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Query: UMLS:C0020538 (hypertension)
 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Plasma parathyroid hormone (pPTH) levels have been assessed in three separate radioimmunoassay systems in samples from Wistar-Kyoto rats. The animals were subjected to one of three dietary regimens throughout the study period: Group 1 animals consumed normal rat chow and drank tap water; Group 2 animals consumed normal rat chow and tap water was replaced with 0.5% saline solution; Group 3 animals consumed normal rat chow to which 2.5% CaCO3 (by weight) had been added and also drank 0.5% saline solution. Animals had consumed these diets for approximately 7 months prior to sacrifice for blood collection. Blood pressure was measured by tail cuff plethysmography in these animals and, as previously reported, saline consuming animals showed a moderate hypertension (Gp 2) only when diets did not contain added calcium (Gp 3). In the week prior to sacrifice, mean blood pressures were: Gp 1: 128.0 +/- 3.46 mmHg; Gp 2: 140.2 +/- 3.15 mmHg; and Gp 3: 133.5 +/- 2.90 mmHg. Three assay systems were used to measure pPTH levels from trunk blood samples obtained by guillotine decapitation. One assay used an antiserum directed toward the vasoactive N terminal fragment 1-34 and produced pPTH measurements of 0.74 +/- 0.05 ng/ml in Gp 1 animals, 1.04 +/- 0.07 ng/ml in Gp 2 animals and 1.12 +/- 0.08 ng/ml in Gp 3 animals. This pattern was consistent with that obtained by another antiserum which had been raised against the intact 1-84 PTH molecule and produced values of 0.25 +/- 0.03 ng/ml in Gp 1 animals, 0.55 +/- 0.07 ng/ml in Gp 2 animals and 0.74 +/- 0.04 ng/ml in Gp 3 animals. Antiserum raised against the C-terminal did not show any difference in pPTH across groups. We conclude that saline consumption may increase some portions of circulating PTH. Such elevation of pPTH may not be a pathophysiological component in the sodium dependent elevation of blood pressure since animals concurrently consuming both saline and calcium supplemented diets retained elevated pPTH levels even though blood pressures did not differ from controls. Rather, elevation of circulating PTH levels may be a response to prolonged increases in sodium consumption.
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PMID:Parathyroid hormone in sodium-dependent hypertension. 362 62

Hypertension is common in primary hyperparathyroidism, but the mechanisms are not clear. Significant hypercalcemia induces elevation in blood pressure (BP), whereas excessive parathyroid hormone (PTH) lowers BP. However, in chronic renal failure (CRF) and secondary hyperparathyroidism, the hypercalcemia-induced hypertension is more severe. We examined the interaction between PTH and calcium on BP in normal rats and in those with CRF. Calcium caused a dose-related rise in serum calcium and a rise in mean arterial pressure (MAP). For a comparable rise in serum calcium, the increment in MAP in parathyroidectomized (PTX) rats (7 +/- 3 mmHg) was significantly lower (P less than 0.05) than in sham PTX rats (19 +/- 7.3 mmHg). In PTX rats receiving PTH, the MAP response to calcium infusion (17 +/- 2.4 mmHg) was similar to that in the sham PTX rats. The infusion of similar amounts of calcium in CRF rats caused a greater rise in serum calcium. In CRF-PTX rats, the changes in MAP during calcium infusion were significantly lower (P less than 0.05) than in CRF-sham PTX animals, despite similar rise in serum calcium. For a comparable rise in serum calcium, the rise in MAP in CRF rats was greater than in normal rats. These data suggest that the presence of PTH plays an important permissive role for the hypertensive action of the hypercalcemia.
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PMID:Effects of hypercalcemia and parathyroid hormone on blood pressure in normal and renal-failure rats. 370 44

