Effects of disodium ethane-l-hydroxy-1,1-diphosphonate (EHDP) in adult normal and selectively parathyroidectomized rats. I. Effects on plasma calcium,bone tissue,and adrenal glands at low or normal calcium intake

One-year-old intact and selectively parathyroidectomized rats were given a normal or low calcium diet for 8 months and, during the last 3 weeks, diphosphonates (EHDP) at a low dose level of 1.0 mg EHDPIkg body weight/day intraperitoneally. The administration of EHDP impaired the animals' ability to maintain the blood calcium level during a low calcium intake. Calcium-deficient intact animals had significantly reduced plasma calcium during EHDP treatment, while calcium-deficient parathyroidectomized animals showed no further reduction. Calcium deficiency alone resulted in osteoporosis which was prevented by parathyroidectomy. The short period of EHDP treatment had no significant effect on the bone mass in control, osteoporotic, and parathyroidectomized animals. The calcium accretion rate by bone became significantly increased upon a low calcium intake in intact rats but not in parathyroidectomized ones. This increase was counteracted by EHDP which gave rise to reduced accretion in both parathyroidectomized and osteoporotic animals. In addition EHDP caused hypertrophy of the adrenal cortex in all treated groups.     

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.     

Hyperphosphatemia modestly retards parathyroid hormone suppression during calcitriol-induced hypercalcemia in normal and azotemic rats

BACKGROUND/AIMS: In in vitro studies, a high phosphate concentration has been shown to directly stimulate parathyroid hormone (PTH) secretion in a normal calcium concentration and to reduce PTH suppression in a high calcium concentration. In hemodialysis patients during dialysis-induced hypercalcemia, the effect of hyperphosphatemia on PTH secretion was less than in vitro studies. Our goal was to determine whether hyperphosphatemia retards PTH suppression during calcitriol-induced hypercalcemia in azotemic rats with hyperparathyroidism. METHODS: Rats underwent a two-stage 5/6 nephrectomy or sham operations. After surgery, rats received a high phosphate diet (P 1.2%, Ca 0.6%) for 4 weeks to induce hyperparathyroidism and then were placed on a normal diet (P 0.6%, Ca 0.6%) for two additional weeks to normalize serum calcium values in azotemic rats. At week 7, rats were divided into five groups and before sacrifice received at 24-hour intervals, three doses of calcitriol (CTR) or its vehicle. The five groups and dietary phosphate content were: group 1--normal renal function (NRF) + 0.6% P + vehicle; group 2--NRF + 0.6% P + CTR; group 3--renal failure (RF) + 0.6% P + vehicle; group 4--RF + 1.2% P + CTR; and group 5--RF + 0.6% P + CTR. RESULTS: In the two CTR-treated groups with marked hypercalcemia (groups 2 and 5), 15.52 +/- 0.26 and 15.12 +/- 0.13 mg/dl, respectively, stepwise regression showed that hyperphosphatemia retarded PTH suppression. When the two azotemic groups treated with CTR (groups 4 and 5) were combined to expand the range of serum calcium values, stepwise regression showed that hypercalcemia suppressed and hyperphosphatemia modestly retarded PTH suppression. Similarly, in groups 4 and 5 combined, correlations were present between PTH and both serum calcium (r = -0.70, p < 0.001) and serum phosphate (r = 0.64, p = 0.001). CONCLUSIONS: Hypercalcemia and high doses of calcitriol markedly reduced PTH secretion in azotemic rats despite severe hyperphosphatemia. Even though hyperphosphatemia did retard PTH suppression during hypercalcemia, its effect was small.     

The relationship between calcium content and aluminum and silicon content in uraemic rats

The relationship between calcium (Ca) content and aluminum (Al) and silicon (Si) content in uraemic rats was examined. Significant correlations with serum [Ca]×[Pi] products and serum Al levels and serum Si values were found (r=0.73, p<0.01). There were significant (r=−0.26, p<0.05; r=−0.46, p<0.05) relationships between corpuscular [Ca]×[Pi] products and corpuscular Al levels and corpuscular Si values. We found that renal tissue [Ca]×[Pi] products tend to increase with the increase of renal tissue Al content and renal tissue Si content. Serum and corpuscular Al content and Si content can be used as one of the indicators of renal osteodystrophy.     

