Amphetamine and chlorpromazine modify cerebral insulin levels in rats

Rats treated with chlorpromazine (CPZ) (1 mg/kg/day i.p.) experienced a marked decline in cerebral insulin levels (0.057 +/- 0.01 ng/g wet weight) with respect to a control group (0.38 +/- 0.05 ng/g wet weight), while rats given D-amphetamine bitartrate (AMPH) chronically (20 mg/kg/day p.o.) showed a rise in cerebral insulin (0.55 +/- 0.04 ng/g wet weight). Combined treatment with both drugs at the same dosages produced lower cerebral insulin levels (0.46 +/- 0.10 ng/g wet weight) than in the AMPH animals. In the groups of rats treated with CPZ and with AMPH + CPZ, there was a slight elevation in serum insulin levels. Serum glucose values did not vary.     

Fed-batch fermentation studies with Bacillus thuringiensis H-14 synthesising endotoxin.

Cell yield and toxicity of B. thuringiensis H-14 was improved markedly by adopting a simple fed-batch fermentation technique based on controlling glucose concentration. Maintenance of steady glucose concentration (0.3-0.5%) in the culture medium was achieved by the continuous addition of concentrated glucose solution. Addition of glucose at 3 g/hr/l of culture starting from 3rd hr till 16th hr of fermentation was found to yield cell densities of 80 g/l (wet weight) which represented a nearly 3-fold increase over the batch mode. A fivefold increase in toxicity was obtained by fed-batch fermentation. Cultivation of B. thuringiensis H-14 to high cell densities had no negative effect on sporulation and toxin synthesis. The rate of pH drop and dissolved oxygen level were within manageable limits.     

The effect of ethanol or sorbitol on glucose production from pyruvate in isolated hepatocytes from 48-hour fasted guinea-pigs

Hepatocytes isolated from 48-hour, fasted guinea-pigs were incubated with glucose precursors to compare relative rates of glucose production. Glucose production from lactate and pyruvate was similar (2.61 vs 3.18 mumol/hr per 100 mg wet weight). Glucose production from fructose was greater than that from sorbitol (4.68 vs 1.63 mumol/hr per 100 mg wet weight). When ethanol was added to pyruvate-containing buffer, the flux of pyruvate to glucose and lactate was synergistically enhanced (5.28 vs 3.76 and 7.51 vs 2.88 mumol/hr per 100 mg wet weight, respectively). When sorbitol was added to buffer containing pyruvate, glucose and lactate production were even greater than that seen with ethanol (8.32 vs 5.38 and 15.99 vs 7.51 mumol/hr per 100 mg wet weight, respectively).     

Heterogeneity of glycogen synthesis upon refeeding following starvation.

1. Starvation of rats for 40 hr decreased the body weight, liver weight and blood glucose concentration. The hepatic and skeletal muscle glycogen concentrations were decreased by 95% (from 410 mumol/g tissue to 16 mumol/g tissue) and 55% (from 40 mumol/g tissue to 18.5 mumol/g tissue), respectively. 2. Fine structural analysis of glycogen purified from the liver and skeletal muscle of starved rats suggested that the glycogenolysis included a lysosomal component, in addition to the conventional phosphorolytic pathway. In support of this the hepatic acid alpha-glucosidase activity increased 1.8-fold following starvation. 3. Refeeding resulted in liver glycogen synthesis at a linear rate of 40 mumol/g tissue per hr over the first 13 hr of refeeding. The hepatic glycogen store were replenished by 8 hr of refeeding, but synthesis continued and the hepatic glycogen content peaked at 24 hr (approximately 670 mumol/g tissue). 4. Refeeding resulted in skeletal muscle glycogen synthesis at an initial rate of 40 mumol/g tissue per hr. The muscle glycogen store was replenished by 30 min of refeeding, but synthesis continued and the glycogen content peaked at 13 hr (approximately 50 mumol/g tissue). 5. Both liver and skeletal muscle glycogen synthesis were inhomogeneous with respect to molecular size; high molecular weight glycogen was initially synthesised at a faster rate than low molecular weight glycogen. These observations support suggestions that there is more than a single site of glycogen synthesis.     

