Effect of Magnesium Depletion on Responsiveness to Parathyroid Hormone in Parathyroidectomized Rats

Hypocalcemia and resistance to exogenous parathyroid hormone have been reported in several clinical states associated with magnesium deficiency. On the basis of such observations, it has been suggested that magnesium depletion per se may result in impaired responsiveness of the adenyl cyclase-adenosine 3',5'-monophosphate (3',5'-AMP) system. To test this hypothesis, 4 wk old male parathyroidectomized rats were maintained on normal or magnesium-deficient diets for 4 wk and their responses to parathyroid hormone compared.Serum magnesium and calcium fell progressively in the magnesium-deficient group. Despite clinical and biochemical evidence of severe magnesium deficiency in these animals, renal production and excretion of 3',5'-AMP in response to parathyroid hormone was normal both in vitro and in vivo. Additionally, administration of either dibutyryl 3',5'-AMP or parathyroid extract to fasting magnesium-depleted rats produced a normal increase in serum calcium. Parathyroid hormone infusion studies demonstrated normal renal and skeletal responsiveness as measured by urinary excretion of calcium, magnesium, phosphate, and hydroxyproline. These data show that the effect of parathyroid hormone on 3',5'-AMP formation and excretion, the responsiveness of skeletal tissue to 3',5'-AMP, and the renal and skeletal system responses to parathyroid hormone are not altered by pure magnesium deficiency in the parathyroidectomized rat.     

Cardiac and Renal Prostaglandin I2: BIOSYNTHESIS AND BIOLOGICAL EFFECTS IN ISOLATED PERFUSED RABBIT TISSUES

Both the isolated perfused rabbit heart and kidney are capable of synthesizing prostaglandin (PG) I(2). The evidence that supports this finding includes: (a) radiochemical identification of the stable end-product of PGI(2), 6-keto-PGF(1alpha), in the venous effluent after arachidonic acid administration; (b) biological identification of the labile product in the venous effluents which causes relaxation of the bovine coronary artery assay tissue and inhibition of platelet aggregation; and (c) confirmation that arachidonic acid and its endoperoxide PGH(2), but not dihomo-gamma-linolenic acid and its endoperoxide PGH(1), serve as the precursor for the coronary vasodilator and the inhibitor of platelet aggregation. The rabbit heart and kidney are both capable of converting exogenous arachidonate into PGI(2) but the normal perfused rabbit kidney apparently primarily converts endogenous arachidonate (e.g., generated by stimulation with bradykinin, angiotensin, ATP, or ischemia) into PGE(2); while the heart converts endogenous arachidonate primarily into PGI(2). Indomethacin inhibition of the cyclo-oxygenase unmasks the continuous basal synthesis of PGI(2) by the heart, and of PGE(2) by the kidney. Cardiac PGI(2) administration causes a sharp transient reduction in coronary perfusion pressure, whereas the intracardiac injection of the PGH(2) causes an increase in coronary resistance without apparent cardiac conversion to PGI(2). The perfused heart rapidly degrades most of the exogenous endoperoxide probably into PGE(2), while exogenous PGI(2) traverses the heart without being metabolized. The coronary vasoconstriction produced by PGH(2) in the normal perfused rabbit heart suggests that the endoperoxide did not reach the PGI(2) synthetase, whereas the more lipid soluble precursor arachidonic acid (exogenous or endogenous) penetrated to the cyclooxygenase, which apparently is tightly coupled to the PGI(2) synthetase.     

Effects of Parathyroid Hormone on Skeletal Muscle Protein and Amino Acid Metabolism in the Rat