Effect of salmon calcitonin onin vivo calcium absorption in rats

Young calcitonin-deficient rats were prepared by thyroparathyroidectomy, and some of these received replacement therapy of parathyroid hormone and/or thyroxine. Disappearance of⁴⁵Ca from the intestinal tract by 4 hours and appearance of the radioactivity in the carcass at 4 hours were measured as indexes of absorption. Salmon calcitonin in physiological or pharmacological dosages failed to alter thein vivo net⁴⁵Ca absorption in the rats which were deficient in calcitonin alone, or in calcitonin and thyroxine, or in calcitonin, thyroxine and parathyroid hormone. Restoration of parathyroid hormone enhanced⁴⁵Ca absorption above that in parathyroid deficient rats.     

Fluoride,parathyroid hormone and calcitonin: Inter-relationships in bone calcium metabolism

The influence of fluoride, parathyroid hormone and calcitonin on bone calcium metabolism was investigated in a bone culture system using half-calvaria of five-day old mice. Fluoride levels in the ash of half-calvaria of 0.007% (low fluoride group), 0.041% (moderate fluoride group), and 0.107% (high fluoride group) were achieved by varying the maternal and neonatal intake of fluoride. Fluoride inhibited the loss of calcium from bones cultured in control medium and parathyroid hormone-containing media, and promoted the uptake of calcium by bones cultured in medium containing calcitonin. Dead bones of the moderate and high fluoride groups took up more calcium from the culture medium than bones of the low fluoride group. Fluoride appears to exert its effect on bone calcium metabolism predominantly via a reduction in mineral solubility.Supported by Grant No. DE-01850, National Institute of Dental Research, Bethesda, Maryland.     

The relationship between long bone growth rate and duodenal calcium transport in female rats

Studies were carried out to determine the relationship between long bone growth and duodenal calcium (Ca) transport in female rats and the regulation of these two parameters by ovarian hormones. Female rats were ovariectomized (ovx) at 6 weeks of age. Some animals were implanted with silastic implants containing either estradiol or progesterone at the time of ovx. Studies were carried out 3 weeks later when the rats were 9 weeks old. Ovx resulted in an increase in long bone growth rate and duodenal Ca transport without any alteration in circulating levels of parathyroid hormone or 1,25-dihydroxyvitamin D [1,25-(OH)2D]. Animals receiving estradiol exhibited decreased long bone growth rate and duodenal Ca transport relative to ovx animals. These animals were mildly hypercalcemic and had lower levels of 1,25-(OH)2D than ovx or intact animals. The results of these studies suggest that the effects of ovarian hormone status on duodenal Ca transport are more closely related to long bone growth rate than to circulating levels of 1,25-(OH)2D. Further studies are required to determine whether the two parameters are coregulated by some as-yet-unidentified factor or whether bone growth is able to emit some signal, directly or indirectly, to increase duodenal Ca transport.     

Effects of altered calcium intake on diurnal and calcium-stimulated plasma calcitonin in normal women

We sought to determine if any protective effect of dietary calcium (Ca) or Ca supplements on bone could be at least partially mediated by increased calcitonin (CT) secretion. First we studied 10 healthy premenopausal women (median age, 35.5 years) who were randomized to high or low dietary Ca intake (1752 versus 391 mg elemental Ca per day) for 2 weeks and then crossed over. At the end of each dietary period, blood was drawn on 1 day at 0800, 1200, 1700, and 2000 h to assess diurnal variation of plasma CT levels. CT secretory reserve was assessed on the next day by Ca infusion (2 mg Ca per kg body weight over 5 minutes). Next, we studied 10 healthy premenopausal women who took a low-Ca diet (approximately 400 mg Ca per day) for a 2 week control period. The women were then randomized to high- or low-Ca intake [400 mg dietary Ca +/- 1500 mg Ca per day (as supplemental CaCO3)] and then crossed over. At the end of each study period, the diurnal variation in CT was tested on day 1; the CT secretory reserve was assessed on day 3 by an oral Ca load (500 mg as CaCO3)] and on day 5 by Ca infusion. Plasma immunoreactive CT was measured in whole plasma (iCT) and after silica extraction (exCT), predominantly monomeric CT. Neither increased dietary Ca nor Ca supplements affected the diurnal levels of iCT or exCT or augmented plasma CT responses to an oral Ca load.(ABSTRACT TRUNCATED AT 250 WORDS)     

