Effect of 1,25-dihydroxyvitamin D3 on intestinal disaccharidases in uremic rats

The effect of 1,25-dihydroxyvitamin D3 (1,25-D) on the activity of intestinal disaccharidases, maltase, sucrase, trehalase and lactase, was studied in five-sixths nephrectomized uremic rats. In uremic rats, maltase, sucrase and trehalase activities were lower than in sham-operated rats. Administration of 1,25-D produced significant improvement of maltase, sucrase, trehalase and lactase activities in uremic rats. These results suggest that activities of intestinal disaccharidases are reduced in uremic rats and these activities are normalized after 1,25-D administration.     

Intravenous 1,25 dihydroxycholecalciferol corrects glucose intolerance in hemodialysis patients.

The effects of intravenous 1,25 dihydroxycholecalciferol [(OH)2D3] on glucose tolerance and insulin secretion were studied in eleven uremic patients on regular hemodialysis and compared with eleven healthy controls. Intravenous glucose tolerance tests (IVGTT) were used to assess glucose tolerance, and the hyperglycemic clamp technique was used to quantitate endogenous insulin secretion. Three days after they had discontinued oral 1,25(OH)2D3, the dialysis patients were then studied with (+D) and without (-D) a single intravenous dose of 1,25(OH)2D3 at 2 micrograms/m2, given two hours before the IVGTT or clamp studies. During the -D studies, the uremic patients were glucose intolerant but not hyperinsulinemic. Intravenous 1,25(OH)2D3 in dialysis patients increased glucose uptake (K values) during IVGTT by 38% (P less than 0.02) and increased early component of insulin secretion during hyperglycemic clamps by 48% (P less than 0.01) and the late component by 32% (P less than 0.01). After intravenous 1,25(OH)2D3, the dialysis patients became hyperinsulinemic and regained glucose tolerance. Intravenous 1,25(OH)2D3 did not change the K values during IVGTT nor the insulin secretion during hyperglycemic clamps in the control subjects. During the -D studies, serum concentrations of 1,25(OH)2D3 were significantly lower in uremic patients compared with controls. Serum 1,25(OH)2D3 during the +D studies increased to supraphysiological levels in both uremic patients and controls. Serum concentrations of intact parathyroid hormone, total and ionized calcium, magnesium, potassium, urea nitrogen and creatinine were not different between the +D and -D studies in neither the uremic patients nor the controls. These results suggest that 1,25(OH)2D3 deficiency, independent of parathyroid hormone and calcium, may contribute to the abnormalities in glucose tolerance and insulin secretion in dialysis patients.     

Effect of oral carnitine supplementation on disturbances of lipid metabolism in the uremic rat

Carnitine deficiency has recently been incriminated in the pathogenesis of the disturbed lipid metabolism observed in hemodialysis patients. The present study was performed to investigate the effects of L-carnitine administration on the lipid metabolism of rats with experimental chronic renal failure as compared to normal rats. Three groups of rats were studied: the first had induced chronic uremia, the second was sham-operated and pair-fed with the first, and the third was sham-operated and fed ad libitum. Serum triglycerides were significantly higher in uremic rats than in control animals of both groups. In addition to triglycerides, serum total cholesterol and phospholipids were also increased in uremic rats. The fractional clearance rate of Intralipid [K2(%)] was decreased in uremic as compared to control animals. The in vivo oxidation of radiolabeled palmitate was lower in uremic than in ad libitum-fed control animals but not lower than in pair-fed control rats. The daily oral administration of L-carnitine to uremic rats was associated with stable serum triglycerides. On the contrary, serum triglycerides increased significantly in the untreated uremic rats over the same period of time. Serum total cholesterol and phospholipids remained similar in the presence and the absence of L-carnitine treatment. The intravenous fat tolerance test of carnitine-supplemented uremic rats improved slightly, although not significantly, when compared to that of untreated uremic rats. In conclusion, oral L-carnitine supplementation in chronically uremic rats had only modest or no effects on several plasma lipid parameters.(ABSTRACT TRUNCATED AT 250 WORDS)     

