Extrarenal expression of α-klotho, the kidney related longevity gene, in Heterocephalus glaber, the long living Naked Mole Rat.

The Naked Mole Rat (NMR), Heterocephalus glaber, provides an interesting model for studying biomarkers of longevity due to its long lifespan of more than 30 years, almost ten times longer than that of mice and rats. α-Klotho (klotho) is an aging-suppressor gene, and overexpression of klotho is associated with extended lifespan in mice. Klotho is predominantly expressed in the kidney. The expression profile of klotho in the NMR has not previously been reported. The present investigation studied the expression of klotho in the kidney of NMR with that of Rattus Norvegicus (RN) and demonstrated that klotho was expressed in the kidney of NMR at the same level as found in RN. Besides, a significant expression of Kl mRNA was found in the liver of NMR, in contrast to RN, where no hepatic expression was detected. The Klotho expression was further confirmed at the protein level. Thus, the results of the present comparative study indicate a differential tissue expression of klotho between different species. Besides its important function in the kidney, Klotho might also be of significance in the liver of NMR. It is suggested that the hepatic extrarenal expression of klotho may function as a further longevity-related factor in supplement to the Klotho in the kidney.

Tuning structure and mechanical properties of Ta-C coatings by N-alloying and vacancy population.

Tailoring mechanical properties of transition metal carbides by substituting carbon with nitrogen atoms is a highly interesting approach, as thereby the bonding state changes towards a more metallic like character and thus ductility can be increased. Based on ab initio calculations we could prove experimentally, that up to a nitrogen content of about 68% on the non-metallic sublattice, Ta-C-N crystals prevail a face centered cubic structure for sputter deposited thin films. The cubic structure is partly stabilized by non-metallic as well as Ta vacancies - the latter are decisive for nitrogen rich compositions. With increasing nitrogen content, the originally super-hard fcc-TaC0.71 thin films soften from 40 GPa to 26 GPa for TaC0.33N0.67, accompanied by a decrease of the indentation modulus. With increasing nitrogen on the non-metallic sublattice (hence, decreasing C) the damage tolerance of Ta-C based coatings increases, when characterized after the Pugh and Pettifor criteria. Consequently, varying the non-metallic sublattice population allows for an effective tuning and designing of intrinsic coating properties.

Hard and crack resistant carbon supersaturated refractory nanostructured multicomponent coatings.

The combination of ceramic hardness with high crack resistance is a major challenge in the design of protective thin films. High entropy alloys have shown in earlier studies promising mechanical properties with a potential use as thin film materials. In this study, we show that small amounts of carbon in magnetron-sputtered multicomponent CrNbTaTiW films can lead to a significant increase in hardness. The film properties were strongly dependent on the metal composition and the most promising results were observed for TaW-rich films. They crystallised in a bcc structure with a strong (110) texture and coherent grain boundaries. It was possible to deposit films with 8 at.% C in a supersaturated solid-solution into the bcc structure without carbide formation. A major effect of carbon was a significant grain refinement, reducing the column diameter from approximately 35 to 10 nm. This resulted in an increase in hardness from 14.7 to 19.1 GPa while the reduced E-modulus stayed constant at 322 GPa. The carbon-containing films exhibited extremely little plastic deformation around the indent and no cracks were observed. These results show that supersaturation of carbon into high entropy films can be a promising concept to combine superior hardness with high crack resistance.

Soil diversity and hydration as observed by ChemCam at Gale crater, Mars.

The ChemCam instrument, which provides insight into martian soil chemistry at the submillimeter scale, identified two principal soil types along the Curiosity rover traverse: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic soil component is representative of widespread martian soils and is similar in composition to the martian dust. It possesses a ubiquitous hydrogen signature in ChemCam spectra, corresponding to the hydration of the amorphous phases found in the soil by the CheMin instrument. This hydration likely accounts for an important fraction of the global hydration of the surface seen by previous orbital measurements. ChemCam analyses did not reveal any significant exchange of water vapor between the regolith and the atmosphere. These observations provide constraints on the nature of the amorphous phases and their hydration.

Calcium-sensing receptor and recovery from hypocalcaemia in thyroparathyroidectomized rats.