The relationship between the actions of vitamin D,parathyroid hormone and calcitonin

The effect of PTH and CT upon hydroxyproline and electrolyte excretion, plasma calcium and phosphate, calcium balance, and the excretion of radiocalcium was examined in vitamin D-deficient thyroparathyroidectomized rats. The results were compared to those obtained in D-fed animals. An increase in urinary hydroxyproline, which persisted for many hours, occurred in D-deficient animals approximately 30 h after thyroparathroidectomy, but was not seen in D-fed animals. It was suppressed by high calcium infusion. Infusion of PTH or CT increased the hydroxyprolinuria even further in D-deficient animls. PTH increased hydroxyprolinuria in D-fed animals, but CT caused a significant decrease. In the D-deficient animals both PTH and CT caused a decrease in urinary calcium excretion, and an increase of the already positive calcium balance. In D-fed animals CT had similar effects, but PTH caused a significant increase in calcium excretion and a negative calcium balance. Young animals injected with⁴⁵Ca while on a D-deficient diet were studied 3 weeks later at a time when they had developed D-deficiency. When these animals were thyroparathyroidectomized and maintained on a constant glucose and electrolyte perfusion, the excretion of calcium was relatively constant and the specific activity of urnary calcium declined only slightly over a 28 h period. When PTH was given, both total and radioactive calcium excretion diminished initially, leading to a significant decrease in specific activity. The specific activity declined for the first 3 h of hormone infusion, then rose gradually and became greater than normal during the last 4 h of hormone infusion. When CT was given with PTH, total calcium excretion fell and remained below the control rate throughout the experiment. Specific activity rose markedly during the first 2 h, then fell rapidly to values below the control levels for the remainder of the experiment.

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Zusammenfassung Die Wirkung von PTH und CT auf Hydroxyprolin- und Elektrolytausscheidung, auf Plasma-Calcium und-Phosphat, Calciumbilanz und die Ausscheidung von radioaktivem Calcium wurde in Vitamin D-defizienten, thyroparathyreoidektomierten Ratten untersucht. Die Resultate wurden mit denjenigen von Ratten verglichen, welche Vitamin D erhielten. Es wurde eine Zunahme von Hydroxyprolin im Urin D-defizienter Tiere festgestellt, welche etwa 30 Std nach der Thyroparathyreoidektomie auftrat und viele Stunden anhielt. Tiere mit Vitamin D zeigten keine solche Zunahme. Hohe Calciuminfusionen unterdrückten diese Zunahme. Bei D-defizienten Tieren wurde die Hydroxyprolinurie durch Infusion von PTH oder CT noch weiter erhöht. Bei mit Vitamin D gefütterten Tieren steigerte PTH die Hydroxyprolinurie, CT jedoch bewirkte eine signifikante Abnahme. Bei den D-defizienten Tieren bewirkten PTH und CT eine Abnahme der Calciumausscheidung im Urin und eine Zunahme der bereits positiven Calciumbilanz. Bei mit Vitamin D gefütterten Tieren hatte CT ähnliche Wirkungen, aber PTH bewirkte eine signifikante Zunahme in der Calciumausscheidung und eine negative Calciumbilanz. Jungen Tieren wurde⁴⁵Ca injiziert, während sie eine D-Mangel-Diät erhielten, und sie wurden 3 Wochen später — zu einer Zeit, da sie eine D-Defizienz entwickelt hatten — untersucht. Nachdem diese Tiere thyroparathyreoidektomiert worden waren und auf einer konstanten Glucose- und Elektrolyt-Perfusion gehalten wurden, blieb die Calciumausscheidung relativ konstant und die spezifische Aktivität des Urincalciums nahm während einer Periode von 28 Std nur wenig ab. Eine PTH-Gabe verminderte anfänglich die gesamte und die radioaktive Calciumausscheidung und führte zu einer signifikanten Abnahme der spezifischen Aktivität. Die spezifische Aktivität nahm während der ersten 3 Std der Hormoninfusion ab, dann nahm sie allmählich zu und wurde während der letzten 4 Std der Hormoninfusion größer als normal. Wurde CT zusammen mit PTH gegeben, so fiel die Gesamtcalciumausscheidung und blieb während der ganzen Untersuchungsperiode unter dem Kontrollwert. Die spezifische Aktivität stieg während der ersten 2 Std stark an, fiel dann rasch auf Werte unterhalb des Kontrollniveaus und verblieb während der restlichen Untersuchung auf diesen Werten.

