The differentiation of proximal and distal tubules in the male rat kidney: the appearance of aldolase isozymes, aminopeptidase and alkaline phosphatase during ontogeny

1. The specific activities of aminopeptidase, alkaline phosphatase and aldolase isozymes were measured in homogenates of kidneys taken at different stages of ontogeny. The cellular localization of these enzymes was studied in cryostat tissue sections using substrate linked assays for aminopeptidase and alkaline phosphatase and the mixed aggregation immuno-cytochemical technique for aldolase isozymes; local enzyme concentrations were estimated photometrically. 2. The presence of both aldolase-A and aldolase-B was demonstrated in all metanephrogenic cells (and at still higher concentrations in collecting tubule cells) of the rat fetus 16 days after conception and in the undifferentiated cells of the neogenetic zone of kidney up to 8 days after birth; no aminopeptidase or alkaline phosphatase could be found in these cells. 3. Measurements made on stained tissue sections show that the shift towards aldolase-B, seen in homogenate analyses, is due to a change in the relative amounts of proximal tubules. No evidence was seen for repression in the synthesis of aldolase-A or aldolase-B monomers in the different kidney cells during ontogeny. 4. Two transitions in the mode of nephron differentiation were observed: one was shortly after birth, the other followed weaning. Before the first transition the concentrations of the enzymes increased to different degrees, such that the enzymes reached concentrations comparable with those as in the cells of adult rats by 2 to 4 days post partum. After the second transition proximal tubule size and specific activity of brush border membrane enzymes increased 3 fold. In contrast, the distal tubules did not increase significantly in size, but their aldolase-A concentration increased 3 fold. 5. Evidence based on enzyme quantification and morphometry in kidney sections is presented to demonstrate that the proximal tubule cells show functional adaptation by two independent mechanisms: specific amplification of gene expression and hypertrophy. In contrast, the distal tubule shows functional adaptation only by specific amplification of gene expression.     

Sister chromatid differentiation and exchanges in adult mudminnows (Umbra limi) after in vivo exposure to 5-bromodeoxyuridine

Sections from human jejunum were stained histochemically for aminopeptidase and alkaline phosphatase and the aldolase isozymes were detected with the mixed aggregation immuno-cytochemical technique. All enzyme concentrations increased from the bottom to the upper part of the crypt. The concentration of aldolase-A per cell was the same in the upper part of the crypt and the villus, whereas the concentration of the other three enzymes was still higher. Therefore, high amounts of aldolase-B, aminopeptidase and alkaline phosphatase are present in cells highly active in absorption in a fashion similar to that found in the proximal tubule cells of kidney. The relatively undifferentiated cells of the crypts contained both aldolase-A and aldolase-B. Alkaline phosphatase gains its full activity later than aminopeptidase. The synthesis of microvillar membrane enzymes comes to an end earlier than that of the cytosol enzymes.     

Immunologic characterization of plasma membranes from the renal proximal tubule of the dog

Plasma membrane fractions from the brush border (BBM) and antiluminal (ALM) surfaces of the dog's renal proximal tubule cell were separated using free-flow electrophoresis. Rabbits immunized with BBM rapidly produced antibody, but rabbits immunized with ALM did not respond. Indirect immunofluorescence and immunoferritin studies showed that the antibody reacts with the brush border of the proximal tubules in the normal kidney of the adult dog. It also reacts with the surface membranes of certain other absorptive and secretory epithelia, such as gall bladder, small intestine, epididymis, and lacrimal gland. The antibody has affinity for the membrane maltase without affecting its catalytic activity, but does not appear to have affinity for the membrane alkaline phosphatase or the high affinity binding site for phlorizin present in the BBM. Polyacrylamide electrophoresis of solubilized BBM showed approximately 37 protein bands and four glycoproteins. We conclude that the proximal tubule cell is immunologically polarized with respect to the distribution of antigenic proteins, and that the BBM is highly antigenic. The antigenic components appear to be high molecular weight glycoproteins present in the glycocalyx.     