BACKGROUND: Plasma ionized calcium (p-Ca(2+)) is kept within a very narrow range and deviations are rapidly corrected by flux of Ca(2+) between extracellular fluid and the labile calcium pool at the quiescent bone surface. The calcium sensing at the bone surface represents a physiological interesting model for the rapid minute-to-minute regulation of p-Ca(2+). Our aim was to study whether the calcium-sensing receptor (CaR) has a role in the rapid recovery of p-Ca(2+) from acute induced hypocalcaemia. MATERIAL AND METHODS: Male Wistar rats were thyroparathyroidectomized (TPTX). Acute hypocalcaemia in the animals was induced by infusion of EGTA (40-50 mM EGTA, 3.0 mL h(-1) for 30 min). Thereafter the recovery of p-Ca(2+) was followed. Vehicle or the CaR activators, R-568 (2 mg as a bolus twice) or gentamycin were administrated intravenously. RESULTS: EGTA infusion resulted in significantly lower nadir of hypocalcaemia in R-568- or gentamycin-treated rats compared to vehicle-treated rats (P < 0.01). During recovery phase p-Ca(2+) remained significantly lower in R-568 rats (P < 0.001). As such p-Ca(2+) levels recovered to basal levels in the vehicle group within 70 min after stopping EGTA, while R-568 or gentamycin rats remained significantly hypocalcaemic. CONCLUSIONS: The CaR activators R-568 and gentamycin, both significantly delayed the recovery of p-Ca(2+) from acute EGTA-induced hypocalcaemia in TPTX rats. This novel finding suggests the existence of calcium sensing by bone of importance for the rapid minute-to-minute regulation of p-Ca(2+).

Influence of parathyroid mass on the regulation of PTH secretion.

In advanced uremia, parathyroid hormone (PTH) levels should be controlled at a moderately elevated level in order to promote normal bone turnover. As such, a certain degree of parathyroid gland (PG) hyperplasia has to be accepted. No convincing evidence of apoptosis or of involution of PG hyperplasia exists. However, even considerable parathyroid hyperplasia can be controlled when the functional demand for increased PTH levels is abolished. When 20 isogenic PG were implanted into one parathyroidectomized (PTX) rat normalization of Ca(2+) and PTH levels and normal suppressibility of PTH secretion by high Ca(2+) was obtained. Similarly, normal levels of Ca(2+) and PTH and suppressibility of PTH secretion were obtained when Eight isogenic PG from uremic rats were implanted into normal rats or when long-term uremia and severe secondary hyperparathyroidism (sec. HPT) was reversed by an isogenic kidney transplantation. Normalization of PTH levels after experimental kidney transplantation took place despite a persistent decrease of vitamin D receptor (VDR) mRNA and calcium sensing receptor (CaR) mRNA in PG. Thus, in experimental models PTH levels are determined by the functional demand and not by parathyroid mass, per se. When non-suppressible sec. HPT is present in patients referred to PTX, nodular hyperplasia with differences in gene expression between different nodules has been observed in most cases. An altered expression of some autocrine/paracrine factors has been demonstrated in the nodules. Enhanced expression of PTH-related peptide (PTHrP) has been demonstrated in PG from patients with severe secondary HPT. PTHrP has been shown to stimulate PTH secretion in vivo and in vitro. PTH/PTHrP receptor was demonstrated in the parathyroids. The low Ca(2+) stimulated PTH secretion was enhanced by 300% by PTHrP 1-40. The altered quality of the parathyroid mass and not only the increased parathyroid mass, per se, might be responsible for non-controllable hyperparathyroidism in uremia and after kidney transplantation.

Rate-dependency of calcitonin secretion in response to increased plasma Ca2+.