Plasma catecholamines and plasma corticosterone following restraint stress in juvenile alligators

Ten juvenile alligators, mean body mass 793 g, hatched from artificially incubated eggs and raised under controlled conditions, were held out of water with their jaws held closed for 48 hr. An initial blood sample was taken and further samples collected at 1, 2, 4, 8, 24, and 48 hr. Epinephrine, norepinephrine, and dopamine were measured in plasma aliquots of 1.5 ml using high pressure liquid chromatography with electrochemical detection. Corticosterone was measured by radioimmunoassay. Plasma glucose was measured using the Trinder method and plasma calcium, cholesterol, and triglycerides were measured in an autoanalyzer. Epinephrine was about 4 ng/ml at the initial bleed, but declined steadily to < 0.4 ng/ml by 24 hr. Norepinephrine was also about 4 ng/ml at the initial bleed, but rose to over 8 ng/ml at 1 hr, and then declined to < 0.2 ng/ml at 24 hr. A second, but smaller increase in plasma norepinephrine was seen at 48 hr. Plasma dopamine was low at the initial bleed (< 0.7 ng/ml), rose to over 8 ng/ml at 1 hr, then declined to < 0.2 ng/ml. Plasma corticosterone rose progressively for the first 4 hr, declined at 8 hr and 24 hr, then rose again at 48 hr. Plasma glucose rose significantly by 24 hr and remained elevated for 48 hr. Plasma calcium increased at 1, 2, and 4 hr then returned to levels not significantly different from the initial sample at 24 and 48 hr. The white blood cells showed changes indicating immune system suppression. By the end of the treatment the hetorophil/lymphocyte ratio increased to 4.7. These results suggest that handling alligators, taking multiple blood samples, and keeping them restrained for more than 8 hr is a severe stress to the animals.     

Fetal development, and placental and maternal plasma concentrations of progesterone in the little brown bat (Myotis lucifugus)

Progesterone concentrations measured in plasma samples from 280 bats captured during pregnancy or early lactation were related to fetal attributes indicative of stage of pregnancy. Fetal weight increased exponentially from 40 mg at crown-rump length of 6 mm to 2000 mg at 23 mm (term). Fetal weights at term accounted for up to 35% of the weight of intact pregnant animals. Progesterone concentrations increased from less than 5 ng/ml at 2 mm estimated crown-rump length to plateau values of approximately 65 ng/ml (geometric means) from 16 mm crown-rump length until the most advanced stages of pregnancy. Mean concentration in 8 post-partum bats, most of which were actively lactating, was 8.4 ng/ml; 11.6 ng/ml was measured in one animal that was carrying a wet neonate when sampled yet was still pregnant when captured 5 h earlier. Placental concentrations of progesterone ranged from 43 to 964 ng/g wet weight of tissue and mean values increased in a similar fashion though were about 4-fold greater than changes in plasma concentrations of the steroid. The concentrations in placental tissue were at least 15- to 20-fold higher than could be expected from blood contamination, indicating that placental steroidogenesis is likely to occur in this species.     

Aerobic glucose disposal in the oyster: An in vivo kinetic analysis

• 1.1. Aerobic glucose disposal in starved oysters exposed to 1 mM external glucose was 2.29 μg C/g wet wt/min.
• 2.2. It was hypothesized that the maximum disposal rate is limited by the maximum rate of transepithelial glucose transport.
• 3.3. The major recipients of glucose-carbon were glycogen and amino acids. 4. The rate of glucose-carbon disposal to these two pools was 0.80 and 0.42 μg C/g/min, respectively.
• 4.5. The internal energy state determines the pathways of glucose disposal.
• 5.6. Disposal of glucose-carbon in “glucose-primed” oysters is primarily into glycogen.
• 6.7. In fasted bivalves the disposal is primarily into amino acids and carboxylic acids.
• 7.8. The uptake of dissolved glucose has the potential of contributing significantly to growth under conditions where the external glucose concentration is kept artificially high.

     

Age-, cycle- and topographic dependency of human myometrial prostaglandin (6-keto-PGF1 alpha, PGF2 alpha)-synthesis in vitro