Okadaic acid inhibits alkaline phosphatase activity in MC3T3-E1 cells

Alkaline phosphatase activity is regulated by various hormones and growth factors at least in part through the phosphorylation of target proteins during the bone cell differentiation. To investigate the role of protein phosphorylation in alkaline phosphatase activity in MC3T3-E1 osteoblast, we used okadaic acid which is a potent specific inhibitor of serine/threonine protein phosphatases to type 1 and 2A. Alkaline phosphatase activity in cellular layer was measured by spectrophotometer using p-nitrophenyl phosphate as substrate and data were expressed as p-nitrophenyl of nmol/min/mg of protein. Okadaic acid (1-50 ng/ml) caused the inhibition of alkaline phosphatase activity in MC3TC-E1 cells. At 50 ng/ml of okadaic acid showed the maximal inhibitory effect on alkaline phosphatase activity. Okadaic acid (50 ng/ml) also inhibited alkaline phosphatase activity in all differentiation stages. These results indicate that okadaic acid inhibits alkaline phosphatase activity in MC3T3-E1 cells.     

Posttranslational modifications of trichomonad tubulins; identification of multiple glutamylation sites

A method of conjugating poly(glutamic acid) poly(phosphorothioate)-cross-linked alkaline phosphatase to maleimide-derivatized immunoglobulin is described. Intramolecular autocatalyzed cross-linking of alkaline phosphatase at 2:1 to 4:1 polymer:enzyme ratios introduced 32-68 thiolates on the surface of the enzyme. Depending on the stoichiometry of polymer to enzyme, the cross-linked alkaline phosphatase retained 75-90% of its native catalytic activity. The cross-linked thiolate-functionalized alkaline phosphatase was conjugated to maleimide-derivatized immunoglobulin. Compared to a control prepared using non-cross-linked alkaline phosphatase, these conjugates were smaller in size and more stable to heat. The enzymatic activity of the cross-linked conjugates after incubation at 45 degrees C and pH 7.5 for 25 days was 35% higher than those of the highest-activity control conjugates. The conjugation process could be controlled by varying the stoichiometries of poly(glutamic acid) poly(phosphorothioate), alkaline phosphatase, and immunoglobulin.     

Inhibition of alkaline phosphatase by several diuretics

Acetazolamide, furosemide, ethacrynic acid and chlorothiazide, diuretics of considerable structural diversity, inhibit alkaline phosphatase. The inhibition is reversible and the mechanism is of the mixed type, having both competitive and non-competitive characteristics. Ki is calculated to be 8.4, 7.0, 2.8 and 0.1 mmol/l for acetazolamide, furosemide, ethacrynic acid and chlorothiazide, respectively. Chlorothiazide is a much more potent inhibitor of alkaline phosphatase than the other three diuretics. The combination of ethacrynic acid and cysteine, itself an alkaline phosphatase inhibitor, is less inhibitory than ethacrynic acid alone. Rat and human kidney alkaline phosphatase are equally sensitive to chlorothiazide, ethacrynic acid and furosemide.     

Nephron target sites in chronic exposure to lead

With established urinary markers of kidney integrity the early renal effects of lead have previously been considered to be mainly tubular or tubulointerstitial. In a cross-sectional study on 81 male lead-exposed workers and 45 age-matched controls (median blood lead concentrations 2.03 and 0.34 mumol/l respectively) not only well-established but also new urinary markers of renal integrity preferentially or exclusively located along the different nephron segments were analysed. Markers related to the glomerulus were 6-keto-prostaglandin 1 alpha, thromboxane B2, mainly produced in the glomerulus, and the extracellular matrix protein fibronectin. Markers of the proximal tubule were the brush-border antigens BBA, BB50, and HF5 and the intestinal alkaline phosphatase. Prostaglandin E2 and F2 alpha, preferentially synthesized in the collecting duct and medullary interstitial cells, served as markers of these more distal nephron segments. In contrast to previous studies on the early phase of lead nephrotoxicity, not only tubular but also glomerular involvement could be shown in the study presented here by increases in the median values of 6-keto-prostaglandin 1 alpha and decreases in fibronectin. The proximal tubular markers intestinal alkaline phosphatase and BBA confirmed that this particular segment of the nephron is affected by lead. Effects on the collecting tubule or medullary interstitial cells could also be observed. It is concluded that lead affects both the glomerulus and the tubular apparatus and that combinations of new and established markers could be valuable for a better definition and early detection of lead nephropathy.     