The site of insulin resistance in acute uremia

In order to define the mechanism of glucose intolerance in acutely uremic rats, various studies were carried out 24 hours after bilateral nephrectomy. Glucose removal following intravenous glucose was significantly (p is less than 0.001) decreased in uremic rats compared with sham-operated rats (k = 2.1 +/- 0.03 per cent vs. 5.1 +/- 0.2 per cent). This deterioration in glucose tolerance was associated with higher insulin levels in uremic rats from one to 40 minutes after glucose administration, suggesting that insulin resistance accounted for the decrease in glucose removal by uremic rats. To identify the site of the insulin resistance, we compared the ability of insulin to enhance net glucose uptake by isolated perfused liver and muscle (hindlimb) preparations obtained from uremic and sham-operated rats. Insulin suppressed glucose outflow from perfused livers of uremic rats at least as well as it did from livers of sham-operated rats, and suppression occurred at both maximal ( greater than 600 micromicron./ml.) and threshold (75 micromicron./ml.) perfusate insulin levels. In contrast, there was a significant decrease in the ability of insulin (mean perfusate level = 225 micromicron./ml.) to enhance glucose uptake of perfused hindlimbs of uremic as compared with sham-operated rats. These results suggest that the insulin resistance of acute uremia may be due primarily to decreased insulin-mediated uptake of glucose by skeletal muscle without any decrease in sensitivity of the liver to insulin.     

Differential skeletal responses of hindlimb unloaded rats on a vitamin D-deficient diet to 1,25-dihydroxyvitamin D3 and its analog, seocalcitol (EB1089)

Conditions of disuse in bed rest patients, as well as microgravity experienced by astronauts are accompanied by reduced mechanical loading, reduced calcium absorption, and lower serum levels of 1,25(OH)2D3 (1,25-D), the active metabolite of vitamin D, all contributing to bone loss. To determine whether 1,25-D or a less calcemic analog, Seocalcitol or EB1089 (1 alpha,25-dihydroxy-22,24-diene-24,26,27-trihomovitamin D3) can alleviate bone loss in a rat hindlimb unloading model of disuse osteopenia, mature male rats originally on a vitamin D replete diet containing 1.01% calcium were transferred to a vitamin D-deficient diet containing 0.48% calcium and then tail suspended and treated for 28 days with vehicle, 0.05 microg/kg 1,25-D, or 0.05 microg/kg EB1089. The vitamin D-deficient diet caused a substantial decrease in bone mineral density (-8%), which may be compounded by hindlimb unloading (-10%). Exogenous 1,25-D not only prevented the bone loss but also increased the bone mineral density to greater than the baseline level (+7%). EB1089 was less effective in preventing bone loss. Analysis of site and cell-specific effects of 1,25-D and EB1089 revealed that 1,25-D was more active than EB1089 in the intestine, the site of calcium absorption, and in inducing osteoclastogenesis and bone resorption whereas EB1089 was more effective in inducing osteoblast differentiation. These studies suggest that elevating circulating 1,25-D levels presumably increasing calcium absorption can counteract bone loss induced by disuse or microgravity with its associated reductions in circulating 1,25-D and decreased calcium absorption.     

Attenuated up-regulation of vitamin D-dependent calcium-binding proteins by 22-oxa-1,25-dihydroxyvitamin D3 in uremic rats: A possible mechanism for less-calcemic action