BACKGROUND: Calcitonin (CT) is a polypeptide hormone secreted from C-cells of the thyroid gland in response to hypercalcemia. The physiological contribution of CT to calcium homeostasis has not been completely clarified. The present study therefore further characterized the sigmoidal relationship between plasma ionized calcium (P-Ca2+) and CT in normal rats, and examined the possibility of rate-dependency of CT secretion in response to changes in P-Ca2+. DESIGN: Hypercalcaemia was induced by an infusion of calcium gluconate at rate of 4.5 x 10(-2) mmol h-1 rat-1 i.v. (n = 8) and hypocalcaemia was induced by an EGTA infusion at a rate of 4.5 x 10(-2) mmol h-1 rat-1 (n = 7) in one protocol: the 'slow' protocol. In another protocol an increased rate of infusion of calcium gluconate or EGTA was used to induce a more rapid change in P-Ca2+. Calcium gluconate was infused at a rate of 6.0 x 10(-2) mmol h-1 rat-1 (n = 6) and EGTA infused at a rate of 7.5 x 10(-2) mmol h-1 rat-1 (n = 7): the 'rapid' protocol. RESULTS: The infusions of both the 'slow' and 'rapid' protocols resulted in linear changes in P-Ca2+, but with significantly different slopes (P < 0.01). The Ca2+/CT curves of both protocols were represented by sigmoidal curves. The 'rapid' increase of P-Ca2+ resulted in a higher maximal CT secretion (2032 +/- 215 pg mL-1) than the 'slow' increase of P-Ca2+ (1213 +/- 85 pg mL-1; P < 0.001), despite similar minimal and maximal levels being obtained in P-Ca2+ in the two protocols. Thus, a significantly greater CT response was obtained with a more rapid increment in P-Ca2+. CONCLUSION: The relationship between P-Ca2+ and CT is represented by a sigmoidal curve, as previously shown. The CT response depended, however, not only upon the concentration of P-Ca2+ obtained but also upon the rate of increase in P-Ca2+, demonstrating rate-dependency as another significant physiological relation between Ca2+ and CT.

Role of calcitonin in the rapid minute-to-minute regulation of plasma Ca2+ homeostasis in the rat.

BACKGROUND: Plasma ionized calcium (Ca2+) is maintained at a very stable concentration in mammals. The hormones or factors involved in the very rapid regulation of calcium homeostasis are still debated. Thus, previous results from our laboratory have clearly shown that parathyroid hormone (PTH) and 1,25(OH)2D3 are not responsible for the rapid up-regulation of plasma Ca2+ after a brief induction of hypocalcaemia. The present investigation therefore examined in vivo the possible role of calcitonin (CT) in the very rapid, minute-to-minute regulation of plasma Ca2+ in rats. STUDY DESIGN: The rapid calcaemic response to acute thyroparathyroidectomy (TPTX) and to acute selective thyroidectomy (TX) (n = 10), as well as the possible effect of CT on the very rapid recovery of plasma Ca2+ after termination of a brief induction of hypocalcaemia were studied. Hypocalcaemia was induced by a 30-min EGTA infusion in ras in three different protocols: 1 h after TPTX (n = 9) compared with control TPTX rats not given EGTA (n = 13); 1 h after TX (n = 7); and 1 h after TPTX, but during supplementation with exogenous CT (n = 8) and compared with the response in TPTX rats infused with vehicle (n = 8). RESULTS: An immediate and significant increase of plasma Ca2+ was found after TPTX (P < 0.01) as well as after selective TX (P < 0.01) in the nonfasting rats. Significant hypercalcaemia (P < 0.05) was still present in rats fasting for 2 days before these procedures, but the increase in plasma Ca2+ was considerably less (P < 0.01). After induction of a brief period of hypocalcaemia by infusion of EGTA a significant (P < 0.01) and rapid recovery of plasma Ca2+ took place within 10 min and a further increase within the next 60 min (P < 0.01), whether or not the rats were normal, TPTX, TX or were supplemented by CT during the experiments. The plasma Ca2+ recovery curves after termination of a brief induction of hypocalcaemia all had similar appearances, indicating that presence or absence of CT had no influence on this very rapid Ca2+ recovery after induction of hypocalcaemia. CONCLUSIONS: Acute removal of the tonus of CT results in an acute increase in plasma Ca2+ for up to 3 h. This effect of CT is probably mainly related to the postprandial maintenance of normocalcaemia, but is also seen in fasting rats, although to a lesser degree. The very rapid calcaemic recovery after discontinuation of a brief induction of hypocalcaemia is, however, not a result of suppressed plasma calcitonin levels.

Prevention of uremic bone disease using calcimimetic compounds.

