Nephrogenous Cyclic AMP Excretion Research Articles

Possible mechanism of impaired calcium and vitamin D metabolism in nephrotic rats.

Patients who have nephrotic syndrome and normal renal function are hypocalcemic in spite of the elevated levels of serum parathyroid hormone (PTH) caused by a low serum concentration of 1,25-dihydroxyvitamin D[1,25(OH)2D], presumably because of its loss in urine. However, it has not been established whether the conversion of 25-hydroxyvitamin D[25(OH)D] into 1,25(OH)2D is impaired in the kidney. In this study, we examined the serum levels of vitamin D metabolites, and kinetics of renal 25(OH)D-1-hydroxylase activity in vitro, and nephrogenous cyclic AMP excretion in response to exogenous PTH administration in puromycin aminonucleoside-induced nephrosis in rats. Plasma ionized calcium and the serum levels of vitamin D metabolites were lower, and conversely, the serum PTH level was higher, in nephrotic rats than in controls. Serum 1,25(OH)2D levels were higher in 25(OH)D3-treated nephrotic rats than in untreated nephrotic rats, indicating that the low 1,25(OH)2D level in nephrotic rats is partially due to the low concentration of 25(OH)D. Although PTH levels were higher in nephrotic rats than in control rats, the Vmax of renal 25(OH)D-1-hydroxylase and nephrogenous adenosine 3',5'-monophosphate (cyclic AMP) excretion in response to exogenous PTH were significantly lower in nephrotic animals than in controls. These results suggest that abnormalities in calcium and vitamin D metabolism in nephrotic rats are partially attributable to impaired proximal tubular function.

Urinary excretion of parathyroid hormone-related protein fragments in patients with humoral hypercalcemia of malignancy and hypercalcemic tumor-bearing nude mice

To investigate whether parathyroid hormone-related protein (PTHrP), a hypercalcemia-inducing factor responsible for malignancy-associated hypercalcemia (MAH), is excreted into urine of these patients, radioimmunoassay was established using antiserum specific for the C-terminal region of PTHrP-(127-141). Immunoreactive PTHrP (iPTHrP) was detected in the urine of all patients with MAH (n = 6) in whom nephrogenous cyclic AMP excretion was elevated. However, iPTHrP was not detected in the urine of normal subjects (n = 25) or hypercalcemic patients with primary hyperparathyroidism (n = 8). In normocalcemic patients with malignant disorders iPTHrP was not detected in the urine in most cases (24 of 25 patients) but was detectable in 1 of 25 patients. iPTHrP was also detected in the urine of hypercalcemic nude mice transplanted with PTHrP-producing tumors, but not in the urine of control and normocalcemic nude mice transplanted with PTHrP-nonproducing tumor. Furthermore, size-exclusion high-performance liquid chromatography revealed that the molecular weight of iPTHrP is about 2000-6000 daltons in the urine of patients as well as tumor-bearing nude mice. These data indicate that the fragments of the C-terminal region of PTHrP are excreted into the urine of patients with MAH and in a few normocalcemic patients with malignancies, suggesting that the measurement of iPTHrP in the urine is potentially useful in the differential diagnosis of hypercalcemia, particularly in differentiating humoral hypercalcemia of malignancy and primary hyperparathyroidism.

Treatment of humoral hypercalcemia of malignancy in rats with inhibitors of carbonic anhydrase

The enzyme carbonic anhydrase has been suggested as a critical participant in osteoclast-mediated bone resorption. In humoral hypercalcemia of malignancy (HHM) intense osteoclastic bone resorption is principally responsible for the observed hypercalcemia. We therefore undertook to examine the effect of the carbonic anhydrase inhibitor acetazolamide on the hypercalcemia induced by the H500 Leydig cell tumor in Fisher rats, a well-described model of HHM. Acetazolamide treatment for 10 h at 10 mg/h resulted in a significant fall in serum calcium in the five drug-treated animals (14.2 +/- 0.9 to 11.5 +/- 0.1 mg/dl, p less than 0.05). Conversely, the six animals infused with vehicle alone showed a significant rise in serum calcium (12.5 +/- 0.5 to 13.8 +/- 0.1 mg/dl, p less than 0.05). At the end of the infusion, the acetazolamide-treated animals had a significantly lower mean serum calcium than those receiving vehicle alone (11.5 +/- 0.1 versus 13.8 +/- 0.1, p less than 0.05). There was no significant change in serum phosphorus, urine calcium, urine phosphorus, or nephrogenous cyclic AMP excretion between the two groups. Acetazaolamide and HTS 5-(3-hydroxybenzoyl)-2-thiophenesulfonamide, another carbonic anhydrase inhibitor, both significantly inhibited in vitro bone resorption induced by 5 X 10(-9) M 36Tyr(1-36)-PTHrP-amide (PTHrP, parathyroid hormone-related protein). Acetazolamide also inhibited the resorption induced by 10(-8) M (1-141)-PTHrP and 2.5 X 10(-9) M (1-74)-PTHrP. We conclude that acetazolamide is effective in lowering the serum calcium in animals with humoral hypercalcemia of malignancy. The data are consistent with the hypothesis that the mechanism of action for this effect is direct inhibition of osteoclast-mediated bone resorption.