Specimens of human myometrium (isthmus and fundus) freshly obtained at hysterectomy were immediately transferred in ice cold Tyrode solution and placed in superfusion chambers. Spontaneous contractions were recorded, the effluent of the myometrium was analyzed for PGF2 alpha and 6-keto-PGF1 alpha by use of specific radioimmunoassay systems. Dating of the menstrual cycle was achieved by histological evaluation of the endometrium. The PG release rates expressed as ng/min/g wet weight were correlated to the patients age and to the phase of the menstrual cycle. The production rates of 6-keto-PGF1 alpha were negatively correlated to the age of the patients and declined in fundus specimens from 2.89 +/- 0.35 ng/min/g wet weight in 39-42 years old patients to 0.52 +/- 0.17 ng/min/g wet weight in 48-52 years old women during the secretory phase (p less than 0.001). Similar significant correlations were found in specimens obtained from the isthmus uteri. During the proliferative phase fundus specimens produced on average 1.61 +/- 0.67 ng/min/g wet weight in 39-42 years old patients and 0.49 +/- 0.12 ng/min/g wet weight 6-keto-PGF1 alpha in 48-52 years old women respectively (p les than 0.001). The PGF2 alpha synthesis in myometrial specimens of fundus or isthmus origin was significantly lower than 6-keto-PGF1 alpha and did not correlate to the age of the patients during the proliferative phase. However, PGF2 alpha release rates during the secretory phase were significantly (p less than 0.001) higher in younger women. These results suggest an age-, cycle- and topographic dependency of PGI2 synthesis in human myometrial tissue.     

Biochemical effects of thiabendazole and cambendazole on Hymenolepis diminuta (Cestoda) in vivo

An investigation of the chemotherapeutic and biochemical effects of two benzimidazole anthelmintics, thiabendazole (TBZ) and cambendazole (CBZ), on Hymenolepis diminuta in experimentally infected rats is reported. Thiabendazole was active against H. diminuta at a relatively high dosage. A single oral dose of TBZ at 250 mg/kg body weight on day 15 of infection eliminated 100% of the tapeworms as determined at necropsy 5 days after treatment. The chemotherapeutic actions of TBZ on H. diminuta were accompanied by marked changes in worm weight and chemical composition. Tapeworms recovered from rats that had received a therapeutically effective dose of TBZ 24 hr earlier were significantly smaller and contained much less glycogen (as a percent of the wet weight) than worms from unmedicated controls. Protein concentrations increased in TBZ-treated worms and at a rate sufficient to offset the decline in glycogen concentration. Glycogen/protein ratios in TBZ-treated worms were significantly lower than the corresponding control values. Cambendazole proved to be five times more potent than TBZ against H. diminuta and produced the same basic changes in worm weight and chemical composition within 18 hr of treatment of the host. Administration of a single oral dose of TBZ or CBZ to the host produced in H. diminuta another change, the onset of which coincided with, or preceded, the gross alterations in worm weight and chemical composition. That change, observed in in vitro studies carried out 14 hr after treatment, revealed that tapeworms from drug-treated rats absorbed and metabolized much smaller quantities of exogenous glucose than did the controls, and the ability of the worm to accumulate glucose against a concentration difference was significantly depressed.     

Effect of glutamate on the control of fatty-acid synthesis in white adipose tissue of the rat. Inhibition of pyruvate dehydrogenase.

Glutamate (5mM) inhibited glucose conversion to fatty acids by approximately one-third in adipocytes from fed rats. This inhibition was significantly less in the pressence of pyruvate or 2-oxoglutarate. After incubation of adipose tissue from fed rats with glucose and insulin, pyruvate dehydrogenase activity was 180 plus or minus 17 mU/g wet weight. Addition of glutamine to the incubation medium decreased this activity significantly (118 plus or minus 14 mU/g wet weight). This inhibition by glutamate was also diminished when 2-oxoglutarate or pyruvate were present. Glutamate added to homohentates of adipose tissue had no effect on the activation of pyruvate dehydrogenase by Mg-2+. However, glutamate inhibited the active form of the enzyme and enhanced the rate of inactivation of the enzyme complex by ATP and Mg-2+. Aminooxyacetate, a transaminase inhibitor, did not reverse the effects of glutamate on pyruvate dehydrogenase nor fatty acid synthesis.     

Glycogen metabolism in human hormone-producing trophoblastic cells in continuous culture

Summary Glycogen metabolism was studied in human hormone-producing trophoblastic cells (BeWo line). Cells supplemented daily with high glucose (3 g per liter in medium) contained 5.5% glycogen and utilized glucose at an initial rate of 12.2 mμmoles per min per mg of protein. In cells supplemented daily with low glucose (1 g per liter), the initial rate of glucose consumption was 23 mμmoles per min per mg of protein and the glycogen content reached only 0.4% of wet weight 24 hr after medium replenishment. When glycogen-depleted cultures were refed glucose, an accumulation of glycogen was observed, with initial deposition occurring in areas near the cell surface. After exhaustion of extracellular glucose, cytoplasmic glycogen was utilized at a rate of 2.8 mμmoles per min per mg of protein. Addition of either low or high glucose to glycogen-depleted cells resulted in the same rate of glycogen synthesis (approximately 8 mμmoles per min per mg of protein). It was suggested that unique regulatory mechanisms function in the control of glycogen metabolism in glycoprotein hormone-producing cytotrophoblastic cells. This work was supported in part by Public Health Service Research Contract PH43-68-1010, Research Grant CA 05524 from the National Cancer Institute, and by grants from the Milwaukee Division of the American Cancer Society, Inc., and the Damon Runyon Memorial Fund for Cancer Research, Inc.     

