Effect of some non-steroidal antifertility agents on biochemistry of the uterus and uterine fluid in rats

The effect of 3 postcoital antifertility agents (4 and 20 mg/kg DBF, 2 and 10 mg/kg NF, and .25 and 1.25 mg/kg Centchroman) on histology and biochemistry of the uterus and uterine fluid of mated rats was investigated. The low and high doses of all the compounds showed, in general, estrogenic type histologic changes. They generally caused an increase in uterine dry matter, protein, RNA, glycogen, and alkaline phosphatase, and a decrease in wet weight, nonprotein nitrogen, and acid phosphatase (p.01). In uterine fluid, alkaline phosphatase was markedly stimulated after high dosages of DBF and NF and low dosages of Centchroman (p.01). .25 mg Centchroman possessed estrogenic activity, whereas 1.25 mg showed antiestrogenicity. The compounds appeared to interfere with the action of both estrogen and progesterone in varying degrees.     

Lysozyme, alkaline phosphatase and neutrophils in uterine secretions of mares with differing resistance to endometritis

A study was conducted to 1) determine differences in the inflammatory response following bacterial challenge between normal mares and mares with chronic endometritis and 2) to determine if enzyme activity in uterine fluid can be used to evaluate degree of inflammation in the equine uterus. Six normal mares (Group 1) and four mares with chronic endometritis (Group 2) received an intrauterine infusion of beta-hemolytic streptococci on the second day of estrus. Neutrophil concentration as well as lysozyme and alkaline phosphatase activity were determined in uterine secretions obtained by placing tampons in the uterus of mares. All mares had a similar inflammatory response following bacterial challenge of the uterus, as indicated by a neutrophil response of the same magnitude. Neutrophil numbers, lysozyme and alkaline phosphatase concentrations were all increased 12 h postinoculation and declined rapidly to normal preinoculation values by 48 h after inoculation. In spite of the similarity of the clinical signs, neutrophil concentrations and enzyme activity, mares in group 1 demonstrated a markedly higher ability to eliminate the infection than mares in group 2. It is concluded that factors other than neutrophil numbers, lysozyme and alkaline phosphatase activity account for the inability of the mare to eliminate uterine infections.     

Oxytocin-induced biochemical changes in cervical mucus of the goat

This study was conducted to investigate the effects of oxytocin administration on plasma progesterone concentration and cervical mucus content of protein and acid and alkaline phosphatase activity in the goat. Oxytocin administered to goats (100 IU, S.C. daily) between Days 3 and 6 of estrous cycle induced estrus and resulted in a corresponding decrease in the levels of plasma progesterone, as well as in the contents of protein and in acid and alkaline phosphatase in the cervical mucus. Administration of indomethacin (10 mg/kg body weight, S.C.) inhibted oxytocin-induced estrus and changes in progesterone, protein and enzymes. It is suggested that oxytocin-induced changes are mediated via the production and release of prostaglandin F(2alpha) (PGF(2alpha)).     

Chelation therapy and vanadium: effect on reproductive organs in rats

Present investigation was planned to evaluate the therapeutic effectiveness of chelating agents against vanadium intoxication on blood and reproductive organs of rats. Male and female albino rats were injected vanadyl sulphate (7.5 mg/kg, po, for 21 days, 5 days in a week). Chelating agents tiron (T) alone and in combination with lipoic acid (LA), vitamin E (vit E) and selenium (Se) were given for 2 days/week. With the administration of vanadyl sulphate to rats fructose level in seminal vesicles was significantly (P< or =0.05) declined. The activities of alkaline phosphatase and adenosine triphosphatase were also decreased, whereas glycogen content and acid phosphatase activity increased in testis, seminal vesicles, ovaries and uterus after toxicant exposure. Significant changes in serum transaminases, serum alkaline phosphatase and lactate dehydrogenase were recouped by chelation therapy. Lipid peroxidation, reduced glutathione level and triglycerides levels altered significantly after exposure to vanadium in rats. The ultrastructural damage in spermatogenic stages in treated animals showed recovery pattern after therapy. Co-treatment with antioxidants restored these activities. The most effective combination was tiron + selenium followed by tiron + vitamin E, and tiron + lipoic acid.     

