Stimulated Alkaline Phosphatase Activity Research Articles

Thyroid hormone stimulates alkaline phosphatase activity in cultured rat osteoblastic cells (ROS 17/2.8) through 3,5,3'-triiodo-L-thyronine nuclear receptors.

To investigate the increased alkaline phosphatase activity of bone origin in patients with hyperthyroidism, we studied the thyroid hormone effects on alkaline phosphatase activity in a clonal rat osteoblastic cell line (ROS 17/2.8). T4 and T3 increased alkaline phosphatase activity in ROS 17/2.8 cells in a dose-dependent manner. The minimal effective T4 and T3 concentrations in medium containing 10% thyroid hormone-depleted fetal calf serum were 10(-8) M (free T4, 8 X 10(-11) M) and 10(-9) M (free T3, 4 X 10(-11) M), respectively. ROS 17/2.8 cells possessed high affinity, low capacity nuclear receptors specific for T3 [dissociation constant (Kd) approximately 150 pM; maximal binding capacity, approximately 2000 T3 binding sites per nucleus]. The relative affinity of T3, T4, rT3, MIT, and DIT were in good agreement with their biological activity. These findings suggest that rat osteoblast-like cells contain T3 nuclear receptors and that alkaline phosphatase activity is stimulated by thyroid hormone via a nuclear receptor-mediated process at free thyroid hormone concentrations attainable in patients with Graves' disease.

Parathyroid hormone stimulation of alkaline phosphatase activity in cultured neonatal mouse calvarial bone cells: Involvement of cyclic AMP and calcium

The involvement of cAMP and calcium in the rise in alkaline phosphatase (AP) activity observed when confluent, serum-free primary cultures of neonatal mouse calvarial cells are treated with parathyroid hormone (PTH) has been studied. Synthetic bovine PTH [bPTH-(1-34)] increased cellular cAMP at concentrations (10(-9) to 10(-7) M) previously found to elevate AP activity. Other substances that increase cAMP in these cells (forskolin, prostaglandin E2, 8-bromoadenosine cAMP and 3-isobutyl-1-methylxanthine) also increased enzyme activity. By comparison, increasing the concentration of calcium in the culture medium from 1.8 to 3.8 or 5.8 mM lowered the magnitude of the maximal AP response. In addition, treatment of cultures with the divalent cation ionophore A23187 caused a significant decrease in AP activity. These results suggest that: 1) cAMP mediates the rise in the specific activity of AP in cultured neonatal mouse calvarial cells treated with bPTH-(1-34) and 2) the concentration of calcium in the environment significantly influences the responsivity of bone cells to the hormone.

Effects of levamisole on primary cultures of adult rat hepatocytes

Levamisole represents one of several new compounds that exhibit immunomodulating activity. Pharmacological data have documented a relationship between liver drug metabolism of levamisole and its subsequent immunomodulating activity. To directly investigate this relationship in a controlled manner, primary cultures of adult rat hepatocytes were treated with levamisole, and ultrastructural and biochemical effects were analyzed. Ultrastructurally, levamisole did not disrupt the cellular architecture of the hepatocytes. Biochemically, levamisole stimulated alkaline phosphatase activity and elevated microsomal cytochrome P-450 content after a 48-hr incubation. High pressure liquid Chromatographie analysis of levamisole metabolites produced by cultured hepatocytes suggested the formation of a hepatocyte-specific metabolite(s) that may be associated with its immunological mode of action.

Phenotype-associated changes in the effects of 1,25-dihydroxyvitamin D3 on alkaline phosphatase and bone GLA-protein of rat osteoblastic cells.

The effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on alkaline phosphatase (AP) activity and the synthesis of gamma-carboxy-glutamic acid containing protein (BGP) were compared in phenotypically distinct cloned cell lines derived from the osteoblast-like rat osteogenic sarcoma line ROS 17/2-8. 1,25(OH)2D3 stimulated AP activity and BGP synthesis in phenotypes which exhibited relatively low basal AP activity and high basal BGP levels. In contrast 1,25(OH)2D3 inhibited AP activity in phenotypes that exhibited high basal AP activity. The latter cells had undetectable BGP levels and the synthesis of this protein failed to respond to the 1,25(OH)2D3 stimulus. In the cells that responded to 1,25(OH)2D3 with an increase in AP activity the effect of the hormone on AP could be blocked by actinomycin-D. However in the cells that responded to 1,25(OH)2D3 with inhibition of AP the effect of the hormone on AP was not influenced by actinomycin-D. The directly opposite effects of 1,25(OH)2D3 on the AP activity of the respective clones did not change qualitatively at different stages of culture and could not be accounted by differences in the 1,25(OH)2D3 receptor status nor by different effects of the hormone on cell proliferation. These data raise the possibility that the response of AP to 1,25(OH)2D3 in osteoblastic cells depends on their state of phenotypic differentiation. The stimulatory effect of the hormone in low AP-producing cells might be related to differentiation promoting properties of 1,25(OH)2D3. The inhibitory effect of 1,25(OH)2D3 on AP, unlike the stimulatory effect of the hormone does not appear to be mediated by the classical mechanism of 1,25(OH)2D3 action on the genome and might be associated with dedifferentiated osteoblastic cells.

