Effect of Small Increments in Plasma Calcium Concentration on the Responsiveness of Forearm Resistance Vessels to Verapamil in Normal Subjects

1984 ◽  
Vol 67 (6) ◽  
pp. 613-618 ◽  
Author(s):  
B. F. Robinson ◽  
R. J. W. Phillips
Keyword(s):  
Calcium Concentration ◽  
Venous Blood ◽  
Normal Subjects ◽  
Plasma Calcium ◽  
Calcium Handling ◽  
Membrane Function ◽  
Resistance Vessels ◽  
Initial Control ◽  
Plasma Calcium Concentration ◽  
Small Increments

1. The effect of a small increase in local plasma calcium concentration on the responsiveness of the forearm resistance vessels to verapamil has been examined in normal subjects, by using a plethysmographic method with infusion of calcium and other agents into the brachial artery. 2. Infusion of calcium at a rate which increased the concentration in forearm venous blood by about 0.5 mmol/l caused basal blood flow to fall by 19% and the dilator response to verapamil to fall by 35% (n = 8; P<0.02). 3. When, after 46 min, the infusion of calcium was discontinued, the dilator response to verapamil increased to reach a level 53% higher than the initial control (n = 8; P<0.02). 4. Infusion of calcium had no effect on the dilator response to sodium nitroprusside. 5. Infusion of noradrenaline at a rate which caused a greater reduction in basal flow than that induced by calcium had no effect on the response to verapamil. 6. It is concluded that the dilator response to verapamil, which is thought to reflect activity of the potential operated system for calcium entry, is selectively depressed by a small elevation of plasma calcium concentration, but subsequently becomes elevated. These findings point to an important role for calcium in the regulation of membrane function in the resistance vessels and support the view that altered calcium handling may contribute to the development of primary hypertension.

Parathyroid Hormone-like Biological Activity in Urine

1978 ◽  
Vol 54 (4) ◽  
pp. 349-353 ◽  
Author(s):  
N. Nijs-De Wolf ◽  
N. De Nutte ◽  
H. Brauman ◽  
J. Corvilain
Keyword(s):  
Biological Activity ◽  
Parathyroid Hormone ◽  
Secondary Hyperparathyroidism ◽  
Calcium Concentration ◽  
Normal Volunteer ◽  
Normal Subjects ◽  
Plasma Calcium ◽  
Surgical Removal ◽  
Before And After ◽  
Plasma Calcium Concentration

1. The parathyroid hormone-like biological activity of concentrated urine was measured by the increase of plasma calcium concentration after intravenous injection of the sample into chickens. 2. Urine was tested in hypoparathyroid patients, normal volunteer subjects, primary hyperparathyroid patients before and after surgery and patients with secondary hyperparathyroidism. 3. In primary and secondary hyperparathyroidism the biological activity was significantly higher than in urine from normal subjects, which was in turn significantly higher than the activity in the urine of hypoparathyroid patients. This bioactivity diminished after surgical removal of a hyperparathyroid adenoma. 4. Decreased activity after trypsinization indicated the peptidic nature of the hypercalcaemic substance.

ABOLITION OF MAGNESIUM-INDUCED HYPOCALCAEMIA BY ACUTE THYRO-PARATHYROIDECTOMY IN THE CAT

1970 ◽  
Vol 64 (1) ◽  
pp. 150-158 ◽  
Author(s):  
S. Pors Nielsen
Keyword(s):  
Sodium Chloride ◽  
Flow Rate ◽  
Magnesium Chloride ◽  
Calcium Concentration ◽  
Plasma Calcium ◽  
Magnesium Concentration ◽  
Isotonic Sodium Chloride ◽  
Plasma Calcium Concentration ◽  
High Concentrations ◽  
Plasma Magnesium

ABSTRACT Intravenous infusion of isotonic magnesium chloride into young cats with a resultant mean plasma magnesium concentration of 7.7 meq./100 g protein was followed by a significant lowering of the plasma calcium concentration in 90 minutes. The rate of decrease of plasma calcium is consistent with the hypothesis that calcitonin is released by magnesium in high concentrations. There was no decrease in the plasma calcium concentration in cats of the same weight thyroparathyroidectomized 60 min before an identical magnesium chloride infusion or an infusion of isotonic sodium chloride at the same flow rate. The hypercalciuric effect of magnesium could not account for the hypocalcaemic effect of magnesium. Plasma magnesium concentration during magnesium infusion into cats with an intact thyroid-parathyroid gland complex was slightly, but not significantly higher than in acutely thyroparathyroidectomized cats.

