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The present study determined the effects of 1,25-dihydroxycholecalciferol on serum immunoactive parathyroid hormone and on parathyroid hormone secretion in vitro. Rats injected i.p. with 1,25-dihydroxycholecalciferol, 130 pmol (2 U)/140 g body wt, which is probably a physiologic dose, had a significant 43% decrease in serum immunoreactive parathyroid hormone at 4 h. In addition, this dose of 1,25-dihydroxycholecalciferol inhibited the serum immunoreactive parathyroid hormone response to hypocalcemia induced by phosphate injection. Because the increment in serum immunoreactive parathyroid hormone was less but the decrement in serum calcium more in phosphate plus 1,25-dihydroxycholecalciferol-treated than in phosphate plus vehicle-treated rats, the impaired serum immunoreactive parathyroid hormone response to 1,25-dihydroxycholecalciferol could not be attributed to the change in serum calcium. In studies of parathyroid hormone secretion from bovine parathyroid tissue in vitro, the concentration of 1,25-dihydroxycholecalciferol used for most experiments was 1nM, which is in the range found in rat serum. 1,25-Dihydroxycholecalciferol at 1 or 100 nM significantly inhibited parathyroid hormone secretion when medium calcium concentration was normal (1.5 mM), high (3.0 mM), and low (1.0 mM). Maximum inhibition ranged from 19 to 74%; inhibition was generally seen after 2 h of incubation; and inhibition was sustained or progressive thereafter. Vitamin A, 0.1 muM, caused a marked stimulation of parathyroid hormone secretion. 1,25-Dihydroxycholecalciferol at 1 nM markedly reduced (44%) the effect of vitamin A to stimulate parathyroid hormone secretion. This effect of 1,25-dihydroxycholecalciferol was maximal at 1 h and persisted thereafter. Another steroid, hydrocortisone, 10 muM, did not inhibit parathyroid hormone secretion, suggesting that the 1,25-dihydroxycholecalciferol effect was not a nonspecific inhibitory effect on parathyroid cells. Because other workers have shown that parathyroid hormone directly stimulates 1,25-dihydroxycholecalciferol secretion, our results are consistent with the concept that there is a feedback loop where parathyroid hormone directly stimulates secretion of 1,25-dihydroxycholecalciferol, which in turn directly inhibits secretion of parathyroid hormone.
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
January 1978,
Advances in experimental medicine and biology,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
January 1979,
Endocrinology,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
November 1977,
Acta endocrinologica,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
January 1986,
Calcified tissue international,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
August 1980,
Endocrinology,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
March 1984,
Acta endocrinologica,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
May 1977,
Calcified tissue research,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
December 1983,
Kidney international. Supplement,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
January 1995,
Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association,
B S Chertow, and
D J Baylink, and
J E Wergedal, and
M H Su, and
A W Norman
July 1984,
Calcified tissue international,
