Potassium bicarbonate supplementation and calcium metabolism in postmenopausal women: are we barking up the wrong tree?

A recent study of postmenopausal women has shown that the administration of 60-120 mmol potassium bicarbonate can neutralize net acid excretion and significantly lower urinary calcium (Ca). The changes in urinary calcium loss were sufficient to improve calcium balance and skeletal metabolism in these subjects. However, the design of the study was such that the relevance of these findings to the prevention and treatment of osteoporosis is suspect.

Growth hormone and parathyroid hormone stimulate intestinal calcium absorption in aged female rats

Aged (16-month-old) female rats (n = 8/treatment) were injected for 12 days with GH (100 micrograms/100 g x day), PTH (8 micrograms/100 g x day), GH plus PTH, or vehicle (V) in an experiment designed to determine the effects of these hormones on intestinal mineral absorption in senescent rats. PTH and GH increased fractional net calcium absorption to a similar extent (PTH, 1.6-fold; GH, 1.4-fold) even though PTH increased serum 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] 3.7-fold, and GH had no significant effect. GH plus PTH caused no further increase in serum 1,25-(OH)2D3 above that caused by PTH alone, but resulted in an additive effect on net calcium absorption (2.3-fold increase). PTH and GH also had statistically independent effects on phosphate absorption; magnesium absorption was elevated only by PTH. Duodenal calbindin-D9k levels were increased by GH (from 3.79 +/- 0.72 to 6.98 +/- 0.73 micrograms/mg protein) and PTH (from 3.23 +/- 0.46 to 7.55 +/- 0.75 micrograms/mg protein); PTH plus GH treatment resulted in an additive effect on calbindin-D9k levels. Additional in vitro transport studies in the human intestinal cell line Caco-2 showed that 72 h of pretreatment with the local mediator of GH action, insulin-like growth factor-I (at 10 and 100 ng/ml), stimulated transcellular calcium transport (22% and 44%, respectively) regardless of concomitant 1 nM 1,25-(OH)2D3 pretreatment (80% increase). Our findings suggest a 1,25-(OH)2D3-mediated mechanism for PTH-induced changes in calcium and phosphorus absorption. In contrast, the effects of GH in the senescent rat are independent of changes in circulating 1,25-(OH)2D3 and our data suggest that these effects may be mediated by insulin-like growth factor-I.

Identification of calbindin D-9k mRNA and its regulation by 1,25-dihydroxyvitamin D3 in Caco-2 cells

We have identified and quantified specific mRNAs in the human colonic carcinoma cell line Caco-2 by reverse transcriptase-polymerase chain reaction. Initial examination revealed that like rat duodenal mucosa, Caco-2 cells possessed mRNA for the vitamin D receptor. Using primers for human calbindin we found a 237-bp PCR product in Caco-2 cell RNA, but not from rat duodenal RNA. Primers for rat calbindin did not amplify calbindin mRNA in Caco-2 RNA, confirming a high degree of mismatch between rat and human sequences. 1,25(OH)2 vitamin D3 treatment (10 nM) significantly elevated calbindin mRNA levels 50% by 12 h, with maximal levels occurring by 48 h (fivefold elevation). Increasing concentrations of 1,25(OH)2 vitamin D3 (from 15 pM to 100 nM) caused progressive increases in calbindin mRNA levels following 48 h of treatment. Elevated calbindin mRNA levels were associated with enhancement of transcellular calcium transport. Our results are the first demonstration of vitamin D-regulated calbindin mRNA in a human intestinal cell line.

Measurement of zinc bioavailability from beef and a ready-to-eat high-fiber breakfast cereal in humans: application of a whole-gut lavage technique

We measured zinc absorption in humans from two different foods, using a whole-gut lavage technique. Healthy adults (n = 8) were given test foods containing approximately 4 mg (61.2 mumol) Zn as either beef or a high-fiber, ready-to-eat breakfast cereal. Basal zinc loss in the gut was measured after giving only 200 mL water alone after an overnight fast. Mean polyethylene glycol (PEG) recovery, a nonabsorbable fecal marker, was 95 +/- 2% (mean +/- SE). There was no significant difference of PEG recoveries with the various treatments. True absorption of zinc was 11.0 +/- 5.4 mumol (716.3 +/- 355.9 micrograms) for breakfast cereal and 34.8 +/- 3.5 mumol (2274.1 +/- 230.2 micrograms) for beef. Fractional zinc absorption was significantly lower for breakfast cereal compared with beef, 14.7 +/- 6.7% vs 55.1 +/- 4.6%, respectively. Our findings demonstrate that zinc absorption can be measured in humans from single foods containing a physiological dose of zinc by using the whole-gut lavage absorption technique and that zinc bioavailability from beef is about fourfold greater than from a high-fiber breakfast cereal.

