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.

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.

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.

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.

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.

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.

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.

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.

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.

The calcium/parathyroid hormone concept of the parathyroid glands

Plasma ionized calcium is the major determinant of parathyroid hormone (PTH) secretion. The minute-to-minute secretory response of the parathyroids to changes in plasma ionized calcium is described by the calcium/PTH concept, but the detailed mechanism is not yet well understood. The recent cloning of a calcium-sensing receptor in the plasma membrane of the parathyroid cells will probably yield important information concerning the mechanisms by which calcium and other ions control the parathyroid function. It is likely that autocrine and paracrine factors also participate in the regulation of PTH secretion. PTH, chromogranin A, chromogranin A-related peptides and endothelin-1 have been suggested as autocrine factors. More documentation is needed on the impact of these factors in the physiology of the parathyroid gland. In-vivo investigations of the parathyroid function are difficult to interpret because of the complexity of the PTH secretory response to hypo- and hypercalcaemia. Rate dependency and the ability of the parathyroids to sense the direction of changes in calcium make the existing models for investigating the calcium/PTH relationship inappropriate. In vitro, the models are compromised by a rapid drop in the expression of the calcium-sensing receptor of the cultured parathyroid cells. We, therefore, recommend caution when using the calcium/PTH concept in clinical or experimental investigations.

Regulation of renal calbindin-D28K: the role of calcitonin

Infusion of calcitonin lowers circulating calcium, but in the distal tubule of the kidney, pharmacological doses of calcitonin increase the active calcium reabsorption. Calbindin-D28k plays a significant role in the calcium reabsorption in the distal convoluted tubule of the kidney. The effect of calcitonin on renal calbindin-D28k in relation to calcium metabolic changes was therefore examined. In study 1, thyroparathyroidectomy followed by autotransplantation of the parathyroid glands (TX) was compared with a sham operation in rats. TX reduced plasma calcitonin from 54 +/- 2 to 9 +/- 1 pg/ml (P < 0.001), whereas ionized calcium and parathyroid hormone were returned to the control value after an initial decrease, indicating a successful implantation of the parathyroid glands. No changes were seen in calbindin-D or plasma 1,25(OH)2D. In study 2, subcutaneous infusion of salmon calcitonin 2.5 U/kg/hour via osmotic pumps was compared with infusion of vehicle in rats. Ionized calcium was reduced from 1.37 +/- 0.01 to 1.33 +/- 0.02 mmol/liter (P < 0.05), whereas no changes were seen in renal or intestinal calbindin-D or in plasma 1,25(OH)2D. After TX, only calcitonin decreased whereas the other calcium metabolic parameters showed no change. This indicates that in rats, selective elimination of calcitonin does not influence other parameters of the calcium metabolism and that the effect of calcitonin on calcium transport in the distal tubule is not mediated via an increase in renal calbindin-D28k.

Calcium metabolic changes and calbindin-D in experimental hypertension

OBJECTIVE

To examine renal and intestinal calbindin-D in relation to calcium metabolic changes in three different models of experimental hypertension.

DESIGN

Spontaneously hypertensive rats (SHR), hypertension-prone Dahl salt-sensitive (Dahl-S) rats and the Goldblatt two-kidney, one clip rat model of renovascular hypertension were examined.

RESULTS

Both prehypertensive and hypertensive SHR had significantly lower concentrations of both renal calbindin-D28k and intestinal calbindin-D9k than Wistar control rats. This was accompanied by hypocalcaemia, hypomagnesaemia and increased plasma 1,25(OH)2 vitamin D levels. Induction of hypertension in Dahl-S rats reduced intestinal calbindin-D9k and increased plasma levels of 1,25(OH)2 vitamin D, while renal calbindin-D28k levels, plasma calcium levels and plasma magnesium levels were unchanged. Renovascular hypertension was associated with a significant increase in the intestinal calbindin-D9k, plasma 1,25(OH)2 vitamin D, parathyroid hormone and magnesium levels, while renal calbindin-D2k, plasma calcium and phosphorus levels were unaffected.

