Search PubMed⌕ Search

Biomedical subjects

D B Lee

Publications and source records attributed to D B Lee.

At least 73 records · Page 4Linked to original sources
PubMed1986

Jejunal phosphate transport is not regulated by the PTH-adenylate cyclase system. Further studies on the contrasting features between intestinal and renal phosphate transport mechanisms.

Direct application of parathyroid hormone (PTH) to renal proximal tubule in vitro stimulates the adenylate cyclase system which in turn causes reduction in phosphate (P) reabsorption. Similar application of parathyroid extract to rat jejunum fails to induce changes in P transport. In the present study we examined the basis for this PTH-unresponsiveness in rat jejunum. The effect of PTH, and another peptide hormone, salmon calcitonin (SCT) and sodium fluoride (NaF) on jejunal adenylate cyclase activity was first examined in both vitamin D-deficient (-D) rats and similar rats after 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] repletion. Jejunal cyclic 3',5'-AMP (cAMP, pmol/mg protein/min) increased from 11.0 +/- 1.1 in -D rats to 23.0 +/- 2.2 in 1,25(OH)2D3-repleted rats (p less than 0.001). Neither PTH nor SCT had any effect on adenylate cyclase activity in jejunum from either -D or 1,25(OH)2D3-repleted rats. NaF caused the anticipated stimulation in cAMP generation, a response independent of the vitamin D nutritional status of the animal [-D: 76.8 +/- 1,25(OH)2D3: 86.9 +/- 8.5]. We then examined the question if exogenous cAMP, which reduces renal P reabsorption, also causes decrease in intestinal P absorption. The effect of dibutyryl cAMP (DbcAMP) on transepithelial, net P absorption was examined in short-circuited jejunal epithelia from rats maximally stimulated by 1,25(OH)2D3. DbcAMP caused the anticipated increase in short-circuit current (+212%) without affecting the net, active P absorption. We conclude that, unlike the renal proximal tubule, the adenylate cyclase system in jejunum is insensitive to PTH, and the P absorptive mechanism is resistant to cAMP.

Adenylyl Cyclases↗
PubMed1985

Neurospora glucamylase and a mutant affected in its regulation.

Neurospora glucamylase is a glucose-repressible extracellular enzyme. The enzyme was purified to homogeneity and found to have a molecular weight of 82,000 and to release glucose from either maltose or amylose. The rate of glucamylase synthesis increases more than 100-fold when cells are transferred from a glucose-containing medium to a glucose-free medium. Increased from a glucose-containing medium to a glucose-free medium. Increased production of glucamylase begins within 30 min of the transfer. Glucamylase is rapidly secreted into the medium. A mutant affecting the ability of glucose to repress the synthesis of the glucose-repressible extracellular enzymes glucamylase and invertase has been isolated and studied. The mutant constitutively synthesizes and secretes a glucamylase which is indistinguishable from the wild-type enzyme.

Electrophoresis, Polyacrylamide Gel↗
PubMed1985

Neurospora trehalase and its structural gene.

We have isolated Neurospora trehalaseless mutants and mapped the trehalase structural gene to linkage group I. The structural gene mutations not only affect thermostability and other characteristics of the enzyme but also affect the production of an inhibitor of the wild-type trehalase. The inhibitor appears to be the mutant trehalase. We suggest that the mutant subunits act as inhibitors by entering into the multimeric forms of the enzyme and altering the ability of the normal wild-type subunits to catalyze the cleavage of trehalose.--Wild type trehalase has been purified to near homogeneity, and its characteristics have been studied. It was purified as a tetramer, with each subunit having a molecular weight of 88,000.--We have studied the regulation of trehalase and found the production of trehalase to be glucose repressible. Cells begin to produce trehalase 60 min after being transferred to glucose-free medium.

Genes↗
PubMed1984

Isolation of cells from rabbit renal proximal tubules by using a hyperosmolar intracellular-like solution.