Vitamin D-sensitive and quinacrine-sensitive zinc transport in human intestinal cell line Caco-2

We studied the mechanism of transepithelial zinc (Zn) transport using monolayers of Caco-2 cells grown on permeable filter supports. 65Zn transport could be fitted to a modified Michaelis-Menten equation, which includes a nonsaturable [linear diffusion constant of nonsaturable component (Kd) = 0.08%.cm-2.90 min-1] and a saturable component [upper well Zn concentration at half Jmax (Kt) = 226 microM and maximal rate of saturable Zn transport (Jmax) = 1.06 nmol.cm-2.90 min-1]. Caco-2 cells contained metal-inducible metallothionein (MT) protein and mRNA as well as mRNA for cysteine-rich intestinal protein (CRIP). Cells pretreated with 10 nM 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] for 3 days transported more Zn (159%) than controls (0.48 +/- 0.02 nmol.cm-2.90 min-1) when each was incubated with 100 microM Zn for 90 min. This effect was significant after 24 h of 1 alpha,25-(OH)2D3 pretreatment and continued to increase up to 72 h, with concomitant increases in MT mRNA levels being observed (4-fold by 24 h, 10-fold by 72 h). MT protein levels were only modestly elevated by 72 h 1 alpha,25(OH)2D3 treatment (from 0.32 +/- 0.04 to 0.45 +/- 0.03 nmol MT/mg protein). CRIP mRNA levels were reduced by 1 alpha,25(OH)2D3 treatment. The lysosome-disrupting agent quinacrine (0.5 mM) inhibited basal Zn transport by 68%, suggesting the possible presence of a lysosome-mediated component for transepithelial Zn transport in Caco-2 cells. 1 alpha,25(OH)2D3-stimulated Zn transport was not affected by quinacrine, suggesting that 1 alpha,25(OH)2D3-induced Zn transport is distinct from the putative lysosome-mediated Zn transport pathway.

Lower serum ionized calcium and abnormal calciotropic hormone levels in preeclampsia

Relative hypocalciuria has been reported in women with preeclampsia. However, there has been no systematic explanation for this finding. We measured serum and urinary calcium and serum calciotropic hormones in third trimester women with preeclampsia (n = 12, gestational hypertension and proteinuria) and with normotensive pregnancies (n = 24) to try to explain these changes. We confirmed that the women with preeclampsia have a relative hypocalciuria (2.9 +/- 0.7 vs. 6.5 +/- 0.2 mmol/day, P less than 0.01). Preeclamptic women also had lower serum ionized calcium than normotensive third trimester pregnant women (1.20 +/- 0.01 vs. 1.26 +/- 0.01 mmol/L, P less than 0.02). Intact PTH levels were significantly higher in preeclamptic women (29.9 +/- 4.3 vs. 15.4 +/- 1.3 ng/L, P less than 0.01) and a significant inverse relationship was observed between PTH and both urine calcium (r = -0.60, P less than 0.0001) and serum ionized calcium (r = -0.36, P less than 0.05). We measured vitamin D metabolites in a subgroup of both normotensive and preeclamptics. Preeclamptic and normotensive pregnant women had equivalent levels of 25-hydroxyvitamin D [25(OH)D]; however, preeclamptics had significantly lower 1,25-dihydroxyvitamin D [1,25-(OH)2D] levels (172.1 +/- 18.5 vs. 219.6 +/- 12.7 pmol/L, P less than 0.05). Lower 1,25-(OH)2D may contribute to suboptimal intestinal absorption of calcium during a time of increased calcium demand resulting in lower ionized calcium, increased PTH, and hypocalciuria in preeclampsia. Abnormalities in calcium homeostasis may contribute to the increased vascular sensitivity documented in preeclampsia.

