intracellular Pb concentrations in nuclear inclusion bodies within renal proximal tubule cells. Inhibition of renal mitochondrial respiration for both succinate and NAD-linked substrates was found in 50- and 250-ppm Pb exposure groups at 9 months but not at 6 months. Mitochondrial δ-aminolevulinic acid synthetase and ferrochelatase, but not δ-aminolevulinic dehydratase, were also found to be inhibited at these Pb levels at 9 months. The lowest exposure level resulting in a detectable effect of Pb (cytomegaly/karyomegaly in renal proximal tubule cells) was 5 ppm associated with a median blood Pb concentration of 11 μg/dl.     

Altered pattern of prenatal toxicity in rats due to different treatment schedules with mirex

The effect of two slightly different treatment schedules on the pattern of mirex-induced prenatal toxicity was examined. Albino female rats were treated orally with 10 mg/kg mirex on gestation Days 5–14 or 6–15 or with corn oil vehicle on Days 5–15. All dams were killed on gestation Day 20 and examined for early and late resorptions, late fetal deaths, and edematous fetuses. Mirex treatment on gestation Days 5–14 produced a significantly higher incidence of total prenatal deaths than the Day 6–15 treatment schedule. This difference was attributed to a fourfold higher incidence of late resorptions in the Day 5–14 mirex group. The Day 6–15 treatment schedule produced significantly more late fetal deaths than in the Day 5–14 group. These data indicate that prenatal deaths occurred earlier and at a higher frequency among litters on the gestation Day 5–14 mirex treatment schedule. However, when total prenatal deaths and edematous fetuses were combined to determine total affected, there was no difference between the two mirex treatment schedules. Furthermore, mirex treatment depressed net weight gain and produced lethality similarly in dams on both treatment schedules. Thus, the two mirex treatment schedules appear to alter the pattern and severity of prenatal toxicity but not the overall incidence of effect. These results demonstrate the importance of considering the specific endpoints (e.g., malformation, prenatal death, growth retardation, maternal toxicity) in response to a prenatal insult, as well as combining the various endpoints for an estimate of overall toxicity.     

Acetaminophen-induced hepatic glycogen depletion and hyperglycemia in mice

Two hours following administration of a hepatotoxic dose of acetaminophen (500 mg/kg, i.p.) to mice, liver sections stained with periodic acid Schiff reagent showed centrilobular hepatic glycogen depletion. A chemical assay revealed that following acetaminophen administration (500 mg/kg) hepatic glycogen was depleted by 65% at 1 hr and 80% at 2 hr, whereas glutathione was depleted by 65% at 0.5 hr and 80% at 1.5 hr. Maximal glycogen depletion (85% at 2.5 hr correlated with maximal hyperglycemia (267 mg/100 ml at 2.5hr). At 4.0 hr following acetaminophen administration, blood glucose levels were not significantly different from saline-treated animals; however, glycogen levels were still maximally depleted. A comparison of the dose-response curves for hepatic glycogen depletion and glutathione depletion showed that acetaminophen (50–500 mg/kg at 2.5 hr) depleted both glycogen and glutathione by similar percentages at each dose. Since acetaminophen (100 mg/kg at 2.5 hr) depleted glutathione and glycogen by approximately 30%, evidence for hepatotoxicity was examined at this dose to determine the potential importance of hepatic necrosis in glycogen depletion. Twenty-four hours following administration of acetaminophen (100 mg/kg) to mice, histological evidence of hepatic necrosis was not detected and serum glutamate pyruvate transaminase (SGPT) levels were not significantly different from saline-treated mice. The potential role of glycogen depletion in altering the acetaminophen-induced hepatotoxicity was examined subsequently. When mice were fasted overnight, hepatic glutathione and glycogen were decreased by 40 and 75%, respectively, and fasted animals showed a dramatic increase in susceptibility to acetaminophen-induced hepatotoxicity as measured by increased SGPT levels. Availability of glucose in the drinking water (5%) overnight resulted in glycogen levels similar to those in fed animals, whereas hepatic glutathione levels were not significantly different from those of fasted animals. Fasted animals and animals given glucose water overnight were equally susceptible to acetaminophen-induced hepatotoxicity, as quantitated by increases in SGPT levels 24 hr after drug administration. The potential role of a reactive metabolite in glycogen depletion was investigated by treating mice with N-acetylcysteine to increase detoxification of the reactive metabolite. N-Acetylcysteine treatment of mice prevented acetaminophen-induced glycogen depletion.     

Activation of the O-glucuronide of the carcinogen N-hydroxy-N-2-fluorenylacetamide by enzymatic deacetylation in vitro: formation of fluorenylamine-tRNA adducts.