Phosphatase-negative mutants of Legionella pneumophila and their behavior in mammalian cell infection

Microbial phosphatases are known or suspected to play a role in the pathogenesis of several intracellular pathogens, including Legionella micdadei. Legionella pneumophila also possess phosphatase activities, but their possible roles in cellular infection are unknown. We generated mutants of a serogroup 1 isolate of L. pneumophila that lack the major phosphatase. Isolation of a Pho- mutant after random mutagenesis with transposon MudII4041 allowed us to dissociate the major alkaline phosphatase (pH optimum approximately 8) from a minor acid phosphatase activity. Both activities were concentrated in the bacterial periplasm. The gene encoding the major alkaline phosphatase (pho) was cloned by expression in E. coli and used to generate a site directed mutation in two L. pneumophila strains. Each parent-mutant pair was compared in a U937 cell tissue culture assay for capacity to infect, lyse, and grow within mammalian cells. Although the parental stains differed in their U937 cell cytopathicity, neither was significantly more infective than its Pho- derivative, suggesting that the alkaline phosphatase activity is not essential for cellular infection. Because they are not attenuated, Pho- mutants can be used to generate gene fusions with E. coli alkaline phosphatase to study and secretion and cellular infectivity in L. pneumophila.     

Effect of Azadirachta indica leaves on testis and its recovery in albino rats

Histological and biochemical changes in the testis of rats treated with the leaf powder of A. indica are reported. The pattern of recovery is also studied at 8, 16 and 24 day after withdrawal of the treatment. In the treated rats, a general reduction in the diameters of seminiferous tubule, nuclei of the germinal elements and a mass atrophy of the spermatogenic elements has been observed. The Leydig cells are found to be atrophic. Biochemically, a decrease in the protein content and the activity of acid phosphatase and an increase in the total free sugar, glycogen, cholesterol contents and the activities of alkaline phosphatase and lactate dehydrogenase have been observed. A gradual recovery is observed in both the histological and biochemical parameters after 8.16 and 24 day of cessation of the treatment. The result suggest a possible reversible antiandrogenic property of the leaves of A. indica in male albino rats.     

Hypophosphatasia: a developmental anomaly of alkaline phosphatase?

This report deals with quantitative and qualitative investigations of alkaline phosphatase in two unrelated infants with the severe infantile form of hypophosphatasia. Both affected infants had no detectable leukocyte alkaline phosphatase activities and both sets of parents and one sibling tended to have low but variable leukocyte enzyme activities. Normal duodenal juice alkaline phosphatase activity was present in the one patient in whom it was measured and a wide range of variation in enzymic activity was observed in the stools. There was no significant difference in the stool enzyme activity between both patients with hypophosphatasia (42.01 +/- 9.77 U) and control infants (40.55 +/- 6.29 U). However, the heterozygous parents had values significantly lower than the control adults (2.10 +/- 0.47 as compared with 19.10 +/- 4.44 U). Intestinal bacteria did not contribute significantly to the stool alkaline phosphatase activity. Enzyme activity was present in the bile of one of the patients and nearly absent in that of the other. Three "inducers" of alkaline phosphatase were given to both patients (phenobarbital, vitamin A, and corticosteroid). No clinical improvement or rise in serum alkaline phosphatase activity was observed during the trial of therapy with these agents. However, a significant increase in the activity of serum acid phosphatase was demonstrated during the course of vitamin A administration, suggesting an in vivo action of vitamin A on the lysosomes through decreasing the stability of the membrane and releasing acid phosphatase to the serum. Quantitative determination of tissue alkaline phosphatases from autopsy tissues was highly variable: no activity was found in bone, lungs, or spleen of either infant; there was a discrepancy in liver and kidney alkaline phosphatase values (zero in one patient and present in the other) and activity was present in the intestinal mucosa of both. Qualitative analysis of kidney, liver, and intestinal alkaline phosphatase revealed some differences between the patients and control subjects in heat inactivation and phenylalanine inhibition (Table 3). Starch gel electrophoresis of the liver preparation of one patient disclosed a single band which had greater mobility than that of six control subjects matched for age. Liver extracts from a premature and from full term newborns showed two bands. The single band of the patient's liver enzyme corresponded to the newborn's fast moving component. In addition, the intestinal enzyme prepared from the same patient had an extra band when compared with age-matched control subjects.     

