Search Results

You are looking at 1 - 2 of 2 items for

  • Author: N. H. BELL x
  • Refine by access: All content x
Clear All Modify Search
A. D. CARE
Search for other papers by A. D. CARE in
Google Scholar
PubMed
Close
,
N. H. BELL
Search for other papers by N. H. BELL in
Google Scholar
PubMed
Close
, and
R. F. L. BATES
Search for other papers by R. F. L. BATES in
Google Scholar
PubMed
Close

SUMMARY

The influence of magnesium on calcitonin (CT) secretion rate has been studied in pigs by perfusion of porcine thyroid glands, isolated in situ, under controlled conditions of flow rate and blood electrolyte composition. At concentrations of 4·4–12·7 mequiv./l, magnesium stimulated CT secretion in the presence of a normal calcium concentration in the perfusate. The maximum effect was reached at a concentration of about 7 mequiv. Mg/l. At higher magnesium concentrations, the secretion rate of CT tended to revert towards that found with concentrations of calcium and magnesium within the normal range. When hypermagnesaemia was superimposed on hypercalcaemia there was a fall in the secretion rate of CT as the Mg: Ca ratio in the perfusing blood plasma approached 1. The stimulatory effect of hypermagnesaemia was usually less than that caused by an equimolar increase in plasma calcium concentration. The results suggest that changes in plasma magnesium concentration probably do not influence CT secretion under normal conditions.

Restricted access
SHERRY F. QUEENER
Search for other papers by SHERRY F. QUEENER in
Google Scholar
PubMed
Close
,
N. H. BELL
Search for other papers by N. H. BELL in
Google Scholar
PubMed
Close
,
SARAH M. LARSON
Search for other papers by SARAH M. LARSON in
Google Scholar
PubMed
Close
,
D. P. HENRY
Search for other papers by D. P. HENRY in
Google Scholar
PubMed
Close
, and
EDUARDO SLATOPOLSKY
Search for other papers by EDUARDO SLATOPOLSKY in
Google Scholar
PubMed
Close

Studies were carried out to characterize the secretion and the effects of calcitonin in the Buffalo rat. Mean basal concentrations of calcitonin and parathyroid hormone were significantly increased in serum of rats older than 6 months of age as compared with rats between 2 and 3 months of age. The mean concentration of calcium in serum was independent of age. In both age groups, serum calcitonin was increased by administration of calcium (1 mmol/kg body wt) or isoproterenol (100 μg/kg body wt), was diminished by β-adrenergic blockade with dl-propranolol (1 mg/kg body wt) and was not altered by either pentagastrin or glucagon (200 and 100 μg/kg body wt respectively). The average weight of the thyroid glands was significantly greater in the old than in the young animals but the mean concentration of calcitonin in the thyroids was the same. Thyroparathyroidectomy produced a transient increase followed by a fall in mean serum calcium in the old rats. In contrast, a progressive decline in the mean concentration of calcium in serum was observed after thyroparathyroidectomy in the young rats. Treatment of old animals with reserpine (2·5 mg/kg body wt) markedly depleted noradrenaline in the thyroid, lowered calcitonin in serum and converted the pattern of response of serum calcium to thyroparathyroidectomy to that observed in young animals. The results provide evidence that hypercalcitonaemia occurs in aged Buffalo rats, as does hyperparathyroidism, and that the concentrations of calcitonin in blood are modulated by β-adrenergic affectors. Glucagon and pentagastrin exhibit little if any effects on calcitonin secretion in this strain of rat regardless of age.

Restricted access