The O-glucuronide of N-hydroxy-N-2-fluorenylacetamide (N-GIO-FAA) was deacetylated by guinea pig liver. tRNA reacted with the product of this deacetylation, the O-glucuronide of N-2-fluorenylhydroxylamine (N-GIO-FA), to give fluorenylamine-substituted nucleic acid adducts. The quantity of adduct formation was used to determine deacetylase activity.Of the various guinea pig tissues assayed, only the liver contained enzyme activity, and this activity was confined to the microsomal fraction of the cell. Guinea pig liver microsomes were about four times as active as rabbit liver microsomes and about fourteen times as active as rat liver microsomes in promoting fluorenylamine-tRNA adduct formation. Adduct formation induced by guinea pig microsomes was about seven times greater at pH 8.5 than at pH 7.0.The aglycone of the O-glucuronide, N-hydroxy-N-2-fluorenylacetamide (N-hydroxy-FAA) also yielded flourenylamine-substituted nucleic acid adducts following deacetylation at pH 8.5 by guinea pig liver microsomes in the presence of tRNA. In contrast to resuls obtained with N-GIO-FAA, adduct formation with N-hydroxy-FAA was not as efficient, and it was independent of pH over the range 7.0–8.5. Rabbit and rat liver microsomes were more active in promoting adduct formation of tRNA with N-hydroxy-FAA than with N-GIO-FAA.The differential inhibition of the microsome-induced formation of adducts of N-GIO-FAA and N-hydroxy-FAA with tRNA affirms that the first step in the binding mechanism of N-GIO-FAA with tRNA is enzymatic deacetylation and not hydrolysis to the aglycone N-hydroxy-FAA.     

The potential laboratory health hazard of 210Pb and a simple procedure for separation of 210Pb from the daughters 210Bi and 210Po

Lead 210 (Radium D) is a naturally occurring radionuclide which is frequently used in toxicological studies due to its long half-life. The use of ²¹⁰Pb in tracer studies poses two problems. First, ²¹⁰Pb, along with its daughters ²¹⁰Bi and ²¹⁰Po, presents a significant health hazard to laboratory personnel. Second, the presence of the daughter products may interfere with the detection of ²¹⁰Pb, particularly by techniques which discriminate poorly between different radioactive emissions, e.g., autoradiography. The potential laboratory health hazards of ²¹⁰Pb and its daughters are briefly reviewed and a simple dithiozone extraction procedure which allows quantitative separation of ²¹⁰Pb from the daughters ²¹⁰Po and ²¹⁰Bi is described. The purified ²¹⁰Pb may then be utilized to reduce the health hazard from the daughter products and to construct calibration curves for the quantitation of ²¹⁰Pb in the presence of ²¹⁰Bi and ²¹⁰Po by liquid scintillation counting.     

Caffeine metabolism in liver slices during postnatal development in the rat

The metabolism of caffeine was investigated in liver slices of young and adult rats. Liver slices from adult male rats metabolized caffeine at an initial rate of 48.31 ± 3.71 nmoles · (g liver)^?1 · hr^?1 to four main metabolite fractions. By a combination of thin-layer radiochromatography and high performance liquid chromatography, theophylline, paraxanthine and 1, 3, 7-trimethyldihydrouric acid were identified as caffeine metabolites. Apparent V_max of the overall reaction was 83.30 nmoles caffeine metabolites formed · (g liver)^?1 · hr^?1. Theophylline competitively inhibited caffeine metabolism [the apparent K_m was 19.20, μM in the absence of theophylline, the apparent k_i was 36.50 μM in the presence of theophylline (100 μM)]. SKF 525-A inhibited caffeine metabolism; the formation of all of the metabolite fractions was inhibited to a similar extent. Allopurinol (100 μM) had no effect. The specific activity of the enzyme system was extremely low when liver slices of 2-day-old-rats were used [1.46 ± 0.08 nmoles caffeine metabolites formed · (g liver)^?1 · hr^?1]; the reaction velocity increased gradually with increasing age and reached a peak [52.26 ± 1.41 nmoles caffeine metabolites formed · (g liver)^?1 · hr^?1]at 30 days of age. Changes in the formation of the four metabolite fractions with age followed the pattern of the overall caffeine metabolism. These results demonstrate that the liver of the newborn rat has an extremely limited capacity to metabolize caffeine in vitro and are consistent with the proposed involvement of the liver microsomal cytochromes P-450 monooxygenase system in the metabolism of caffeine. N-Demethylation is the main pathway of in vitro caffeine metabolism in the rat liver at all ages.     