Hormonal control of the intestinal brush border enzyme activities in developing anuran amphibians: I. Effects of hydrocortisone and insulin during and after spontaneous metamorphosis

The effects of hydrocortisone and insulin on the intestinal brush border membrane enzymatic activities in an anuran amphibian, Alytes obstetricans, were investigated at the end of spontaneous metamorphosis and 2 weeks after its completion. At the end of metamorphosis, the brush border is differentiating in the apical region of a developing neoformed epithelium. Two weeks after the completion of metamorphosis, this epithelium is entirely formed. The animals received one hormone injection per day for 2 or 3 days running (hydrocortisone: 1, 5, or 25 μg/g body wt/day; insulin: 0.5, 1, or 5 mU/g body wt/day). The hydrolases studied were three glucosidases (maltase, glucoamylase, trehalase), γ-glutamyl-transferase and alkaline phosphatase. In animals reaching the end of metamorphosis, hormonal treatments rarely modify the three glucosidase activities. Two weeks after metamorphosis, a 5 μg/g body wt/day hydrocortisone injection usually results in a significant increase of the three glucosidase activities. Conversely, a 0.5 mU/g body wt/day insulin injection induced a marked decrease in these activities. At the end of metamorphosis, hydrocortisone has variable effects on γ-glutamyl-transferase activity; insulin, however, does not significantly modify this activity. Two weeks later, insulin and sometimes hydrocortisone inhibit γ-glutamyl-transferase activity. Whatever the developmental stage is, hydrocortisone is able to stimulate alkaline phosphatase activity. At the end of metamorphosis, insulin has no influence on this activity, but 2 weeks after metamorphosis, low doses of the hormone (0.5 mU/g body wt/day) significantly reduce it. These results emphasize the possibility that after spontaneous metamorphosis the enzymatic activities of the new intestinal brush border are hormone controlled. This control could be related to the development of the interrenal and pancreatic islet functions.

Dexamethasone stimulates osteogenesis in chick periosteum in vitro.

Folded periosteal explants derived from 16-day-old chick embryo calvariae differentiate and form bone when cultured for 6 days in chemically defined, hormone-supplemented medium or on plasma clots. We studied the effect of dexamethasone on generation of cells with osteoblastic phenotype in such cultures. Bone cell phenotype was evaluated by determination of alkaline phosphatase (AP) activity. Cellular proliferation was assessed by measuring ornithine decarboxylase (ODC) activity, [3H]thymidine uptake, and radioautography of cultures that had incorporated [3H]thymidine. Cultures were exposed to various medium concentrations of dexamethasone (10(-6) M, 10(-7) M, 10(-8) M) from the outset or from the second or fourth day of culture onwards. In cultures continuously exposed to dexamethasone and maintained in chemically defined media or on plasma clots, dexamethasone increased AP activity measured at day 6. This effect was maximal at 10(-7) M dexamethasone. Cultures exposed to dexamethasone after day 2 in culture also showed increased AP activity, but only in the cultures maintained on plasma clots. There was no stimulation of AP activity when dexamethasone was added at day 4 of culture with either medium, thus suggesting that the effect of glucocorticoids depends on the stage of differentiation of the cultures. In addition to AP stimulation, dexamethasone also stimulated ODC activity. Since ODC activity has been associated with mesenchymal cell proliferation, this suggested that dexamethasone stimulated the proliferation of similar cells in the cultured periostea. Measuring [3H]thymidine uptake in and performing autoradiography of control cultures and cultures treated with dexamethasone confirmed that stimulation of proliferation did occur and located this proliferation within the cell layer adjacent to the bone surface. These results demonstrate that dexamethasone stimulates in vitro osteogenesis, and that this effect appears to be mediated through stimulation of progenitor cell proliferation. In addition, our data indicate that factors in the clot medium modulate the responsiveness of the precursor cell population.