The discovery, characterization, and cloning of the calcium-sensing receptor (CaR) in 1993 was soon followed by the creation of a new type of drug, the calcimimetics-NPS R-568 and NPS R-467-which are small phenylalkylamine derivative compounds that act as CaR agonists and increase the sensitivity of the CaR to activation by extracellular calcium (Ca2+). As expected, these compounds turned out to have a significant effect on the Ca2+/parathyroid hormone (PTH) relationship, resulting in a dramatically greater suppression of the PTH level than would otherwise occur at the actual extracellular Ca2+ levels. Renal osteodystrophy (RO) due to secondary hyperparathyroidism (HPT) in chronic renal failure was an obvious target for studying the effects of NPS R-568. In a study on experimental animals, the results clearly showed that this first generation of calcimimetics, NPS R-568, had an acute dose-dependent and short-lived suppressive effect on PTH secretion from the parathyroid glands. A similar effect was found in patients with chronic renal failure and secondary HPT. At the same time, the calcimimetics induced a slight degree of hypocalcemia. Such a significant suppressive effect on PTH secretion would be expected to result in therapeutic potential for a preventive or therapeutic effect on the RO accompanying chronic uremia. Administration would probably be in close concert with present strategies, phosphate binders and vitamin D analogs. A wide distribution of CaRs have now been demonstrated in the body, and an important question is how calcimimetics will affect the function of different tissues and organs when used for long-term treatment or prevention of secondary HPT and RO. Although relatively few experimental and clinical investigations have been completed, they clearly confirm the suppressive effect of calcimimetics on PTH secretion. In rats with experimental chronic renal failure, a significant and beneficial effect on the prevention of RO has been demonstrated. The effect of calcimimetic compounds is presently being evaluated in humans. Besides induction of hypocalcemia, the adverse effects in these mainly short-term studies have been few. Future studies with calcimimetics will further define the physiology and pathophysiology of the CaR and the long-term benefit of calcimimetic compounds in patients with chronic renal failure.

PTHrP enhances the secretory response of PTH to a hypocalcemic stimulus in rat parathyroid glands.

BACKGROUND: The secretion of parathyroid hormone (PTH) from the parathyroid glands might be regulated by autocrine/paracrine factors, and a feedback regulatory mechanism of PTH on the secretion of PTH has been suggested. Because of the existence of a common receptor between PTH and PTH-related peptide (PTHrP), the aim of the present study was to examine the possible effects of PTHrP 1-40 and 1-86 on PTH secretion in rats. METHODS: In vivo, the effect of PTHrP on Ca++-regulated PTH secretion was examined by the induction of hypocalcemia and hypercalcemia by an infusion of EGTA and Ca++, with and without PTHrP. The eventual effects of PTHrP on the peripheral metabolism of PTH were examined by infusion of human PTH (hPTH) with and without PTHrP. hPTH was measured by an intact hPTH assay not cross reacting with rat PTH or PTHrP. To examine whether near physiological levels of circulating PTH have an autoregulatory effect in vivo on PTH secretion from the parathyroid gland, an acute reduction of the circulating PTH was induced by an acute unilateral parathyroidectomy (UPTX). PTH secretion from the remaining parathyroid gland was followed in response to EGTA-induced hypocalcemia. In vitro investigations on the effect of PTHrP 1-40 on PTH secretion from whole rat parathyroid glands incubated in media containing a calcium concentration of 0.6 or 1.35 mmol/L were performed to confirm whether the effect of PTHrP was directly on the gland. The rat PTH assay was examined for cross reaction with PTHrP. RESULTS: In vivo, the same rate of decrease of plasma Ca++ was induced in the experimental groups. The maximal response of PTH to hypocalcemia (218 +/- 16 pg/mL, N = 6) was significantly enhanced by PTHrP 1-40 (525 +/- 79 pg/mL, N = 6) and by PTHrP 1-86 (465 +/- 29 pg/mL, N = 6, P < 0.001). No effect of PTHrP on PTH secretion was found during normocalcemia or hypercalcemia. UPTX resulted in a 50% reduction of PTH secretion, and no compensatory increase of PTH was observed. PTHrP had no effect on the metabolism of PTH. In vitro, low-Ca++-induced PTH secretion was significantly augmented by 300% (P < 0.01) when the medium contained PTHrP 1-40. PTHrP did not cross react with the PTH assay. CONCLUSIONS: PTHrP significantly enhanced the low-Ca++-stimulated PTH secretion in vivo and in vitro. An autocrine/paracrine role of PTHrP in the parathyroid glands is suggested. An autoregulatory effect of circulating PTH on the PTH secretion from parathyroid glands seems unlikely. The "maximal secretory capacity" of the parathyroid glands induced by hypocalcemia in vivo and in vitro is not the maximum, as PTH secretion can be increased even further, by several-fold.