Chronic toxicity and carcinogenicity to the urinary bladder of sodium saccharin in the in utero-exposed rat

In utero-exposed Charles River CD strain rats, the offspring of parents treated from weaning through mating, gestation and lactation, were fed sodium saccharin chronically at dietary levels of 0, 0.01, 0.1, 1.0, 5.0, and 7.5%. Calcium cyclamate was fed as a reference compound at a level of 5.0%. Groups of 48 male and 48 female weanlings were placed on the same regimen as their parents. The study was continued until the number of survivors in a group fell to 20% with the last survivors being killed approximately 28 months after the first weanlings were selected for the chronic study. Serial sacrifices were performed at 14 and 18 months. Treatment-related effects were not observed in hematological values, organ weights, and survival. Average weaning weights were decreased in litters from parents receiving 5.0 and 7.5% sodium saccharin and 5.0% calcium cyclamate. Some of the initial weaning weight depression was overcome, but the rats on these dose levels had lower average body weights throughout the study. The incidence and types of neoplasms and nonneoplastic lesions, other than urinary bladder neoplasms and hyperplasia, were typical of the aged rat and were not treatment related. A significantly increased incidence of urinary bladder hyperplasia occurred in female rats that received 7.5% sodium saccharin, but the lesion was not morphologically precancerous. A significantly increased incidence of urinary bladder neoplasms occurred in the males fed 7.5% sodium saccharin. A total of 11 bladder neoplasms was observed in rats on study longer than 18 months; nine in the 7.5% saccharin group and one each in the control and 5.0% saccharin groups. There were nine neoplasms in males and two in females. Histologically, six of the neoplasms were classified as benign and five as malignant. All the malignant neoplasms occurred in the 7.5% saccharin group. The occurrence of the urinary bladder neoplasms could not be related to such predisposing factors as gross calculi, parasites, or hyperplasia.     

The distribution of inorganic lead in guinea pig brain and neural barrier tissues in control and lead-poisoned animals.

The central neural distribution of radiolabeled lead nitrate (²¹⁰Pb) and total lead concentrations were investigated in adult pigs after intravenous injection of the tracer. Control animals were fed ad libitum, whereas lead encephalopathy was induced by feeding other animals 165 mg lead carbonate daily for 6 days. Lead was not detected in choroid plexus (CP). (Average concentration in control animals <1.2 μg/g; <1.5 μg/g in poisoned animals.) Brain lead concentrations averaged 0.095 ± 0.016 μg/g wet weight in control nimals and 0.427 ± 0.067 μg/g in poisoned animals. CP concentrated the pulsed radiolabel more than 70 times as avidly as brain, and in meninges and ependyma the concentration of ²¹⁰Pb also exceeded markedly that occurring in brain. The high initial uptake of radiolead by CP indicates that this organ may act as a “sink”, tending to reduce lead entry into CSF and brain. Pretreatment with ouabain iv (1.6 – 1.7 × 10^?9 mol/kg) reduced significantly ²¹⁰Pb accumulation by CP and by brain 5 and 60 min after label injection in control animals but not in lead-poisoned animals. These results suggest that active transport of cations by the barrier tissues may influence the central neural distribution of lead.     

The effect of lead toxicity and milk deprivation of myelination in the rat

During a defined postnatal developmental period, the 2nd through the 28th postnatal day, rats were exposed daily to either an oral administration of 200 mg lead (as lead acetate) per kilogram of body weight, an 8-hr maternal milk deprivation schedule, or a combination of the two insults. On the 29th day the rats were killed. Either lead exposure or milk deprivation alone decreased brain (10%) and body (15%) weights, and an additive effect was observed in rats exposed to both lead and milk deprivation (brain: 20%; body: 35%). Neither the lead nor the deprivation insult alone produced a perturbation in the process of myelination. However, when the two conditions were combined an interaction was evident as a 25% decrease in myelin accumulation in females. No effect was seen in males. The myelination deficit in females was specific in that neither accumulation of glial fibrillary acidic protein (a marker for astroglial cells) nor neurofilament protein (a marker for neurons, especially axons) was perturbed. Tissue lead concentrations did not suggest that this increased sensitivity in females was due to a selective increase in their body burden of lead.     

Behavioral toxicity of chronic postweaning lead exposure in the rat.