A Case of Leiomyosarcoma Associated with Humoral Hypercalcemia of Malignancy: Demonstration of Biological and Immunological Activities of Parathyroid Hormone‐related Protein in the Tumor Extract

Hypercalcemia occurred in a patient with leiomyosarcoma when multiple lung metastases developed. Despite normal plasma parathyroid hormone (PTH) levels and low 1,25‐dihydroxyvitamin D, this hypercalcemic patient had a marked hypercakiuria and phosphatnria associated with an increased excretion of nephrogenous cyclic AMP (NcAMP). Administration of cisplatin ameliorated both the hypercalcemia and hypercalciuria without any reduction in tumor size or NcAMP excretion. Terminally, acute pancreatitis occurred producing a profound hypocalcemia. In the extract of tumor tissue obtained post mortem, bioactivity stimulating the generation of cyclic AMP in osteogenic cells was demonstrated along with the immunoreactive PTH‐related protein (PTH‐rP). This is the first report of a solid non‐epithelial malignancy producing PTH‐rP and associated with humoral hypercalcemia of malignancy. The hypercalcemia in this case caused acute pancreatitis, which led to a profound hypocalcemia

Effects of the intravenous administration of magnesium sulfate on corrected serum calcium level and nephrogenous cyclic AMP excretion in normal human subjects.

The effect of intravenous magnesium sulfate infusion on corrected serum calcium level and parathyroid function assessed by determination of nephrogenous cAMP (NcAMP) excretion were studied in normal human subjects. Significant hypermagnesemia induced by the magnesium sulfate infusion for 120 minutes was accompanied by a gradual and progressive decrease in the corrected serum calcium level. NcAMP excretion fell rapidly, reaching a nadir between 60 and 120 minutes after the infusion began, and after that rose above the baseline excretion. Urinary calcium excretion gradually increased, reaching a peak between 120 and 180 minutes after the infusion began and then gradually decreased. Since magnesium was given as the sulfate, it is not clear whether these changes were attributable to magnesium or sulfate or both. As a control study, we performed intravenous sodium sulfate infusion. The sodium sulfate infusion caused slight hypocalcemia, slight hypercalciuria, and a significant increase in NcAMP excretion. These findings indicate that the hypocalcemia and the hypercalciuria caused by the magnesium sulfate infusion is mainly due to the effect of magnesium, and that the decrease in NcAMP excretion during the infusion is due to the effect of magnesium alone. We conclude that the hypocalcemia caused by the magnesium sulfate infusion is mainly due to the renal calcium loss, and that the inhibition of parathyroid function caused by hypermagnesemia may be only partially involved in the early phase of this hypocalcemia.

Hypercalcemia of malignancy.

Hypercalcemia is frequently associated with malignant disease (Stewart et al, 1980, Mundy et al, 1984). The primary underlying cause is an increase in osteoclastic bone resorption but the mechanisms which lead to this increase are still the focus of current research. A number of investigators have utilized different approaches to identify factors which are secreted from tumors associated with hypercalcemia and which are responsible for increased bone resorption. It is now apparent that different classes of protein factors are responsible for the hypercalcemia observed in different types of malignancies. For example, in patients with myeloma the lymphokine, osteoclast-activating factor, is most likely the humoral factor secreted from myeloma cells and causing bone resorption (Mundy et al, 1974). Hypercalcemia can also occur in patients who have solid tumors without bone metastases and bone resorption in this type of hypercalcemia is often associated with hypophosphatemia and an increase in nephrogenous cyclic AMP excretion (Stewart et al, 1980).KeywordsEpidermal Growth Factor ReceptorBone ResorptionParathyroid HormoneTranslation ProductOsteoclastic Bone ResorptionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Changes in nephrogenous cyclic AMP excretion and plasma cyclic AMP following treatment of hyperthyroidism