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Résumé L'effet de la PTH et de la CT sur l'excrétion d'hydroxyleproline et des électrolytes, le calcium et le phosphate plasmatique, l'équilibre calcique et l'excrétion du radiocalcium est étudié à l'aide de rats thyro-parathyroïdectomisés et déficients en vitamine D. Les résultats sont comparés à ceux obtenus chez des animaux recevant de la vitamine D. Une augmentation de l'hydroxleproline urinaire, qui persiste plusieurs heures, est observée chez les animaux, déficients en vitamine D, environ 30 heures après thyro-parathyroïdectomie. Cette augmentation disparait après administration élevée de calcium. L'administration de la PTH et de la CT accroit même l'hydroxyleprolinurie chez les animaux soumis à la vitamin D, mais la CT provoque une diminution nette. Chez les animaux déficients en vitamine D, la PTH et la CT diminuent la calciurie, et augmentent l'équilibre calcique, déjà positif. Chez les animaux recevant la vit. D, la CT a des effets analogues, mais la PTH provoque une augmentation nette de l'excrétion calcique, ainsi qu'un équilibre calcique négatif. De jeunes ani maux, recevant du⁴⁵Ca, alors qu'ils sont soumis à un régime pauvre en vit. D, sont examinés, trois semaines plus tard, en avitaminose D. Lorsque ces animaux sont thyro-parathyroïdectomisés et perfusés, de façon constante, en glucose et électrolytes, l'excrétion calcique est relativement constante et l'activité spécifique du calcium urinaire ne diminue que fort peu en 28 heures. Lorsqu'on administre de la PTH, l'excrétion, à la fois, du calcium total et radioactif diminue initialement en provoquant une décroissance nette de l'activité spécifique. L'activité spécifique décroit pendant les 3 premières heures d'administration d l'hormone, puis s'élève progressivement et devient plus élevée que la normale, au cours des 4 denières heures d'administration. Lorsque la CT est administrée simultanément, l'excrétion calcique totale s'abaisse et reste à des niveaux inférieurs à ceux des témoins pendant toute l'expérience. L'activité spécifique s'élève nettement pendant les 2 premières heures, puis s'abaisse rapidement à des niveaux inférieurs que ceux des témoins jusqu'à la fin de l'expérience.