Effects in the rat of chronic postweaning exposure to 50, 300, or 1000 ppm lead acetate in drinking water were assessed on responding maintained by a fixed-interval 30-s food reinforcement schedule. On this schedule, food reinforcement followed the first lever press response occurring at least 30 s after the preceding food delivery. Exposure to 50 and 300 ppm lead acetate increased response rates and intersubject variability, while latency, or time to initiation of responding in the interval, decreased. Exposure to 1000 ppm initially decreased rates and increased latency values. Following termination of exposure to 50 ppm, response rates and latency values gradually returned to control levels. Behavioral effects produced by exposure to 50 and 300 ppm lead were similar in magnitude but varied in time to onset and decline, suggesting time-dependent, rather than concentration-dependent effects of lead.     

Effect of chronic phenobarbital treatment on folates and one-carbon enzymes in the rat

Chronic oral phenobarbital treatment (50 mg/kg every 12 hr for 8 weeks), which was nontoxic and continuously protective against seizures in rats, significantly decreased folate concentration in liver (29%) but not in brain or plasma. The apparent activity of 5,10-methylenetetrahydrofolate reductase (MTR) in liver decreased with initiation of treatment but then increased with a significant correlation to the length of treatment. Phenobarbital also stimulated the activity of this enzyme slightly in vitro. Methionine adenosyltransferase (MAT) activity was inhibited by high concentrations of phenobarbital in vitro but was not affected in vivo. No significant effects of phenobarbital on the activities of serine hydroxymethyltransferase (SHMT) or 5-methyltetrahydrofolate:homocysteine methyltransferase (MHMT) were observed either in vivo or in vitro.     

Effect of the inhalation of zinc and dietary zinc on paraquat toxicity in the rat.

A possible pharmacological effect of zinc against the pulmonary toxicant paraquat has been studied. Rats were treated with zinc either by inhalation of zinc oxide fume aerosol or consumption of zinc supplemented food. The animals were then injected with paraquat ip (30 mg/kg) and lethality monitored for 7 days. Neither zinc inhalation nor dietary zinc protected the animals against paraquat-induced lethality. In fact, exposure of rats to zinc oxide fume aerosol potentiated the lethal effects of paraquat. The mechanism of paraquat-induced lung toxicity at the cellular level does not appear to directly involve a zinc-dependent step. This distinguishes paraquat from other injurious agents which have been reported to respond to zinc.     

Alcohol and local anesthetic effects on Na+-dependent Ca2+ fluxes in brain synaptic membrane vesicles

Resealed synaptic plasma membrane vesicles exhibit Na+-dependent Ca2+ transport activity which may participate in regulation of free Ca2+ concentrations in nerve endings. Sodium chloride-loaded vesicles took up Ca2+ from the external medium (150 mM KCl-25 mM Tris/HCl) in the presence of an outward-directed Na+ gradient, a Ca2+ concentration of 38.6 microM producing half-maximal uptake at 23 degrees. Methanol (5-200 mM) and low concentrations of ethanol (5-25 mM) enhanced the Na+-dependent Ca2+ influx measured at 23 degrees. Higher ethanol concentrations (100-600 mM), as well as 1-propanol and 1-butanol (10-200 mM), produced only inhibition of Ca2+ fluxes. Dixon plot analysis of the inhibitory phase revealed that ethanol inhibited Ca2+ uptake in an apparently competitive manner with respect to Ca2+ concentration, and the Ki obtained from these experiments was 1.01 M ethanol. The inhibition of Ca2+ fluxes by butanol was non-competitive, and the Ki was 68.6 mM. The local anesthetics dibucaine and tetracaine also inhibited Ca2+ fluxes with IC50 values of 1.8 mM for tetracaine and 0.46 mM for dibucaine. The possible physiologic consequences of this inhibition of Na+-Ca2+ countertransport is synaptic membranes by the alcohols and local anesthetics are discussed with regard to neuronal transmission and membrane conductance.     

Metabolism of clomiphene in the rat: Estrogen receptor affinity and antiestrogenic activity of clomiphene metabolites

Incubation of the nonsteroidal antiestrogen clomiphene with rat liver microsomes resulted in the formation of the 4-hydroxy-, N-desethyl-, and N-oxide metabolites, in qualitative contrast to results previously obtained analogously with rabbit microsomes, with which only the first two metabolites were detected. Metabolites were characterized by thin-layer chromatography in comparison with synthetic standards. They were similarly compared using low resolution electron ionization mass spectrometry, except for the N-oxide which was best characterized by fast atom bombardment mass spectrometry. Oral administration of clomiphene resulted in no detectable urinary elimination of the drug or its metabolites; 4-hydroxyclomiphene was the sole detectable elimination product in fecal extracts. The relative uterine cytosol estrogen receptor binding affinities, at 4°, of 4-hydroxyclomiphene and the E-isomers of clomiphene, desethylclomiphene, and clomiphene N-oxide were, in turn, 331, 0.71, 0.62, and 0.88 (estradiol = 100). In the 3-day immature rat uterotropic assay, 4-hydroxyclomiphene had no significant uterotropic effect at doses up to 50 μg/day, but substantially inhibited that of estradiol (0.5 μg/day) at doses of 2 μg/day.     