Plasma cyclic AMP (PcAMP) concentration and the excretion of cyclic AMP/dl GF were estimated in 11 thyrotoxic patients before and after medical treatment. PcAMP concentrations were significantly higher during hyperthyroidism (2.30 +/- 0.69 vs 1.88 +/- 0.71 nmol/dl; P less than 0.05), and total urinary cyclic AMP (TcAMP) excretion showed no significant changes (3.24 +/- 0.64 vs 3.44 +/- 1.77 nmol/dl GF). Nephrogenous (NcAMP) excretion rose significantly (1.00 +/- 0.82 vs 1.68 +/- 1.31 mmol/dl GF; P less than 0.025). The increase in NcAMP excretion correlated significantly with the decrease in serum T3 levels (r = -0.46; P less than 0.05). Serum iPTH levels showed no significant change. Both the serum Ca, corrected for serum total protein and TmPO4/GFR declined after treatment (respectively 2.44 +/- 0.13 vs 2.33 +/- 0.08 mmol/l; P less than 0.05 and 1.18 +/- 0.29 vs 1.05 +/- 0.22 mmol/l; P less than 0.05). It is concluded that the rise in NcAMP excretion corroborates the concept of increasing parathyroid activity following the treatment of hyperthyroidism.

Urinary and nephrogenous cyclic AMP and renal phosphate handling in normal subjects and patients with parathyroid dysfunction.

Studies were performed in 60 patients with proven primary hyperparathyroidism pre-operatively and in 54 of these patients post-operatively, 22 patients with permanent hypoparathyroidism and 34 normal subjects. Urinary and nephrogenous cyclic AMP excretion were increased in the hyperparathyroid patients with an overlap of values with the normal group of 10 and 9%, respectively. Values fell in all patients post-operatively, and were decreased in those with permanent hypoparathyroidism. TmPO4 /GFR was decreased in the preoperative hyperparathyroid patients and rose postoperatively while it was increased in the hypoparathyroid patients with an overlap of values with the normal group of 9%. Post-operative hypocalcaemia due to bone hunger was associated with continuing normo- or hypophosphataemia and urinary cyclic AMP that exceeded 4.5 nM/dl GF while those who developed permanent hypoparathyroidism had hyperphosphataemia, increased TmPO4 /GFR and urinary cyclic AMP that was less than 3.5 nM/dl GF. Urinary and nephrogenous cyclic AMP were equally effective in characterizing patients with primary hyperparathyroidism and less effective in distinguishing patients with hypoparathyroidism from normal while TmPO4 /GFR estimates were more effective in delineating the hypoparathyroid state.

Vitamin D status after total gastrectomy.

Serum levels of 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, 1,25-dihydroxyvitamin D, immunoreactive parathyroid hormone, and urinary excretion of nephrogenous cyclic AMP were measured in 25 patients after total gastrectomy. Two types of reconstruction after total gastrectomy were also compared. Serum 25-hydroxyvitamin D levels were significantly decreased and serum 24,25-dihydroxyvitamin D levels were markedly reduced, whereas serum 1,25-dihydroxyvitamin D levels were significantly increased in the patients. Although serum levels of immunoreactive parathyroid hormone did not show a significant difference, serum alkaline phosphatase levels and urinary excretion of nephrogenous cyclic AMP were significantly increased in the patients. The results suggest that defective vitamin D storage and enhanced vitamin D action coexist in patients after total gastrectomy and that the enhanced vitamin D action, possibly derived from slightly increased parathyroid function, would be a compensatory mechanism to sustained calcium deficiency. No substantial difference of vitamin D status was observed between the two types of reconstruction which differed in passage through the duodenum.

Effects of growth hormone replacement therapy on 1,25-dihydroxyvitamin D and calcium metabolism.