Epidemiological studies suggest an association between reduced calcium uptake and hypertension, while clinical trials and rat experiments indicate a small but significant hypotensive effect with oral calcium supplements. These data imply that calcium deficiency has a role in genetic hypertension. We reasoned that if the hypothesis is correct, the hypertension should be aggravated by further reducing calcium balance but attenuated by augmenting calcium balance. We tested this hypothesis by evaluating the blood pressure response in spontaneously hypertensive rats (SHR) as calcium balance was decreased by dietary restriction of calcium or increased by supplementation with magnesium or 1 alpha, 25-dihydroxycholecalciferol (calcitriol). A low calcium diet within the physiological range did not accentuate the hypertension in SHR during the 11 weeks of treatment, even though calcium balance was reduced by half. Similar results were obtained with dietary calcium restriction in parathyroidectomized SHR, which excludes any offsetting effects of changes in parathyroid hormone levels. Conversely, 7 weeks of a high magnesium diet, which increased calcium balance without reducing PO4 balance, did not correct the hypertension of SHR. Similarly, long-term administration of calcitriol failed to reduce the blood pressure of parathyroidectomized SHR and normotensive Wistar-Kyoto (WKY) controls, despite the presence of increased serum calcium levels comparable to those produced by oral calcium loading. Finally, external calcium balance was measured directly in 25-day-old, prehypertensive SHR. As a result of the increased calcium absorption and reduced calcium excretion, SHR retained more calcium than did the normotensive WKY, which directly refutes the existence of calcium deficiency at this normotensive stage. These data do not support the role of calcium deficiency in genetic hypertension.
Hypertension 1986 Jan
PMID:Evidence against the role of calcium deficiency in genetic hypertension. 375 98

Ten children with end stage renal disease on chronic hemofiltration (HF) were studied for a 1-yr period to evaluate the efficacy of 1,25-dihydroxyvitamin-D3 (1,25(OH)2D3) therapy on biohumoral parameters of renal osteodystrophy and bone mineral content. In six of these children an acute study was done of the direct effect of the HF procedure on calcium and phosphate balance during 12 HF sessions. During the first 6 months of the study all children were treated with 1,25(OH)2D3 (0.25-0.50 microgram/day) to maintain plasma calcium at 9.5-11.0 mg/dl. There was a significant increase in plasma calcium (p less than 0.05) and a significant decrease in plasma phosphate (p less than 0.01) and alkaline phosphatase concentrations (p less than 0.05). The circulating levels of NH2 immunoreactive parathyroid hormone did not change, remaining at the upper limits of reference values. Immunoreactive parathyroid hormone-COOH terminal fragment levels decreased significantly (p less than 0.05). Bone mineral content rose significantly (p less than 0.01). During the last 6 months of the study, to evaluate the possibility that HF alone might control secondary hyperparathyroidism, 1,25(OH)2D3 treatment was discontinued in five children; plasma calcium and phosphate were well controlled whereas hyperparathyroidism worsened in all five, and one also developed intense pruritus and hypertension. The other five children remained on 1,25(OH)2D3 treatment; two of these were transplanted, and the other three continued to show an improvement of mineral balance. The results of the acute study showed that calcium balance was positive with a mean Ca++ gain of 140 mg/HF session. The mean total phosphate removed per HF run was 574 mg.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of 1,25-dihydroxyvitamin-D3 treatment on mineral balance in children with end stage renal disease undergoing chronic hemofiltration. 375 54

Depending on their symptomatology 152 cured (i.e., normocalcemic) patients with surgically proven primary hyperparathyroidism (pHPT) showed typical symptoms preoperatively. Besides hypercalcemia and elevated parathyroid hormone levels, 15 patients suffered only from hypertension and/or diffuse osteoporosis and/or complaints caused by the hypercalcemic syndrome (oligosymptomatic patients). Nine patients had no complaints (asymptomatic patients). The long-term clinical course of all patients was analyzed up to 22 years. Although the formation of urinary calculi was stopped in 94% of cases, a deterioration of renal function and hypertension was seen in symptomatic (12.5% and 9.2%, respectively) and oligosymptomatic patients (6.7% and 13.3%, respectively). Renal function and hypertension were unpredictable despite normalization of the hyperactive parathyroid metabolism and were of decisive prognostic significance; 6% died of acute or chronic renal failure, or of the consequences of hypertension. Multiple bone lesions, even large, healed functionally and were of no prognostic significance. In the majority of symptomatic patients gastrointestinal manifestations held postoperatively, but two patients died of acute pancreatitis without gastrointestinal complaints preoperatively. Almost all symptoms of the hypercalcemic syndrome disappeared immediately and permanently in symptomatic and oligosymptomatic patients. No deterioration of renal function and no elevation of blood pressure was observed in cured asymptomatic patients postoperatively. Immediate surgical treatment even in asymptomatic patients may have avoided complications of chronic renal failure or of hypertension. As soon as organic manifestations, even in a mild form, have been established, it seems impossible to predict the course and to prevent an unfavorable clinical outcome.
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PMID:[Clinical experiences following the surgical therapy of asymptomatic, oligosymptomatic and symptomatic parathyroid gland hyperfunction]. 378 42