Extracellular matrix components and proteolytic enzymes in uterine cervical carcinoma

The important components of mucopolysaccharides and collagen have been analyzed in tissues of control and carcinoma of uterine cervix. Among these components hyaluronic acid and chondroitin sulphate levels were found to be increased, whereas decreased level of collagen was observed in uterine cervical carcinoma. Serum cathepsin B, D and acid and alkaline phosphatases have also been analyzed in controls and carcinoma patients before and after treatments. The activities of these enzymes have been found to increase prominently in advanced stages. Among these enzymes cathepsin B and alkaline phosphatase have exhibited remarkable increase in activity in uterine cervical carcinoma. Different modes of treatment exerted reversion of the elevated activities of these enzymes. However, combined therapy type II (radiation combined with cisplatin and cyclophosphomide) seems to be more effective in reverting the activities of these enzymes to normal levels.     

Effects of estradiol and progesterone on vertebral collagen, glycosaminoglycans and phosphatases in ovariectomized adult rats.

Vertebral collagen, glycosaminoglycans (GAGs), tartrate-resistant acid phosphatase (TRAP) and alkaline phosphatase (ALP) were measured in ovariectomized (ovx) adult Wistar rats treated with estradiol (E 2 ) (10 micro g/kg BW for 35 days on alternate days, and progesterone (P 4 ) (140 micro g/kg BW for 35 days on alternate days) in E 2 + P 4 treated rats. P 4 given alone or in combination with E 2 significantly increased the levels of collagen in the vertebral bone. Neither ovx nor E 2 treatment altered the concentration of collagen in these rats. Administration of E 2 or P 4 significantly decreased the concentration of hyaluronic acid (HA), but remaining unaffected when a combination of these steroids was given. In contrast to their effect on HA, E 2 and P 4 each significantly increased the levels of chondroitin sulfate (CS) in the vertebral bone. The specific activity of ALP was decreased after ovx. E 2 and P 4 alone or in combination also registered a significant decrease in the activities of ALP and TRAP. The results suggest that E 2 and P 4 each exert definite effects on vertebral bone turnover in ovariectomized rats.     

Variations in free secretory component levels in mucosal secretions of the rat

The present studies were conducted to compare the levels of free secretory component (SC) in a number of rat mucosal secretions and to determine whether SC content varies significantly during the four stages of the estrous cycle. Levels of SC, as measured by radioimmunoassay, were markedly different in various external secretions. Bile contained the highest amount, irrespective of whether SC was normalized to volume or protein. Concentrations of SC in saliva or uterine fluid from intact rats were approximately 20- to 30-fold less than measured in bile. When SC levels were normalized to protein, the SC to protein ratios in uterine, vaginal, and respiratory secretions were six to 18 times greater than values calculated in salivary and small intestinal fluids. Analysis of SC levels in mucosal secretions during the estrous cycle indicated significant variations occur in uterine and vaginal samples, but not in saliva or small intestinal secretions. In the uterine lumen, SC levels were highest at proestrus, partially elevated at estrus, and lowest at both days of diestrus. In contrast, vaginal SC levels were maximal at estrus and reduced at all other stages of the cycle. Immunoglobulin A content was also measured in uterine and vaginal secretions during the estrous cycle. Significant changes in IgA levels were found and these coincided with the changing pattern of SC. These results suggest hormones may modulate SC levels in reproductive tissues. In addition, our findings indicate variations in SC during the estrous cycle may direct the movement of IgA from tissue to lumen.     

Influence of dietary partially hydrogenated fat high in trans fatty acids on lipid composition and function of intestinal brush border membrane in rats

The effect of dietary hydrogenated fat (Indian vanaspati) high in trans fatty acids (6 en%) on lipid composition, fluidity and function of rat intestinal brush border membrane was studied at 2 and 8 en% of linoleic acid. Three groups of weanling rats were fed rice-pulse based diet containing 10% fat over a ten week period: Group I (groundnut oil), Group II (vanaspati), Group III (vanaspati + safflower oil). The functionality of the brush border membrane was assessed by the activity of membrane bound enzymes and transport of D-glucose and L-leucine. The levels of total cholesterol and phospholipids were similar in all groups. The data on fatty acid composition of membrane phospholipids showed that, at 2 en% of linoleic acid in the diet, trans fatty acids lowered arachidonic acid and increased linoleic acid contents indicating altered polyunsaturated fatty acid metabolism. Alkaline phosphatase activity was increased while the activities of sucrase, gamma-glutamyl transpeptidase and transport of D-glucose and L-leucine were not altered by dietary trans fatty acids. However at higher intake of linoleic acid in the diet, trans fatty acids have no effect on polyunsaturated fatty acid composition and alkaline phosphatase activity of intestinal brush border membrane. These data suggest that feeding dietary fat high in trans fatty acids is associated with alteration in intestinal brush border membrane polyunsaturated fatty acid composition and alkaline phosphatase activity only when the dietary linoleic acid is low.     