Stimulation of alkaline phosphatase activity in cultured neonatal mouse calvarial bone cells by parathyroid hormone

The effect of parathyroid hormone (PTH) on alkaline phosphatase activity was examined in confluent, serum-free primary cultures of neonatal mouse calvarial cells. It was found that synthetic bPTH-(1-34) caused an increase in the specific activity of skeletal alkaline phosphatase isoenzyme by 18 hours. Between 10 and 500 ng/ml, the magnitude of the change was directly related to peptide concentration. The change occurred in the absence of any effect on cell number, total cell protein, or DNA and was not the result of an effect on either proliferation or survival of a specific cell population. Results of histochemical studies indicate that bPTH-(1-34) caused an increase in the proportion of cells containing enzyme activity. The response was duplicated by intact bPTH-(1-84) and DBcAMP, but not by oxidized bPTH-(1-34) or insulin and did not require prostaglandin synthesis or hydroxylation of 25-hydroxyvitamin D3. These results demonstrate that bPTH has a direct effect on osteoblast maturation in vitro, that the effect is specific for PTH, and suggest that it is mediated by cAMP.

Synergistic stimulation of alkaline phosphatase activity in bovine aortic endothelial cells grown in the presence of retinoids and glucocorticoids.

Low concentrations of retinol (10 nM-10 microM) and dexamethasone (0.1 nM-1.0 microM) elevated activity of alkaline phosphatase (E.C. 3.1.3.1) in bovine endothelial cells in culture. The effect was apparent after 48 hr of growth in the presence of either of the two compounds, prior to any growth stimulatory effects. A synergistic stimulation of alkaline phosphatase was achieved in the presence of both retinol and dexamethasone implying different mechanisms of induction. Retinoic acid and retinyl acetate also elevated alkaline phosphatase but the retinol analogue reduced in the side chain (perhydroretinol) was inactive. The ability of steroids to elevate alkaline phosphatase activity was associated with the structure commonly required for glucocorticoid activity; however, competitors for the steroid receptor binding failed to prevent the elevation by dexamethasone or the synergism in the presence of retinol and dexamethasone.

La,25-Dihydroxyvitamin D3 Stimulates Alkaline Phosphatase Activity and Inhibits Soft-Tissue Proliferation in Implants of Bone Matrix

Skeletal cryptococcosis is an uncommon infection. Isolated osteomyelitis due to Cryptococcus neoformans is quite rare. Only seven cases of skeletal cryptococcosis with involvement of vertebrae but no systemic infection have been reported. In only one was there paraplegia. Since vertebral cryptococcosis seems not to have been reported previously in Japan, this case of a 50-year-old coal miner successfully treated for paraparesis caused by cryptococcal spondylitis of the ninth, tenth, and 11th thoracic vertebrae is noteworthy. Two decompression operations and combined amphotericin B and flucytosine therapy reduced the patient's paraparesis, and no sign of recurrence was seen for 21 months after the second operation.

Calcitonin stimulates maturation of mammalian growth plate cartilage.

To determine whether calcitonin (CT) might effect maturation of mammalian growth plate cartilage, we administered salmon CT (sCT) to young rats and used the growth plate from the distal metatarsal as our in vivo growth plate model. Growth plate alkaline phosphatase activity and histological examination were assessed after 3 days of sCT treatment. Alkaline phosphatase activity, a marker of hypertrophied chondrocytes, increased 85%, and the zone of maturation enlarged in rats receiving sCT. In addition, sCT treatment was associated with an increased growth plate 35SO4 incorporation 84% above animals receiving buffer alone. We tested whether this might be a direct effect of CT by using an in vitro model, the growth plate from the fetal pig scapula. Organ culture of these cartilages in serum-free medium with and without sCT (1 U/ml) was performed for 3 days. sCT stimulated alkaline phosphatase activity 49% above growth plates incubated in medium alone. Furthermore, sCT treatment increased the number of hypertrophied chondrocytes leading to widening of the zone of maturation. These studies suggest that CT might have a role growing mammals by promoting maturation of growth plate cartilage.

Effect of sodium vanadate on deoxyribonucleic acid and protein syntheses in cultured rat calvariae.