Effects of synthetic detergents on in vivo activity of tissue phosphatases and succinic dehydrogenase from Mystus vittatus

African catfish (Mystus vittatus) were exposed to three sub-lethal concentrations of Swascofix E45 (13.8, 9.2 and 4.6 mg/l) and Swascol 3L (69.3, 46.2 and 23.1 mg/l) for 15 and 30 days, and their effects on alkaline and acid phosphatase, and succinic dehydrogenase in liver, kidney and intestine were measured. The enzymes were found to be inhibited in all the tissues. Maximum inhibition (38.44%) was observed in liver alkaline phosphatase activity after 30 days with the highest concentration of Swascofix E45 and the lowest inhibition (0.118%) was found in kidney acid phosphatase activity with the lowest concentration of Swascol 3L after 15 days. Insignificant enzyme stimulation in some cases was also observed.     

Tissue distribution of DNA adducts in rats treated by intramammillary injection with dibenzo[a,l]pyrene, 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene

Recombinant human bone morphogenetic protein (rhBMP-2) was examined for its in vitro effects on biochemical markers representing osteoblast phenotype. Primary cultures of fetal rat calvarial osteoblasts were used in this study. The results indicated that rhBMP-2 stimulated alkaline phosphatase activity, parathyroid hormone (PTH)-induced cyclic AMP production, and collagen biosynthesis in a dose-dependent manner in confluent cultures. The percent collagen synthesis also increased in a dose-dependent manner. Alkaline phosphatase activity was stimulated in a time-dependent manner by rhBMP-2 that reached its maximum 5 days after initiation. Cycloheximide (2 micrograms/ml) inhibited rhBMP-2-stimulated alkaline phosphatase indicating de novo protein synthesis of the enzyme. Transforming growth factor-beta 1 (TGF-beta 1)-induced inhibition of alkaline phosphatase activity observed in confluent primary cultures was completely abolished by rhBMP-2 at a concentration that was 43 times greater than the TGF-beta 1 concentration. Also, rhBMP-2 produced a small stimulation of alkaline phosphatase activity in cells grown in the absence of ascorbic acid; however, the effect was greatly enhanced in cells cultivated in the presence of ascorbic acid (50 micrograms/ml). In view of the potentiating effect of ascorbic acid on rhBMP-2-induced stimulation of alkaline phosphatase, we speculate that ascorbic acid could amplify the osteoinductive effects of rhBMP-2 and thereby augment the efficacy of the BMP when used as bone repair material in vivo. rhBMP-2 (4.3-86 ng/ml) did not exhibit mitogenic effects on cultured osteoblasts. These data suggest that rhBMP-2 has the ability to induce expression of various markers associated with the osteoblast phenotype in primary cultures of fetal rat calvarial osteoblasts. In addition, we speculate that TGF-beta 1 may play a regulatory role in BMP-induced bone formation and ascorbic acid may potentiate the effects of rhBMP-2 in vivo.     

Intrinsic differences in various segments of the proximal convoluted tubule

Until recently it has not been possible to compare directly the function of superficial and juxtamedullary nephrons. The present studies, using in vitro microperfusion, were designed to examine whether functional differences exist between proximal convoluted tubule segments of superficial and juxtamedullary nephrons. Electrophysiological studies showed that major differences exist between the relative chloride and sodium permeabilities of these segments. In the 1st mm of the superficial proximal convoluted tubule, the permeability to sodium was greater than that to chloride, whereas in the 2nd mm of the superficial proximal convoluted tubule and all later segments, the permeability to chloride was greater than that to sodium. The juxtamedullary proximal convoluted tubule was found to differ from the superficial proximal convoluted tubule in two respects: first, the relative permeabilities to chloride and sodium did not differ in the various segments of the juxtamedullary proximal convoluted tubule; second, the permeability to sodium was greater than to chloride throughout. When perfused with a solution lacking glucose and amino acids, the superficial and juxtamedullary convolutions exhibited the same transepithelial potential change, a reversible decrease to less than -- 1 mV. It thus appears that in both convolutions there exists electrogenic sodium transport coupled to the transport of these organic solutes. This differs from pars recta of both of these nephrons, which have been shown to exhibit electrogenic sodium transport independent of organic solutes. However, when perfused with a solution lacking glucose and amino acids but also containing high chloride and low bicarbonate concentrations, the superficial convolution developed a significantly more positive potential than the juxtamedullary. This difference reflects greater relative chloride permeability in the superficial proximal convolution. These studies show that intrinsic functional differences exist between proximal convoluted tubules obtained from the superficial and juxtamedullary nephron populations.     