Evidence for a role for a uterine renin-angiotensin system in decidualization in rats.

Experiments were performed in vivo and in vitro to determine the effects of enalaprilat, a specific inhibitor of angiotensin-converting enzyme, on various aspects of the decidual cell reaction in rats. Ovariectomized, adult female rats were sensitized for the decidual cell reaction with steroid treatments. For in vivo experiments, intrauterine infusions of enalaprilat alone, and in combination with angiotensin II and prostaglandin E2 (PGE2), were initiated on the day of uterine sensitivity. Enalaprilat inhibited the increases in uterine PG concentrations, endometrial vascular permeability, alkaline phosphatase activity and uterine weight that occurred sequentially following infusion of vehicle. Concurrent infusion of angiotensin II did not reverse any of these inhibitory effects; PGE2 infusion partially, but not completely, reversed the inhibition of increase in uterine weight, although it did not alter the inhibition of endometrial vascular permeability. For in vitro experiments, endometrial stromal cells were obtained from uteri on the day of sensitivity and cultured for up to 3 days in the presence of enalaprilat and angiotensin II. Enalaprilat inhibited in a dose-dependent manner the increases in stromal cell alkaline phosphatase activity and media PGE concentration that occurred in the control cultures; these effects were fully reversed by concurrent treatment with angiotensin II. The inhibition of stromal alkaline phosphatase activity was also reversed by PGE2; conversely, the ability of angiotensin II to reverse the effect of enalaprilat was lost in the presence of indomethacin. These studies provide evidence of a requirement for angiotensin II during the decidual cell reaction in rats and suggest that it acts, at least in part, through a PG-dependent mechanism.     

Therapeutic efficacy of lipoic acid in combination with dimercaptosuccinic acid against lead-induced renal tubular defects and on isolated brush-border enzyme activities

The combined therapeutic potentials of lipoic acid and dimercaptosuccinic acid were compared against their sole administrations in restoring the altered lead sensitive indices in urine and isolated renal brush-border preparations. Toxicity was induced in male albino rats (Wistar strain) by administering lead acetate (0.2%) in drinking water for 5 weeks, followed by therapy comprising lipoic acid (25 mg/kg body weight) and dimercaptosuccinic acid (20 mg/kg body weight) solely as well as combined during the 6th week. Changes in kidney weights encountered upon lead administration improved after therapy with lipoic acid and dimercaptosuccinic acid. Renal integrity was assessed by measuring the activities of alkaline phosphatase, acid phosphatase, lactate dehydrogenase, leucine aminopeptidase, N-acetyl-beta-D-glucosaminidase, gamma-glutamyl transferase and beta-glucuronidase in urine along with some urinary constituents (urea, uric acid, creatinine, protein and phosphorous). The effects of lead were also studied on isolated brush-border enzymes (alkaline phosphatase, acid phosphatase, gamma-glutamyl transferase and beta-glucuronidase) that showed a decline upon its administration. Increased activities of urinary enzymes were accompanied by increase in the urinary constituents. Increase in renal lead content was paralleled by a drastic fall in the renal delta-aminolevulinic acid dehydratase and a rise in urinary lead levels. Relative to the administration of lead, the combined therapy showed betterment on the renal integrity with respect to the functional parameters assessed, thereby indicating its efficacy over the monotherapies.     

The beneficial effect of OST-6 (OsteoCare), a herbomineral formulation, in experimental osteoporosis.

OST-6 (OsteoCare), a herbomineral formulation, was evaluated for its inhibitory effect on the progress of bone loss induced by ovariectomy in rats. Ovariectomized (Ovx) rats were administered with OST-6 at 250 and 500 mg/kg b.wt., orally daily for 90 days. On 91st day, ovariectomized rats showed reduced bone mineral content and increased serum alkaline phosphatase levels, excretion of urinary calcium and pyridinium cross-links levels. Histologically, bone sections revealed narrowed and disappearance of trabeculae and widened medullary spaces. The total numbers of Tartrate-resistant acid phosphatase (TRAP) positive cells were significantly increased both in-vivo and in-vitro methods. OST-6, at a dose of 500 mg/kg, significantly improved bone mineral contents, serum alkaline phosphatase levels, reduced the elevated urinary calcium and pyridinium cross-links excretion, number of TRAP positive cells and reversal of the above mentioned histological features. These results indicate the usefulness of OST-6 in the management of osteoporosis in a natural way through herbal resources.     