Somatic production of two species: Crassostrea virginica and Ischadium recurvum Bivalvia in Mecoacán, Tabasco, México

The Mexican oyster fishery, 90% supported by the coastal lagoons of the Gulf of Mexico, has decreased drastically in the last six years as a result of anthropogenic pollution and improper management. The mussel Ischadium recurvum has proliferated and competes with oysters for space and probably food. Crassostrea virginica and Ischadium recurvum were studied to evaluate somatic production with biometry and physiological condition indices (PCI's) during an annual cycle. A random sample of 200 organisms was taken montly for each species. Condition indices wet flesh weigth: wet shell weight ratio (WFW/WSW), dry flesh weight: wet flesh weight ratio (DFW/WFW), dry flesh wet: dry shell weight ratio (DFW/DSW), and ash free dry weight: tissue dry weight (AFDW/TDW) were calculated. In order to stablish physiological condition and temporal variability, these indices were compared between species and months. The somatic production of mussels was higher than in oysters. This enhancement in production could be explained by: 1) Mussel uses less energy for shell production, 2) a constant recruitment of mussel almost year-round, and 3) the mesohalin lagoon was more favourable to the mussel.     

Measurement of concentrations of metabolites in adipose tissue and effects of insulin, alloxan-diabetes and adrenaline

1. Methods are described for the extraction and assay of ATP, ADP, AMP, glucose 6-phosphate, l-glycerol 3-phosphate and citrate in rat epididymal adipose tissue incubated in vitro for 1hr. At this time of incubation rates of glucose uptake and outputs of glycerol, free fatty acids, lactate and pyruvate were shown to be constant. 2. In fat pads incubated in medium containing glucose (3mg./ml.) and albumin (20mg./ml.) the concentrations (in mmumoles/g. wet wt.) were: ATP, 70; ADP, 36; AMP, 9.0; glucose 6-phosphate, 3.0; l-glycerol 3-phosphate, 3.3; citrate, 8.1. 3. The volume of intracellular water calculated from ([(3)H]water space-[(14)C]sorbitol space), ([(14)C]urea space-inulin space) and (weight loss on drying-[(14)C]sorbitol space) was 1.4ml./100g. wet wt. of tissue. The intracellular volume was not changed by insulin, alloxan-diabetes or adrenaline. 4. When compared in terms of mumoles/ml. of intracellular water the concentration of ATP in adipose tissue was less than in heart and diaphragm muscles. The concentrations of ADP and AMP were greater both in absolute terms and relative to ATP. Insulin, alloxan-diabetes and adrenaline had no significant effects on the concentrations of the adenine nucleotides in adipose tissue. 5. The concentration of glucose 6-phosphate was increased by insulin and lowered by alloxan-diabetes and adrenaline. The concentration of l-glycerol 3-phosphate was increased by insulin, unchanged by alloxan-diabetes and lowered by adrenaline. The concentration of citrate was increased by adrenaline and alloxan-diabetes and unchanged by insulin. 6. The effect of glucose concentration in the medium on rates of glucose uptake in adipose tissue from normal rats and alloxan-diabetic rats was investigated. The K(u) of glucose uptake was 29-44mg./100ml. and the V(max.) was 0.77mg./g. wet wt. of tissue/hr. Insulin increased the V(max.) and alloxan-diabetes diminished it, but neither agent significantly altered the K(u). 7. The significance of these results in relation to control of metabolism of adipose tissue is discussed.     

The time-course of appearance and net accumulation of horseradish peroxidase (HRP) presented orally to juvenile carp Cyprinus carpio (L.)