CONCLUSIONS

These three models of experimental hypertension have clearly demonstrated three separate patterns in the regulation of renal and intestinal calbindin-D, which relate to different alterations of factors involved in calcium and magnesium metabolism. In all three models hypertension was accompanied by a significant increase in plasma concentrations of 1,25(OH)2 vitamin D. Only rats with renovascular hypertension showed increased intestinal calbindin-D9k levels, whereas reduced concentrations were found in the SHR and in the hypertensive Dahl-S rats. This indicates the existence of a resistance at the cellular level to 1,25(OH)2 vitamin D affecting the expression of calbindin-D in both SHR and Dahl-S rats.

Metabolism of intact PTH by isolated perfused kidney and liver from uremic rats

The metabolism of synthetic human intact PTH (1-84), 1,000 or 3 pmol/l, was studied in isolated perfused livers and in filtering and nonfiltering kidneys from normal rats and rats made chronically uremic by 5/6 nephrectomy. Clearances were measured by assays specific for intact PTH, and NH2-terminal, mid-molecule, and COOH-terminal iPTH. Release of PTH fragments was analyzed by HPLC. Clearance of the added intact PTH by the uremic kidneys was reduced by the same order of magnitude as GFR. Neither the uremic nor the normal kidneys released any iPTH fragments. No peritubular metabolism of intact PTH was found in the uremic nonfiltering kidneys. Clearance of intact PTH by uremic and control livers was not significantly different. The uremic and control livers released equal amounts of COOH-terminal iPTH fragments, but no NH2-terminal fragments. Thus, uremia per se did not influence the renal and hepatic metabolism of PTH.

GABAA and glutamate receptor subunit mRNAs in cortex of mice chemically kindled with FG 7142

Messenger RNA (mRNA) for several subunits of the GABAA receptor was measured in the cortex of mice chemically kindled with FG 7142. At 10 days after the final FG 7142 injection, beta 2 and gamma 2S subunit mRNA were significantly increased. At 31 days, alpha 1, alpha 3, beta 2, and gamma 2L mRNA were elevated. In contrast, levels of mRNA for four subunits of the glutamate receptor in the cortex of FG 7142-kindled mice killed at 31 days were not significantly increased. Previous investigations have shown a reduction in GABA-gated chloride channel function and density in mice kindled with FG 7142, and the increases in subunit mRNA found in the present studies may be a response to these decreases. These results indicate that chemical kindling produces long-lasting changes in expression of genes coding for specific neurotransmitter receptor subunits.

Metabolism of N-terminal and C-terminal parathyroid hormone fragments by isolated perfused rat kidney and liver

The metabolism of added N-terminal and C-terminal synthetic human PTH (synhPTH) fragments was studied in isolated perfused rat livers and in filtering and nonfiltering kidneys. Initial concentrations: synhPTH-(1-34), 14 pmol/liter, synhPTH-(39-84) 85 pmol/liter, synhPTH-(1-84) 3 pmol/liter, or 1000 pmol/liter of each fragment and intact PTH. Clearances were measured by assays specific for intact PTH, N-terminal, midmolecule, and C-terminal immunoreactive PTH. Metabolism of the added PTH into smaller circulating fragments was analyzed by HPLC. The clearance of synhPTH-(1-34) in the filtering kidneys was not significantly different from the clearance of synhPTH-(39-84) and inulin, and HPLC demonstrated no metabolism of synhPTH-(1-34) or synhPTH-(39-84) in the kidneys. The livers did not clear synhPTH-(39-84), while the clearance of synhPTH-(1-34) was significant (P < 0.005). HPLC demonstrated no metabolism of synhPTH-(39-84) by the livers, but extensive metabolism of synhPTH-(1-34). The livers cleared synhPTH-(1-34) significantly (P < 0.05) faster than synhPTH-(1-84). In conclusion, the kidneys cleared N-terminal PTH fragments at the same rate as C-terminal fragments mainly by filtration. The livers cleared N-terminal fragments faster than intact PTH, but did not clear C-terminal fragments. This differential hepatic clearance may play a major role in maintaining the differences between the circulating levels of N-terminal and C-terminal immunoreactive PTH.