Because prominent skeletal muscle dysfunction and muscle wasting are seen in both chronic uremia and in primary hyperparathyroidism, and because markedly elevated parathyroid hormone levels occur in both disorders, potential effects of parathyroid hormone on skeletal muscle protein, amino acid, and cyclic nucleotide metabolism were studied in vitro using isolated intact rat epitrochlearis skeletal muscle preparations. Intact bovine parathyroid hormone and the synthetic 1-34 fragment of this hormone stimulated the release of alanine and glutamine from muscle of control but not from chronically uremic animals. This stimulation was dependent upon the concentration of parathyroid hormone added: At 10⁵ ng/ml parathyroid hormone increased alanine release 84% and glutamine release 75%. Intracellular levels of alanine and glutamine were not altered by parathyroid hormone. Increasing concentrations of the 1-34 polypeptide decreased [³H]leucine incorporation into protein of muscles from both control and uremic animals. Using muscles from animals given a pulse-chase label of [guanido-¹⁴C]arginine in vivo, parathyroid hormone increased the rate of loss of ¹⁴C label from acid-precipitable protein during incubation and correspondingly increased the rate of appearance of this label in the incubation media. Parathyroid hormone increased muscle cAMP levels by 140% and cGMP levels by 185%, but had no effect on skeletal muscle cyclic nucleotide phosphodiesterase activities as assayed in vitro. Adenylyl cyclase activity in membrane preparations from control but not uremic rats was stimulated by parathyroid hormone in a concentration-dependent fashion. However, no stimulation of guanylyl cyclase activity was noted by parathyroid hormone, although stimulation by sodium azide was present. Incubation of muscles with added parathyroid hormone produced a diminished responsiveness towards epinephrine or serotonin regulation of amino acid release and cAMP formation in the presence compared to the absence of parathyroid hormone. In the absence of parathyroid hormone, detectable inhibition of alanine and glutamine release was produced by 10⁻⁹ M epinephrine, whereas in the presence of parathyroid hormone (1,000 ng/ml) inhibition of alanine and glutamine release required 10⁻⁶ M or greater epinephrine. Resistance to cyclic AMP action as well as inhibition of cyclic AMP formation by parathyroid hormone was found. Preincubation of rat sarcolemma with 1-34 parathyroid hormone produced a decreased activity of the isoproterenol-stimulable adenylyl cyclase activity but there was no apparent change in the concentration of isoproterenol required for one-half maximal and maximal stimulation of the enzyme.     

Pathogenesis of Hypocalcemia in Primary Hypomagnesemia: Normal End-Organ Responsiveness to Parathyroid Hormone, Impaired Parathyroid Gland Function

Hypocalcemia is a frequent feature of hypomagnesemia in man and several other species. To elucidate the cause of this hypocalcemia, we have studied a child with primary hypomagnesemia and secondary hypocalcemia during magnesium supplementation when he was normomagnesemic and normocalcemic and after magnesium restriction for 16 days when he quickly became hypomagnesemic (0.5 meq/liter) and hypocalcemic (3.4 meq/liter) and had positive Chvostek's and Trousseau's signs.     

Very Low Density Lipoprotein: METABOLISM OF PHOSPHOLIPIDS, CHOLESTEROL, AND APOLIPOPROTEIN C IN THE ISOLATED PERFUSED RAT HEART

The fate of rat plasma very low density lipoprotein (VLDL) constituents was determined in the isolated perfused rat heart. VLDL was labeled with [(14)C]palmitate, (32)P-phospholipids, [(3)H] cholesterol, and (125)I-apolipoprotein C (apoC). Perfusions were performed with an albumin-containing buffer and without plasma. Radioactivity was followed in fractions of d < 1.019, d 1.019-1.04, d 1.04-1.21, and d > 1.21 g/ml, prepared by ultracentrifugation.VLDL triglycerides were progressively hydrolyzed to fatty acids (10-120-min perfusions). Concomitantly, phospholipids, cholesterol (predominantly unesterified), and apoC were removed from the VLDL to all other fractions. About 30-35% of the phosphatidylcholine was hydrolized to lysophosphatidylcholine and was recovered at d > 1.21 g/ml. The phosphatidylcholine-and triglyceride-hydrolyzing activities were confined to membrane supported enzyme(s). The other 60-65% of the phosphatidylcholine was removed unhydrolyzed and was found in fractions of d 1.019-1.04 (10-15%), d 1.04-1.21 (25-30%), and d > 1.21 g/ml (15-20%). [(32)P]Sphingomyelin accumulated at the fraction of d 1.04-1.21 g/ml. Unesterified cholesterol was found in the fraction of d 1.04-1.21 g/ml. ApoC was recovered predominantly in fractions of d 1.04-1.21 (50-60%) and d > 1.21 g/ml (30-40%). Cholesteryl esters were associated with VLDL during the hydrolysis of 50-70% of the triglycerides, but with advanced lipolysis, appeared in higher densities, mainly d 1.019-1.04 g/ml.The fraction of d 1.04-1.21 g/ml, (containing phosphatidylcholine, sphingomyelin, unesterified cholesterol, and apoC) contained by negative staining, many disk-like structures.The study demonstrated that removal of surface constituents (phospholipids, unesterified cholesterol, and apoC) during lipolysis of VLDL is an intrinsic feature of the lipolytic process, and is independent of the presence of plasma. It also indicated that surface constituents may be removed in a particulated form.     