A sensitive enzyme-linked immunosorbent assay (ELISA) technique was used in order to determine horseradish peroxidase (HRP) uptake from the carp gut. HRP was detected in blood plasma and various tissues within 15 min of oral intubation. The time-course of net accumulation (uptake-degradation) over a 2 hr period was recorded. The presence of HRP reached a maximum in the body tissues approximately 1 hr after intubation and on a microgram/g wet weight basis the order of accumulation within the tissues was spleen greater than kidney greater than liver. The total organ accumulation (net) was in the order liver greater than kidney greater than spleen.     

Dietary carbohydrate level and glucose metabolism in turkey poults.

1. Feeding British United turkeys (BUT) and Nicholas turkeys (NT) diets with varying carbohydrate levels for 24 hr post-hatch resulted in lower hepatic glucose-6-phosphatase activity and higher plasma glucose levels as dietary carbohydrate level was increased. 2. There were no differences between the strains in liver weight or glucose-6-phosphatase activity, but BUT exhibited higher plasma glucose values than did NT at the two highest levels of carbohydrate. Plasma glucose did not differ between strains at the lowest level of carbohydrate or in fasted poults. 3. Blood glucose values were consistently higher in both strains when sampled 1 hr after initial sampling of fasted poults. 4. Both strains were able to maintain the 1 hr blood glucose levels through 24 hr when kept at approximately 37 degrees C. 5. When held at approximately 21 C for the first hour and at approximately 37 degrees C through 24 hr fasted NT were able to maintain the initial blood glucose rise while BUT were not.     

Identification of relaxin in the placenta of the ewe

Sheep placentomes were collected at the abattoir and the stage of gestation was estimated from the crown-rump length and appearance of the fetus. Samples were extracted and either freeze dried (crude extracts) or fractionated on Sephadex G-50 and CM-cellulose. Relaxin immunoreactivity (RXN-IR) was detected in all samples by a pig relaxin RIA and diluted in parallel with the standard curve. Two patterns of RXN-IR were seen after Sephadex G50 purification: (a) a single main peak of RXN-IR eluting at a position similar to pig relaxin; or (b) a 3-peak pattern with additional higher (void volume) and lower (approximately 1000) molecular weight peaks. These peaks were all found with 4 different and specific antisera. The 6000 molecular weight peak eluted at a similar position to pig relaxin on CM cellulose and inhibited electrically stimulated rat uterine contractions in vitro. The amount of relaxin measured in crude extracts of placentomes from different ewes was very variable. Most samples were within the range 0.05-11.2 ng/g wet weight of tissue (3.0 +/- 0.45 (s.e.m.), n = 44) but a few contained much higher concentrations (25.5-61.4 ng/g, n = 3). There was no obvious variation in concentration with stage of pregnancy (20 days to term). Samples of intercotyledonary endometrium, allantochorion and whole ovaries from pregnant ewes were also extracted. All contained low concentrations of RXN-IR (0.6 +/- 0.13 ng/g, n = 4; 0.6 +/- 0.29 ng/g, n = 3; 1.0 +/- 0.66 ng/g, n = 7, respectively). We conclude that relaxin-like peptides are present in the pregnant ewe and that, as the placentomes are the largest component by weight, they represent the major source.     

Relationship Between Energy Substrate Utilization and Specific Growth Rate in Aspergillus nidulans

The maintenance coefficient of glucose-limited Aspergillus nidulans chemostat cultures at 30 C was 0.018 g per g (dry weight) per hr for glucose and 0.55 mmoles per g (dry weight) per hr for oxygen. These values can only be approximate because melanin was produced by the mold at low growth rates and because it is unlikely that this polymer contributed to the maintenance energy requirement although it contributed to the dry weight. Biomass (defined here as dry weight minus melanin) was used to calculate a more meaningful maintenance coefficient for glucose (0.029 g of glucose per g of biomass per hr). At the highest growth rates examined, a nonlinear relationship between growth rate and glucose utilization rate was obtained, suggesting a qualitative change in the metabolic activities of the mold at high growth rates. The oxidative capacity of the mold was highest at the highest growth rates. This observation indicates that the increased substrate utilization rate observed at the higher growth rates is a reflection of enhanced enzyme synthesis. This hypothesis was verified by assaying the specific activities of several enzymes at different growth rates. However, in contrast to all the other enzymes assayed, the activities of reduced nicotinamide adenine dinucleotide phosphate: (acceptor) oxido-reductases were highest at the lowest growth rates.     