The in vivo effect of a new, in vitro, extremely potent vitamin D3 analog KH1060 on the suppression of renal allograft rejection in the rat

KH1060 is a new 20-epi-vitamin D3 analog, which has exerted a considerable immunosuppressive potency in vitro. We have tested in vivo the effect of KH1060 on the suppression of renal allograft rejection in the rat. Allogenic kidney transplantation from DA donor rats to Lewis recipient rats treated intraperitoneally with KH1060 in doses from 0.2 to 6 micrograms/kg/day, or saline (placebo group), or CyA 10 mg/kg/day for 10 days (positive control group), was performed. Median graft survival time in KH1060-treated groups was 7-9 days, in the placebo group 6 days, whereas CyA led to long-term graft survival, 34 days in 50% of rats and > 100 days in 50% of rats. In vivo, KH1060 failed to prolong renal allograft survival considerably, and led to development of hypercalcemia. Our results stress the existence of a large discrepancy between the in vitro and in vivo immunoregulatory effects of this vitamin D analog.

Parathyroid hormone dependent T cell proliferation in uremic rats

Chronic renal failure (CRF) is combined with an impairment of the immune system. The T cell may be a target for the action of parathyroid hormone (PTH). Rats with CRF have high blood levels of PTH. Therefore, the present investigation examined some aspects of the T cell function in both normal and CRF rats before and after parathyroidectomy and after an isogenic kidney transplantation. The T cell proliferative response to phytohemagglutinin (PHA) stimulation was significantly higher in peripheral blood mononuclear cell (PBMC) cultures obtained from CRF rats than from normal rats. After parathyroidectomy the T cells of normal as well as of uremic rats could still be significantly stimulated by PHA, but now no significant difference was seen. When CRF was reversed after an isogenic kidney transplantation and PTH reversed to levels in the normal range, the T cell proliferative response to PHA was normalized. Rat PTH 1-84 stimulated in vitro the PHA-induced proliferation of T cells in a dose dependent manner. This effect was significant in CRF rat lymphocytes, but not in lymphocytes obtained from normal rats. Based upon the present results it is suggested that the secondary hyperparathyroidism in chronic uremia is responsible for the enhanced proliferative response to PHA of T cells from CRF rats.

A model of reversible uremia employing isogenic kidney transplantation in the rat. Reversibility of secondary hyperparathyroidism

Kidney transplanted patients with normalized kidney function may still exhibit a variety of problems such as bone problems, vascularly problems, and hormonal dysfunctions. A part of the symptoms may be persisting uremic symptoms, secondary to the pretransplanted period of chronic uremia. An experimental rat model, designed to the study of the reversibility of the chronic uremic implications is therefore described. A stable, severe chronic uremia was induced by 5/6 nephrectomy to inbred Lewis rats. Ten weeks later uremia was reverted by a successful isogenic rat kidney transplantation. During the period of chronic uremia the p-urea was elevated to an average of 21.8 +/- 0.9 mmol/l and p-creatinine to 105.7 +/- 5.7 microM/l. The isogenic kidney transplantation resulted in reestablishment of normal kidney function with an average level of p-urea of 7.6 +/- 0.2 mmol/l and p-creatinine 42.5 +/- 1.9 microM/l perfectly corresponding to the sham-operated rats, i.e. one-kidney rats. Reversibility of the secondary hyperparathyroidism due to chronic uremia was investigated in the model. In rats with chronic renal failure PTH increased from 52 +/- 4.9 pg/ml to 152 +/- 12.2 pg/ml and was normalized after transplantation. It is therefore concluded that the present described technique of introducing long term uremia followed up by a successful kidney transplantation in the rat may be a useful model to study the reversibility of different uremic manifestations.

Glucocorticoid-induced osteoporosis in the lumbar spine, forearm, and mandible of nephrotic patients: a double-blind study on the high-dose, long-term effects of prednisone versus deflazacort