Sodium vanadate, an agent known to have multiple cellular actions, was studied for its effects on aspects of bone formation in cultures of 21-day-old fetal rat calvariae. Vanadate (0.1-10 microM) stimulated the incorporation of [3H] thymidine into acid-insoluble residues (DNA); the effect appeared after 3 h and was sustained for 96 h. Vanadate increased the bone DNA content and mitotic index. Treatment with vanadate at 10 microM for 24 h or at 0.3-1 microM for 96 h increased the incorporation of [3H]proline into collagenase-digestible protein (CDP), but the effect was not specific for collagen; vanadate also increased the labeling of noncollagen protein (NCP). Vanadate increased the incorporation of [3H]proline into type I collagen without affecting other collagen types. Vanadate (100 microM) caused a marked and irreversible inhibitory effect on the labeling of DNA, CDP, and NCP. Treatment with vanadate at multiple doses for 3-96 h did not stimulate alkaline phosphatase activity, but this enzyme was inhibited in bones exposed to 1 mM vanadate for 24 h or 10 microM vanadate for 96 h. The stimulatory effect on DNA labeling was primarily observed in the periosteum, while that on CDP labeling was seen only in the periosteum-free bone. These studies indicate that sodium vanadate stimulates bone DNA, collagen, and NCP syntheses in vitro, although high doses of vanadate have an irreversible inhibitory effect.

Inductive effects of prostaglandins on alkaline phosphatase in osteoblastic cells, clone MC3T3-E1.

The effects of prostaglandins (PGs) on the induction of alkaline phosphatase (ALP) were investigated in osteoblastic clone MC3T3-E1 cells cultured in serum-free medium. Prostaglandin E2 (PGE2) stimulated ALP activity in the cells in a dose-dependent fashion with a maximal effect which was about twice that in the control cells at concentrations of 100-500 ng/ml. Actinomycin D and cycloheximide inhibited the stimulative effect of PGE2 on ALP activity in the cells. PGE2-induced and native ALPs in the cells were of the same type as that in adult mouse calvaria, being heat-labile, L-homoarginine- and levamisole-sensitive, and L-phenylalanine-insensitive. Isobutyl methylxanthine (IBMX), a cAMP phosphodiesterase inhibitor, stimulated the inductive effect of PGE2 on ALP activity at 0.1 mM, at which concentration IBMX alone had little effect on the activity. PGE2 also increased the intracellular cAMP content in a dose-dependent fashion with a maximal effect at 100 ng/ml. PGE1, PGF1 alpha, and PGF2 alpha (primary PGs like PGE2) increased the activity. Our present results suggest that PGs stimulate the differentiation of osteoblasts and are involved in bone formation in vivo, as well as in bone resorption.

Effect of cortisol on periosteal and nonperiosteal collagen and DNA synthesis in cultured rat calvariae.

The effects of cortisol on bone formation are complex and may be modulated by the presence of periosteal cells or by factors released by the periosteal tissue. To test these possibilities, cortisol was examined for its effects on the incorporation of 3H-proline into collagenase-digestible protein (CDP) and noncollagen protein (NCP), on DNA synthesis and on alkaline phosphatase activity in intact and in the periosteum and nonperiosteal bone of dissected calvariae from 21-day-old fetal rats. After 24 h of treatment, cortisol increased the incorporation of 3H-proline into CDP in intact bones and in the nonperiosteal bone of calvariae dissected after the culture. Cortisol inhibited the incorporation of 3H-thymidine into calvarial DNA but it caused a small increase in nonperiosteal DNA content. Cortisol did not affect the incorporation of 3H-proline into CDP in calvariae dissected prior to the culture if the periosteum and nonperiosteal central bone were incubated separately; the stimulatory effect was observed only if the two tissues were cultured in the same vial and were in contact. In contrast, cortisol stimulated alkaline phosphatase activity in the central nonperiosteal bone of calvariae dissected before or after the culture. After 72-96 h of treatment, cortisol inhibited the labeling of CDP, NCP, and DNA and the DNA content in intact bones and in both periosteal and nonperiosteal central bone of calvariae dissected after the culture. In contrast, when the periosteum was removed before the incubation, these inhibitory effects were observed in the periosteum and not in the nonperiosteal bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of alkaline phosphatase activity in mouse epidermis by tumor promoters

Complete as well as incomplete (second stage) tumor promoters increase alkaline phosphatase (AP) activity in mouse epidermis in vivo but not in vitro. This indicates that the high level of AP in epidermis after application of a tumor promoter arises from an extraepidermal site, possibly from leaky endothelial cells of promoter-damaged blood vessels. Quercetin, which is known to stabilize the microvasculature as well as to inhibit tumor promotion, very effectively suppresses tumor promoter-stimulated AP activity. Quercetin is also a potent inhibitor of calcium, phospholipid-dependent protein kinase (Ca, PL-PK). Since inhibitors of other enzymes also suppressable by quercetin are ineffective, the damage of microvasculature and the increase in AP activity in epidermis might be Ca, PL-PK mediated effects of tumor promoters.