Dual energy X-ray absorptiometry in small rats with low bone mineral density.

The feasibility of dual energy X-ray absorptiometry (DXA) using the Norland XR-26 Mark II bone densitometer for measurements of bone mineral content (BMC) and bone mineral density (BMD) in small rats was evaluated. Thirty-two young, isogenic, Lewis rats (weights from 119 g to 227 g) were used; normal rats (n = 7) and rats with low BMD obtained from three different vitamin D-depleted models (n = 25). DXA measurements were performed using the special software for small animals. Duplicate scans of excised femurs performed at 2 mm/second (pixel size of 0.5 mm x 0.5 mm) were very precise measurements with a coefficient of variation (CV) below 1.6% in animals with normal BMD; in rats with low BMD, the CV was significantly higher (P = 0.02-0.04), 7.8% and 4.4% for BMC and BMD, respectively. Regression analysis demonstrated that these measurements were related to the ash weight (R2 > 98.6%). The CV for measurements of the lumbar spine at 10 mm/second (pixel size 0.5 mm x 0.5 mm) was 2.6% and 2.2% for BMC and BMD, respectively in rats with normal BMD, and again higher (P = 0.03-0.14) in rats with low BMD, 7.3% and 4.7%, respectively, for BMC and BMD. Even though low CVs were obtained for total body duplicate scans (scan speed of 20 mm/second and a pixel size of 1.5 mm x 1.5 mm), the measurements were problematic for accuracy because of an overestimation of both BMC and the area of bone. Using these scan parameters the measurements of total body bone mineral could not be recommended in small rats with low BMD.

The influence of rivers on marine boron isotopes and implications for reconstructing past ocean pH.

Ocean pH is particularly sensitive to atmospheric carbon dioxide content. Records of ocean pH can therefore be used to estimate past atmospheric carbon dioxide concentrations. The isotopic composition of boron (delta11B) contained in the carbonate shells of marine organisms varies according to pH, from which ocean pH can be reconstructed. This requires independent estimates of the delta11B of dissolved boron in sea water through time. The marine delta11B budget, however, is still largely unconstrained. Here we show that, by incorporating the global flux of riverine boron (as estimated from delta11B measurements in 22 of the world's main rivers), the marine boron isotope budget can be balanced. We also derive ocean delta11B budgets for the past 120 Myr. Estimated isotope compositions of boron in sea water show a remarkable consistency with records of delta11B in foraminiferal carbonates, suggesting that foraminifera delta11B records may in part reflect changes in the marine boron isotope budget rather than changes in ocean pH over the Cenozoic era.

1,25(OH)2D3 only affects long-term levels of plasma Ca2+ but not the rapid minute-to-minute plasma Ca2+ homeostasis in the rat.

Results from our lab have shown previously that parathyroid hormone (PTH) is not the key factor in the rapid regulation of plasma Ca2+. The possible role of 1,25(OH)2D3 in the rapid minute-to-minute regulation of plasma Ca2+, as addressed by a possible rapid non-genomic action of 1,25(OH)2D3, was therefore studied in vivo in rats. The rapid calcemic recovery from induction of hypocalcemia by a brief EGTA infusion was examined in vitamin D-depleted rats with intact parathyroid glands and in vitamin D depleted rats 1 h after parathyroidectomy (PTX). The influence of different levels of plasma 1,25(OH)2D3 on the rapid calcemic recovery from hypocalcemia was examined in PTX rats treated with 1,25(OH)2D3 for two days at two different doses of 0.2 microg/day, 0.05 microg/day or vehicle, and in PTX rats being BNX for two days, as well. Additionally, the long-term effect of 1,25(OH)2D3 on plasma Ca2+ homeostasis was examined. Plasma Ca2+ recovered significantly (P<0.05) 10 min after discontinuing EGTA in vitamin D-depleted rats with or without parathyroid glands. Plasma Ca2+ increased significantly (P<0.05) and at the same rate after induction of hypocalcemia in PTX rats with different levels of plasma 1,25(OH)2D3. The final levels of plasma Ca2+ obtained were set by 1,25(OH)2D3 in a dose-related manner. 1,25(OH)2D3 did not affect the rapid calcemic recovery from EGTA induced hypocalcemia, but only had an effect on the long-term plasma Ca2+ homeostasis in the rat.