A novel method of isolation of cells from rabbit kidney proximal tubules by using an intracellular-like solution (ICS) and gentle mechanical agitation in the absence of enzymes or chelators is described. Metabolic and functional characteristics of these cells were studied after washing and resuspension in modified Hanks medium, and the results were compared with those obtained in cells similarly prepared in extra-cellular-like solution (ECS). Trypan Blue exclusion and protein content were not different between the two preparations. However, oxygen consumption, ATP content and time- and concentration-dependent rates of uptake of phosphate, alpha-methyl glucoside and L-alanine were severalfold higher in cells prepared in ICS. Na+-dependent uptake of these solutes was 95% and 80% of total uptake in cells prepared in ICS and ECS respectively. Maximum transport rates (Tmax.) of phosphate, alpha-methyl glucoside and L-alanine were significantly higher in cells prepared in ICS. We propose that the use of ICS in the isolation procedure would yield a functionally more viable cell preparation, and therefore provides an ideal model for transport and metabolic studies at a cellular level.

Alanine↗
PubMed1984

Isolation and characterization of Neurospora mutants affected in invertase synthesis.

We have outlined a procedure that allows the large-scale screening of mutagenized Neurospora crassa populations for invertaseless mutants. We have isolated and characterized three mutations, inv(DBL1), inv(DBL9) and inv(DBL14), which have been mapped at or near the invertase structural gene. One of these, inv(DBL1), is particularly interesting. Our experiments indicate that the reduced level of invertase activity in the inv(DBL1)-containing cell can be explained as the result of a reduced number of normal enzyme molecules. We also show that wild-type Neurospora is able to respond rapidly to a change of medium and can dramatically increase its production of invertase within 20 min after a transfer to a carbon-free medium.

Chromosome Mapping↗
PubMed1983

A new low-molecular-weight calcium-binding ligand in rat small intestine.

Three calcium-binding ligands in the cytosol of rat small intestine have been separated using Sephadex G-75 column chromatography. The estimated molecular weights of these ligands were 85,000, 10,000, and 800, respectively. The two high-molecular-weight ligands were found only in young rats, while the low-molecular-weight calcium-binding ligand was found in all age groups and appeared to be a calcium-bound prostaglandin metabolite. Oral administration of arachidonic acid increased and PGE2 decreased in vivo calcium absorption, while PGF2 administration showed no discernible effect on this parameter. These results suggest that the intestinal calcium transport mechanism may be modulated by prostaglandins and related metabolites.

Aging↗
PubMed1983

Preliminary trials with 24,25-dihydroxyvitamin D3 in dialysis osteomalacia.

Fifteen patients with dialysis osteomalacia were treated with 24,25-dihydroxyvitamin D3 in dosages up to 10 micrograms per day for two to 24 months. All had previously had no improvement during treatment with calcitriol but had been remarkably susceptible to hypercalcemia. When 24,25-dihydroxyvitamin D3 was given with either calcitriol or dihydrotachysterol, serum calcium levels were significantly lower than during treatment with calcitriol or dihydrotachysterol alone. Eight of nine patients who received combined therapy with 24,25-dihydroxyvitamin D3 and calcitriol for longer than two months had clinical improvement; six patients underwent repeated bone biopsy and showed evidence of improved bone mineralization. Patients who received 24,25-dihydroxyvitamin D3 alone did not improve clinically. Since 24,25-dihydroxyvitamin D3 appears to improve calcium homeostasis and bone mineralization in some patients with severe dialysis osteomalacia when administered with 1-hydroxylated vitamin D metabolites, further controlled studies are warranted.

24,25-Dihydroxyvitamin D 3↗
PubMed1983

Unanticipated stimulatory action of glucocorticoids on epithelial calcium absorption. Effect of dexamethasone on rat distal colon.