5'-deoxypyridoxal interaction with dexamethasone receptor: a new probe for structure and function of steroid receptors.

5'-Deoxypyridoxal, a vitamin B-6 analogue, increased the rate of dissociation of [3H]dexamethasone from HeLa S3 cytoplasmic glucocorticoid receptor complexes in vitro. This effect was achieved at millimolar concentrations of 5'-deoxypyridoxal, suggesting a low-affinity interaction of 5'-deoxypyridoxal with receptor. Loss of [3H]dexamethasone-receptor binding in the presence of 5'-deoxypyridoxal was pH dependent, and a plot of Kdiss vs. pH fit a simple sigmoidal titration curve with an inflection point at pH 7.8, suggesting that deprotonation of a single functional group on 5'-deoxypyridoxal increases Kdiss. Loss of [3H]dexamethasone binding in the presence or absence of unlabeled steroid also increased with pH, but no inflection point occurred over the range of pH tested. A titration of 5'-deoxypyridoxal indicated a pK of 7.94 for the pyridinium proton, suggesting deprotonation of the pyridinium nitrogen may account for the pH dependence of Kdiss of dexamethasone from receptor. 5'-Deoxypyridoxal also caused a decrease in nuclear [3H]-dexamethasone-receptor binding when incubated with whole HeLa S3 cells at 37 degrees C. Furthermore, 5'-deoxypyridoxal was effective in reducing nuclear binding of dexamethasone when added either simultaneously with [3H]dexamethasone or after achievement of equilibrium of steroid with receptor. The reduction in nuclear [3H]dexamethasone binding is highly specific for 5'-deoxypyridoxal. Several analogues of this compound, including 5'-deoxypyridoxamine, were ineffective. In addition, this effect was reversible following removal of extracellular 5'-deoxypyridoxal. Under these conditions, 5'-deoxypyridoxal was competitive with dexamethasone for binding to nuclear receptor, with KI = 8.1 X 10(-6) M. Scatchard plot analysis of dexamethasone-receptor binding in the presence or absence of 5'-deoxypyridoxal was consistent with an apparent reduced affinity of [3H]dexamethasone for receptor, which again suggests competitive interaction or allosteric interaction mediated dissociation. Glucocorticoids are known to stimulate alkaline phosphatase activity within HeLa S3 cells. In whole cell incubations, 5'-deoxypyridoxal was effective in reducing the dexamethasone-induced increase in alkaline phosphatase activity by 60% under conditions in which cell viability and cell growth were not affected.

Triiodothyronine stimulation of in vitro growth and maturation of embryonic chick cartilage.

We studied the direct effect of T3 on cartilage growth and maturation in vitro. Pelvic cartilages from 9-day-old chick embryos were incubated in a serum-free organ culture system which supported cartilage growth over a 5-day interval. The addition of T3 (15 nM) to the medium increased cartilage wet weight (approximately 100%), dry weight (77%), length (35%), and total soluble protein (67%) over 3 days compared to cartilage incubated in medium alone. The DNA content was only slightly increased (2%) by T3 over the interval. T3 stimulated the same parameters of growth similarly after 5 days of incubation. In addition, T3 increased the incorporation of [14C]leucine into protein (82%) and 35SO4 into proteoglycan (53%). A dose-dependent increase in cartilage wet weight was seen with T3 (0.0015-15 nM) over 3 days of incubation. Cartilage incubated with T3 demonstrated microscopic changes in maturation, with development of large numbers of hypertrophied chondrocytes, and biochemical evidence of maturation, with increased alkaline phosphatase activity (130%). The dose-response range for T3 stimulation of alkaline phosphatase activity (0.015-0.15 nM) was considerably more restricted than that for stimulation of growth (0.0015-15 nM). These studies demonstrate that T3 in physiological concentrations directly affects cartilage growth and maturation, primarily through stimulating chondrocyte hypertrophy.

In vitro stimulation of alkaline phosphatase activity in immature embryonic chick pelvic cartilage by adenosine 3'5'-monophosphate.