SUMMARY: 22-Oxa-1,25-dihydroxyvitamin D₃ (OCT) is an analogue of vitamin D with less calcemic action than 1,25-dihydroxyvitamin D₃ (1,25D3), and thus may be advantageous in the treatment of secondary hyperparathyroidism in dialysis patients. to further elucidate the mechanisms of less-calcemic action of OCT in chronic renal failure, we examined the effects of OCT and 1,25D3 on mRNA levels for vitamin D-dependent 9-KDa calcium binding protein (CaBP-D_9K) in the intestinal mucosa and 28-KDa (CaBP-D_28K) in the kidney. In Sprague-Dawley rats made uremic by 5/6 nephrectomy for three months, OCT at doses of 0.25, 1.25 and 6.25 μg/kg, or 1,25D3 at 0.025,0.125 and 0.625 μg/kg were administered intravenously three times per week for two weeks. At 24 h after the final injection, enhanced serum PTH and PTH mRNA levels were successfully suppressed both by OCT and 1,25D3 in a dose dependent manner. However, OCT induced less hypercalcemia than 1,25D3. 1,25D3 markedly upregulated the expression of CaBP-D_9K and CaBP-D_28K genes, while they were not affected by OCT at all. In conclusion, such attenuated effects of OCT on calcium-binding proteins may play a role in the noncalcemic action, because number of CaBP-D_9K has been suggested to correlate with calcium absorption in the intestine.     

Efficacy of 19-Nor-1,25-(OH)2D2 in the prevention and treatment of hyperparathyroid bone disease in experimental uremia

BACKGROUND: The control of parathyroid hyperplasia and high circulating parathyroid hormone (PTH) levels is crucial in preventing secondary hyperparathyroidism (SH) in renal failure. Parathyroid gland enlargement and elevated levels of PTH are major contributors to increase bone resorption, a feature of renal osteodystrophy. METHODS: These studies assessed the efficacy of the 1,25(OH)2D3 analog, 19-Nor-1,25(OH)2D2 (19-Nor), in the prevention (protocol I) and treatment (protocol II) of SH and renal osteodystrophy in uremic rats. In protocol I, normal and uremic rats were fed a high phosphorus diet for 2 months; uremic rats were administered intraperitoneal injections of either vehicle or 19-Nor (200 ng three times a week). In protocol II, normal and uremic rats were fed a high phosphorus diet for 4 months; 2 months after the onset of uremia, rats were administered either intraperitoneal vehicle or 19-Nor (200 ng three times a week). Serum PTH and bone histology were used to assess the degree of SH. RESULTS: 19-Nor was effective in preventing (protocol I) and suppressing (protocol II) the significant SH induced by uremia and further enhanced by a high phosphorus diet. In protocol I, bone histology in uremic controls showed a threefold increase in the cancellous bone mass compared to normal rats. This expansion in unmineralized bone was accompanied by 5-, 1.5-, and 7-fold increases in eroded surface, mineralization lag time (MLT), and bone formation rate (BFR/BS), respectively. Moreover, cortical bone porosity in untreated uremic rats increased 267-fold compared to normal animals. 19-Nor ameliorated these changes in cancellous and cortical bone. In protocol II, the reported indices worsened even further. In contrast, 2 months of 19-Nor treatment improved bone histology by reducing cortical bone porosity, woven bone formation, MLT, and BFR/BS. CONCLUSION: In an experimental model of chronic renal failure (CRF), 19-Nor prevents SH and ameliorates the histomorphometric changes induced by uremia and high phosphorus diet. In addition, 19-Nor suppresses serum PTH and improves bone histology in uremic rats with established severe SH. Further studies in patients with CRF are necessary to define the clinical applicability of 19-Nor on bone histology in humans.     

The mechanism of diabetes control after gastrointestinal bypass surgery reveals a role of the proximal small intestine in the pathophysiology of type 2 diabetes