UNLABELLED: We studied the action of a glucocorticoid (GC, dexamethasone) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on transepithelial calcium (Ca) transport in rat distal colon. GC 1.2 mg or 1,25(OH)2D3 270 ng were given daily for 4 d and Ca fluxes were measured in vitro in the absence of electrochemical gradients (Ussing technique). RESULTS: (a) Both 1,25(OH)2D3 and GC increased Ca absorptive flux from 24 +/- 3 (SEM) to 50 +/- 1 and from 23 +/- 1 to 38 +/- 4 nmol/cm2 per h, respectively (in each case n = 9, P less than 0.01); both steroid hormones had no effect on Ca secretory flux. (b) GC, but not 1,25(OH)2D3 increased the short-circuit current Isc) from 30 +/- 5; to 111 +/- 13 microA/cm2 (P less than 0.01), reflecting stimulation of electrogenic sodium (Na) transport. Choline replacement of Na in the bathing buffer abolished both the Isc and the active Ca transport induced by GC, but has no effect on the 1,25(OH)2D3-stimulated active Ca absorption. (c) When the buffer Ca concentration ([Ca]) on both sides of the epithelium was reduced from 1.25 to 1.25 X 10(-2) mM, the GC-induced, but not the 1,25(OH)2D3-induced, stimulation in Ca absorption was abolished. This suggests that the GC-stimulated Ca absorption may require a "threshold" Ca gradient across the luminal membrane through which Ca influx occurs. Thus, contrary to the current consensus, this study demonstrates that GC stimulates active Ca transport and that this action is mediated through a mechanism dependent on the presence of Na and a critical [Ca] in the ambient medium.

Analysis of Variance↗
PubMed1981

Intestinal and metabolic effect of 1,25-dihydroxyvitamin D3 in normal adult rat.

We examined the effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on intestinal 45Ca and [32P]phosphate uptake in normal and mineral- and vitamin D-replete adult rats. The results indicate that 45Ca uptake by adult rat duodenum was stimulated by "physiological" doses of 1,25(OH)2D3. With increasing dosage of 1,25(OH)2D3, 45Ca uptake also became stimulated first in the colon and then in the jejunum and ileum. The increase in duodenal and jejunal 45Ca uptake was paralleled by an increase in [32P]phosphate uptake, but this parallelism was not always seen in the ileum and was never observed in the colon. The dissociated calcium and phosphate transport response to 1,25(OH)2D3 stimulation in the colon was further confirmed by the measurement of transmural fluxes using a modified Ussing technique. These responses to 1,25(OH)2D3 are similar to those observed in younger vitamin D-deficient rats. However, supraphysiological doses of 1,25(OH)2D3 caused weight loss in normal adult rats, whereas the same metabolite, even when given in large doses, led to weight gain in vitamin D-deficient rats. We propose the normal adult rat as an additional model for evaluating the biological action of 1,25(OH)2D3.

Animals↗
PubMed1981

Vitamin-D-resistant osteomalacia in hemodialysis patients lacking secondary hyperparathyroidism.

We describe a sporadic, vitamin-D-resistant osteomalacic syndrome in 19 patients undergoing hemodialysis. The syndrome was found in less than 1.5% of patients from referring dialysis centers. All 19 patients had multiple fractures, severe myopathy, and many developed spontaneous hypercalcemia. Severe osteomalacia without evidence of secondary hyperparathyroidism distinguished this syndrome from other forms of renal osteodystrophy. Bone aluminum, measured in six patients, was greatly elevated. Therapy with calcitriol (1 alpha, 25-dihydroxycholecalciferol) lad to clinical improvement in seven patients with reduced pain and myopathy, decreased serum alkaline phosphatase, or both, but no improvement in bone histology. Patients who did not respond clinically to calcitriol developed marked hypercalcemia. The cause of this severe osteomalacia, which occurs despite normal or slightly elevated levels of serum calcium and phosphorus and fails to mineralize with calcitriol, is unclear.

Adult↗
PubMed1980

Role of growth hormone in experimental phosphorus deprivation in the rat.