To elucidate the changes in mineral metabolism and blood concentrations of calciotropic hormones which accompany GH therapy, we studied 12 GH-deficient children for 5 days before and for 1 week after high dose (5 IU/day) GH therapy, and again at 1 month, 3 months, and 1 yr of replacement therapy (0.1 IU/kg to a maximum dose of 2 IU three times weekly). All responded with acceleration of height velocity, and bone ages advanced appropriately. Fasting serum ionized calcium levels did not change: 4.11 +/- 0.06 (SEM) mg/dl before, 4.19 +/- 0.05 for the week of high dose therapy, and 4.20 +/- 0.14 during replacement therapy. Likewise, fasting serum parthormone did not vary: 38.9 +/- 2.6 muleq/ml before to 44.1 +/- 9.2 at 1 yr. Twenty four-hour nephrogenous cyclic AMP (NcAMP) did not vary over the first week (1.2 +/- 0.7 nmol/dl glomerular filtrate before, 1.3 +/- 0.4 after 1 week), but increased to 5.3 +/- 1.9 after 1 yr (alpha less than 0.001). The response of ionized calcium and parathormone to a standardized disodium EDTA infusion of 50 mg/kg also did not change. The mean fasting serum calcitonin level was not different before therapy (29.4 +/- 2.8 pg/ml), after 1 week (21.5 +/- 1.8), or after 1 yr (42.4 +/- 11.0). However, the mean serum 1,25-dihydroxyvitamin D concentration rose from 33.1 +/- 3.3 pg/ml before therapy to 68.3 +/- 12.3 on the seventh day of high dose therapy (alpha less than 0.01), returning to pretherapy values by 1 month. We conclude that high dose GH therapy in GH-deficient children raises 1,25-dihydroxyvitamin D concentration acutely, but that long term, physiological replacement therapy does not cause such an effect. Because NcAMP excretion rose in the absence of an increase in serum parathormone concentration, we conclude that GH sensitizes the kidney to a cAMP-mediated effect of parathormone.

Hypercalcemia associated with gynecologic malignancies: biochemical characterization.

Fasting calcium excretion, renal phosphorus threshold, plasma 1,25 dihydroxyvitamin D, immunoreactive PTH, nephrogenous cyclic AMP excretion, and tumor burden were assessed in nine patients with gynecologic neoplasms and hypercalcemia. Gynecologic neoplasms were responsible for hypercalcemia in seven of 34 (20.5%) consecutive patients with malignancy-associated hypercalcemia. The tumor burden in each patient was large. Three of four endometrial carcinomas contained squamous elements. All patients displayed biochemical evidence of nonparathyroid humorally mediated hypercalcemia (bone resorption). Treatment of hypercalcemia did not appear to diminish production of the humoral calcemic factor but eradication of tumor eliminated biochemical evidence of the humoral syndrome. It can be concluded that (1) gynecologic neoplasms are a frequent cause of malignancy-associated hypercalcemia, (2) humoral mechanisms appeared to be responsible for the hypercalcemia in 100% of the patients in this series, (3) squamous features occur with unexpected frequency in hypercalcemic endometrial carcinoma, (4) the presence of hypercalcemia connotes a large tumor burden, and (5) treatment directed at the neoplasm (but not treatment directed at hypercalcemia) may eliminate evidence of ectopic calcemic hormone production.

Nephrogenous cyclic AMP in streptozotocin-induced diabetic rat

The effect of streptozotocin-induced diabetes, in the rat, on the excretion of nephrogenous cyclic AMP was investigated. This excretion was significantly less than that observed in control animals (P < 0.001). Administration of insulin partly restored the excretion of nephrogenous cyclic AMP to control values. In view of the reported elevated parathyroid hormone levels in the diabetic rat, the present findings suggest target organ resistance to parathyroid hormone in this diabetic animal model.

Biochemical evaluation of patients with cancer-associated hypercalcemia: evidence for humoral and nonhumoral groups.

In 50 consecutive patients with cancer-associated hypercalcemia, we measured nephrogenous cyclic AMP, tubular phosphorus threshold, fasting calcium excretion, plasma 1,25-dihydroxyvitamin D, and immunoreactive parathyroid hormone as determined by four region-specific antiserums. Nephrogenous cyclic AMP excretion was elevated in 41 patients and suppressed in nine (means, 5.85 vs. 0.51 nmol per 100 ml of glomerular filtrate). There was no overlap between these groups. When compared with 15 patients with primary hyperparathyroidism, the group with increased cyclic AMP excretion had similar reductions in tubular phosphorus threshold; higher fasting calcium excretion (means, 0.66 vs. 0.25 mg per 100 ml of glomerular filtrate, P < 0.01); marked reductions in 1,25-dihydroxyvitamin D (means, 20 vs. 83 pg per milliliter, P < 0.001); and lower levels of immunoreactive parathyroid hormone in all four assays. The data suggest that elevated excretion of nephrogenous cyclic AMP may be a useful marker of humorally mediated cancer-associated hypercalcemia, that this type of hypercalcemia is common, that the humoral factor responsible for this syndrome is not native 1-84 parathyroid hormone, and that the various subtypes of cancer-associated hypercalcemia are biochemically distinguishable from primary hyperparathyroidism.