Gastric acidity, atrophic gastritis, and calcium absorption

The deleterious effects of increased gastric pH on calcium absorption from calcium carbonate supplements were observed about 25 years ago. Increasing use of calcium supplements, especially by the elderly, has raised questions about bioavailability from various calcium sources. Decreased gastric acidity is common in the elderly and in patients taking antiulcer medications. A critical review of the available human studies that have investigated the role of gastric acidity in calcium bioavailability suggests that the effects of increased gastric pH are only apparent when poorly soluble calcium salts are taken after an overnight fast. Soluble calcium sources, such as calcium citrate and calcium from milk, are absorbed normally in elderly subjects with atrophic gastritis. Moreover, calcium carbonate, a relatively insoluble calcium salt, is well absorbed in atrophic gastritis patients if administered with a meal. In order to maximize calcium bioavailability, elderly subjects should increase their calcium intakes to at least recommended levels, preferably by increasing milk consumption. When calcium supplements are used to augment dietary calcium sources, a highly soluble source should be of benefit or calcium carbonate may be taken with a meal.

Cellular antioxidant status and human immunodeficiency virus replication

The factors that stimulate replication of the human immunodeficiency virus (HIV) and determine the period of disease latency are poorly understood. Recent evidence from in vitro cell culture studies of HIV-infected cells suggest that HIV activity is profoundly affected by the presence of antioxidants, such as glutathione and ascorbic acid, in the cell culture medium. These in vitro observations and reports of global glutathione deficiency in nonsymptomatic HIV-seropositive subjects suggest that cellular antioxidant status may be an important factor determining the latency period of HIV infection. The molecular mechanisms underlying HIV activation are beginning to be understood and point to a potentially important role for NK-kappa B, a cellular transcription factor that may be modulated by cellular antioxidant status.

Controlled expansion of peripheral nerves: comparison of nerve grafting and nerve expansion/repair for canine sciatic nerve defects

The inherent disadvantages of nerve grafting have made it necessary to find alternative techniques for treating segmental nerve loss. This study compares the techniques of nerve grafting and nerve expansion/repair for the management of nerve injuries with segmental nerve loss in an animal model. Bilateral segmental sciatic nerve defects were created in eight dogs. On one side a 2-cm segment was excised and replaced with a nerve graft; on the other side a 2-cm defect was created with ligatures and the nerve underwent preliminary expansion and then repair. Eighteen months later nerve conduction velocity (NCV), gastrocnemius contraction force (GCF), and muscle weight (GMW) were determined for the seven surviving animals. NCV for the expanded repair was 58.66 +/- 34.18 m/sec and 47.73 +/- 7.93 for the grafted repair (p = 0.4); GCF was 619.04 +/- 353.70 gm for the expanded repair and 726.80 +/- 415.78 gm (p = 0.2) for the grafted repair; and GMW was 82.80 +/- 5.68 gm for the expanded repair and 109.55 +/- 20.63 gm (p = 0.02) for the grafted repair. The data suggest that: 1) conventional tissue expansion techniques can be used successfully to repair segmental peripheral nerve defects; 2) NCV and GCF are comparable for grafting and expansion/repair techniques although GMW is significantly higher in the grafted group; and 3) nerve expansion/repair may prove to be a useful alternative to grafting.

Characterization of the vitamin D receptor from the Caco-2 human colon carcinoma cell line: effect of cellular differentiation

The human colon carcinoma cell line, Caco-2, is the only intestinal cell line to spontaneously differentiate in culture to a population exhibiting structural and biochemical characteristics of mature enterocytes. We conducted studies to establish the presence of the vitamin D receptor (VDR), determine changes in VDR concentration and affinity with differentiation and determine whether 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) mediates a functional response in this cell line. We found that Caco-2 cells possess a specific 1,25(OH)2D3 binding protein similar to the mammalian VDR. It has an equilibrium dissociation constant (Kd) of 0.72 nM, binds vitamin D analogues in order of their biological activities in vivo (1,25(OH)2D3 greater than 25(OH)D3 greater than 24,25(OH)2D3), sediments as a single peak on sucrose density gradients at 3.7 S, and is eluted from a DNA-cellulose column by 0.16 M KCl. The maximum number of binding sites was 2.6-fold greater in the differentiated cell (Day 15) compared to the preconfluent, undifferentiated (Day 4) cell (23 fmol/mg protein vs 56 fmol/mg protein). Cell growth was reduced 59% when exposed to 10(-7) M 1,25(OH)2D3 for 8 days. Alkaline phosphatase activity significantly increased in cultures incubated with 10(-8) M 1,25(OH)2D3 for up to 4 days when treatment was started in both undifferentiated cells (Day 5) and differentiated cells (Day 11). These findings suggest that the VDR present in undifferentiated and differentiated Caco-2 cells is functional. Caco-2 cells provide a unique in vitro model to study vitamin D-regulated functions in differentiated mammalian enterocytes.