Embryonic ecdysteroids in a mole crab,Emerita asiatica (Milne-Edwards)

Using radioimmunoassay (RIA) and high performance liquid chromatography (HPLC), the presence of a complex mixture of free and conjugated ecdysteroids is reported in the embryonated eggs of a mole crab,Emerita asiatica. From an initial low value of 6.5 ng/g egg wet weight in stage I, the total ecdysteroids increased in concentration to 15.2 ng/g egg wet weight in stage III. This was followed by a sharp fall in stage IV, but again increased to 15.0 ng/g egg wet weight in stage VI. After a further decline in stage VII, the total ecdysteroids registered the highest value of 36.2 ng/g egg wet weight in stage VIII. This value, however, declined to a low level in the prehatching stage (IX). The concentration of the free ecdysteroids always predominated over the conjugated ones. The HPLC analysis of free ecdysteroids demonstrated the presence of 20-hydroxyecdysone and ecdysone in the ratio of 2.5. Purified lipovitellin II also contained free and conjugated ecdysteroids. The functional significance of the embryonic ecdysteroids as well as their nature of synthesis and storage within the eggs is discussed in the light of the information available on insect embryogenesis.     

Growth hormone alters metabolic effects and proteolysis of insulin in adipose tissue during lactation.

To study the regulation of lipogenesis in adipose tissue by insulin and growth hormone during lactation, tissue was biopsied from primiparous bovines at 30 days antepartum and 60 days postpartum. Tissue was cultured for 24 hr or 48 hr in M199 with acetate and glucose, with a change of medium at 24 hr. The three in vitro treatments were: insulin and hydrocortisone at 10 and 50 ng/ml, respectively (IH); IH + 10 ng/ml of growth hormone (G10); and IH + 100 ng/ml of growth hormone (G100). IH allowed lipogenesis rates from 50% to 85% of those in fresh tissue. Addition of 10 ng/ml of growth hormone reduced (P less than 0.05) lipogenesis; at 100 ng/ml, the effect was only slightly greater. The hypothesis that insulin and growth hormone could be degraded by bovine adipose tissue was tested. Adipose tissue cell-free extracts degraded 125I-labeled insulin, but did not degrade labeled growth hormone. The insulin protease activity was further characterized and had a pH optimum of 7.1, a maximum hydrolysis of approximately 70%, and a hydrated molecular mass of approximately 23,000 daltons. Insulin proteolysis was inhibited by specific insulin protease inhibitors and stimulated by disulfide reducing agents. Bovine growth hormone, prolactin, and histone inhibited (P less than 0.05) the proteolysis of insulin, while bovine serum albumin, egg albumin, trypsin inhibitor, and lysozyme did not. Adipose tissue from pregnant and lactating bovines was sensitive to insulin and growth hormone, and growth hormone may modulate activity of an insulin-specific protease.     

Transport of monosaccharides in kidney-cortex cells

1. The aerobic transport of d-glucose and d-galactose in rabbit kidney tissue at 25 degrees was studied. 2. In slices forming glucose from added substrates an accumulation of glucose against its concentration gradient was found. The apparent ratio of intracellular ([S](i)) and extracellular ([S](o)) glucose concentrations was increased by 0.4mm-phlorrhizin and 0.3mm-ouabain. 3. Slices and isolated renal tubules actively accumulated glucose from the saline; the apparent [S](i)/[S](o) fell below 1.0 only at [S](o) higher than 0.5mm. 4. The rate of glucose oxidation by slices was characterized by the following parameters: K(m) 1.16mm; V(max.) 4.5mumoles/g. wet wt./hr. 5. The active accumulation of glucose from the saline was decreased by 0.1mm-2,4-dinitrophenol, 0.4mm-phlorrhizin and by the absence of external Na(+). 6. The kinetic parameters of galactose entry into the cells were: K(m) 1.5mm; V(max) 10mumoles/g. wet wt./hr. 7. The efflux kinetics from slices indicated two intracellular compartments for d-galactose. The galactose efflux was greatly diminished at 0 degrees , was inhibited by 0.4mm-phlorrhizin, but was insensitive to ouabain. 8. The following mechanism of glucose and galactose transport in renal tubular cells is suggested: (a) at the tubular membrane, these sugars are actively transported into the cells by a metabolically- and Na(+)-dependent phlorrhizin-sensitive mechanism; (b) at the basal cell membrane, these sugars are transported in accordance with their concentration gradient by a phlorrhizin-sensitive Na(+)-independent facilitated diffusion. The steady-state intracellular sugar concentration is determined by the kinetic parameters of active entry, passive outflow and intracellular utilization.