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Regulation of 1,25-dihydroxyvitamin D3 by calcium in the parathyroidectomized, parathyroid hormone-replete rat

Parathyroid hormone (PTH) is a major stimulus for the renal production of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Elevated arterial blood ionized calcium ([Ca2+]) depresses serum 1,25-(OH)2D3 in nonparathyroidectomized rats even when serum PTH is maintained at high levels by infusion. However, suppression by [Ca2+] of endogenous PTH, causing the fall in 1,25-(OH)2D, cannot be excluded. To determine whether [Ca2+] regulates 1,25-(OH)2D3 in the absence of a variation in PTH, we parathyroidectomized (PTX) rats (post-PTX calcium levels less than 7.0 mg/dl), inserted arterial and venous catheters, and then replaced PTH using an osmotic pump. We varied [Ca2+] by infusing either 75 mM sodium chloride (control), 0.61 mumol/min of EGTA (EGTA), or calcium chloride at 0.61 mumol/min (low calcium) or 1.22 mumol/min (high calcium) for 24 h 5 days after surgery. Blood was then drawn from the rat through the arterial catheter. Compared with the control, [Ca2+] fell with EGTA, remained constant with the low-calcium infusion, and rose with the high-calcium infusion. 1,25-(OH)2D3 was correlated inversely with [Ca2+] in all four groups together (r = -0.635, n = 34, p less than 0.001), within the control group alone (r = -0.769, n = 11, p less than 0.002), and within the EGTA group alone (r = -0.774, n = 10, p less than 0.003). Serum phosphorus, PTH, and arterial blood pH were not different in any group, and none correlated with serum 1,25-(OH)2D3. We conclude that 1,25-(OH)2D3 levels are regulated by [Ca2+] independently of serum PTH, phosphorus, and acid-base status, all of which support the hypothesis that [Ca2+] is a principal regulator of serum 1,25-(OH)2D3 in the rat.     

Dissimilar PTH, gastrin, and calcitonin responses to oral calcium and peptones in hypocalciuric hypercalcemia, primary hyperparathyroidism, and normal subjects: a useful tool for differential diagnosis.

We analyzed gastrin, PTH, and calcitonin responses to oral calcium and peptones in hypocalciuric hypercalcemia, mild primary hyperparathyroidism, and normal controls. We observed diverse hormonal responses that may help in the differential diagnosis of these conditions. INTRODUCTION: Hypocalciuric hypercalcemia (HH) is consequent to calcium-sensing receptor (CaSR) genetic mutations or anti-CaSR antibodies. CaSR is expressed in parathyroid tissue, thyroid C cells, and gastrin-secreting cells, where it has been suggested that on calcium and/or amino acid allosteric activation, promotes gastrin secretion. MATERIALS AND METHODS: We evaluated gastrin, PTH, and calcitonin responses to oral calcium (1 g) and peptones (10 g) in 10 patients with HH (mean age, 58.5 +/- 10.3 years; F/M = 9/1), 15 patients with primary hyperparathyroidism (PH; mean age, 60.4 +/- 8.3 years; F/M = 11/4), and 30 healthy controls (mean age, 60.3 +/- 8.1 years). Statistical analyses for differences during oral loading tests were calculated with ANOVA for repeated measurements and comparisons between two groups were performed with Student's t-test. RESULTS: PTH response to peptones was markedly increased in patients with PH compared with flat responses in controls and HH patients (p < 0.05). Gastrin increase after oral calcium was absent in HH and PH subjects (p < 0.05 versus controls), and gastrin responses to peptones were blunted in HH and PH subjects compared with controls (p < 0.05). PTH drop and calcitonin increase after calcium load observed in controls were absent in HH and PH subjects (p < 0.05). CONCLUSIONS: The marked difference in PTH response elicited by peptones observed in PH compared with subjects with HH may help in the differential diagnosis of these conditions without genetic studies. Peptones may stimulate CaSR-controlled hormones as an allosteric regulatory pathway. CaSR abnormalities may help to explain the different calcium- and peptones-induced hormonal responses observed in PH and HH compared with normal subjects.     

Effect of endothelin receptor antagonist on parathyroid gland growth, PTH values and cell proliferation in azotemic rats.