The long-term effects of high dose steroid treatment with either prednisone (PDN) or deflazacort (DFZ) were examined on various parts of the skeleton in 29 patients with nephrotic syndrome. All had normal skeleton at the start of the steroid treatment. At the beginning, PDN was given as 80 mg/day and tapered down to 20 mg/day for 1 year and DFZ was given in an equipotent dosage. Twenty-three patients completed 6 months of treatment, and 18 patients completed 12 months of treatment. Beside laboratory parameters to ensure the effect of treatment on the nephrotic syndrome, all had measurements of the bone mineral content (BMC) at 0, 6, and 12 months of treatment. BMC was measured by single photon absorptiometry of both forearms and by dual photon absorptiometry of the mandible, forearms, and lumbar spine. The effect of DFZ was compared to that of PDN due to a potential "calcium sparing" effect of DFZ. The therapeutical effects on the nephrotic syndrome were not different between the two drugs. Urinary 24-hour protein decreased from 9.9 to 1.1 g in the DFZ-treated patients and from 8.0 to 1.4 g in the PDN-treated patients. Plasma albumin concentration normalized in both groups. Both groups of steroid-treated patients had a significant reduction of the BMC levels in all parts of the skeleton. However, the bone decay rates per month were significantly different between different bone regions and between different drug regimes. In the forearm, the bone decay rate was 5.3%/year in the PDN group and 2.0%/year in the DFZ group (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Is a short femur length a useful ultrasound marker for Down's syndrome?

To assess the significance of a short femur in the antenatal diagnosis of Down's syndrome a retrospective analysis was made of all Down's syndrome fetuses diagnosed over a 3 year period. 11 fetuses were found to have had a biparietal diameter and femur length measurement taken between 15 and 24 weeks gestation. Normal graphs were plotted for femur length against gestational age, femur length against biparietal diameter and biparietal diameter/femur length against gestational age. When the Down's syndrome measurements were plotted on the normal graphs there were four abnormal measurements. These four measurements, however, represented two fetuses both of which demonstrated other abnormalities, one cystic hygroma and one duodenal atresia with choroid plexus cysts. We do not feel that the femur length measurement is useful in the antenatal diagnosis of Down's syndrome.

Diazepam sensitizes mice to FG 7142 and reduces muscimol-stimulated 36Cl- flux

Chronic treatment with benzodiazepine receptor agonists increases sensitivity to the convulsant action of FG 7142, an inverse agonist. We investigated whether or not changes in the number and function of GABA-gated chloride channels accompanies this increased sensitivity. Diazepam, 5 mg.kg-1, was administered to mice daily for five days, and mice were then tested with a single injection of FG 7142, 40 mg.kg-1, at several intervals thereafter. At 24 hours after the last diazepam dose, 10 of 15 mice had clonic seizures following FG 7142 and four of the remaining five had myoclonic jerks. At 48 hours, only one of six mice developed a clonic seizure, and none were observed in mice tested at 96 or 144 hours. Muscimol-stimulated chloride flux was reduced in cortical synaptosomes from diazepam-treated mice at 24 hours but not at 48 or 96 hours. However, the binding of [35S]TBPS, a ligand closely associated with the chloride channel, was unchanged at 24 hours. These results suggest that a transient diminution in GABA-gated chloride channel function; unaccompanied by a reduction in channel number, may underlie the sensitization to the convulsant action of FG 7142 observed after withdrawal from chronic diazepam treatment.

Chemical kindling decreases GABA-activated chloride channels of mouse brain

The repeated administration of N-methyl-beta-carboline-3-carboxamide (FG 7142) to mice leads to 'chemical kindling', i.e. the development of seizures in response to doses which were initially insufficient to produce convulsive activity. To determine if chemical kindling produced changes in the GABAA receptor/chloride channel complex, we measured the binding of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) to the convulsant site of the complex by quantitative autoradiography. As a measure of chloride channel function, we studied muscimol-stimulated uptake of 36Cl- by isolated brain synaptosomes. Kindling decreased the Bmax of [35S]TBPS binding in cortex but not in cerebellum or hippocampus. Kindling did not alter binding affinities in any of these brain regions. Some mice injected with FG 7142 did not kindle despite receiving the same treatment as kindled mice. These 'injected but not kindled' mice did not display decreased receptor binding in any of these brain areas. Muscimol-stimulated 36Cl- uptake into cortical synaptosomes was also diminished by chemical kindling. These findings suggest that a decrease in functioning GABA-regulated chloride channels may be responsible for chemical kindling with FG 7142.