A decrease in plasma Ca2+ and increases in plasma immunoreactive parathyroid hormone (PTH) have been reported in spontaneously hypertensive (SH) rats as compared with normotensive Wistar-Kyoto (WKy) rats. These changes should lead to a higher plasma 1,25(OH)2D (1,25-dihydroxycholecalciferol/1,25-dihydroxyergocalciferol) concentration in SH rat if the kidney responds appropriately. Plasma 1,25(OH)2D, however, has been reported to be normal in SH rats, suggesting possible impairments of vitamin D metabolism in this animal model of hypertension. To test this possibility, we studied the effect of PTH on renal production of 1,25(OH)2D in SH rats before (4 weeks of age) and after (12 weeks of age) the onset of hypertension. Basal serum levels of 1,25(OH)2D were normal in SH rats at both ages. At 4 weeks of age, the rise in serum 1,25(OH)2D after PTH injection (50 units subcutaneously every 2 h; four times) was also normal in SH rats. By contrast, at 12 weeks of age, the rise in serum 1,25(OH)2D was approximately one-half of that in WKy rats, despite the similar rises in serum Ca2+ levels in both groups by PTH injection. The attenuated rise in serum 1,25(OH)2D in SH rats was consistent with the impaired response of renal 1-hydroxylase (25-hydroxycholecalciferol 1 alpha-hydroxylase) activity to PTH. Basal 1,25(OH)2D production by the kidney in SH rat was higher than that in WKy rats both at 4 and 12 weeks of age. These data suggest that, in SH rats: serum 1,25(OH)2D is inappropriately low in relation to the elevated PTH and this may be due, at least in part, to the impaired responsiveness to PTH of renal 1-hydroxylase and to the enhanced metabolism of 1,25(OH)2D, and elevated PTH or other agents may stimulate the 1-hydroxylase in the kidney even before the onset of hypertension.
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PMID:Altered vitamin D metabolism in the kidney of the spontaneously hypertensive rat. 380 Sep 24

Calcium homeostasis is a complex process involving calcium, other involved ions, and three calcitropic hormones, parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D3. The principal maternal adjustment during pregnancy is an increasing parathyroid hormone secretion which maintains the serum calcium concentration in the face of a falling albumin level, an expanding extracellular fluid volume, an increasing renal excretion, and placental calcium transfer. The placenta transports calcium ions actively, making the fetus hypercalcemic relative to its mother, which in turn stimulates calcitonin release and perhaps suppresses parathyroid hormone secretion by the fetus. A unique extrarenal system for 1 alpha-hydroxylation of 25-hydroxyvitamin D3 exists in the placenta and/or decidua, providing a source of 1,25-dihydroxyvitamin D3 for the fetus. With the abrupt cessation of the placental source of calcium at birth, the neonate's serum calcium level falls for 24 to 48 hours, then stabilizes and rises slightly. Hyperparathyroidism during pregnancy causes complications in both mother and infant and should usually be treated surgically as soon as diagnosed. Maternal hypoparathyroidism can be treated satisfactorily with high doses of supplemental calcium and vitamin D. Osteopenia accompanying long-term heparin administration may respond to 1,25-dihydroxyvitamin D3 (calcitriol) therapy. Diabetes in pregnancy is associated with disturbed neonatal calcium homeostasis, perhaps due to chronic hypomagnesemia. A possible etiologic role of calcium deficiency in pregnancy-related hypertension has been suggested. Dietary deficiency of calcium and/or vitamin D during gestation may lead to several adverse effects in the newborn infant.
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PMID:Calcium metabolism in pregnancy and the perinatal period: a review. 388 Oct 31