Resistance to the Phosphaturic and Calcemic Actions of Parathyroid Hormone during Phosphate Depletion: PREVENTION BY 1,25-DIHYDROXYVITAMIN D3

Recent observations indicate that in thyroparathyroidectomized (TPTX) rats fed a low (0.2 g/100 g) phosphorus diet, the tubular phosphaturic response to parathyroid hormone (PTH) remains markedly blunted even when it is assessed at normal or high plasma concentration and filtered load of inorganic phosphate (Pi). Because 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] decreases the tubular capacity to reabsorb Pi when chronically administered to TPTX rats, we have studied whether this vitamin D(3) metabolite could specifically increase the phosphaturic response to PTH in phosphate-deprived animals. The results show that in Vitamin D-replete TPTX rats fed a low (0.2 g/100 g) phosphorus diet, 1,25(OH)(2)D(3) (2 x 13 pmol/d i.p. for 7 d) markedly enhanced the acute tubular phosphaturic response to PTH (2.5 IU/h i.v.) without affecting the action of the peptide hormone on Ca reabsorption and cyclic-3',5'-AMP excretion. The influence of 1,25(OH)(2)D(3) on the phosphaturic response to PTH could not be ascribed to an increased plasma concentration and(or) filtered load of Pi during the administration of the peptide hormone. However, it could be, at least in part, related to the elevation in the basal level of plasma Pi which was observed in the 1,25(OH)(2)D(3)-treated animals. The results also indicate that 1,25(OH)(2)D(3) significantly enhanced the calcemic response to PTH, which was blunted in these conditions of phosphate deprivation. Unlike 1,25-(OH)(2)D(3), 25-hydroxyvitamin D(3) did not unmask the phosphaturic effect of PTH in phosphate-depleted animals, even when given in doses 100 times larger. Thus, 1,25(OH)(2)D(3) displays a selective and powerful activity in preventing the occurrence of tubular resistance to the phosphaturic action of PTH during Pi depletion. This finding suggests the existence of an important interaction between dietary Pi, 1,25(OH)(2)D(3), and PTH in the homeostasis of phosphate.     

Parathyroid Hormone Responses to Catecholamines and to Changes of Extracellular Calcium in Cows

Modifications of the plasma level of immunoreactive parathyroid hormone (PTH) in cattle were induced by changes of the plasma concentrations of epinephrine, isoproterenol, or calcium.During abrupt hypocalcemia, PTH, obtained by infusions with ethylene glycol-bis (beta-aminoethylether) N, N'-tetraacetate (EGTA), increased during the first 4-8 min. After a transient decline, the hormone levels rose again and remained elevated. Infusions of calcium suppressed the hypocalcemia-induced augmentation of PTH levels within a few minutes. Prolonged epinephrine (and isoproterenol) infusions also rapidly increased PTH levels, however, in this case, they returned to basal concentrations after 50-60 min. Additional epinephrine infusions could not further raise PTH values. Moreover, three short-lasting infusions of epinephrine (7 min each), given at 30-min intervals, increased PTH levels to the same extent, whereas additional infusions were much less effective. The PTH response to epinephrine was completely restored, when the interval after a prolonged epinephrine infusion had been prolonged to > 100 min. During moderate hypocalcemia, occurring at the end of EGTA infusions and lasting for 90 min, the PTH response to a short-lasting epinephrine infusion (7 min) was more pronounced than in normocalcemic animals. During severe hypocalcemia, in which superimposed short-lasting infusions of EGTA (7 min) led to an additional abrupt fall of plasma calcium concentrations but not to a corresponding additional rise of the PTH levels, epinephrine rapidly and further increased PTH concentrations. On the other hand, at the end of prolonged infusions of epinephrine, when additional infusions of epinephrine were ineffective in raising PTH levels, EGTA-induced hypocalcemia consistently increased PTH concentrations. The EGTA-induced augmentation of PTH levels was enhanced by epinephrine and isoproterenol but not by propranolol.The present findings indicate, that variations of the extracellular calcium concentrations and beta-adrenergic agonists modify PTH levels by two different and independent mechanisms. On the other hand, it appears that the magnitude of change of the PTH levels to either stimulus is partially modulated by exposure to the other.     