Alloxan toxicity in isolated rat hepatocytes and protection by sugars

Suspensions of isolated rat hepatocytes incubated in the presence of the diabetogenic agent alloxan exhibit time- and concentration-dependent damage. At concentrations of 3.5 mM and above, alloxan caused an increase in lactate dehydrogenase (LDH), glutamate-pyruvate transaminase (GPT) and intracellular potassium (K⁺) leakage, all of which are indices of plasma membrane damage, and decreased the intracellular reduced glutathione content (GSH) of the cells. Preincubation (10 min) in d-glucose (50 or 100 mM, but not 10 mM) partially protected the hepatocytes from LDH, GPT and K⁺ leakage and the decrease in GSH produced by alloxan (7mM) during a 60-min incubation period. Other sugars (d-galactose, 2-deoxy-d-glucose, d-fructose, d-mannoheptulose and d-mannitol) were also found to protect hepatocytes against damage caused by alloxan. d-Fructose was found to be the most potent protective sugar. These results indicate that alloxan is not selectively toxic to the pancreatic (β-cell and that sugars can protect against alloxan-induced cytotoxicity in hepatocytes.     

Chemical and biochemical characteristics of O-demethylation of chlorotrianisene in the rat

The effects of NADPH concentration and of two inhibitors of the microsomal mixed function oxidase system [2-diethylaminoethyl-2,2-diphenyl valerate hydrochloride (SKF 525-A) and metyrapone] on rat liver microsomal O-demethylation of the triphenylethylene estrogen chlorotrianisene (CTA) were studied. Comparative data were obtained using untreated and phenobarbital-pretreated rats of both sexes. In the presence of microsomes from males, O-demethylation was induced slightly by phenobarbital (PB), and it was inhibited substantially by SKF 525-A, particularly with uninduced microsomes. Metyrapone had little inhibitory effect. In the presence of microsomes from females, O-demethylation was neither induced by PB nor inhibited significantly by SKF 525-A or metyrapone. Incubation of CTA with male rat microsomes afforded, after purification, a mixture of monophenolic metabolites which consisted primarily of a 1:1 mixture of E- and Z-desmethylchlorotrianisene (DMCTA).     

Perinatal toxicity of endrin in rodents. II. Fetotoxic effects of prenatal exposure in rats and mice

The fetotoxic potential of endrin in the CD rat and CD-1 mouse was investigated. Endrin was administered as a solution in corn oil to groups of pregmant animals by gastric intubation at multiple dose levels throughout the period of organogenesis. The dams were sacrified prior to term and the fetuses were examined for skeletal and visceral anomalies. In addition, maternal livers and fetuses from rats in each dose level were analyzed for endrin content. In the mouse, endrin caused maternal liver enlargement at a dose of 0.5 mg/kg/day and reduced maternal weight gain at a dose of 1.0 mg/kg/day. Fetal weight and skeletal and visceral maturity were adversely affected at a dose of 1.0 mg/kg/day, but no teratogenic effect or embryo lethality was evident even at a dose level that produced maternal lethality (1.5 mg/kg/day). In the rat, endrin markedly reduced maternal weight at doses above 0.150 mg/kg/day but produced no apparent effects on the fetus. The data suggest that species differences in sensitivity to endrin may in part be due to differences in metabolism. Although endrin levels in rat fetuses at a maximally tolerated dosage level resembled those previously reported for the hamster, relatively less 12-ketoendrin was present, paralleling the change in fetal sensitivity.     

Effects of ethanol and lead ingestion on urinary sodium excretion and related enzyme activity in rat kidney

The present study was undertaken to examine lead-ethanol interaction with respect to previously reported lead enhancement of urinary Na⁺ excretion [Y. Suketa, S. Hasegawa and T. Yamamoto, Toxic. appl. Pharmac.47, 203 (1980)]. Simultaneous administration of ethanol reduced the enhancement due to lead alone. A decrease in serum Na⁺ concentration followed lead administration and the decrease appears to be less when ethanol was administered simultaneously. Renal (Na⁺ + K⁺ATPase activity was suppressed after lead administration, but it was stimulated after ethanol administration. the suppression of renal (Na⁺ + K⁺ATPase activity after lead administration was diminished after simultaneous administration of ethanol and lead. the diminution of the suppression appeared to be associated with a corresponding reduction in urinary Na⁺ excretion.