Pine oil toxicity in the horse: drug detection, residues and pathological changes

Histochemical activity of hydroxysteroid dehydrogenases as well as alkaline and acid phosphatase was investigated in porcine granulosa cells cultured in vitro. Granulosa cells, isolated from preovulatory procine ovarian follicles, during in vitro culture showed activity of enzymes participating in steroid biosynthesis. High activity of delta53betta0H-SDH and G6P-DH as well as the activity of alkaline phosphatase, appearing in the course of culture, could be evidence of progressive luteinization of the cells. Activity of 17beta0H-SDH was lower and exhibited strong fluctuations, similarly low was 20xOH-SDH. Gonadotropic hormones caused the increase of synthesis and accumulation of intracellular lipids. They stimulated alkaline and acid phosphatase, and also the activity of the dehydrogenases. LH had the most visible effect. Estradiol stimulated the activity of acid but not alkaline phosphatase and was not influencing, even lowering the activity of dehydrogenases.     

Loop diuretics reduce hypoxic damage to proximal tubules of the isolated perfused rat kidney

The straight portion (S3) of the proximal tubule lies in close proximity to the thick ascending limbs (TALs) at the cortico-medullary junction. Since a delicate balance exists between oxygen demand and the limited oxygen supply in this region, we hypothesized that reduction of thick limb metabolic activity might augment oxygen availability to S3 segments, which depend heavily upon aerobic metabolism, and prevent hypoxic damage. The degree of functional deterioration and morphological damage to S3 was assessed in isolated rat kidneys perfused with an erythrocyte-free medium. Bumetanide (10(-5) M) and furosemide (10(-4) M) reduced S3 fragmentation from 9.8 +/- 3.9% of tubules in controls to 0 and 1.4 +/- 0.9%, respectively (P < 0.0005). Tubular glucose reabsorption was better preserved in kidneys exposed to loop diuretics than in control kidneys (P < 0.01), and urinary alkaline phosphatase (P < 0.05) and the total amount of LDH released into the perfusate and urine (P < 0.01) were lower in the treatment groups. Morphological damage to S3 was closely correlated with medullary TAL necrosis (r = 0.66, P < 0.001), urinary alkaline phosphatase excretion (r = 0.89, P < 0.001) and glycosuria (r = 0.83, P < 0.001). We conclude that under hypoxic conditions TALs and S3 segments may compete with each other for a limited oxygen supply. Reduction of active transport in the mTAL might augment oxygen availability to S3 segments and improve their survival.     

Gallium nitrate inhibits alkaline phosphatase activity in a differentiating mesenchymal cell culture

The effect of gallium nitrate on alkaline phosphatase activity in a differentiating chick limb-bud mesenchymal cell culture was monitored in order to gain insight into the observation that rachitic rats treated with gallium nitrate failed to show the expected increase in serum alkaline phosphatase activity. Cultures maintained in media containing 15 microM gallium nitrate showed drastically decreased alkaline phosphatase activities in the absence of significant alterations in total protein synthesis and DNA content. However, addition of 15 microM gallium nitrate to cultures 18 h before assay for alkaline phosphatase activity had little effect. At the light microscopic and electron microscopic level, gallium-treated cultures differed morphologically from gallium-free cultures: with gallium present, there were fewer hypertrophic chondrocytes and cartilage nodules were flatter and further apart. Because of altered morphology, staining with an antibody against chick cartilage alkaline phosphatase appeared less extensive; however, all nodules stained equivalently relative to gallium-free controls. Histochemical staining for alkaline phosphatase activity was negative in gallium-treated cultures, demonstrating that the alkaline phosphatase protein present was not active. The defective alkaline phosphatase activity in cultures maintained in the presence of gallium was also evidenced when cultures were supplemented with the alkaline phosphatase substrate, beta-glycerophosphate (beta GP). The data presented suggest that gallium inhibits alkaline phosphatase activity in this culture system and that gallium causes alterations in the differentiation of mesenchymal cells into hypertrophic chondrocytes.     