The aging kidney suffers reduction both in mass and in glomerular filtration rate. These changes may be totally or partially due to atherosclerosis and hypertension, which reduce renal blood flow. Superimposed on these processes, and perhaps responsible for primary loss of renal mass irrespective of renal vascular disease, is glomerular damage and involution that is a consequence of adaptive increases in glomerular perfusion pressure that occurs as the number of nephrons decline with age. The data available at this time do not allow us to distinguish between these two potential mechanisms of renal senescence. The decline in GFR is in turn responsible for reduced renal acidification and the reduced renal clearance of drugs that are normally removed by the kidney. Certain renal functions, however, are depressed to a greater extent than is GFR. Both the ability to maximally dilute the urine and to maximally concentrate it are controlled by serum ADH concentrations and by the action of that hormone on the collecting duct. Aged rats do not maximally secrete ADH under conditions of dehydration and the effect of ADH on the kidney is also attenuated. Elderly humans also cannot maximally suppress ADH secretion when serum osmolality is reduced. Likewise, the renin-angiotensin-aldosterone axis is poorly responsive to volume depletion in aging subjects. As a result, elderly individuals cannot maximally retain sodium under conditions of plasma volume contraction out of proportion to reduction in GFR. The kidney is the site of vitamin D1 hydroxylation. Hydroxylation of vitamin D is reduced out of proportion to any reduction in GFR in the rat. There are no data as yet available on the effect of aging and the production of erythropoietin, a principal regulator of red blood cell mass. Neither are there data available on changes that might occur with advancing age in the ability of the aging kidney to metabolize various hormones, such as parathyroid hormone, glucagon, and insulin. The mechanisms and the full biochemical and physiologic consequences of renal senescence remain to be fully elucidated.
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PMID:The aging kidney. 391

We activated three known components of the adenylate cyclase system in renal membranes from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. The basal adenylate cyclase activity and responses to plasma membrane receptor activation by parathyroid hormone, isoproterenol and vasopressin were not different between the two strains. The response to prostaglandin E2 (PGE2), however, was less in the SHR than in the WKY at five, (P less than 0.05), 12 (P less than 0.01) and 16 (P less than 0.01) weeks of age. Activation of either the guanosine-5'-triphosphate (GTP) binding regulatory protein (N) with sodium fluoride (NaF) and guanyl-5'-yl-imidodiphosphate [Gpp(NH)p], or the catalytic unit with manganese chloride (MnCl2) or forskolin were not different between the two groups. When the medullary and cortical plasma membrane adenylate cyclase responses were studied separately, the observed decreased response to PGE2 (of SHR) was found to be entirely in the cortex. Also, the NaF response was reduced in the cortical region of the 12-week-old rats, a finding suggesting a possibility of a post receptor defect. These results show that there is a defective renal adenylate cyclase response specific to prostaglandin E2 in SHR. This defect could be related to the development of hypertension, by changing the natriuretic and/or renal vasodilating effects of these prostaglandins.
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PMID:Defective renal adenylate cyclase response to prostaglandin E2 in spontaneously hypertensive rats. 392 77

Evidence to support an association between dietary calcium and blood pressure is presented in this article. Epidemiological surveys, animal experiments, and clinical trials support an inverse relationship between calcium and blood pressure. Several independent diet surveys have reported reduced consumption of calcium by individuals with hypertension. Animal experiments demonstrate an inverse correlation between calcium intake and blood pressure and reveal disturbances in calcium metabolism in hypertensive animals. Similar metabolic disturbances, including lower serum ionized calcium, elevated parathyroid hormone values, and increased urinary calcium excretion, have been reported in human hypertensives compared with normotensives. In addition, three recent experimental trials using 1 gm calcium carbonate supplements demonstrated that increasing calcium intake may reduce blood pressure in some human beings. Further clinical investigations are necessary to define the subset of patients who will respond to calcium therapy. Dietary sources of calcium to provide at least the RDA are recommended. Dairy products are suggested because in addition to calcium, they are valuable sources of potassium and magnesium, which may also lower blood pressure. If a patient cannot tolerate dairy products, oral calcium supplements are indicated.
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PMID:Increasing calcium intake lowers blood pressure: the literature reviewed. 396 54


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