Parathyroid Hormone in Human Plasma: IMMUNOCHEMICAL CHARACTERIZATION AND BIOLOGICAL IMPLICATIONS

Antigenic recognition of four anti-bovine parathyroid hormone antisera was characterized by their reactivity with bovine hormonal fragments (1-34, 1-13, 14-34, 19-34, 53-84) and human hormone extracted from parathyroid adenomas. All antisera were found to have antibody populations which recognized more than one antigenic determinant and all antisera differed in their specificity and reactivity for the fragments of bovine hormone. By modification of two antisera, GP-1 and GP-133, by preincubation with excess concentrations of 1-34 or 53-84 fragments, antigenic recognition was restricted to defined regions of the hormonal sequence.     

The Pathogenesis of Idiopathic Hypercalciuria: Evidence for Parathyroid Hyperfunction

We studied the effect of calcium deprivation and loading in17 healthy subjects and 76 patients with renal calculi. Fivehad primary hyperparathyroidism with an elevated plasma ionisedcalcium and detectable plasma parathyroid hormone. Forty-ninehad idiopathic hypercalciuria, defined by a urine calcium greaterthan 7 mmol/day on a free diet. Twenty-two were normo-calciuric.Fasting plasma calcium, corrected for albumin, was higher inthe patients with idiopathic hypercalciuria (2.40±0.10mmol/1) than in controls (2.28 ±0.05 mmol/1, p < 0.005).Plasma calcium was intermediate in the normocalciuric stoneformers (2.35 ±0.08 mmol/1) and elevated in the patientswith primary hyperparathyroidism (2.62 ± 0.07 mmol/1).Nephrogenous cyclic adenosine monophosphate (cAMP) and parathyroidhormone levels were highest in the primary hyperparathyroidgroup and did not differ significantly within the other groups.Nephrogenous cAMP correlated positively with plasma calciumin the patients with primary hyperparathyroidism and negativelyin controls; there was no correlation in the idio-pathic hypercalciuriagroup. Following an oral calcium load, plasma calcium rose andnephro-genous cAMP fell similarly in all groups. Fasting urinarycalcium and its increase after load were greatest in the idiopathichypercalciuria and primary hyperparathyroid groups, with inter-mediateresults in the normocalciuric patients. Neither the initialmetabolic patterns nor the response to thiazide fitted withthe previously described patterns of absorptive and renal hypercalciuria.Increased parathyroid gland activity is the most probable causeof idiopathic hypercalciuria.     

甲状旁腺激素预防和治疗绝经后骨质疏松症疗效的系统评价

目的系统评价甲状旁腺激素（PTH）预防和治疗绝经后骨质疏松症的疗效和安全性。方法计算机检索MEDLINE（1966～2008．3）、EMBASE（1974—2008．3）、Cochrane图书馆临床试验资料库（2008年第1期）、Current Controlled Trials、The National Reseach Register、中国生物医学文献数据库（1983—2008．3）、中国期刊全文数据库（1994～2008．3），并手工检索相关领域其它杂志。检索不受语种限制，时间截至2008年3月。纳入以患原发性质疏松症或骨量减少的绝经后女性为研究对象、比较甲状旁腺激素与其它疗法疗效的随机对照试验，评价纳入研究的质量，并用RevMan4．2．10软件进行Meta分析。结果共纳入12个随机对照试验，包括5550例患者。Meta分析结果显示：PTH单用或与其它药物联用与对照组比较，减少椎体骨折风险达66％[RR=0．34，95％CI（0．26，0．45），P〈0．00001]；增加腰椎[SMD=0．41，95％CI（0．19，O．63），P=0．0003]和股骨颈[SMD=0．19，95％CI（0．10，0．28），P〈0．0001]的骨密度优于对照组。PTH发生副作用导致的退出和失访多于对照组[Peto—OR=1．69，95% CI（1．39，2．05），P〈0．00001]。结论PTH预防和治疗绝经后骨质疏松症疗效肯定，能提高腰椎及股骨颈的骨密度，降低椎体骨折的风险。PFH对绝经后骨质疏松症的疗效优于阿伦磷酸盐，但不宜和阿伦磷酸盐联合使用，骨量严重低下和有骨质疏松性骨折的绝经后女性是PTH较适合的人群。     