Parathyroid hormone is not a key hormone in the rapid minute-to-minute regulation of plasma Ca2+ homeostasis in rats.

BACKGROUND: The role of parathyroid hormone (PTH) in the rapid minute-to-minute regulation of plasma Ca2+ (p-Ca2+) was studied in vivo in rats. MATERIALS AND METHODS: The rapid calcaemic response to exogenous rat PTH1-34 (16 microg) was examined in normal rats, and the long-term calcaemic response was examined in parathyroidectomized (PTX) rats receiving PTH1-34 for 24 h at 0.2, 0. 4 and 0.8 microg h-1. Acute hypocalcaemia was induced by EGTA for 30 min, and then the rapid recovery of p-Ca2+ was studied for 130 min in normal rats, 24 h after PTX and in PTX rats infused with exogenous rat PTH1-34. The dynamics of the rapid recovery of p-Ca2+ was studied at two additional doses of EGTA. RESULTS: No rapid calcaemic response was observed in the first 60 min after administration of PTH and no hypocalcaemia was seen for 2 h after acute PTX. This slow effect of PTH suggests that PTH might not be responsible for maintaining the stable p-Ca2+ on a rapid minute-to-minute basis. EGTA induced acute hypocalcaemia in both normal and PTX rats (P < 0.01). In both groups a rapid and similar increase in p-Ca2+ took place 10 min after discontinuing EGTA (P < 0. 05). Within 60 min, p-Ca2+ increased further, independently of the presence of PTH. Infusion of PTH to PTX rats did not affect the rapid recovery of p-Ca2+ (P < 0.05) from EGTA induced hypocalcaemia. CONCLUSION: PTH is not a key hormone in the rapid recovery of p-Ca2+ after induction of hypocalcaemia, but might, however, set the long-term levels of p-Ca2+ maintained by mammalian organisms. The involvement of an as yet unknown factor in the rapid regulation of p-Ca2+ is suggested.

Rapid recovery of plasma ionized calcium after acute induction of hypocalcaemia in parathyroidectomized and nephrectomized rats.

BACKGROUND: Plasma ionized calcium (Ca2+) is extremely tightly regulated in normal mammals. Even a small decline in Ca2+ is followed by a fast and steep increase of the parathyroid hormone (PTH) secretion and the current understanding of the calcium homeostasis indicates that PTH is the main factor responsible for this tight minute-to-minute regulation of the normal plasma Ca2+ concentration. However, experiments from our laboratory and some clinical experiences points towards the existence of factors, other than PTH, involved in the rapid minute-to-minute calcium homeostasis. Thus, the aim of the present study was to examine whether PTH plays an important role in the rapid upregulation of plasma Ca2+ after induction of hypocalcaemia in the rat. METHODS AND RESULTS: I. Parathyroidectomy (PTX) was performed in seven rats; 60 min later no PTH was detectable in the circulation. Then by a brief infusion of EGTA plasma Ca2+ was reduced from 1.26+/-0.02 to 0.86+/-0.02 mmol/l, P<0.001. Despite there being no PTH in the circulation plasma Ca2+ increased significantly to 0.97+/-0.02 mmol/l already 10 min after discontinuation of the EGTA infusion, P<0.04, and plasma Ca2+ was normalized within another 2 h. II. To evaluate a possible role of renal Ca2+ handling in the rapid upregulation of plasma Ca2+ a group of eight rats had acute PTX and bilateral nephrectomy (NX) performed; 60 min later plasma Ca2+ was reduced from 1.18+/-0.01 to 0.86+/-0.02 mmol/l by an EGTA infusion. Despite there being no PTH and no kidneys present plasma Ca2+ increased significantly already 10 min after discontinuation of EGTA to 0.96+/-0.02 mmol/l, P<0.02. After another 1.5 h the plasma Ca2+ reached the levels of the PTX/NX control rats. III. In order to exclude a possible action of receptor-bound PTH, which may have lasted for more than 1 h, seven rats were PTX 24 h before the induction of hypocalcaemia. Basal plasma Ca2+ was significantly reduced to 1.07+/-0.01 mmol/l, P<0.01. Then plasma Ca2+ was further reduced to 0.79+/-0.03 mmol/l by EGTA. Ten minutes after discontinuing EGTA plasma Ca2+ increased to 0.91+/-0.02 mmol/l, P<0.03 and 60 min later plasma Ca2+ reached the level of the control PTX rats. Normal rats with intact parathyroid glands had an exactly similar response of plasma Ca2+ to EGTA as that of 24 h PTX rats, but at significantly higher levels of plasma Ca2+ with a fall from 1.28+/-0.01 to 0.96+/-0.03 mmol/l and again a significant increase of plasma Ca2+ to 1.13+/-0.03 (P<0.001) 10 min after discontinuation of EGTA. After another hour basal levels were reached. CONCLUSIONS: Despite there being no PTH in the circulation a rapid increase of plasma Ca2+ occurs immediately after a brief induction of hypocalcaemia. The kidneys are not responsible for this phenomenon. The present results suggest the existence of a mechanism other than the effect of PTH, which is responsible for the rapid minute-to-minute regulation of plasma Ca2+ in the rat.