Vitamin D-regulated calcium transport in Caco-2 cells: unique in vitro model

The human colon adenocarcinoma cell line Caco-2 is the only intestinal cell line to differentiate spontaneously in culture exhibiting structural and biochemical characteristics of mature enterocytes and to possess a vitamin D receptor in the fully differentiated state. Transepithelial calcium transport was characterized in differentiated Caco-2 cells grown on permeable filters supports to assess the potential utility of this cell line as an in vitro model to study 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-induced calcium transport. Calcium transport was increased in a dose-dependent manner by 1,25(OH)2D3. Total calcium transport at different calcium concentrations could be fitted to a modified Michaelis-Menten equation containing a linear transport component. The maximum rate of saturable calcium transport was increased by 4.3-fold (P less than 0.005) in cells treated with 10(-8) M 1,25(OH)2D3. This treatment also increased the apparent buffer calcium concentration that results in half-maximal velocity from 0.4 to 1.3 mM but had no significant effect on nonsaturable calcium transport. Caco-2 cells grown on permeable filter supports provide a unique in vitro human cell culture model to study the mechanism of vitamin D-regulated transepithelial intestinal calcium transport.

Milk consumption and zinc retention in postmenopausal women

We measured intestinal 65Zn absorption and whole-body retention in postmenopausal women following a meal extrinsically labeled with 65Zn. The meal was consumed with 200 mL of milk or with a calcium phosphate supplement. Fifteen elderly (mean age 69) subjects were studied during three 12-d experimental periods in which they were fed either a basal diet containing 16 mg Zn or the basal diet supplemented either with 400 mL of milk or with dibasic calcium phosphate supplements containing an equivalent amount of calcium (468 mg) and phosphorus (360 mg). Measurements of fractional zinc absorption were made in 9 of the 15 subjects by a dual-isotope technique using 65Zn and 51Cr (as nonabsorbable fecal markers). Fractional zinc absorption was 0.22 +/- 0.06 (mean +/- SEM) after the standard meal, 0.23 +/- 0.06 with added milk and 0.22 +/- 0.03% with the added calcium phosphate supplement. The corresponding values for 65Zn retention in 15 subjects 12 d after dosing were 0.10 +/- 0.01% for all treatments. No significant effect of milk or calcium phosphate supplementation was observed on either 65Zn absorption or retention. We conclude that increased milk consumption with meals has no detrimental consequences on zinc nutriture in elderly women.

Management of the difficult split-thickness donor site

Split-thickness skin graft donor sites are often areas of significant morbidity in the elderly, in immunocompromised patients, and in steroid-dependent patients. We found that managing these donor sites with split-thickness skin and transparent dressings greatly increases the rate of healing and diminishes morbidity.

Acetate and hypercalciuria during total parenteral nutrition

Hypercalciuria and negative calcium balance are complications of total parenteral nutrition (TPN). Because metabolism of the TPN formula generates an acid load that can induce hypercalciuria, we evaluated the effect of supplementing the formula with acetate. In a randomized crossover study six patients on continuous and six on cyclic TPN received no added acetate or 160 mmol acetate/d replacing 160 mmol chloride/d for 3 d each. Blood and urine measurements were obtained on day 3 of each formula. Acetate, which is metabolized to bicarbonate, increased blood pH and decreased renal acid excretion. Urinary Ca decreased in every patient from 422 +/- 63 to 240 +/- 46 mg/d (10.5 +/- 1.6 to 6.0 +/- 1.4 mmol/d) and from 468 +/- 68 to 285 +/- 54 mg/d (11.7 +/- 1.7 to 7.1 +/- 1.3 mmol/d) during continuous and cyclic TPN, respectively. Filtered Ca load decreased slightly whereas renal tubular Ca reabsorption increased significantly with acetate. Serum parathyroid hormone, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and urinary cyclic AMP were not different.