Effect of a polyherbal formulation, Ambrex, on butylated hydroxy toluene (BHT) induced toxicity in rats

Effect of polyherbal formulation Ambrex was evaluated in butylated hydroxytoluene (BHT) induced toxicity of lungs and liver in rats. Toxicity was produced by administering BHT (500 mg/kg/day) for 3 days. Lung damage was evidenced by elevated levels of broncho alveolar lavage fluid (BAL) parameters such as protein, lactate, lactate dehydrogenase (LDH), alkaline phosphatase (ALP), acid phosphatase (ACP) and glucose-6-phosphate dehydrogenase (G6PDH). Liver damage was proved by elevated levels of serum protein and markers such as LDH, ALP, aspartate amino transferase (AST), alanine amino transferase (ALT), decreased level of lipid peroxides (LPO) in serum and glutathione (GSH) in liver. Administration of aqueous suspension of Ambrex (50 mg/kg orally) retained these elevated levels of BAL-protein, lactate, LDH, ALP, ACP, G6PDH and serum-protein, LDH, ALP, AST and ALT at near normal values. Decreased level of liver GSH was retained at near normalcy in Ambrex pretreated BHT-administered animals. There was no change in liver LPO in all the four groups.     

A study of the uterine protein variations during the estrus cycle in the cow: a comparison with the serum proteins

To investigate uterine protein changes during the estrus cycle in the bovine, 115 pluriparous genital tracts and blood samples were collected from the abattoir in Urmia. Genital tracts were considered healthy based on gross examination of the uterus and uterine histopathological findings. The phase of the estrus cycle was determined by the examination of the structures present on the ovaries and the uterine tonicity. Of the collected samples, 24 were pro-estrus, 21 estrus, 24 met-estrus and 46 diestrus. The uterus was incised and uterine fluid was collected by gentle scraping of the uterine mucosa with a curette. The total protein concentration, protein profiles (on agarose gel electrophoresis) in the uterine fluid were evaluated and compared with those of the serum. Total protein, alpha1, alpha2, beta1 and beta2 globulin values in the uterus were significantly higher than those of the serum (P<0.05), while, the albumin, gamma1 and gamma2 globulin values in the serum were higher than those of the uterus throughout the cycle. During pro-estrus, uterine fluid beta2 (1.96 g/dl) and serum gamma1 (1.07 g/dl) and gamma2 (1.27 g/dl) globulins were higher than those in the other phases of the cycle. During estrus, serum total protein was lower than the other phases (4.92 g/dl), which was considered to be due to a reduction in serum alpha1 (0.25 g/dl), gamma1 (0.65 g/dl) and gamma2 (0.64 g/dl) globulins in this phase. In met-estrus uterine fluid beta1 globulin was in the lowest (1.19 g/dl) and serum gamma2 globulin at a high level (1.24 g/dl). It was concluded that uterine proteins as well as serum proteins fluctuate during the estrus cycle and, except for the albumin and gamma globulins, its protein content is higher than the serum. During the follicular phase of the cycle uterine alpha globulins are higher than those in other phases, with an elevation in beta1 and a reduction in beta2 and gamma globulin values during estrus, which may reflect the preparation of the uterus for receiving spermatozoa for the conception in this phase.     

Effects of nutritional deficiencies during neonatal and post-weaning period on rat intestinal phytase and phosphatase activities

Studies were made of the effects of pre- and post-weaning undernutrition and/or protein deficiency on intestinal phytase and phosphatase activities in albino rats and reversibility of the same by subsequent dietary rehabilitation. Neonatal undernutrition induced by rearing the pups in litters of 16 caused a marked decrease in alkaline phytase activity (as compared to those reared in litters of 8), while acid phytase activity decreased to a lesser extent and acid and alkaline phosphatase activities did not change. When neonatally undernourished rats were subsequently continued on a 4 or a 20% protein diet in restricted amounts (2.5 g/day) for 6 weeks the decreases in the alkaline phytase activity but not in that of acid phytase were further aggravated. Acid and alkaline phosphatases were not influenced by these treatments either. On dietary rehabilitation of these rats for subsequent 6 weeks on a 20% protein diet (ad libitum) acid and alkaline phytase activities of intestine recovered partially. These studies indicate the importance of alkaline phytase activity as a marker of intestinal maturation and is also suggestive of interrelationships between nutrition, intestinal development and its alkaline phytase activity.     