Parathyroid hormone does not increase nephrogenous cyclic AMP excretion by the dog.

The renal excretion of nephrogenous cyclic AMP (NcAMP) increases in response to parathyroid hormone (PTH) in man, and thereby serves as a test of parathyroid function. However, during studies of calcium-PTH (PTH) in man, and thereby serves as a test of parathyroid function. However, during studies of calcium-PTH interrelationships in dogs we observed no change in total urinary cAMP (UcAMP) excretion when endogenous plasma PTH levels were increased up to 10-fold. This study was designed to investigate the effects of physiologic and pharmacologic levels of PTH on NcAMP and UcAMP excretion in the dog. Maintaining plasma Ca 2 mg/dl below normal for 40 minutes caused an 8-fold increase in plasma PTH concentration, a 50% increase in the urinary fractional excretion of phosphate (FEP) but no changes in plasma cAMP levels or in UcAMP or NcAMP excretion. Infusion of a pharmacologic amount of parathyroid extract (15 U/min for 20 min) increased plasma cAMP 5-fold, UcAMP excretion 3-fold and FEP by 50% but was without effect on NcAMP excretion. We conclude that NcAMP excretion is not stimulated by PTH in the dog and thus cannot be used as an index of PTH action in vivo. The increase in UcAMP excretion by pharmacologic amounts of PTH results from glomerular filtration of increased plasma cAMP, which may be generated in bone.

The parathyroid hormone receptor-adenylate cyclase system in chicken kidney.

There is a wealth of evidence that the renal actions of parathyroid hormone (PTH) result, at least in part, from receptor- mediated stimulation of adenylate cyclase and a consequent increase in renal cell cyclic AMP. Thus, infusions of cyclic AMP (or its dibutyryl derivative) have been shown to reproduce the physiological effects of PTH on the kidney including inhibition of PO4 reabsorption (1–4), stimulation of distal calcium reabsorption (1, 4) and increased production of 1,25(OH)2D3 (5). Numerous studies have demonstrated PTH-stimulation of adenylate cyclase in renal tissue in vitro, and under certain circumstances nephrogenous cyclic AMP excretion can be used as a valid index of parathyroid function (6).

Effects of the Intravenous Administration of Calcium on Nephrogenous Cyclic AMP:Use as a Parathyroid Suppression Test*

The question of parathyroid autonomy in primary hyperparathyroidism has been the subject of conflicting immunoassay data. We studied the effects of calcium infusion (12 mg/kg/3h) and calcium injection (3 mg/kg/10 min) on peripheral plasma parathyroid hormone (iPTH) determined with a multivalent antiserum and on the excretion of nephrogenous cyclic AMP in normal subjects and in 7 patients with primary hyperparathyroidism who displayed only mild, intermittent hypercalcemia. In control subjects, calcium administration resulted in small (13-20%) reductions in iPTH, whereas some 4/5 (77-81%) of the nephrogenous cyclic AMP was rapidly and uniformly suppressed. In the patients with primary hyperparathyroidism, both analyses revealed a lack of absolute parathyroid autonomy in response to calcium, with overlapping iPTH responses between a majority of the patients and the control group. In contrast, the nephrogenous cyclic AMP responses provided a clear separation of the 2 groups after both calcium infusion and calcium injection (mean values for both studies, patients: 2.93 nmol/100 ml GF vs. normal sugjects: 0.38 nmol/100 ml GF), and measurements of total cyclic AMP excretion also clearly distinguished the 2 groups. When a sensitive antiserum with predominantly carboxy-terminal reactivity was employed, the iPTH responses to calcium injection provided an improved separation of patients and normal subjects. The data suggest that 1) although parathyroid autonomy is not, in general, a feature of primary hyperparathyroidism, abnormal parathyroid suppressibility is easily demonstrated even in patients with a subtle form of the disorder; 2) the determination of nephrogenous cyclic AMP provides an optimal method for assessing rapid changes in parathyroid function; and 3) the interpretation of iPTH results from such studies is dependent on a number of technological features of the assay employed.