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  • 1
    Electronic Resource
    Electronic Resource
    Reduction of Brain Calcium After Consumption of Diets Deficient in Calcium or Vitamin D (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 36 (1981), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Rats fed diets deficient in calcium or vitamin D for 4 weeks displayed hypocalcemia, as indicated by a 50% reduction in serum calcium and a sevenfold elevation of serum parathyroid hormone. These treatments also decreased the calcium content of brain tissue. On a regional basis. this effect was greatest in the brain stem (24% decrease) and least in striatum (10% decrease). Subcellular analysis indicated that the depletion of brain calcium was greatest in the soluble and the microsomal fractions. Infusion of calcium solutions reversed the depletion of brain calcium produced by dietary deficiencies. In control rats. parathyroidectomy or infusion of parathyroid hormone did not alter the calcium content of brain tissue, although these treatments affected the levels of calcium in the serum. In general, these treatments had no effect on the magnesium content of serum or brain tissue. However, vitamin D deficiency did increase the magnesium content of the myelin and synaptosomal fractions. This increase was reversed by parathyroidectomy. These observations demonstrate that long-term hypocalcemia produces distinct changes in the localization of calcium and magnesium in brain tissue. Furthermore. these studies suggest that though brain calcium levels are influenced by serum concentrations, serum changes must be of large magnitude and long duration for brain calcium levels to be affected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1981.tb01615.x
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanisms of Guanylin Action Via Cyclic GMP in the Kidney (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 62 (2000), S. 673-695 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Guanylin, uroguanylin, and lymphoguanylin are small peptides that activate cell-surface guanylate cyclase receptors and influence cellular function via intracellular cGMP. Guanylins activate two receptors, GC-C and OK-GC, which are expressed in intestine and/or kidney. Elevation of cGMP in the intestine elicits an increase in electrolyte and water secretion. Activation of renal receptors by uroguanylin stimulates urine flow and excretion of sodium, chloride, and potassium. Intracellular cGMP pathways for guanylins include activation of PKG-II and/or indirect stimulation of PKA-II. The result is activation of CFTR and/or ClC-2 channel proteins to enhance the electrogenic secretion of chloride and bicarbonate. Similar cellular mechanisms may be involved in the renal responses to guanylin peptides. Uroguanylin serves as an intestinal natriuretic hormone in postprandial states, thus linking the digestive and renal organ systems in a novel endocrine axis. Therefore, uroguanylin participates in the complex physiological processes underlying the saliuresis that is elicited by a salty meal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physiol.62.1.673
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  • 3
    Electronic Resource
    Electronic Resource
    Maintenance of normocalcemia by continuous infusion of the synthetic bovine parathyroid hormone (1–34) in parathyroidectomized rats (1982)
    Springer
    Calcified tissue international 34 (1982), S. 553-557 
    Details
    ISSN: 1432-0827
    Keywords: Serum calcium ; Parathyroidectomized rat ; Parathyroid hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary This work was conducted to estimate the replacement dose of the synthetic bovine parathyroid hormone [PTH(1–34)] that is required for maintenance of serum calcium (Ca) in parathyroidectomized (PTX) rats. Male rats were PTX and used in this study only if serum Ca was reduced to at least 7 mg/dl. We found that a solution of 2% cysteine, 150 mM NaCl, and 1 mM HCl was superior to 20 mM acetic acid for maintenance of biological activity of PTH (1–34) in situ during the period of hormone infusion studied. The PTH dose—calcemic response relationship was investigated using PTH in doses of 0.6, 1, and 3 U/h. The infusion of 1 U PTH per hour raised Ca to the normal level, whereas rats infused with 0.6 U/h were hypocalcemic and 3 U/h resulted in marked hypercalcemia. To extend this observation we carried out an infusion of 1 U PTH per hour for 14 days. We found that this infusion rate of bovine PTH (1–34) provided a relatively stable level of serum calcium with modest fluctuation from normocalcemic to somewhat hypercalcemic levels for the entire 14-day period of PTH infusion. Serum calcitonin was also elevated during the infusion period and then returned to the initial level when PTH treatment was stopped. After the minipumps containing PTH were removed, the serum Ca dropped rapidly to 5 mg/dl, which was significantly lower than the control (vehicle-infused) or initial values of serum Ca (7 mg/dl). Infusion of PTH at 3 U/h for 4 days did not produce this rebound hypocalcemia after the pumps were removed. Serum Ca in those experiments returned to the initial level after hormone treatment was discontinued.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02411303
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  • 4
    Electronic Resource
    Electronic Resource
    Regulation of the receptor-mediated cyclic AMP response of kidney to parathyroid hormone in the vitamin D-deficient rat (1978)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 9 (1978), S. 179-188 
    Details
    ISSN: 0091-7419
    Keywords: kidney ; vitamin D ; parathroid hormone ; cyclic AMP ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Rats fed a diet deficient in vitamin D were found to exhibit a refractory cyclic AMP response of kidney slices to parathyroid hormone and a marked decrease in membrane parathyroid hormone-dependent adenylate cyclase activity. Both the characteristic calcium deficiency (hypocalcemia) and secondary elevation of circulating parathyroid hormone appeared before the first noticeable decrease in hormone-dependent enzyme activity. After repletion of D-deficient rats with vitamin D2, we found that serum calcium and parathyroid hormone were both restored to normal levels before the depressed enzyme response to the hormone was reversed. Moreover, infusion of parathyroid hormone into vitamin D-replete rats led to a marked reduction in parathyroid hormone-dependent adenylate cyclase activity, which was partly restored to control level 3 hours after discontinuing the hormone infusion. Taken as a whole, this study suggests that the elevated endogenous parathyroid hormone in the vitamin D-deficient rat is involved in the “down-regulation” of renal cyclic AMP responsiveness to the hormone. However, these experiments do not rule out the possibility that calcium deficiency and/or vitamin D per se participate in the regulation of the renal cyclic AMP response to parathyroid hormone.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400090204
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    Paper (German National Licenses)
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