An experimental model for studies on the effects of food and digestive secretions on the digestive-absorptive capacity of rat small intestine

At an average of 32 days after a modified Roux-en-y repositioning of rat small intestine, the mucosal mass, mucosal composition, in vivo absorption of galactose and the activity of maltase, sucrase and alkaline phosphatase were measured. In the gut segment with digestive secretions but without food (A) the only change was a decrease of sucrase activity which occurred most probably at the cellular level. In the gut segment with food and gastric juice and a reflux of digestive secretions (B) complex changes took place. An increase in mucosal mass was not accompanied by an increase in galactose absorption. There was a high increase of sucrase activity, a moderate increase of maltase activity and a tendency of the alkaline phosphatase activity to decrease. The changes (increase in mucosal mass and total enzyme activity, but no changes in activity at the cellular level) in the segment exposed to both digestive secretions and food (C) were compatible with a more proximal promotion of a distal gut segment.     

Deoxypyridinoline and other biochemical markers of bone resorption in distinct pathologies

Collagen type 1 represents more than 90% of bone matrix. Therefore, quantitation of collagen crosslinks, such as deoxypyridinoline, can provide information on bone resorption degree. An evaluation was made of deoxypyridinoline as well as other bone markets, such as alkaline phosphatase, tartrate resistant acid phosphatase, and hydroxyproline in patients with the diagnosis of osteoporosis. Paget's disease, hyperthyroidism, and chronic renal failure on haemodialysis or not. Deoxypyridinoline levels were significantly increased in patients with osteoporosis, Paget's disease, and hyperthyroidism. Hydroxyproline levels were increased in patients with Paget's disease, and tartrate resistant acid phosphatase was increased in all the entities studied. Deoxypyridinoline can be a more sensitive marker than hydroxyproline, with some advantages, such as its quantitation in a urine specimen and its high bone specificity. In patients with renal failure, tartrate resistant acid phosphatase was the only biochemical marker of bone resorption with increased levels.     

Micropuncture studies of glucose transport in the dog: mechanism of renal glycosuria

Clearance and micropuncture studies were performed in 23 dogs without glucose loading to examine the tubule mechanism of renal glycosuria. Studies were carried out in three groups of animals before and after 10% extracellular volume expansion, and administration of maleic acid in low dose at 150 mumol/kg and in high dose at 300 mumol/kg. Specific hexokinase methods were used for the determination of glucose in tubule fluid and urine. Under control conditios, glucose reabsorption occurred predominantly in the proximal tubule. In all three groups, proximal tubule reabsorption of both sodium and glucose was inhibited in the second phase, showing a good correlation between the two. In contrast, fractional urinary glucose excretion remained unchanged after volume expansion and low-dose maleic acid, indicating reabsorption of virtually all the increased glucose load at a further "distal" site. On the other hand, significant glycosuria developed after high-dose maleic acid that was a result of reduced glucose reabsorption in the distal nephron, in addition to the proximal effect. It was concluded that distal glucose transport plays a significant role in regulating urinary glucose excretion and maintains renal thershold for glucose,     

Postcholestatic alkaline phosphatase activity after relief of bile duct obstruction in the rat

The effects of obstructive cholestasis on the activity of alkaline phosphatase have been extensively studied in serum and liver tissue. However, very little is known about the activity of this enzyme in the postcholestatic condition after relief of the biliary obstruction. The purpose of this study has been to characterize alkaline phosphatase activity in serum, liver and bile in the postcholestatic period and to relate it to changes in bile acid secretory rate. Serum activity and biliary secretory rates of alkaline phosphatase were markedly increased in rats subjected to a reversible obstructive cholestasis for 24 hr or 48 hr and progressively declined along the postcholestatic period to values not significantly different from those of control rats within 48 hr. A significant direct linear relationship between the biliary secretory rates of enzyme activity and bile salts was apparent both in cholestatic groups and in the control groups. The slope of the regression line (units of alkaline phosphatase secreted per micromole of bile salts) was 1.5-fold to 3-fold higher in cholestatic animals. Remarkably, a positive y-intercept of regression lines suggested that a significant fraction of the enzyme was secreted independently of bile salts; this fraction was 18-fold and 34-fold greater in 24-hr and 48 hr cholestatic rats, respectively, compared with that in controls. Sodium taurocholate administered intravenously, either as a bolus or as an infusion at increasing submaximal rates, resulted in parallel increases of bile salt and alkaline phosphatase secretory rates into bile. The enzyme activity secreted per micromole of taurocholate was significantly greater in cholestatic than in control rats.(ABSTRACT TRUNCATED AT 250 WORDS)