BACKGROUND: A variety of stimuli are involved in the pathogenesis of parathyroid gland hyperplasia in renal failure. Recently, it was shown that blocking the signal from the endothelin-1 (ET-1) receptor (ET(A)R/ET(B)R) by a non-selective receptor antagonist, bosentan, reduced parathyroid cell proliferation, parathyroid gland hyperplasia and parathyroid hormone (PTH) levels in normal rats on a calcium deficient diet. Our goal was to determine whether in 5/6 nephrectomized (NPX) rats with developing or established hyperparathyroidism, the endothelin receptor blocker, bosentan, reduced the increase in parathyroid cell proliferation, parathyroid gland hyperplasia and PTH values. METHODS: High (HPD, 1.2%) or normal phosphorus diets (PD) (NPD, 0.6%) were given to 5/6 NPX rats for 15 days (NPX(15)). In each dietary group, one-half the rats were given bosentan (B) i.p. 100 mg/kg/day. The four groups of rats were: (1) NPX(15)-1.2% P; (2) NPX(15)-1.2% P+B; (3) NPX(15)-0.6% P; and (4) NPX(15)-0.6% P+B. In a second study in which hyperparathyroidism was already established in 5/6 NPX rats fed a HPD for 15 days, rats were divided into two groups in which one group was maintained on a HPD and the other group was changed to very low PD (VLPD, <0.05%) for an additional 15 days. In each dietary group, one-half the rats were given bosentan i.p. 100 mg/kg-day. The four groups of rats were: (1) NPX(30)-1.2% P; (2) NPX(30)-1.2% P+B; (3) NPX(30)-0.05% P and (4) NPX(30)-0.05% P+B. Parathyroid cell proliferation was measured by proliferating cell nuclear antigen (PCNA) staining and ET-1 expression by immunohistochemical techniques. RESULTS: In the study of developing hyperparathyroidism, bosentan reduced ET-1 expression in the parathyroid glands of rats on the NPD and HPD (P<0.05). But only in rats on the NPD did bosentan result in a reduced increase in parathyroid gland weight (P<0.05). In the study of established hyperparathyroidism, in which 5/6 NPX rats were given a HPD for 15 days, bosentan started on day 15 reduced (P<0.05) ET-1 expression in rats maintained for 15 additional days on the HPD or the VLPD. On the VLPD, parathyroid gland weight was less (P<0.05) than that in rats on the HPD sacrificed at 15 or 30 days. Bosentan did not reduce parathyroid cell proliferation or parathyroid gland weight in rats maintained on the HPD or further reduce these parameters beyond that obtained with dietary phosphorus restriction. PTH values were lowest in the VLPD group, intermediate in the NPD group, and highest in the HPD group, but in none of the three groups did bosentan decrease PTH values. CONCLUSIONS: In azotemic rats with developing hyperparathyroidism, bosentan resulted in a reduced increase in parathyroid gland weight when dietary phosphorus content was normal. Despite a reduction in ET-1 expression in rats on a HPD with developing or established hyperparathyroidism, bosentan did not reduce the increase in parathyroid cell proliferation, parathyroid gland growth or PTH values. Thus, ET-1 blockade with bosentan did not prevent parathyroid gland growth in the azotemic rat.     

Age-related changes in the normal sagittal relationship between globe and orbit.

PURPOSE: To establish the pattern of change in globe protrusion with advancing age. The findings contribute to our understanding of orbital ageing, and are useful in the longitudinal assessment of patients with orbital disease, craniofacial abnormalities and trauma. METHODS: Ocular protrusion from the lateral orbital rim to the corneal apex was measured in 653 Caucasians aged 21-80 years. Healthy subjects only were included in the study excluding those with ocular or orbital diseases. Measurements were taken using a single instrument and observer. Data were analysed for both sexes and each eye separately. RESULTS: The mean exophthalmometry reading in both sexes (318 female and 335 male) was 19+/-2mm. Ninety-eight percent of readings between the two eyes were within 1mm of each other and no subject had greater than 2mm of asymmetry. In all groups there was a negative linear correlation between ocular protrusion and age. This correlation was found to be highly statistically significant in all groups (r=0.56-0.65, p<0.0001). There was no statistically significant difference between change in ocular protrusion with age between the left and right eye for females or males. This study demonstrates a strong association between ocular protrusion and age in a Caucasian population. This association is an almost linear reduction in ocular protrusion with increasing age between the ages of 31 and 80. Asymmetry in ocular protrusion between the two eyes does not develop with increasing age.     