Reversibility of experimental secondary hyperparathyroidism.

Chronic uremia is associated with secondary hyperparathyroidism (HPT). The purpose of the present investigation was to study the reversibility of secondary HPT after reversal of uremia by an isogenic kidney transplantation in the rat. Secondary HPT was induced in two models: Model A comprised 5/6 nephrectomized rats kept on a standard diet (N = 12; PTH 210 +/- 43 pg/ml; plasma urea 24 +/- 2 mmol/liter; and normal control rats, N = 12; PTH 45 +/- 5 pg/ml; plasma urea 6 +/- 0.2 mmol/liter); and Model B comprised 5/6 nephrectomized rats kept on a high phosphorus diet (N = 12; PTH 769 +/- 157 pg/ml; plasma urea 18 +/- 2 mmol/liter). The parathyroid function was examined by measuring the secretory response of PTH to an acute induction of hypo- and hypercalcemia. Acute hypocalcemia in the hyperphosphatemic uremic rats did not significantly increase serum PTH levels (N = 6, delta Ca2+ -0.56 mmol/liter; maximal PTH 1045 +/- 164 pg/ml; basal PTH 690 +/- 134 pg/ml; NS). During hypercalcemia the PTH levels were significantly higher than in the normal controls (N = 6; minimal PTH 24 +/- 5 pg/ml vs. normal controls 5 +/- 0.2 pg/ml, P < 0.05). After 20 weeks of uremia, the uremia was reversed by the isogenic kidney transplantation. One week after reversal of the uremia the PTH levels became normal in both models A and B (28 +/- 6 and 63 +/- 16 pg/ml, respectively) and the kidney transplanted rats from model B had a normal secretory response of PTH to both hypo- and hypercalcemia. To study whether both parathyroid cell hypertrophy and hyperplasia could be down-regulated, 8 uremic glands (N = 9) or 20 normal glands (N = 6) were implanted into one normal rat. Within two weeks the rats regained normocalcemia and PTH levels remained normal from the third day after the increase of glandular mass. The 20 gland rats all had normal PTH suppressibility in response to calcium (minimal PTH 5 +/- 0.3 pg/ml). In conclusion, experimental severe secondary hyperparathyroidism is reversible very quickly after the reversal of uremia. Hyperphosphatemia in uremia is important for the non-suppressibility of the parathyroid glands to calcium. In non-uremic rats even severe parathyroid hyperplasia can be controlled, resulting in normal plasma PTH and Ca2+ levels and in a normal response to hypercalcemia. Thus, the minimal PTH secretion obtained during the induction of hypercalcemia is not an expression of the parathyroid mass.

Effect of vitamin D metabolites and analogs on renal and intestinal calbindin-D in the rat.