Nature of calcemic effect of 1,25-dihydroxyvitamin D3 in experimental hypoparathyroidism

1983 ◽  
Vol 244 (4) ◽  
pp. E313-E316
Author(s):  
E. Hefti ◽  
U. Trechsel ◽  
H. Fleisch ◽  
J. P. Bonjour
Keyword(s):  
Calcium Concentration ◽  
Calcium Absorption ◽  
Single Injection ◽  
Plasma Calcium ◽  
Constant Infusion ◽  
Feeding Period ◽  
Daily Fluctuation ◽  
Dihydroxyvitamin D3 ◽  
1,25 Dihydroxyvitamin D3 ◽  
Plasma Calcium Concentration

The influence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] treatment on the daily fluctuation of plasma calcium concentration ( [Ca]P1) in relation to the feeding-fasting alternation has been studied in vitamin D-replete sham-operated (sham) and thyroparathyroidectomized (TPTX) rats fed a normal Ca diet. 1,25(OH)2D3 was given (26 or 39 pmol/day) intraperitoneally either by single injection or constant infusion using osmotic minipumps. After 7 days of treatment [Ca]P1 was measured at 4-h intervals for 24 h. Pair-fed, sham and TPTX animals received the solvent vehicle intraperitoneally. The results show that in sham rats the very moderate daily fluctuation of [Ca]P1 was not accentuated by 1,25(OH)2D3. A marked fluctuation of [Ca]P1 in relation to the food intake was observed in untreated TPTX as compared with sham rats. In TPTX rats 1,25(OH)2D3 increased the fasting [Ca]P1. In contrast the rise in [Ca]P1 during feeding was not significantly accentuated by 1,25(OH)2D3. The daily fluctuation of [Ca]P1 was the same whether the dose of 1,25(OH)2D3 was given in one single injection or by constant infusion, suggesting that this hormone is not involved in the hour-to-hour regulation of [Ca]P1. In conclusion, in the absence of parathyroid glands, 1,25(OH)2D3 given in doses that stimulate intestinal calcium absorption has a much more pronounced effect on the fasting calcemia than on the rise in calcemia observed during the feeding period. These results suggest that the mobilization of calcium from bone could play an important role in the calcemic effect of 1,25(OH)2D3 when given in the hypoparathyroid state.

CALCIUM AND THE CONTROL OF CIRCADIAN MITOTIC ACTIVITY IN RAT BONE MARROW AND THYMUS

1974 ◽  
Vol 62 (3) ◽  
pp. 451-462 ◽  
Author(s):  
N. H. HUNT ◽  
A. D. PERRIS
Keyword(s):  
Bone Marrow ◽  
Mitotic Activity ◽  
Calcium Homeostasis ◽  
Calcium Concentration ◽  
Plasma Calcium ◽  
Ionized Calcium ◽  
Plasma Phosphate ◽  
Circadian Changes ◽  
Plasma Calcium Concentration ◽  
Rat Bone

SUMMARY Circadian changes in mitotic activity in rat bone marrow and thymus have been demonstrated to closely parallel variations in total and ionized calcium concentrations in plasma. These fluctuations in plasma calcium concentration and tissue mitosis were abolished by parathyroidectomy. Significant changes in plasma phosphate and magnesium concentrations were also observed over the 24 h period. The evidence suggests that hour-to-hour variations in the systems controlling calcium homeostasis determine the levels of mitosis in rat bone marrow and thymus.

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