Experimental Membranous Glomerulonephritis in Rats: QUANTITATIVE STUDIES OF GLOMERULAR IMMUNE DEPOSIT FORMATION IN ISOLATED GLOMERULI AND WHOLE ANIMALS

Quantitation of immune deposit formation in glomeruli and correlation with immunohistologic and functional changes has been accomplished only in models of anti-glomerular basement membrane antibody-induced nephritis, or indirectly in immune complex disease by measuring radiolabeled antigen deposition. The kinetics of subepithelial immune deposit formation and the relationship between the quantity of antibody deposited and proteinuria are defined here for the first time in an established model of membranous immune complex nephritis (passive Heymann nephritis) induced by a single intravenous injection of ¹²⁵I-labeled sheep immunoglobulin (Ig)G antibody to rat tubular brush border antigen (Fx1A). Measurement of antibody deposition in glomeruli (GAb) isolated from rats injected with 10 mg of anti-Fx1A demonstrated a mean of 12 μg GAb in 4 h, which increased linearly to 48 μg in 5 d. GAb represented only 20 and 44% of total kidney antibody binding at these times. Proteinuria occurred only after 4-5 d of antibody deposition in rats with total kidney antibody binding exceeding ~200 μg/2 kidneys. Steroid treatment and vasoactive amine blockade did not significantly alter the quantity or localization of immune deposits. It was also demonstrated that isolated rat glomeruli specifically bound nephritogenic quantities of anti-Fx1A in vitro within hours. Analysis of the quantitative aspects of glomerular antibody deposition in vivo and glomerular antibody binding in vitro provides additional evidence that subepithelial immune deposits in passive Heymann nephritis may form in situ by reaction of free antibody with antigenic constitutents of the normal rat glomerulus. The observed kinetics of deposit formation differ markedly from those in anti-glomerular basement membrane disease and suggest a role for factors in addition to antigen-antibody interaction in determining this unique pattern of glomerular immune deposit formation.     

精氨酸与可乐定激发试验对儿童生长激素缺乏症的诊断价值

目的 评价生长激素（GH） 精氨酸与可乐定激发试验对儿童生长激素缺乏症（GHD）的诊断价值.方法 选取166例身材矮小患儿,均符合身材矮小诊断标准,无骨代谢、糖尿病等其他内分泌代谢疾病.对患儿均进行GH精氨酸与可乐定激发试验,采用化学发光法进行GH检测.以激发试验后测得的GH最高值为峰值,峰值≥10 μg/L为GH不缺乏,激发试验阳性;10 μg/L〉峰值≥5 μg/L为GH部分缺乏;峰值〈5 μg/L者为GH完全缺乏,激发试验均为阴性.结果 激发试验的阳性率精氨酸为9.0%（15/166）,可乐定为31.3%（52/166）,而精氨酸＋可乐定为36.1%（60/166）.精氨酸激发的峰值多出现在30 min（100/166）,可乐定激发的峰值出现在60～90 min（153/166）,两种药物GH激发试验显示GH完全缺乏的为24.1%（40/166）.结论 可乐定激发试验阳性率优于精氨酸激发试验,两种药物激发试验联合使用将提高GH缺乏症诊断的准确性.     