The effects on renal and intestinal calbindin-D of vitamin D3 metabolites and synthetic 20-epi-vitamin D3 analogs with different calcemic actions were examined in Wistar rats. The compounds were administered intraperitoneally once daily for 5 days. The dosages of the metabolites were 1,25-(OH)2D3 0.01, 0.05, 0.1, and 0.4 microg/kg x d, 24,25-(OH)2D3 0.1, 1 and 10 microg/kg x d, and 25-(OH)D3 10 and 400 microg/kg x d. The dosage of the synthetic analogs were MC903 0. 1, 10, and 100 microg/kg x d, EB1213 0.1 and 10 microg/kg x d, KH1060 0.1 and 0.4 microg/kg x d, and GS1725 0.01 and 0.1 microg/kg x d. Two control groups had either vehicle alone or no treatment. N = 8 in each group. 1,25-(OH)2D3 increased renal and intestinal calbindin-D levels, induced hypercalcemia, and suppressed plasma PTH and magnesium concentrations. 24,25-(OH)2D3 increased intestinal calbindin-D9k and plasma calcium, but had no effect on renal calbindin-D28k, plasma PTH, and magnesium. The dosage of 24, 25-(OH)2D3 that was required to increase plasma calcium was larger than the dosage required to increase intestinal calbindin-D9k. 25-(OH)D3 did not change the calcium metabolic parameters. MC903, a low calcemic analog with a relative high affinity for the vitamin D receptor and a short half-life, increased renal calbindin-D28k without increasing ionized calcium or intestinal calbindin-D9k. EB1213, an analog with a reduced calcemic action and short half-life, increased renal calbindin-D28k and ionized calcium without increasing intestinal calbindin-D9k. The effect of the high calcemic vitamin D analogs KH1060 and GS1725 on calbindin-D was directly related to their calcemic activity. In conclusion, these results demonstrate that 24,25-(OH)2D3 increases intestinal calbindin-D9k, but has no effect on renal calbindin-D28k, that low calcemic analogs may increase renal calbindin-D28k without increasing intestinal calbindin-D9k, and that the effect of high calcemic analogs on calbindin-D is directly related to their calcemic activity.

Effect of parathyroid hormone on renal calbindin-D28k.

The present investigation was conducted to examine the effects of parathyroid hormone (PTH) and parathyroid hormone related peptide (PTHrP) on renal calbindin-D28k in rats. Four groups of studies were performed: (1) parathyroidectomy (PTX) or a sham operation followed by infusion of 1,25-dihydroxyvitamin D (1,25[OH]2D) or vehicle; (2) infusions of PTH(1-34), PTH(1-84), 1,25(OH)2D, or vehicle; (3) infusion of PTHrP(1-34), PTHrP (1-86), PTH(1-34), or vehicle; and (4) injections of calcium or vehicle. PTX reduced renal calbindin-D28k levels even when plasma concentrations of 1,25(OH)2D were kept constant by infusion of 1,25(OH)2D. Infusions of PTH(1-34), PTH(1-84), and 1,25(OH)2D all increased renal calbindin-D28k and plasma calcium, whereas PTHrP(1-34) and PTHrP(1-86) increased renal calbindin-D28k before an increase of plasma calcium took place. Hypercalcemia induced by the injection of calcium did not affect the levels of renal calbindin-D28k. The present data suggest that PTH and PTHrP exert a direct effect on renal calbindin-D28k, which is not mediated by changes of 1,25(OH)2D or calcium.

Kainate, GABAA and NMDA receptors in Xenopus oocytes expressing mRNA from the cortex of mice kindled with FG 7142.

The repeated administration of the beta-carboline, FG 7142, to mice leads to 'chemical kindling', i.e., the development of seizures following doses which were initially insufficient to produce convulsive activity. Messenger RNA (mRNA) was prepared from the cortex of control and FG 7142-treated mice killed at 10-12 days or at 28-45 days after the last kindling injection, and this mRNA was injected into Xenopus oocytes. At 3-4 days following injection, a voltage clamp technique was used to record responses to kainic acid, gamma-aminobutyric acid (GABA), and N-methyl-D-aspartate (NMDA). Kainate was significantly more potent in oocytes expressing mRNA from kindled mice killed at either 10-12 or 28-45 days than in those injected with control mRNA. GABA also was more potent in oocytes with mRNA from kindled mice killed at 10-12 days, but this difference was not present at the longer interval. Chemical kindling did not change the response to NMDA. The current-voltage relation for kainate responses was linear, and plots from kindled and control mRNA were similar. The persistent increase in potency of kainate, an excitatory glutamate ligand, may play a role in producing the lowered FG 7142 threshold characteristic of kindled mice.