Reduction of lead-induced hypercalcemia by calcitonin: Comparison between thyroid-intact and thyroidectomized rats

Summary This report examines the ability of either exogenous or endogenous calcitonin to reduce the degree of hypercalcemia and hyperphosphatemia which follows an intravenous injection of lead acetate (20 mg/kg body weight). Blood samples were obtained prior to and 1 h after lead injection. The experimental groups were normal young adult rats; rats with autotransplanted parathyroid glands and functional thyroids (TI); and rats bearing transplanted parathyroids which were also thyroidectomized (TX). The normal rats were fed ad libitum and injected with calcitonin (40 pg/g body weight) after an overnight fast. Rats with parathyroid transplants were trained to a 0900 h feeding schedule and studied at sequential times related to feeding. TX rats were compared to TI animals and to TX rats injected postprandially with calcitonin. The following results were obtained: (a) When lead was injected into fasted normal rats, the ability of calcitonin to reduce the lead-induced hypercalcemia developed within 1 h after hormone administration. By 4 h after calcitonin injection this effect of the hormone had essentially disappeared. (b) In TI rats trained to a 0900 h feeding schedule, the degree of lead-induced hypercalcemia was less than that in TX rats for most time periods after consuming either a calcium-containing or a calcium-free meal. (c) Calcitonin injected postprandially into TX rats brought the response in these rats back in line with TI animals but only for the projected biological life of the hormone. It is concluded that the reduction in lead-induced hypercalcemia seen in TI rats is indicative of the presence of circulating endogenous calcitonin. It is suggested that this effect of calcitonin is a reflection of its biochemical action in bone cells and may be related to accumulation of phosphate induced by the hormone.     

Oral calcium tolerance test and serum calcitonin in calcium stone formers

Ninety-seven male patients with idiopathic calcium urolithiasis and 17 normal male subjects were studied to evaluate the mechanism of idiopathic hypercalciuria with an oral calcium tolerance test, which has been useful in differentiating hypercalciuria. The changes in parathyroid function, such as parathormone and urinary cyclic AMP, and calcium after calcium load differed between absorptive hypercalciuria and renal hypercalciuria. We have confirmed that the change in serum calcitonin after calcium load was also different in these two hypercalciurias. The increase in serum calcium was sufficient to reduce parathyroid function but serum calcitonin was unchanged after calcium load in the control group, in patients with normocalciuria, and those with renal hypercalciuria. Although serum and urinary calcium were more elevated in absorptive hypercalciuria than in the other three groups, parathyroid function was not significantly reduced after loading in absorptive hypercalciuria. In this group only, the serum calcitonin was significantly elevated after calcium load. It is reasonable to suggest that, in this group, because parathyroid function is usually suppressed by intestinal hyperabsorption of calcium, parathyroid function may not be further suppressed by even calcium load. Possibly the significant stimulation of calcitonin may compensate for the lack of suppression of parathyroid function and maintain normal serum calcium levels in absorptive hypercalciuria. These results suggest that the change in serum calcitonin is also useful to differentiate abnormalities of calcium metabolism in patients with hypercalciuria.     

Calcitonin-induced change in serum calcium levels and its relationship to osteoclast morphology and number of calcitonin receptors