Effect of inosine on seizures induced with pentylenetetrazole, bicuculline, or picrotoxin

The effect in mice of inosine administered subcutaneously on the threshold of seizures induced with pentylenetetrazole (PTZ), bicuculline, and picrotoxin was studied, and brain inosine levels were measured. Following inosine, 1,000 mg/kg, the threshold to PTZ was increased at 10-30 min after injection as determined by a tail vein infusion method. Bicuculline and picrotoxin thresholds were significantly elevated only at 5 min. The time to the first myoclonic jerk after intraperitoneal administration of each of these convulsants was significantly prolonged by the lowest dose of inosine tested (250 mg/kg for PTZ, 100 mg/kg for bicuculline, and 500 mg/kg for picrotoxin). Inosine was given subcutaneously 10 min before the convulsant. The mean control brain inosine concentration was 2.9 microM. After subcutaneous inosine, 1,000, 500, and 250 mg/kg, the highest levels reached were 14.4, 7.9, and 4.3 microM, respectively. It is concluded that micromolar concentrations of inosine in brain are antiepileptic.

Pentylenetetrazol seizures in mice: effect on brain inosine and hypoxanthine

Brain inosine and hypoxanthine were measured in mice at intervals following the intraperitoneal injection of pentylenetetrazol (PTZ), 100 mg/kg. These purines increased only after myoclonic jerks appeared and were maximal at the time of tonic hindlimb extension. Phenytoin and phenobarbital, which prevent tonic hindlimb extension, delayed the elevations of inosine and hypoxanthine. Although inosine has been found to have both epileptogenic and antiepileptic actions, the late increase in inosine found following PTZ probably has no physiological role.

Antagonism of the anxiolytic action of diazepam and chlordiazepoxide by the novel imidazopyridines, EMD 39593 and EMD 41717

The imidazopyridines EMD 35993 and EMD 41717 antagonized the anticonflict actions of diazepam and chlordiazepoxide in rodent models which are predictive for anxiolytic action in man. In contrast to other described benzodiazepine antagonists, these compounds did not antagonize either the anticonvulsant or muscle relaxant properties of either benzodiazepine. Both EMD 39593 and EMD 41717 competitively inhibit the binding of [3H]diazepam to brain membranes, but do not exhibit regional differences in potency. These observations suggest that both EMD 39593 and EMD 41717 display some selectivity in antagonizing the anxiolytic properties of benzodiazepines, and as such may be useful tools in identifying neuronal substrates of anxiety.

Electroshock raises pentylenetetrazol threshold: possible role of inosine

A series of 15 single electroshocks administered through electrodes applied to the scalp of mice raised the threshold to pentylenetetrazol-induced seizures as determined by a tail vein infusion method. The same stimulus increased brain inosine and hypoxanthine. Phenytoin, which blocks the increase in inosine produced by this stimulus, reversed the elevation in threshold may be electroshock. The effect of electroshock on threshold may be mediated by inosine.

Electroshock seizures in mice: effect on brain adenosine and its metabolites

Adenosine and its immediate metabolites, inosine and hypoxanthine, were measured in mouse brain following the induction of electroshock seizures and after a subconvulsive series of electric shocks. Electroshock seizures resulted in a marked and prolonged rise in inosine, with maximal values at 5 min. Hypoxanthine increased more slowly but reached high levels by 10 min. Adenosine was unchanged. Phenytoin and to a lesser extent phenobarbital reduced these effects. Following the subconvulsive stimulus, 15 single shocks over an interval of 5 sec, inosine increased rapidly, adenosine rose slightly, and hypoxanthine did not change. Both phenytoin and phenobarbital blocked these increases in adenosine and inosine. Early elevations in inosine may play some role in seizure generation and propagation. The high levels of inosine and hypoxanthine found after recovery may be involved in the termination of epileptic activity, possibly by interacting with the benzodiazepine receptor for which they are ligands.

Vaginal colonization with invasive Escherichia coli during pregnancy

Escherichia coli containing the K1 antigen was isolated from women throughout their pregnancy and at delivery. The number of positive isolations varied from 5% to 7% throughout pregnancy, and 50% of the babies were coloinized if their mothers were positive for this organism at the time of delivery. In contrast to group B streptococci, the spontaneous loss or acquisition of E. coli K1 was uncommon.