Cyclic AMP content in embryonic chick pelvic cartilage increases significantly as the embryo ages from 8 to 10 d. This in ovo elevation in cyclic AMP content precedes maximal cartilage alkaline phosphatase activity by some 24 h. We studied whether this temporal relationship may be causally related, using an in vitro organ culture. Incubation of pelvic cartilage from 9- and 10-d embryos in medium containing monobutyryl cyclic AMP (BtcAMP) resulted in significant increases in alkaline phosphatase activity (220 and 66 percent, respectively) as compared to that of cartilages incubated in medium alone. This stimulation was both concentration- and time-dependent with maximal response at 0.5 mM BtcAMP and 4-h incubation, respectively. Similar incubations of cartilage in medium containing 1-methyl-3-isobutyl xanthine (MIX), 0.25 mM, also resulted in increased alkaline phosphatase activity (114 percent). However, pelvic cartilage from 11-d embryos incubated in medium containing BtcAMP or MIX showed no increase in alkaline phosphatase activity. We postulated that developmental age was the factor responsible for this difference in response and that immature cartilage (that with little or no alkaline phosphatase activity) would respond to BtcAMP whereas mature cartilage (that with significant alkaline phosphatase activity) would not. This was tested by incubating end sections of 11-d cartilage, which have little alkaline phosphatase activity, and center sections, which have significantly alkaline phosphatase activity, with both BtcAMP and MIX. Alkaline phosphatase activity in end sections (immature cartilage) was stimulated by BtcAMP and MIX, whereas it was not stimulated in the center sections. Actinomycin D and cycloheximide inhibited BtcAMP and MIX stimulation of alkaline phosphatase activity. Thus, the in vitro data suggest that cyclic AMP is a mediator for the stimulation of alkaline phosphatase activity in embryonic cartilage.

Early stimulation of alkaline phosphatase activity in response to 1α,25-dihydroxycholecalciferol

Alkaline phosphatase activity (APA) stimulation in response to 1,25-dihydroxycholecalciferol (1,25 (OH) 2D 3) has been studied in vitamin-D-deficient rat intestinal brush borders prepared from ex - vivo -perfused duodeno-jejunal segments. Basal APA in intestines perfused with ethanol remained constant throughout the experiments. APA was significantly increased when intestines were perfused with 1,25 (OH) 2D 3 (3 nM) for 30, 45 or 60 min. A dose-effect response was observed when 1,25 (OH) 2D 3 increased in the perfusion medium. The maximal alkaline phosphatase activity after a 45-min perfusion (2404 ± 379 m TU/mg prot.) was observed when 1,25 (OH) 2D 3 concentration was 6 nM. Cholecalciferol had no effect in this system.

The effect of 1,25-dihydroxyvitamin D-3 on the distribution of alkaline phosphatase activity along the chick intestinal villus

Rachitic chicks received 2.5 nmol of 1,25-dihydroxyvitamin D-3 (1,25(OH) 2D 3) at 4, 8, 12, 24 and 48 h, respectively, before killing. A small piece of the duodenum from each chick was frozen and divided into two parts. One part was serially sectioned perpendicular to the longitudinal axis of the villi. Each section was analyzed for alkaline phosphatase and sucrase activities. The second part was sectioned parallel to the longitudinal axis of the villus to determine villar length by morphometry. The results indicate that: 1. 1. A gradient of alkaline phosphatase activity exists along the villus with maximal activity at the tip. 2. 2. 1,25(OH) 2D 3 stimulated alkaline phosphatase activity along the entire length of the villus. The responses of different regions of the villus to 1,25(OH) 2D 3 were parallel in time for the first 12–24 h indicating a lack of differential response according to cell age. By 48 h the alkaline phosphatase activity at the base of the villus had returned to control values whereas the activity at the tip of the villus remained fully stimulated. 3. 3. A significant increase in villar length was observed in the duodenal specimens from the 1,25(OH) 2D 3-treated chicks. 4. 4. Sucrase activity does not parallel alkaline phosphatase activity but is greater in the region just distal to the crypts with little activity at the villar tip or in the bottom of the crypts. 5. 5. 1,25(OH) 2D 3 had no significant effect on the amount or distribution of sucrose activity.

Vascular perfusion of isolated rat gut: norepinephrine and glucocorticoid requirement.

Vascular perfusion of isolated rat gut: norepinephrine and glucocorticoid requirement.