Linked Life Data

8941917

Source:http://linkedlifedata.com/resource/pubmed/id/8941917

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PredicateObject
rdf:type
lifeskim:mentions
pubmed:dateCreated
1997-2-25
pubmed:abstractText
The relationship between PTH and calcium is best represented as a sigmoidal curve. In the normal animal and human, basal PTH is positioned at approximately 25% of maximal PTH and responds rapidly to small changes in calcium in either direction. Since PTH secretion is designed to respond to either hypo- or hypercalcemia, the study was performed to evaluate whether the parathyroid gland would respond differently to hypocalcemia when the reduction in serum calcium was initiated from sustained hypercalcemia with maximal PTH suppression. Nine dogs were studied and the experimental protocol consisted of two separate parts in which the same dogs were used and the order of study was randomly assigned. For the hypercalcemic part, calcium chloride was infused intravenously to increase serum calcium to between 1.60 and 1.70 mM at 30 minutes and then continued for another 90 minutes to clamp the serum calcium at this level. Sodium EDTA was then infused to lower the serum calcium at a constant rate to less than 0.85 mM. For the normocalcemic part, 5% dextrose in water was infused for two hours to control for fluid volume and time, and then EDTA was infused to lower the serum calcium at a constant rate to less than 0.85 mM. The results show that for the same serum calcium concentration at every 0.05 mM decrement in serum calcium below normal, PTH was less in the hypercalcemic than the normocalcemic dogs (P < 0.02). During the induction of hypocalcemia in the normocalcemic dogs, a characteristic sigmoidal curve was observed in which a small decrease in the serum calcium induced a brisk increase in PTH and a maximal PTH level was rapidly attained; however, during the induction of hypocalcemia in the hypercalcemic dogs, the increase in PTH was progressive, but linear and it was not certain that a maximal PTH level was attained. In conclusion, a sustained period of hypercalcemia resulted in a decreased PTH response to hypocalcemia and reduced the efficiency of the sigmoidal PTH-calcium relationship. Whether the mechanism for this difference in PTH secretion is due to secretory products, modification of the calcium receptor, or changes in intercellular communication among parathyroid cells deserves further study.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Dec
pubmed:issn
0098-6577
pubmed:author
pubmed:issnType
Print
pubmed:volume
57
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
S18-22
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1996
pubmed:articleTitle
A reduced PTH response to hypocalcemia after a short period of hypercalcemia: a study in dogs.
pubmed:affiliation
Departamento de Cirugía y Nefrología, y Unidad de Investigación del Hospital Universitario Reina Sofía, Spain.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't