SUMMARY BACKGROUND DATA: Most patients who undergo Roux-en-Y gastric bypass (RYGB) experience rapid resolution of type 2 diabetes. Prior studies indicate that this results from more than gastric restriction and weight loss, implicating the rearranged intestine as a primary mediator. It is unclear, however, if diabetes improves because of enhanced delivery of nutrients to the distal intestine and increased secretion of hindgut signals that improve glucose homeostasis, or because of altered signals from the excluded segment of proximal intestine. We sought to distinguish between these two mechanisms. METHODS: Goto-Kakizaki (GK) type 2 diabetic rats underwent duodenal-jejunal bypass (DJB), a stomach-preserving RYGB that excludes the proximal intestine, or a gastrojejunostomy (GJ), which creates a shortcut for ingested nutrients without bypassing any intestine. Controls were pair-fed (PF) sham-operated and untreated GK rats. Rats that had undergone GJ were then reoperated to exclude the proximal intestine; and conversely, duodenal passage was restored in rats that had undergone DJB. Oral glucose tolerance (OGTT), food intake, body weight, and intestinal nutrient absorption were measured. RESULTS: There were no differences in food intake, body weight, or nutrient absorption among surgical groups. DJB-treated rats had markedly better oral glucose tolerance compared with all control groups as shown by lower peak and area-under-the-curve glucose values (P < 0.001 for both). GJ did not affect glucose homeostasis, but exclusion of duodenal nutrient passage in reoperated GJ rats significantly improved glucose tolerance. Conversely, restoration of duodenal passage in DJB rats reestablished impaired glucose tolerance. CONCLUSIONS: This study shows that bypassing a short segment of proximal intestine directly ameliorates type 2 diabetes, independently of effects on food intake, body weight, malabsorption, or nutrient delivery to the hindgut. These findings suggest that a proximal intestinal bypass could be considered for diabetes treatment and that potentially undiscovered factors from the proximal bowel might contribute to the pathophysiology of type 2 diabetes.     

Insulin release from column-perifused isolated islets of uremic rats

In order to examine the insulin secretion in chronic renal failure, isolated pancreatic islets either from uremic rats or from control rats were mixed into a short column of Bio-Gel P-2 polyacrylamide beads and perifused. Uremic rats had higher concentrations of blood urea nitrogen, serum creatinine, and immunoreactive insulin and lower concentration of plasma 1,25-(OH)2D3 than control rats. Although the basal insulin release in the presence of 5.0 mM glucose showed no difference between uremic and control rats, the initial insulin release in the presence of 16.2 mM glucose was significantly lower (p less than 0.05) in uremic than in controls rats. The insulin content in islets was not different between both groups. These findings suggest that there might be impairment of the initial insulin secretion without changes of insulin content in pancreatic islets in uremia.     

Differential effects of 19-nor-1,25-(OH)(2)D(2) and 1alpha-hydroxyvitamin D(2) on calcium and phosphorus in normal and uremic rats

BACKGROUND: Calcitriol, 1,25-(OH)(2)D(3) (1,25D), the most active metabolite of vitamin D, has been used in the treatment of secondary hyperparathyroidism (SH) because it controls parathyroid gland growth and suppresses parathyroid hormone (PTH) synthesis and secretion. Due to the calcemic and phosphatemic actions of 1,25D, two analogs with potentially less side effects, 19-nor-1,25-(OH)(2)D(2) (19-nor) and 1alpha(OH)D(2) (1alphaD(2)) are currently being used in the treatment of SH. METHODS: This study compares the effects of these two analogs on calcium (Ca) and phosphorus (P) metabolism in normal, uremic, and parathyroidectomized (PTX) rats. Using doses of 50 to 250 ng of 19-nor or 1alphaD(2), experiments were conducted in normal and uremic rats. RESULTS: In uremic rats, 19-nor did not increase plasma Ca or P while 1alphaD2 caused a dose-dependent increase in both. In addition, while the Ca x P product remained unchanged in 19-nor-treated rats, it increased progressively with 1alphaD(2)administration. In metabolic studies in normal rats treated with vehicle, 10 ng of 1,25D, 100 ng of 19-nor or 100 ng 1alphaD(2), intestinal calcium absorption and urinary calcium excretion were significantly higher in 1alphaD(2)-treated rats compared to those receiving 19-nor. Similar results were seen for intestinal phosphorus absorption and urinary phosphorus excretion. Finally, the skeletal response to these two analogs was tested in PTX rats fed a calcium-deficient diet and treated daily with 100 ng of 19-nor or 1alphaD(2). The increase in plasma calcium in 1alphaD2-treated rats was markedly higher than in those receiving 19-nor. Similar results were seen in plasma phosphorus when these studies were repeated using a phosphorus-deficient diet. CONCLUSIONS: These studies demonstrate that when given in large doses to rats 19-nor is less calcemic and phosphatemic than 1alphaD(2). The lower Ca x P product in 19-nor treated rats may be an important consideration in patient therapy. Further studies in patients are necessary to define the clinical applicability of these differences.     