Response of fractional calcium absorption in women to various coadministered oral glucose doses

Previous studies found an enhancing effect of glucose on fractional calcium absorption in humans but little information is available on the effect of different amounts of carbohydrate on Ca absorption. Thus, we studied the response of fractional Ca absorption to various loads of oral glucose coadministration with Ca in ten female subjects. After an overnight fast, 47Ca was administered orally on four occasions in solutions that contained varying doses of glucose (0 control, 56, 222, and 444 mmol). Seven of the ten subjects showed a positive response to glucose. In this group of responders there was a linear response to glucose between 0 and 222 mmol. No further increase was achieved at the higher dose of glucose. The response to 222 mmol glucose represented a 49% increase in Ca absorption compared with absorption without carbohydrate.

Traumatic abdominal hernia: a case report and review of the literature

Traumatic abdominal hernia remains a rare clinical entity despite an overall increase in blunt abdominal trauma. What appears to be the most extensive traumatic abdominal hernia so far described is presented. Traumatic abdominal herniae fall into three general categories: small lower quadrant abdominal defects and inguinal hernias, typically the result of blunt trauma with bicycle handlebars, are the most common; larger abdominal wall defects sustained in motor vehicle accidents are the next most common hernias; intra-abdominal herniations through rents in the retroperitoneum are rarely seen. The diagnosis may often be established with physical examination alone. Conventional radiology, computerized tomography, and ultrasound have also proven useful. Because of the high incidence of other associated intra-abdominal injuries, early exploration and repair through a midline incision is advocated. Adequate debridement and solid repair of fascial planes with non-absorbable sutures are required to prevent recurrence.

Glucose enhancement of transcellular calcium transport in the intestine

Glucose stimulates calcium transport in vitro in rat duodenal tissue and isolated enterocytes. Under short-circuited conditions, glucose increased mucosal to serosal calcium flux (JCa(m----s)) without altering serosal to mucosal calcium flux (JCa(s----m)) in the duodenum, the primary site of active calcium absorption in the rat small intestine. The half-maximal dose (ED50) of the glucose stimulatory effect was less than 1 mM, and an increase in JCa(m----s) of 80% over control was seen at a glucose concentration of 50 mM. Glucose did not increase calcium flux in the ileum where active calcium absorption is minimal. Glucose stimulated net calcium uptake by 35% in isolated duodenal enterocytes. Glucose did not alter calcium efflux from preloaded enterocytes suspended in calcium-free buffer. Glucose enhancement of net calcium uptake in enterocytes was not caused by altered cell membrane integrity or functional viability. The nonmetabolizable glucose analogue alpha-methylglucoside did not stimulate calcium transport. Our findings suggest that glucose can stimulate intestinal calcium absorption, at least partially, by enhancing transcellular calcium transport and that cellular glucose metabolism is necessary for stimulation of this route of calcium transport.

Effect of phosphorus on endogenous calcium losses during total parenteral nutrition

Intravenous phosphorus can reduce urinary calcium losses in patients receiving total parenteral nutrition (TPN). We investigated the effect of intravenous P on urinary and fecal Ca loss in intravenously fed normal and thyroparathyroidectomized (TPTX) rats to assess the role of parathyroid hormone (PTH) and endogenous fecal Ca losses. Doubling the intravenous P load during TPN decreased urinary Ca losses by 54% (0.299 vs 0.137 mmol/d) in intact rats and by 43% (0.514 vs 0.294 mmol/d) in TPTX rats. Increased P load in normal rats had no effect on urinary cyclic AMP excretion, serum Ca, serum P, serum 1,25-dihydroxycholecalciferol, or endogenous fecal Ca losses. These observations suggest that the hypocalciuric effect of P during TPN is independent of PTH and is not caused by a repartitioning of obligatory Ca losses from the renal to the intestinal route.

Effect of milk and lactose on zinc absorption in lactose-intolerant postmenopausal women

We evaluated the effect of lactose intolerance on intestinal zinc absorption under various test conditions in a group of postmenopausal women. Fractional zinc absorption was studied with a dual-isotope technique using 65Zn and 51Cr (as nonabsorbable fecal markers). We performed four absorption tests on sixteen subjects with water (control), whole cow milk, lactose-free cow milk and lactose alone. Mean (+/- SEM) fractional zinc absorption was 0.558 +/- 0.032 with water, 0.276 +/- 0.031 with milk, 0.246 +/- 0.028 with lactose-free milk and 0.564 +/- 0.051 with lactose. No significant differences in zinc absorption were found under any of the test conditions between lactose-tolerant and lactose-intolerant subjects. Milk and lactose-free milk significantly reduced zinc absorption in both groups.