It has been shown that, in live subjects, the ability of calcitonin (CT) to decrease serum calcium (Ca) levels can be lost in response to its continued or repeated administration. The present study investigated the relationship between such changes of in vivo serum Ca levels and the response of osteoclasts to CT administration, including the downregulation of their CT receptors (CTRs). Rats were either given a single injection of CT or repeated injections at either 6- or 24-h intervals, after which their serum Ca levels were evaluated. Their parietal bones were dissected, and the amount of 125I-labeled elcatonin (125I-eCT) binding to their osteoclasts measured using autoradiography. Ultrastructural changes in the osteoclasts were also examined. Twenty-four hours after a single CT administration, serum Ca levels had dropped, and there was an absence of ruffled borders on the osteoclasts. Less 125I-eCT binding to the osteoclast was found than in the control group. Forty-eight and 72 h after CT administration, serum Ca levels had almost returned to control levels, and the osteoclasts showed ruffled borders once again. The amount of 125I-eCT binding to the osteoclast also recovered to control levels. When these osteoclasts were then incubated in CT, their ruffled borders once again disappeared. In the 6-h interval multiple CT administration schedule subjects, upon inspection 72 h after their first administration (6 h following the final one), serum Ca levels were found to have almost returned to control levels with the presence of osteoclast ruffled borders. The amount of 125I-eCT binding to these osteoclasts was remarkably limited, and no disappearance of the ruffled borders occurred in response to additional CT incubation. In the 24-h interval multiple administration schedule subjects, upon inspection 72 h after their first CT administration (24 h following the final one), there was less 125I-eCT binding than in the single-dose subjects tested 24 h after their injection, and the ability of CT to lower their serum Ca levels was reduced. The ability of CT to lower serum Ca levels was therefore related to the response of osteoclasts to the CT (the disappearance of the ruffled borders), and this response was related to the amount of CTRs available for binding with CT on the osteoclast surface. Furthermore, the reduced effectiveness of CT in response to repeated CT administration was found to be related to the downregulation of the CTRs on the osteoclast surface.     

老年髋部骨折与降钙素受体基因多态性的关系

目的研究降钙素受体(CTR)基因多态性与老年髋部骨折患者骨密度(BMD)的关系,探讨原发性骨质疏松症(OP)发病的分子机制。方法选取老年髋部骨折患者105人为病例组,并以年龄、性别作配比因素,选取107例非骨折人群为对照组。采用聚合酶链反应-限制性长度多态性(PCR-RFLP)技术对受试者CTR基因进行多态性分析,比较不同基因型各部位BMD值的差异。结果 212例受试对象中,CTR基因型分别为CC型187例(88.21%),CT型25例(11.79%)。病例组和对照组及不同性别间基因型无显著差异。212例受试者各部位的骨密度与年龄呈负相关,与体质量指数正相关。分析基因型与骨密度的关系显示,CT型除在腰椎侧位(L2～L4)及Ward'三角的骨密度比CC型的骨密度值有显著性升高外,其他部位骨密度值之间的差异无统计学意义。结论 CTR基因多态性尚不能作为老年髋部骨折危险性的遗传标志。     

糖尿病患者肾血流与内皮素及降钙素基因相关肽关系

目的为了解内皮素（ＥＴ）及降钙素基因相关肽（ＣＧＲＰ）与糖尿患者不同阶段时肾血流的关系。方法肾彩色多普勒超声检查确定为糖尿病肾血流正常组（Ａ组）１５例、糖尿病肾血流减少组（Ｂ组）１５例，正常对照组１８例。分别采血测定血浆ＥＴ－１和ＣＧＲＰ浓度。结果Ａ组ＥＴ－１水平低于正常对照组（Ｐ＜０．０１），Ｂ组ＥＴ－１水平高于正常对照组（Ｐ＜０．０１）。二组ＥＴ－１水平与肾动脉收缩期峰值血流速度（Ｖｍａｘ）、肾动脉血流量（Ｑ）呈负相关（Ｐ＜０．０１），与尿白蛋白排泄率（ＵＡＥＲ）呈正相关（Ｐ＜０．０５）。二组的ＣＧＲＰ水平均低于正常组（Ｐ均＜０．０１），但Ａ与Ｂ组的ＣＧＲＰ水平差异无显著性（Ｐ＞０．０５）。未发现ＣＧＲＰ水平与Ｖｍａｘ、Ｑ和ＵＡＥＲ呈相关关系。结论ＥＴ－１在糖尿病不同阶段时对肾血流量的病理生理作用可能不同；糖尿病患者呈现低ＣＧＲＰ血症，但它对不同阶段的糖尿病肾血流的影响尚有待探讨。