Calcemic activity of 19-Nor-1,25(OH)(2)D(2) decreases with duration of treatment

19-Nor-1,25(OH)(2)D(2) (19-norD(2)) has been shown to suppress parathyroid hormone effectively, but with lower calcemic activity than 1,25(OH)(2)D(3). The present study investigated potential mechanisms to explain the reduced calcemic response to 19-norD(2). Tissue localization of [(3)H]19-norD(2) or[(3)H]1,25(OH)(2)D(3) after a single injection was not different. Intestinal calcium absorption and bone mobilization, measured in vitamin D-deficient rats 24 h after single injections of 60 or 600 pmol of 19-norD(2) or 1,25(OH)(2)D(3), were enhanced to a similar degree by the two compounds. However, when normal rats were treated every other day with 240 pmol of 19-norD(2) or 1,25(OH)(2)D(3), increases in serum calcium were identical 24 h after the first injection but diverged thereafter with significantly lower serum calcium in the 19-norD(2)-treated rats by 5 d. Intestinal calcium absorption and bone calcium mobilization were reassessed in vitamin D-deficient rats after seven daily injections of 600 pmol of 19-norD(2) or 1, 25(OH)(2)D(3), and both parameters were significantly lower in the 19-norD(2)-treated rats. Pharmacokinetic analysis after seven daily injections of 600 pmol of 19-norD(2) or 1,25(OH)(2)D(3) showed similar localization to the intestine and bone. In addition, intestinal vitamin D receptor levels were not different after 1 wk of treatment with 19-norD(2) or 1,25(OH)(2)D(3). In conclusion, the low calcemic activity of 19-norD(2) seems to be due to an acquired, postreceptor resistance of the intestine and bone to chronic treatment with the analog.     

Evidence for reduced catabolism by the antiglucocorticoid RU 38486 in acutely uremic rats

Previous studies suggested that increased blood levels of, or increased tissue sensitivity to, glucocorticoids may contribute to catabolism in acute uremia. To examine this possibility we determined urea nitrogen (urea-N) appearance, plasma levels of Nt-methylhistidine and the activity of the alkaline myofibrillar proteinase in acutely uremic rats with and without treatment with RU 38486, a selective antiglucocorticoid. Forty-eight hours after bilateral nephrectomy, the rats had markedly elevated serum levels of urea-N, creatinine, potassium and phosphorus. In uremic rats receiving RU 38486, comparable levels of serum creatinine were found, but the serum levels of urea-N (221 +/- 4 vs. 259 +/- 5 mg/dl) and phosphorus (6.5 +/- 0.3 vs. 8.5 +/- 0.4 mmol/l) were significantly decreased as compared to uremic animals without RU 38486. In comparison to sham-operated rats, urea-N appearance (net urea production) was increased by 56% 48 h after bilateral nephrectomy. This increment was almost completely reversed in uremic animals receiving the antiglucocorticoid. In untreated uremic rats, plasma levels of Nt-methylhistidine were 10.3 +/- 0.9 microgram/dl, whereas the administration of RU 38486 caused a significant decline in the levels of this amino acid (7.6 +/- 0.5 microgram/dl). This reduction in Nt-methylhistidine was associated with a concomitant decrease of myofibrillar proteinase activity in muscle tissue homogenates. Compared to sham-operated animals, this proteinase activity was increased by 30% in uremic rats, but was normal in those given RU 38486. Taken together, these data support the view that in acute uremia accelerated ureagenesis occurs, while enhanced muscle protein breakdown, owing to an increment in myofibrillar proteinase activity, provides the necessary amino acid precursors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of magnesium deficiency on lipid metabolism in uremic rats