The demands of growth are known to exacerbate the effect of phosphorus deprivation (PD). We examined whether changes associated with PD could be prevented in young rats in which growth and growth hormone (GH) were eliminated by hypophysectomy (HPX) and whether PD in normal intact rats (INT) was associated with increased secretion of GH. INT or thyroxine- and ACTH-replaced HPX rats were fed one of the three diets: 0.31% P (NP); 0.027% P (LP), and 0.31% P, pair-fed with LP-mates (NP-PF). The results indicate that HPX did not qualitatively alter several physiologic responses to PD: (a) serum and urinary phosphorus (P) decreased and urinary calcium (Ca) increased; (b) net intestinal Ca retention fell and duodenal sac uptake of 45Ca rose; and (c) external P balance was restored and duodenal sac uptake of 32P-phosphate increased. Only the hypercalcemia seen in INT, LP rats was prevented by HPX. In INT rats serum immunoassayable GH levels, measured in single samples, were not different between different dietary groups while pituitary bioassayable GH was reduced in both LP and NP-PF rats when compared to the NP rats. Thus, except for hypercalcemia, the physiologic responses associated with PD are not prevented by the elimination of growth and GH, and the development of these responses in INT rats was not associated with a consistent or specific alteration in GH secretion.

Animals↗
PubMed1980

The diagnostic and therapeutic uses of saralasin in renal transplant hypertension.

Saralasin was used as a functional test of the renin-angiotensin axis in 4 renal transplant patients with hypertension. Blood pressure was recorded by an automatic recording device and plasma renin activity was measured by radioimmunoassay of angiotensin I. A positive saralasin test suggested renin-mediated hypertension despite normal peripheral renin levels in a 40-year-old man whose original kidney disease was nephrosclerosis. Since the blood pressure was refractory to intravenous sodium nitroprusside saralasin was used for 14 hours to control blood pressure before and after arteriography in the patient. Removal of the native kidneys markedly ameliorated the hypertension. A 35-year-old woman with transplant hypertension was responsive to angiotensin blockade only during a period of abrupt worsening of blood pressure associated with an acute rejection episode. Finally, 2 patients with advanced chronic rejection responded to saralasin administration. These studies confirm that 1) angiotensin blockade is a useful tool in the diagnosis of renin-dependent hypertension even when plasma renin levels are not elevated, 2) saralasin can be used to control renin-dependent forms of hypertension that are refractory to intravenous sodium nitroprusside therapy and 3) transplant hypertension associated with acute and chronic rejection appears to be renin-dependent.

Adult↗
PubMed1980

Effects of vitamin D and diet magnesium on magnesium metabolism.

Effects of 6-9 days of vitamin D3 (D3), 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], 24,25-dihydroxyvitamin D3 [24,25(OH)2D3], or 1,24,25-trihydroxyvitamin D3 [1,24,25(OH)3D3] on Mg metabolism were studied in vitamin D-deficient (-D) rats. Mg absorption expressed as percent intake increased with 1,25(OH)2D3 and 1,24,25(OH)3D3. Urinary Mg (UMg) increased with no change in serum Mg (SMg) or Mg balance. 1,25(OH)2D3 was threefold more potent than 1,24,25(OH)3D3 in raising serum Ca and Mg absorption. In a separate experiment in pair-fed rats given D3, 1,25-(OH)2D3, or 1,24,25(OH)3D3, the diet contained either 0.03 or 0.2% Mg; 1,25(OH)2D3 and D3 lowered SMg after 3 days; UMg increased after 24 h to remain elevated. D3 and 1,25(OH)2D3 augmented Mg absorption; feeding 0.2% Mg lowered Mg absorption in -D animals. All sterols augmented Mg absorption in -D rats; both the earlier action of 1,25(OH)2D3 and 1,24,25(OH)3D3 suggests that 1-hydroxylation is necessary. Suppressed Mg absorption with 0.2% Mg in -D rats suggests two transport processes, with one vitamin D dependent. Higher UMg with decreased SMg with 1,25(OH)2D3 suggests reduced tubular reabsorption.

Animals↗
PubMed1980

Effect of metabolic acidosis in intestinal absorption of calcium and phosphorus.