STUDIES ON ORGANOGENESIS : I. THE ABILITY OF ISOLATED BLOOD CELLS TO FORM ORGANIZED VESSELS IN VITRO

1. Isolated blood cells, when placed for incubation in a plasma substratum, are capable of constructing highly organized, tubular processes that project from the explanted cell mass into the surrounding medium. 2. The tubular structures have fibrillar walls that may be covered, eventually, by a membranous layer of leukocytes. Their lumina contain blood cells suspended in fluid. 3. The formation of the tubules is initiated by the red cells. The leukocytes, and more particularly the thrombocytes, are responsible for the construction of the walls. 4. The phenomenon occurs only in the presence of plasma, the coagulation of which has been slightly delayed. Once the surrounding medium has become firmly coagulated, no further change occurs either in the length of the tubules or in their diameter. 5. The development of the tubules is not suppressed by substances that enhance cellular activity unless they induce, at the same time, the immediate coagulation of the medium. The addition of embryo tissue juice prevents their formation by producing early coagulation. 6. The phenomenon as a whole is dependent upon the physicochemical nature of the medium, the character and thickness of the explanted fragment, and the physical and physiological peculiarities of the cells that comprise it. It is the expression of various physicochemical and physiological events that have occurred in a definite order, or sequence.     

The Acute Parathyroid Hormone Response to Changes in Ionized Calcium during Phosphate Infusions in the Cow

Abstract. The concentration of plasma immunoreactive parathyroid hormone ([IPTH]) increased within one minute after the plasma ionized calcium concentration ([Ca⁺⁺]) had been lowered by phosphate infusions in 8 cows. The decrease in [Ca++] could be accounted for by a rise in nonultrafiltrable calcium. The plasma total calcium concentration ([CaTot]) remained unchanged during the first 4 minutes of the phosphate infusion. Until this time [IPTH] was inversely related to [Ca⁺⁺] and directly related to plasma phosphorus concentrations, but not to [CaTot]. Peak levels of [IPTH] were attained at 4 minutes, before the nadir of [Ca⁺⁺] was reached and prior to a significant fall in [CaTot]. The data suggest that initial decreases in ionized but not in total calcium stimulate parathyroid hormone secretion. They provide evidence for a model of parathyroid hormone secretion which includes a small storage pool available for immediate release in response to a lowering of the [Ca++]. Between 4 and 12 minutes [IPTH] remained approximately constant in association with a continued fall in [Ca^], whereas between 13 and 16 minutes (the end of the phosphate infusions) [IPTH] was decreasing in association with still falling [Ca++]. It can be speculated that the synthesis of PTH is insufficient to account for a sustained increase in [IPTH], or that abrupt decreases of [Ca⁺⁺] inside the parathyroid cells inhibit the secretion coupling mechanisms. Finally after 16 minutes [IPTH] continued decreasing in relation to the rising [Ca⁺⁺].     

Susceptibility of Enterobacter to Cefamandole: Evidence for a High Mutation Rate to Resistance

Cefamandole minimum inhibitory concentrations (MICs) of 10 strains of Enterobacter were determined by the ICS agar dilution and broth dilution procedures. Agar dilution MICs ranged from 1 to 8 μg/ml, with an inoculum of 10⁴ organisms/spot. Broth dilution MICs were consistently higher, with an inoculum of approximately 7 × 10⁵ organisms/ml. Seven strains showed MICs of ≥64 μg/ml. There was a marked inoculum effect in broth, and skipped tubes were often observed. Variants resistant to 32 μg/ml or more were isolated by direct selection and were shown to occur at a frequency of approximately 10⁻⁶ to 10⁻⁷. A mutant showing a 16-fold increase in agar dilution MIC was also isolated by indirect selection. These variants and others isolated from broth in the presence of cefamandole were tested for ability to inactivate the antibiotic, using both a biological and a chemical procedure. Two distinct classes of variants were seen. Twelve of 28 were shown by both methods to inactivate the antibiotic, whereas the others, including the indirectly selected mutant, did not. The wild types were also negative by both tests. The higher cefamandole MICs of Enterobacter in broth, thus, appeared to reflect a high frequency of resistant variants that were not detected with the inoculum and end point criteria usually used in agar dilution methods. The ability of some variants to inactivate cefamandole may have resulted from a mutation that extended the activity of Enterobacter cephalosporinase to include this antibiotic.