The effects of acute magnesium deficiency on lipid metabolism were examined in five-sixths nephrectomized uremic rats and sham-operated rats. Three weeks after the surgery, both groups were divided into two subgroups. Half of the uremic and sham-operated rats received a magnesium-deficient diet. The rest of the experimental animals received a control diet. After 2 weeks on this regimen, all animals were sacrificed. In uremic rats, magnesium deficiency increased serum triglyceride levels and decreased high-density lipoprotein cholesterol levels as in sham-operated rats. Total serum cholesterol levels were higher in uremic rats than in sham-operated rats with or without magnesium deficiency. Serum free fatty acid levels were increased only in uremic rats with magnesium deficiency. These results suggest that magnesium deficiency worsens several parameters of lipid in uremic rats.     

不同肠段小肠旷置术对非肥胖型2型糖尿病大鼠的治疗作用

目的 探讨不同肠段小肠旷置术对非肥胖型2型糖尿病大鼠的治疗作用及其可能机制.方法 将40只自发性糖尿病GK大鼠随机分为胃窄肠始端Roux-en-Y吻合组(旷置十二指肠,A组)、胃空肠近端Roux-en-Y吻合组(旷置十二指肠和近端空肠8 cm,B组)、胃回肠始端Roux-en-Y吻合组(旷置十二指肠和全部空肠,C组)、胃回肠中段Roux-en-Y吻合组(旷置次全小肠,D组)和假手术组(SO组)5组,每组8只.观察术前、术后1、3、6、12、24周各组大鼠体质量、日均摄食量和空腹血糖水平;测定术前、术后1、24周各组葡萄糖负荷后胰岛素和胰高血糖素样肽(GLP)-1浓度.结果 各组手术时间无显著性差异(P>0.05),术后1周各组摄食量和体质量显著下降(P<0.01).与术前比较,各手术组术后1～24周空腹血糖明显降低(P<0.05);而SO组空腹血糖术后1、3、6周均未发生明显变化(P>0.05),术后12、24周显著升高(P<0.01).与SO组比较,各手术组术后1～24周空腹血糖均显著下降(P<0.05).各手术组之间比较,B组术后1～24周空腹血糖均显著低于A组(P<0.05),对血糖控制效果优于A组;但与C组和D组相比无显著性差异(P>0.05).与术前比较,各手术组术后1、24周葡萄糖负荷后30 min胰岛素和GLP-1浓度显著增高(P<0.01),SO组未见显著变化(P>0.05).B组术后1、24周葡萄糖负荷后30 min胰岛素和GLP-1浓度显著高于A组(P<0.05),但与C组和D组差异无统计学意义(P>0.05).结论 小肠旷置术对血糖的控制并不依赖于体质量和摄食量的减少,可能与促进GLP-1分泌进而改善第一时相胰岛素分泌有关.从血糖控制和体质最变化方面评估,旷置十二指肠和近端空肠对非肥胖型2型糖尿病大鼠效果最佳.     

Peroxidation of the small intestine and its effect on absorption of amino acids in burned rats

The purpose of this study was to investigate the dynamic changes of the level of lipid peroxidation products (malonaldehyde, MDA) of intestine, intestinal water, Na-K ATPase activity of intestinal mucosa and the intestinal leucine absorption rate of rats subjected to 30% III degrees burns. The results showed that the value of the intestinal MDA was higher, the Na-K ATPase activity of the intestinal mucosa reduced markedly, the wet/dry ratio of intestinal weight was increased significantly and the intestinal leucine absorption rate in vivo was distinctly reduced postburn. However, the content of intestinal MDA and the wet/dry ratio of intestine weight was significantly reduced, and the Na-K ATPase activity and leucine absorption rate was increased in burn rats treated with SOD and CAT than in untreated burn rats. These results strongly suggested that lipid peroxide may play an important role in the impairment of leucine absorption rate of intestine after burns, and the edema and reduced Na-K ATPase activity of intestinal mucosa resulted from the increased lipid peroxide might take active parts impairing the intestinal absorption.     