Effects of vitamin A and β-carotene on plasma progesterone and uterine protein secretions in gilts

Twenty-four gilts detected in estrus were fed a barley-soybean meal diet which was essentially free of vitamin A and β-carotene. At the second estrus, gilts were randomly assigned to be fed daily the same basal control diet (CON), CON + 8200 IU vitamin A in the diet (VIT), CON + 4100 IU vitamin A + 8.2 mg β-carotene in the diet (CAR), or VIT + 16.4 mg β-carotene injected intramuscularly every other day (INJ). All gilts were sham-bred at the third estrus (day 0). On day 15, uterine secretions were flushed and uterine protein fractions were quantified after sequential chromatographic separations on Sephadex G-200 and G-50. Acid phosphatase activity in uterine flushings was measured also. Results showed nonsignificant treatment differences in the number of corpora lutea, ovarian weight, length of the estrous cycle and concentrations of plasma progesterone on days 0, 3, 6, 9, 12 and 15. The amount of total secretory protein was not different among treatment groups. However, CON had the lowest quantity of serum-like proteins and uterine-specific proteins and in the total and specific acid phosphatase activities. Group INJ tended to have the highest amount of each uterine protein fraction examined. Thus, deficiencies in vitamin A and β-carotene decreased certain uterine protein components while injected β-carotene tended to have an opposite effect. Such differences in uterine proteins may influence embryonic survival in pigs.     

Oxytocin and glucose oxidation in the rat uterus

The effects of oxytocin on the biochemical pathways of glucose oxidation were investigated in the rat uterus. In the presence of oxytocin, glucose oxidation in uterine segments obtained from Sprague-Dawley rats at diestrus increased 1.5–2.0-fold above the basal rate. A half-maximal response was observed at about 3 nM oxytocin; the maximum response was equal to or greater than the response to 1.7 nM insulin. In stripped myometrial segments (denuded of the endometrial component), oxytocin stimulated glucose oxidation at estrus only; whereas in intact uterine segments, the stimulation of oxidation was observed at both estrus and diestrus. In contrast, stimulation of oxidation by carbachol in stripped myometrial segments was independent of the estrous state of the tissue. The ratio of [1-¹⁴C]glucose to [6-¹⁴C]glucose oxidation was measured to estimate the relative involvement of the pentose phosphate and the tricarboxylic acid pathways of metabolism. In myometrial tissue, stimulation of glucose oxidation by oxytocin appeared to proceed through the tricarboxylic acid cycle. In intact uterine segments, at diestrus, glucose oxidation involved largely the pentose phosphate pathway (suggesting increased glucose metabolism in endometrial tissue), whereas at estrus, in the intact tissue segments, oxytocin increased glucose oxidation largely via the tricarboxylic acid cycle, and appeared to do so predominantly in the myometrial tissue. Carbachol-stimulated glucose oxidation appeared to proceed mainly via the tricarboxylic cycle in the myometrial tissue, irrespective of the stage of the estrous cycle. In the uterus of the Brattleboro rat (either intact uterine segments or stripped myometrial strips), oxytocin stimulated glucose oxidation only at estrus, predominantly through the tricarboxylic acid cycle. These findings suggest that oxytocin, in addition to its known effect on the contractility of uterine and myoepithelial smooth muscle, may regulate glucose metabolism in both the myometrial and endometrial components of uterine tissue.     

A novel short-chain alcohol dehydrogenase from rats with retinol dehydrogenase activity,cyclically expressed in uterine epithelium

Retinoic acid is necessary for the maintenance of many lining epithelia of the body, such as the epithelium of the luminal surface of the uterus. Administration of estrogen to prepubertal rats induces in these epithelial cells the ability to synthesize retinoic acid from retinol, coincident with the appearance of cellular retinoic acid-binding protein, type two, which is normally present in these cells only at estrus in the mature, cycling animal. Here, we report the isolation, from a cDNA library prepared from uterine mRNA collected at the estrous stage and from a rat mammary adenocarcinoma cell line, of a cDNA that encodes a novel retinol dehydrogenase. A member of the short-chain alcohol dehydrogenase family, the encoded enzyme was capable of metabolizing retinol to retinal when expressed in cells after transfection of its cDNA. When cotransfected with the cDNA of human aldehyde 6, a known retinaldehyde dehydrogenase, the transfected cells synthesized retinoic acid from retinol. Immunohistochemical analysis revealed that the protein was present in the uterine lining epithelium of the mature animal only at estrus, coincident with the presence of cellular retinol-binding protein and cellular retinoic acid-binding protein, type two. Consequently, this novel short-chain alcohol dehydrogenase is an excellent candidate for the retinol dehydrogenase that catalyzes the first step in retinoic acid biosynthesis that occurs in uterine epithelial cells.     