To investigate the effect of metabolic acidosis on intestinal calcium (Ca) and phosphorus (P) absorption and vitamin D metabolism, metabolic balance studies and in vitro gut sac uptake of 45Ca and [32P]phosphate were performed in rats maintained on low-Ca and moderately low-P diet and fed NH4Cl for 3 or 9 days and pair-fed controls. Plasma 1,25(OH)2D concentration was measured in the rats fed NH4Cl for 9 days and their controls. Net Ca and P absorption was 87-92% in the acidotic rats and did not differ from control. Moreover, gut sac uptakes of 45Ca and [32P]phosphate were not different from control. Plasma 1,25(OH)2D was higher in the ammonium chloride-fed rats than in controls (213 +/- 44 vs. 110 +/- 12 pg/ml), and serum P was lower in the acidotic animals (4.6 +/- 0.7 vs. 7.6 +/- 0.3 mg/dl). These data indicate that metabolic acidosis does not depress the augmented intestinal absorption of calcium and phosphorus noted during their dietary deprivation nor reduce the plasma level of 1,25(OH)2D.

Acid-Base Equilibrium↗
PubMed1980

Calcium and inorganic phosphate transport in rat colon: dissociated response to 1,25-dihydroxyvitamin D3.

In the small intestine, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] stimulates both calcium (Ca) and inorganic phosphate (Pi) absorption. This is mediated through an increase in mucosal-to-serosal flux (Jms) whereas the serosal-to-mucosal flux (Jsm) remains unchanged. We now report that in rat proximal colon, 1,25(OH)(2)D(3) produces active Ca absorption without affecting Pi transport, and that this induced active Ca absorption is associated with alterations in kinetics of both Jms and Jsm so that both processes demonstrate saturable components. Vitamin D-deficient rats were given daily injections of solvent (-D) or 270 ng 1,25(OH)(2)D(3) (+D) for 3 d. (45)Ca and [(32)P]phosphate fluxes were measured employing the Ussing technique using a modified Krebs-Ringer-HCO(3) buffer ([Ca] 1.25, [Pi] 1.18, [glucose] 11 mM). In -D rats there was no net flux (Jnet) of either Ca or Pi. In +D rats net active Ca absorption was observed (-D = 3.3 nmol/cm(2) per h +/-3.4 (SEM); +D = 27.3 +/-3.8, n = 11, P < 0.001) whereas Pi transport was unchanged, i.e., still no Jnet. Pi Jms was not different from Pi Jsm measured at the following buffer [Pi]: 0.0118, 0.118, 1.18, and 2.36 mM. Ca saturation kinetics were estimated using buffer [Ca] from 0.0125 to 5.0 mM. Saturable processes were demonstrated for both Jms and Jsm. Jnet for Ca across colon from +D rats exhibited saturation at [Ca] > 3 mM, with an estimated V(max) of 44.0 nmol/cm(2) per h and a K(m) of 0.9 mM. This colonic model may provide a useful system for studying 1,25(OH)(2)D(3)-induced molecular events related to Ca but not Pi transport. The apparent action of 1,25(OH)(2)D(3) on Ca secretory process may furnish new insights into the mechanism of action of vitamin D.

Animals↗
PubMed1980

Kidney stones.

The prevalence of kidney stones has steadily risen during this century; passage of a calculus and a positive family history increase the probability of recurrence. Findings from recent studies on the cause of renal calculi have stressed crystallization and crystal aggregation of stone minerals from supersaturated urine, rather than excessive organic matrix. Absence of normal urine inhibitors of calcium salts is also stressed. Formation of calcium oxalate stones is the major problem. Therapy with decreased calcium and oxalate intake, thiazides, phosphate salts and allopurinol in various combinations has substantially decreased the prevalence of recurrent stones. The rationale for the use of allopurinol is that uric acid salts enhance the tendency for calcium oxalate to crystallize from supersaturated urine. The hypercalciuria seen in 30 percent to 40 percent of patients with oxalate stones is usually caused by intestinal hyperabsorption of calcium. Although patients with uric acid calculi constitute only a small fraction of those in whom stones form, they represent a group in whom good medical therapy, based on sound physiologic principles, has proved extremely successful. Renal tubular syndromes lead to nephrocalcinosis and lithiasis through hypercalciuria, alkaline urine and hypocitraturia, the latter an inhibitor of calcium salt precipitation. Recent advances in surgical techniques are discussed, including the rationale for removing staghorn calculi. The ileal ureter and coagulum pyelolithotomy deserve special emphasis.

Acidosis, Renal Tubular↗