Effects of oral adsorbent in the rat model of chronic renal failure.

The effects of oral adsorbent, AST-120 (Kureha Chemical Ind. Co., Tokyo), were studied in the rat model of subtotal nephrectomy. In 34 female Sprague-Dawley rats, three quarters of the renal mass were removed from the left kidney by ligation of 3 branches of the left renal artery. One week later, the right kidney was removed. Two days after right nephrectomy, control rats were fed standard rat chow ad libitum, while AST-120-treated rats were fed standard rat chow containing AST-120 ad libitum. The animals were observed for 9 weeks. Of the control rats, some became severely ill and appeared to be almost dying before 9 weeks, while paired AST-120-treated rats appeared well. Body weight was maintained better in AST-120-treated rats than in control rats. At completion of the study, levels of BUN and serum creatinine were lower and glomerular filtration rate and renal plasma flow rate were higher in AST-120-treated than in control rats (p < 0.05), although there was no statistically significant difference in proteinuria. Serum uremic peak 2a measured by high-performance liquid chromatography, which is considered to correspond to uremic toxins, was statistically lower in AST-120-treated rats (p < 0.05). Finally, a marked reduction in the degree of glomerular sclerosis was noted in AST-120-treated versus control rats (p < 0.05). The results indicate that AST-120 is effective in the treatment of chronic renal failure in terms of reducing uremic symptoms as well as preserving renal function and glomerular architecture. The data also indicate that a reduction in uremic toxins could delay the progressive damage of renal function and glomerular architecture in chronic renal failure.     

Effect of 25-hydroxycholecalciferol on calcium absorption in chronic renal disease.

Calcium absorption was measured in eight uremic patients before and after eight days of treatment with 100 or 500 mug of 25-hydroxycholecalciferol (25(OH)D3) per day. Fractional calcium absorption was estimated by administering 47Ca i.v. and orally on separate days and counting forearm radioactivity four hours later. Calcium absorption in four patients with residual renal function rose from 16.3 +/- 2.5 to 40.8 +/- 5.5% after treatment. In order to determine if the increased calcium absorption was mediated by an increase in the production of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) by virtue of increased substrate delivery to the 25-hydroxycholecalciferol-1-hydroxylase system present in the residual renal tissue, identical studies were performed in four anephric patients. Calcium absorption in these patients averaged 15.7 +/- 2.2% during the control period and rose to 46.0 +/- 11.1% after treatment. Increments in serum calcium after treatment were similar in both groups of patients; the mean concentration rose from 9.6 +/- 0.3 to 11.0 +/- 0.6 mg/100 ml. The results indicate that 25(OH)D3 can improve calcium absorption in the absence of renal tissue suggesting that its conversion to 1,25(OH)2D3 may not be necessary for its effect on the gastrointestinal tract in the uremic patient.     

Diminished response of ovarian cAMP to luteinizing hormone in experimental uremia