Modulation of cyclophosphamide-induced early lung injury by curcumin,an anti-inflammatory antioxidant

Cyclophosphamide causes lung injury in rats through its ability to generate free radicals with subsequent endothelial and epithelial cell damage. In order to observe the protective effects of a potent anti-inflammatory antioxidant, curcumin (diferuloyl methane) on cyclophosphamide-induced early lung injury, healthy pathogen free male Wistar rats were exposed to 20 mg/100 g body weight of cyclophosphamide, intraperitoneally as a single injection. Prior to cyclophosphamide intoxication oral administration of curcumin was performed daily for 7 days. At various time intervals (2, 3, 5 and 7 days post insult) serum and lung samples were analyzed for angiotensin converting enzyme, lipid peroxidation, reduced glutathione and ascorbic acid. Bronchoalveolar lavage fluid was analyzed for biochemical constituents. The lavage cells were examined for lipid peroxidation and glutathione content. Excised lungs were analyzed for antioxidant enzyme levels. Biochemical analyses revealed time course increases in lavage fluid total protein, albumin, angiotensin converting enzyme (ACE), lactate dehydrogenase, N-acetyl--D-glucosaminidase, alkaline phosphatase, acid phosphatase, lipid peroxide levels and decreased levels of glutathione (GSH) and ascorbic acid 2, 3, 5 and 7 days after cyclophosphamide intoxication. Increased levels of lipid peroxidation and decreased levels of glutathione and ascorbic acid were seen in serum, lung tissue and lavage cells of cyclophosphamide groups. Serum angiotensin converting enzyme activity increased which coincided with the decrease in lung tissue levels. Activities of antioxidant enzymes were reduced with time in the lungs of cyclophosphamide groups. However, a significant reduction in lavage fluid biochemical constituents, lipid peroxidation products in serum, lung and lavage cells with concomitant increase in antioxidant defense mechanisms occurred in curcumin fed cyclophosphamide rats. Therefore, our results suggest that curcumin is effective in moderating the cyclophosphamide induced early lung injury and the oxidant-antioxidant imbalance was partly abolished by restoring the glutathione (GSH) with decreased levels of lipid peroxidation.     

Human bone cell enzyme expression and cellular heterogeneity: correlation of alkaline phosphatase enzyme activity with cell cycle

Alkaline phosphatase, long implicated in biomineralization, is a feature of the osteoblast phenotype. Yet in cultured bone cells, only a fraction stain positive histochemically. To determine whether osteoblast enzyme expression reflects cellular heterogeneity with respect to cell cycle distribution or length of time in culture, the activities of alkaline phosphatase, tartrate-resistant and -sensitive acid phosphatases, and non-specific esterases were assayed kinetically and histochemically. In asynchronous subconfluent cultures, less than 15% of the cells stained positive and assayed activity was 0.04 IU/10(6) cells/cm2. After 1 week, the percent of alkaline phosphatase positive-staining cells increased 5-fold, while activity increased 10-fold. Non-specific esterases and tartrate-sensitive acid phosphatase were constitutive throughout time in culture, whereas tartrate-resistant acid phosphatase activity appeared after 2 weeks. Cell cycle analysis of human bone cells revealed a growth fraction of 80%, an S phase of 8.5 h, G2 + 1/2 M of 4 h, and a G1 of 25-30 h. In synchronous cultures induced by a thymidine-aphidicolin protocol, alkaline phosphatase activity dropped precipitously at M phase and returned during G1. A majority of the alkaline phosphatase activity lost from the cell surface at mitosis was recovered in the medium. Tartrate-sensitive acid phosphatase and non-specific esterase levels were relatively stable throughout the cell cycle, while tartrate-resistant acid phosphatase activity was not assayable at the density used in synchronous cultures. From these data, variations in alkaline phosphatase activity appear to reflect the distribution of cells throughout the cell cycle.