In prepuberal female rats with acute bilateral nephrectomy or chronic subtotal nephrectomy, the increase of ovarian cAMP concentration in response to submaximal doses of luteinizing hormone (LH 10 micrograms) and human chorionic gonadotropine (hCG 2.5 IU) was diminished (CO + 2.5 IU hCG 488 +/- 49 pmoles cAMP/mg protein; NX + 2.5 IU hCG 366 +/- 56. P less than 0.05). The cAMP response to follicle stimulating hormone (FSH) was unchanged. The abnormality was found both after administration of LH in vivo and incubation of ovaries with LH in vitro. Similarly, plasma estradiol concentrations in response to submaximal hCG stimulation were diminished. Basal cAMP concentrations and cAMP concentrations after maximal stimulation were unchanged. The defect was observed both in ovaries of untreated prepuberal rats, of pregnant mare serum (PMS)-treated rats (follicular phase) and PMS/hCG-treated rats (luteal phase). Diminished ovarian cAMP response to LH was observed both in parathyroid intact and in parathyroidectomized rats. Administration of 1,25(OH)2D3 in physiological doses (60 ng/kg) to acutely uremic rats restored diminished ovarian cAMP response to submaximal LH stimulation irrespective of parathyroid status. The effect of 1,25(OH)2D3 could not be reproduced by hypercalcemia resulting from intraperitoneal calcium injection. In vivo administration of indomethacin further diminished ovarian cAMP response in uremic animals and had no effect in control animals. Incubation of ovaries with PGE1 and PGE2 increased basal and stimulated cAMP concentrations and abolished the difference between control and uremic animals. The diminished response of ovarian cAMP content to submaximal doses of hCG was not corrected by bromocriptine (1 mg/kg) despite normalization of hyperprolactinemia. The present study shows diminished ovarian cAMP and plasma estradiol response to LH in experimental uremia. It documents a role of 1,25(OH)2D3 and prostaglandins in the genesis of this abnormality.     

Effect of long-term low-dose 1α, 25-dihydroxy vitamin D3 on the expression of aquaporin 2 in kidneys of uremic rats

Objective To investigate the effect of long-term low-dose 1α, 25-dihydroxy vitamin D3 [1,25(OH)2D3] on rat kidney aquaporin (AQP) 2 expression in 5/6 nephrectomized rats. Methods Twelve Sprague-Dawley rats underwent 5/6 nephrectomy surgery were divided into model group (n＝6) and 1,25(OH)2D3 group (n＝6) randomly; sham-operated rats only received the renal capsule stripping (control group, n＝6). Rats in 1,25(OH)2D3 group received 1,25(OH)2D3 (3 ng•100 g-1•d-1, ip) for 24 weeks. Serum and 24-hour urine specimens were collected for measurement of serum creatinine, arginine vasopressin (AVP) and urine protein. Animals were sacrificed at week 24 and kidneys were removed for routine pathological, immunohistochemistry and immunoblotting analysis. Results At week 24, plasma AVP level in 1,25(OH)2D3 and model group was much higher than that in control group (all P＜0.05), with no significant differences between the former two groups (P＞0.05). Lower serum creatinine and urinary protein were presented in 1,25(OH)2D3 group compared with the model group rats at week 24 (P＜0.05). Renal medullar fibrosis and inflammatory cell infiltration were improved significantly in 1,25(OH)2D3 group compared with model group (P＜0.01, P＜0.05). Immunohistochemistry analysis revealed abundant AQP2 and p-AQP2 expressed in the renal medulla of sham group, mainly in apical membrane of collecting duct cells. AQP2 expression in model group was down-regulated (P＜0.05) and p-AQP2 expression in apical membrane was reduced. AQP2 expression in 1,25(OH)2D3 group increased compared with model group, with increased p-AQP2 expression in apical membrane. Western blotting revealed same results of these expressions (all P＜0.05). Correlation analysis showed a negative correlation of AQP2 expression with urine volume, medullary fibrosis, and inflammatory cell infiltration (P＜0.05). Conclusion Long-term low-dose 1,25(OH)2D3 improves AQP2 expression and response to AVP in collecting duct, which may involve in the anti-polyuric effect of 1,25(OH)2D3 in uremic rat.     

1,25-Dihydroxycholecalciferol increases bone resorption in thyroparathyroidectomised mice

Mice, 1 week old, prelabelled with⁴⁵Ca, were either thyroparathyroidectomised or sham-operated; 1 day later half of the mice of each group were injected with 1,25-dihydroxycholecalciferol (5 ng/g), and 20 h later all the mice were killed. Bone resorption in explants was then measured by an in vivo/in vitro technique previously published; compared with untreated mice it was found that 1,25-dihydroxycholecalciferol had increased resorption irrespective of whether the mice had been thyroparathyroidectomised or not. These data suggest that 1,25-dihydroxycholecalciferol is able to increase bone resorption independently of parathyroid hormone.